Dissertations / Theses on the topic 'Brain nuclei'

Dorsal raphe nucleus (DRN) neurons projects to widespread areas throughout the brain and are involved in many physiological functions and neuropsychiatric disorders. In particular, DRN serotonin (5-HT) neurons are thought to be implicated in major depressive disorder (MDD) as are steroid hormones. Therefore, the aim of this thesis was to assess the effects of some neurosteroids on DRN neurons in non-anaesthetized rats. Initially, we examined electrophysiological properties of dorsal raphe cells across the sleep---wake cycle in non-anaethetized rats. In this first study we characterized six distinct neuronal populations in the DRN based on spike waveform and firing pattern. We then examined the effects of DHEA-S and testosterone (T) on the firing properties of DRN neuronal populations previously characterized. We observed that most populations exhibited an initial decrease in firing activity following one week of treatment. However, there was a great variability in responses across the populations.

Nuclei/Cell detection is usually a prerequisite procedure in many computer-aided biomedical image analysis tasks. In this thesis we propose two automatic nuclei/cell detection frameworks. One is for nuclei detection in skeletal muscle fiber images and the other is for brain tumor histopathological images. For skeletal muscle fiber images, the major challenges include: i) shape and size variations of the nuclei, ii) overlapping nuclear clumps, and iii) a series of z-stack images with out-of-focus regions. We propose a novel automatic detection algorithm consisting of the following components: 1) The original z-stack images are first converted into one all-in-focus image. 2) A sufficient number of hypothetical ellipses are then generated for each nuclei contour. 3) Next, a set of representative training samples and discriminative features are selected by a two-stage sparse model. 4) A classifier is trained using the refined training data. 5) Final nuclei detection is obtained by mean-shift clustering based on inner distance. The proposed method was tested on a set of images containing over 1500 nuclei. The results outperform the current state-of-the-art approaches. For brain tumor histopathological images, the major challenges are to handle significant variations in cell appearance and to split touching cells. The proposed novel automatic cell detection consists of: 1) Sparse reconstruction for splitting touching cells. 2) Adaptive dictionary learning for handling cell appearance variations. The proposed method was extensively tested on a data set with over 2000 cells. The result outperforms other state-of-the-art algorithms with F1 score = 0.96.

In the present Master\'s Dissertation, a detailed cytoarchtectonic study of the brain of the juvenile catfish - Steindachneridion parahybae, has been performed. The animals used for this Atlas were juvenile specimens of one hundred days post-fertilization. The coronal (transverse) sections (5µm-thick) were obtained by using a rotary microtome, stained with cresyl-violet and examined under a photomicroscopy with the help of a digital system of analysis. Some criteria have been used to classify the different cell masses of the catfish brain: (i) characteristic size, shape and intensity of the staining from the perykarya; (ii) packing density and distribution pattern of the cell bodies; (iii) neuropil surrounding the cell groups and (iv) consistency of cell groups in both hemispheres and different brains of catfish. Thus, around one hundred and thirty nuclei have been described in the catfish brain, which are distributed in four main region that are from rostral to caudal: telencephalon, diencephalon, mesencephalon and rhombencephalon. Although we have observed important similarities between the brain of catfish and other teleosts, we have also noticed some differences in the characteristics and placement of several nuclei in relation to other teleosts, or even when compared to the brain of species of the same Order, the Siluriformes. Some of these differences could be related with the age of the animals studied here, but probably represent species-specific differences because the brain of adult catfish specimens has a great similarity in cytoarchitecture and overall organization compared to younger animals. The main outcome of this study has been the availability of a complete Atlas of the brain of catfish, which has been used to localize precisely the distribution of cells and fibers of the Gonadotropin-releasing hormone in the brain. This Atlas will also represent a valuable tool for future endocrine analyses, allowing the precise mapping of the different neurohormones in the brain of catfish, as well as for the study of neural connections among different brain areas<br>Esta Dissertação de Mestrado, apresenta-se estruturalmente como um Atlas, em que é apresentado um detalhado estudo citoarquitetônico do encéfalo de catfish- Steindachneridion parahybae. Para a realização deste, foram utilizados 7 juvenis de 100 dias após a eclosão, analisados por técnicas rotineiras de histologia, cujas secções coronais(transversais) - 5&um;m de espessura-, foram obtidas utilizando-se de um micrótomo rotativo, coradas com violeta de cresil e examinadas a partir de sistema digital de análise. Alguns critérios foram utilizados para classificar as diferentes massas de células do cérebro catfish, tais como: (i) o tamanho característico, forma e intensidade da coloração do pericário; (ii) padrão de densidade de agrupamento e distribuição dos corpos celulares; (iii) a presença de neurópilos ao redor dos desses agrupamentos celulares e (iv) a consistência/coerência destes agrupamentos em ambos os hemisférios dos diferentes encéfalos, então analisados. Dessa forma, são descritos aproximadamente130 massas celulares para o encéfalo de S. parahybae, as quais estão distribuídas em quatro principais regiões que, da parte rostral para caudal, são: telencéfalo, diencéfalo, mesencéfalo e rombencéfalo. Embora são observadas semelhanças entre o cérebro de S. parahybae e de outros teleósteos, nota-se, também, certas diferenças quanto às características e/ou localização das massas celulares em relação ao encéfalo de outros teleósteos, ou mesmo quando comparado com o cérebro de espécies da mesma ordem, Siluriformes. Algumas destas diferenças pode estar relacionada com a idade dos animais estudados, no entanto,também podem representar diferenças espécie-específicas, uma vez que o encéfalo adultos de S. parahybae apresentam grande similaridade citoarquitetônica, além da organização geral do encéfalo, previamente observadas em animais acima dos 100 dias após a eclosão. Portanto, como resultado deste estudo tem-se a disponibilidade de um Atlas completo do encéfalo de S. parahybae, o qual representa uma ferramenta valiosa para o estudo das conexões neurais entre diferentes áreas do encéfalo, bem como para futuras análises endócrinas, permitindo o mapeamento preciso de neuro-hormônios nesta espécie, como demonstrado ao longo deste estudo, para o hormônio liberador de gonadotropinas

Previous findings from this laboratory demonstrating changes in dopamine (DA) transporter and D2 receptors in the amygdaloid complex of subjects with major depression indicate that disruption of dopamine neurotransmission to the amygdala may contribute to behavioral symptoms associated with depression. Quantitative real-time RT-PCR was used to investigate the regional distribution of gene expression of DA receptors in the human amygdala. In addition, relative levels of mRNA of DA receptors in the basal amygdaloid nucleus were measured postmortem in subjects with major depression and normal control subjects. All five subtypes of DA receptor mRNA were detected in all amygdaloid subnuclei, although D1, D2, and D4 receptor mRNAs were more abundant than D3 and D5 mRNAs by an order of magnitude. The highest level of D1 mRNA was found in the central nucleus, whereas D2 mRNA was the most abundant in the basal nucleus. Levels of D4 mRNA were highest in the basal and central nuclei. In the basal nucleus, amounts of D4, but not D1 or D2, mRNAs were significantly higher in subjects with major depression as compared to control subjects. These findings demonstrate that the D1, D2 and D4 receptors are the major subtypes of DA receptors in the human amygdala. Elevated DA receptor gene expression in depressive subjects further implicates altered dopaminergic transmission in the amygdala in depression.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) and DBS of the pedunculopontine nucleus (PPN) have been shown to be effective surgical therapies for Parkinson’s disease (PD). To better understand the PPN and STN as DBS targets for PD, this research compares the anatomy, electrophysiology, and motor control roles of these nuclei. PPN and STN connections were examined in vivo in human subjects and in the non-human primate using probabilistic diffusion tractography. Both the PPN and STN were connected with each other and with the motor cortex (M1) and basal ganglia. After studying these anatomical connections in primates, their functional significance was further explored in an anesthetized rat model of PD. Examination of the electrophysiological relationship between the PPN and basal ganglia in the presence of slow cortical oscillatory activity suggested that excitatory input from the STN may normally modulate PPN spike timing but that inhibitory oscillatory input from the basal ganglia output nuclei has a greater effect on PPN spike timing in the parkinsonian brain. To examine transmission and modulation of oscillatory activity between these structures at higher frequencies, LFP activity was recorded from the PPN and STN in PD patients performing simple voluntary movements. Movement-related modulation of oscillatory activity predominantly occurred in the α (8-12 Hz) and low β (12-20 Hz) frequencies in the STN but in the high β (20-35 Hz) frequencies in the PPN, supporting observations from rodent studies suggesting that oscillatory activity is not directly transmitted from the STN to the PPN in PD. Finally, to better understand the roles of the STN and PPN in large-scale movement, the effects of STN and PPN DBS on gait abnormalities in PD patients were studied. DBS of the STN appeared to improve gait by optimising executive gait control while DBS of the PPN appeared to restore autonomic gait control. These results have several implications for DBS patient selection, surgical targeting, and for understanding the mechanisms underlying DBS efficacy.

Stress has long lasting effects on physiology, development, behavior, reproductive success and survival. These effects are mediated by glucocorticoids, such as corticosterone (Cort), via glucocorticoid receptors (GR), though the exact mechanisms underlying these effects are unknown. Early developmental stress affects the size of the avian song control nuclei (particularly HVC; proper name) and song quality in many songbirds, suggesting a direct link between brain and behavior. HVC is required for song learning and production. The complexity of the male zebra finch (Taeniopygia guttata) courtship song is important in female mate choice. Although the mechanisms behind the effects of developmental stress on song nuclei size and song quality are unknown, it is likely that elevated levels of Cort via GR within brain song nuclei play a significant role. We investigated the distribution, quantity, and subcellular-localization of GR- immunoreactive (GR-ir) neurons in the brains of male zebra finches 10 days post-hatch and in adulthood using immunohistochemistry. There was wide distribution of GR-ir neurons including two song nuclei HVC and robust nucleus of the arcopallium (RA). Distribution did not vary between the two ages but there were significant differences in the overall number of GR-ir neurons and their subcellular localization. We hypothesized that early Cort treatment would reduce song quality and HVC size in adult males. We inserted Cort implants in males at four days post-hatch and quantified the effects of early Cort treatment on adult song quality. Early Cort treatment decreased song similarity between the tutor and tutee’s songs and resulted in poorer copies of tutor song, but did not alter mean amplitude or song duration. Early Cort treatment reduced the HVC size in both juvenile and adult birds. This result suggests that the effect of developmental stress on the HVC size may be mediated through Cort via activation of GR within HVC as a mechanism by which HVC size and song quality are altered in developmentally stressed birds. These results suggest a potential role for Cort in mediating adverse effects of developmental stress in adult male zebra finches and highlight the developmental plasticity of the zebra finch brain.

