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PubMed1988

Dendritic morphology and axon collaterals of corticotectal, corticopontine, and callosal neurons in layer V of primary visual cortex of the hooded rat.

Recent evidence indicates that corticotectal neurons belong to only one of the three morphological classes of pyramidal cells in layer V. The present study compares the dendritic morphology and axon collaterals of corticotectal, corticopontine, and layer V callosal neurons by using techniques based on the retrograde transport of horseradish peroxidase and fluorescent dyes as well as in vitro intracellular dye injections. Our results indicate that corticotectal and corticopontine neurons are located predominantly in the upper middle part of layer V. These neurons have medium to large somas with 5 or 6 primary basal dendrites and a single apical dendrite ascending to layer I. Approximately 60% of these cells send axon collaterals to both the superior colliculus and the pons. In contrast, callosal neurons form a heterogeneous group. In general, they have small pyramidal or ovoid cell bodies which give rise to 3 or 4 primary basal dendrites. Many cells have an apical dendrite that bifurcates and terminates in layer V or IV. We find that callosal neurons do not send an axon collateral to either the superior colliculus or the pons. We conclude that the corticotectal and corticopontine systems are similar in their intralaminar distribution, dendritic morphology, and pattern of axon collaterals, whereas the callosal system differs in these characteristics.

Animals↗
PubMed1975

The origin of efferent pathways from the primary visual cortex, area 17, of the macaque monkey as shown by retrograde transport of horseradish peroxidase.

The retrograde transport of horseradish peroxidase has been used to identify efferent cells in area 17 of the macaque. Cells projecting to the lateral geniculate nucleus are small to medium sized pyramidal neurons with somata in lamina 6 and the adjacent white matter. The projection to the parvocellular division arises preferentially from the upper half of lamina 6, while that to the magnocellular division arises preferentially from the lower part of the lamina. The projection to both superior colliculus and inferior pulvinar arises from all sizes of pyramidal neurons lying in lamina 58 (Lund and Boothe, '75); at least pyramidal neurons of lamina 5B send collateral axon branches to both destinations. Injections with extensive spread of horseradish peroxidase show that many cells of lamina 4B and the large pyramidal neurons of upper lamina 6 also project extrinsically but their terminal sites have not been identified. Other studies have indicated that cells of laminae 2 and 3 project to areas 18 and 19. Therefore every lamina of the visual cortex, with the exception of those receiving a direct thalamic input, contains cells projecting extrinsically. Further, each lamina projects to a different destination and from Golgi studies can be shown to contain cells with specific patterns of dendritic branching which relate to the distribution of thalamic afferents and to the patterns of intracortical connections. These findings emphasise the significance of the horizontal organisation of the cortex with relation to the flow of information through it and contrast with the current concept of columnar organisation shown in physiological studies.

Animals↗
PubMed1985

Anatomical organization of primary visual cortex (area 17) in the ferret.

The present report describes the intrinsic and extrinsic cortical connectivity of striate cortex (area 17) in the ferret. Injections of horseradish peroxidase demonstrate periodic intrinsic connections over an extent of 2.5-3.0 mm, mainly in the supragranular layers but also occurring secondarily in layer 5. These connections have a stripelike configuration, with a center-to-center spacing of 0.5-0.7 mm. Their laminar distribution and stripelike configuration resemble the pattern in the cat (Gilbert and Wiesel, '83), another member of the carnivore family, but not that in monkeys. In both macaque and squirrel monkeys, these connections have a bilaminar distribution in layers 2-3 and 4B, and a more complicated latticelike geometry (Rockland and Lund, '83). Their interperiod spacing, of about 0.5 mm, however, is relatively constant across species. Extrinsic connections in the ferret link striate cortex with territories probably homologous to feline areas 18 and 19, and to the suprasylvian region. Callosal connections extend on the lateral surface about 1.5 mm into area 17 and 4.0 mm into area 18 beyond their common border. There are homotopical connections between striate cortices and heterotopical connections from at least areas 18 and 19 to contralateral area 17. In addition to gray matter connections, intracortical injections also result in labeled interstitial neurons in the subgriseal white matter. These occur both subjacent to an injection site in area 17, and below labeled foci in area 18 projecting back to area 17, as if interstitial neurons shared the connectivity of overlying layer 6.

