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C Dehay

Publications and source records attributed to C Dehay.

At least 19 recordsLinked to original sources
PubMed1992

Synaptic connections of physiologically identified geniculocortical axons in kitten cortical area 17.

Single geniculocortical axons were recorded in the cortical white matter of kittens and adult cats by using micropipettes filled with horseradish peroxidase (HRP). Of 41 axons recovered in 4-5 week old kittens, three well-filled axons arborized in area 17; the remainder were incomplete or arborized in area 18. One axon had Y-like physiological properties, two were X-like. They were recovered from two 34-day-old kittens. All three axons formed clustered arborizations, mainly in layer 4A. Electron microscopic (EM) analysis of 50 boutons from kitten and 38 boutons from adult controls revealed that the boutons from kitten made synapses more frequently on spines (91% of targets) than did the boutons from the adult (71%). One X-like axon in kitten also had a collateral projection that made synapses in layer 1; this has not been seen in adult cats. In overall extent, the axons from kitten fell within the adult range.

Aging↗
PubMed1991

The effects of bilateral enucleation in the primate fetus on the parcellation of visual cortex.

Bilateral enucleation in the macaque fetus causes an areal reduction of an otherwise normal striate cortex. Here we show that in early operated animals this reduction is accompanied by a separation of striate and prostriate cortices which are normally contiguous. However this induced separation does not correspond to the areal reduction of striate cortex, indicating that extrinsic signals regulate either the proliferation and/or survival of striate cortical neurons.

Animals↗
PubMed1991

Excitation by geniculocortical synapses is not 'vetoed' at the level of dendritic spines in cat visual cortex.

1. We used anatomical methods to examine whether the geniculocortical afferent input to dendritic spines could be gated or 'vetoed' by an inhibitory input to the same spine. 2. Physiologically identified X- and Y-type afferents were injected intra-axonally with horseradish peroxidase (HRP), processed, and drawn under the light microscope. Selected regions of the terminal arbors were then serially sectioned for examination under the electron microscope. 3. Three-dimensional reconstructions of thirty-nine HRP-filled terminal boutons forming fifty asymmetric (type 1) synapses showed that thirty-one synapses were on the heads of dendritic spines. Only two of thirty-one spine heads received an additional symmetric (type 2) synapse, which is presumed to be inhibitory. 4. Examination of twenty-three boutons from two clutch cells (a GABA (gamma-aminobutyric acid)-ergic smooth cell) that form symmetric (type 2) synapses on spines indicated that their preferred location was opposite the asymmetric synapse on the head of the spine. Synaptic input to the necks of spines appears rare. 5. We conclude that most of the excitation provided by the geniculocortical afferent input to the heads of spines cannot be gated or vetoed by inhibition at the level of the spine.

Animals↗
PubMed1991

Segregation of callosal and association pathways during development in the visual cortex of the primate.

The segregation of callosal and association pathways in the developing visual cortex of the monkey was studied using the retrograde tracers fast blue and diamidino yellow. Quantitative analysis of the laminar distribution of labeled callosal and association neurons made it possible to reveal the shifting pattern of connections that characterizes the development of these two pathways. In the adult, callosal neurons are restricted to supragranular layers, where they are concentrated at the bottom of layer 3. Association neurons are located both in infra- and supragranular layers. Supragranular layer association neurons are concentrated in layer 2, with limited spread into layer 3 so that there is little overlap with callosal neurons. In the immature brain, callosal neurons are characterized by a tangential distribution that is more widespread than in the adult, while their laminar distribution undergoes little developmental change. Association neurons show two types of changes in their laminar distribution: (1) in the early fetus, there is a large excess of association neurons in supragranular layers, the adult distribution being achieved some time after birth; and (2) during maturation there is a selective elimination of at least 50% of the projections originating from the lower part of layers 2/3. Hence, the adult radial segregation of association and callosal pathways is achieved in part by regressive phenomena. The developmental reduction of bihemispheric projections is largely independent of changes in the organization of association neurons. Quantitative analysis of the morphology and spatial location of neurons sending axon collaterals to both hemispheres suggests that they constitute a subset of callosal neurons and that their frequency is determined by factors that regulate directly this population. These results are discussed with respect to the specification of visual cortical pathways during ontogenesis.

