Dissertations / Theses on the topic 'Cerebellar nuclei'

Le cervelet, composé d'un cortex et de noyaux, est responsable du contrôle moteur fin des mouvements et de la posture. En combinant une approche génétique (basée sur l'utilisation de lignées de souris transgéniques) avec des traçages anatomiques, des marquages immunohistochimiques et des expériences d'électrophysiologie et d'optogénétique, nous établissons les caractères distinctifs des neurones inhibiteurs des noyaux cérébelleux et en détaillons la connectivité ainsi que les fonctions dans le circuit cérébelleux. Les neurones inhibiteurs glycinergiques des noyaux profonds constituent une population de neurones distincts des autres types cellulaires identifiables par leur phénotype inhibiteur mixte GABAergique/glycinergique. Ces neurones se distinguent également par leur plexus axonal qui comporte une arborisation locale dans les noyaux cérébelleux où ils contactent les neurones principaux et une projection vers le cortex cérébelleux où ils contactent les cellules de Golgi. Ces neurones inhibiteurs reçoivent également des afférences inhibitrices des cellules de Purkinje et pourraient être contactés par les fibres moussues ou les fibres grimpantes.Nous apportons ainsi la première étude d'une transmission mixte fonctionnelle par les neurones inhibiteurs des noyaux cérébelleux, projetant à la fois dans les noyaux et le cortex cérébelleux. L'ensemble de nos données établissent les neurones inhibiteurs mixtes des noyaux cérébelleux comme la troisième composante cellulaire des noyaux profonds. Leur importance dans l'organisation modulaire du cervelet, ainsi que leur impact sur l'intégration sensori-motrice, devront être confirmés par des études optogénétiques in vivo
The cerebellum is composed of a three-layered cortex and of nuclei and is responsible for the learned fine control of posture and movements. I combined a genetic approach (based on the use of transgenic mouse lines) with anatomical tracings, immunohistochemical stainings, electrophysiological recordings and optogenetic stimulations to establish the distinctive characteristics of the inhibitory neurons of the cerebellar nuclei and to detail their connectivity and their role in the cerebellar circuitry.We showed that the glycinergic inhibitory neurons of the cerebellar nuclei constitute a distinct neuronal population and are characterized by their mixed inhibitory GABAergic/glycinergic phenotype. Those inhibitory neurons are also distinguished by their axonal plexus which includes a local arborization with the cerebellar nuclei where they contact principal output neurons and a projection to the granular layer of the cerebellar cortex where they end onto Golgi cells dendrites. Finally, the inhibitory neurons of the cerebellar nuclei receive inhibitory afferents from Purkinje cells and may be contacted by mossy fibers or climbing fibers.We provided the first evidence of functional mixed transmission in the cerebellar nuclei and the first demonstration of a mixed inhibitory nucleo-cortical projection. Overall, our data establish the inhibitory neurons as the third cellular component of the cerebellar nuclei. Their importance in the modular organization of the cerebellum and their impact on sensory-motor integration need to be confirmed by optogenetic experiments in vivo

It is a general assumption that the cerebellum plays a pivotal role in learning and memory of sensory-motor information, although the mechanisms through which the cerebellum is able to process information are still largely unknown. Several studies both in in vivo and in in vitro conditions support the existence of synaptic and non-synaptic plasticity in the cerebellum not confined to the sole cerebellar cortex although less is known about plastic changes mechanisms at the level of deep cerebellar nuclei (DCN). Moreover, the discovery that alterations in cerebello-cortical interconnections are related to cognitive diseases such as schizophrenia and autism suggests a cerebellar role in cognition. Further evidence of cerebellar role in cognition comes tracing studies in humans and electrophysiological recordings in rodents in vivo. In this work, putative changes underlying DCN neurons capability to integrate sensory information were investigated by delivering a theta sensory stimulation pattern (TSS) at the level of the peri-oral area of urethane anesthetized mice while recording single-units activity in the Fastigial nucleus. Our results show that TSS is able to evoke several discharge patterns in DCN neurons in vivo, likely depending on the synaptic pathways engaged by the stimulation. Moreover, our results show that long-lasting changes detected in DCN following TSS were related to oscillations in the theta frequency range. The employment of pharmacological tools and optogenetics helped to better characterize some of the processes underlying plasticity in the DCN. The second part of this work is focused on cerebellar involvement in neocortical processing. In particular, we investigated the functional connectivity of fastigial and dentate nuclei (FN and DN, respectively) with the prelimbic area (PrL) of medial prefrontal cortex (mPFC). Herein, we characterized the single-unit pattern changes in PrL neurons following electrical stimulation of the contralateral FN or DN in urethane anesthetized mice. Two main anatomical pathways connect the cerebellum to the prefrontal area: the dopaminergic pathway, passing through the ventral tegmental area, and the glutamatergic pathway arising from the thalamus. Pharmacological approaches helped to discriminate these two pathways and investigate whether and how specific neuromodulators or neurotransmitters affect prefrontal neurons responses to cerebellar stimulation. PrL neurons showed spontaneous activity and responded to electrical stimulation of FN and DN with two response patterns, both characterized by an initial pause, in some cases followed by a rebound excitation detected as a peak in PSTHs. The perfusion of dopamine receptors antagonists did not abolish PrL neurons responses, thus supporting the hypothesis that dopamine released in PrL modulates neuronal responses, presumably affecting neurons intrinsic excitability. Following previous results, we focused our attention on the contribution of GABAergic synaptic inhibition within the PrL, presumably mediated by thalamic projections activated by DN stimulation. The majority of thalamic glutamatergic projections reach the mPFC at the level of interneurons in cortical Layers III/V. Our results showed that for almost all PrL responding units the inhibitory component was abolished by blocking GABAA receptors. Therefore, a reasonable explanation of our data is that the cerebellum is mainly involved in the activation of inhibitory cells regulating pyramidal neurons activity in PrL. Hence, the cerebellum may exert a crucial role in cognition, by preferentially leading to PrL neurons inhibition and therefore controlling the level of excitation/inhibition in mPFC circuitry. Overall, the findings reported in this work are relevant not only for understanding cerebellar functioning itself, but also for understanding cerebellar contribution to higher order cognitive processes.

