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PubMedDate not supplied

Transitory corpus callosum axons projecting throughout developing rat visual cortex revealed by Dil.

Anatomical tracing was used to determine the extent and distribution of CC axons in mammalian visual cortex. Postnatal development of rat CC was studied by in vitro callosal labeling with the lipophilic carbocyanine dye Dil in 59 rats. Solid Dil crystals were placed in the mid-sagittal region of the CC in aldehyde-fixed brain slabs. Coronal sections through visual cortex were photographed and reconstructed to show the overall distribution of Dil-labeled callosal projections as well as the locations of individual callosal axons and their presumed synaptic boutons. During postnatal weeks 1 and 2, CC axons were found to project to layer I throughout the entire mediolateral extent of areas 17, 18a, and 18b. Numerous varicosities on callosal axons are located en passant and at axon terminals in layer I. During postnatal week 3 the tangential density of callosal projections was significantly reduced, so that fewer callosal axons extended to layer I throughout areas 17, 18a, and 18b than in younger postnatal rats. However, at this age some CC axons could still be found extending to layer I throughout the mediolateral extent of areas 17, 18a, and 18b. By postnatal week 4 the tangential distribution of callosal projections was greatly restricted; most callosal axons projecting to layer I were located at the borders of the visual cortical areas. Nevertheless, there were still callosal axons projecting into cortex and terminating in supragranular and infragranular layers in areas 17, 18a, and 18b; this was most pronounced in area 18a. Thus, in the rat there are many elaborately formed transitory CC axons projecting throughout visual cortex for several weeks postnatal. These projections extend to layer I and have varicosities in all cortical layers. With increasing age, fewer axons extended to layer I; subsequently most axons not at cytoarchitectonic borders fail to extend to layer I. If some of the varicosities on the transitory rat callosal axons were to form synapses, there would be extensive opportunities for the CC to provide input to all layers of visual cortical areas while cortical microcircuitry is being established. The same type of study in the cat has shown similar results during early postnatal development. Cat CC axons project to all parts of primary and association visual cortical areas; even in regions found to be acallosal in the adult, the neonatal callosal axons extend through all layers of cortex to reach layer I (Elberger, 1993).(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed2002

Vascularization in the primate visual cortex during development.

We studied the relationship between vascularization and neuronal activity in the visual cortex during postnatal development in the primate. Analyses were focused on layer IVC that displays a sequential pattern of maturation for the magno- and parvocellular systems in separate sublayers, respectively IVC alpha and IVC beta. Cytochrome oxidase and endogenous alkaline phosphatase histochemistry was used to analyse, on the same sections, the laminar patterns of cortical activity and vessel density in the primary visual cortex of the marmoset (Callithrix jacchus). Experiments were carried out in five young and two adult animals. We showed that the temporal pattern of angiogenesis differs in layer IVC alpha and IVC beta. During the first postnatal month, vessel density is higher in IVC alpha than in IVC beta and runs parallel to cytochrome oxidase intensity. In 2-month-old animals, both vessel densities and cytochrome oxidase activity are similar in IVC alpha and IVC beta. In adults, the vessel densities in IVC alpha and IVC beta are the reverse of those observed during the first postnatal month. Vessel diameter does not account for this evolution in vascular patterns. In the discussion, we suggest that such a developmental time-course of angiogenesis might be linked to the synaptogenesis requirements that proceed differently for the magno- and parvocellular systems in the primate striate cortex.

Alkaline Phosphatase↗
PubMed2001

Structure and projections of white matter neurons in the postnatal rat visual cortex.

Transient contributions of subplate neurons to the initial development of the cortex are well-characterized, yet little data are available on a subpopulation of subplate neurons that persist in the white matter (WM) of the cerebral cortex across development. To characterize the WM neurons, differential interference contrast and Nomarski optics were used to visualize individual cells in the WM in slices of rat visual cortex at postnatal ages 9-23. Soma-dendritic morphology and local axonal projection patterns, including probable synaptic innervation sites of their axons, were identified by intracellular filling with biocytin during electrophysiologic recordings. Dendritic branches of all WM neurons, tripartitioned here into upper, middle, and deep divisions, extend throughout the WM and frequently into the overlying cortex. Axonal arborizations from most WM neurons, including apparent boutons, project into adjacent WM with many also innervating overlying cortical layers, whereas some project into the stratum oriens/alveus of the hippocampal formation. Processes of a subset of WM neurons appear to be confined to the WM itself. By using antimicrotubule associated protein (MAP2) immunostaining to quantify the density of WM neurons in rat visual cortex, we find that their overall numbers decrease to approximately 30% of initial levels during postnatal development. During this same developmental period, an increasing percentage of WM neurons contain the synthetic enzyme for nitric oxide, nitric oxide synthase (NOS), as evaluated by immunostaining. Thus, WM neurons that survive the initial perinatal period of cell death are positioned under the laminae of the maturing cortex to potentially modulate the integration of visual signals through either conventional synaptic or nonconventional (diffusible NO signaling) mechanisms.

