Pierre Buisseret

Receptive field characteristics and plastic properties of visual cortical cells in kittens reared with or without visual experience

SummaryThe functional organization of visual cortical cells was studied in two groups of five week old kittens: one group normally reared, the other reared in total darkness from the third day after birth. The following results were obtained:1.The cells of the normally reared kittens were similar to adult cells except for some aspects of immaturity. In contrast, the cells of the dark-reared kittens were totally non-specific. Their receptive field showed neither orientational nor directional properties.2.The distribution of cells according to the ocular dominance was not different in either group and was similar to that previously described for ‘adult’ cells.3.A few hours of visual experience was sufficient to provide specific receptive field properties to the cortical cells of a dark-reared kitten.4.Conditioning exposure with an oriented grating induced changes in orientational sensitivity in normally reared kittens but not in dark-reared kittens.

The Sensitive Period for Strabismic Amblyopia in Humans

PURPOSE In order to assess the sensitive period for strabismic amblyopia, the period of susceptibility to monocular occlusion was investigated in 407 children who ranged in age from 21 months to 12 years. METHODS Patients were treated between 1975 and 1990 by occlusion of the best eye. The efficiency of the treatment was measured as the ratio of reduction of the amblyopia at the end of the occlusion. RESULTS The efficiency of the occlusion is shown to depend on the age of the onset of the treatment: recovery of acuity of the amblyopic eye was maximum when the occlusion was initiated before 3 years of age, decreased as a function of age and was about null by the time the patient was 12 years of age. CONCLUSION This is assumed to be an indication of the sensitive period for strabismic amblyopia in humans. The results are discussed on the basis of the neurophysiological mechanisms of amblyopia established in animals.

Trigeminal Projections to Hypoglossal and Facial Motor Nuclei in the Rat

This study was undertaken to identify the trigeminal nuclear regions connected to the hypoglossal (XII) and facial (VII) motor nuclei in rats. Anterogradely transported tracers (biotinylated dextran amine, biocytin) were injected into the various subdivisions of the sensory trigeminal complex, and labeled fibers and terminals were searched for in the XII and VII. In a second series of experiments, injections of retrogradely transported tracers (biotinylated dextran amine, gold‐horseradish peroxidase complex, fluoro‐red, fluoro‐green) were made into the XII and the VII, and labeled cells were searched for in the principal sensory trigeminal nucleus, and in the pars oralis, interpolaris, and caudalis of the spinal trigeminal nucleus. Trigeminohypoglossal projections were distributed throughout the ventral and dorsal region of the XII. Neurons projecting to the XII were found in all subdivisions of the sensory trigeminal complex with the greatest concentration in the dorsal part of each spinal subnucleus and exclusively in the dorsal part of the principal nucleus. Trigeminofacial projections reached all subdivisions of the VII, with a gradual decreasing density from lateral to medial cell groups. They mainly originated from the ventral part of the principal nucleus. In the spinal nucleus, most of the neurons projecting to the VII were in the dorsal part of the nucleus, but some were also found in its central and ventral parts. By using retrograde double labeling after injections of different tracers in the XII and VII on the same side, we examined whether neurons in the trigeminal complex project to both motor nuclei. These experiments demonstrate that in the spinal trigeminal nucleus, neurons located in the pars caudalis and pars interpolaris project by axon collaterals to XII and VII. J. Comp. Neurol. 415:91–104, 1999.

