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1
HOSHINO, NORIAKI, KAZUYA TSURUDOME, HIDEKI NAKAGAWA, and NOBUYOSHI MATSUMOTO. "Current source density analysis of contra- and ipsilateral isthmotectal connections of the frog." Visual Neuroscience 23, no. 5 (September 2006): 713–19. http://dx.doi.org/10.1017/s0952523806230037.
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The nucleus isthmi (NI) of the frog receives input from the ipsilateral optic tectum and projects back to both optic tecta. After ablation of NI, frogs display no visually elicited prey-catching or threat avoidance behavior. Neural mechanisms that underlie the loss of such important behavior have not been solved. Electrophysiological examination of the contralateral isthmotectal projection has proved that it contributes to binocular vision. On the other hand, there are very few physiological investigations of the ipsilateral isthmotectal projection. In this study, current source density (CSD) analysis was applied to contra- and ipsilateral isthmotectal projections. The contralateral projection produced monosynaptic sinks in superficial layers and in layer 8. The results confirmed former findings obtained by single unit recordings. The ipsilateral projection elicited a prominent monosynaptic sink in layer 8. Recipient neurons were located in layers 6–7. These results, combined with those from the former intracellular study, led to the following neuronal circuit. Afferents from the ipsilateral NI inhibit non-efferent pear shaped neurons in the superficial layers, and strongly excite large ganglionic neurons projecting to the descending motor regions. Thus feedback to the output neurons strengthens the visually elicited responses.
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Rosengren, Sally M., Konrad P. Weber, Sendhil Govender, Miriam S. Welgampola, Danielle L. Dennis, and James G. Colebatch. "Sound-evoked vestibular projections to the splenius capitis in humans: comparison with the sternocleidomastoid muscle." Journal of Applied Physiology 126, no. 6 (June 1, 2019): 1619–29. http://dx.doi.org/10.1152/japplphysiol.00711.2018.
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The short-latency vestibulo-collic reflex in humans is well defined for only the sternocleidomastoid (SCM) neck muscle. However, other neck muscles also receive input from the balance organs and participate in neck stabilization. We therefore investigated the sound-evoked vestibular projection to the splenius capitis (SC) muscles by comparing surface and single motor unit responses in the SC and SCM muscles in 10 normal volunteers. We also recorded surface responses in patients with unilateral vestibular loss but preserved hearing and hearing loss but preserved vestibular function. The single motor unit responses were predominantly inhibitory, and the strongest responses were recorded in the contralateral SC and ipsilateral SCM. In both cases there was a significant decrease or gap in single motor unit activity, in SC at 11.7 ms for 46/66 units and in SCM at 12.7 ms for 51/58 motor units. There were fewer significant responses in the ipsilateral SC and contralateral SCM muscles, and they consisted primarily of weak increases in activity. Surface responses recorded over the contralateral SC were positive-negative during neck rotation, similar to the ipsilateral cervical vestibular evoked myogenic potential in SCM. Responses in SC were present in the patients with hearing loss and absent in the patient with vestibular loss, confirming their vestibular origin. The results describe a pattern of inhibition consistent with the synergistic relationship between these muscles for axial head rotation, with the crossed vestibular projection to the contralateral SC being weaker than the ipsilateral projection to the SCM. NEW & NOTEWORTHY We used acoustic vestibular stimulation to investigate the saccular projections to the splenius capitis (SC) and sternocleidomastoid (SCM) muscles in humans. Single motor unit recordings from within the muscles demonstrated strong inhibitory projections to the contralateral SC and ipsilateral SCM muscles and weak excitatory projections to the opposite muscle pair. This synergistic pattern of activation is consistent with a role for the reflex in axial rotation of the head.
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Ueta, Yoshifumi, Jaerin Sohn, Fransiscus Adrian Agahari, Sanghun Im, Yasuharu Hirai, Mariko Miyata, and Yasuo Kawaguchi. "Ipsi- and contralateral corticocortical projection-dependent subcircuits in layer 2 of the rat frontal cortex." Journal of Neurophysiology 122, no. 4 (October 1, 2019): 1461–72. http://dx.doi.org/10.1152/jn.00333.2019.
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In the neocortex, both layer 2/3 and layer 5 contain corticocortical pyramidal cells projecting to other cortices. We previously found that among L5 pyramidal cells of the secondary motor cortex (M2), not only intratelencephalic projection cells but also pyramidal tract cells innervate ipsilateral cortices and that the two subtypes are different in corticocortical projection diversity and axonal laminar distributions. Layer 2/3 houses intratelencephalically projecting pyramidal cells that also innervate multiple ipsilateral and contralateral cortices. However, it remained unclear whether layer 2/3 pyramidal cells can be divided into projection subtypes each with distinct innervation to specific targets. In the present study we show that layer 2 pyramidal cells are organized into subcircuits on the basis of corticocortical projection targets. Layer 2 corticocortical cells of the same projection subtype were monosynaptically connected. Between the contralaterally and ipsilaterally projecting corticocortical cells, the monosynaptic connection was more common from the former to the latter. We also found that ipsilaterally and contralaterally projecting corticocortical cell subtypes differed in their morphological and physiological characteristics. Our results suggest that layer 2 transfers separate outputs from M2 to individual cortices and that its subcircuits are hierarchically organized to form the discrete corticocortical outputs. NEW & NOTEWORTHY Pyramidal cell subtypes and their dependent subcircuits are well characterized in cortical layer 5, but much less is understood for layer 2/3. We demonstrate that in layer 2 of the rat secondary motor cortex, ipsilaterally and contralaterally projecting corticocortical cells are largely segregated. These layer 2 cell subtypes differ in dendrite morphological and intrinsic electrophysiological properties, and form subtype-dependent connections. Our results suggest that layer 2 pyramidal cells form distinct subcircuits to provide discrete corticocortical outputs.
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Harman, AM, DP Crewther, JE Nelson, and SG Crewther. "Retinal Projections in the Northern Native Cat, Dasyurus-Hallucatus (Marsupialia, Dasyuridae)." Australian Journal of Zoology 35, no. 2 (1987): 115. http://dx.doi.org/10.1071/zo9870115.
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The retinal projections of the northern native cat, Dasyurus hallucatus, were studied by the anterograde transport of tritiated proline and by autoradiography. Seven regions in the brain were found to receive direct retinal projections: (1) the suprachiasmatic nucleus; (2) the dorsal lateral geniculate nucleus; (3) the ventral lateral geniculate nucleus; (4) the lateral posterior nucleus; (5) the nuclei of the accessory optic tract; (6) the pretectal nuclei; (7) the superior colliculus. All nuclei studied received a bilateral retinal projection except the medial terminal nucleus of the accessory optic system, in which only a contralateral input was found. The contralateral eye had a greater input in all cases. As with the related species, Dasyurus viverrinus, there is extensive binocular overlap in the dorsal lateral geniculate nucleus (LGNd). In the LGNd contralateral to the injected eye, the autoradiographs show four contralateral terminal bands occupying most of the nucleus. The axonal terminations in the ipsilateral LGNd are more diffuse but show a faint lamination pattern of four bands. The ventral portion of the LGNd receives only contralateral retinal input, and therefore probably represents the monocular visual field. The other principal termination of the optic nerve, the superior colliculus, has a predominantly contralateral input to both sublayers of the stratum griseum superficiale. However, the ipsilateral fibres terminate only in patches in the more inferior sublayer.
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Chapman, Angela M., and Elizabeth A. Debski. "Neuropeptide Y immunoreactivity of a projection from the lateral thalamic nucleus to the optic tectum of the leopard frog." Visual Neuroscience 12, no. 1 (January 1995): 1–9. http://dx.doi.org/10.1017/s0952523800007264.
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AbstractUsing rhodamine-labelled latex beads as a retrograde tracer, we have shown that a subset of the neurons projecting from the lateral thalamic nucleus to the optic tectum of the leopard frog are neuropeptide Y-like immunoreactive (NPY-IR). In juvenile frogs, approximately twice as many lateral thalamic nucleus cells from this area project to the ipsilateral tectum as project to the contralateral tectum. NPY-IR cells make up 25% of the projection to the ipsilateral tectum and 13% of the projection to the contralateral tectum. The ipsilateral NPY-IR projection from the lateral nucleus was present in tadpoles and was similar in its characteristics to that found in the juvenile frog. However, the contralateral tectal projection was virtually nonexistent in these animals. The results of these experiments suggest that NPY from the lateral nucleus is released into the ipsilateral tectal neuropil in both the developing and adult frog.
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Klug, A., T. J. Park, and G. D. Pollak. "Glycine and GABA influence binaural processing in the inferior colliculus of the mustache bat." Journal of Neurophysiology 74, no. 4 (October 1, 1995): 1701–13. http://dx.doi.org/10.1152/jn.1995.74.4.1701.
