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P Angaut

Publications and source records attributed to P Angaut.

At least 37 records · Page 2Linked to original sources
PubMed1987

The dentato-olivary projection in the rat as a presumptive GABAergic link in the olivo-cerebello-olivary loop. An ultrastructural study.

It is here shown that autoradiographically labelled axon terminals of the dentato-olivary projection form a heterogeneous population. However, a majority of them constitute an even class of synapses, characterized by their small axonal size, their content in pleimorphic vesicles, and the establishment of symmetric synapses on small dendrites, about 5% of which are linked through a gap junction. The same material, used for immunocytochemistry of GABA with the postembedding technique, discloses that a majority of boutons with cytological features similar to the dentato-olivary terminals are GABA-immunoreactive, especially those synapsing on dendrites linked by gap junctions. The cerebello-olivary projection, despite its heterogeneity, thus appears as part of the GABAergic system which governs the synaptic modulation of the electrotonic coupling between olivary neurons.

Animals↗
PubMed1987

The interposito-rubrospinal system. Anatomical tracing of a motor control pathway in the rat.

The cerebello-rubromotor pathway, impinging on both spinal and facial motor nuclei, has been traced in the rat, using the bidirectional transport of horseradish peroxidase-wheat germ agglutinin conjugate. After injection of the tracer in the red nucleus (NR), retrograde labelling shows a topical arrangement of the cerebellorubral connection. The nucleus lateralis projects to the parvocellular NR (NRp) and the nucleus interpositus to the magnocellular NR (NRm). The nucleus interpositus anterior (NIA) reaches the entire NRm and this projection is topographically arranged: the medial NIA sends fibres ventrally, the lateral NIA dorsally. The medial two-thirds of the nucleus interpositus posterior (NIP) project only to the medial aspect of the NRm, with no apparent organization. No connection has been found between the lateral third of NIP and the NRm. After injection of the tracer in the spinal cord or the nucleus of the facial nerve, retrograde labelling is observed almost throughout the entire caudorostral extent of the NR, although labelling is more scant in NRp than in NRm. Rubrospinal and rubrofacial projections are somatotopically arranged in the dorsoventral direction: ventrolateral regions of NR reach the lumbar cord, medioventral regions the lower cervical levels, intermediary regions the upper cervical levels and finally the dorsalmost part of the NR projects to the nucleus of the facial nerve. After injection of the tracer in the cerebellar nuclei, anterograde labelling in the NR shows that interpositorubral connections determine two subregions in the NR: a lateral one under the exclusive control of the NIA, and a medial one under the control of both NIA-NIP afferents. It confirms in addition the topography of the NIA-NRm projection and shows the preponderant participation of the NIA afferents to the interpositorubral connection. Thus, it appears from our results that the cerebellorubral arrangement matches, to a great extent, the "rubromotor" efferent organization.

Animals↗
PubMed1987

The dentatorubral projection. An autoradiographic study in rats.

Although the dentatorubral projection is known to end specifically in the parvocellular part of the red nucleus, its topographical arrangement has never been elucidated. We therefore selectively injected the lateral cerebellar nucleus (homologous to the dentate nucleus of primates) of adult Wistar rats with tritiated leucine or proline in order to trace the dentatorubral boundaries. In all cases, the projection was found to extend rostrocaudally throughout the parvocellular red nucleus; dorsoventrally as well as mediolaterally, the fibers were distributed according to the location of the injection within the lateral cerebellar nucleus. Hence, caudal regions of the lateral nucleus send fibers dorsally at the rubral level, rostral regions project ventrally. This dorsoventral arrangement matches the segregation of the parvocellular red nucleus into a dorsal 'forelimb' region and a ventral 'hindlimb' region corresponding to its spinal efferents. In addition, only the ventral part of the lateral cerebellar nucleus, particularly the parvocellular region (subnucleus lateralis parvocellularis), projects to the lateral aspect of the parvocellular red nucleus. These results suggest a common pattern of organization of the dentatorubral and the dentatothalamic projections.

Animals↗
PubMed1986

The cerebellorubral projection in the rat: retrograde anatomical study.