The primary objective of my thesis is to explore the involvement of the amygdala, a neural structure underlying emotion, in the circuit underlying motivated behaviour as modelled by brain stimulation reward (BSR). In the first experiment, the functional links between the lateral hypothalamus (LH) and the amygdala were assessed using the metabolic marker, cytochrome oxidase. Following lesions of LH sites that supported BSR, we obtained a significant reduction of oxidative metabolism in the cortical sub-nuclei of the amygdala, suggesting their involvement in modulating the reward signals elicited from the LH. In order to test this functional relationship further, we extended our exploration of this link to another reward site, the ventral tegmental area (VTA), on both hemispheres of the brain. Following lesions to the cortical nuclei of the amygdala, some animals exhibited significant and sustained decreases in the rewarding value of LH as well as of VTA stimulation. In addition, modifications in the rewarding value of the stimulation from the MFB site contralateral to the lesion resembled ipsilateral ones, suggesting the existence of interhemispheric links in amygdaloid alteration of MFB reward signals. The nature of interhemispheric connectivity as well as a more detailed investigation of the amygdaloid sites involved in the modulation of MFB reward were explored in the final study of the thesis. Thresholds for BSR obtained from a continuum of MFB sites were tracked following serial bilateral lesions to the amygdala. One group of animals showed marked increases in thresholds that further augmented or were maintained after the second lesion. Damage to the most anterior sites encompassing cortical amygdaloid nuclei were confirmed as being more efficient than other lesions in producing substantial threshold changes. Equally exceptional was the finding that contralateral lesions were more effective than ipsilateral ones in affecting thresholds, confirming our earlier finding of interhemispheric connectivity. This interpretation was corroborated in a metabolic sub-study using cytochrome oxidase. Reaction product density within lesion sites was significantly and negatively correlated with substantial decreases in reward from the MFB electrode contralateral to them. Taken together, these data indicate that the anterior portions of the amygdaloid cortical nuclei modulate MFB reward signals. Furthermore, a significant interhemispheric communication appears to occur between these sub-nuclei in the context of reward.

The Australian zebra finch (Taeniopygia guttata) serves as an excellent model organism for studying the mechanisms that influence brain sexual differentiation. The brain and behavior of the zebra finch are sexually dimorphic. The regions of the brain that control the learning and production of song (song control nuclei) are significantly larger in the male brain than in the female brain and only males sing courtship songs, thus the majority of past research has focused on the development of these sex differences. In the majority of mammals, brain sexual differentiation occurs because hormones secreted from the gonads act to initiate male or female brain development. In zebra finches, estradiol is sufficient to masculinize the male brain, however manipulations of developmental hormone exposure fail to fully reverse the sex differences in song nuclei size. Furthermore, genetic females induced to develop functional testicular tissue do not develop a completely masculinized song system and castration has no effect on development of the song system in males. The source of the increased estrogenic signal in male zebra finch brain has yet to be identified, but data suggest that other neuronal factors play a role in development of the song control nuclei. Coregulators, such as coactivators and corepressors, are proteins and RNA activators that work by enhancing or depressing transcriptional activity of the nuclear steroid receptor with which they associate. Coregulators also modulate the development of sex-specific brain morphology and behavior in rodents and birds and may help to explain the difficulties observed in altering song nuclei development via castration and gonadal hormone replacement. As an estrogen receptor-α coactivator, ribosomal protein L7 (RPL7) is able to make the brain more sensitive to estradiol by enhancing the effects of steroid receptor action. Therefore, this dissertation addressed the following questions regarding RPL7: (1) is RPL7 expression sexually dimorphic in the song nuclei of the zebra finch brain?; (2) is RPL7 protein expression regulated by steroid hormones?; and (3) does decreasing RPL7 protein expression with antisense oligonucleotides alter neuronal survival in vivo and song nuclei size and neuron number in vitro? Collectively, these studies will provide valuable information about the role of steroid receptor coactivators in development of the zebra finch song system and on the role of coactivators on sexual differentiation of the brain.

U ovoj doktorskoj disertaciji je uspe&scaron;no izvr&scaron;eno izolovanje&nbsp;opijatnih alkaloida iz humanih biolo&scaron;kih uzoraka (moždanog&nbsp;tkiva, krvi, urina i žuči) kao i biolo&scaron;kih uzoraka&nbsp;eksperimentalnih životinja (moždanog tkiva i krvi) primenom&nbsp;postupka čvrsto-tečne ekstrakcije (SPE-Solid Phase Extraction).&nbsp;Modifikovan je postupak za kvalitativnu i kvantitativnu GC-MS&nbsp;(Gas Chromatography-Mass Spectrometry) analizu biolo&scaron;kih&nbsp;uzoraka.&nbsp;Utvrđena je distribucija opijatnih alkaloida: morfina, kodeina,&nbsp;acetilkodeina, 6-acetilmorfina i heroina u humanim biolo&scaron;kim&nbsp;uzorcima moždanog tkiva (moždanoj kori, moždanom stablu,&nbsp;amigdali i bazalnim jedrima), pri čemu je najveći sadržaj&nbsp;opijata određen u moždanoj kori i bazalnim jedrima,&nbsp;podjednako kod mu&scaron;kih i ženskih osoba.&nbsp;Utvrđena je distribucija opijatnih alkaloida: morfina, kodeina,&nbsp;acetilkodeina, 6-acetilmorfina i heroina u biolo&scaron;kim uzorcima&nbsp;moždanog tkiva (moždanoj kori, moždanom &nbsp;stablu, amigdali i&nbsp;bazalnim jedrima) i krvi eksperimentalnih životinja (pacova), u&nbsp;različitim vremenskim periodima (5, 15, 45 i 120 minuta) od&nbsp;tretiranja životinja heroinom.&nbsp;Najveći sadržaj opijata je određen u moždanoj kori i bazalnim&nbsp;jedrima, podjednako kod mužjaka i ženki pacova ali u različitim&nbsp;vremenskim periodima. U uzorcima krvi je najveći sadržaj&nbsp;opijata određen u istom vremenskom periodu kod životinja oba&nbsp;pola, pri čemu su kod mužjaka određene znatno veće vrednosti&nbsp;koncentracija, &scaron;to ukazuje na bržudistribuciju opijata iz krvi u&nbsp;mozak kod ženki u &nbsp;odnosu na mužjake pacova.&nbsp;Utvrđeno je da je distribucija opijata u humanom moždanom&nbsp;tkivu kod pripadnika suprotnih polova kao i moždanom tkivu&nbsp;mužjaka i ženki pacova (nakon 120 minuta od tretiranja&nbsp;heroinom), identična.&nbsp;Ispitivanjem uticaja opijata &nbsp;na markere oksidativnog stresa u&nbsp;jetri eksperimentalnih životinja suprotnih polova, utvrđeno je&nbsp;smanjenje aktivnosti enzima: katalaze (CAT), glutation-peroksidaze (GSH- Px), peroksidaze (Px) i ksantin-oksidaze&nbsp;(XOD).<br>Opiate alkaloids were successfully isolated from human biological samples (brain tissue, blood, urine, and bile) as well as from biological samples of experimental animals (brain tissue and blood) by applying procedure of solid-phase extraction (SPE). A modified procedure was worked out for qualitative and quantitative analysis of biological samples by gas chromatography-mass spectrometry (GC-MS). The distribution of opiate alkaloids:morphine, codeine, acetylcodeine, 6-acetylmorphine, and heroine in human biological samples of brain tissue (cortex, brain stem, amigdala and basal nuclei) was established, showing the highest content of opiates &nbsp; in the cortex and basal nuclei, equal with male and female persons. It was established how the opiatealkaloids: morphine codeine, acetylcodeine, 6-acetylmorphine&nbsp; and heroine are distributed in biological samples of brain tissue (cortex, brain stem, amigdala and basal nuclei) and blood of experimental animals&nbsp; (rats) in different time periods (5, 15, 45 and 120 min) after the animal treatment with&nbsp;heroine. The highest content of opiates was found in the cortex and basal nuclei,&nbsp;equal in the male and female rats, but in different time periods. In blood samples, the highest content of opiates was measured in the same period with animals of both sexes, the concentration in the males being significantly higher, indicating a faster passage of the opiates from blood to brain in the female compared to male rats.&nbsp;Identical distribution of opiates was found in human brain tissue of both male and female subjects as in rats of both sexes (120 min after treatment with heroine).&nbsp;Study of the effect of opiates on the markers of oxidative stress in the liver of tested animals of opposite sexes showed a lowered activity of the following enzymes: &nbsp;catalase (CAT), glutathion-peroxidase (GSH-Px), peroxidase (Px) and xanthine-xidase &nbsp;(XOD).

Mestrado em Biologia Molecular e Celular<br>O Sistema Nervoso (SN) dos mamíferos é uma rede complexa de células especializadas na recepção, transmissão e integração de informação. O desempenho de cada um dos subsistemas depende da forma como a comunicação entre as diferentes áreas se organiza. Várias ferramentas têm vindo a ser desenvolvidas para o efeito, sendo actualmente os traçadores neuroanatómicos aquelas de uso mais abrangente. Após injecção do traçador seleccionado na área pretendida do SN, este é incorporado e subsequentemente transportado de forma retrógrada ou anterógrada de acordo com as suas propriedades. O estudo dos sistemas supraespinais de controlo da dor tem em muito beneficiado do uso desta tecnologia. Várias áreas do encéfalo e, em particular, da formação reticular do tronco cerebral, participam na modulação supraspinal da dor. O núcleo reticular ventral (VRt) do bolbo raquidiano continua a ser uma área pouco explorada do encéfalo, contrariamente ao seu homólogo dorsal (DRt), cujo envolvimento na modulação da dor se encontra bem estabelecido. No presente trabalho, as projecções encefálicas (eferentes e aferentes) do VRt são analisadas no rato, recorrendo-se para tal a injecções intracerebrais de traçadores neuronais anterógrados e retrógrados, respectivamente o dextrano-amina biotinilado (BDA) e a subunidade B da toxina da cólera (CTb). Verificou-se que os neurónios do VRt recebem projecções e projectam para áreas do encéfalo implicadas no processamento somatosensitivo, emocional e cognitivo da dor. Estes resultados corroboram com o papel do VRt na modulação da dor. As projecções encefálicas do VRt e DRt para o tronco cerebral são em si muito semelhantes, com o VRt a projectar para áreas mais restritas do diencéfalo. O papel de cada um dos núcleos na modulação da dor poderá estar relacionado com as diferenças observadas nas projecções dos núcleos. ABSTRACT: The nervous system (SN) of a mammal is a complex network of cells specialized for the reception, transmission and integration of information. The performance of each subsystem depends on how the communication between different areas is organized. Several tools have been developed for this purpose, being currently the neuroanatomical tracers those of wider use. After selected tracer injection in the desired area of the SN, this one is incorporated and subsequently transported anterogradely and retrogradely according to their properties. The study of the supraspinal pain control systems has greatly benefited from the use of this technology. Several areas of the brain and, in particular, the reticular formation of the brainstem, are involved in supraspinal pain modulation. The ventral portion of the caudal reticular formation (VRt) remains a relatively unexplored area of the brain contrary to its dorsal counterpart (DRt), whose involvement in pain modulation is well established. In the present work, the VRt brain connections (efferent and afferent projections) are investigated in the rat, using iontophoretic injections of the anterograde tracer biotinylated-dextran amine (BDA) and the retrograde tracer cholera toxin-subunit (CTb). It was found that neurons from the VRt receive and project to areas of the brain involved in somatosensitive, emotional and cognitive pain processing. The set of brain projections observed in VRt is compatible with a role in pain modulation. VRt and DRt brain projections to the brainstem are similar; however, concerning to the diencephalon, VRt has a narrower set of targets. It remains unclear how these differences relate to differential roles in pain modulation.