The deep cerebellar nuclei (DCN) function as output gates for a large majority of the Purkinje cells of the cerebellar cortex and thereby determine how the cerebellum influences the rest of the brain and body. In my PhD programme I have investigated how the DCN process two kinds of input patterns received from Purkinje cells: irregularity of spike intervals and pauses in Purkinje cell activity resulting from the recognition of patterns received at the synapses with the upstream parallel fibres (PFs). To that objective I have created a network system of biophysically realistic Purkinje cell and DCN neuron models that enables the exploration of a wide range of network structure and cell physiology parameters. With this system I have performed simulations that show how the DCN neuron changes the information modality of its input, consisting of varying regularity in Purkinje cell spike intervals, to varying spike rates in its output to the nervous system outside of the cerebellum. This was confirmed in simulations where I exchanged the artificial Purkinje cell trains for those received from experimental collaborators. In pattern recognition simulations I have found that the morphological arrangement present in the cerebellum, where multiple Purkinje cells connect to each DCN neuron, has the effect of amplifying pattern recognition already performed in the Purkinje cells. Using the metric of signal-to-noise ratio I show that PF patterns previously encountered and stored in PF - Purkinje cell synapses are most clearly distinguished from those novel to the system by a 10-20 ms shortened burst firing of the DCN neuron. This result suggests that the effect on downstream targets of these excitatory projection neurons is a decreased excitation when a stored as opposed to novel pattern is received. My work has contributed to a better understanding of information processing in the cerebellum, with implications for human motor control as well as the increasingly recognised non-motor functions of the cerebellum.

本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである
Kyoto University (京都大学)
0048
新制・課程博士
博士(医学)
甲第5999号
医博第1665号
新制||医||608(附属図書館)
UT51-95-D318
京都大学大学院医学研究科生理系専攻
(主査)教授 水野 昇, 教授 本田 孔士, 教授 川口 三郎
学位規則第4条第1項該当

Thesis (Ph. D.)--University of California, San Diego, 2008.
Title from first page of PDF file (viewed January 15, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Absence epilepsy is a neurological disorder that commonly occurs in children. Some studies have shown that absence seizures predominantly originate either in the thalamus or the cerebral cortex. Some cerebellar nuclei (CN) neurons project to these brain areas, as explained further in Fig. 2.6 in Chapter 2. Also, some CN neurons have been observed to show modulation during the absence seizures. This indicates that they somehow participate in the seizure and hence are referred to as "participating neurons" in this thesis. In this research, I demonstrate how machine learning techniques and computer simulations can be applied to investigate the properties and the input conditions present in these participating neurons. My investigation found a sub-group of CN neurons, with similar interictal spiking activity, spiking activity between the seizures, that are most likely to participate in seizures. To investigate the input conditions present in the CN neurons that produce this type of interictal activity, I used a morphologically realistic conductance based model of an excitatory CN projection neuron [66] and optimised the input parameters to this model using an Evolutionary Algorithm (EA). The results of the EA revealed that these participating CN neurons receive a synchronous and bursting input from Purkinje cells and bursting input with long intervals(approx. 500ms) from mossy fibre. The same interictal activity can also be produced when the Purkinje cell input to the CN neuron is asynchronous. The excitatory input in this case also had long interburst intervals but there is a decrease in excitatory and inhibitory synaptic weight. Surprisingly, a slight change in these input parameters can change the interictal spiking pattern to an ictal spiking pattern, the spiking pattern observed during absence seizures. I also discovered that it is possible to prevent a participating CN neuron from taking part in the seizures by blocking the Purkinje cell input.

Includes bibliographical references (leaves 73-79).
In vivo magnetic resonance spectroscopy (MRS) is an imaging technique that allows the chemical study of human tissue non-invasively. The method holds great promise as a diagnostic tool once its reliability has been established. Inter-scanner variability has, however, hampered this from happening as results cannot easily be compared if acquired on different scanners. In this study a phantom was constructed to determine the localisation efficiency of the 3 T Siemens Allegra MRI scanner located at the Cape Universities Brain Imaging Centre (CUBIC). Sufficient localisation is the key to acquiring useful spectroscopic data as only the signal from a small volume of interest (VOI) is typically acquired. The phantom consisted of a Perspex cube located inside a larger Perspex sphere. Solutions of the cerebral metabolites N-acetyl aspartate (NAA) and choline (Cho) were placed in the inner cube and outer sphere respectively. The phantom was scanned at a range of voxel sizes and echo times in order to determine parameters that typically indicate the performance of the scanner in question. The resultant full width at half maximum (FWHM) and signal to noise ratio (SNR) values indicated that optimal results were obtained for a voxel with dimensions 20 x 20 x 20 mm3. The selection efficiency could not be measured due to limitations in the scanner, but two other performance parameters ' extra volume suppression (EVS) and contamination ' could be determined. The EVS showed that the scanner was able to eliminate the entire background signal from the out-of-voxel region when voxel sizes with dimensions (20 mm)3 and (30 mm)3 were used. This performance decreased to 96.2% for a voxel size of (50 mm)3. The contamination indicated that the unwanted signal, weighted by the respective proton densities of the chemicals, ranged from 12% in the (20 mm)3 voxel to 24% in the (50 mm)3 voxel. These ranges are well within acceptable limits for proton MRS. Analysis of the water suppression achieved in the scanner showed an efficiency of 98.84%, which is acceptable for proton spectroscopy. It was also found that manual iv shimming of the scanner improved the spectra obtained, as compared to the automated shimming performed by the scanner. The second objective of the study was to quantify absolute metabolite concentrations in the familiar SI units of mM as results were previously mostly expressed as metabolite ratios. The LCModel software was used to assess two methods of determining absolute metabolite concentrations and the procedure using water scaling consistently showed superior performance to a method using a calibration factor. The method employing water scaling was then applied to a study of fetal alcohol spectrum disorder (FASD) where the deep cerebellar nuclei of children with FASD and a control group were scanned. The cerebellar nuclei were of interest as children with FASD show a remarkably consistent deficit in eye blink conditioning (EBC). The cerebellar deep nuclei is known to play a critical role in the EBC response. The results show significant decreases in the myo-inositol (mI) and total choline (tCho) concentrations of children with FASD in the deep cerebellar nuclei compared to control children. The FAS/PFAS subjects have a mean mI concentration of 4.6 mM as compared to a mean of 5.3 mM in the controls. A Pearson correlation showed that there was a significant relationship between decreasing mI concentrations with increasing prenatal alcohol exposure. The mean tCho concentrations are 1.3 mM for FAS/PFAS and 1.5 mM for the controls. There was no significant differences between the heavily exposed group and either the FAS/PFAS or the control subjects for either metabolite. The decreased mI and tCho concentrations may indicate deficient calcium signalling or decreased cell membrane integrity ' both of which can explain the compromised cerebellar learning in FASD subjects.