The cerebellorubral projections have been studied in the rat using the retrograde transport of horseradish peroxidase-wheat germ agglutinin conjugate. The lateral cerebellar nucleus projects to the parvocellular red nucleus (RN), the anterior (NIA) and posterior (NIP) interposed nuclei project to the magnocellular RN. Whereas the projections from the NIP are limited to the medial aspect of the RN, those from the NIA extend throughout the magnocellular RN. NIA-RN projections are topographically arranged: the medial NIA projects ventrally, the lateral NIA projects dorsally. Functionally, this differential distribution seems to fit the hindlimb-forelimb areas of origin of the rubrospinal tract.

Animals↗
PubMed1986

Functional organization of thalamic projections to the motor cortex. An anatomical and electrophysiological study in the rat.

In rats, horseradish peroxidase crystals were injected in motor cortical foci functionally identified by means of the motor effects evoked by electrical stimulations. The location in the thalamus of the neurons linked to different motor cortical foci was studied. Thalamic neurons were retrogradely labeled in both "motor" (ventralis lateralis and ventralis medialis) and "non-motor" nuclei: centralis lateralis, lateralis posterior, mediodorsalis and posterior thalamic nuclear group, as well as the ventrobasal complex. The ventrobasal complex was labeled after horseradish peroxidase injections in hindlimb and trunk motor areas. The ascending projections toward the motor cortex from both "motor" and "non-motor" thalamic nuclei are organized more precisely and more elaborately than previously reported. The motor cortical afferents from the nucleus ventralis lateralis are organized in three planes, rostrocaudally, dorsoventrally and mediolaterally. An inverted relation exists in the rostrocaudal plane between the nucleus ventralis lateralis and the motor cortex: the caudal motor cortex region (hindlimb) receives fiber inputs from the rostral region of the nucleus ventralis lateralis, whereas the caudal zone of the nucleus ventralis lateralis projects to the rostral motor cortex region (forelimb and vibrissae). A dorsoventral organization has also been observed in the rostral region of the nucleus ventralis lateralis: the ventral aspect is the source of fibers directed to the distal hindlimb region, whereas fibers originating from the dorsal aspect are directed to the proximal hindlimb area. A mediolateral relationship exists between medial and lateral sides of the nucleus ventralis lateralis and, respectively, proximal and distal forelimb cortical areas. There is some overlap between the various nuclear regions thus delineated. Four functional zones were found in the lateral half of the nucleus ventralis medialis and were classified according to their projection to the motor cortex; these are involved in motor control of the proximal and distal forelimb, vibrissae and ocular movements. The projection is topographically organized according to both an inverted rostrocaudal and a direct dorsoventral-mediolateral arrangement. Caudally, dorsal and ventral nuclear parts project to rostromedial (vibrissae) and rostrolateral (distal forelimb) regions of the motor cortex, respectively. More rostral nuclear zones project to more caudal (proximal forelimb, eye) cortical regions. There is little overlap between these four nuclear subdivisions. The nucleus centralis lateralis projects to vibrissae and proximal, as well as distal, forelimb areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Compensatory climbing fiber innervation after unilateral pedunculotomy in the newborn rat: origin and topographic organization.

In neonatal rats the unilateral transection of the cerebellar peduncles causes a fast and complete degeneration of the contralateral inferior olive. Axons from the remaining olive recross the cerebellar midline and partially innervate the deprived hemicortex. Analysis of the topographic organization of this compensatory projection studied with the axonal tracing method provided the following results: Retrograde tracing experiments revealed that the bulk of compensatory afferents originates from neurons in the ipsilateral medial accessory olive, especially from its medial region, whereas afferents from the principal olive and the dorsal accessory olive contribute to a much lesser degree. In case of incomplete neonatal pedunculotomy, neurons with a similar location in the ipsilateral intact olive still contribute to the innervation of the partially deprived hemicortex, along with the atrophic contralateral olive. Moreover, these experiments revealed important information about the organization of the compensation. Although its specificity was not totally maintained, the mediolateral distribution of sprouted afferents in the cerebellum matched the caudorostral disposition of parent neurons in the olive, as in the case in normal olivocerebellar projection. Anterograde studies showed that compensatory fibers recrossing the cerebellar midline spread throughout the whole extent of the deprived cortex and terminate solely in the molecular layer as typical climbing fibers. The latter were not homogeneously distributed, their density being markedly reduced according to a mediolateral gradient. Compensatory projection followed a sagittal striped pattern, as does the normal climbing fiber projection. Moreover, if the cortex is divided broadly into vermal, intermediate, and hemispheral regions, an apparent reciprocity seems to exist concerning the relative involvement of the various cortical subdivision in both hemicerebella. Our present results indicate that the immature olivocerebellar system is capable of anatomical plasticity, although to a limited extent. More important, they suggest that a certain degree of specificity is maintained during the process of sprouting, resulting in a topographical arrangement of the transcommissural climbing fiber projection. This indicates, in turn, that cues which guide the growth of olivocerebellar fibers during normal development could also direct the compensatory innervation.