Action Potentials↗
PubMed1986

Bilateral projections of neurons in the lateral geniculate nucleus and nucleus lateralis posterior to the visual cortex in the neonatal rat.

The projection from the lateral geniculate nucleus (LGN) and nucleus lateralis posterior (LP) to the visual cortex was examined in rat pups 3-7 days of age using the fluorescent tracers True Blue, Fast Blue and Nuclear Yellow. Our data provide the first evidence that (1) these projections are bilateral, (2) the ipsilateral projection from these nuclei to the visual cortex in the neonatal rat is well localized and is similar in distribution and organization to that reported by others in the adult and (3) bilaterally projecting geniculocortical cells are morphologically heterogeneous; bilaterally projecting cells in LP are morphologically homogeneous.

Animals↗
PubMed2000

Adaptation-induced plasticity of orientation tuning in adult visual cortex.

A key emergent property of the primary visual cortex (V1) is the orientation selectivity of its neurons. The extent to which adult visual cortical neurons can exhibit changes in orientation selectivity is unknown. Here we use single-unit recording and intrinsic signal imaging in V1 of adult cats to demonstrate systematic repulsive shifts in orientation preference following short-term exposure (adaptation) to one stimulus orientation. In contrast to the common view of adaptation as a passive process by which responses around the adapting orientation are reduced, we show that changes in orientation tuning also occur due to response increases at orientations away from the adapting stimulus. Adaptation-induced orientation plasticity is thus an active time-dependent process that involves network interactions and includes both response depression and enhancement.

Adaptation, Physiological↗
PubMed1979

[Characteristics of the responses of cat visual cortex neurons to photic stimulation of different areas of their receptive fields].

The functions of intensity, thresholds of reactions, thresholds of inhibitory effects and differential sensitivity to intensity of local light stimulation of central and different peripheral regions of receptive fields of 96 units in the 17th field of visual cortex were investigated in immobilized and nonanesthetized cats in dark adaptation. Receptive fields of cells had wide threshold and superthreshold reliefs (3-30 degrees). Some of them had V-shape reliefs, while others--reliefs with alternating zones of high and low excitability. As a rule, sensitivity of excitatory and inhibitory inputs was maximal in the centre of the receptive field. In the investigated population of cells the inhibitory inputs were more standard in sensitivity and on the average of lower excitability. The threshold relief of the receptive fields was markedly narrowed under light adaptation mainly due to a decrease in the peripheral inputs sensitivity. The number of low-threshold units, the differential brightness sensitivity and sensitivity of the inhibitory system increased in the visual cortex as compared to the lateral geniculate and retinal units. The mechanisms of receptive field formation in the visual cortex and their plasticity depending on the adaptation level, the role of excitatory and inhibitory inputs in these effects and behavioral significance of the obtained data are discussed.

Animals↗
PubMed1985

Increased dependence of superior colliculus metabolic activity on visual cortex after eye enucleation.

Metabolic activity, as previously shown by the 2-deoxy-D-[14C]glucose technique, is depressed in the superior colliculus after eye enucleation and recovers substantially by 30 days. To determine whether or not this recovery involves an increase in visual cortex control over superior colliculus metabolic activity, rats that had undergone either monocular or binocular enucleation 30 days earlier received visual cortex ablations. In the monocularly enucleated group, a bilateral visual cortex lesion produced greater depression in the recovered superior colliculus than in the opposite control colliculus, and increased the metabolic differences between the two colliculi compared with those of rats recovered from monocular enucleation but cortically intact. In the binocularly enucleated group a unilateral cortex lesion produced greater ipsilateral depression than did the same ablation in the otherwise intact rat. These findings led to the conclusion that the recovery in the superior colliculus that follows eye enucleation involved an increase in cortical control over metabolic activity.

Animals↗
PubMed1989

The callosal projection in cat visual cortex as revealed by a combination of retrograde tracing and intracellular injection.

The neuronal composition of callosally projecting cells in cat visual cortex was determined with a combination of retrograde labelling and intracellular injection. Fluorescent tracers were stereotaxically injected into the proximity of the area 17/18 border, corresponding to the representation of the visual vertical meridian. In fixed slice preparations of homotopic regions of the contralateral hemisphere retrogradely labelled cells were filled with Lucifer Yellow. Of more than a hundred injected cells a morphological variety of pyramidal cells, located in cortical layers II-IV and VI, constituted the prevalent cell class in the contralateral projection. A minor proportion of spiny stellate cells was encountered in layer IV. Despite the presence of a contralaterally projecting smooth stellate cell, presumed to be a basket cell, it is concluded that the efferents to contralateral visual cortex predominantly arise from pyramidal and spiny stellate cells. Thus, in agreement with findings from anterograde degeneration studies, the interhemispheric pathway most likely conveys a direct excitatory input to postsynaptic target cells.