The pathophysiology of traumatic brain injury (TBI) includes perturbations to energy metabolism. Improving our understanding of cerebral energy metabolism will lead to strategies that improve clinical outcomes. For the studies in my thesis I used microdialysis to deliver carbon-13 labelled substrates to the human brain. I combined this with nuclear magnetic resonance (NMR) spectroscopy of interstitial fluid sampled from the brain to interrogate glucose, lactate and tricarboxylic acid (TCA) cycle metabolism. Study I: I defined the optimal parameters for quantitative proton and carbon-13 NMR of cerebral microdialysates. Study II: I measured baseline microdialysate metabolite concentrations for brain and muscle and investigated the influence of muscle activity and cerebral catheter placement in grey or white matter on metabolite concentrations. Study III: I used 1,2-13C2 glucose to measure glycolysis and pentose phosphate pathway activity. Glycolysis is the dominant lactate-producing pathway but the pentose phosphate pathway also contributes and is increased in some TBI patients. Study IV: I used arterio-venous gradients to measure glucose and lactate delivery to the brain. There are periods after injury when lactate is imported from the circulation despite relatively high brain lactate levels suggesting up-regulation of lactate transport. Study V: I followed the metabolism of 3-13C lactate and demonstrated that lactate is metabolised by the TCA cycle. This occurs in both normal and injured brain but not in muscle. Study VI: I used 2,3-13C2 succinate to investigate the role of the TCA cycle in producing metabolites that are exported into the interstitium. The TCA cycle is found to be a source of lactate. Succinate delivered to the brain improves redox and enhances glutamate uptake into cells. The implications of the findings in my thesis on existing knowledge of cerebral metabolism are discussed. Strategies that might potentiate cerebral metabolism and improve clinical outcomes are suggested.

Certes malalties neurològiques estan associades amb problemes en els sistemes de neurotransmissió. Una aproximació a l'estudi d'aquests sistemes és la tomografia d'emissió SPECT (Single Photon Emission Computed Tomography) com a tècnica<br/>no-invasiva que proporciona imatges funcionals representatives de l'activitat neuronal. Aquesta tècnica permet la visualització i l'anàlisi de diferents òrgans i teixits dins l'àmbit de la Medicina Nuclear.<br/><br/>Malgrat que la inspecció visual de la imatge a vegades és suficient per establir el diagnòstic, la quantificació dels paràmetres de la imatge reconstruida poden millorar la fiabilitat i exactitud del diagnòstic precoç de la malaltia. En particular, la quantificació d'estudis de neurotransmissors de dopamina pot ajudar a detectar els estadis inicials de malalties com el Parkinson. Així mateix, la quantificació permet un seguiment més acurat de l'evolució de la malaltia i una evaluació dels efectes de la terapèutica aplicada.<br/><br/>La quantificació es veu afectada pels efectes degradants de la imatge com són el soroll estadístic, la resposta del sistema col.limador/detector i l'efecte de dispersió i/o atenuació dels fotons en la seva interacció amb la matèria. Alguns d'aquests efectes poden ser corregits mitjançant l'ús d'algoritmes de reconstrucció iteratius.<br/><br/>L'objectiu d'aquesta tesi és aconseguir una quantificació tant absoluta com relativa dels valors numèrics de la imatge reconstruida de manera que reprodueixin la distribució d'activitat real del pacient en el moment de l'adquisició de l'estudi de SPECT. Per aconseguir-ho s'han desenvolupat diferents codis i algoritmes per millorar els mètodes de reconstrucció existents i validar-ne els seus resultats.<br/><br/>La validació i millora dels algoritmes s'ha basat en l'ús de tècniques de simulació Monte Carlo. S'han analitzat els diferents codis Monte Carlo disponibles en l'àmbit de la Medicina Nuclear i s'ha escollit SimSET. La interpretació dels resultats obtinguts i la comparació amb els resultats experimentals ens van dur a incorporar modificacions en el codi original. D'aquesta manera vam obtenir i validar SimSET com a generador d'estudis de SPECT a partir de pacients i objectes virtuals.<br/><br/>La millora dels algoritmes es va basar en la incorporació de models analítics de la resposta del sistema col.limador/detector. La modelització del sistema es va implementar per diferents configuracions i energies de la font amb la utilització del codi Monte Carlo PENELOPE. Així mateix es va dissenyar un nou algoritme iteratiu que incorporés l'efecte 3D del sistema i es va tenir en compte la valoració de la imatge en tot el seu volum.<br/><br/>Finalment, es va proposar una correcció de l'scattering utilitzant el simulador SimSET modificat per tal d'accelerar el procés de reconstrucció. Els valors reconstruits de la imatge ens han permès recuperar més d'un 95\% dels valors originals, permetent per tant la quantificació absoluta de les imatges de SPECT.<br>Many forms of brain diseases are associated with problems in the neurotransmission systems. One approach to the assessment of such systems is the use of Single Photon Emission Computed Tomography (SPECT) brain imaging. Neurotransmission SPECT has become an important tool in neuroimaging and is today regarded as a useful method in both clinical and basic research. SPECT is able to non-invasively visualize and analyze different organs and tissues functions or properties in Nuclear Medicine.<br/><br/>Although visual inspection is often sufficient to assess neurotransmission imaging, quantification might improve the diagnostic accuracy of SPECT studies of the dopaminergic system. In particular, quantification of neurotransmission SPECT studies in Parkinson Disease could help us to diagnose this illness in the early pre-clinical stages. One of the main research topics in SPECT is to achieve early diagnosis, indeed preclinical diagnosis in neurodegenerative illnesses. In this field detailed analysis of shapes and values of the region of interest (ROIs) of the image is important, thus quantification is needed. Moreover, quantification allows a follow-up of the progression of disease and to assess the effects of potential neuroprotective treatment strategies. Therefore, the aim of this thesis is to achieve quantification of both the absolute activity values and the relative values of the reconstructed SPECT images.<br/><br/>Quantification is affected by the degradation of the image introduced by statistical noise, attenuation, collimator/detector response and scattering effects. Some of these degradations may be corrected by using iterative reconstruction algorithms, which thus enable a more reliable quantification. The importance of correcting degradations in reconstruction algorithms to improve quantification accuracy of brain SPECT studies has been proved.<br/><br/>Monte Carlo simulations are the --gold standard' for testing reconstruction algorithms in Nuclear Medicine. We analyzed the available Monte Carlo codes and we chose SimSET as a virtual phantom simulator. A new stopping criteria in SimSET was established in order to reduce the simulation time. The modified SimSET version was validated as a virtual phantom simulator which reproduces realistic projection data sets in SPECT studies.<br/><br/>Iterative algorithms permit modelling of the projection process, allowing for correction of spatially variant collimator response and the photon crosstalk effect between transaxial slices. Thus, our work was focused on the modelling of the collimator/detector response for the parallel and fan beam configurations using the Monte Carlo code PENELOPE. Moreover, a full 3D reconstruction with OS-EM algorithms was developed.<br/><br/>Finally, scattering has recognized to be one of the most significant degradation effects in SPECT quantification. Nowadays this subject is an intensive field of research in SPECT techniques. Monte Carlo techniques appear to be the most reliable way to include this correction. The use of the modified SimSET simulator accelerates the forward projection process although the computational burden is already a challenge for this technique.<br/><br/>Full 3D reconstruction simultaneously applied with Monte Carlo-based scattering correction and the 3D evaluation procedure is a major upgrade technique in order to obtain valuable, absolute quantitative estimates of the reconstructed images. Once all the degrading effects were corrected, the obtained values were 95\% of the theoretical values. Thus, the absolute quantification was achieved.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.<br>Includes bibliographical references (p. 53-56).<br>Selective vascular irradiation enables the critical examination of the vasculature and its role in the onset of late radiation effects. It is a novel approach to expose the endothelial cells to much higher levels of ionizing radiation relative to normal cells by utilizing the boron neutron capture reaction. When boron-containing compounds are restricted to the lumen of the blood vessel, the resulting high-LET alpha and lithium particles cannot deposit their energy in the normal cells beyond the vasculature after the target is exposed to thermal neutrons. This allows for a 2- to 3-fold increase in the calculated dose to the endothelial cells. However, this technique has been criticized because there is no direct evidence that the endothelial cells receive an absorbed dose from the selective vascular irradiation. The objective of this work is to provide corroborating experimental evidence that selective vascular irradiation physically damages the endothelial cells. An established assay utilizing blood-brain barrier disruption was adopted to quantify the radiation damage to the endothelial cells in female BALB/C mice, 8-12 weeks of age. A dye that attaches to the plasma proteins in the blood and that is ordinarily kept out of the brain by the blood-brain barrier is injected into the blood supply before the irradiation, and following irradiation, damage to the vasculature will result in disruption of the blood-brain barrier that allows blood stained with the dye to enter the brain. After sacrificing, the blood in the vessel lumen is cleared by performing a trans-cardiac perfusion, and the brain is homogenized and prepared for analysis. The absorbance of the resulting supernatant of each brain sample is measured with a spectrophotometer at the optimal wavelength of the dye.<br>(cont.) The absorbance is related to the quantity of blood that leaked through the blood-brain barrier, which is also related to the damage caused to the vasculature from exposure to ionizing radiation. Increased leakage through the blood-brain barrier was observed for those mice exposed to selective vascular irradiation, indicating a direct relationship between the leakage through the blood-brain barrier and the 10B concentration in the blood. The most significant increase in the leakage through the blood-brain barrier (p<0.002) was observed at the highest lOB concentration in the blood (161 ppm). The compound biological effectiveness (CBE) for sulfhydryl borane (BSH) was calculated to be 0.28, which is consistent with the published value of the CBE for BSH in the rat spinal cord. This suggests that the assumptions used for calculating the absorbed doses for selective vascular irradiation are reasonable and approximate to what the endothelial cells receive.<br>by Rebecca L. Raabe.<br>S.M.