Animals↗
PubMed1985

Topographic organization of the cerebellothalamic projections in the rat. An autoradiographic study.

The topographical organization of the subnuclear projections towards the thalamus was studied with autographic methods in adult Wistar rats. The four cerebellar deep nuclei give rise to projections to the ventral region of the rostral thalamus. Most of the fibers end contralaterally, according to a topographical pattern; however, some fibers from each of the cerebellar nuclei recross the midline at the thalamic level and terminate ipsilaterally, within regions symmetric to those receiving the densest contralateral projection. These ipsilateral cerebellothalamic components arise in decreasing order from the caudal nucleus lateralis, the ventrocaudal nucleus medialis and the nucleus interpositus, respectively. The projections of the nucleus lateralis directed to the contralateral thalamus are topographically organized. (1) Within the nucleus ventralis lateralis, the rostral and caudal parts of the cerebellar nucleus lateralis project respectively to rostral and caudal regions; lateral and medial zones of the nucleus lateralis project, respectively, to medial and central aspects of the nucleus ventralis lateralis. (2) The nucleus ventralis medialis and particularly its caudal portion appears to receive the bulk of its afferents from the ventromedial portion of the nucleus lateralis including the "subnucleus lateralis parvocellularis". (3) The nucleus centralis lateralis receives fibers from most parts of the nucleus lateralis including the "dorsolateral hump". (4) The nucleus interpositus anterior projects to the dorsomedial aspect of the rostral nucleus ventralis lateralis. In the latter nucleus, the ventrolateral aspect of the central region receives projections in cases in which the nucleus interpositus posterior is largely involved. A particular emphasis is put on the different projections from the various subnuclear regions of the lateral nucleus. A comparison is attempted with the situation in the primates, particularly with regard to the question of the parvocellular subdivision of the lateral nucleus.

Animals↗
PubMed1985

An autoradiographic study of the cerebellopontine projections from the interposed and lateral cerebellar nuclei in the rat.

The projections from the cerebellar lateral and interposed nuclei onto the basilar pontine gray and nucleus reticularis tegmenti pontis (NRTP) have been studied in the rat by the use of the autoradiographic technique. Projections from both nuclei are mainly contralateral. Fibers from the lateral nucleus cover most of the NRTP, except its medial, parvocellular portion. In the pontine gray proper, fibers from the lateral nucleus are distributed to three rostrocaudally oriented columns: (i) in the medial nucleus, (ii) in the ventral nucleus, and (iii) in the dorsolateral and lateral nuclei. The projection is topographically arranged, so that caudal parts of the lateral cerebellar nucleus tend to project to more rostral regions than rostral parts of the lateral nucleus. The interposed nucleus gives rise to a sparser projection, apparently limited to the ventral NRTP and immediate peripeduncular zones. The functional implications of these results are discussed, with particular emphasis on the convergence of corticopontine afferents to the pontine regions involved, and on the reciprocal pontocerebellar pathways from these same regions.

Animals↗
PubMed1984

The distribution and origin of the ipsilateral descending limb of the brachium conjunctivum. An autoradiographic and horseradish peroxidase study in the rat.