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1. The mammalian inferior colliculus contains large populations of binaural cells that are excited by stimulation of the contralateral ear and are inhibited by stimulation of the ipsilateral ear, and are called excitatory/inhibitory (EI) cells. Neurons with EI properties are initially created in the lateral superior olive (LSO), which, in turn, sends strong bilateral projections to the inferior colliculus. The questions that we address in this report are 1) whether the inhibition evoked by stimulation of the ipsilateral ear occurs at the inferior colliculus or whether it occurs in a lower nucleus, presumably the LSO; and 2) if the ipsilaterally evoked inhibition occurs at the inferior colliculus, is the inhibition a consequence of glycinergic innervation or is it a consequence of GABAergic innervation. To study these questions, we recorded from 61 EI neurons in the inferior colliculus of the mustache bat before and during the iontophoretic application of the glycine receptor antagonist, strychnine. We also tested the effects of the gamma-aminobutyric acid-A (GABAA) receptor antagonist, bicuculline, on 38 of the 61 neurons that were tested with strychnine. The main finding is that glycinergic or GABAergic inhibition, or both, contribute to the ipsilaterally evoked inhibition in approximately 50% of the EI neurons in the inferior colliculus. 2. Strychnine and bicuculline had different effects on the magnitude of the spike counts evoked by stimulation of the contralateral (excitatory) ear. On average, strychnine caused the maximum spike count evoked by contralateral stimulation to increase by only 23%. The relatively small effects of strychnine on response magnitude are in marked contrast to the effects of bicuculline, which usually caused much larger increases in spike counts. For example, although strychnine caused spike counts to more than double in approximately 25% of the collicular neurons, bicuculline caused a doubling of the spike count in approximately 60% of the cells. 3. The inhibitory influences of ipsilateral stimulation were evaluated by driving the neurons with a fixed intensity at the contralateral ear and then documenting the reductions in spike counts due to the presentation of progressively higher intensities at the ipsilateral ear. In 64% of the neurons sampled, blocking glycinergic inhibition with strychnine had little or no effect on the ipsilaterally evoked inhibition. These cells remained as strongly inhibited during the application of strychnine as they did before its application. In addition, the ipsilateral intensity that produced complete or nearly complete spike suppression in the predrug condition was also unchanged by strychnine. 4. In 36% of the neurons, strychnine markedly reduced the degree of ipsilaterally evoked spike suppression. In five of these neurons, there was a complete elimination of the ipsilateral inhibition: these neurons were transformed from strongly inhibited EI neurons into monaural neurons. 5. The influence of both strychnine and bicuculline was tested sequentially in 38 neurons. In about one-half of these cells, (53%, 20/38) the ipsilaterally evoked inhibition was unaffected by either drug. In 10 other units (26%), both drugs substantially reduced or eliminated the ipsilaterally evoked inhibition. In most of these cells, both bicuculline and strychnine reduced the ipsilaterally evoked inhibition to a similar degree. In the remaining eight cells studied with both drugs (21%), the ipsilaterally evoked inhibition was reduced or eliminated by one of the drugs, but not by both. 6. These results show that both glycinergic and GABAergic projections influence the ipsilaterally evoked inhibition in about one-half of the EI neurons in the inferior colliculus. The glycinergic inhibition elicited by ipsilateral stimulation is most likely due to projections from the ipsilateral lateral superior olive, whereas the GABAergic inhibition evoked by ipsilateral stimulation is most likely caused b
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Vigouroux, Robin J., Karine Duroure, Juliette Vougny, Shahad Albadri, Peter Kozulin, Eloisa Herrera, Kim Nguyen-Ba-Charvet, et al. "Bilateral visual projections exist in non-teleost bony fish and predate the emergence of tetrapods." Science 372, no. 6538 (April 8, 2021): 150–56. http://dx.doi.org/10.1126/science.abe7790.
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In most vertebrates, camera-style eyes contain retinal ganglion cell neurons that project to visual centers on both sides of the brain. However, in fish, ganglion cells were thought to innervate only the contralateral side, suggesting that bilateral visual projections appeared in tetrapods. Here we show that bilateral visual projections exist in non-teleost fishes and that the appearance of ipsilateral projections does not correlate with terrestrial transition or predatory behavior. We also report that the developmental program that specifies visual system laterality differs between fishes and mammals, as the Zic2 transcription factor, which specifies ipsilateral retinal ganglion cells in tetrapods, appears to be absent from fish ganglion cells. However, overexpression of human ZIC2 induces ipsilateral visual projections in zebrafish. Therefore, the existence of bilateral visual projections likely preceded the emergence of binocular vision in tetrapods.
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Naeem, Nazratan, James Bowman Whitley, Arkadiusz S. Slusarczyk, and Martha Elise Bickford. "Ultrastructure of ipsilateral and contralateral tectopulvinar projections in the mouse." Journal of Comparative Neurology 530, no. 7 (October 24, 2021): 1099–111. http://dx.doi.org/10.1002/cne.25264.
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Berlot, Eva, George Prichard, Jill O’Reilly, Naveed Ejaz, and Jörn Diedrichsen. "Ipsilateral finger representations in the sensorimotor cortex are driven by active movement processes, not passive sensory input." Journal of Neurophysiology 121, no. 2 (February 1, 2019): 418–26. http://dx.doi.org/10.1152/jn.00439.2018.
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Hand and finger movements are mostly controlled through crossed corticospinal projections from the contralateral hemisphere. During unimanual movements, activity in the contralateral hemisphere is increased while the ipsilateral hemisphere is suppressed below resting baseline. Despite this suppression, unimanual movements can be decoded from ipsilateral activity alone. This indicates that ipsilateral activity patterns represent parameters of ongoing movement, but the origin and functional relevance of these representations is unclear. In this study, we asked whether ipsilateral representations are caused by active movement or whether they are driven by sensory input. Participants alternated between performing single finger presses and having fingers passively stimulated while we recorded brain activity using high-field (7T) functional imaging. We contrasted active and passive finger representations in sensorimotor areas of ipsilateral and contralateral hemispheres. Finger representations in the contralateral hemisphere were equally strong under passive and active conditions, highlighting the importance of sensory information in feedback control. In contrast, ipsilateral finger representations in the sensorimotor cortex were stronger during active presses. Furthermore, the spatial distribution of finger representations differed between hemispheres: the contralateral hemisphere showed the strongest finger representations in Brodmann areas 3a and 3b, whereas the ipsilateral hemisphere exhibited stronger representations in premotor and parietal areas. Altogether, our results suggest that finger representations in the two hemispheres have different origins: contralateral representations are driven by both active movement and sensory stimulation, whereas ipsilateral representations are mainly engaged during active movement. NEW & NOTEWORTHY Movements of the human body are mostly controlled by contralateral cortical regions. The function of ipsilateral activity during movements remains elusive. Using high-field neuroimaging, we investigated how human contralateral and ipsilateral hemispheres represent active and passive finger presses. We found that representations in contralateral sensorimotor cortex are equally strong during both conditions. Ipsilateral representations were mostly present during active movement, suggesting that sensorimotor areas do not receive direct sensory input from the ipsilateral hand.
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Rahman, Tasnia N., Martin Munz, Elena Kutsarova, Olesia M. Bilash, and Edward S. Ruthazer. "Stentian structural plasticity in the developing visual system." Proceedings of the National Academy of Sciences 117, no. 20 (May 4, 2020): 10636–38. http://dx.doi.org/10.1073/pnas.2001107117.
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In a small fraction of Xenopus tadpoles, a single retinal ganglion cell (RGC) axon misprojects to the ipsilateral optic tectum. Presenting flashes of light to the ipsilateral eye causes that ipsilateral axon to fire, whereas stimulating the contralateral eye excites all other RGC inputs to the tectum. We performed time-lapse imaging of individual ipsilaterally projecting axons while stimulating either the ipsilateral or contralateral eye. Stimulating either eye alone reduced axon elaboration by increasing branch loss. New branch additions in the ipsi axon were exclusively increased by contralateral eye stimulation, which was enhanced by expressing tetanus neurotoxin (TeNT) in the ipsilateral axon, to prevent Hebbian stabilization. Together, our results reveal the existence of a non−cell-autonomous “Stentian” signal, engaged by activation of neighboring RGCs, that promotes exploratory axon branching in response to noncorrelated firing.
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Rodman, Hillary R., and Michael J. Consuelos. "Cortical projections to anterior inferior temporal cortex in infant macaque monkeys." Visual Neuroscience 11, no. 1 (January 1994): 119–33. http://dx.doi.org/10.1017/s0952523800011160.
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AbstractInferior temporal (IT) cortex is a “high-order” region of extrastriate visual cortex important for visual form perception and recognition in adult primates. The pattern of cortical afferents from both ipsilateral and contralateral hemispheres to anterior IT cortex was determined in infant macaque monkeys 7–18 weeks of age following injections of wheat-germ agglutinin-HRP. Within the ipsilateral hemisphere, the locations and laminar distribution of labeled cells were similar to those observed after comparable injections in adult monkeys. Specifically, ipsilateral afferents derived from visual areas V4, TEO, anterior and posterior IT, and STP, from parahippocampal, perirhinal, and parietal zones, and from several anterior zones including lateral and ventral frontal cortex, the insula, and cingulate cortex. Within the contralateral hemisphere, we observed labeled cells in homotopic regions of IT and in parahippocampal and perirhinal areas, as has been reported for adult monkeys. However, we also identified additional contralateral regions not previously known to provide input to anterior IT, including lateral and ventral frontal cortex, cingulate cortex, and STP. Overall, the strongest and most widespread projections from outside the temporal lobe were found in the youngest monkey, suggesting that some of these projections may represent transient circuitry necessary for the development of complex visual response properties in anterior IT.
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Knickmeyer, Max D., Juan L. Mateo, and Stephan Heermann. "BMP Signaling Interferes with Optic Chiasm Formation and Retinal Ganglion Cell Pathfinding in Zebrafish." International Journal of Molecular Sciences 22, no. 9 (April 27, 2021): 4560. http://dx.doi.org/10.3390/ijms22094560.
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Decussation of axonal tracts is an important hallmark of vertebrate neuroanatomy resulting in one brain hemisphere controlling the contralateral side of the body and also computing the sensory information originating from that respective side. Here, we show that BMP interferes with optic chiasm formation and RGC pathfinding in zebrafish. Experimental induction of BMP4 at 15 hpf results in a complete ipsilateral projection of RGC axons and failure of commissural connections of the forebrain, in part as the result of an interaction with shh signaling, transcriptional regulation of midline guidance cues and an affected optic stalk morphogenesis. Experimental induction of BMP4 at 24 hpf, resulting in only a mild repression of forebrain shh ligand expression but in a broad expression of pax2a in the diencephalon, does not per se prevent RGC axons from crossing the midline. It nevertheless shows severe pathologies of RGC projections e.g., the fasciculation of RGC axons with the ipsilateral optic tract resulting in the innervation of one tectum by two eyes or the projection of RGC axons in the direction of the contralateral eye.
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Izawa, Y., Y. Sugiuchi, and Y. Shinoda. "Neural Organization From the Superior Colliculus to Motoneurons in the Horizontal Oculomotor System of the Cat." Journal of Neurophysiology 81, no. 6 (June 1, 1999): 2597–611. http://dx.doi.org/10.1152/jn.1999.81.6.2597.
