Interhemispheric connections of ocular-dominance columns in cats with binocular vision impairment

We have investigated the interhemispheric connections of areas 17 and 18 in cats with impaired binocular vision (monocular deprivation, uni- and bilateral strabismus). Monosynaptic neuronal connections were studied using microionophoretic injections of horseradish peroxidase in the single cortical columns and analsys of spatial distribution of retrogradely labelled callosal cells was performed. In the cases of monocular deprivation and strabismus, the spatial asymmetry and eye-specificity of interhemispheric connections are retained. Quantitative changes of connections are more pronounced in strabismic cats. In cats with binocular vision impairments, as well as in control ones, the width of callosal-recipient zone is larger than of the callosal cells zone. This may indicate that interhemispheric connections are non-reciprocal in the areas of cortex that are more distant from the projection of vertical meridian of visual field. We expect that there should be morpho-functional in the cells that are providing connections in opposite directions.     

Cortical neuronal connections and reconstruction of visual space

We investigated distribution of retrograde-labelled cells in cortical areas 17, 18, and the transition zone 17/18 of both hemispheres in cats after microiontophoretic horseradish peroxidase (HRP) injections into the single cortical columns of area 17, 18, 19 or 21a. On the base of clustered pattern of intrinsic labelling, asymmetric location of labelled callosal cells that was associated with the appropriate pattern of labelling in layers A and A1 of lateral geniculate nucleus, we suggest that cortical neuronal connections are eye-specific and may provide for each eye a separate binding of visual hemifields. After HRP injections into columns of area 19 or 21a, the disparate inputs from areas 17, 18 and transition zone 17/18 were revealed. Such connections may provide a local depth information and the selection of stereoscopic surfaces in central sectors of visual space.     

The influence of strabismus and monocular deprivation on the size of callosal cells in cortical areas 17 and 18 of the cat

To reveal the changes in visual cortex structure following impaired early binocular experience, the size (somatic area) of callosal cells in areas 17, 18 ofmonocularly deprived and convergent strabismic cats was measured. Horseradish peroxidase was injected into the single ocular dominance columns of areas 17, 18 and the transition zone 17/18. In both groups of impaired cats the mean size of callosal cells in area 17 was increased in comparison to intact cats. In area 18, the similar difference was found in monocularly deprived cats only. It was shown that the differences in the mean sizes of cells are due to the increase of the number of large cells. In strabismic cats, the portion of large cells (soma > 200 mkm2) in area 17 was 58% and in area 18 was 8%. The relative share of large cells in areas 17 and 18 of monocularly deprived cats was similar (28 and 26 % correspondingly). These data show that early binocular vision impairments may lead to the changes in cytoarchitecture of cortical layers where the interhemispheric connections originate.     

The size of cells providing interhemispheric and intrahemispheric connections in the visual cortex of binocular vision-impaired cats

The size (somatic area) of 658 cells located in layers 2/3 of cortical areas 17, 18 of both hemispheres in intact monocularly deprived and bilateral strabismic cats was measured. These cells were retrogradely labelled after injections of horseradish peroxidase into ocular dominance columns in areas 17, 18. In all groups of cats, the mean somatic area of callosal cells was significantly larger than the mean somatic area of intrahemispheric cells. It was found that the mean somatic area of callosal cells was increased by 26.6% in monocularly deprived cats and by 20.2% in strabismic cats in relation to the mean somatic area of callosal cells in intact cats. In addition, the mean somatic area of intrahemispheric cells in monocularly deprived cats was indistinguishable from the mean somatic area of intrahemispheric cells in strabismic cats and in intact cats. It is concluded that early binocular vision impairments produce enlargement of callosal cells' size in the visual cortex.     