The role of the pedunculopontine tegmental nucleus (PPTg) in the control of behavioural processes was investigated in this thesis. This was achieved through examination of: (1) Conditioned place preference formation: PPTg lesioned rats were not impaired in forming an appropriate place preference, regardless of their deprivation state. (2) Reward-related responding: both food deprived and non-deprived lesioned rats displayed disinhibited intake across a gradient of sucrose rewards, the degree of disinhibition increasing as the reward became stronger. This disinhibited responding was disassociated from simple approach behaviour as shown by similar runway completion times across control and lesioned rats. (3) Radial arm maze performance: PPTg lesioned rats were impaired in their ability to retrospectively plan and forage in a random foraging task. This impairment was seen in both acquisition and retention tasks. PPTg lesioned rats were also impaired in the acquisition of a spatial working memory task in which they had to prospectively plan and execute responses. (4) These behavioural tasks are related to striatal output. To complement them anatomical experiments examining altered striatal outflow on neurotransmitter expression in the PPTg were conducted. Neither dopamine receptor blockade nor 6- hydroxydopamine (6-OHDA) lesions of striatal dopamine produced changes in nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase expression in the PPTg. This work did, however, lay the foundation for future experimentation to address this question. The combination of these findings extends current literature to outline a role for the PPTg in the control of complex behaviours that have been previously associated with sites higher up the neuraxis. This thesis demonstrates that removal of the PPTg results in behaviours that are inappropriate and disinhibited. In conclusion the PPTg is important for both accurate response selection and execution of goal directed behaviours, elements crucial for effective behavioural responding.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2016.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references.<br>Incoming sensory information from all modalities, with the exception of olfaction, synapses in the thalamus on the way to neocortex. This sensory relay is uniquely positioned to act as a gate, to determine which inputs from the periphery are processed by the neocortex. A key 'guardian' of the gate may be the thalamic reticular nucleus (TRN). The TRN is a primary source of GABAergic input to thalamic relay nuclei. The TRN projects directly to the rest of thalamus, generating feedforward and feedback inhibition. It is therefore positioned to mediate forebrain function, and specifically the computations of the neocortex-thalamic loop. Accordingly, failures of the normal dynamics of the TRN are prominent in disease Thalamocortical and corticothalamic projections synapse within this nucleus, and it is subject to a variety of neuromodulatory influences. Depolarization of TRN neurons, and their subsequent firing, is driven by a variety of sources on a range of time scales. The TRN receives excitatory inputs ranging from single spikes to sustained tonic firing to bursting in thalamic relay neurons or layer 6 of neocortex. The temporal dynamics of these inputs, and their spatial organization, can drive different types of firing behavior in TRN. Layer 6 cells form strong synapses in the TRN and even sparse activity in this layer would be predicted to drive substantial inhibition in vivo. Primary thalamocortical relay projections branch into the TRN on their way to sensory cortices, and the nature of this excitatory input reflects the functional modes of the relay nuclei. Inputs include tonic firing that reflects high fidelity to peripheral input, as well as extended bouts of bursting, similar to that seen in TRN itself. In sum, a variety of inputs can excite TRN neurons on different time scales. Understanding how these different patterns may regulate excitability in general, and burst activity specifically, is key to understanding thalamocortical function. The Moore laboratory previously showed that TRN activation could modulate firing and bursting in relay neurons, and induce spindles in the neocortex. In these experiments, the activity of TRN cells during stimulation could only be inferred from downstream effects on spiking and spindle rhythms. Characterizing responses within TRN using a similar stimulation protocol provided a more complete view of the circuit activity underlying this evoked behavior. In Chapter 2 I provided optogenetic input while characterizing multi-unit responses in the TRN and well-sorted single units. I found that longer duration activation drove enhanced bursting and decreased latency to bursting. I also discovered two new -types of cell responses, a more sensitive 'non-linear' cell type that was prone to sustained responses and to bursting, and a more 'linearly' responsive cell class that fired in direct proportion to the duration of stimulation. These findings provide direct predictions as to the behavior of TRN neurons in response to a range of natural depolarizing inputs, and a guide for the optical control of this key structure in studies of network function and behavior. As indicated by the availability of neuromodulatory inputs to TRN, and its apparent role in basic state changes such as sleep and wakefulness, long-term shifts in its depolarization are also likely essential to normal brain function. Optogenetics has rapidly become a standard technique in systems neuroscience, and its genetic specificity and rapid development of new compounds has revolutionized our ability to causally manipulate neural circuits. While the use of light to drive cellular reactions brings a number of advantages when compared to electrical stimulation, there are still many limitations, especially in vivo. Light delivery through tissue is problematic in the intact brain, so targeting deep structures relies on implanted fiber optics and/or LEDs. These methods are not ideal for illuminating large or irregularly-shaped regions without using high light intensity or large arrays of invasive devices. I have been key in inventing a new approach using bioluminescent light to drive optogenetic responses ('BL-OG'). This approach leverages the variety of light sensitive molecules and bioluminescent emitters while providing a means of chemical control. BL-OG combines the cell-type specificity of conventional optogenetics with the potential for noninvasive, system-wide activation. In Chapter 3, I review both this new method and some of my contributions to its realization, specifically demonstrating its functionality in the TRN in vitro and in vivo.<br>by Bryan T. Higashikubo.<br>Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2016.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 24-27).<br>Stressors are known to impact eating behaviors. However, recapitulating the intricate interplay between chronic stress and aberrant human eating patterns in an animal model remains a challenge. Notably, binge eating, a diagnostic feature associated with many types of eating abnormalities, particularly pertains to the binge eating disorder. To more closely investigate the etiology underlying eating behavior-associated maladaptation, the present study provides a novel and ethologically relevant animal model based on predatory odor stress. My data show that chronic stress in female mice selectively increases consumption of highly palatable, but not the regular, diet, when it is presented during a limited time following stress exposure. In addition, the nucleus accumbens (NAc), a key component in the neural circuitry of reward, is also an established neural substrate susceptible to the effects of stress. Given the cellular complexity in NAc, identifying the neuronal subtypes that are selectively involved in chronic stress-elicited physiological and behavioral alterations will provide grounds for further understanding in the underlying cellular changes. Because deficits in the somatostatin (SOM) neurons have been implicated in mice exhibiting traits of anxiety and depression, this neuron subtype may play an important role in modulating negative behavioral emotionality. Here I report an abundance of somatostatin neurons, majority of which are located in the rostral-ventral region of the NAc and are activated by chronic stress exposure. Together, these results provide the first line of evidence in linking chronic stress and the somatostatin neurons within the NAc to binge eating. Further fluorescent labeling quantification and cell-type-specific optogenetic manipulation will be needed to further delineate the role of SOM neurons in orchestrating the inhibitory components of stress-modulated reward circuitry.<br>by Elizabeth Liu.<br>S.M.

Background Swallowing problems are common in Parkinson’s disease, and these affect morbidity and mortality largely due to aspiration-induced pneumonia. Even mild dysphagia affects patient Quality of Life. Deep Brain Stimulation (DBS), a surgical treatment for Parkinson’s disease, improves overall motor function, though the effect of DBS on swallowing function is not clear. The aim of the studies in this thesis was to improve our understanding of the effect from DBS of caudal zona incerta and subthalamic nucleus on pharyngeal swallowing function. Specific aims were to compare DBS effects over time postoperatively (6 &amp; 12 months) for swallowing function, on and off stimulation, with a preoperative baseline assessment in order to identify possible negative swallowing effects of DBS. Methods Eight patients with DBS in caudal zona incerta and eleven patients with DBS in subthalamic nucleus were included in the two studies. The effect of DBS on swallowing function was evaluated by self-estimation on a visual analogue scale and fiberoptic endoscopic evaluation of swallowing function with a predefined swallowing protocol including Rosenbek’s Penetration/Aspiration Scale, Secretion Severity Scale,preswallow spillage, pharyngeal residue and pharyngeal clearance. The patients with caudal zona incerta DBS also answered questions regarding swallowing-related Quality of Life. All patients received L-dopa treatment during postoperative assessments. Results There was no clear effect of DBS on swallowing function in the two samples. The occurrence of aspiration, secretions, pharyngeal residue or clearance was not affected by the surgery or the stimulation. In the subthalamic nucleus DBS sample, self-estimations revealed an improvement with stimulation turned on. For the caudal zona incerta DBS patients, no effect of DBS was seen on the results from the swallowing-related QOL questions. Conclusion Subthalamic nucleus DBS and caudal zona incerta DBS did not appear to have a negative effect on swallowing function in this cohort. Patients with subthalamic nucleus DBS reported a self-perceived improvement in swallowing function after DBS. There appears to be no increased risk for aspiration or penetration due to surgery or stimulation regardless of stimulation site. Since the sample sizes in these cohorts are small, the findings need to be confirmed in larger studies.