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Neural organization from the superior colliculus to motoneurons in the horizontal oculomotor system of the cat. The neural organization of the superior colliculus (SC) projection to horizontal ocular motoneurons was analyzed in anesthetized cats using intracellular recording and transneuronal labeling. Intracellular responses to SC stimulation were analyzed in lateral rectus (LR) and medial rectus (MR) motoneurons and internuclear neurons in the abducens nucleus (AINs). LR motoneurons and AINs received excitation from the contralateral SC and inhibition from the ipsilateral SC. The shortest excitation (0.9–1.9 ms) and inhibition (1.4–2.4 ms) were mainly disynaptic from the SC and were followed by tri- and polysynaptic responses evoked with increasing stimuli or intensity. All MR motoneurons received excitation from the ipsilateral SC, whereas none of them received any short-latency inhibition from the contralateral SC, but some received excitation. The latency of the ipsilateral excitation in MR motoneurons (1.7–2.8 ms) suggested that this excitation was trisynaptic via contralateral AINs, because conditioning SC stimulation spatially facilitated trisynaptic excitation from the ipsilateral vestibular nerve. To locate interneurons mediating the disynaptic SC inputs to LR motoneurons, last-order premotor neurons were labeled transneuronally after injecting wheat germ agglutinin–conjugated horseradish peroxidase into the abducens nerve, and tectoreticular axon terminals were labeled after injecting dextran-biotin into the ipsilateral or contralateral SC in the same preparations. Transneuronally labeled neurons were mainly distributed ipsilaterally in the paramedian pontine reticular formation (PPRF) rostral to retrogradely labeled LR motoneurons and the vestibular nuclei, and contralaterally in the paramedian pontomedullary reticular formation (PPMRF) caudomedial to the abducens nucleus and the vestibular nuclei. Among the last-order premotor neuron areas, orthogradely labeled tectoreticular axon terminals were observed only in the PPRF and the PPMRF contralateral to the injected SC and seemed to make direct contacts with many of the labeled last-order premotor neurons in the PPRF and the PPMRF. These morphological results confirmed that the main excitatory and inhibitory connections from the SC to LR motoneurons are disynaptic and that the PPRF neurons that receive tectoreticular axon terminals from the contralateral SC terminate on ipsilateral LR motoneurons, whereas the PPMRF neurons that receive tectoreticular axon terminals from the contralateral SC terminate on contralateral LR motoneurons.
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Chimoto, Sohei, Yoshiki Iwamoto, and Kaoru Yoshida. "Projections and Firing Properties of Down Eye-Movement Neurons in the Interstitial Nucleus of Cajal in the Cat." Journal of Neurophysiology 81, no. 3 (March 1, 1999): 1199–211. http://dx.doi.org/10.1152/jn.1999.81.3.1199.
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Projections and firing properties of down eye-movement neurons in the interstitial nucleus of Cajal in the cat. To clarify the role of the interstitial nucleus of Cajal (INC) in the control of vertical eye movements, projections of burst-tonic and tonic neurons in and around the INC were studied. This paper describes neurons with downwardon directions. We examined, by antidromic activation, whether these down INC (d-INC) neurons contribute to two pathways: a commissural pathway to the contralateral (c-) INC and a descending pathway to the ipsilateral vestibular nucleus (i-VN). Stimulation of the two pathways showed that as many as 74% of neurons were activated antidromically from one of the pathways. Of 113 d-INC neurons tested, 44 were activated from the commissural pathway and 40 from the descending pathway. No neurons were activated from both pathways. We concluded that commissural and descending pathways from the INC originate from two separate groups of neurons. Tracking of antidromic microstimulation in the two nuclei revealed multiple low-threshold sites and varied latencies; this was interpreted as a sign of existence of axonal arborization. Neurons with commissural projections tended to be located more dorsally than those with descending projections. Neurons with descending projections had significantly greater eye-position sensitivity and smaller saccadic sensitivity than neurons with commissural projections. The two groups of INC neurons increased their firing rate in nose-up head rotations and responded best to the rotation in the plane of contralateral posterior/ipsilateral anterior canal pair. Neurons with commissural projections showed a larger phase lag of response to sinusoidal rotation (54.6 ± 7.6°) than neurons with descending projections (45.0 ± 5.5°). Most neurons with descending projections received disynaptic excitation from the contralateral vestibular nerve. Neurons with commissural projections rarely received such disynaptic input. We suggest that downward-position-vestibular (DPV) neurons in the VN and VN-projecting d-INC neurons form a loop, together with possible commissural loops linking the bilateral VNs and the bilateral INCs. By comparing the quantitative measures of d-INC neurons with those of DPV neurons, we further suggest that integration of head velocity signals proceeds from DPV neurons to d-INC neurons with descending projections and then to d-INC neurons with commissural projections, whereas saccadic velocity signals are processed in the reverse order.
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Jacquin, M. F., M. R. Wiegand, and W. E. Renehan. "Structure-function relationships in rat brain stem subnucleus interpolaris. VIII. Cortical inputs." Journal of Neurophysiology 64, no. 1 (July 1, 1990): 3–27. http://dx.doi.org/10.1152/jn.1990.64.1.3.
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1. Spinal trigeminal (SpV) subnucleus interpolaris (SpVi) receives inputs from trigeminal (V) first- and second-order neurons, monoamine-containing brain stem nuclei, and somatosensory cortex. Prior studies suggest that SpVi receptive-field (RF) properties cannot be predicted solely on the basis of primary afferent inputs. To assess the cortico-V projection and its role in SpVi RFs, anatomic and electrophysiological experiments were conducted. 2. Phaseolus vulgaris leucoagglutinin (PHA-L) or wheat-germ-agglutinized horseradish peroxidase (WGA-HRP) were used as anterograde tracers to study cortico-V axons in 24 normal adult rats. Injections into SI barrel cortex-labeled pyramidal fibers that decussated at all levels of the V brain stem complex, though crossing fibers were most numerous in the pyramidal decussation and pons. A small number of axons projected to ipsilateral V brain stem subnuclei. PHA-L-labeled pyramidal fibers did not give rise to collaterals in their descent through the pons and medulla. 3. Heaviest terminal labeling occurred contralaterally and in the maxillary portion of caudalis laminae III-V. Moderately dense reaction product was seen in ventral portions of all other contralateral V brain stem subnuclei, as well as in laminae I and II of caudalis. Subnucleus oralis contained the least amount of label contralateral to the injection site. Ipsilateral projections were weak and most dense in principalis. 4. Cortico-V projections were topographic between matching whisker representations. Axons most commonly had longitudinal orientations and stringy shapes. Terminal boutons occurred at the ends of short collateral branches. Many of these collaterals were derived from axons that ascended through caudal V brian stem subnuclei after crossing in the lower medulla. 5. Cortico-V labeling was heavier in septal regions between single whisker representations. This “honeycomb-like” termination pattern was most pronounced in contralateral caudalis and SpVi and ipsilateral principalis. 6. In 13 other adult rats, right SI cortex was aspirated followed by single-unit recordings in left SpVi under pentobarbital sodium anesthesia. In 9 of these, chronic effects were evaluated by recording the responses of 346 left SpVi cells 4-55 days after the lesion. In the remaining four rats, acute effects were analyzed by recording the responses of 190 SpVi cells on the day of the lesion.(ABSTRACT TRUNCATED AT 400 WORDS)
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Rosa, Marcello G. P., and Leisa M. Schmid. "Topography and extent of visual-field representation in the superior colliculus of the megachiropteran Pteropus." Visual Neuroscience 11, no. 6 (November 1994): 1037–57. http://dx.doi.org/10.1017/s0952523800006878.
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AbstractIt has been proposed that flying foxes (genus Pteropus) have a primate-like pattern of representation in the superficial layers of the superior colliculus (SC), whereby the visual representation in this structure is limited by the same decussation line that limits the retino-geniculo-cortical projection (Pettigrew, 1986). To test this hypothesis, visual receptive fields were plotted based on single- and multi-unit recordings in the SC of ten flying foxes. A complete representation of the contralateral hemifield was observed in the SC. Although the binocular hemifield of vision in Pteropus is 54 deg wide, receptive-field centers invaded the ipsilateral hemifield by only 8 deg, and the receptive-field borders by 13 deg. This invasion is similar to that observed at the border between visual areas VI and V2 in the occipital cortex. The extent of the ipsilateral invasion was not affected by a lesion that completely ablated the occipital visual areas, thus suggesting that this invasion may be consequence of a zone of nasotemporal overlap in the retinal projections to the two colliculi. Neurones located in the superficial layers typically responded briskly to stimulation of both eyes, with a bias towards the contralateral eye. After cortical lesions the neuronal responses to the ipsilateral eye were depressed, and the ocular-dominance histograms shifted towards an even stronger dominance by the contralateral eye. However, cells located in the rostral pole of the SC remained responsive to the ipsilateral eye after cortical lesions. Responses in the stratum opticum and stratum griseum intermediate were more severely affected by cortical lesions than those in the stratum griseum superficiale. Our results demonstrate that the SC in flying foxes retain some generalized mammalian characteristics, such as the stronger direct projections of the contralateral eye and the location of the upper, lower, central, and peripheral representations in the SC. Nonetheless, the extent of visual representation in the SC demonstrates a specialized, primate-like pattern. These observations are consistent with the hypothesis that megachiropterans are members of a group that branched off early during the differentiation of primates from basal mammals.
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Murcia-Belmonte, Verónica, and Lynda Erskine. "Wiring the Binocular Visual Pathways." International Journal of Molecular Sciences 20, no. 13 (July 4, 2019): 3282. http://dx.doi.org/10.3390/ijms20133282.