Amidines↗
PubMed1990

Incidence of visual cortical neurons which have axon collaterals projecting to both cerebral hemispheres during prenatal primate development.

Fast blue was injected massively in extrastriate cortex of one hemisphere Diamidino yellow in area 17 of the other hemisphere, in adult and prenatal cynomolgus monkeys. After a suitable survival period the brains were processed for fluorescent dyes. Counts were made of the total number of labeled neurons and of those neurons which were labeled by both dyes and which project therefore to both hemispheres by means of bifurcating axon collaterals. At 122 and 135 days after conception (E122 and E135), shortly after cortico-cortical pathways are established, double-labeled neurons constituted 0.45% and 0.46% of the total population of labeled neurons in area V2. In V2 in the adult the range of values of double-labeled neurons was 0.03-0.08%.

Animals↗
PubMed1989

Maturation and connectivity of the visual cortex in monkey is altered by prenatal removal of retinal input.

In several species, the peripheral input from the eyes partly determines the pattern of interconnections between the visual areas of the two cerebral hemispheres through the fibre tract termed the corpus callosum. In the macaque monkey, the neurons projecting through the callosum are largely restricted to area 18 throughout ontogeny, whereas area 17 is characterized by few or no callosal projections. Here, we show that suppressing the peripheral input by prenatal removal of the eyes leads to a marked reduction in the extent of area 17, resulting in a large shift in the position of the histologically identifiable boundary between the two areas. Even so, the boundary continues to separate an area rich with callosal connections (area 18) from one poor in such projections (area 17), indicating there is no effect on the callosal connectivity of area 17. In contrast, in area 18, eye removal results in many more neurons with callosal projections than in normal animals. The results suggest that the factors that determine the parcellation of cortical areas also specify their connectivity.

Animals↗
PubMed1989

Transient projection from the superior temporal sulcus to area 17 in the newborn macaque monkey.

Area 17 in the neonate of numerous species receives projections from cortical areas that do not project to area 17 in the adult. To investigate if this were the case in the developing primate, we have made injections of retrograde tracers in area 17 of newborn monkeys (Macaca irus) and examined the areal distribution of labeled neurons. Neurons projecting to area 17 were found to be restricted to those cortical regions that project to area 17 in the adult. The projection to area 17 in the neonate did appear to be very different in that in the superior temporal sulcus there was a large contingent of labeled neurons in supragranular layers. This constitutes a transient projection because in the adult area 17 projecting neurons in this cortical region originate almost exclusively from infragranular layers. To test if a change in the laminar distribution of area 17 projecting neurons in extrastriate cortex is a general feature of postnatal development, we have computed in neonates and adults the proportion of area 17 afferent neurons in infra- and supragranular layers for each cortical region that projects to area 17. This revealed (i) that in the adult the laminar distribution of area 17 afferents is characteristic for each cortical area and (ii) that this distribution emerges during development from an immature state in which labeled neurons are more numerous in supragranular layers. These results show that there is an extensive remodeling of the neuronal circuitry connecting visual cortical areas during postnatal development in the monkey and that the transient connectivity of primate area 17 is very different from that observed in other mammalian species.

Aging↗
PubMed1988

Characterization of transient cortical projections from auditory, somatosensory, and motor cortices to visual areas 17, 18, and 19 in the kitten.