The present experiments were designed to examine the hypothesis that the hippocampus and caudate nucleus are parts of independent memory systems which differ in the type of memory they mediate. In experiment 1, the mnemonic functions of the hippocampus and caudate were doubly dissociated; lesions of the caudate nucleus impaired acquisition of the "habit memory" component of the 4 x 4 radial maze task, but had no effect the "cognitive memory" component of the task. Lesions of the fimbria-fornix produced the opposite behavioral dissociation. In experiment 2, lesions of the caudate nucleus produced a transient deficit in cognitive win-shift radial maze behavior when rats were allowed to obtain food from maze arms on an unlimited basis prior to win-shift training. In contrast, lesions of the caudate had no effect on win-shift acquisition when rats were allowed to explore an empty maze prior to win-shift training. These results suggest that reinforcement contingencies may be important in determining the type of memory process initiated by a training experience. In experiments 3ab, systemic post-training injection of the dopamine (DA) agonist D-amphetamine (D-AMP) and the DA D2 receptor agonist LY 171555, but not the DA D1 receptor agonist SKF-38393, improved acquisition on both a habit memory win-stay radial maze task, and a cognitive memory win-shift radial maze task. In experiments 4ab, the mnemonic functions of the hippocampus and caudate nucleus were doubly dissociated using post-training intracerebral injections of these same DA agonists. Post-training intracaudate injection of D-AMP, LY 171555, and SKF-38393 improved acquisition of win-stay, but not win-shift radial maze behavior. Post-training intrahippocampal injection of these DA agonists produced the opposite behavioral dissociation. Taken together, the results are consistent with the hypothesis that the caudate nucleus mediates the acquisition of habit memory, while the hippocampus mediates the acquisition

It has been demonstrated that by using 1H NMR spectroscopy in combination with multivariate statistical modelling (PLS) it is possible, using urine samples obtained from rats, to distinguish between different types of CNS lesions. Against this background this thesis will explore whether the combination of 1H NMR and PLS modelling on biofluids can be used q-1eientify biomarkers in .. - different neurological diseases and in clinically relevant animal models of neurologic disease. The results in this thesis demonstrate that it is possible to separate sets of animals at different stages of disease in models of multiple sclerosis and to identify the presence of early brain metastasis. The same methodology was also applied to human biofluids. In MS patient cohorts (RR- MS, PP-MS and SP-MS) it was also possible to differentiate between RR-MS and SP-MS as well between MS and healthy controls. Therapy for these two stages of MS are very different and therefore a rapid test to determine a patient's stage of MS would be hugely beneficial in the clinic. Further investigation revealed that it is possible to separate MS patients from individuals with Alzheimer's disease. Metabolomics was then combined with other eo- variants in a study of cerebrospinal fluid obtained from patients with HIV associated dementia (HAD) to discover whether disease progression could be followed in this manner. The results show that it is possible to detect neurocognitive changes in patients with HAD. Indeed, the results demonstrate. that metabolomics is a far more sensitive tool for the following progression than other non-PLS biomarker techniques and should provide a useful method for early diagnosis of CNS disease and the evaluation of therapy in prospective studies.

Glioblastoma multiforme is the most aggressive form of malignant brain tumor with poor prognosis. The efficacy of brain cancer treatment by chemotherapeutics is limited by the blood-brain barrier (BBB) which allows less than 2% of the small molecules and blocks almost all the macromolecules to transport into the brain. Delivery of the large molecules such as proteins and nucleic acids across the BBB is a great challenge for brain-targeted drug delivery. To overcome this obstacle, cell-penetrating peptides (CPPs) were used as vectors for delivery of nucleic acids across the BBB targeting glioblastomas. The CPPs have shown such promising carriers to deliver various cargoes ranging from small molecules to large molecules into the cells. This thesis is focused on the development of glioblastoma-targeting vectors based on modifications of the CPPs and the targeting peptides. The peptide-based vectors were developed to improve the transport of the nucleic acids across the BBB and specifically target glioblastomas. In this thesis, a series of peptide-based vectors targeting glioblastomas were synthesized and modified with targeting peptides by either covalent conjugation or non-covalent complex formation. The delivery of plasmid DNA (pDNA) in the complex with the peptide-based vectors was studied in the in vitro model of the BBB. The role of receptors expressed on the BBB was investigated. Scavenger receptors class A and B were found to be expressed on the BBB, and they were involved in the delivery of the pDNA across the BBB model. Moreover, various targeting peptides were modified with hexaglutamate to form non-covalent complexes with the CPPs for small interfering RNA (siRNA) delivery to glioblastoma cells. The non-covalent complex of the CPP and the targeting peptide showed greater gene-silencing efficiency than the consecutively covalent conjugation of the CPP and the targeting peptide for siRNA delivery to glioblastoma cells. Lastly, a number of novel, amphipathic peptides were developed based on the model amphipathic peptide. The prediction of the biological effect of the designed peptides using quantitative structure-activity relationship model showed a correlation with the experimental data. Finally, the CPP-based nucleic acid delivery vectors with homing peptide strategy have a potential for the BBB shuttle and the future use as a glioblastoma-targeted drug carrier in the in vivo studies and the clinical applications.<br><p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Abstract Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been gaining importance in the treatment of advanced Parkinson's disease. This study was undertaken to evaluate the beneficial effects of bilateral STN stimulation on patient's clinical symptoms and quality of life related to the potential risks and side effects of the treatment. A consecutive series of 42 patients operated on for Parkinson's disease with STN DBS in Oulu University Hospital were included. A subgroup of these patients was evaluated using the Unified Parkinson's Disease Rating Scale (UPDRS), neuropsychological tests, and Health Related Quality of Life (HRQoL) instruments i.e. the Parkinson's Disease Questionnaire (PDQ-39) and the Finnish version of the Nottingham Health Profile (NHP). The costs of the treatment were calculated from the perspective of the health care provider. The possible effects of bilateral STN-operation on cardiovascular autonomic function were analyzed by measuring various time- and frequency domain indexes as well as non-linear indexes of heart rate variability (HRV) from 24-hour EKG recording before and 12 months after the operation. This study showed that STN DBS significantly improves the clinical symptoms and HRQoL of parkinsonian patients. The dyskinesia and clinical fluctuation scores were reduced very significantly in the UPDRS IV subscale. The clinical fluctuations were reduced by 53 %. After DBS best motor response (UPDRS III) scores also improved significantly. The HRQoL measured with both instruments improved significantly. Improvement was seen in the PDQ-39 summary index and the subscales of activities of daily living, emotional well-being, stigma and bodily discomfort. Only communication became worse during the follow-up. There was a statistically significant improvement in the score of the subscales of NHP measuring problems with energy, sleep, emotional reactions and social isolation. One patient died from pulmonary embolism and another contracted a late postoperative intracerebral hemorrhage leading to a permanent deterioration of her neurological condition to the bedridden stage. Other complications were much milder. Clinical improvement and improvement in HRQoL were positively correlated. STN DBS does not influence tonic autonomic cardiovascular regulation. The incremental costs of performing bilateral STN DBS in Finland compared to preoperative medical treatment amounted to an average of 25 591 EUR per patient during the first postoperative year. The majority of parkinsonian patients experienced significant and long lasting relief in their motor symptoms and an improvement in HRQoL following STN stimulation.

Orientador: Gabriela Castellano<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas<br>Made available in DSpace on 2018-08-24T17:19:19Z (GMT). No. of bitstreams: 1 Pereira_FabricioRamosSilvestre_D.pdf: 32802688 bytes, checksum: 367566b29c460e1b33f48f861845217a (MD5) Previous issue date: 2013<br>Resumo: O conectoma cerebral refere-se ao mapeamento dos circuitos neurais com os objetivos de 1) identificar regiões que dão suporte às atividades mentais e comportamentais, e 2) detectar alterações nesses circuitos que levam a distúrbios de ordem psiquiátrica e neurológica. Na prática, os estudos de conectoma cerebral consistem na integração de técnicas multimodais de imageamento como ressonância magnética (RM), eletroencefalograma (EEG) e magnetoencefalograma (MEG) com o intuito de estimar os tipos e os níveis de conexão entre regiões cerebrais remotas. Essa "conectividade" entre regiões cerebrais é geralmente classificada em três tipos: anatômica, funcional e efetiva. No presente trabalho, as técnicas de conectividade, usando dados de MR, foram aplicadas na comparação de grupos saudáveis e patológicos. Pela técnica de conectividade anatômica observou-se anomalias na substância branca de pacientes com mutação no gene SPG11. Essa anomalias foram detectadas através da redução da anisotropia fracional (FA) e aumento da difusividade média (MD), difusividade radial (RD) e difusividade axial (AD) em regiões subcorticais dos lobos temporal e frontal, bem como no giro do cíngulo, cuneus striatum, corpo caloso e tronco cerebral. Tais achados indicam que o dano neuronal é mais difuso do que indicava a literatura. Um segundo estudo de conectividade anatômica demonstrou que esses índices de difusividade não foram robustos para diferenciar idosos com e sem diagnóstico de depressão indicando a necessidade de avanços na formulação de novos índices com maior sensibilidade. A técnica de conectividade funcional foi empregada em três estudos. No primeiro, observou-se que pacientes com epilepsia de lobo temporal medial unilateral apresentam redução da conectividade funcional durante a execução de tarefas de memória verbal e visual. Essa redução foi predominantemente ipslateral à lesão e associada ao material-específico utilizado no teste de memória. No segundo estudo, verificou-se uma redução dos padrões de conectividade funcional hipotalâmica em sujeitos obesos e a sua parcial elevação após a cirurgia bariátrica concomitantemente à redução de indicadores bioquímicos de inflamação. No terceiro estudo, observou-se que pacientes com doença de Alzheimer apresentaram elevação dos níveis de conectividade funcional na rede saliente (Salience Network) e redução na rede de modo padrão (Default-mode network). Adicionalmente, verificou-se nos pacientes a correlação positiva da síndrome hiperativa com os níveis de conectividade funcional no cíngulo anterior e em áreas da ínsula direita. O conjunto desses resultados ilustra um possível significado clínico para futuro diagnóstico e tratamento da doença de Alzheimer. Pela técnica de conectividade efetiva observou-se que em função do envelhecimento sadio há uma mudança dos parâmetros de conectividade durante a codificação de palavras com conteúdo emocional. A influência do hipocampo sobre a amígdala ipslateral é reduzida nos sujeitos mais velhos enquanto a influência da amígdala direita sobre o hipocampo direito é elevada. Tais achados reforçam a tese da ininterrupta plasticidade etária e da dinâmica cerebral normal. Essa mesma técnica foi também empregada para demonstrar os diferentes padrões de influência entre os lobos frontal e temporal de pacientes com ELTM esquerda e sujeitos controle. Encontrou-se alteração nos padrões de conectividade efetiva dos pacientes, indicando que estes podem ser potenciais biomarcadores para a epilepsia<br>Abstract: Connectome refers to the neural circuitry mapping aiming to identify brain regions that support mental and behavioral functions as well as to detect circuit changes that are linked to psychiatric or neurologic disorders. In practice, connectome studies link several neuroimaging approaches such as MRI, EEG and MEG by means of the estimation of connections among remote brain regions. This "connectivity" among brain regions is usually classified as anatomic, functional or effective. In this work, the technique of connectivity, using MR data, was applied to compare healthy and pathological groups. By means of the anatomical connectivity abnormalities in the white matter of patients with SPG11 mutation were observed. These abnormalities were expressed as the reduction of the levels of fractional anisotropy (FA) and the increase in mean (MD) and radial diffusivities (RD) in sub-cortical regions of temporal and frontal lobe as well as in cingulated gyrus, cuneus, striatum, corpus callosum and brainstem. These findings suggest that neuronal damage/dysfunction is more widespread than previously recognized in this condition. Another anatomical connectivity study showed that such indices of diffusivity were not robust to statistically differentiate between old subjects with and without depression. This lacking on finding differences between both groups indicates that new indices of diffusivity have to emerge in order to provide complementary information about brain subtle microstructures. Functional connectivity was applied to three studies. In the first study, it was observed that patients with unilateral medial temporal lobe epilepsy presented lower levels of functional connectivity during visual or verbal memory tasks. Such reduction was ipsilateral to the side of the lesion and associated to the specific-material used in the memory task. In the second work, the levels of functional connectivity were reduced in hypothalamic regions of obese patients but a partial reversibility of hypothalamic dysfunction was observed after bariatric surgery. In the third, patients with Alzheimer disease presented higher values of functional connectivity in the salience network and a reduction of connectivity values in the default-mode network. Also in these patients, significant correlations between the levels of hyperactivity syndrome and the salience network were observed in the anterior cingulate cortex and right insula areas. These results indicate the potential clinical significance of resting state alterations in future diagnosis and therapy of Alzheimer disease. The effective connectivity approaches demonstrated that old and young subjects have significant differences when encoding words with emotional contents. The influence of the hippocampus on the ipsilateral amygdale was lower for older subjects whereas the influence of the right amygdale on the right hippocampus was increased for these subjects. These findings suggest that brain plasticity also happens as function of age. The same approach was used to estimate the influence from frontal to temporal lobes in patients with left MTLE compared to healthy subjects. The patterns of effective connectivity were changed in patients and may be potentially considered as biomarkers for epilepsy<br>Doutorado<br>Neurociencias<br>Doutor em Ciências

