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PubMedDate not supplied

Segregation of pathways leading from area V2 to areas V4 and V5 of macaque monkey visual cortex.

V5 and V4 are areas of macaque monkey prestriate visual cortex that are specialized for involvement in different aspects of visual perception, namely motion for V5 (refs 1-4) and colour vision, with other possible functions, for V4 (refs 2, 5-9). Thus, it is unlikely that they should be fed the same information for further processing, yet both receive a strong input from patches of the upper layers of V2 (refs 10, 11), the area immediately adjoining the primary visual cortex, V1. V2, however, seems to comprise functionally distinct subregions, which can be revealed by staining the tissue for the mitochondrial enzyme cytochrome oxidase. Here we report that V4 and V5 are connected with separate cytochrome oxidase-defined subregions of V2, suggesting that cortical pathways dealing with motion and colour perception are segregated in their passage through V2, and reinforcing evidence for functional specialization in the visual cortex.

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↗
PubMed1976

[Biochemical correlates of functional features of visual cortex neurons].

Changes of protein concentration and of different metabolic ferments activity were studied in the rabbit visual cortex after visual deprivation. Two groups of neurons with different sensitivity to visual deprivation were found. The less sensitive are supposed to have an additional source of activation. These findings corroborate the microelectrode data showing that the activity of about 40% of the visual cortex neurons are modulated by a different nonvisual stimulus.

Acetylcholinesterase↗
PubMed1995

Development of the visual cortex in a wallaby--phylogenetic implications.

The visual cortex of one of the smallest macropod marsupials, a wallaby, the quokka Setonix brachyurus, was examined at maturity and during development from postnatal day 1 to 150 in Nissl-stained or Golgi-stained sections. Injections of horseradish peroxidase into the primary visual centres in adults identified cortical neurons projecting to these regions. The pattern of cell generation was determined by tritiated thymidine/autoradiography. The adult visual cortex was composed of the usual six layers of cells with dendritic morphologies similar to those seen in eutherian (placental) mammals. The margin of Layer 6 overlapped slightly with the white matter, and pyramidal cells projecting to subcortical regions were located at all depths of Layer 6. Cortical development was similar to that of eutherian mammals, with the formation of transient cellular layers below the developing cortical plate. Autoradiographic studies confirmed that the cortical plate was composed of two layers: a compact zone of densely packed cells located pial to a striated layer containing more loosely packed cells. Postnatal cell generation of Layers 6-2 took place from postnatal day 3 to day 85, with Layer 4 neurons, the main target of incoming visual axons, being generated around postnatal day 40. Cells located at maturity in the white matter, mostly of glial morphology, were generated from postnatal day 40. A subplate zone containing early differentiating cells was not evident, and postnatal 3H-thymidine labelling did not identify a population of early generated neurons below the cortical plate. In the tammar wallaby Macropus eugenii, the majority of target neurons for incoming geniculate axons are generated about 20 days after the first axons enter directly into the cortical plate without a waiting period in a subplate. Geniculate axons in the wallabies have a relatively longer 'wait' for their target neurons than do those in cats or monkeys. Therefore, if geniculate axons in marsupials make temporary synapses, while they wait for their target neurons to be generated, their temporary connections must, unlike those in cats or monkeys, be with cells already in the cortical plate.

Aging↗
PubMed1987

Morphology of corticotectal cells in the primary visual cortex of hooded rats.

In primary visual cortex of hooded rats, pyramidal cells in layer V may be classified as long, medium, or short, on the basis of the layer in which the apical dendrite terminates. The present study determines which of these types of pyramidal cells project to the superior colliculus. Two different strategies were used to label corticotectal cells with horseradish peroxidase (HRP). In the first set of experiments, a large number of corticotectal cells were labeled by retrograde transport following injection of HRP into the superior colliculus. In the second set of experiments, single unit recording was used to identify corticotectal cells physiologically by antidromic activation from the superior colliculus. These cells were then impaled and labeled by intracellular iontophoresis of HRP. The results from both techniques suggest that only long pyramidal cells send an axon to the superior colliculus. These cells are distinguished by an apical dendrite that extends into layer I. We conclude that in hooded rats corticotectal cells in primary visual cortex are the long pyramids in layer V.

Action Potentials↗
PubMed1986

Binocular impulse blockade prevents the formation of ocular dominance columns in cat visual cortex.