Trigemino‐reticulo‐facial and trigemino‐reticulo‐hypoglossal pathways in the rat

This study was undertaken to identify premotor neurons in the pontomedullary reticular formation serving as relay neurons between the sensory trigeminal complex and the motor nuclei of the VIIth and XIIth nerves. Trigeminoreticular projections were first investigated after injections of anterogradely transported tracers (biotinylated dextran amine, biocytin) into single subdivisions of the sensory trigeminal complex. The results show that the trigeminoreticular projections were abundant from the pars interpolaris (5i) and caudalis (5c) and moderate from pars oralis (5o) of the spinal trigeminal nucleus. Injections into the 5i and 5c produce dense anterograde labeling (1) in the dorsal medullary reticular field; (2) in the parvocellular reticular field, medially adjacent to the 5i; and (3) more rostral in the region dorsal and lateral to the superior olivary nucleus. Some labeled terminals were also found in the intermediate reticular field, whereas only light anterograde labeling was observed in the gigantocellular and oral pontine reticular formation. The 5o sends fibers and terminals throughout the whole reticular formation, with no clear preferential projections within a particular field. Only light projections originated from the principal nucleus (5P). In a second series of experiments, we examined whether premotor neurons in the reticular formation are afferented by trigeminal fibers. Double labeling was performed by injection of an anterograde tracer in the 5i and 5c and retrograde tracer (gold–horseradish peroxidase complex) into the VII or the XII motor nucleus on the same side. Retrogradely labeled neurons in contact with anterogradely labeled boutons were found throughout the reticular formation with predominance in the parvocellular and intermediate reticular fields. These experiments demonstrate the existence of trigeminal disynaptic influences, via reticular neurons of the pontomedullary reticular formation, in the control of orofacial motor behaviors. J. Comp. Neurol. 429:80–93, 2001.

TRIGEMINOCEREBELLAR AND TRIGEMINO-OLIVARY PROJECTIONS IN RATS

Retrograde and anterograde neuronal tracers (HRP, biocytin, biotinylated dextran-amine) were used to study the organisation of trigeminocerebellar and trigemino-olivary connections, focusing on the connectivity between trigeminal nuclear regions and the sagittal zones of the rat cerebellar cortex. Trigeminocerebellar projections were bilateral, but mostly ipsilateral. Direct trigeminocerebellar fibres originated mostly in the principal trigeminal nucleus (VP) and pars oralis (Vo), pars interpolaris (Vi), and to a lesser extent in pars caudalis (Vc) of the spinal trigeminal nucleus. Consistent projections were found from the Vc to cerebellar lobules IX and X. The trigeminal fibres terminated in the cerebellum in an organised fashion. The ventral part of the VP, Vo and Vi projected to the medial A zone and the C3 and D2 subzones, whereas the dorsal part of the nuclei projected to the lateral A zone and the C2, D0 and D1 subzones. In lobules IX and X, the organisation was different. The medial half of the VP, Vo, Vi and Vc projected to the lateral aspects of these lobules whereas their lateral part projected to their medial aspects. Trigeminal projections to the deep cerebellar nuclei were also present. Projections to a given sagittal zone concomitantly reached its corresponding nuclear target. Trigemino-olivary projections were principally contralateral. The Vo, Vi and Vc projected to the rostromedial dorsal accessory olive, the adjacent dorsal leaf and the dorsomedial part of the ventral leaf of the principal olive, which are known to project subzones C3, D0 and D1 of the rat cerebellar cortex.

Central projections of extraocular muscle afferents in cat

The extraocular muscles (EOMs) of adult cats were injected with wheat germ agglutinin-horseradish peroxidase (WGA-HRP). In addition to motoneurons, labelled cells corresponding to the sensory receptors were found in both the Gasser ganglion and the mesencephalic trigeminal nucleus. Central transganglionic terminals were observed in the pars interpolaris and caudalis of the spinal trigeminal nucleus, in the paratrigeminal nucleus, and in the dorsal horn of the cervical spinal cord. Double labelling experiments were carried out with either Fast blue or Complex gold tracer, injected in the EOM, and either Diamidino yellow or HRP tracer injected in the cervical dorsal horn. Some Gasser ganglion neurons were found to contain both tracers, providing evidence that the transganglionic terminals are localized in the cervical segments of the spinal cord.

Plasticity in the kitten's visual cortex: effects of the suppression of visual experience upon the orientational properties of visual cortical cells.