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Retinal ganglion cells (RGCs) extend axons out of the retina to transmit visual information to the brain. These connections are established during development through the navigation of RGC axons along a relatively long, stereotypical pathway. RGC axons exit the eye at the optic disc and extend along the optic nerves to the ventral midline of the brain, where the two nerves meet to form the optic chiasm. In animals with binocular vision, the axons face a choice at the optic chiasm—to cross the midline and project to targets on the contralateral side of the brain, or avoid crossing the midline and project to ipsilateral brain targets. Ipsilaterally and contralaterally projecting RGCs originate in disparate regions of the retina that relate to the extent of binocular overlap in the visual field. In humans virtually all RGC axons originating in temporal retina project ipsilaterally, whereas in mice, ipsilaterally projecting RGCs are confined to the peripheral ventrotemporal retina. This review will discuss recent advances in our understanding of the mechanisms regulating specification of ipsilateral versus contralateral RGCs, and the differential guidance of their axons at the optic chiasm. Recent insights into the establishment of congruent topographic maps in both brain hemispheres also will be discussed.
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WINKOWSKI, DANIEL E., and EDWARD R. GRUBERG. "The representation of the ipsilateral eye in nucleus isthmi of the leopard frog, Rana pipiens." Visual Neuroscience 19, no. 5 (September 2002): 669–79. http://dx.doi.org/10.1017/s0952523802195125.
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The retina of the leopard frog projects topographically to the superficial neuropil of the entire contralateral tectum. In the rostromedial neuropil of the tectum, there is a map of the binocular region of the visual field seen from the ipsilateral eye that is in register with the map of the binocular region of the visual field seen from the contralateral eye. The ipsilateral eye projects indirectly to the tectum through nucleus isthmi (n. isthmi), a midbrain tegmental structure. N. isthmi receives input from the ipsilateral optic tectum and sends projections bilaterally that cover both tectal lobes. Previous workers have not been able to find visual activity from the ipsilateral eye in the caudolateral optic tectum, representing the monocular visual field of the contralateral eye. We show electrophysiologically that across the entire extent of n. isthmi there are two superimposed maps, one map representing the entire visual field of the contralateral eye, the other map representing the binocular visual field of the ipsilateral eye. We also studied the behavioral consequences of localized lesions to n. isthmi and compared them to the behavioral consequences of localized lesions to the optic tectum representing equivalent areas of the visual field. Lesions to the optic tectum produce scotomas in the corresponding portion of the visual field. Lesions to n. isthmi, even medial n. isthmi representing the superior visual field, lead to scotomas in the temporal-most portion of the contralateral ground level visual field. Thus, the representation of visual space in n. isthmi is not a simple copy of the tectal representation of visual space.
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Innocenti, G. M., and P. Berbel. "Analysis of an Experimental Cortical Network: ii) Connections of Visual Areas 17 and 18 After Neonatal Injections of Ibotenic Acid." Journal of Neural Transplantation 2, no. 1 (1991): 29–54. http://dx.doi.org/10.1155/np.1991.29.
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Lesions of cortical areas 17 and 18 were produced in newborn kittens by local injections of the excitotoxin ibotenic acid. In the adult this results in a microcortex which consists of superficial layers I, II and III, in the absence of granular and infragranular layers. Horseradish peroxidase, alone or wheat germ agglutinin conjugated, was injected in the microcortex or in the contralateral, intact areas 17 and 18. The microcortex maintains several connections characteristic of normal areas 17 and 18 of the cat. It receives afferents from the dLGN, and several visual areas of the ipsilateral and contralateral hemisphere. However, it has lost its projections to dLGN, superior colliculus, and, at least in part, those to contralateral visual areas. Thus some parts of the microcortex receive from, but do not project into, the corpus callosum. In addition, the microcortex maintains afferents from ipsilateral and contralateral auditory areas AI and AII which are normally eliminated in development.
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Bredenkötter, Manfred, and Hans-Joachim Bischof. "Differences between ipsilaterally and contralaterally evoked potentials in the visual wulst of the zebra finch." Visual Neuroscience 5, no. 2 (August 1990): 155–63. http://dx.doi.org/10.1017/s0952523800000201.
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AbstractThe telencephalic target of the thalamofugal visual pathway in birds, the visual wulst, is part of the hyperstriatum accessorium/dorsale in the bird's brain. In this study, we tried to determine the exact location of the visually responsive area in the zebra finch by recording visually evoked potentials (VEPs) from different sites throughout the hyperstriatum and calculating current source densities (CSDs). In addition, we examined the influence of ipsilateral and contralateral stimuli on stimulus processing within this area, and tried to get insight into the neuronal machinery of the thalamofugal pathway by application of drugs such as tetrodotoxin (TTX) and picrotoxin.About two-thirds of the hyperstriatum is responsive to contralateral stimuli but only a small portion responds to ipsilateral stimuli. Contralateral visual information arrives in the hyperstriatum dorsale (HD) and is processed further to the hyperstriatum accessorium (HA).The small influence of ipsilaterally evoked potentials is not due to inhibition by the activity of the contralateral eye, as could be demonstrated previously for the ectostriatum. Instead, our results show that ipsilaterally evoked potentials are inhibited at least in part by a projection from the contralateral visual wulst.
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Sugiuchi, Y., Y. Izawa, M. Takahashi, J. Na, and Y. Shinoda. "Physiological Characterization of Synaptic Inputs to Inhibitory Burst Neurons From the Rostral and Caudal Superior Colliculus." Journal of Neurophysiology 93, no. 2 (February 2005): 697–712. http://dx.doi.org/10.1152/jn.00502.2004.
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The caudal superior colliculus (SC) contains movement neurons that fire during saccades and the rostral SC contains fixation neurons that fire during visual fixation, suggesting potentially different functions for these 2 regions. To study whether these areas might have different projections, we characterized synaptic inputs from the rostral and caudal SC to inhibitory burst neurons (IBNs) in anesthetized cats. We recorded intracellular potentials from neurons in the IBN region and identified them as IBNs based on their antidromic activation from the contralateral abducens nucleus and short-latency excitation from the contralateral caudal SC and/or single-cell morphology. IBNs received disynaptic inhibition from the ipsilateral caudal SC and disynaptic inhibition from the rostral SC on both sides. Stimulation of the contralateral IBN region evoked monosynaptic inhibition in IBNs, which was enhanced by preconditioning stimulation of the ipsilateral caudal SC. A midline section between the IBN regions eliminated inhibition from the ipsilateral caudal SC, but inhibition from the rostral SC remained unaffected, indicating that the latter inhibition was mediated by inhibitory interneurons other than IBNs. A transverse section of the brain stem rostral to the pause neuron (PN) region eliminated inhibition from the rostral SC, suggesting that this inhibition is mediated by PNs. These results indicate that the most rostral SC inhibits bilateral IBNs, most likely via PNs, and the more caudal SC exerts monosynaptic excitation on contralateral IBNs and antagonistic inhibition on ipsilateral IBNs via contralateral IBNs. The most rostral SC may play roles in maintaining fixation by inhibition of burst neurons and facilitating saccadic initiation by releasing their inhibition.
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Krumbholz, Katrin, Nicola Hewson-Stoate, and Marc Schönwiesner. "Cortical Response to Auditory Motion Suggests an Asymmetry in the Reliance on Inter-Hemispheric Connections Between the Left and Right Auditory Cortices." Journal of Neurophysiology 97, no. 2 (February 2007): 1649–55. http://dx.doi.org/10.1152/jn.00560.2006.
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The aim of the current study was to measure the brain's response to auditory motion using electroencephalography (EEG) to gain insight into the mechanisms by which hemispheric lateralization for auditory spatial processing is established in the human brain. The onset of left- or rightward motion in an otherwise continuous sound was found to elicit a large response, which appeared to arise from higher-level nonprimary auditory areas. This motion onset response was strongly lateralized to the hemisphere contralateral to the direction of motion. The response latencies suggest that the ipsilateral response to the leftward motion was produced by indirect callosal projections from the opposite hemisphere, whereas the ipsilateral response to the rightward motion seemed to receive contributions from direct thalamocortical projections. These results suggest an asymmetry in the reliance on inter-hemispheric projections between the left and right auditory cortices for auditory spatial processing.
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Scudder, C. A., and A. F. Fuchs. "Physiological and behavioral identification of vestibular nucleus neurons mediating the horizontal vestibuloocular reflex in trained rhesus monkeys." Journal of Neurophysiology 68, no. 1 (July 1, 1992): 244–64. http://dx.doi.org/10.1152/jn.1992.68.1.244.
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1. To describe in detail the secondary neurons of the horizontal vestibuloocular reflex (VOR), we recorded the extracellular activity of neurons in the rostral medial vestibular nucleus of alert, trained rhesus monkeys. On the basis of their activity during horizontal head and eye movements, neurons were divided into several different types. Position-vestibular-pause (PVP) units discharged in relation to head velocity, eye velocity, eye position, and ceased firing during some saccades. Eye and head velocity (EHV) units discharged in relation to eye velocity and head velocity in the same direction so that the two signals partially canceled during the VOR. Two cell types discharged in relation to eye position and velocity but not head velocity; other types discharged in relation to head velocity only. 2. The position in the neural path from the primary vestibular afferents to abducens motoneurons was examined for each type. Direct input from the vestibular nerve was indicated if the cell could be activated by shocks to the nerve at latencies less than or equal to 1.4 ms. A projection to abducens motoneurons was indicated if spike-triggered averaging of lateral rectus electromyographic (EMG) activity yielded responses with a sharp onset at monosynaptic latencies. 3. PVP neurons were the principal interneuron in the VOR “three-neuron arc.” Eighty percent received primary afferent input, and 66% made excitatory connections with contralateral abducens motoneurons. Surprisingly few, approximately 11%, made inhibitory connections with ipsilateral abducens motoneurons. This imbalance in the ipsi- and contralateral projections was confirmed by measuring the EMG activity evoked by electrical microstimulation in regions where PVP neurons were located. 4. EHV neurons whose activity increased during contralaterally directed head or eye movements were also interneurons in the ipsilateral inhibitory pathway. Eighty-nine percent received ipsilateral primary afferent input, and 25% projected to ipsilateral abducens motoneurons. EHV neurons excited during ipsilateral movements received neither direct primary afferent input nor projected to either abducens nucleus. A small proportion of each of two other cell types having sensitivity to contralateral eye position made excitatory connections with contralateral abducens motoneurons. Other types rarely were activated from the eighth nerve or projected to the abducens nucleus. 5. The significance of the connections of VOR interneurons and the signals they convey is discussed for three situations: smooth pursuit of a moving target, suppression of the VOR, and the VOR itself. PVP neurons convey a signal with a ratio of eye position and velocity components that is inappropriate to drive motoneurons during pursuit or the VOR.(ABSTRACT TRUNCATED AT 400 WORDS)
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Mathiasen, Mathias L., Rebecca C. Louch, Andrew D. Nelson, Christopher M. Dillingham, and John P. Aggleton. "Trajectory of hippocampal fibres to the contralateral anterior thalamus and mammillary bodies in rats, mice, and macaque monkeys." Brain and Neuroscience Advances 3 (January 2019): 239821281987120. http://dx.doi.org/10.1177/2398212819871205.