Magnetic Resonance Imaging (MRI) has a high soft-tissue contrast with a high sensitivity for detecting pathological changes in the brain. Conventional MRI is a time-consuming method with multiple scans that relies on the visual assessment of the neuroradiologist. Synthetic MRI uses one scan to produce conventional images, but also quantitative maps based on relaxometry, that can be used to quantitatively analyse tissue properties and pathological changes. The studies presented here apply the use of synthetic MRI of the brain in different clinical settings. In the first study, synthetic MR images were compared to conventional MR images in 22 patients. The contrast, the contrast-to-noise ratio, and the diagnostic quality were assessed. Image quality was perceived to be inferior in the synthetic images, but synthetic images agreed with the clinical diagnoses to the same extent as the conventional images. Patients with early multiple sclerosis were analysed in the second study. In patients with multiple sclerosis, contrast-enhancing white matter lesions are a sign of active disease and can indicate a need for a change in therapy. Gadolinium-based contrast agents are used to detect active lesions, but concern has been raised regarding the long-term effects of repeated use of gadolinium. In this study, relaxometry was used to evaluate whether pre-contrast injection tissue-relaxation rates and proton density can identify active lesions without gadolinium. The findings suggest that active lesions often have relaxation times and proton density that differ from non-enhancing lesions, but with some overlap. This makes it difficult to replace gadolinium-based contrast agent injection with synthetic MRI in the monitoring of MS patients. Malignant gliomas are primary brain tumours with contrast enhancement due to a defective blood-brain barrier. However, they also grow in an infiltrative, diffuse manner, making it difficult to clearly delineate them from surrounding normal brain tissue in the diagnostic workup, at surgery, and during follow-up. The contrast-enhancing part of the tumour is easily visualised, but not the diffuse infiltration. In studies three and four, synthetic MRI was used to analyse the peritumoral area of malignant gliomas, and revealed quantitative findings regarding peritumoral relaxation changes and non-visible contrast enhancement suggestive of non-visible infiltrative tumour growth. In conclusion, synthetic MRI provides quantitative information about the brain tissue and this could improve the diagnosis and treatment for patients.

The pedunculopontine tegmental nucleus (PPTg) lies within the pontomesencephalon and contains cholinergic and non-cholinergic neurones. It has extensive afferent and efferent connections throughout the brain. Early research suggested a role for the PPTg in the mediation of locomotor activity, and it was believed to form the major substrate of the electrophysiologically identified mesencephalic locomotor region (rviLR). Studies using selective excitotoxic lesions of the PPTg demonstrated that it has no role in the mediation of spontaneous or nucleus accumbens-induced (NAcc) locomotion. However evidence has suggested that the cuneiform nucleus (CNF) and not the PPTg is the main locus of the .MLR. The effects of bilateral ibotenate CNF lesions on spontaneous and amphetamine-induced locomotion stimulated from the NAcc were therefore investigated. CNF lesions had no effect on either type of locomotor activity. Bilateral ibotenate lesions of the PPTg have been shown to influence the expression of orofacial stereotypies following administration of systemic amphetamine. Oral stereotypies can be elicited reliably by direct stimulation of the ventrolateral caudate-putamen (VLCP). This thesis sought to clarify the role of the PPTg in the mediation of oral stereotypies, by combining bilateral ibotenate lesions of the PPTg with direct microinjection of amphetamine into the VLCP. Lesions of the PPTg caused a shift in the dose response curve to amphetamine resulting in an increase in the incidence and intensity of oro facial stereotypies at lower doses. Thus the PPTg appears to have inhibitory control over the expression of orofacial behaviors. It is hypothesised that while neither the PPTg nor the CNF have a role in the mediation of locomotor activity per se they may provide an integrative functional role, which influences motor outflow. The role of the CNF in the transmission of nociception and a role for the PPTg in the mediation of striatal outflow is discussed.

Magnetic Resonance Spectroscopy (MRS) was used to study the relationship between brain regional concentrations of metabolites and normal aging in Chinese. Our goal in this study is to create a database of normal aging and hence enhance further understanding on the degenerative process leading to dementia and related neurodegenerative diseases. Thirty cognitively normal healthy volunteers of age 22-82 years were recruited and the bias on gender effect in data sampling was minimized by recruiting 15 females and 15 males. In the first part of the study, 1H MRS was obtained using single-voxel-spectroscopy (SVS). Offline software java-based version of Magnetic Resonance User Interface (jMRUI) was employed for data analysis. Cerebrospinal fluid was normalized using software voxel based morphormetry (VBM). Brain morphometry data was also analyzed. Brain metabolites choline (Cho), creatine (Cr) and N-acetyl aspartate (NAA) were quantified using internal water as reference. It was found that brain metabolite concentrations of Cr, Cho and NAA increase significantly with age. Gender effect on metabolite concentrations were also discovered, being higher in the female group. For brain morphometry, white matter and grey matter volumes and fractions all reveal a siginificant negative correlation with age, whereas CSF volume and fraction show a significant positive correlation with age. Gender effect was found on grey matter, white matter and intracranial volume, being higher in the male group. In the second part of the study, 31P SVS MRS was performed on the same population of volunteers. jMRUI was also employed for data analysis. Metabolic ratios were obtained. Similar to the 1H MRS study, apart from creating a database in studying normal aging, an additional aim of this 31P MRS study is to correlate with 1H MRS and assist in interpreting the corresponding metabolic activity. Brain metabolite concentrations were found to increase significantly with age. The increase of PCr (phosphocreatine)/Ptot (total phosphorus content) in posterior cingulate suggests lower metabolic activity throughout the course of aging. The strong evidence of PDE (phosphodiester) increase with age in left hippocampus proposes the fact that phospholipid membrane breakdown will be enhanced by aging. In conclusion, MRS can act as a non-invasive tool to study aging at molecular level. Metabolite levels are significant means to investigate the metabolic change in the human brain during the process of aging as the variations in metabolite levels are believed to be footprints of biochemical changes.<br>published_or_final_version<br>Diagnostic Radiology<br>Master<br>Master of Philosophy

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1998.<br>Includes bibliographical references (p. 45-46).<br>The ferret dorsal lateral geniculate nucleus (dLGN) undergoes two periods of retinal afferent segregation during postnatal development. The first establishes the eye-specific laminae, A and A 1, and the second establishes ON/OFF sublaminae within laminae A and At. In contrast to eyespecific segregation, which seems to rely only on presynaptic activity, ON /OFF sublamination requires both pre- and postsynaptic activity. Because of its dependence on postsynaptic (relay cell) activity, sub lamination may be influenced by extra retinal inputs which alter relay cell excitability. We have examined the postnatal development of cholinergic brainstem inputs to the dLGN to determine whether these inputs arrive in time to influence sublamination and whether the cholinergic innervation is present in laminar zones (i.e., whether it might target relay cells). Choline acetyltransferase (ChA1) immunoreactivity is not detected in the dLGN until a few days after the second postnatal week Gust after sublamination begins), at which time it can be seen in both A and C laminae. ChA T labeling increases in intensity until two days before the end of the fourth postnatal week (when ON/OFF sublamination is complete), when it drops dramatically throughout the dLGN . ChAT labeling returns a few days later, but appears in the interlaminar and intersublaminar zones instead of within the A and C laminae. However, the pattern of ChA T labeling reverses once more, so that in the adult, ChA T labeling appears in the A and C laminae and is relatively absent from interlaminar zones. Acetylcholinesterase (AChE) labeling in the dLGN shows a similar ontogenetic pattern and time course. Retrngrade labeling of brainstem cholinergic nuclei demonstrates that these inputs are in place in the dLGN after the second postnatal week. Thus, cholinergic inputs to A and A 1 laminae of the ferret dLG N do arrive in time to influence ON/OFF sublamination.<br>by Sherri Lynn Hitz.<br>S.M.

With approximately 7% of the adult population reporting to have taken illicit substances over the course of a year and the chronically relapsing nature of substance use disorders there is a great need for effective forms of treatment and therapies to reduce relapse. Deep brain stimulation (DBS) is a process of neuromodulation where electrodes are implanted in a target region to modulate the electrophysiological activity of the target region. DBS has been postulated as a potential therapy for treatment-refractory addiction, with a great deal of focus on the nucleus accumbens (NAc). Forty male Long Evans rats were implanted with unilateral stimulating electrodes within the right NAc prior to exposure to chronic cocaine self-administration (0.5 mg/kg/infusion). Following self administration, the animals were withdrawn from cocaine and treated with 14 consecutive days of sham, low frequency (LF, 20 Hz) or high frequency (HF, 160 Hz) stimulation sessions (30 min/day). The animals underwent drug seeking tests on days 1, 15 and 30 of the withdrawal phase with context-induced relapse paired with a drug challenge (5 mg/kg i.p). Relapse rates were highest on day 15 after withdrawal, with both LF and HF attenuating cocaine during this drug-seeking test, however this was not the case for tests on days 1 and 30. Motivation to respond for saccharin solution (0.1 %) remained intact following both LF and HF stimulation intake sessions. These results demonstrate that unilateral DBS of the NAc effectively attenuated cocaine-seeking following chronic exposure to stimulation although these beneficial effects appeared to diminish following cessation of daily treatment with stimulation. The results obtained in this experiment provide support for DBS as a potential therapy for patients with treatment-resistant cases of substance use disorders.