Ocular dominance columns in the cat's visual cortex appear to develop out of an initially overlapping projection by a progressive segregation of the geniculocortical afferents serving the 2 eyes (reviewed in LeVay and Stryker, 1979). To determine whether electrical activity in the visual afferent pathway is involved in this normal, developmental rearrangement of synaptic connections, we blocked the discharge of retinal ganglion cells in both eyes by making repeated intravitreal injections of tetrodotoxin (TTX) during the period in which geniculocortical afferent segregation would normally be taking place. Control experiments for the side effects of the injection procedure, the systemic effects of TTX, and the effects of visual deprivation were carried out, and a series of normal animals of appropriate ages was also studied. We then examined the effects of retinal blockade and the various control procedures on the formation of ocular dominance columns using an anatomical assay, the autoradiographic labeling of geniculocortical afferent terminals in layer IV of the visual cortex by the transneuronal transport of tritiated proline injected into 1 eye, and a physiological assay, the ocular dominance of single cortical cells recorded extracellularly. After retinal TTX blockade, layer IV was labeled uniformly without periodic fluctuation in grain density, and nearly all cortical cells were driven well through both eyes. These assays thus indicated that retinal blockade completely blocked the formation of ocular dominance columns, unlike any of the control procedures, suggesting that the spontaneous maintained discharge of retinal ganglion cells may have an important role in the normal development of binocular connections in the visual cortex.

Animals↗
PubMed1991

Distribution of glial fibrillary acidic protein and vimentin immunoreactivity during rat visual cortex development.

The postnatal maturation of astrocytes in the rat visual cortex was analysed by immunostaining the astroglial proteins vimentin and glial fibrillary acidic protein with poly- and monoclonal antibodies. Vimentin immunoreactivity was present in the visual cortex up to the third postnatal week, whereas immunolabelling first disappeared in the cortical layers and then in the white matter. In the early postnatal period, vimentin antibodies labelled radial glial fibres. After the first postnatal week staining of radial glial fibres gradually disappeared and vimentin immunoreactivity was localized in a few protoplasmic astrocytes in the grey matter and fibrous astrocytes in the white matter. The development of glial fibrillary acidic protein-positive astrocytes was not fully complete until postnatal day 50. Glial fibrillary acidic protein-positive radial glial fibres were present after birth and disappeared towards the end of the third postnatal week. Staining of astrocytes in the white matter and in cortical layers I and VI reached an adult density at postnatal days 8 and 20, respectively. A progressively later development of glial fibrillary acidic protein-positive astrocytes was observed in cortical layers II-V which was completed between postnatal days 47 and 50. In the adult rat visual cortex glial fibrillary acidic protein-positive astrocytes were especially dense in layers I and VI, moderate in layers II/III and V and nearly absent in layer IV and lower layer III. The time course of the loss of vimentin and the gradual appearance of glial fibrillary acidic protein immunoreactivity in the visual cortex is considered as an index of astrocytic maturation and the spatiotemporal sequence of this maturation pattern is discussed in terms of reciprocal neuron-astrocyte interactions during brain development.

Animals↗
PubMedDate not supplied

Projections from V1 to lateral suprasylvian cortex: an efferent pathway in the cat's visual cortex that originates preferentially from CO blob columns.

The patchy pattern of retrograde labeling produced by injections of anatomical tracers into the lateral suprasylvian (LS) visual area was compared to the cytochrome oxidase (CO) blobs in cat visual cortex. Following large injections of anatomical tracers in LS, retrograde labeling formed an irregular lattice of patches with a spacing of slightly less than 1 mm in area 17, and slightly greater than 1 mm in area 18. By comparing labeling in alternate serial sections, patches of LS-projecting cells in both areas were found to align with CO blobs. The conclusion of alignment between CO blob columns and patches of LS-projecting cells was confirmed by a quantitative analysis which showed a significant correlation between the local density of LS-projecting cells in reconstructions of charted cells and the intensity of CO staining in the CO-reacted sections. As for areas 17 and 18, labeling in other afferent areas of LS was also patchy with a spacing on the order of 1 mm except for area 19 where we found patches of LS-projecting cells with a larger spacing, roughly 2 mm. No matching fluctuations in CO density could be discerned in area 19, however. In conjunction with recent evidence that CO blob columns in cats receive strong input from Y-cells of the lateral geniculate nucleus (Boyd & Matsubara, 1996; Shoham, et al., 1996), these data support the hypothesis (Shipp & Grant, 1991) that the patches of LS-projecting cells correspond to Y-cell input columns. As a relationship between the CO architecture and certain classes of efferent cells has previously been shown in primates, these findings show new similarities between CO blobs in different mammalian species.