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The routes by which the hippocampal formation projects bilaterally to the anterior thalamic nuclei and mammillary bodies were examined in the mouse, rat, and macaque monkey. Despite using different methods and different species, the principal pattern remained the same. For both target areas, the contralateral hippocampal (subiculum) projections arose via efferents in the postcommissural fornix ipsilateral to the tracer injection, which then crossed hemispheres both in or just prior to reaching the target site within the thalamus or hypothalamus. Precommissural fornix fibres could not be followed to the target areas. There was scant evidence that the ventral hippocampal commissure or decussating fornix fibres contribute to these crossed subiculum projections. Meanwhile, a small minority of postsubiculum projections in the mouse were seen to cross in the descending fornix at the level of the caudal septum to join the contralateral postcommissural fornix before reaching the anterior thalamus and lateral mammillary nucleus on that side. Although the rodent anterior thalamic nuclei also receive nonfornical inputs from the subiculum and postsubiculum via the ipsilateral internal capsule, few, if any, of these projections cross the midline. It was also apparent that nuclei within the head direction system (anterodorsal thalamic nucleus, laterodorsal thalamic nucleus, and lateral mammillary nucleus) receive far fewer crossed hippocampal inputs than the other anterior thalamic or mammillary nuclei. The present findings increase our understanding of the fornix and its component pathways while also informing disconnection analyses involving the hippocampal formation and diencephalon.
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Leichnetz, George R. "Inferior frontal eye field projections to the pursuit-related dorsolateral pontine nucleus and middle temporal area (MT) in the monkey." Visual Neuroscience 3, no. 2 (August 1989): 171–80. http://dx.doi.org/10.1017/s0952523800004478.
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AbstractInferior frontal eye field (FEF) projections to the dorsolateral pontine nucleus (DLPN), and corticocortical connections with the superior temporal sulcal (STS) cortex, were studied in five macaque monkeys which had received horseradish peroxidase (HRP) gel implants into the inferior prearcuate cortex (including area 45 of Walker, 1940). These connections were contrasted with those from the dorsal FEF (area 8a) in another macaque monkey. Findings of heavy inferior FEF projections to the ipsilateral DLPN (light to the contralateral DLPN) and reciprocal connections with the deep caudal bank and fundus of the superior temporal sulcus (STS), presumed to be the middle temporal (MT) visual area (Maunsell & Van Essen, 1983a), appeared to go hand in hand with more pronounced projections to the stratum superficialis of the superior colliculus (SC). In contrast, the HRP gel implant in the dorsal prearcuate cortex (area 8a of Walker, 1940) resulted in only very light projections to the ipsilateral DLPN, more pronounced projections to the dorsomedial pontine nucleus (DMPN), almost no projection to the stratum superficialis (SS), and more pronounced reciprocal connections with the upper bank of the STS, presumed to be the medial superior temporal (MST) area (Maunsell & Van Essen, 1983a). Both the inferior and dorsal FEF also had extensive reciprocal connections with the ventral intraparietal area (VIP; Maunsell & Van Essen, 1983a) in the caudal bank of the intraparietal sulcus. The correlated projections of the inferior FEF to the DLPN, MT area, and SS may explain its reported role in smooth pursuit (Lynch, 1987), in addition to its well-established role in the production of voluntary purposeful saccadic eye movements (Bruce et al., 1985).
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Agarwala, Seema, Heywood M. Petry, and Jack G. May. "Retinal projections in the ground squirrel (Citellus tridecemlineatus)." Visual Neuroscience 3, no. 6 (December 1989): 537–49. http://dx.doi.org/10.1017/s0952523800009871.
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AbstractThe retinal projections of the thirteen-lined ground squirrel were determined by tracing anterograde transport of intravitreally injected horseradish peroxidase (HRP) or wheat-germ conjugated horseradish peroxidase (WGA-HRP). Label was seen in the suprachiasmatic nucleus and adjacent anterior hypothalamic area, the accessory optic system (the medial, dorsal, and lateral terminal nuclei), the dorsal and ventral lateral geniculate nuclei, the intergeniculate leaflet, the pretectal nuclei (the anterior, posterior, and olivary pretectal nuclei and the nucleus of optic tract), and the superior colliculus. Most of these structures were labeled bilaterally, with dense contralateral label and sparse ipsilateral label, a pattern typical for animals with laterally placed eyes. However, the suprachiasmatic nucleus and the nucleus of the optic tract received input only from the contralateral eye. In contrast to previous degeneration studies, the sensitive HRP tracers (in conjunction with cytochrome-oxidase reactivity) revealed an elaborate organization within the lateral geniculate nucleus (dorsal LGN, ventral LGN, and intergeniculate leaflet) that is consistent with existing organizational schemes for other mammalian species.
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Quinet, Julie, and Laurent Goffart. "Cerebellar control of saccade dynamics: contribution of the fastigial oculomotor region." Journal of Neurophysiology 113, no. 9 (May 2015): 3323–36. http://dx.doi.org/10.1152/jn.01021.2014.
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The fastigial oculomotor region is the output by which the medioposterior cerebellum influences the generation of saccades. Recent inactivation studies reported observations suggesting an involvement in their dynamics (velocity and duration). In this work, we tested this hypothesis in the head-restrained monkey with the electrical microstimulation technique. More specifically, we studied the influence of duration, frequency, and current on the saccades elicited by fastigial stimulation and starting from a central (straight ahead) position. The results show ipsilateral or contralateral saccades whose amplitude and dynamics depend on the stimulation parameters. The duration and amplitude of their horizontal component increase with the duration of stimulation up to a maximum amplitude. Varying the stimulation frequency mostly changes their latency and the peak velocity (for contralateral saccades). Current also influences the metrics and dynamics of saccades: the horizontal amplitude and peak velocity increase with the intensity, whereas the latency decreases. The changes in peak velocity and in latency observed in contralateral saccades are not correlated. Finally, we discovered that contralateral saccades can be evoked at sites eliciting ipsilateral saccades when the stimulation frequency is reduced. However, their onset is timed not with the onset but with the offset of stimulation. These results corroborate the hypothesis that the fastigial projections toward the pontomedullary reticular formation (PMRF) participate in steering the saccade, whereas the fastigiocollicular projections contribute to the bilateral control of visual fixation. We propose that the cerebellar influence on saccade generation involves recruiting neurons and controlling the size of the active population in the PMRF.
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Bradnam, Lynley V., Cathy M. Stinear, Gwyn N. Lewis, and Winston D. Byblow. "Task-Dependent Modulation of Inputs to Proximal Upper Limb Following Transcranial Direct Current Stimulation of Primary Motor Cortex." Journal of Neurophysiology 103, no. 5 (May 2010): 2382–89. http://dx.doi.org/10.1152/jn.01046.2009.
Full textAbstract:
Cathodal transcranial DC stimulation (c-tDCS) suppresses excitability of primary motor cortex (M1) controlling contralateral hand muscles. This study assessed whether c-tDCS would have similar effects on ipsi- and contralateral M1 projections to a proximal upper limb muscle. Transcranial magnetic stimulation (TMS) of left M1 was used to elicit motor evoked potentials (MEPs) in the left and right infraspinatus (INF) muscle immediately before and after c-tDCS of left M1, and at 20 and 40 min, post-c-tDCS. TMS was delivered as participants preactivated each INF in isolation (left, right) or both INF together (bilateral). After c-tDCS, ipsilateral MEPs in left INF and contralateral MEPs in right INF were suppressed in the left task but not in the bilateral or right tasks, indicative of task-dependent modulation. Ipsilateral silent period duration in the left INF was reduced after c-tDCS, indicative of altered transcallosal inhibition. These findings may have implications for the use of tDCS as an adjunct to therapy for the proximal upper limb after stroke.
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VO, BRADLY Q., A. JOSEPH BLOOM, and SUSAN M. CULICAN. "Phr1 is required for proper retinocollicular targeting of nasal–dorsal retinal ganglion cells." Visual Neuroscience 28, no. 2 (February 16, 2011): 175–81. http://dx.doi.org/10.1017/s0952523810000386.
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AbstractPrecise targeting of retinal projections is required for the normal development of topographic maps in the mammalian primary visual system. During development, retinal axons project to and occupy topographically appropriate positions in the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC). Phr1 retinal mutant mice, which display mislocalization of the ipsilateral retinogeniculate projection independent of activity and ephrin-A signaling, were found to have a more global disruption of topographic specificity of retinofugal inputs. The retinocollicular projection lacks local refinement of terminal zones and multiple ectopic termination zones originate from the dorsal–nasal (DN) retinal quadrant. Similarly, in the dLGN, the inputs originating from the contralateral DN retina are poorly refined in the Phr1 mutant. These results show that Phr1 is an essential regulator of retinal ganglion cell projection during both dLGN and SC topographic map development.
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WINKOWSKI, DANIEL E., and EDWARD R. GRUBERG. "Superimposed maps of the monocular visual fields in the caudolateral optic tectum in the frog, Rana pipiens." Visual Neuroscience 22, no. 1 (January 2005): 101–9. http://dx.doi.org/10.1017/s0952523805221132.