Parkinson’s disease is a neurodegenerative process with several motor and non-motor manifestations. Among non-motor symptoms, cognitive decline is a major cause of disability, and its neural bases are poorly understood. In recent years, multimodal neuroimaging techniques have proven to be useful tools in the investigation of the bases of cognitive impairment related to neurological diseases. The objective of this thesis was to evaluate the neuroimaging substrates of Parkinson’s disease-related cognitive and neuropsychiatric manifestations through a network approach, using state-of-the art magnetic resonance imaging techniques to assess associated connectivity and structural changes. In this work, two samples of Parkinson’s disease patients and healthy controls underwent neuropsychological evaluation as well as structural and functional magnetic resonance imaging. One of these samples included 121 Parkinson’s disease patients and 49 healthy controls. The data obtained were used in 2 studies addressing the resting-state functional connectivity changes associated with mild cognitive impairment in Parkinson’s disease; one using a graph-theory approach, and the second assessing large-scale intrinsic connectivity networks through an independent-component analysis/dual regression approach. A third was performed to assess connectivity disruptions in frontostriatal circuits associated with the presence of apathy in Parkinson’s disease. And a fourth study was made assessing cortical thickness changes associated with the presence of mild cognitive impairment in Parkinson’s disease. The second sample included the longitudinal evaluation of 17 Parkinson’s disease patients and 15 healthy controls, and the data obtained resulted in two studies regarding progressive cortical thickness and subcortical volumes in early-stage Parkinson’s disease patients. A seventh study, using subjects from both samples, was performed to evaluate microstructural white matter changes (using diffusion tensor imaging) and gray matter changes (through voxel-based morphometry) related to the presence of facial emotion recognition deficits in Parkinson’s disease. We have found that a high percentage of Parkinson’s disease patients had mild cognitive impairment. These patients showed altered patterns of resting-state functional connectivity characterized by the loss of long range connections and strengthening of local connectivity. From a graph-theory perspective, these changes translated as increased small-world coefficients, modularity and clustering coefficients, which correlated with visuospatial/visuoperceptual and memory performance. The study of large-scale networks showed that patients with mild cognitive impairment had reduced connectivity between the dorsal attention network and the right frontoinsular region, and that this reduction was associated with attention/executive deficits. Additionally, parieto-occipital regions that belong to the dorsal attention network showed reduced connectivity with anterior task­positive regions and loss of the normal anticorrelated pattern with the default mode network; furthermore, these posterior regions showed structural degeneration. Finally, these posterior structural and functional changes were associated with the presence of visuospatial/visuoperceptual deficits. The analysis of Parkinson’s disease patients with mild cognitive impairment revealed a pattern of cortical thinning predominating in parieto­occipito-temporal regions. The longitudinal analysis of progressive structural changes in early Parkinson’s disease revealed that these patients had more marked cortical thinning in frontotemporal regions, even before the onset of clinically evident cognitive manifestations. The functional analysis of a recognition memory network likewise showed signs of progressive connectivity changes without overt clinical deterioration. We conclude that different types of cognitive decline in Parkinson’s disease are associated with different patterns of resting-state functional connectivity, structural connectivity and GM structural changes involving distinct neural systems. Different techniques and different conceptual frameworks can provide useful information in the characterization of the neural bases of cognitive deficits associated with Parkinson’s disease.<br>La malaltia de Parkinson és un procés neurodegeneratiu que té diverses manifestacions motores i no motores. Entre les manifestacions no motores, el deteriorament cognitiu és una causa important i comú de discapacitat; al cap de 20 anys des de l’inici de la malaltia, més de 80% dels pacients desenvolupen demència. Tot i tenir una alta prevalença i representar un factor de pèrdua de qualitat de vida tant pels pacients com per als seus cuidadors, les bases neurals d’aquestes alteracions són poc conegudes. En els últims anys, les tècniques d’imatge multimodals han demostrat ser útils en la investigació de les bases dels dèficits cognitius associats a les malalties neurològiques, i alguns estudis previs han trobat alteracions cerebrals tant estructurals com funcionals en subjectes amb la malaltia de Parkinson. D’altra banda, el concepte de deteriorament cognitiu lleu (DCL), utilitzat per definir la presència d’un rendiment cognitiu inferior al esperat segons l’edat i el nivell educatiu – i un major risc de desenvolupament de demència – s’ha començat a aplicar en el context de la malaltia de Parkinson. A més, en estudis epidemiològics s’ha vist que la presència d’alguns tipus d’alteració cognitiva – concretament, aquells que tenen substrats neurals predominants en regions corticals posteriors, com són dèficits visuoespacials i visuoperceptius – indiquen una major probabilitat de desenvolupar demència. Al contrari, en els dèficits relacionats amb els desequilibris en la neurotransmissió dopaminèrgica (com són els dèficits d’atenció i executius), no s’ha trobat que siguin marcadors de pitjor pronòstic cognitiu. L’objectiu d’aquesta tesi va ser avaluar els substrats neuroanatòmics i neurofuncionals de les diferents alteracions cognitives i neuropsiquiàtriques relacionades amb la malaltia de Parkinson mitjançant un abordatge de xarxes, tot utilitzant tècniques avançades de ressonància magnètica per estudiar les disfuncions de la connectivitat cerebral. En aquesta tesi, es van utilitzar dues mostres de pacients amb malaltia de Parkinson i subjectes sans que es van sotmetre a avaluació neuropsicològica i de ressonància magnètica funcional i estructural. La primera d’aquestes mostres va incloure 121 malalts de Parkinson i 49 controls sans. Les dades obtingudes amb aquesta mostra han sigut utilitzades en cinc estudis (estudis 1, 2, 3, 4 i 5), tres dels quals van abordar la connectivitat funcional cerebral en repòs i les alteracions estructurals associats a la presència de DCL. Per definir la presència de DCL, en dos estudis (estudis 1 i 2) s’han avaluat els déficits en tres dominis cognitius (atenció/funcions executives, memòria i funcions visuoespacials/visuoperceptives); en l’altre estudi (estudi 3), s’ha utilitzat un mqtode de classificació d’acord amb les recents directrius proposades per la Movement Disorder Society Task Force, que consideren el rendiment en cinc dominis (atenció/memòria de treball, funcions executives, memòria, llenguatge i funcions visuoespacials/visuoperceptives). En els estudis 1 i 2, es van avaluar 66 pacients i 36 controls utilitzant tècniques d’avaluació de la connectivitat cerebral en repòs i les alteracions corresponents associats a la presència de DCL. Trenta cinc per cent dels pacients amb malaltia de Parkinson van complir criteris de DCL. Estudi 1: En aquest estudi, s’ha aplicat un abordatge de teoria de grafs per avaluar les alteracions globals de connectivitat. Per tal de reconstruir les xarxes cerebrals, la substància grisa cortical i subcortical s’ha dividit en 90 regions definides amb l’atles Automated Anatomical Labelling. Posteriorment, s’ha calculat la correlació temporal de l’activitat entre cada parell de regions, obtenint-se així una matriu representativa de la connectivitat funcional de tot el cervell. En un primer pas, s’han comparat directament aquestes matrius de correlació per tal d’avaluar el patró de reducció o augment de connectivitat en els diferents subgrups de pacients. Aquest anàlisi va revelar que els pacients amb DCL tenien reduccions de connectivitat, sobretot afectant les connexions interlobulars de llarga distància, així com alguns augments de connectivitat, sobretot en connexions mps curtes. Posteriorment, s’han utilitzat les matrius de correlació per calcular mesures globals i regionals de teoria de grafs. Concretament, s’han avaluat paràmetres que mesuren la integració (l’eficiència d’intercanvi d’informació entre distintes àrees cerebrals): el characteristic path length i l’eficiència global;i paràmetres de segregació, que mesuren la interconnectivitat local: el clustering coefficient i l’eficiència local. També s’ha avaluat el grau de modularitat de les xarxes cerebrals, és a dir, quant de bé aquestes xarxes es podien dividir en mòduls o comunitats de nodes densament interconnectats, amb poques connexions entre diferents mòduls. S’ha observat que els pacients amb DCL presentaven augments en les mesures de segregació i de modularitat. Les anàlisis de correlació han revelat que aquestes mesures es correlacionaven amb el rendiment en funcions visuoespacials/visuoperceptives i de memòria. En l’anàlisi de les mesures de centralitat dels nodes – és a dir, la importància que tenen en el tràfic d’informació dins de la xarxa –, s’ha observat que els nodes que solen ser més centrals en subjectes sans (els anomenats hubs cerebrals) perden centralitat en els pacients amb malaltia de Parkinson. Aquest resultat indica una reorganització d’aquestes xarxes caracteritzat per un augment del flux d’informació neural a travès de nodes que en subjectes sans són menys rellevants. Aquest estudi es va publicar a la revista Human Brain Mapping a l’any 2014 (Cognitive impairment and resting-state network connectivity in Parkinson’s disease). Estudi 2: s’ha utilitzat la mateixa mostra que en l’estudi 1. S’ha utilitzat, però, un altre tipus d’anàlisi amb l’objectiu d’estudiar els patrons de connectivitat dins d’un conjunt de xarxes cerebrals que, segons estudis previs, tenen un paper rellevant en els processos cognitius: la default mode network, la xarxa dorsal de l’atenció i la xarxa frontoparietal. Inicialment, s’ha realitzat un anàlisi de components independents amb les dades de ressonància magnètica funcional en repòs per tal d’identificar les xarxes d’interès a nivell grupal. Posteriorment, s’ha utilitzat la tècnica de dual regression per identificar les mateixes xarxes a nivell individual, i que permet comparacions entre els grups. En aquesta anàlisi, s’ha observat que els pacients amb DCL presentaven reduccions de connectivitat entre la xarxa dorsal de l’atenció i l’ínsula anterior i regions adjacents del lòbul frontal dret. En el grup de pacients, el nivell de connectivitat en aquestes regions es correlacionava amb el rendiment en el domini d’atenció/executiu. A més, s’ha vist que els pacients amb DCL presentaven un augment de connectivitat entre extenses àrees parieto-occipitals i la default