Neuronal connections of ocular dominance columns in the cortex of monocularly deprived cats

We have investigated the developmental changes of intrahemispheric neuronal connections of the areas 17 & 18 ocular dominance columns in monocularly deprived cats. Single cortical columns were microiontophoretically injected with horseradish peroxidase and 3D reconstruction of retrogradely labelled cells' region was done. Ocular dominance of injected columns and their coordinates in the visual field map were determined. In area 17 it was shown that for non-deprived eye the connections of columns that are driven via the crossed pathways were longer than connections of columns driven via uncrossed ones, and in both cases they were longer than connections in intact cats. The connections of deprived eye columns are significantly reduced. We have observed some changes in the spatial organization of long-range connections in area 17 for columns driven by the non-deprived eye (more rounded shape of regions of labeled cells, non-uniform distribution of cells within it). Maximal length of such connections did not exceed the length of connections in strabismic cats. We speculate that the length of cell axons providing for the horizontal connections of cortical columns has some intrinsic limit that does not depend on visual stimulation during the critical period of development.     

Structure of reciprocal connections in visual cortical areas 17 and 18 in cats

Single cortical columns of areas 17, 18 in the cat were microiontophoretically injected with horseradish peroxidase. Spatial and laminar distributions of retrogradell labelled cells in both areas were investigated. Following injections in area 17 or in area 18 the labelled cells' region in area 17 was elongated (in a tangential plane) along the representation of visual field horizontal meridian. However the labelled cells' region in area 18 was elongated along the representation of vertical meridian. Such projection patterns appear to be common in these cortical areas throughout the central 10 degrees on various elevations (from -40 degrees to +10 degrees) of the visual field representation. Thus the spatial arrangement of intrinsic and extrinsic connections in each area coincides, at the same time in area 17 they are orthogonal to area 18. The following visual information exchange scheme may be suggested. Area 17 may supply the area 18 with more detailed information on the horizontal component of the visual image, and in the opposite direction the information on the vertical component of the same image may be supplied.     

The organization of corticocortical projections from area 17 to area 18 of the cat's visual cortex

Retrogradely transported tracers were injected into area 18 of the visual cortex of the adult cat to study the organization of corticocortical projections from area 17 to area 18. All injections, whether very small or relatively large, and irrespective of their exact location in area 18, produced a discontinuous, clustered distribution of labelled cells, mainly in layers II, III and upper IV, in a topographically related region of area 17. The mean centre-centre distance between neighbouring patches was about 750 microns. We conclude that the overall population of cells projecting to area 18 is genuinely distributed in a patchy fashion and that they provide an efficient spatial sample of information from area 17. Comparison of the dimensions of each injection site and of the retrogradely labelled territory suggested that each region in area 18 receives a convergent input from a zone in area 17 whose visual field representation is about 0.8 M-1 deg larger in all directions (where M is the magnification factor in millimetres per degree at the termination site in area 18). Pairs of injection were made in area 18 by placing small volumes of two fluorescent tracers, fast blue and diamidino yellow, side-by-side in either a rostrocaudal or a mediolateral plane, with different distances between them. When the boundaries of the dense central cores of two injection sites were separated, at their closest points, by about 1.6 mm, the two corresponding distributions of labelled cells in area 17 were just non-overlapping, suggesting that each group of cells in area 17 sends a divergent projection in innervate a zone about 0.8 mm larger in all directions in area 18. More closely spaced injections led to overlap of the distributions of labelling by the two dyes, with shared clusters containing a mixture of labelled cells. The proportion of double-labelled cells in these shared clusters never exceeded 4.4% (but was 70% after sequential injection of the two dyes at a single point). We conclude that, although each cluster of cells sends a divergent projection to area 18, the majority of individual axons terminate more discretely, perhaps providing specific inter-connections between functionally corresponding 'columns' in the two areas.     

Organization of the cortico-ponto-cerebellar pathway to the dorsal paraflocculus. An experimental study with anterograde and retrograde transport of WGA-HRP in the cat.