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The superficial layers of the frog optic tectum receive a projection from the contralateral eye that forms a point-to-point map of the visual field. The monocular part of the visual field of the contralateral eye is represented in the caudolateral region of the tectum while the binocular part of the visual field is represented in the rostromedial tectum. Within the representation of the binocular field (rostromedial tectum), the maps of visual space from each eye are aligned. The tectal representation of the binocular visual field of the ipsilateral eye is mediated through a crossed projection from the midbrain nucleus isthmi. This isthmotectal projection also terminates in the caudolateral region of the optic tectum, yet there has been no indication that it forms a functional connection. By extracellular recording in intermediate layer 7 of the caudolateral tectum, we have discovered electrical activity driven by visual stimulation in the monocular visual field of the ipsilateral eye. The units driven from the ipsilateral eye burst upon initial presentation of the stimulus. At individual layer 7 recording sites in the caudolateral tectum, the multiunit receptive field evoked from the ipsilateral eye is located at the mirror image spatial location to the multiunit receptive field driven by the contralateral eye. Thus, as revealed electrophysiologically, there are superimposed topographic maps of the monocular visual fields in the caudolateral tectum. The ipsilateral eye monocular visual field representation can be abolished by electrolytic ablation of contralateral nucleus isthmi.
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Einum, James F., and James T. Buchanan. "Membrane Potential Oscillations in Reticulospinal and Spinobulbar Neurons During Locomotor Activity." Journal of Neurophysiology 94, no. 1 (July 2005): 273–81. http://dx.doi.org/10.1152/jn.00695.2004.
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Feedback from the spinal locomotor networks provides rhythmic modulation of the membrane potential of reticulospinal (RS) neurons during locomotor activity. To further understand the origins of this rhythmic activity, the timings of the oscillations in spinobulbar (SB) neurons of the spinal cord and in RS neurons of the posterior and middle rhombencephalic reticular nuclei were measured using intracellular microelectrode recordings in the isolated brain stem-spinal cord preparation of the lamprey. A diffusion barrier constructed just caudal to the obex allowed induction of locomotor activity in the spinal cord by bath application of an excitatory amino acid to the spinal bath. All of the ipsilaterally projecting SB neurons recorded had oscillatory membrane potentials with peak depolarizations in phase with the ipsilateral ventral root bursts, whereas the contralaterally projecting SB neurons were about evenly divided between those in phase with the ipsilateral ventral root bursts and those in phase with the contralateral bursts. In the brain stem under these conditions, 75% of RS neurons had peak depolarizations in phase with the ipsilateral ventral root bursts while the remainder had peak depolarizations during the contralateral bursts. Addition of a high-Ca2+, Mg2+ solution to the brain stem bath to reduce polysynaptic activity had little or no effect on oscillation timing in RS neurons, suggesting that direct inputs from SB neurons make a major contribution to RS neuron oscillations under these conditions. Under normal conditions when the brain is participating in the generation of locomotor activity, these spinal inputs will be integrated with other inputs to RS neurons.
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Weber, Brett C., Robert F. Waldeck, and Edward R. Gruberg. "Seeing beyond the midline: The role of the contralateral isthmotectal projection in the leopard frog." Visual Neuroscience 13, no. 3 (May 1996): 467–76. http://dx.doi.org/10.1017/s0952523800008142.
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AbstractThe ground level visual field of each eye of the leopard frog includes the entire ipsilateral 180-deg field and approximately 60 deg into the frontal contralateral field. When one eye is covered with an opaque patch, a frog responds to prey stimuli over the entire field of the other eye. Nevertheless, when one optic nerve is cut, the animal responds to prey in the ipsilateral hemifield of the connected eye, but only responds as far as about 30 deg past the frontal midline. If one optic tract is cut, the animal does not respond to prey past the frontal midline. We hypothesized that the responses past the frontal midline might be mediated by input from contralaterally projecting isthmotectal fibers. These fibers originate in the nucleus isthmi, a posterior midbrain structure. We found that when we placed an opaque patch over one eye and either ablated the ipsilateral nucleus isthmi, or cut crossing isthmotectal fibers in the optic chiasm, or blocked input to nucleus isthmi by ablating the ipsilateral tectal lobe, animals did not respond to prey stimuli past the frontal midline. We found that when we placed an opaque patch over one eye and cut crossing optic fibers in the anterior part of the optic chiasm (sparing crossing isthmotectal fibers), animals responded to prey stimuli in the nasal half of the seeing eye's contralateral frontal field. Our results suggest that contralaterally projecting isthmotectal fibers enable the frog to respond to stimuli past the frontal midline. We suggest a one-dimensional model of how nucleus isthmi influences tectal function.
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Glendenning, K. K., B. N. Baker, K. A. Hutson, and R. B. Masterton. "Acoustic chiasm V: Inhibition and excitation in the ipsilateral and contralateral projections of LSO." Journal of Comparative Neurology 319, no. 1 (May 1, 1992): 100–122. http://dx.doi.org/10.1002/cne.903190110.
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Schönwald, Marina Zmajević, and Maja Rogić Vidaković. "Contralateral and ipsilateral corticobulbar pathway projections for laryngeal muscles in healthy subjects and patients." Brain Stimulation 8, no. 2 (March 2015): 320. http://dx.doi.org/10.1016/j.brs.2015.01.038.
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Villanueva, L., D. Chitour, and D. Le Bars. "Involvement of the dorsolateral funiculus in the descending spinal projections responsible for diffuse noxious inhibitory controls in the rat." Journal of Neurophysiology 56, no. 4 (October 1, 1986): 1185–95. http://dx.doi.org/10.1152/jn.1986.56.4.1185.
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Recordings were made from convergent neurons in the lumbar dorsal horn of the spinal cord of the rat. These neurons were activated by both innocuous and noxious mechanical stimuli applied to their excitatory receptive fields located on the extremity of the hindpaw. Transcutaneous application of suprathreshold 2-ms square-wave electrical stimuli to the center of the excitatory field, resulted in responses to C-fiber activation being observed. This type of response was inhibited by applying a noxious thermal conditioning stimulus on the muzzle. The immersion of the muzzle in a 52 degrees C waterbath resulted in a strong reduction of the response during the application of the noxious conditioning stimulus and this was followed by long lasting poststimulus effects. Such inhibitory processes have been termed diffuse noxious inhibitory controls (DNIC). The effects on these inhibitions of lesions including the dorsolateral funiculus (DLF) were investigated in acute experiments: tests were performed before and at least 30 min after the DLF lesion. A lesion including the DLF ipsilateral to the neuron under study completely abolished the inhibitory processes triggered from the muzzle. Concomitantly, a facilitation of C-fiber responses was observed. Nevertheless, DNIC was still impaired even using a juxtathreshold current to elicit a weak C-fiber response. To ascertain further the main, if not entire, participation of the ipsilateral DLF in the descending projections responsible for the heterotopic inhibitory processes, the effects of a lesion of the contralateral DLF were investigated. Neither the inhibitory processes nor the unconditioned C-fiber responses were altered by this procedure. Again, a second lesion including the ipsilateral DLF induced a blockade of DNIC. It is concluded that the descending projections involved in the triggering of DNIC are mainly, if not entirely, confined to the DLF ipsilateral to the neuron under study. The contralateral DLF did not appear to play a role in these processes.
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Scherer, Warren J., and Susan B. Udin. "Differential intertectal delay between Rana pipiens and Xenopus laevis: Implications for species-specific visual plasticity." Visual Neuroscience 12, no. 5 (September 1995): 1007–11. http://dx.doi.org/10.1017/s0952523800009548.
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AbstractIn the frog Xenopus laevis, the isthmotectal projection, which relays input from the ipsilateral eye, exhibits anatomical reorganization following surgical eye rotation performed during tadpole stages while the isthmotectal projection in the frog Rana pipiens fails to show reorganization. This plasticity has been shown to be dependent upon activation of the N-methyl-D-aspartate (NMDA) receptor located on tectal cell dendrites. The reorganization process in Xenopus is hypothesized to employ a Hebbian mechanism requiring correlated firing of ipsilateral and contralateral inputs to a given tectal cell; when an ipsilateral axon synapses onto a tectal cell that receives input from a contralateral axon with a matching receptive-field location, the correlation in activity triggers stabilization of the ipsilateral synapse. However, in neither Xenopus nor Rana do ipsilateral and contralateral inputs begin to fire simultaneously in response to a given visual stimulus; the ipsilateral input is delayed because it reaches the tectum indirectly, through a polysynaptic relay via the opposite tectum and nucleus isthmi. The objective of this experiment was to test whether there is a significant difference in this intertectal delay between Xenopus laevis and Rana pipiens in order to determine whether intertectal delay could be a contributing factor in this species-specific ability to exhibit visual plasticity. We have found that intertectal delay is 26.16 ms longer in Rana pipiens (36.53 ms) than in Xenopus laevis (10.37 ms).
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Umeda, Tatsuya, Masahito Takahashi, Kaoru Isa, and Tadashi Isa. "Formation of Descending Pathways Mediating Cortical Command to Forelimb Motoneurons in Neonatally Hemidecorticated Rats." Journal of Neurophysiology 104, no. 3 (September 2010): 1707–16. http://dx.doi.org/10.1152/jn.00968.2009.
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Neonatally hemidecorticated rats show fairly normal reaching and grasping behaviors of the forelimb contralateral to the lesion at the adult stage. Previous experiments using an anterograde tracer showed that the corticospinal fibers originating from the sensorimotor cortex of the intact side projected aberrant collaterals to the spinal gray matter on the ipsilateral side. The present study used electrophysiological methods to investigate whether the aberrant projections of the corticospinal tract mediated the pyramidal excitation to the ipsilateral forelimb motoneurons and, if so, which pathways mediate the effect in the hemidecorticated rats. Electrical stimulation to the intact medullary pyramid elicited bilateral negative field potentials in the dorsal horn of the spinal cord. In intracellular recordings of forelimb motoneurons, oligosynaptic pyramidal excitation was detected on both sides of the spinal cord in the hemidecorticated rats, whereas pyramidal excitation of motoneurons on the side ipsilateral to the stimulation was much smaller in normal rats. By lesioning the dorsal funiculus at the upper cervical level, we clarified that the excitation was transmitted to the ipsilateral motoneurons by at least two pathways: one via the corticospinal tract and spinal interneurons and the other via the cortico-reticulo-spinal pathways. These results suggested that in the neonatally hemidecorticated rats, the forelimb movements on the side contralateral to the lesion were modulated by motor commands through the indirect ipsilateral descending pathways from the sensorimotor cortex of the intact side either via the spinal interneurons or reticulospinal neurons.