The orientation selectivity of visual cortical cells was tested in two groups of kittens. In one group the animals were reared normally for the first 4-6 weeks of life then kept in darkness. Those in the other group were dark-reared for the first 6 weeks then exposed to light for 6 h and returned to the dark. The properties of the receptive fields of visual cortical cells were examined in these kittens after periods of dark-rearing ranging from 3 days to 12 weeks. In both groups, the proportion of orientation selective cells was found to decrease with time spent in the dark. The critical period for orientation appeared to end at 10-12 weeks of age. Two populations of visual cells were distinguished functionally by their different behaviour during prolonged dark-rearing. Most of the cells which retained their orientation specificity longest during dark-rearing were tuned to horizontal or vertical orientations and more of them were monocular than in normal kittens. These functional characteristics resemble those exhibited by neurons of very young kittens. Changes in specificity observed during loss of selectivity are compared to those observed during early development. We suggest that the extent to which the orientation selectivity of a cell is plastic depends very largely upon the time, during the course of development, at which its selectivity was acquired.

Primary trigeminal afferents to the vestibular nuclei in the rat: existence of a collateral projection to the vestibulo-cerebellum.

Projections from the mesencephalic trigeminal nucleus to the vestibular nuclei were analyzed using retrograde and anterograde tracing methods. The results show that neurons in the caudal part of the trigeminal mesencephalic nucleus project mainly to the medial, inferior and lateral vestibular nuclei and moderately to the peripheral part of the superior vestibular nucleus. Using the double-labeling technique we demonstrate that individual neurons of the mesencephalic nucleus send collaterals to the vestibular nuclei and the vestibulo-cerebellum. These results suggest that these anatomical connections are involved in mechanisms of eye-head coordination.

Development of visual cortical orientation specificity after dark-rearing: role of extraocular proprioception.

Six-week-old dark reared kittens exposed to light for 6 h: (1) with head and body tightly cast into plaster; or (2) free to move around in the animal room. A few days before the visual experience, the ophthalmic branch of the 5th nerve was severed bilaterally in experimental kittens, in order to suppress most of the proprioceptive afferents from extraocular muscles. Electrophysiological analysis of the properties of the receptive fields of visual cortical cells shows that only 6% (group 1) and 11% (group 2) of the cells were selective to orientation as opposed to 67% (group 1) or 32% (group 2) observed in the non-operated kittens.

Trigeminovestibular and trigeminospinal pathways in rats: Retrograde tracing compared with glutamic acid decarboxylase and glutamate immunohistochemistry

This study identified neurons in the sensory trigeminal complex with connections to the medial (MVN), inferior (IVN), lateral (LVN), and superior (SVN) vestibular nuclei or the spinal cord. Trigeminovestibular and trigeminospinal neurons were localized by injection of retrograde tracers. Immunohistochemical processing revealed γ‐aminobutyric acid (GABA)‐ and glutamate‐containing neurons in these two populations. Trigeminovestibular neurons projecting to the MVN and the IVN were in the caudal principal nucleus (5P), pars oralis (5o), interpolaris (5i), and caudalis (5c) and scattered throughout the rostral 5P. Projections were bilateral to the IVN, with an ipsilateral dominance to the MVN, except from the rostral 5P, which was contralateral. Neurons projecting to the LVN were numerous in the ventral caudal 5P and the 5o and less abundant in the rostral 5P, 5i, and 5c. Our results suggested that only 5P and 5o project to the dorsal LVN. Neurons projecting to the SVN were in the dorsal 5P, 5o, and 5i but not in 5c. Trigeminospinal neurons were mainly in the ventral 5o and 5i and in the lateral 5c, rarely or never in 5P. Among trigeminovestibular neurons, most of the somas were immunoreactive for glutamate, but some reacted for GABA. Among trigeminospinal neurons, the number of somas immunoreactive for each of the two amino acids was similar. Trigeminal terminals were observed in contact with vestibulospinal neurons in the IVN and LVN, giving evidence of a trigeminovestibulospinal pathway. Therefore, inhibitory and excitatory facial inputs may contribute through trigeminospinal or trigeminovestibulospinal pathways to the control of head/neck movements. J. Comp. Neurol. 496:759–772, 2006.