To reveal the organization and relative magnitude of connections from various parts of the cerebral cortex to the dorsal paraflocculus via the pontine nuclei, WGA-HRP was injected in the dorsal paraflocculus in conjunction with injection of the same tracer in various parts of the cerebral cortex in 17 cats. Termination areas of cortical fibres (anterogradely labelled) and pontine neurons projecting to the dorsal paraflocculus (retrogradely labelled) were carefully plotted in serial transverse sections. As an average of countings in ten cats, 90% of the labelled cells were found in the pontine nuclei contralateral to the injection, and the majority (70%) were located in the rostral half of the nuclei. The highest degree of overlap between anterograde and retrograde labelling was found after injections of the parietal association cortex (areas 5 and 7). In an experiment with double anterograde tracing, it was shown that both area 5 and 7 contribute substantially to the cerebral inputs to the dorsal paraflocculus. High degree of overlap also occurred after injections of several visual cortical areas (areas 17, 18, 19, 20 and the posteromedial lateral suprasylvian visual area, PMLS). Cases with injections restricted to individual visual areas indicate that they all contribute to the parafloccular input. Considerably less overlap occurred after injections of the primary sensorimotor region (SI, MI) and second somatosensory area (SII), while the supplementary motor area, the auditory cortex and gyrus cinguli probably have no or very restricted access to the dorsal paraflocculus. It is concluded that the dorsal paraflocculus has its major cortical input from the parietal association cortex and the visual cortical areas. Since all the various cortical regions studied project to largely different parts of the pontine nuclei, and overlap with neurons projecting to the dorsal paraflocculus takes place at numerous places, it follows that the pontine neurons projecting to the dorsal paraflocculus must consist of many subgroups differing with regard to their cortical input.     

Bilateral receptive fields in cortical area SII: contribution of the corpus callosum and other interhemispheric commissures

The corpus callosum contributes to the interhemispheric transfer of somatosensory information. Since the somatosensory pathways are essentially crossed, a number of studies have postulated that the corpus callosum may be responsible for the presence of bilateral receptive fields (RFs) in cortical area SII. Moreover, subcortical structures, as well as some of the other commissures, may also contribute to the bilateral nature of these cells. In order to assess the relative importance of the corpus callosum, this study compared the RF properties of cells in area SII of callosum-sectioned cats to normal cats, using single-cell recordings. Results showed that the corpus callosum makes an important contribution to the bilateral activation of cells in SII, since the proportion of cells with bilateral RFs found in callosum-sectioned cats was less than half that obtained in normal cats. The decrease in the proportion of bilateral RFs was found for all body regions with the exception of the face. However, the substantial number of bilateral RFs remaining in callosotomized cats indicates that this structure is not the sole contributor to the bilateral activation of cells in SII. In order to determine whether this residual bilateral activation might be mediated by the other interhemispheric commissures, a group of cats was subjected, besides the callosotomy, to the additional transection of their subcortical commissures, including the anterior, posterior, habenular, and intertectal commissures, as well as the massa intermedia. When this group of deep-split cats was compared to the callosotomized group, the results indicated that the contribution of the other commissures to bilateral activation is negligible, since approximately the same proportion of bilateral RFs was encountered in the two groups. The relative importance of the callosal contribution to bilateral RFs of different body regions is discussed with respect to the roles commonly attributed to this structure.     

Post-tetanic modification of the efficacy of excitatory transmission in neuronal networks with interhemispheric connections

The modifiable reciprocal transcallosal monosynaptic excitatory connections were for the first time detected in vivo experiments in rat motor cortex using multiunit recording and crosscorrelation analysis, It was shown that high-frequency microstimulation (MCS) of a small group of cortical cells of one hemisphere produces long-term changes in the efficacy of transcallosal excitatory connections, and also ipsilateral connections in both hemispheres. The posttetanic changes appear as long-term potentiation (LTP) and long-term depression (LTD). The bursting neurons were found to have more favorable conditions for the induction of LTP of most converging inputs (in contrast to cells with other discharge patterns). Both LTP and LTD could be simultaneously induced in synapses formed by axon collaterals of a callosal cell on several neurons. LTP and LTD could be simultaneously obtained at diverse synapses of the same cell. The number of spontaneously active callosal neurons as well as the number and efficacy of transcallosal connections increased after the MCS, whereas the number and efficacy of ipsilateral connections decreased. Basing on these data we assume that the ipsilateral inhibition is more effective than the transcallosal inhibition. MCS results in the modification of the pattern of initially existing connections between numerous neurons of an ensemble including cells of both hemispheres.     