The distribution, organization and origin of the ipsilateral descending limb of the Brachium Conjunctivum (B.C.), have been studied in the rat by using anterograde and retrograde tracing techniques. After injections of tritiated leucine/proline into the lateral cerebellar nucleus, covering both its medial part, corresponding to the dorsolateral hump (DLH) of Goodman et al. (1963) and its lateral part, (designated here as the lateral dentate, LD), and the neighboring interposed nucleus (NI), emerging fibres are numerous and leave laterally from the B.C. On the contrary, injections restricted to LD reveal very few such fibers. Within the lateral parvocellular reticular formation (LPRF) terminal labelling is heavy, and moderate to sparse within the adjacent trigeminal complex. Rostro-caudally, silver grain accumulation within the LPRF extends from the level of the motor trigeminal nucleus (VM) to the pyramidal decussation, exhibiting a cephalocaudal decrease of grain density. Within the trigeminal complex, labelling occurs in the caudal VM, the dorsal portion of the principal sensory nucleus, and within and around the trigeminal spinalis oralis. In addition, the area surrounding the VM (in part corresponding to the supratrigeminal region of Lorente de Nó 1922, 1933) is moderately labelled. After injections of HRP into various levels of the ipsilateral descending B.C.'s projection field, retrogradely labelled cells are numerous within the DLH. A slightly lesser amount of labelled cells are found in the lateral half of the NI, primarily concerning the nucleus interpositus posterior. Within the LD, only a few labelled cells are observed: these are mainly restricted to the dorsal portion at rostral levels of the nucleus. The results obtained by both the anterograde and retrograde studies suggest an absence of a topographic organization within this descending B.C. component. The possible functional meaning of these results is discussed.

Animals↗
PubMed1982

An autoradiographic study of the cerebellopontine projections in the rat. I. Projections from the medial cerebellar nucleus.

The medial cerebellar nucleus of the rat is shown by the autoradiographic technique to project to both the contralateral nucleus reticularis tegmenti pontis and the pontine nuclei proper. The former projection is more concentrated in the medial--parvocellular --region. In the pontine gray, the bulk of the projection concerns the dorsal aspect of the medial nucleus. Rostral parts of the medial cerebellar nucleus project to caudal pontine levels whereas caudal parts seem to project throughout the rostrocaudal extent of the basilar pons.

Animals↗
PubMed1982

Ultrastructural evidence for compensatory sprouting of climbing and mossy afferents to the cerebellar hemisphere after ipsilateral pedunculotomy in the newborn rat.

Unilateral section of the inferior and middle cerebellar peduncles was performed in rats at postnatal days 1 or 2. The ultrastructure of the cerebellar hemispheric cortex ipsilateral to the lesion was examined 3 months later. The absence of contralateral inferior olive and of ipsilateral middle peduncle, together with a marked regression of the contralateral pontine gray, were indicative of successful pedunculotomy. In spite of a relative atrophy of the hemisphere, its cytological structure was qualitatively normal. Mossy and climbing fibers were present and their terminal varicosities disclosed normal features. The density of climbing fiber terminals was reduced compared to control cerebellum, whereas the density of mossy terminals seemed unchanged. subsequent to the reduction of climbing afferents two subclasses, or types, of Purkinje cells were present: A "normal" type characterized by its climbing fiber innervation and a "hyperspiny" type devoid of climbing fiber. In some of the adult rats pedunculotomized at birth, section of the contralateral peduncles was performed 24 hours before fixation. Terminal degeneration of climbing and mossy fibers was observed in the neonatally deprived hemisphere, providing the proof that these fibers result from a compensatory transcommissural sprouting of afferents destined to the contralateral hemicerebellum. These results demonstrate that the cerebellar cortex neonatally deprive of its main afferents can be innervated by climbing and mossy fibers through a process of transcommissural sprouting. Although the newly formed synapses maintain their target specificity, a functional reorganization must occur because of the altered distribution of both systems of afferents.

Afferent Pathways↗
PubMed1981

Comparative study of the posterior red nucleus in baboons and gibbons.

The posterior red nucleus (PRN) was studied in two species of primates by the technique of retrograde degeneration of rubrospinal cells following transection of the spinal cord at different levels. The form of the PRN was reconstructed for both a quadruped monkey (baboon) and an anthropoid with erect posture (gibbon). The PRN contains polymorphic cells characterized by their very chromophilic and granular Nissl substance. These neurons vary in diameter from 25 micrometer to 70 micrometer. Some of them give rise to the rubrospinal tract. Baboon: The approximately 1,300 rubrospinal cells in this species are divided into two equal groups, one related to the contralateral forelimb, with axons ending between the second cervical and third thoracic segment, and the other related to the contralateral hindlimb, projecting caudally beyond T3. Following a high cervical lesion, nondegenerated cells of similar description remain throughout the nucleus. A significantly large group of these cells occurs medially and may be the source of fibers ending in the brain stem or cerebellum. Gibbon: In this species, the number of rubrospinal cells controlling the hindlimb is less than half that found in the baboon. This reduction in the gibbon is much greater for medium-sized cells, but is also significant for the giant cells. These results obtained from primates are compared with those reported for the cat. A possible function for the PRN in the control of limb movements is discussed from the viewpoint of phylogeny.