Le cervelet permet l’apprentissage moteur et la coordination des mouvements fins. Pour ce faire, il intègre les informations sensorielles provenant de l’ensemble du corps ainsi que les commandes motrices émises par d’autres structures du système nerveux central. Les noyaux cérébelleux profonds (DCN) constituent la sortie du cervelet et intègre les informations provenant des cellules de Purkinje (PC), des fibres moussues et des fibres grimpantes. Nous avons étudié les connexions fonctionnelles entres les PC et les DNC in vivo, grâce à une stimulation optogénétique des lobules IV/V du cortex cérébelleux et à l’enregistrement multi unitaire du noyau médian. Nous avons ainsi identifié deux groupes de cellules au sein des DCN, présentant des caractéristiques propres au niveau de leur fréquence de décharge et de la forme des potentiels d’action, en accord avec la dichotomie établie par une précédente étude in vitro permettant de séparer les neurones GABAergiques des autres neurones. Nos résultats suggèrent que les PC contrôlent la sotie du cervelet d’un point de vue temporel. De plus, la ciruiterie interne des DCN conforte ce résultat de part le fait que les cellules GABAergiques ne produisent pas d’effet temporel au travers de l’inhibition locale
The cerebellum integrates motor commands with somatosensory, vestibular, visual and auditory information for motor learning and coordination functions. The deep cerebellar nuclei (DCN) generates the final output by processing inputs from Purkinje cells (PC), mossy and climbing fibers. We investigated the properties of PC connections to DCN cells using optogenetic stimulation in L7-ChR2 mice with in vivo multi electrode extracellular recordings in lobule IV/V of the cerebellar cortex and in the medial nuclei. DCN cells discharged phase locked to local field potentials in the beta, gamma and high frequency bands. We identified two groups of DCN cells with significant differences in action potential waveforms and firing rates, matching previously discriminated in vitro properties of GABAergic and non-GABAergic cells. PCs inhibited the two group of cells gradually (rate coding), however spike times were controlled for only non-GABAergic cells. Our results suggest that PC inputs temporally control the output of cerebellum and the internal DCN circuitry supports this phenomenon since GABAergic cells do not induce a temporal effect through local inhibition

The neuronal circuitry between the cerebellum and inferior olive is of crucial importance in motor function. While the climbing fibres that send olivary signals to the cerebellum have been shown to play a significant role in modulating cerebellar output, little is known of the origins or function of the nucleo-olivary neurons of the cerebellar nuclei that send reciprocal feedback to the inferior olive. In this thesis, the Sox14 gene is identified as a novel genetic developmental marker for nucleo-olivary neurons of the lateral and interposed, but not medial, cerebellar nuclei. Using Sox14-GFP and Sox14-Cre knock-in and Sox14 knock-out mouse lines, in combination with birth dating, marker analysis and tract tracing techniques, I characterised the projections and development of nucleo-olivary neurons. These experiments established that Sox14 is expressed in early born GABAergic nuclear projection neurons that exclusively target the inferior olive. A separate population of Sox14+ cells in Nucleus Y target the oculomotor nucleus. Sox14 expression is observed from E12.5 directly ventral to the nuclear transitory zone, where glutamatergic nuclear cells are known to reside during development. Injection of Cre-dependent AAV-mCherry-flex-dtA was used to drive expression of diphtheria toxin A subunit in Sox14 expressing cells. Ablation of Sox14+ nucleo-olivary neurons leads to some deficits in motor performance and motor learning. However, no deficits in associative motor learning were observed, suggesting that models of associative learning that invoke a key role for the nucleo-olivary feedback may be incorrect or incomplete. This work establishes that nucleo-olivary neurons of the lateral and interposed cerebellar nuclei comprise a homogeneous and genetically distinct population and sheds light on the function of this projection in cerebellar function. Furthermore, this thesis establishes Sox14 transgenic mice as a unique tool in cerebellar research that will provide an important window on the function of the cerebellum in future studies.

Neurons can encode information using the rate of their action potentials, making the relation between input rate and output rate a prominent feature of neuronal information processing. This relation, known as I{O function, can rapidly change in response to various factors or neuronal processes. Most noticeably, a neuron can undergo a multiplicative operation, resulting in a change of the slope of its I{O curve, also know as gain change. Gain changes represent multiplicative operations, and they are wide- spread. They have been found to play an important role in the encoding of spatial location and coordinate transformation, to signal amplification, and other neuronal functions. One of the factors found to introduce and control neuronal gain is synaptic Short Term Depression (STD). We use both integrate-and- re and conductance based neuron models to identify the effect of STD in excitatory and inhibitory modulatory input. More specifically, we are interested in the effect of STD at the inhibitory synapse from Purkinje cells to cerebellar nucleus neurons. Using a previously published, biologically realistic model, we find that the presence of STD results in a gain change. Most importantly we identify STD at the inhibitory synapse to enable excitation-mediated gain control. To isolate the mechanism that allows excitation to control gain, even though STD is applied at a different synapse, we first show that the overall effect is mediated by average conductance. Having done this, we find that the effect of STD is based on the non-linearity introduced in the relation between input rate and average conductance. We find this effect to vary, depending on the position of the I{O function on the input rate axis. Modulatory input shifts the I{O curve along the input rate axis, consequently shifting it to a position where STD has a different effect. The gain differences in the STD effects between the two positions enable excitation to perform gain control.