冷冻取消胼胝体传递对猫皮层17/18区边界细胞部分电生理特性的影响

用IBM-XT微机控制产生各种取向的可移动正弦光栅作为视觉刺激,用金属微电极在猫皮层一侧17/18区边界附近进行胞外记录,神经信号由微机实时采集并进行数据处理;对11只猫的62个细胞进行了冷冻取消另一侧胼胝体向记录侧传递前后细胞的取向选择性,最佳取向和最大反应的测定与比较.发现冷冻后有至少50%细胞的取向选择性强度发生了变化,其中选择性减少与增加的数目基本相等;有20-30%细胞的最佳取向发产了10°至20°的变化;有一半以上细胞的最大反应发生了变化,其中三分之二细胞的反应减少,其余的增加.通过部分细胞的恢复实验证明以上变化基本是可逆的,说明胼胝体对这些特性有一定影响.     

Microglia and astrocytes may participate in the shaping of visual callosal projections during postnatal development.

In the adult cat, axons running through the corpus callosum interconnect the border between the visual cortical areas 17 and 18 (A17 and A18) of both hemispheres. This specific pattern emerges during postnatal development, under normal viewing conditions (NR), from the elimination of initially exuberant callosal projections. In contrast, if the postnatal visual experience is monocular from birth (MD), juvenile callosal projections are stabilised throughout A17 and A18. The present study aimed at using such a model in vivo to find indications of a contribution of glial cells in the shaping of projections in the developing CNS through interactions with neurones, both in normal and pathological conditions. As a first stage, the distribution and the morphology of microglial cells and astrocytes were investigated from 2 weeks to adulthood. Microglial cells, stained with isolectin-B4, were clustered in the white matter below A17 and A18. Until one month, these clustered cells displayed an ameboid morphology in NR group, while they were more ramified in MD animals. Their phenotype thus depends on the postnatal visual experience, which indicates that microglial cells may interact with axons of visual neurones. It also suggests that they may differentially contribute to the elimination and the stabilisation of juvenile exuberant callosal fibres in NR and MD animals respectively. Beyond one month, microglial cells were very ramified in both experimental groups. Astrocytes were labelled with a GFAP-antibody. The distributions of connexins 43 (Cx43) and 30 (Cx30), the main proteic components of gap junction channels in astrocytes, were also investigated using specific antibodies. Both in NR and MD groups, until 1 month, GFAP-positive astrocytes and Cx43 were mainly localised within the subcortical white matter. Then GFAP, Cx43 and Cx30 stainings progressively appeared within the cortex, throughout A17 and A18 but with a differential laminar expression according to the age. Thus, the distributions of both astrocytes and connexins changed with age; however, the monocular occlusion had no visible effect. This suggests that astrocytes may contribute to the postnatal development of neuronal projections to the primary visual cortex, including visual callosal projections.     

A function of the corpus callosum in the Siamese cat

Recordings were made from 180 single cells, or cell clusters, in the Clare-Bishop area of two Siamese cats. In one cat, the corpus callosum had been sectioned prior to recording and all cells were driven by the contralateral eye exclusively. In the other recordings were made before and after callosal section. Before callosal section, most cells were binocularly driven but dominated by the contralateral eye. There were striking examples of binocular interaction and some cells could only be activated by simultaneous binocular stimulation. After callosal section, cells were driven by the contralateral eye only. The same experiment performed in a normal cat revealed no change in binocularity following section of the corpus callosum. We conclude that one of the functions of the corpus callosum in the Siamese cat is to generate binocular neurons.     

胼胝体输入对猫皮层17/18交界区细胞方向和取向选择性的影响

用抑制性神经递质GABA阻断胼胝体输入、用微机控制的运动光棒作为视觉刺激,用金属电极胞外记录技术,研究猫皮层17/18区交界附近细胞方向选择性和取向选择性的变化.在被检测的48个细胞中,50%细胞的方向选择性强度,54.2%细胞的取向选择性强度发生了改变;约20%细胞的最优反应方向或.及最优取向发生了10-30°的偏移;共有56.2%细胞的方向选择性、58.3%细胞的取向选择性受到明确的影响.这些结果表明胼胝体对皮层细胞视觉反应的贡献是多方面的.     

