Robert Marty

The onset of synaptogenesis in rat temporal cortex.

SummaryThe onset of synaptogenesis was studied in the temporal cortex of rat fetuses whose age ranged between 15 and 19 days of gestation. First synapses were found at a surprisingly early stage of cortical development: on day 16. These contacts showed relatively few vesicles and very inconspicuous membrane-thickenings. They were located in the marginal layer, above as well as below the narrow band formed by the newly arrived first neuroblasts of the prospective cortical plate. The postsynaptic structures were probably dendrites of the horizontally or obliquely orientated neurons scattered throughout the marginal layer (such neurons were seen even within the cell-dense band).On day 17, the cortical plate separated the differentiated cells definitely into a superficial and a deep population. As on the following days, synapses were found above and below the cortical plate but not within it. In addition to contacts showing the same features as those described on day 16, there were already synapses with numerous vesicles and clearly asymmetric membrane thickenings. On days 18 and 19 the borders of the cortical plate became more clear-cut. The well-differentiated neurons situated above and below this plate could now be identified as Retzius-Cajal cells of the prospective molecular layer and as polymorphous cells of the layer VI b respectively. The presence of axo-somatic contacts on these neurons provided direct evidence that both cell types are targets for synapses.Desmosome-like junctions were found even in the youngest fetuses studied. Their roughly symmetric membrane thickenings were clearly more conspicuous than those of earliest synapses. Desmosome-like junctions occurred very frequently between structures which subsequently were never seen to become synaptically linked. During the entire period studied, numerous coated vesicles fused with cell membranes were noted. Such “open” vesicles were seen on neurons (sometimes in the immediate vicinity of synapses) but also on non-nervous, extracortical as well as intracortical structures. Thus there does not seem to be a specific relationship between desmosome-like junctions and coated vesicles on the one hand and synapse formation on the other.

The time of origin of Cajal-Retzius cells in the rat temporal cortex. An autoradiographic study.

Rat fetuses received tritiated thymidine on one of each of the following days of gestation: 9, 10, 11, 12, 13, 14 and 16. Animals were sacrificed on day 1 post partum. Perpendicular and tangential sections including temporal cortex were studied by electron microscopy and light microscopic autoradiography. Our results suggest that the formation of Cajal-Retzius cells (CRs) begins on day 12, reaches a peak on day 13, and continues on day 14. Earliest non-CR neurons of the temporal cortex (cells of the deepest stratum of layer VI) appear to be generated on day 13.

Postnatal maturation of the cochlear nuclei in the cat: A neurophysiological study

The study of the postnatal maturation of the ventral cochlear nuclei (VCN) and the dorsal cochlear nuclei (DCN) was carried out on the cat by means of recordings of the extra-cellular neuronal activity. At birth it is already possible to obtain toneburst responses in the VCN and DCN. At this age the responses are characterised by a small number of spikes grouped in three bursts when the tone-bursts lasted 500 msec. Subsequently, the number of bursts increases until, from 9 or 10 days onwards the responses become sustained. These responses do not acquire their adult characteristics until more than a month after birth. During postnatal maturation of the cochlear nuclei, the VCN is distinguishable from the DCN by the greater number of units revealing spontaneous activity. Another criterion, such as latency, differentiates the VCN from the DCN from the point of view of the kinetics of maturation.

Voies et projections vestibulaires ascendantes emanant des noyaux primaires: Etude radioautographique

Abstract A study of the pathways and ascending vestibular projections was carried out in the cat after unilateral injection of tritiated leucine into the rostral vestibular complex. Radioautographic analysis revealed a gradual decline in the density of labeling as ascending fibers were found to progress towards more rostral relays. The pathways and projections were very compact in the oculomotor nuclei, became less intense in the Cajal and Darkschewitsch nuclei, and thinned out considerably until they reached a transitional zone in the thalamus between the ventrobasal and ventrolateral complexes. These results confirm established and previous findings in this laboratory obtained by neurophysiological and neurohistological examination procedures. They provide the first anatomical evidence concerning the existence of vestibulothalamic projections and pathways.