Anodal cerebellar transcranial direct current stimulation (tDCS) is known to enhance motor learning and it is suggested to hold promise as a therapeutic intervention. However, the neural mechanisms underpinning the effects of cerebellar tDCS are unknown. In addition, it is unclear whether this effect is robust across varying task parameters as if cerebellar tDCS is to be used clinically it must have a consistent effect across a relatively wide range of behaviours. Therefore, I performed four studies to address these questions. In the first three studies, I investigated the neural changes associated with cerebellar tDCS using magnetic resonance spectroscopy (MRS) and resting state functional magnetic resonance imaging (fMRI). My goal was to understand how cerebellar tDCS affected the metabolites within the cerebellum and functional connectivity between the cerebellum and distant brain areas. In addition, I wanted to understand if individual differences in how cerebellar tDCS influenced visuomotor adaptation could be explained by the effect tDCS had on neurobiology. Therefore, healthy participants underwent 3 sessions in which they received concurrent anodal cerebellar tDCS during visuomotor adaptation, MRS and resting state fMRI. I found that in 21% of participants cerebellar tDCS caused enhanced visuomotor adaptation, a decrease in GABA and increase in functional connectivity between the cerebellum and parietal cortex. This work suggests an ‘all-or-nothing’ type effect of cerebellar tDCS. In my final study, I examined the consistency of the cerebellar tDCS effect on visuomotor adaptation across a wide range of task parameters which were systematically varied. Each experiment examined whether cerebellar tDCS had a positive effect on adaptation when a unique feature of the task was altered. I found cerebellar tDCS to have an inconsistent effect on visuomotor adaptation. I conclude that such inconsistencies could be dependent on the amount of participants in each group that are receptive to cerebellar tDCS and suggest that at the very least it warrants substantially large sample size in cerebellar tDCS studies.

Le système circadien des mammifères est constitué d´une horloge principale dans le noyau suprachiasmatique (SCN) et d´autres oscillateurs du cerveau. Sa fonction exige des mécanismes de rétroaction entre ces régions. Dans cette thèse, des méthodes d´électrophysiologie ont été utilisées pour étudier certains signaux influençant le signal de sortie neuronal du SCN et pour identifier ce signal dans l'horloge du cervelet. D´abord, l'activation du récepteur à la glycine dans le SCN a été confirmée. Des enregistrements en champs de microélectrodes (MEA) ont montré des effets excitateurs et inhibiteurs de la glycine, dont les proportions varient avec le temps circadien. La glycine induit des déphasages de l'activité circadienne en fonction du temps circadien. Ensuite, un rôle de l´oréxine a été montré dans le SCN. Les enregistrements patch-clamp et MEA ont montré qu´elle influence l'excitabilité des neurones du SCN. De plus, des avances de phase du rythme circadien de l'activité électrique ont été induites par l´oréxine pendant le jour subjectif en culture de coupes. Ainsi, l'hypothalamus latéral fournirait des informations sur l'éveil au SCN à l´aide de l´oréxine. Enfin, la fréquence de décharge des cellules de Purkinje du cervelet a été examinée. Aucun rythme circadien n´a été observé en conditions constantes. Cependant, un stimulus quotidien induit un rythme, suggérant que les cellules de Purkinje sont des oscillateurs esclaves. Ce travail décrit des mécanismes afférents modulant l'horloge du SCN. Savoir comment les signaux de sorties des oscillateurs du cerveau influencent le système circadien pourrait aider à traiter les pathologies liées au dysfonctionnement de l'horloge
The circadian system of mammals controls biological processes that last 24 hours. It is constituted by a master clock in the suprachiasmatic nucleus (SCN) and other brain oscillators. A coherent function of the system requires feedback mechanisms between these regions. In this thesis, electrophysiological methods were used to study some feedback signals influencing SCN neuronal output and to identify this output in the cerebellar clock. In a first part, patch-clamp recordings confirmed glycine receptor activation in the SCN. Microelectrode arrays (MEA) recordings showed excitatory and inhibitory effects of glycine, which proportions varied with circadian time. Importantly, glycine induced phase-shifts of the circadian activity depending on the circadian time. In a second part, a role of the neuropeptide orexin in the SCN was shown. Patch-clamp and MEA recordings showed that orexin influences the excitability of SCN neurons. Long-term recordings showed orexin-induced phase-advances of the circadian rhythm in electrical activity during the subjective day in slice culture. Thus, the lateral hypothalamus may provide information on arousal to the SCN via orexin. In the last part, the firing rate of Purkinje cells of the cerebellum was examined. No circadian rhythm was observed in either single electrode or MEA recordings on acute and cultured slices, respectively. Interestingly, a daily stimulus induced a rhythm, suggesting that Purkinje cells are slave oscillators. The present work describes afferent mechanisms modulating the SCN clock. Knowing how outputs of brain oscillators influence the circadian system could help to treat pathologies associated with clock dysfunction