Animals↗
PubMed1987

Quantitative analysis of the choline acetyltransferase-immunoreactive axonal network in the cat primary visual cortex: I. Adult cats.

The laminar distribution of cholinergic axons was analyzed quantitatively in the visual cortex of adult cats by using immunocytochemistry with a monoclonal antibody against choline acetyltransferase (ChAT). ChAT(+) fibers and varicosities were counted at different locations within area 17 and the distribution patterns in various animals were compared. Choline acetyltransferase-immunoreactivity was localized in fine, varicose fibers, which were present in all layers of the visual cortex. The density of labeled fibers was highest in layer I, which contained 14% of all fibers and 19.5% of all varicosities, and decreased toward deeper layers. The number of varicosities decreased more markedly toward deeper layers than the frequency of fibers. These distribution patterns were very consistent, showing only slight intra- and interindividual variability.

Animals↗
PubMed1987

Quantitative analysis of the choline acetyltransferase-immunoreactive axonal network in the cat primary visual cortex: II. Pre- and postnatal development.

The pre- and postnatal development of cholinergic projections was investigated in the cat striate cortex by applying immunohistochemical methods based on a monoclonal antibody against choline acetyltransferase (ChAT). The earliest age investigated was gestational day 54. At this stage a sparse network of ChAT(+) fibers was distributed throughout the striate cortex. Subsequent postnatal maturation of ChAT(+) fibers was characterized by an increase in fiber density that started in layer VI and gradually progressed toward more superficial layers. By 4 weeks of age the density of ChAT(+) fibers and varicosities had reached adult levels in layers V and VI but was still subnormal in layers I-IV. The mature pattern of cholinergic innervation was established by 13 weeks of age. There was no evidence for developmental gradients in the anteroposterior and mediolateral directions within area 17. These results indicate that the cholinergic projection to striate cortex develops continuously in an inside-out sequence as is characteristic for most cortical maturation processes. There was no indication that striate cortex receives an especially dense cholinergic input during the critical period.

Animals↗
PubMed1991

Targets of horizontal connections in macaque primary visual cortex.

Pyramidal neurons within the cerebral cortex are known to make long-range horizontal connections via an extensive axonal collateral system. The synaptic characteristics and specificities of these connections were studied at the ultrastructural level. Two superficial layer pyramidal cells in the primate striate cortex were labeled by intracellular injections with horseradish peroxidase (HRP) and their axon terminals were subsequently examined with the technique of electron microscopic (EM) serial reconstruction. At the light microscopic level both cells showed the characteristic pattern of widespread, clustered axon collaterals. We examined collateral clusters located near the dendritic field (proximal) and approximately 0.5 mm away (distal). The synapses were of the asymmetric/round vesicle variety (type I), and were therefore presumably excitatory. Three-quarters of the postsynaptic targets were the dendritic spines of other pyramidal cells. A few of the axodendritic synapses were with the shafts of pyramidal cells, bringing the proportion of pyramidal cell targets to 80%. The remaining labeled endings were made with the dendritic shafts of smooth stellate cells, which are presumed to be (GABA)ergic inhibitory cells. On the basis of serial reconstruction of a few of these cells and their dendrites, a likely candidate for one target inhibitory cell is the small-medium basket cell. Taken together, this pattern of outputs suggests a mixture of postsynaptic effects mediated by consequence the horizontal connections may well be the substrate for the variety of influences observed between the receptive field center and its surround.

Animals↗
PubMed1991

Synaptic organization of cortico-cortical connections from the primary visual cortex to the posteromedial lateral suprasylvian visual area in the cat.