Animals↗
PubMed1999

Plasticity of 5-hydroxytryptamine(1B) receptors during postnatal development in the rat visual cortex.

The distribution of 5-hydroxytryptamine1A and 5-hydroxytryptamine1B receptors in the visual cortex was studied by quantitative autoradiography during postnatal development. Overall, receptor densities increased throughout development, but exhibited regional rearrangements, particularly in the case of 5-hydroxytryptamine1B receptors. Neonatal treatment with 5,7-dihydroxytryptamine, which causes selective degeneration of serotoninergic neurons, had no effect on the density of 5-hydroxytryptamine1A receptors in the visual cortex. However, a transient increase in 5-hydroxytryptamine1B at postnatal days 10-12 was observed after this treatment, suggesting a regulation of postsynaptic receptors. Neonatal enucleation resulted in a marked increase in 5-hydroxytryptamine1B binding sites in all layers of the visual cortex by P16, whereas it had no effect upon 5-hydroxytryptamine1A binding sites. These results show that both receptor subtypes do not exhibit striking transient features in the visual cortex during postnatal development, but rather undergo discrete reorganizations. 5-Hydroxytryptamine1B receptors show changes in density after either neonatal degeneration of serotoninergic neurons or enucleation, indicating that the serotoninergic system involving this receptor subtype can exhibit some postnatal plasticity in the visual cortex.

5,7-Dihydroxytryptamine↗
PubMed1989

Organization of corticocortical connections in human visual cortex.

Clinical and psychophysical observations indicate that the visual cortex is critical for the perception of color, form, depth, and movement. Little, however, is known about the cortical circuitry that underlies these functions in humans. In an attempt to learn more about these connections, we have traced projections of primary (V1) and secondary (V2) visual cortex in the postmortem, fixed human brain, using the fluorescent dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate as an axonal marker. The results show that V1 makes a forward projection to layers 3 and 4 of V2, and V2 projects back to layers 1, 2, 3, 5, and 6 of V1. Some V2 injections also show an input to layer 4B of V1. Projections to 4B probably originate from cytochrome oxidase (CO)-reactive stripes that we have identified in V2. Differential connections between CO-rich (blobs) and CO-poor regions (interblobs) also exist within V1; blobs are connected to blobs and interblobs are connected to interblobs. The results show that the connections in human visual cortex are similar to those of nonhuman primates and that their organization is consistent with the concept of multiple processing streams in the visual system.

Adult↗
PubMed1989

Evidence for a dopaminergic innervation of cat primary visual cortex.

Experiments have been conducted to determine whether dopamine fulfills the criteria to be considered as a neurotransmitter in cat primary visual cortex. N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, a neurotoxin with high selectivity for noradrenergic terminals, was administered into kitten cerebral ventricles. Two weeks later, the concentration of norepinephrine in visual cortex was reduced to 15% of control while dopamine and serotonin were not depleted. Receptor binding assays with [3H]SCH 23390 showed that membranes prepared from cat primary visual cortex contain a binding site that has the properties of a D1 receptor. This site was localized by autoradiography to two bands, one in layer VI and the second in upper layers of visual cortex. A dopamine-stimulated adenylate cyclase activity was demonstrated that was inhibited by SCH 23390 but not by alprenolol. Norepinephrine was shown to stimulate adenylate cyclase activity through both a beta-noradrenergic receptor and a D1 receptor. Binding assays with [3H]spiperone indicated that D2 dopamine receptors are absent from cat visual cortex or present in very low amounts. Taken together these results strongly suggest the existence of a dopamine innervation of cat primary visual cortex. The neurotoxin experiments show that some of the dopamine in cat visual cortex is not in noradrenergic terminals while the receptor assays demonstrate the presence of D1 receptors functionally linked to the synthesis of cyclic 3',5'-adenosine monophosphate. The demonstration of a dopaminergic innervation in cat primary visual cortex is also relevant to the interpretation of data on the involvement of catecholamines in developmental plastic phenomena.