L'objectif général de cette thèse est d'explorer l'impact des lésions du cervelet sur les séquelles motrices et cognitives des enfants traités pour tumeur du cervelet maligne ou bénigne. En nous basant sur trois études cliniques, nos objectifs généraux ont été (1) d'examiner si ces enfant présentaient des déficits dans l'établissement d'automatismes moteurs et cognitifs, (2) de préciser les facteurs associés aux difficultés d'automatisation et (3) d'examiner l'impact de ces difficultés sur la scolarité et le devenir à long terme de ces enfants. La première étude avait pour objectif spécifique d'examiner le devenir à long terme de 46 adultes et de 18 adolescents traités dans l'enfance chirurgicalement pour un astrocytome pilocytique du cervelet. Elle a mis en évidence un devenir à long terme satisfaisant dans l'ensemble, bien que des difficultés cognitives et motrices aient été rapportées, en particulier par les sujets qui ont le plus réussi leurs parcours scolaires. La perte d'autonomie était associée à des complications postopératoires telles que le mutisme cérébelleux et l'invasion du tronc cérébral. La deuxième étude a porté sur une cohorte de 17 enfants et adolescents traités pour un astrocytome pilocytique cérébelleux. Elle a exploré l'automatisation de la lecture et discuté la théorie cérébelleuse de la dyslexie. Les résultats ont mis en évidence une difficulté de suppression des mouvements articulatoires chez la plupart des sujets qui était associée à un faible indice de Mémoire de Travail Verbale. La troisième étude a porté sur 16 enfants traités pour un astrocytome pilocytique du cervelet et 16 enfants traités pour un médulloblastome. Elle avait pour objectifs (1) d'étudier l'apprentissage moteur et différents automatismes cognitifs intervenant notamment dans la lecture et le calcul mental et (2) de préciser les relations entre les différentes mesures de la difficulté d'automatisation motrice et cognitive. Les résultats ont confirmé la difficulté de suppression des mouvements articulatoires et ont montré que les enfants traités pour tumeur du cervelet se différenciaient des enfants sains de âge par un apprentissage moteur moindre, en particulier avec la main non dominante et par une lenteur en lecture, en calcul mental, en dénomination rapide et en double tâche. Par ailleurs, l'atteinte des noyaux dentelés était liée à une baisse de l'efficience intellectuelle, en particulier chez les enfants traités pour un médulloblastome, à un apprentissage moteur moindre avec la main dominante, à une difficulté de suppression des mouvements articulatoires, et à une lenteur de calcul mental. Ce travail de thèse offre des résultats pionniers dans la compréhension de l'impact des lésions cérébelleuses sur les apprentissages chez l'enfant
The general aim this doctoral dissertation is to explore the impact of cerebellar lesions on motor and cognitive sequelae in children treated for malignant or benign tumor of the cerebellum. In three clinical studies, we in (1) examine whether these children exhibited deficits in motor and cognitive automation, (2) identify factors associated with difficulties in automation and (3) examine the impact of these difficulties on schooling and long-term outcome. The first study examines the long-term outcome of 46 adults and 18 adolescents treated surgically in childhood for cerebellar pilocytic astrocytoma. Most subjects showed a positive long-term outcome, despite report of cognitive and motor difficulties, especially by subjects with successful school careers. The loss of autonomy was associated with postoperative complications, post cerebellar mutism, or invasion of the brain stem. The second study in 17 children and adolescents treated for pilocytic cerebellar astrocytoma aimed to examine the automation of reading and to discuss the cerebellar theory of dyslexia. The results highlighted a difficulty of suppressing articulatory movements in most subjects, associated with low index of Verbal Working Memory. The third study concerned 16 children treated for pilocytic astrocytoma of the cerebellum and 16 children treated for medulloblastoma. Its objectives were to (1) investigate motor learning and different cognitive automations involved in particularly in reading and mental calculation (2) clarify the relationship between different measures of motor and cognitive automation. The results confirmed the difficulty to suppress articulatory movements and showed lower motor learning effect, especially with the non-dominant hand, slowness in reading, mental calculation, rapid naming and dual task. Furthermore, dentate nuclei damage was linked to lower intellectual efficiency (IQ), particularly in children treated for medulloblastoma; to a lesser motor learning for the dominant hand, a difficulty to suppress articulatory movements, and slowness in mental calculation. This work offers pioneer results in understanding the impact of cerebellar lesions in children learning

Le cervelet joue un rôle fondamental dans la coordination, l'ajustement, la planification et l'automatisation des mouvements, dans la modulation des réflexes ou encore dans certaines fonctions cognitives. Pour ce faire, il va collecter des informations motrices et sensorielles provenant aussi bien du cortex cérébral que du reste du corps. Ces informations sont relayées vers le cortex et les noyaux cérébelleux via les fibres grimpantes et les fibres moussues. Les fibres grimpantes, projetant depuis l'olive inférieure, convoient des signaux sensori-moteurs impliqués dans certains apprentissages et dans la régulation temporelle des activités cérébelleuses. Ces processus jouent un rôle modulateur de la décharge et des plasticités des cellules de Purkinje. Ces dernières ciblent les noyaux cérébelleux qui représentent l'unique sortie du cervelet. Les efférences de ces noyaux cérébelleux incluent une projection GABAergique dirigée sur l'olive inférieure. Ainsi, les connexions entre l'olive inférieure et le cervelet constituent potentiellement une boucle fermé olivo-cortico-nucléaire. Nos études se basent sur les enregistrements électrophysiologiques in vitro et in vivo de ces trois structures effectués sur un modèle de souris génétiquement modifiées qui permet un contrôle spécifique de la décharge des cellules de Purkinje par l'utilisation de l'optogénétique. La stimulation lumineuse du cortex cérébelleux de ces souris transgéniques active les cellules de Purkinje ainsi que la boucle olivo-cortico-nucléaire sur un délai total d'environ 100 ms. Ces résultats démontrent pour la première fois que les cellules de Purkinje contrôlent de manière phasique leurs afférences olivaires et que ce processus pourrait participer à la régulation des apprentissages moteurs cérébelleux
The cerebellum plays a fundamental role in coordination, adjustment, planning and automation of movements, in the modulation of reflexes and in some cognitive functions. To do this, it will collect motor and sensory information from both the cerebral cortex and the rest of the body. These information are relayed to the cortex and cerebellar nuclei via climbing fibers and mossy fibers. Climbing fibers, the projections from the inferior olive to the cerebellar cortex, carry sensorimotor error and clock signals that trigger motor learning by controlling cerebellar Purkinje cell synaptic plasticity and discharge. Purkinje cells target the deep cerebellar nuclei, which are the output of the cerebellum and include an inhibitory GABAergic projection to the inferior olive. This pathway identifies a potential closed loop in the olivo-cortico-nuclear network. Therefore, sets of Purkinje cells may phasically control their own climbing fiber afferents. Here, using in vitro and in vivo recordings, we describe a genetically modified mouse model that allows the specific optogenetic control of Purkinje cell discharge. Tetrode recordings in the cerebellar nuclei demonstrate that focal stimulations of Purkinje cells strongly inhibit spatially restricted sets of cerebellar nuclear neurons. Strikingly, such stimulations trigger delayed climbing-fiber input signals in the stimulated Purkinje cells. Therefore, our results demonstrate that Purkinje cells phasically control the discharge of their own olivary afferents and thus might participate in the regulation of cerebellar motor learning

Etude du rôle de l'olive inferieure dans l'inhibition cérébelleuse chez le rat, après destruction sélective de l'O. I. Cette destruction élimine l'action de suppression tonique qu'exercent les fibres grimpantes sur les décharges simples des Purkinje. On observe : a) un accroissement de l'inhibition cérébelleuse dans les premiers jours, ainsi qu'une disfacilitation rubrale et une dépression des activités motrices; b) ces effets régressent jusqu'à 1 mois; c) passe 1 mois le déficit moteur persiste.