The synaptic organization of the projection from the cat striate visual cortex to the posteromedial lateral suprasylvian cortical area (PMLS) was examined. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was iontophorectically delivered into area 17, and anterogradely labeled fibers were revealed in PMLS by means of an immunocytochemical detection method. Most axons and presumptive terminal swellings were found in layers III and IV. The neuronal elements (n = 190) that were postsynaptic to anterogradely labeled boutons were quantitatively analyzed. All anterogradely labeled cortico-cortical boutons (n = 182) established type 1 synapses. The results show that 83% of the postsynaptic targets were dendritic spines, probably belonging to pyramidal cells. Dendritic shafts constituted 17% of the targets. The dendritic shafts postsynaptic to cortico-cortical boutons were studied for the presence of gamma-aminobutyric acid (GABA) with a postembedding immunogold method. Most dendritic shafts (85%) that were tested were found to be GABA-positive, demonstrating that they originate from local inhibitory neurons. Taking into account that most postsynaptic targets were spines and extending the results of the immunocytochemical testing to the total population of postsynaptic dendrites, it was calculated that at least 14% of targets originated from GABA-positive cells. Thus cortico-cortical axons establish direct monosynpatic connections mainly with pyramidal and to a lesser extent with GABAergic nonpyramidal neurons in area PMLS, providing both feedforward excitation and feedforward inhibition to a visual associational area known to be involved in the processing of motion information. The results are consistent with previously demonstrated deficits in physiological properties of neurons in PMLS following removal of cortico-cortical afferents.

Animals↗
PubMed1991

A quantitative analysis of cytochrome oxidase-rich patches in the primary visual cortex of Cebus monkeys: topographic distribution and effects of late monocular enucleation.

We have studied the tangential distribution of cytochrome oxidase (cytox)-rich patches in striate cortex of normal and monocularly enucleated Cebus apella monkeys. Patch spatial density and patch cross-sectional area were analysed in cytox-reacted tangential sections of flat-mounted preparations of V1. In the upper cortical layers of V1, and specially in the middle of layer III, the Cebus has well-delimited cytox-rich patches. Rows of patches are less conspicuous in Cebus than in Old World monkeys. The spatial density of patches is nearly constant throughout the binocular field representation in V1, with a mean value of 4 patches per mm2. In the monocular portions of V1, however, patch spatial density diminishes. In most cases, mean patch cross-sectional area decreases slightly towards the representation of the periphery in V1. However, patches in the representation of the monocular crescent tend to be larger than those in the adjacent binocular representation. The small variation of cytox patch topography with eccentricity contrasts with the large variation of cortical point-image size in V1. In monocularly enucleated monkeys, patches are larger and darker above and below the ocular dominance stripes of the remaining eye than in the alternate stripes. After long-term enucleation, the patches corresponding to the remaining eye columns appeared larger than in normal controls. In contrast, there is no difference in size between the patches located in the deprived and undeprived monocular crescent representations, although both patch and interpatch regions are darker staining in the latter. These results suggest the existence of competitive interactions which modify the cortical intrinsic organization even in adult monkeys.

Animals↗
PubMed1989

Orientation discrimination sensitivity of single units in cat primary visual cortex.

Responses of visual cortex (area 17) neurons to moving oriented stimuli were recorded from anesthetized cats. The variance of response (SD2) to repeated identical stimuli was directly proportional to response magnitude (R), (SD2 = C2R). The values of C were not found to differ significantly between different types of cortical cells. The relationship predicts that the coefficient of variation (SD/R) will be smallest near the peak of the tuning curve, indicating that the peak response is most reliable for detecting an orientation but not necessarily the most sensitive to a change in orientation. Tuning curves and response variability were then examined to determine the orientation at which the neuron was most sensitive to changes in stimulus orientation using signal detection theory. The discrimination index (d' = [R1-R2]/SD) for a 1 degree change in stimulus orientation was greatest along the flanks of the tuning curve. In order to generalize the experimental data, response distributions derived from a model of cells with parameters based on experimental data were examined to determine the minimal discriminable change in stimulus orientation. Changes of stimulus orientation between 0.6 and 5 deg of arc could be detected from single responses of a single cell by an optimal observer with 75% accuracy if the orientation change was centered at the most sensitive part of the tuning curve.

Action Potentials↗
PubMed1989

Cortico-cortical and subcortico-cortical afferent connection of the rabbit's primary visual cortex. A horseradish peroxidase study.