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Haustead, D. J., S. S. Lukehurst, G. T. Clutton, C. A. Bartlett, S. A. Dunlop, C. A. Arrese, R. M. Sherrard, and J. Rodger. "Functional Topography and Integration of the Contralateral and Ipsilateral Retinocollicular Projections of Ephrin-A-/- Mice." Journal of Neuroscience 28, no. 29 (July 16, 2008): 7376–86. http://dx.doi.org/10.1523/jneurosci.1135-08.2008.
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Xiong, Guoxiang, and Matsuo Matsushita. "Ipsilateral and contralateral projections from upper cervical segments to the vestibular nuclei in the rat." Experimental Brain Research 141, no. 2 (November 1, 2001): 204–17. http://dx.doi.org/10.1007/s002210100867.
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Anderson, Hilary. "The development of projections and connections from transplanted locust sensory neurons." Development 85, no. 1 (February 1, 1985): 207–24. http://dx.doi.org/10.1242/dev.85.1.207.
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Neurons innervating wind-sensitive hairs on the locust head form characteristic projections and connections within the CNS. These depend on intrinsic properties of the epidermis from which the hair and its neuron are formed (Anderson & Bacon, 1979; Bacon & Anderson, 1984). To investigate further these intrinsic properties and also extrinsic factors involved in guiding axon growth and determining synaptic connectivity, pieces of epidermis from the head were transplanted to the posterior head, prothorax, or mesothorax. Thus wind-sensitive neurons developing from the grafts were caused to grow into foreign parts of the CNS. The neuronal projections from the graft hairs were examined by filling the axons with cobalt, and their connectivity with an identified interneuron, the Tritocerebral Commissure Giant, was examined by recording electrophysiologically the activity of the interneuron during stimulation of the graft hairs. The results show that 1) the neuronal projections are confined to one tract, the median ventral tract, and to one arborization area, the ventral association centre, in all ganglia; 2) in all ganglia, neurons from different epidermal regions preserve their location-specific properties of forming ipsilateral or additional contralateral projections; 3) the extent of their projection in the CNS is not interpretable in terms of intrinsic instructions only; 4) in foreign ganglia, they fail to form connections with their normal target interneuron.
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Pinco, M., and A. Lev-Tov. "Synaptic transmission between ventrolateral funiculus axons and lumbar motoneurons in the isolated spinal cord of the neonatal rat." Journal of Neurophysiology 72, no. 5 (November 1, 1994): 2406–19. http://dx.doi.org/10.1152/jn.1994.72.5.2406.
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1. We studied the projections of ventrolateral funiculus (VLF) axons to lumbar motoneurons in the in vitro spinal cord preparation of 1- to 6-day-old rats using extracellular and sharp-electrode intracellular recordings. 2. Ipsilateral and contralateral VLF projections to lumbar motoneurons (L4-L5) could be activated in the neonatal rat by stimulation of the surgically peeled VLF at the rostral (L1-L2) and caudal lumbar (L6) cord. Motoneurons were activated ipsilaterally through short- and long-latency projections in all cases and contralaterally through long-latency projections in most cases. 3. Suppression of the excitatory components of VLF postsynaptic potentials (PSPs) by application of the specific antagonists of N-methyl D-aspartate (NMDA) and non-NMDA receptors, 2-amino-5-phosphonovaleric acid (APV) and 6-cyano-7-nitroquin-oxaline-2,3-dione (CNQX), revealed depolarizing PSPs that could be reversed at -55 to -60 mV by injection of depolarizing current steps to the motoneurons. These depolarizing PSPs were blocked by addition of strychnine and bicuculline and are therefore suggested to be glycine and gamma-aminobutyric acid-A (GABAA) receptor-mediated inhibitory PSPs. The identity of a small (< or = 0.2 mV) residual depolarizing component that persisted in the presence of APV, CNQX, strychnine, and bicuculline remains to be determined. 4. Short-latency excitatory PSPs (EPSPs) could be resolved from the ipsilaterally elicited VLF PSPs after the reduction of the polysynaptic activity in the preparation by administration of mephenesin, which was followed by suppression of the glycine and GABAA receptor-mediated components of the PSPs by bath application of strychnine and bicuculline. The latencies of these EPSPs were similar to those of the monosynaptic dorsal root afferent EPSPs recorded from the same motoneurons. These short-latency VLF EPSPs were shortened by the NMDA antagonist APV and revealed an NMDA receptor-mediated component after administration of the non-NMDA receptor antagonist CNQX. Addition of the GABAB receptor agonist L-(-) baclofen or the glutamate analogue L-2-amino-4-phosphonobutyric acid (L-AP4) attenuated the pharmacologically resolved short-latency EPSPs.(ABSTRACT TRUNCATED AT 400 WORDS)
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Kokkoroyannis, T., C. A. Scudder, C. D. Balaban, S. M. Highstein, and A. K. Moschovakis. "Anatomy and physiology of the primate interstitial nucleus of Cajal I. efferent projections." Journal of Neurophysiology 75, no. 2 (February 1, 1996): 725–39. http://dx.doi.org/10.1152/jn.1996.75.2.725.
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1. The efferent projections of the interstitial nucleus of Cajal (NIC) were studied in the squirrel monkey after iontophoretic injections of biocytin and Phaseolus Vulgaris leucoagglutinin into the NIC. To ensure the proper placement of the tracer, the same pipettes were used to extracellularly record the discharge pattern of NIC neurons. 2. Three projection systems of the NIC were distinguished: commissural (through the posterior commissure), descending, and ascending. 3. The posterior commissure system gave rise to dense terminal fields in the contralateral NIC, the oculomotor nucleus, and the trochlear nucleus. 4. The descending system of NIC projections deployed dense terminal fields in the ipsilateral gigantocellular reticular formation and the paramedian reticular formation of the pons, as well as in the ventromedial and commissural nuclei of the first two spinal cervical segments. It also gave rise to moderate or weak terminal fields in the vestibular complex, the nucleus prepositus hypoglossi, the inferior olive, and the magnocellular reticular formation, as well as cell groups scattered along the paramedian tracts in the pons and the pontine and medullary raphe. 5. The ascending system of NIC projections gave rise to dense terminal fields in the ipsilateral mesencephalic reticular formation and the zona incerta as well as moderate or weak terminal fields in the ipsilateral centromedian and parafascicular thalamic nuclei. It also provided dense bilateral labeling of the rostral interstitial nucleus of the medial longitudinal fasciculus and the fields of Forel, and moderate or weak bilateral labeling of the mediodorsal, central medial, and central lateral nuclei of the thalamus. 6. Models of saccade generation that rely on feedback from the velocity-to-position integrators and include the superior colliculus in their local feedback loop are contradicted because no fibers originating from the NIC traveled to the superior colliculus to deploy terminal fields. 7. Consistent with its morphological and functional diversity, these data indicate that the primate NIC sends signals to a multitude of targets implicated in the control of eye and head movements.
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Chomiak, T., S. Peters, and B. Hu. "Functional Architecture and Spike Timing Properties of Corticofugal Projections From Rat Ventral Temporal Cortex." Journal of Neurophysiology 100, no. 1 (July 2008): 327–35. http://dx.doi.org/10.1152/jn.90392.2008.
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Sensory association and parahippocampal cortex in the ventral temporal lobe plays an important role in sensory object recognition and control of top-down attention. Although layer V neurons located in high-order cortical structures project to multiple cortical and subcortical regions, the architecture and functional organization of this large axonal network are poorly understood. Using a large in vitro slice preparation, we examined the functional organization and spike timing properties of the descending layer V axonal network. We found that most, if not all, layer V neurons in this region can form multiple axonal pathways that project to many brain structures, both proximal and remote. The conduction velocities of different axonal pathways are highly diverse and can vary up to more than threefold. Nevertheless for those axonal projections on the ipsilateral side, the speeds of axonal conduction appear to be tuned to their length. As such, spike delivery becomes nearly isochronic along these pathways regardless of projection distance. In contrast, axons projecting to the contralateral hemisphere are significantly slower and do not participate in this lateralized isochronicity. These structural and functional features of layer V network from the ventral temporal lobe may play an important role in top-down control of sensory cue processing and attention.
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Fitzgibbon, T., and W. Burke. "Representation of the temporal raphe within the optic tract of the cat." Visual Neuroscience 2, no. 3 (March 1989): 255–67. http://dx.doi.org/10.1017/s0952523800001176.
Full textAbstract:
AbstractThe retinal topography of the cat's optic tract was determined by means of injections of the enzyme horseradish peroxidase (HRP) into the tract. This analysis was accomplished by the subtraction of all HRP injection sites not labeling a defined retinal area from those injection sites which resulted in ganglion cell labeling (Venn diagram analysis). Using this method, the following correspondences were demonstrated for the ipsilateral and contralateral projections: superior retina represented in medial optic tract; inferior retina in lateral tract; and area centralis in a dorsocentral location (which was part of a larger area representing the visual streak). The temporal raphe was represented in the ipsilateral tract as a band curving from the area centralis region toward the dorsomedial border of the tract. Contralateral fibers from a region superior to the optic disc were found to be displaced with respect to the general retinal representation in the optic tract and this appeared to be related to retinal development. The ratio of contralateral to ipsilateral fibers was determined and found to be nonuniform within the tract.Injection of HRP into the optic tract of the cat also allowed the axons from labeled retinal ganglion cells to be traced within the retina and optic disc. Axons from ganglion cells lying temporal to the raphe curve around the area centralis enter the optic disc on the lateral and inferior aspects. Ganglion cells lying nasal to the raphe send their axons more directly to enter the optic disc on its superior aspect. A schema is proposed whereby the retina is mapped onto the optic tract.