Des lésions (par la 3-acétylpyridine) et des activations (par l'harmaline) de l'olive bulbaire inférieure ont été réalisées, chez le jeune rat, pour étudier le rôle de la voie olivo-cérébelleuse dans l'acquisition du comportement d'équilibration. Les aspects quantitatifs (temps de maintien des rats sur le rota-rod) et qualitatif (comportement des rats sur le rota-rod) ont été abordés. Les animaux sont soit, avant et/ou après la lésion, naïfs ou entraînés, soit, pendant l'activation olivaire, naïfs ou entraînés. Deux facteurs influencent le taux de mortalité l'étendue de la lésion et la réponse à l'harmaline: la quantité de 3-acétylpyridine administrée et sa dureté d'action. La lésion totale ou partielle retarde considérablement l'apprentissage du comportement étudié. Chez les rats entraînés après la lésion, un entraînement pré-lésionnel est plus efficace lorsque la lésion est totale que lorsqu'elle est partielle. L'activation de la voie olivo-cérébelleuse facilite l'acquisition du comportement d'équilibration à condition qu'elle ne soit pas trop importante. La voie olivo-cérébelleuse est impliquée dans l'acquisition du comportement d'équilibration. Son rôle semble plus lié à la quantité de stimulation qu'à leur qualité