mode network; aquestes disfuncions de connectivitat també estaven associats a pitjor rendiment cognitiu, però en aquest cas en el domini visuoespacial/visuoperceptiu. Com anàlisi addicional per definir les alteracions locals de connectivitat, es va realitzar una avaluació de les connexions entre els nodes individuals de les xarxes d’interès; per definir aquests nodes, s’han seleccionat a priori les coordenades disponibles en un estudi de referència. Aquesta anàlisi ha demostrat que els augments de connectivitat de regions corticals posteriors amb la default mode network en realitat estaven caracteritzats per una pèrdua del patró normal d’anticorrelació amb aquesta xarxa observat en controls sans. A més, s’ha vist que aquestes mateixes regions tenien menys connectivitat amb les altres xarxes avaluades. Finalment, s’han realitzat anàlisis complementaris per avaluar la presència de degeneració estructural de la substància grisa que pogués estar associada a les alteracions funcionals observades. L’anàlisi del gruix cortical va revelar la presència de reduccions en els pacients amb DCL en regions parieto-occipitals; aquestes reduccions estaven associades a les alteracions de connectivitat de la default mode network i amb el rendiment visuoespacial/visuoperceptiu. Aquest estudi es va publicar a la revista Human Brain Mapping a l’any 2014 (Functional brain networks and cognitive deficits in Parkinson's disease). Estudi 5: En el tercer estudi en que es va avaluar la connectivitat funcional en repòs, l’objectiu va ser investigar les alteracions en els circuits fronto-estriats en la malaltia de Parkinson amb apatia – un trastorn neuropsiquiàtric molt freqüent en pacients amb aquesta malaltia. Amb aquesta finalitat, es va utilitzar la mateixa mostra que en els dos primers estudis. Es van classificat els subjectes en apàtics o no-apâtics segons la puntuació en l’escala d’apatia de Starkstein. A més, es va tenir en compte la presència de trastorns depressius, que, a més de tenir una alta prevalença en la malaltia de Parkinson, freqüentment coexisteixen amb l’apatia i tenen manifestacions que s’hi solapen. Així doncs, també es va aplicar l’escala de depressió de Beck; la puntuació en els 11 ítems d’aquesta escala que representen els símptomes disfòrics, més específics de la depressió, es va utilitzar com a covariable en totes les anàlisis. Per a realitzar l’anàlisi de connectivitat funcional, es va parcel·lar l’estriat en 3 regions – límbica, executiva i sensorimotora. Així mateix, es va parcel·lar l’escorça frontal en 4 regions – límbica, executiva, rostral motora i caudal motora. Vint pacients (41%) es van classificar com apâtics (puntuació > 13 en l’escala d’apatia). L’anàlisi de connectivitat va revelar que la presència d’apatia estava acompanyada de reduccions, que principalment afectaven les regions límbiques tant del estriat com de l’escoroa prefrontal. Per tal d’avaluar si aquestes alteracions s’acompanyaven de degeneració de les estructures avaluades, es van realitzar anàlisis addicionals amb voxel-based morphometry de les estructures corticals i subcorticals, a més de volumetria i shape analysis dels nuclis del estriat. No s’han obtingut resultats significatius amb cap d’aquests abordatges. Aquest estudi està actualment en revisió en una revista indexada. Estudi 3: En aquest estudi, 90 pacients i 32 controls van ser estudiats mitjançant tècniques d’avaluació del gruix cortical. Trenta dos (52%) pacients van complir criteris de DCL. S’ha observat que el grup de pacients amb DCL presentava reduccions del gruix cortical en regions parieto-temporals, així com augment en mesures d’atròfia global tals com reducció del gruix cortical global i del volum de substància grisa, així com augment del volum ventricular. Les anàlisis de correlació van revelar que el rendiment en totes les proves neuropsicològiques estava associat a la pèrdua de gruix cortical posterior. Aquest estudi es va publicar a la revista Movement Disorders a l’any 2014 (Cortical thinning associated with mild cognitive impairment in Parkinson's disease). Per a la segona mostra de subjectes, es van reclutar 24 pacients amb malaltia de Parkinson inicial i 24 controls sans, els quals es van estudiar mitjançant ressonància magnètica estructural i funcional així com mitjançant exploració neuropsicològica. Disset pacients i 15 controls van ser avaluats longitudinalment, amb una segona avaluació després d’un seguiment mitjà de 35,5 mesos. Estudi 6: En el primer estudi fet amb aquesta mostra, es van incloure 17 pacients i 13 controls, i l’objectiu va ser estudiar la xarxa de memòria de reconeixement. Per això es va utilitzar una seqüència de ressonància magnètica funcional amb un paradigma de memòria de reconeixement que consistia en intentar reconèixer les 35 paraules prèviament apreses entre una llista de 70 paraules. Les dades obtingudes van ser avaluades a través de abordatges convencionals o model-based, així com a través de tècniques model-free (anàlisi de components independents). En la primera anàlisi, es va identificar el patró d’activació associat a la tasca. En l’anàlisi de components independents, també es van identificar els components associats a la tasca; les principals regions activades en la component més associada a la tasca es van utilitzar com a regions d’interès en un anàlisi subsegüent de canvis progressius de connectivitat. Es va trobar una correlació entre la activació de la component independent més associada a la tasca i el rendiment de memòria de reconeixement dels pacients. A més, l’avaluació longitudinal va revelar canvis progressius en la connectivitat entre els principals nodes d’aquesta xarxa, caracteritzats per la pèrdua de connectivitat entre regions frontoparietals i la preservació de la connectivitat frontofrontal (que en els controls sans s’havia reduït). Aquest estudi es va publicar a la revista Journal of Neurology, Neurosurgery and Psychiatry a l’any 2013 (Progressive changes in a recognition memory network in Parkinson's disease). Estudi 7: En aquest segon estudi fet amb la segona mostra, s’ha volgut analitzar el patró d’atròfia progressiva de la substància grisa en la malaltia de Parkinson inicial i la seva relació amb canvis neuropsicològics. Amb aquesta finalitat, les dades de setze pacients i 15 controls van ser avaluades amb tècniques de gruix cortical, volum de substància grisa a través de voxel-based morphometry i volumetria cortical i subcortical. Es van trobar reduccions progressives del gruix cortical en regions frontotemporals bilaterals. L’avaluació neuropsicològica va revelar que els pacients tenien pitjor rendiment en proves d’atenció i de velocitat psicomotora, però aquestes variables no es correlacionaven amb els canvis corticals. Aquest estudi es va publicar a la revista Movement Disorders a l’any 2012 (Progression of cortical thinning in early Parkinson's disease). Un últim estudi (estudi 4) es va realitzar amb subjectes de la primera i de la segona mostra. Es va seleccionar una submostra de 39 pacients i 23 controls amb la finalitat d’avaluar les alteracions de les substàncies blanca i grisa associats als dèficits de reconeixement d’emocions facials en la malaltia de Parkinson. Es van utilitzar imatges potenciades en difusió per l’estudi d’alteracions microestructurals de la substància blanca en els tractes llargs que connecten les estructures cerebrals involucrades en el processament emocional, mitjançant tècniques de imatge per tensor de difusió. A més, les imatges estructurals es van avaluar a través de voxel­based morphometry per estudiar les alteracions de volum de la substància grisa en les estructures cerebrals prèviament descrites com rellevants pel processament d’emocions. El rendiment en el reconeixement d’emocions facials es va mesurar mitjançant la prova d’Ekman. Els pacients amb la malaltia de Parkinson van obtenir un rendiment inferior als controls en la identificació de les emocions negatives (tristesa, ràbia, por i fàstic). L’anàlisi de correlacions va revelar que els dèficits d’identificació de tristesa correlacionaven amb els valors d’anisotropia fraccional –un paràmetre de la microestructura de la substància blanca– sobretot en el fascicle fronto-occipital inferior dret. L’anàlisi de substància grisa, per contra, va revelar que la identificació de tristesa correlacionava amb el volum de l’escoroa orbitofrontal dreta, amígdala i gir postcentral; la identificació de ràbia correlacionava amb el volum de substància grisa de l’estriat ventral, escorça infragenual i gir fusiform occipital dret; i la identificació de fàstic correlacionava amb volum de substància grisa en el còrtex cingulat anterior. Aquest estudi es va publicar a la revista Neuropsychologia a l’any 2012 (Structural correlates of facial emotion recognition deficits in Parkinson's disease patients). Tots aquests estudis ens permeten concloure que un alt percentatge de pacients amb malaltia de Parkinson tenen alteracions cognitives i compleixen criteris de DCL. L’anàlisi de neuroimatge mitjançant diferents estratègies demostra que la presència de DCL en la malaltia de Parkinson s’acompanya d’alteracions estructurals i funcionals. A més, diferents tipus de dèficit cognitiu es relacionen amb diferents patrons d’alteració. A nivell de connectivitat funcional en repòs, els pacients amb malaltia de Parkinson amb DCL presenten un patró predominant de reducció de connectivitat de llarg abast i augment de la connectivitat local, que es tradueix en un augment del caràcter modular i de segregació de les xarxes cerebrals. Així mateix, s’observa una reducció de connectivitat de components de xarxes de connectivitat intrínseca rellevants per al processament cognitiu, que es caracteritza per una reducció de connectivitat d’una xarxa involucrada en processos de l’atenció (xarxa dorsal de l’atenció) i la regió insular anterior dreta. Al mateix temps, s’observa una reducció de connectivitat de regions corticals posteriors amb regions cerebrals anteriors, que s’associa a atròfia cortical posterior i a la presència de dèficits en les funcions visuoespacials/visuoperceptives. L’anàlisi de la connectivitat funcional en repòs revela també que la presència d’apatia en la malaltia de Parkinson s’acompanya de reduccions en circuits fronto-estriats, que sobretot afecten els components del sistema de recompensa, és a dir, l’estriat ventral i l’escorça orbitofrontal. Els resultats de l’anàlisi d’alteracions microestructurals de la substància blanca associats al pitjor reconeixement d’emocions facials semblen indicar que els dèficits de connectivitat estructural també estan implicats en l’ocurrència dels dèficits cognitius en la malaltia de Parkinson. Finalment, en pacients amb malaltia de Parkinson inicial, s’han aportat evidències sobre el poder dels mètodes de neuroimatge per a detectar alteracions estructurals (pèrdua de gruix neocortical) i funcional fins i tot abans de l’inici de símptomes cognitius clínicament evidents. En conclusió, els resultats obtinguts en els diferents estudis d’aquesta tesi ens permeten concloure que distintes tècniques i diferents marcs conceptuals poden proporcionar informació útil per a la caracterització de les bases neurals dels dèficits cognitius i emocionals associats a la malaltia de Parkinson.