We have examined the anatomical features of ipsilateral transient cortical projections to areas 17, 18, and 19 in the kitten with the use of axonal tracers Fast Blue and WGA-HRP. Injections of tracers in any of the three primary visual areas led to retrograde labeling in frontal, parietal, and temporal cortices. Retrogradely labeled cells were not randomly distributed, but instead occurred preferentially at certain loci. The pattern of retrograde labeling was not influenced by the area injected. The main locus of transiently projecting neurons was an isolated region in the ectosylvian gyrus, probably corresponding to auditory area A1. Other groups of transiently projecting neurons had more variable locations in the frontoparietal cortex. The laminar distribution of neurons sending a transient projection to the visual cortex is characteristic and different from that of parent neurons of other cortical pathways at the same age. In the frontoparietal cortex, transiently projecting neurons were located mainly in layer 1 and the upper part of layers 2 and 3. In the ectosylvian gyrus, nearly all the neurons are located in layers 2 and 3. In addition, a few transiently projecting neurons are found in layer 6 and in the white matter. Transiently projecting neurons have a pyramidal morphology except for the occasional spindle-shaped cell of layer 1 and multipolar cells observed in the white matter. Anterograde studies were used to investigate the location of transient fibers in the visual cortex. Injections of WGA-HRP at the site of origin of transient projections gave rise to few retrogradely labeled cells in areas 17, 18, and 19, demonstrating that transient projections to these areas are not reciprocal. Although labeled axons were found over a wide area of the posterior cortex, they were more numerous over certain regions, including areas 17, 18, and 19, and absent from other more lateral cortical regions. Transient projecting fibers were present in all cortical layers at birth. Plotting the location of transient fibers in numerous sections and at all ages showed that these fibers are not more plentiful in the white matter than they are in the gray matter. We found no evidence that the white/gray matter border constituted a physical barrier to the growth of transient axons. Comparison of the organization of this transient pathway to that of other transient connections is discussed with respect to the development of the cortex.

Aging↗
PubMed1988

Absence of interhemispheric connections of area 17 during development in the monkey.

Our understanding of the development of cortical connectivity largely stems from studies of the ontogeny of interhemispheric pathways in carnivores, rodents and lagomorphs. Early in development, cortical neurons projecting to the contralateral hemisphere through the corpus callosum (callosal projection neurons) have a widespread distribution. As maturation proceeds, callosal projection neurons become restricted to those cortical regions that are connected in the adult. In newborn cats and rats, for example, callosal projection neurons are not restricted to the 17-18 border as in the adult, but are found throughout areas 17 and 18. The macaque monkey is an exception, because at birth it has an adult-like distribution of callosal projection neurons in area 18, with practically none in area 17. Here we show that whereas area 17 is devoid of interhemispheric connections throughout prenatal development, the distribution of callosal projection neurons in area 18 shows the common sequence of an early widespread distribution followed by regression. The absence of callosal projection neurons in area 17 throughout ontogeny may well be a feature unique to Old World primates.

Animals↗
PubMed1988

Functional implications of the anatomical organization of the callosal projections of visual areas V1 and V2 in the macaque monkey.

The efferent and afferent connections of the V1/V2 border with the contralateral hemisphere have been examined using anatomical tracers. The V1/V2 border was found to exchange connections with the contralateral V2 area as well as a restricted strip of V1 lying adjacent to the V1/V2 border. Besides these homotopic projections, two heterotopic projections were found to V3/V3A and V5. Anterograde tracing of callosal connections showed that terminals in these heterotopic sites were focused in layer 4, the recipient layer of projections originating from the ipsilateral V1/V2 border. Bilateral injections of fluorescent dyes showed that these heterotopic targets of the V1/V2 border are connected to the homologous ipsilateral V1/V2 border region. The laminar location of callosal projecting neurons as well as their terminals were characteristic for each cortical region. The laminar pattern of callosal connectivity was found to differ markedly from that of associational visual pathways. Two principal hypotheses are suggested by these results. First, the fact that V1 in part is reciprocally callosally connected in all mammals supports the notion that this interhemispheric pathway completes long-range intrinsic cortical connections. Second, the convergence of inter- and intrahemispheric pathways could provide the anatomical basis for the modulation of the sensory processing within one hemisphere by ongoing activity in the contralateral hemisphere.

Animals↗
PubMed1988

The maturational status of thalamocortical and callosal connections of visual areas V1 and V2 in the newborn monkey.