Laminar distribution of sources of ascending spinocerebral fiber systems in the cat spinal cord

The location of labeled neurons that are sources of ascending crossed and uncrossed supraspinal fiber systems was studied in the laminae of gray matter of the spinal cord in 18 cats by the retrograde axonal transport of horseradish peroxidase method. Neurons in the lateral zones of the dorsal horn were shown to make direct, and cells in neighboring regions indirect (through relay nuclei of the dorsal columns) connections with the contralateral thalamus. In the lower segments of the spinal cord sources of crossed spinoreticular and spinothalamic fiber systems are located in the medial regions of the ventral horn and lateral zones of the lateral basilar region. Some large neurons in the motor nuclei were shown to send their axons into the lateral reticular nucleus of the medulla. On the basis of the results a scheme of the laminar organization of sources of ascending fiber systems in the cat spinal cord is constructed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 451–459, September–October, 1979.     

Bilateral receptive field neurons and callosal connections in the somatosensory cortex

Earlier studies recording single neuronal activity with bilateral receptive fields in the primary somatosensory cortex of monkeys and cats agreed that the bilateral receptive fields were related exclusively to the body midline and that the ipsilateral information reaches the cortex via callosal connections since they are dense in the cortical region representing the midline structures of the body while practically absent in the regions representing the distal extremities. We recently found a substantial number of neurons with bilateral receptive fields on hand digits, shoulders-arms or legs-feet in the caudalmost part (areas 2 and 5) of the postcentral gyrus in awake Japanese monkeys (Macaca fuscata). I review these results, discuss the functional implications of this bilateral representation in the postcentral somatosensory cortex from a behavioural standpoint and give a new interpretation to the midline fusion theory.     

Distribution of parasympathetic motoneurones in the oculomotor complex innervating the ciliary ganglion in the marmoset (Callithrix jacchus)

Parasympathetic motoneurones in the oculomotor complex which innervate the ciliary ganglion were identified using the horseradish peroxidase (HRP) retrograde axonal tracer technique. The ciliary ganglion was located behind the eye by a lateral orbital approach and injected with HRP pellets mounted on the tips of microelectrodes. Most of the labelled cells were distributed throughout the whole Edinger-Westphal nucleus (EW). Outside the EW, only a small number of labelled cells were found, and most of these were located in the median zone ventral to the EW. There was no evidence of a division of the EW into rostral and posterior subnuclei, nor for separate cell populations in the EW and the anterior median nucleus (AM), respectively. At rostral levels labelled cells were confined to the EW with no overlap into the AM. In contrast to most previous studies no labelled cells were found in the AM. The possible physiological functions of the EW and the ventral components of the EW are discussed.     

Effects of serum and glucose on the proliferation of different types of cells of the human embryonic pancreas in primary culture

We have utilized primary cultures of free-floating clusters obtained from pancreata of human cadaveric fetuses. Clusters have been incubated for 10 days in RPMI-1640 medium with 3H-thymidine and various concentrations of fetal calf serum and glucose. Viability of clusters was assessed by insulin radioimmunoassay. Cell reproduction was investigated by radioautography. We have revealed 2 populations of proliferating epithelial cells in clusters: the minor population of cells of duct-like structures and the major population of other epithelial cells. Rate of accumulation of labelled cells in both populations in clusters of 17-18-week-old fetuses was significantly higher than in clusters of 23-24-week-old fetuses. Proliferation of cells of duct-like structures was regulated by serum but not by glucose, whereas proliferation of other epithelial cells depended on both serum and glucose concentrations.     

Elementary transcallosal connections of the rabbit sensomotor cortex]

Antidromic responses of two callosal neurones to a local electrical stimulation of the rabbit sensorimotor cortex may be recorded simultaneously with one microelectrode in the homotopic cortical area. In such recording conditions the relative amplitude of extracellularly recorded action potentials of the two neurones is determined primarily by the distance between these neurones and the electrode's tip. In response to the stimulation of the symmetrical area transcallosal monosynaptic excitation of the callosal neurone may occur; two callosal neurones may exite monosynaptically one and the same recorded neurone. The results suggest the existence of clusters or columns, formed jointly by the bodies and terminals of callosal neurones; a functional interconnection between symmetrical clusters or columns may exist, in particular a positive feedback.