Animals↗
PubMed1993

[Experimental study of the characteristics of c-fos genetic expression in the neurons of visual cortex area 17 in amblyopic cats].

After the experimental kitten eyes were exposed to stimulation by the moving sinusoidal grating, the fos proteins, products of c-fos genetic expression in the nuclei of excited neurons in layer IV of the visual cortex area 17, were stained with the immunocytochemical ABC technique. The changes in number and grey scale of the c-fos immunopositive neurons of normal, monocular strabismic and monocular deprived eyes were processed by the computer image analysis system. The results indicated that (1) the PVEP of amblyopic cats was consistent with the dysplasia of visual cortex; and (2) the pathophysiologic defects in visual cortex of the amblyopic cats did have a molecular chemoneurological basis.

Amblyopia↗
PubMed1985

Neurogenesis of the cat's primary visual cortex.

The 3H-thymidine method of birth-dating was used to determine when the cells belonging to each of the principal cellular layers of the cat's primary visual cortex are generated. In order to detect systematic differences in the position of radioactively labeled cells following 3H-thymidine administration at different prenatal ages, a geometric method was devised to represent the distribution of labeled cells in the form of depth histograms. Results show that visual cortical neurogenesis occurs largely during the second half of gestation between embryonic day 31 (E31) and E57. Cells of layer 6 are generated early, between E31 and E38, whereas cells destined for successively more superficial layers are generated at progressively later times. Layer 4 cells, the principal targets of geniculocortical afferents, are generated between E37 and E44. In addition, a special population of cells embedded in the white matter below layer 6 was found to be produced throughout the week-long period immediately prior to the onset of layer 6 neurogenesis. Overall, this radial pattern of cortical neurogenesis closely resembles the inside-first, outside-last, spatiotemporal sequence of development described for the monkey's primary visual cortex (Rakic, '74). In addition to finding this pronounced gradient in the radial dimension, we were also able to detect a less pronounced gradient along the tangential dimension: neurons destined for any given layer in the anterior part of the cortex (inferior visual field representation) are generated slightly in advance of neurons destined for more posterior regions (superior visual field). However even our more quantitative histogram analysis failed to reveal a mediolateral (central to peripheral visual field) gradient within area 17. In the cat, layers 6, 5, and 4 each take about a week to be generated, although their total cell numbers and packing densities differ in the adult. About 2 weeks are required to produce the cells of layers 2 and 3 combined. Furthermore, we found that neurons belonging to different layers and different morphological classes can be generated simultaneously. This suggests that the identity of a cortical neuron is not solely a function of the time of neurogenesis.

Age Factors↗
PubMed1997

Brain energy metabolism in early blind subjects: neural activity in the visual cortex.

As an attempt to better understand the metabolic basis for the previously reported increases in glucose metabolism in the visual cortex of congenitally blind subjects, cerebral blood flow, oxygen consumption and glucose utilization were investigated with multitracer positron emission tomography. Measurements were carried out in three subjects who became blind early in life and in three age-matched blindfolded controls. Regional analysis of cerebral blood flow, metabolic rates for oxygen and glucose utilization revealed that these parameters were relatively higher in the visual cortex in case of early blindness (109.7 +/- 2.4%; 114.3 +/- 1.5%; 118.0 +/- 5.5%, respectively) than in controls (98.1 +/- 3.9%; 108.6 +/- 3.6%; 105.2 +/- 4.8%). There were slight differences, albeit statistically not significant, between early blind and control subjects in terms of oxygen-to-glucose metabolic ratios. The relatively preserved stoichiometry in the visual areas of blind subjects points to the lack of variation in the yield of glucose oxidation in this cortex. Those observations suggest that the high level of energy metabolism disclosed in early blind visual cortex is related to neural activity.

Adult↗
PubMed1988

Synaptic organization of serotonin-immunoreactive fibers in primary visual cortex of the macaque monkey.