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Baker, M., B. Chiasson, and R. Croll. "Contralateral sprouting and compensatory innervation following the permanent lesion of a ganglionic connective in the snail." Journal of Experimental Biology 199, no. 12 (December 1, 1996): 2631–43. http://dx.doi.org/10.1242/jeb.199.12.2631.
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The fate of sprouted fibres was examined following long-term recovery from lesions to the central nervous system of the snail Achatina fulica. Axonal dye-labelling of one of the cerebrobuccal connectives (CBC), following either a cut or a crush to the opposite CBC, revealed supernumerary labelling of neuronal elements in both the cerebral and buccal ganglia in the weeks following treatment. A part of this sprouting response involved the rerouting of axonal projections from injured neurones that project contralaterally into the uninjured CBC. In addition, intracellular dye-fills, immunocytochemistry for detection of serotonin and electrophysiological measurements all revealed that a contralateral, uninjured neurone, the metacerebral giant (MCG) cell, sprouted new processes to invade the buccal ganglion denervated by the lesion. The contralateral MCG also increased synaptic drive over a neurone in the denervated buccal ganglion, a cell that normally receives strong input only from the lesioned ipsilateral MCG. After 5 weeks of recovery, morphological and electrophysiological measurements returned to normal levels in animals receiving a crush to the CBC, suggesting a retraction of sprouted projections following successful regeneration across the lesioned pathway. In contrast, the measurements indicative of sprouted fibres continued for up to 5 months when the regenerative response was prevented by cutting the CBC. Together, these results suggest that both the cessation of sprouting and the eventual retraction of sprouted fibres in Achatina fulica is contingent upon successful regeneration of the damaged axonal pathway.
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Mason, Carol, and Nefeli Slavi. "Retinal Ganglion Cell Axon Wiring Establishing the Binocular Circuit." Annual Review of Vision Science 6, no. 1 (September 15, 2020): 215–36. http://dx.doi.org/10.1146/annurev-vision-091517-034306.
Full textAbstract:
Binocular vision depends on retinal ganglion cell (RGC) axon projection either to the same side or to the opposite side of the brain. In this article, we review the molecular mechanisms for decussation of RGC axons, with a focus on axon guidance signaling at the optic chiasm and ipsi- and contralateral axon organization in the optic tract prior to and during targeting. The spatial and temporal features of RGC neurogenesis that give rise to ipsilateral and contralateral identity are described. The albino visual system is highlighted as an apt comparative model for understanding RGC decussation, as albinos have a reduced ipsilateral projection and altered RGC neurogenesis associated with perturbed melanogenesis in the retinal pigment epithelium. Understanding the steps for RGC specification into ipsi- and contralateral subtypes will facilitate differentiation of stem cells into RGCs with proper navigational abilities for effective axon regeneration and correct targeting of higher-order visual centers.
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Takahashi, M., Y. Sugiuchi, and Y. Shinoda. "Commissural Mirror-Symmetric Excitation and Reciprocal Inhibition Between the Two Superior Colliculi and Their Roles in Vertical and Horizontal Eye Movements." Journal of Neurophysiology 98, no. 5 (November 2007): 2664–82. http://dx.doi.org/10.1152/jn.00696.2007.
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The functional roles of commissural excitation and inhibition between the two superior colliculi (SCs) are not yet well understood. We previously showed the existence of strong excitatory commissural connections between the rostral SCs, although commissural connections had been considered to be mainly inhibitory. In this study, by recording intracellular potentials, we examined the topographical distribution of commissural monosynaptic excitation and inhibition from the contralateral medial and lateral SC to tectoreticular neurons (TRNs) in the medial or lateral SC of anesthetized cats. About 85% of TRNs examined projected to both the ipsilateral Forel's field H and the contralateral inhibitory burst neuron region where the respective premotor neurons for vertical and horizontal saccades reside. Medial TRNs received strong commissural excitation from the medial part of the opposite SC, whereas lateral TRNs received excitation mainly from its lateral part. Injection of wheat germ agglutinin–horseradish peroxidase into the lateral or medial SC retrogradely labeled many larger neurons in the lateral or medial part of the contralateral SC, respectively. These results indicated that excitatory commissural connections exist between the medial and medial parts and between the lateral and lateral parts of the rostral SCs. These may play an important role in reinforcing the conjugacy of upward and downward saccades, respectively. In contrast, medial SC projections to lateral SC TRNs and lateral SC projections to medial TRNs mainly produce strong inhibition. This shows that regions representing upward saccades inhibit contralateral regions representing downward saccades and vice versa.
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LI, ZHENG, and KATHERINE V. FITE. "GABAergic visual pathways in the frog Rana pipiens." Visual Neuroscience 18, no. 3 (May 2001): 457–64. http://dx.doi.org/10.1017/s0952523801183124.
Full textAbstract:
Gamma-aminobutyric acid (GABA) is the most prevalent inhibitory neurotransmitter in the vertebrate brain. It can exert its influence either as GABAergic projection pathways or as local interneurons, which play an essential role in many visual functions. However, no GABAergic visual pathways have been studied in frogs so far. In the present study, GABAergic pathways in the central visual system of Rana pipiens were investigated with double-labeling techniques, combining immunocytochemistry for GABA with Rhodamine microspheres for retrograde tracing. Three GABAergic visual pathways were identified: (1) a retino-tectal projection, from retina to the contralateral optic tectum (OT); (2) an ipsilateral projection from the nucleus of the basal optic root (nBOR) to the pretectal nucleus lentiformis mesencephali (nLM); and (3) a second-order pathway from the nucleus isthmi (NI), bilaterally, to the optic tectum. These results indicate that GABA is involved in both first-order (retina to optic tectum) as well as second-order (nucleus isthmi to optic tectum) visual projections in Rana pipiens, and may play a major role in mediating visuomotor reflexs such as optokinetic nystagmus or other visually guided behaviors.
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Katter, J. T., R. J. Dado, E. Kostarczyk, and G. J. Giesler. "Spinothalamic and spinohypothalamic tract neurons in the sacral spinal cord of rats. I. Locations of antidromically identified axons in the cervical cord and diencephalon." Journal of Neurophysiology 75, no. 6 (June 1, 1996): 2581–605. http://dx.doi.org/10.1152/jn.1996.75.6.2581.
Full textAbstract:
1. A goal of this study was to determine the sites in the diencephalon to which neurons in sacral spinal segments of rats project. Therefore, 95 neurons were recorded extracellularly in spinal segments L6-S2 of rats that were anesthetized with urethan. These neurons were activated initially antidromically with currents < or = 30 microA from a monopolar stimulating electrode placed into the contralateral posterior diencephalon. The mean +/- SE current for antidromic activation from these sites was 16 +/- 0.8 microA. These neurons were recorded in the superficial dorsal horn (4%), deep dorsal horn (89%), and intermediate zone and ventral horn (4%). 2. Systematic antidromic mapping techniques were used to map the axonal projections of 41 of these neurons within the diencephalon. Thirty-three neurons (80%) could be activated antidromically with currents < or = 30 microA only from points in the contralateral thalamus and are referred to as spinothalamic tract (STT) neurons. Eight neurons (20%) were activated antidromically with low currents from points in both the contralateral thalamus and hypothalamus, and these neurons are referred to as spinothalamic tract/ spinohypothalamic tract (STT/SHT) neurons. Three additional neurons were activated antidromically with currents < or = 30 microA only from points within the contralateral hypothalamus and are referred to as spinohypothalamic tract (SHT) neurons. The diencephalic projections of another 51 neurons were mapped incompletely. These neurons are referred to as spinothalamic/unknown (STT/ U) neurons to indicate that it was not known whether their axons ascended beyond the site in the thalamus from which they initially were activated antidromically. 3. For 31 STT neurons, the most anterior point at which antidromic activation was achieved with currents < or = 30 microA was determined. Fourteen (45%) were activated antidromically only from sites posterior to the ventrobasal complex (VbC) of the thalamus. Sixteen STT neurons (52%) were activated antidromically with low currents from sites at the level of the VbC, but not from more anterior levels. One STT neuron (3%) was activated antidromically from the anteroventral nucleus of the thalamus. 4. STT/SHT neurons were antidromically activated with currents < or = 30 microA from the medial lemniscus (ML), anterior pretectal nucleus (APt), posterior nuclear group and medial geniculate nucleus (Po/MG), and zona incerta in the thalamus and from the optic tract (OT), supraoptic decussation, or lateral area of the hypothalamus. No differences in the sites in the thalamus from which STT and STT/SHT neurons were activated antidromically were apparent. Five STT/SHT neurons (62%) were activated antidromically from points in the thalamus in the posterior diencephalon and from points in the hypothalamus at more anterior levels. Three STT/SHT neurons (38%) were activated antidromically with currents < or = 30 microA from sites in both the thalamus and hypothalamus at the same anterior-posterior level of the diencephalon. All three of these STT/SHT neurons projected to the intralaminar nuclei (parafascicular or central lateral nuclei) of the thalamus. 5. Seven STT/SHT neurons were tested for additional projections to the ipsilateral brain. Two (29%) were activated antidromically with currents < or = 30 microA and at longer latencies from sites in the ipsilateral diencephalon. One could only be activated antidromically from the hypothalamus ipsilaterally. The other was activated antidromically at progressively increasing latencies from points in the ipsilateral brain that extended as far posteriorly as the posterior pole of the MG. 6. Fifty-eight STT, STT/SHT, and STT/U neurons were classified as low-threshold (LT), wide dynamic range (WDR), or highthreshold (HT) neurons based on their responsiveness to innocuous and noxious mechanical stimuli applied to their cutaneous receptive fields.(ABSTRACT TRUNCATED)
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Koshiba, Mamiko, Shun Nakamura, Chao Deng, and Lesley J. Rogers. "Light-dependent development of asymmetry in the ipsilateral and contralateral thalamofugal visual projections of the chick." Neuroscience Letters 336, no. 2 (January 2003): 81–84. http://dx.doi.org/10.1016/s0304-3940(02)01162-x.
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