Главно маслинасто једро је највећи део доњег маслинастог комплекса. На пресеку главно маслинасто једро има изглед наборане врећице са дном које гледа ка спољашњој површини продужене мождине и отвором који је окренут унутра и дорзално. Главно маслинасто једро је укључено у просторну и временску организацију покрета и моторног учења, учења које је повезано са вежбањем, просуђивања времена интервала и брзине покретних стимулуса и когнитивних операција у простору. Популацију неурона главног маслинастог једра чине мултиполарни (90%) и интернеурони (10%). Дендритска арборизација неурона главног маслинастог једра је веома комплексна и различитог је облика (сферична или асиметрична), а правац пружања дендрита може да буде радијалан или кружан. Структурну и функционалну потпору неуронима пружају глијалне ћелије (астроцити, олигодендроцити и микроглија). Глијалне ћелије окружују неуроне и окупирају међунеуронске просторе где одржавају микросредину погодну за активност и виталност неурона. Старење представља природан и временски зависан процес који је карактерисан прогресивном појавом иреверзибилних промена у ћелијама, што резултира опадањем саморегулаторних способности јединке. У току старења, долази до нарушавања природног окружења неурона и глијалних ћелија што се одражава на њихов број, величину и изглед тела, дендритску крошњу и синаптичку организацију. Циљеви: Циљеви истраживања су да се утврди да ли се параметри морфологије неурона и глијалних ћелија разликују између старосних група, као и да се квантитативном анализом провери могућност класификације неурона и глијалних ћелија према квалитативном опису. Материјал и методе: Узорак студије је чинило 30 обостраних исечака главног маслинастог једра подељених у три старосне групе (други период сазревања (36-60 год.), рани период старења (61-75 год.) и касни период старења (76-90 год.)). Извршена је хистолошка обрада узорака Голџијевом методом импрегнације а микроскопске слике резова су дигитализоване а затим трансформисане у бинарне и скелетонизоване слике. Квалитативно су процењиване особине слика неурона (259) и глијалних ћелија (419) а квантитативна анализа величине, облика, гранања, дужине и сложености испитиваних ћелија спроведена је израчунавањем 22 (геометријска, компјутациона и фрактална) параметра. Резултати: Квалитативном проценом уочене су разлике у изгледу тела и неуронског поља, дендритске крошње, правца пружања дендрита, и распореда неурона у главном маслинастом једру. Квалитативна процена глијалних ћелија омогућила је њихов опис према врстама (астроцити, олигодендроцити и микроглија). Квантитативно испитивање геометријских параметара је показало да се неурони и глијалне ћелије не могу класификовати према величини. Неурони треће старосне групе имају мање вредности параметара који квантификују сложеност тела, неуронског поља и дендритске крошње, као и параметре дужине неурона. Површина тела, параметри дужине глијалне ћелије и сложеност глијалне крошње астроцита, значајно су мањи у узорку треће старосне групе, у поређењу са првом и другом. Олигодендроцити прве и друге старосне групе имају веће параметре који дефинишу величину и дужину ћелија, а мање вредности фракталне димензије сложености (тела, глијалног поља и глијалне крошње), од треће старосне групе. Закључци: Касни период старења нервног система резултирао је појавом регресивних промена на неуронима. Астроцити већ у раном периоду старења подлежу атрофичним променама на нивоу тела, глијалног поља и наставака, док олигодендроцити у касном периоду старења задржавају сложеност у грађи.
Glavno maslinasto jedro je najveći deo donjeg maslinastog kompleksa. Na preseku glavno maslinasto jedro ima izgled naborane vrećice sa dnom koje gleda ka spoljašnjoj površini produžene moždine i otvorom koji je okrenut unutra i dorzalno. Glavno maslinasto jedro je uključeno u prostornu i vremensku organizaciju pokreta i motornog učenja, učenja koje je povezano sa vežbanjem, prosuđivanja vremena intervala i brzine pokretnih stimulusa i kognitivnih operacija u prostoru. Populaciju neurona glavnog maslinastog jedra čine multipolarni (90%) i interneuroni (10%). Dendritska arborizacija neurona glavnog maslinastog jedra je veoma kompleksna i različitog je oblika (sferična ili asimetrična), a pravac pružanja dendrita može da bude radijalan ili kružan. Strukturnu i funkcionalnu potporu neuronima pružaju glijalne ćelije (astrociti, oligodendrociti i mikroglija). Glijalne ćelije okružuju neurone i okupiraju međuneuronske prostore gde održavaju mikrosredinu pogodnu za aktivnost i vitalnost neurona. Starenje predstavlja prirodan i vremenski zavisan proces koji je karakterisan progresivnom pojavom ireverzibilnih promena u ćelijama, što rezultira opadanjem samoregulatornih sposobnosti jedinke. U toku starenja, dolazi do narušavanja prirodnog okruženja neurona i glijalnih ćelija što se odražava na njihov broj, veličinu i izgled tela, dendritsku krošnju i sinaptičku organizaciju. Ciljevi: Ciljevi istraživanja su da se utvrdi da li se parametri morfologije neurona i glijalnih ćelija razlikuju između starosnih grupa, kao i da se kvantitativnom analizom proveri mogućnost klasifikacije neurona i glijalnih ćelija prema kvalitativnom opisu. Materijal i metode: Uzorak studije je činilo 30 obostranih isečaka glavnog maslinastog jedra podeljenih u tri starosne grupe (drugi period sazrevanja (36-60 god.), rani period starenja (61-75 god.) i kasni period starenja (76-90 god.)). Izvršena je histološka obrada uzoraka Goldžijevom metodom impregnacije a mikroskopske slike rezova su digitalizovane a zatim transformisane u binarne i skeletonizovane slike. Kvalitativno su procenjivane osobine slika neurona (259) i glijalnih ćelija (419) a kvantitativna analiza veličine, oblika, grananja, dužine i složenosti ispitivanih ćelija sprovedena je izračunavanjem 22 (geometrijska, kompjutaciona i fraktalna) parametra. Rezultati: Kvalitativnom procenom uočene su razlike u izgledu tela i neuronskog polja, dendritske krošnje, pravca pružanja dendrita, i rasporeda neurona u glavnom maslinastom jedru. Kvalitativna procena glijalnih ćelija omogućila je njihov opis prema vrstama (astrociti, oligodendrociti i mikroglija). Kvantitativno ispitivanje geometrijskih parametara je pokazalo da se neuroni i glijalne ćelije ne mogu klasifikovati prema veličini. Neuroni treće starosne grupe imaju manje vrednosti parametara koji kvantifikuju složenost tela, neuronskog polja i dendritske krošnje, kao i parametre dužine neurona. Površina tela, parametri dužine glijalne ćelije i složenost glijalne krošnje astrocita, značajno su manji u uzorku treće starosne grupe, u poređenju sa prvom i drugom. Oligodendrociti prve i druge starosne grupe imaju veće parametre koji definišu veličinu i dužinu ćelija, a manje vrednosti fraktalne dimenzije složenosti (tela, glijalnog polja i glijalne krošnje), od treće starosne grupe. Zaključci: Kasni period starenja nervnog sistema rezultirao je pojavom regresivnih promena na neuronima. Astrociti već u ranom periodu starenja podležu atrofičnim promenama na nivou tela, glijalnog polja i nastavaka, dok oligodendrociti u kasnom periodu starenja zadržavaju složenost u građi.
The principal olivary nucleus is the largest part of the inferior olivary complex. On the cross-section, the principal olivary nucleus has the appearance of a folded bag with a bottom looking to the outer surface of the medulla oblongata and hilum that is turned inward and dorsally. The principal olivary nucleus is involved in spatial and temporal organization of movement and motor learning, learning which is related to exercise, coordination of interval time with speed of stimuli and cognitive operations. Neuronal population of principal olivary nucleus is consists of multipolar neurons (90%) and interneurons (10%). Dendritic arborization of olivary neurons is very complex with a spherical and asymmetrical shape and radial or circular dendrites. Structural and functional support for neurons is provided by the glial cells (astrocytes, oligodendrocytes and microglia). Glial cells surround neurons and occupy interneuronal spaces where they maintain a suitable microenvironment for the neuronal activity and vitality. Aging is a physiological and time-dependent process characterized by the progressive irreversible changes of the cells, resulting in a decrease in self-regulatory capabilities. During aging, the natural environment of neurons and glial cells is affected, which reflects on their number, size and body structure, the dendritic arborization, and synaptic organization. Aims: The aims of the research were to determine whether the morphology of neurons and glial cells differ between age groups and to quantitatively analyze the possibility of classification of neurons and glial cells according to their qualitative description. Material and methods: The study sample consisted of 30 two-sided sections of the principal olivary nucleus divided into a three age groups (the second period of maturation (36-60 years), early aging (61-75 years) and late aging (76-90 years)). Histological preparation of samples (by Golgi's method of impregnation) was performed and the microscopic images were digitized and then transformed into a binary and skeletonized forms. Neurons (259) and glial cells (419) were qualitatively evaluated and the quantitative analysis of the size, shape, branching, length and complexity was carried out by calculating 22 (geometric, computer and fractal) parameters. Results: Qualitative estimation revealed the differences in the appearance of the neuronal body and neuronal field, dendritic arborisation, direction of dendrites and position of neurons inside the principal olivary neucleus. A qualitative evaluation of glial cells enabled description of their types (astrocytes, oligodendrocytes and microglia). Quantitative testing of geometric parameters has shown that neurons and glial cells cannot be classified according to their size. Neurons from third age group have lesser values of parameters that quantify the body complexity, the neuronal field, and the dendritic arborization, as well as parameters of the neuronal length. The body area, parameters of the astrocytes length and the astrocyte arborization complexity, are significantly lower in the sample of the third age group, in compared with the first and the second. Oligodendrocytes of the first and second age group have larger parameters that define the cell length, and lower values of the fractal dimension of body, glial field and glial arborization complexity, from the third age group. Conclusions: Late aging period of the nervous system resulted in a regressive changes on neurons. During the early aging period astrocytes undergo to atrophic changes of body, glial filed and processes, while the oligodendrocytes in the late period of aging retain their structure complexity.