Adenylyl Cyclases↗
PubMedDate not supplied

Monocular enucleation prevents retinal ganglion-cell loss following neonatal visual cortex damage in cats.

Damage to primary visual cortex (VC) in young cats leads to severe retrograde degeneration of the dorsal lateral geniculate nucleus (dLGN) and selective transneuronal retrograde degeneration of a class of retinal ganglion cells (RGCs) that have a medium-size soma. Previous studies have shown that "programmed" RGC death associated with normal development in one eye can be attenuated by removal of the other eye, suggesting that binocular interactions can influence developmental RGC death. The present study investigated whether removal of one eye also attenuates the ganglion cell loss that accompanies an early VC lesion. Five one-week-old cats received a unilateral VC lesion (areas 17, 18, and 19), and three of these cats also underwent monocular enucleation at the same time. Two normal control animals also were examined. RGC measurements were made from flat-mounted retinae when the animals were 5 weeks old. Sampling was restricted to a retinal area corresponding to the retinotopic representation included in the VC lesion. Results indicate that there is a marked loss of medium-size RGCs in the hemiretinae projecting to the damaged hemisphere in cats that received a VC lesion alone. However, there is no such loss in VC-lesion animals that also have a monocular enucleation. These results indicate that the transneuronal RGC loss that occurs after an early visual cortex lesion can be influenced by binocular interactions.

Aging↗
PubMed1979

Role of visual cortex in interocular alignment.

The role which the visual cortex plays in the development of interocular alignment in the cat was examined by removing this structure bilaterally in 4 groups of subjects. These included (1) kittens 10 to 14 days of age, (2) 10- to 14-day-old kittens in which one eyelid was sutured shut at the same time, (3) normally reared adult cats, and (4) cats dark-reared until 4 months of age. If the cortex is removed in young kittens, interocular alignment appears to develop normally until the kittens are 60 to 80 days of age. At this time, an abrupt change in alignment resulting in incyclotorsion of the optic axes is observed. If binocular vision is prevented in kittens with neonatal visual cortex lesions by suturing one eyelid shut, convergent strabismus and/or incyclotorsion are frequently observed. This characteristic incyclotorsion does not develop if similar lesions are made in adult cats; no significant alterations of eye alignment occur in these animals even after postoperative survival times of more than 6 months. Incyclotorsion characterizes dark-reared cats when they are first brought into the light, but this diminishes with time and may even be replaced by excyclotorsion after the animals spend a few weeks in the light. If dark-reared cats are decorticated on being brought into the light, these changes are largely prevented. Such animals remain permanently incyclotorted relative to normal cats. The results indicate that the visual cortex plays an important role in the development of torsional alignment of the eyes.

Animals↗
PubMed1997

Fast synaptic signaling by nicotinic acetylcholine and serotonin 5-HT3 receptors in developing visual cortex.

Cholinergic and serotonergic fiber systems invade the developing visual cortex several weeks before eye opening; both transmitters have been implicated in plasticity of neocortical circuits. These transmitters have been presumed to act predominantly through second messenger-coupled receptors, because fast cholinergic or serotonergic neurotransmission has never been observed in neocortex. However, acetylcholine and serotonin also act on ligand-gated ion channels; the nicotinic acetylcholine receptor and the serotonin 5-HT3 receptor, respectively. Here, using whole-cell patch-clamp techniques in developing ferret visual cortex, we pharmacologically isolated fast, spontaneous, and evoked cholinergic and serotonergic synaptic events in pyramidal cells and interneurons of all cortical layers. The number of cells receiving such inputs increased with the ingrowth of thalamic afferents, and the frequencies of the spontaneous events increased at eye opening. Thus, both acetylcholine and serotonin can mediate fast synaptic transmission in the visual cortex; the early onset of these mechanisms suggests a role during initial stages of circuit formation and during subsequent experience-dependent remodeling of cortical connections.

Acetylcholine↗
PubMed1990

Morphological types of projection neurons in layer 5 of cat visual cortex.