Neuroanatomical studies were carried out on the visual system of the adult rabbit brain. Either horseradish peroxidase (HRP) or wheat germ agglutinine-horseradish peroxidase (WGA-HRP) was injected into the area occipitalis 1. Several cortico-cortical, ipsi- and contralateral, and subcortico-cortical projections were demonstrated. In the ipsilateral telencephalon several patches of labelled cell groups, some single HRP-positive cell bodies and some labelled fibres were observed in the area retrosplenialis granularis dorsalis, the areas occipitales, the areas temporales, the area perirhinalis, the area entorhinalis, the area praecentralis 1, the regio cingularis 1 and in the regio diagonalis, as well as in the dorsal part of the claustrum. Efferent preterminal fibres and terminal knobs were seen in the nucleus caudatus. Contralaterally, groups of labelled cell bodies and single HRP-positive neurons were found in the area retrosplenialis granularis dorsalis, the areas occipitales and the areas temporales. In the ipsilateral diencephalon, labelled cell bodies were observed in the corpus geniculatum laterale (pars dorsalis and ventralis), the nucleus lateralis thalami, the nucleus reticularis thalami and in nonspecific nuclei of the midline. Contralaterally, very few labelled cell bodies were seen in the nonspecific nuclei of the midline. Some labelled cell bodies were observed in the ipsilateral substantia griseum centrale and in the nucleus reticularis mesencephali. Numerous anterogradely labelled preterminal fibres and terminal knobs but very few labelled cell bodies were seen in the nucleus praetectalis posterior. In the nucleus of the optic tract and in the colliculus superior, numerous labelled fibres could be observed. In the ipsilateral nuclei pontis numerous labelled fibres were detectable.

Animals↗
PubMed1984

Zero-crossing detectors in primary visual cortex?

David Marr and others have hypothesized that the visual system processes complex scene information in stages, the first of which involves the detection of light intensity edges or "zero-crossings" (Marr, 1982). Ideal zero-crossing detector mechanisms have been described and modeled in terms of their possible physiological implementation (Marr and Hildreth, 1980; Poggio, 1983). We now present evidence of visual cortical receptive fields which resemble in spatial organizational terms the requirements of zero-crossing analysis. The linear and nonlinear summation within and between the receptive field subunits are described and compared with predicted processes. The relative subunit sizes and separations are analyzed in these terms. Our findings support the notion that receptive fields may correspond with zero-crossing filters rather than zero-crossing detector gates.

Animals↗
PubMed1989

Postnatal development of vimentin-immunoreactive radial glial cells in the primary visual cortex of the cat.

In kitten area 17 vimentin-like immunoreactivity is expressed in radial glial fibres up to one month postnatally, i.e. the time for which neuronal migration continues. During this time fibre density gradually decreases. A subpopulation of these fibres also contains S-100 protein and glial fibrillary acidic protein. However, these latter antigens disappear earlier than vimentin. In addition, vimentin immunoreactivity can be observed in astroglial cells of the white matter between the second and fifth postnatal week. Many of these cells resemble mature astrocytes but partially they have an intermediate morphology suggesting the possibility that they originated from radial glia. Such displaced radial glial cells' are also positive for S-100 protein both in the cortex and white matter. Thus it is conceivable that at least part of the astrocytes of mature cat visual cortex originate from vimentin- or S-100-immunoreactive radial glia.

Animals↗
PubMed1992

Laminar, columnar and topographic aspects of ocular dominance in the primary visual cortex of Cebus monkeys.