Cytochrome oxidase (CytOx) is known to preferentially stain those regions of the visual cortex which receive direct projections from the thalamus. The pattern of CytOx stain has been used to investigate the maturation of thalamic input to areas V1 and V2 in the newborn monkey. In both areas, the intensity of CytOx activity was similar in newborns and adults. The distribution of CytOx in area V2 was not found to vary with age. In area V1, the only difference in CytOx activity in newborns was a relative immaturity of staining in layer 4C. The callosal connections of visual areas V1 and V2 were investigated by the axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase and free horseradish peroxidase. In the adult, V1 was found to be reciprocally callosally connected for a distance of 1-2.5 mm from the V1/V2 border, whilst V2 was connected for a distance of 3-8 mm from the border. In both areas, callosal connections showed a certain degree of clustering, particularly in V2 which contained 97-98% of the total number of callosal connections of these two areas. In the newborn, the number, tangential extent and clustered distribution of callosal connections were as in the adult. In the newborn, as in the adult, callosal connections coincided with regions of high CytOx activity in area V2. The results showing a relative maturity of the tangential distribution of callosal projecting neurons on the one hand, and an immaturity of thalamic projections on the other, are discussed in terms of: (1) the maturational status of the newborn monkey compared to other mammals at the moment of birth and (2) the possible role of visual experience in shaping cortical connections.

Aging↗
PubMed1988

Study of HLA antigens in a population of Mali (West Africa).

Eighty-two healthy individuals have been typed for HLA-A, B, C, antigens, and 49 of them also for HLA DR alleles. They were a sample representative of 11 of the 14 Malian ethnic groups living in the area of Bamako (Mali). Phenotypic frequencies have been compared to those of other Negroid and Caucasoid reference populations. As expected, in Negroids the increased frequency of HLA A23, A28, A30, and ATh was confirmed in the present series. Additionally, a significantly increased frequency of HLA B5 (B51 and Bw52) was noted--already observed in some but not all Negroid populations. Conversely, a decreased frequency--compared with that usually found in Negroid population--was observed for the alleles Bw42, Bw58, Cw6, and DRw6. Our results underline the originality of the Malian population among Western Africans.

Black People↗
PubMed1987

HLA and non-HLA phenotyping and genotyping in Austral and Gambier Polynesian Archipelagos.

Forty-one individuals from Rurutu Island (Austral Archipelagos) and 41 individuals from the Gambier Archipelagos have been typed for HLA; for blood groups ABO, Rh, MNSs, P, Kell, Kp, Lewis, Lutheran, Kidd; for the electrophoretic systems G6PD, 6-PGD, PGM1, PGM2, AcP, ADA, GPT, Est-D, GLO I, and for the immunoglobulin allotypes Gm and Km. There is a high degree of homogeneity among these Polynesian populations and among other Polynesian populations previously typed. However, small differences exist between the populations of the two archipelagos, possibly due to endogamy or to the smallness of the samples studied. A variant of HLA-Bw22 (called Bw22x) is described.

Blood Group Antigens↗
PubMed1986

Callosal connectivity of areas V1 and V2 in the newborn monkey.

The callosal connectivity of areas V1 and V2 in the newborn monkey has been investigated with the neuroanatomical tracers wheat germ agglutinin conjugated to horseradish peroxidase and free horseradish peroxidase. In the adult, callosal projecting neurons in cortex subserving the lower parafoveal visual field were found to extend from the V1/V2 border for a distance of 1-2.5 mm into V1 and 8 mm into V2. In the newborn, the tangential extent and total number of callosal projecting neurons were the same as in the adult. Within area V1, callosal projecting neurons in the adult and newborn were limited to supragranular layers. In the adult, axon terminals of callosal projections were located in layers 4B and 5 and were excluded from layer 4C. In the newborn, axon terminals were more extensively distributed than in the adult and invaded layer 4C. In area V2, the laminar distribution and the patchy location of callosal connections in regions of high cytochrome oxidase activity were similar in the newborn and adult animals. In both newborns and adults, the patchy distribution of callosal projections persisted when the neuroanatomical tracers were injected over extensive regions of the contralateral striate and extrastriate cortex. In the adult, area V1 and V2 project contralaterally to two heterotopic sites located in the fundus of the lunate sulcus and the superior temporal sulcus. This was also found to be the case in the newborn. In the adult the terminals of these heterotopic projections were focused in layer 4. This was not the case in the newborn, where after injection limited to the contralateral V1/V2 border they were more evenly distributed among the different cortical layers. Following extensive contralateral injection of tracer, terminals in cortex anterior to V2 were focused over layer 5 and the bottom of layer 4.