Projections thalamiques des noyaux vestibulaires: Etude histologique chez le chat

SummaryElectrolytic lesions were placed into the left vestibular nuclei of 22 adult cats. Silver impregnation for degenerated terminal fibres of serial sections revealed the existence of a relay of the corticopetal vestibular pathway in the contralateral thalamus. Its main afferent fibres originate in the superior and medial vestibular nuclei. By crosschecking the results it was possible to demarcate a focus of vestibular projections in the ventro-caudal part of the thalamus, situated between the centre median, the ventro-basal group and the caudal segment of the ventro-lateral nucleus. The direct ascending afferents of this focus are relatively few in number. The functional significance of this vestibular relay with regard to the proprioceptive influx passing through this region of the thalamus is open to discussion.

Structural and biochemical changes in rat cerebral cortex after neonatal 6-hydroxydopamine administration

SummaryNewborn rats received an intracisternal injection of 6-hydroxydopamine (100 μg) within 16 h after birth. Treatment effects upon noradrenaline uptake (with or without desmethylimipramine pre-incubation), endogenous noradrenaline, dopamine, and serotonin were biochemically assayed. Noradrenaline uptake and endogenous noradrenaline content were permanently reduced to less than 5% of control values. Reduction of endogenous dopamine content was less marked: at day 60, values were about 40% of controls. Serotonin content remained unaffected.Cell density countings in postnatal day 15 temporal cortex revealed an about 16% reduction in layers II and III of treated animals. These modifications of cortical geometry were discussed with reference to measurements of cortical thickness and ultrastructural observations on postnatal days 2, 5 and 15. Both supranormal involution and growth processes might result from the neurotoxin treatment. Whereas some of the degeneration processes might be due to general cytotoxic effects, this is less likely for the supranormal growth processes.

Radio-autographic study of cell proliferation secondary to Wallerian degeneration in the postnatal rat optic nerve

SummaryIn the course of our study on Wallerian degeneration in the young rat optic nerve after unilateral enucleation, cell proliferation was measured by quantitative radio-autography. Ninety-two newborn rats were separated into four groups which were operated at 2, 5, 8 and 20 days postnatal (key stages) respectively. In each of these groups, the animals were sacrificed after progressive delays ranging from 3 h to 30 days (DPO). They received, 3 h before the sacrifice, an intraperitoneal injection of 2 μCi/g weight of tritiated thymidine. After the radio-autographic procedure, semi-thin sections were examined, and labeled as well as unlabeled cells were counted on the whole cross section of the operated nerve, as well as on the contralateral nerve. In the operated nerve, the four key stages may be separated into two reactive patterns, depending on whether the enucleation is performed before or after the myelination gliosis. The two first key stages (2 and 5 DPN) show leveling down of the curve of their proliferative indices, when compared with the control, whereas the two other key stages (8 and 20 DPN) showed a leveling up of the curve. The comparison of these data with those of previous work (Fulerand and Privat, 1977; Valat et al., 1978) permitted the evaluation of cell death, which is specially evident at the key stage 8 DPN. The proliferative ability of neuroglial cells thus appear no to be closely dependent upon an intrinsic genetic program, but rather to be modulated by epigenetic events. The early absence of the axonic signal induces a decrease of this proliferation, whereas the more or less belated interruption of the same signal induces a reactive gliosis, with a net increase of proliferative indices over the control.

A propos d'un cas d'encéphalopathie cirrhotique alcoolique

SummaryThe neuropathologic study of an alcoholic cirrhotic encephalopathy was made after the fixation of the brain by immersion in a solution specially prepared for the electronic microscopy. The histological technics were used then, the Golgi-Cox method among others, confirmed the classic notions of neuronal rarefaction and of the proliferation of the glia cells, particularly in the cerebral cortex. The Bodian method for its part showed in the remaining cortical neuronic population, the existence of voluminous intracytoplasmic aggregates and the hypertrophy of the dendritic apparatus.

Le nerf optique du chat

54 healthy cats were studied. In almost all cases, two types of degenerative signs could be seen: in the primary optic pathways, but also in the posterior funiculi and the spinalcerebellar tracts, lesions of wide-diameter axons seen by their initial demyelination, accompanied by intense neurogJial reactions, and, on the other hand, a Wallerian degeneration of smaller axons situated in the axial part of the nerve. The percentage of these abnormalities must still be evaluated. Their eventual consequences and nature are discussed.

Réactivité cellulaire postnatale du nerf optique après énucléation chez le rat

The use of an experimental procedure based upon progressive postoperative delays allowed the quantification of the effects of enucleation performed at the ages of 2, 8 and 20 days, corresponding to ke