The representation of the two eyes in striate cortex (V1) of Cebus monkeys was studied by electrophysiological single-unit recordings in normal animals and by morphometric analysis of the pattern of ocular dominance (OD) stripes, as revealed by cytochrome oxidase histochemistry in V1 flat-mounts of enucleated animals. Single-unit recordings revealed that the large majority of V1 neurons respond to the stimulation of either eye but are more strongly activated by one of them. As in other species of monkey, neurons with preference for the stimulation of the same eye are grouped in columns 300-400 microns wide, spanning all cortical layers. Monocular neurons are clustered in layer IVc, specially in its deeper half (IVc-beta), and constitute less than 10% of the population of other layers. Neurons with equal responses to each eye are more commonly found in layer V than elsewhere in V1. In the supragranular layers and in granular layer IVc-alpha neurons strongly dominated by one of the eyes tend to be broadly tuned for orientation, while binocularly balanced neurons tend to be sharply tuned for this parameter. No such correlation was detected in the infragranular layers, and most neurons in layer IVc-beta responded regardless of stimulus orientation. Ocular dominance stripes are present throughout most of V1 as long, parallel or bifurcating bands alternately dominated by the ipsi- or the contralateral eye. They are absent from the cortical representations of the blind spot and the monocular crescent. The domains of each eye occupy nearly equal portions of the surface of binocular V1, except for the representation of the periphery, where the contralateral eye has a larger domain, and a narrow strip along the border of V1 with V2, where either eye may predominate. The orderliness of the pattern of stripes and the relationship between stripe arrangement and the representation of the visual meridians vary with eccentricity and polar angle but follow the same rules in different animals. These results demonstrate that the laminar, columnar and topographic distribution of neurons with different degrees of OD in V1 is qualitatively similar in New- and Old World monkeys of similar sizes and suggest that common ancestry, rather than parallel evolution, may account for the OD phenotypes of contemporaneous simians.

Animals↗
PubMed1987

Vasoactive intestinal polypeptide immunoreactive neurons in the primary visual cortex of the cat.

When cat visual cortex (area 17) is reacted with an antibody to vasoactive intestinal polypeptide (VIP) a variety of neuronal types is labelled. Many of the labelled neurons are bipolar in form and are most common in layers II and III, although significant numbers of bipolar neurons are also encountered in layer V. Multipolar cells are also labelled. These are most frequent in layer IV and have a variety of shapes. In layer I, the labelled cells are of three varieties, i.e. horizontal bipolar cells, horizontal bitufted cells and multipolar neurons, while in layer VI the few VIP-positive neurons are horizontal bipolar cells. This suggests that all of the VIP-labelled neurons in cat area 17 are non-pyramidal in form, and this has been confirmed by electron microscopy. In these preparations, axon terminals are also labelled and under the light microscope it can be seen that these terminals occur both within the neuropil and around the cell bodies of some neurons, particularly neurons in layers II and III. Electron microscopy has shown that all of the labelled axon terminals form symmetric synapses and that those in the neuropil synapse with the shafts of smooth dendrites. These axodendritic synapses account for about 90% of the synapses formed by the labelled axon terminals. The remainder of the labelled axon terminals synapse with the cell bodies of pyramidal neurons. Parallels are drawn between these results and those previously obtained by examining those neuronal elements labelled with VIP antibodies in rat visual cortex.

Animals↗
PubMed1987

A new heterotopic callosal projection of primary visual cortex in the monkey, Callithrix jacchus.

A callosal projection of area 17 upon the dorsomedial visual area in the marmoset monkey was demonstrated by means of retrograde transport of neuronal tracers. The projection was restricted to those regions representing the vertical meridian in the two areas. This finding, and the data of other authors, indicate that the monkey area 17 projects transcallosally onto homotopic and several heterotopic targets.

Animals↗
PubMed1989

Induction of LTP in rat primary visual cortex: tetanus parameters.

Long-term potentiation (LTP), intensively studied in the hippocampus as a possible mnemonic device, has begun to be studied in the neocortex. In this study the effects of varying tetanic stimulus parameters on LTP of field potentials recorded from layer II/III induced by white matter stimulation in the in vitro rat visual cortical slice were examined. Low intensity tetanus was more effective in producing LTP than high-intensity tetanus, although single pulses of very high intensity reliably resulted in LTP. LTP consistently occurred following 2 Hz-60 min, or 100 Hz-10 min tetanus; whereas, 10 min of 7 and 25 Hz tetanus usually resulted in long-lasting depression. Although no obvious rule related tetanus frequency and duration to the incidence of LTP, an inverted-U relationship was found between tetanus frequency and LTP magnitude.

Animals↗