Pyramidal cells in layer 5 of the visual cortex have multiple cortical and subcortical projection sites. Previous studies found that many cells possess bifurcating axons and innervate more than one cortical or subcortical target, but cells projecting to both cortical and subcortical targets were not observed. The present study examines the morphology of cells in cat visual cortex projecting to the superior colliculus, the main subcortical target of layer 5, and cells in layer 5 projecting to cortical areas 18 and 19. The neurons that give rise to these different projections were retrogradely labelled and intracellularly stained in living brain slices. Our results show that cells within each projection group have several morphological features in common. All corticotectal cells have a long apical dendrite forming a large terminal tuft in layer 1. Their cell bodies are medium sized to large, and their basal dendrites form a dense and symmetrical dendritic field. Corticocortical cells in layer 5 have a very different morphology: their apical dendrites are short and they never reach higher than layers 2/3. Their cells bodies are small to medium sized and they have fewer basal dendrites than corticotectal cells. Thus there are two morphologically distinct projection systems in layer 5, one projecting to cortical and the other one to subcortical targets, suggesting that these two systems transmit different information from the visual cortex. Among the corticotectal cells with the largest cell bodies we found some cells whose basal and apical dendrites were almost devoid of spines. Spiny and spinefree corticotectal cells also have different intrinsic axon collaterals and therefore play different roles in the cortical circuitry. While many spiny corticotectal cells have axon collaterals that project to layer 6, spinefree corticotectal cells have fewer axon collaterals and these do not arborize in layer 6. We suggest that the two morphological types of corticotectal cells might be related to functional differences known to exist among these cells. We discuss how the presence or absence of spines affects the integration of the synaptic input and how this might be related to the cells' functional properties.

Animals↗
PubMed1989

Functional consequences of modification of callosal connections by perinatal enucleation in rat visual cortex.

The effects of neonatal monocular enucleation (right eye) on the callosal connections in the rat visual cortex were studied by physiological and morphological methods. Evoked activity was recorded in the left hemisphere, i.e. contralaterally to the enucleated eye. After enucleation, trans-callosally evoked responses were recorded in a widened stripe of the lateral visual cortex. Compared with the controls, the responsive area was expanded laterally and medially, i.e. into the lateral part of the primary visual area and within the secondary visual cortex (lateral part). Within about 0.5 mm of the expansion, the responses did not differ from those recorded in areas with "normal" callosal connections. Morphological evidence is presented suggesting that this expansion of evoked responses with high amplitudes and short latencies corresponds to an extension of callosal connections with a high density of axon terminals in layers two and three. Further medially within the primary visual cortex, callosally evoked responses with low amplitudes and longer latencies were recorded. The main types of unit responses and characteristic interactions between visually and callosally evoked responses are shown and discussed. These results suggest that following neonatal enucleation (1) the callosal connections expand and form functional synapses in the lateral part of the visual cortex, (2) these connections can activate cortical neurons either directly or by mediation of associational connections between the lateral secondary and primary visual cortex areas and (3) callosal connections can interact with visually evoked potentials and unit responses.

Animals↗
PubMed1989

Effect of early visual pattern deprivation on development and laminar distribution of cholinergic markers in rat visual cortex.

In order to evaluate the role of cholinergic cortical mechanisms in the shaping of visual cortical plasticity in more detail the present paper summarizes recent studies on the laminar distribution of muscarinic acetylcholine receptors, choline acetyltransferase, and sodium-dependent high-affinity choline uptake sites during postnatal ontogenesis of the visual cortex of monocularly derived rats using autoradiographic techniques as well as quantitative biochemical methods after separating the different cortical layers by a cryocut technique. The data are correlated to the laminar distribution of cholinergic fibers within the visual cortex as studied by the immunohistochemical visualization of choline acetyltransferase. The laminar distribution of cholinergic receptor binding in the visual cortex changes during ontogenesis. In adult rats, the highest muscarinic acetylcholine receptor density is found in layer I. The activity of the choline acetyltransferase is rather uniformly distributed in all cortical layers. Adult activity values are reached at the age of 25 days. In adult rats the enzyme activity is highest in layer V. In all visual cortical layers the highest 3H-hemicholinium-3 binding to choline uptake sites during the postnatal period studied is already detectable at the age of 10 days, then binding decreases sharply until day 25 at which age it nearly equals the value found in the adult brain. Binding sites exhibit highest density in layers I and IV of the adult rat visual cortex. Monocular deprivation resulted in significant changes in all three parameters studied with different cortical laminae preferentially affected. The data suggest that the normal laminar development of the modulatory function of cholinergic transmission in the rat visual cortex depends on the presence of physiological light stimulation.

Aging↗