Animals↗
PubMed1981

Embryonic development of the nucleus isthmo-opticus in the chick: a Golgi and electron microscopic study.

The cytology and the synaptology of the nucleus isthmo-opticus have been studied in the chick embryo at three stages during (incubation days 14 and 15) and after (day 18) the neurone death period of the nucleus. The maturation process is not synchronous throughout the nucleus:the dorsal most region lags behind the rest of the nucleus. On the other hand, cell degeneration is equally distributed over the nucleus at days 14 and 15. At day 14, the nucleus shows little cellular alignment. The neuropil is stocked with immature neurites. Synaptogenesis essentially concerns axodendritic contacts, and the presynaptic partners contain only round vesicles. A few axons undergo myelination; among them, some are degenerating. At day 15, cellular alignment is much more pronounced. Synaptogenesis is very active; it concerns axosomatic as well as axodendritic contacts. A majority of the presynaptic bags contain only round vesicles, although some have a pleomorphic population of vesicles. At day 18, the histological structure of the nucleus is similar to that found in the adult. Although the neuropil presents mature profiles (development of dendritic spines, presence of synaptic glomeruli), it still contains numerous immature features (active synaptogenesis, persistent growth cones). Possible functional implications of this maturation are discussed. In particular, the fact that the nuclear neuropil is not fully developed by the end of the incubation period suggests that the accomplishment of the feedback role of the nucleus is determined by function.

Animals↗
PubMed1978

A light and electron microscopic study of the nucleus isthmo-opticus in the pigeon.

A morphological study of the nucleus isthmo-opticus (NIO) has been carried out using several histological approaches as well as electron microscopic analysis. The nucleus is composed of bipolar cells of relatively constant size. The neurones within a given nuclear region are oriented in the same plane and direction. EM observations show that neighbouring cells often give off complex spinous extensions that come in close contact with each other. The apposed membranes of these extensions display large attachment plaques. The neuropil contains relatively abundantly myelinated axons, thin dendrites, and various types of terminals. A majority of the terminals contain rounded vesicles. The tecto-isthmic projection has been studied electronmicroscopically, by using the degeneration technique. The tecto-isthmic terminals contain predominantly rounded vesicles. They almost always make axo-dendritic contacts. Degeneration and autoradiographic techniques at the light microscope level fully confirm previous data by others on the topologic organization of the projection. The above two techniques were applied to the study of NIO-retinal interrelationships. No retinal projection to NIO could be confirmed. On the other hand, enucleation induces a terminal degeneration of slow time course. This finding suggests the presence of intrinsic fibre collaterals of isthmo-retinal axons. The existence of fibre projections from the oculomotor nuclei is shown by a light microscope degeneration study. Fibres coming from the trochlear nucleus might correspond to collaterals of motor axons.

Animals↗
PubMed1975

Diversity of mossy fibres in the cerebellar cortex in relation to different afferent systems: an experimental electron microscopic study in the cat.

The evolution of the terminal degeneration has been compared in two systems of mossy fibres: the spinocerebellar and the pontocerebellar projections. The two systems exhibit both dense and clear types of terminal degeneration. However, there are important differences between the evolutive processes of terminal degeneration in the two systems: (i) the time course of the degenerating process is much faster for spinocerebellar than for pontocerebellar rosettes, and (ii) the glial phagocytic process accompanying the dense type of degeneration is different for the two systems. Spinocerebellar rosettes are generally removed from their glomerular central position by reactive glia, leaving fragments of the presynaptic membrane attached to their postsynaptic partner. This feature is exceptional for pontocerebellar rosettes which, in the course of their glial engulfment, leave free the postsynaptic differentiation of their former target granule cell dendrites. These differences of terminal degenerative processes have been reconciled with optical microscope observations by Brodal and Drablos1 of morphological differences between the rosettes of two different fibre systems.

Afferent Pathways↗