Animals↗
PubMed1986

Organization of the callosal connections of visual areas V1 and V2 in the macaque monkey.

The interhemispheric efferent and afferent connections of the V1/V2 border have been examined in the adult macaque monkey with the tracers horseradish peroxidase and horseradish peroxidase conjugated to wheat germ agglutinin. The V1/V2 border was found to have reciprocal connections with the contralateral visual area V1, as well as with three other cortical sites situated in the posterior bank of the lunate sulcus, the anterior bank of the lunate sulcus, and the posterior bank of the superior temporal sulcus. Within V1, callosal projecting cells were found mainly in layer 4B with a few cells in layer 3. Anterograde labeled terminals were restricted to layers 2, 3, 4B, and 5. In extrastriate cortex, retrograde labeled cells were in layers 2 and 3 and only very rarely in infragranular layers. In the posterior bank of the lunate sulcus, labeled terminals were scattered throughout all cortical layers except layers 1 and 4. In the anterior bank of the lunate sulcus and in the superior temporal sulcus, anterograde labeled terminals were largely focused in layer 4. Callosal connections in all contralateral regions were organized in a columnar fashion. Columnar organization of callosal connections was more apparent for anterograde labeled terminals than for retrograde labeled neurons. In the posterior bank of the lunate sulcus, columns of callosal connections were superimposed on regions of high cytochrome activity. The tangential extent of callosal connections in V1 and V2 was found to be influenced by eccentricity in the visual field. Callosal connections were denser in the region of V1 subserving foveal visual field than in cortex representing the periphery. In V1 subserving the fovea, callosal connections extended up to 2 mm from the V1/V2 border and only up to 1 mm in more peripheral located cortex. In area V2 subserving the fovea, cortical connections extended up to 8 mm from the V1/V2 border and only up to 3 mm in peripheral cortex.

Animals↗
PubMed1985

Cytochrome oxidase activity in the striate cortex and lateral geniculate nucleus of the newborn and adult macaque monkey.

The laminar location of cytochrome oxidase staining has been compared in the lateral geniculate nucleus and area 17 in newborn and adult macaque monkeys. In area 17 of the adult, the distribution of cytochrome oxidase activity confirmed published findings. In the newborn animals, the tissue reacted as strongly for cytochrome oxidase as in the adult but the pattern of labelling was different in two respects. Firstly in layer 1 activity was stronger and occupied a wider portion of this layer. Secondly, cytochrome oxidase staining in layer 4C occupied two separate bands, a small narrow band at the bottom of 4C beta and a wider one occupying the full width of 4C alpha and spilling over into 4B. The pattern of cytochrome oxidase activity did not appear to be influenced by eccentricity in the newborn whereas, in the adult, label in 4C was more intense in cortex subserving central vision. In the lateral geniculate nucleus of the adult, the magnocellular layers and the most dorsal parvocellular layer reacted most strongly for cytochrome oxidase. In the newborn, parvocellular layers were more uniformly labelled and the difference between parvo- and magnocellular layers more pronounced. These results are discussed in relationship to the development of thalamo-cortical projections in the monkey.

Animals↗
PubMed1979

Seventh allele of the HLA-C series (Cve).

Serum VE reacting with 29.8% of French individuals seemed to define the seventh allele of the HLA-C series as shown by serologic and genetic investigations. The gene frequency of Cve is 0.163.

Alleles↗