In the cerebellum, the corticonuclear projection subserves as the major efferent pathway for the cerebellar cortical networks. This pathway, consists of a direct axonal projection from the Purkinje cells to the neurons of the deep cerebellar nuclei (DCN). It has been demonstrated both in vivo and in vitro that stimulation of the Purkinje cell axons exerts a powerful inhibitory influence on DCN neurons mediated by the neurotransmitter, ƴ-aminobutyric acid (GABA). However, despite the wealth of anatomical and biochemical information, few electrophysiological studies have been done to characterize GABAergic synaptic transmission in DCN neurons. For example, it is not clear whether synaptic release of GABA activates pre- or postsynaptic GABAB receptors despite the finding that GABAB binding sites are present in the DCN. Furthermore, although GABAergic transmission in the DCN exhibits paired-pulse, frequency-dependent, as well as long-term depressions, the mechanisms underlying these plasticity's are yet to be resolved. In the present study, both perforated and whole-cell patch clamp recording techniques were utilized to determine whether preand postsynaptic GABAB receptors are present in the DCN and to test if endogenous release of GABA can activate either of the receptors. In addition, the contribution of GABAB receptors to paired-pulse and frequency-dependent depression of the deep nuclear inhibitory postsynaptic current (IPSC) was also assessed. Finally, experiments were conducted to investigate the properties of a tetanic stimulation-induced deep nuclear long-term depression (LTD) of the IPSC and to examine the role of Ca^2+ and protein phosphatases as potential mediators of the sustained depression. The results of the studies indicated that postsynaptic GABAB receptors are present on the membrane of DCN neurons. Activation of these receptors produces a G-protein-dependent response similar to that observed in other central neurons. In addition, presynaptic GABAB receptors are also present in the DCN. Activation of these receptors produces a suppression of deep nuclear IPSCs. However, deep nuclear preand postsynaptic GABAB receptors were found not to be activated by endogenous release of GABA. Furthermore, these receptors appear not to be involved in pairedpulse and frequency-dependent depressions of the IPSC. In voltage-clamped DCN neurons, LTD of the IPSC was induced reliably if the LTD-inducing train was delivered under current-clamp conditions where the membrane potential was allowed to fluctuate. Using this protocol in subsequent experiments, it was found that currents elicited by iontophoretic applications of THIP, a GABAA agonist, also exhibited LTD following a tetanic stimulation of the input. It was also demonstrated that LTD can be induced heterosynaptically. Furthermore, activation of the IPSC during the train was not required for LTD to occur. However, postsynaptic Ca^2+ accumulations via influx though A/-methyl-D-aspartate receptor-gated channels and/or voltage-gated Ca^2+ channels appear to play an important role in the generation of LTD. Moreover, protein phosphatase activity appears to be necessary for the induction of the depression. It is concluded that postsynaptic mechanisms contribute to LTD of GABAergic transmission in neurons of the DCN. Bhagavatula R. Sastry, Ph.D., Research Supervisor.

The study of cerebellum-like circuits allows many points of entry. These circuits are often involved in very specific systems not found in all animals (for example electrolocation in weakly electric fish) and thus can be studied with a neuroethological approach in mind. There are many cerebellum-like circuits found across the animal kingdom, and so studies of these systems allow us to make interesting comparative observations. Cerebellum-like circuits are involved in computations that touch many domains of theoretical interest - the formation of internal predictions, adaptive filtering, cancellation of self-generated sensory inputs. This latter is linked both conceptually and historically to philosophical questions about the nature of perception and the distinction between the self and the outside world. The computation thought to be performed in cerebellum-like structures is further related, especially through studies of the cerebellum, to theories of motor control and cognition. The cerebellum itself is known to be involved in much more than motor learning, its traditionally assumed function, with particularly interesting links to schizophrenia and to autism. The particular advantage of studying cerbellum-like structures is that they sit at such a rich confluence of interests while being involved in well-defined computations and being accessible at the synaptic, cellular, and circuit levels. In this thesis we present work on two cerebellum-like structures: the electrosensory lobe (ELL) of mormyrid fish and the dorsal cochlear nucleus (DCN) of mice. Recent work in ELL has shown that a temporal basis of granule cells allows the formation of predictions of the sensory consequences of a simple motor act - the electric organ discharge (EOD). Here we demonstrate that such predictions generalize between electric organ discharge rates - an ability crucial to the ethological relevance of such predictions. We develop a model of how such generalization is made possible at the circuit level. In a second section we show that the DCN is able to adaptively cancel self-generated sounds. In the conclusion we discuss some differences between DCN and ELL and suggest future studies of both structures motivated by a reading of different aspects of the machine learning literature.

The first stage of mammalian auditory processing occurs within the dorsal and ventral divisions of the cochlear nucleus. The dorsal cochlear nucleus (DCN) is remarkable in that it shares striking similarities with the cerebellum in terms of its development, gene expression patterns, and anatomical organization. Notably, principal cells of the DCN integrate auditory nerve input with a diverse array of signals conveyed by a mossy fiber- granule cell system. Yet how the elaborate cerebellum-like circuitry of DCN contributes to early auditory processing has been a longstanding puzzle. The work in this thesis shows that, in mice, that the DCN functions to cancel responses to self-generated sounds. While the DCN and ventral cochlear nucleus (VCN) neurons respond similarly to externally-generated acoustic stimuli, sounds generated by licking behavior evoke much weaker responses in DCN than in VCN. Recordings in deafened mice revealed non- auditory signals related to licking in Purkinje-like neurons of DCN. Moreover, silencing somatosensory mossy fiber inputs revealed prominent DCN responses to sounds generated by licking, suggesting that these inputs normally function to cancel responses to self-generated sounds. Finally, I show that this cancellation is not fixed, but involves an adaptive process whereby neural responses correlated with the animal’s own behavior are gradually reduced. Together, these findings suggest that the fundamental process of distinguishing self-generated from external stimuli begins at the very first stage of mammalian auditory processing. Related adaptive filtering functions have been described for cerebellum-like sensory structures in fish and hypothesized for the mammalian cerebellum. Hence our findings also suggest that, despite their wide phylogenetic separation, different cerebellum-like structures and the cerebellum itself may all perform a similar computation.