The macaque neocortex is very densely innervated by serotonin-containing fibers. The highest density of these fibers is in primary sensory regions such as the primary visual cortex. By using an antibody against serotonin, we analyzed the distribution and morphology of serotonin-immunoreactive fibers and synapses in the primary visual cortex of the adult cynomolgus monkey. In addition, we quantified the laminar distribution of labeled varicosities and the distances between varicosities in single fibers. While serotonin-immunoreactive fibers are found in all cortical layers, at least three bands of heightened density of innervation were readily recognized that were coincident with 1) layer IIIB to IVC alpha, 2) layer VA, and 3) layer VIB. Layer IVC alpha of area 17 contained more varicosities per unit area than any other sublayer. There was a high degree of variability in the intervaricosity distances along single fibers; more than half were longer than 10 microns. At the electron microscopic level, synaptic contacts were also observed throughout the entire thickness of area 17, with the highest frequency in layer IV. The labeled varicosities were packed with electron-lucent synaptic vesicles and formed synaptic complexes with small, but conspicuous, post-synaptic densities. Dendritic shafts were the most common postsynaptic target of the labeled synapses. Among these characteristically slender post-synaptic shafts, profiles with structural features of both spiny and smooth dendrites were observed. The small diameter of most of the postsynaptic dendrites indicated that distal dendrites were preferentially contacted by serotonin-immunoreactive varicosities. Although direct identification of the postsynaptic neurons will be required for complete characterization of this circuitry, the distribution of serotonin-immunoreactive varicosities suggests that serotoninergic interactions in the primary visual cortex of the cynomolgus monkey are directed predominantly at the distal dendrites of granular and infragranular neurons rather than at targets in the supragranular layers.

Animals↗
PubMed1981

Short- and long-term effects of neonatal and adult visual cortex lesions on the retinal projection to the pulvinar in cats.

An increased retinal projection to th pulvinar occurred in cats following neonatal ablation of visual cortical areas 17, 18, and 19. After unilateral lesions, the retinopulvinar projection visualized with autoradiography was larger and denser on the lesioned side than on the intact side. This increased projection was first recognized when the lesioned kittens were 1 week old, when increased labeling in the pulvinar was first detected. The retinopulvinar projection on the intact side of the brain decreased in size with age over the first 3 months of life. This decrease in size was not observed on the lesioned side of the brain. The absence of this decrease on the lesioned side may represent a failure of retraction of exuberant connections, but because of the active invasion by retinal fibers immediately after the lesion, observations of the normal retraction may simply be obscured. Severe cellular degeneration in the dorsal lateral geniculate occurred a few days before the changes in the retinopulvinar projection began; this loss of a postsynaptic target for many retinal axons may trigger the reorganization of input to the pulvinar retino-recipient zone (pulivnar-RRZ). After adult visual cortex lesions, no reorganization of the retinopulvinar projection took place. The modification of the projection from the retina to the pulvinar that occurs after ablation of visual cortex in the newborn cat may contribute to the sparing of visual abilities seen after these lesions.

Aging↗
PubMed1993

Single neurons are differently involved in stimulus-specific oscillations in cat visual cortex.

Synchronised oscillatory population events (35-80 Hz; 60-300 ms) can be induced in the visual cortex of cats by specific visual stimulation. The oscillatory events are most prominent in local slow wave field potentials (LFP) and multiple unit spikes (MUA). We investigated how and when single cortical neurons are involved in such oscillatory population events. Simultaneous recordings of single cell spikes, LFP and MUA were made with up to seven microelectrodes. Three states of single cell participation in oscillations were distinguished in spike triggered averages of LFP or MUA from the same electrode: (1) Rhythmic states were characterised by the presence of rhythmicity in single cell spike patterns (35-80 Hz). These rhythms were correlated with LFP and MUA oscillations. (2) Lock-in states lacked rhythmic components in single cell spike patterns, while spikes were phase-coupled with LFP or MUA oscillations. (3) During non-participation states LFP or MUA oscillations were present, but single cell spike trains were neither rhythmic nor phase coupled to these oscillations. Stimulus manipulations (from "optimal" to "suboptimal" for the generation of oscillations) often led to systematic transitions between these states (from rhythmic to lock-in to non-participation). Single cell spike coupling was generally associated with negative peaks in LFP oscillations, irrespective of the cortical separation of single cell and population signals (0-6 mm). Our results suggest that oscillatory cortical population activities are not only supported by local and distant neurons with rhythmic spike patterns, but also by those with irregular patterns in which some spikes occur phase-locked to oscillatory events.

Animals↗
PubMed2005

Laminar organization of response properties in primary visual cortex of the gray squirrel (Sciurus carolinensis).

The gray squirrel (Sciurus carolinensis) is a diurnal highly visual rodent with a cone-rich retina. To determine which features of visual cortex are common to highly visual mammals and which are restricted to non-rodent species, we studied the laminar organization of response properties in primary visual area V1 of isoflurane-anesthetized squirrels using extra-cellular single-unit recording and sinusoidal grating stimuli. Of the responsive cells, 75% were tuned for orientation. Only 10% were directionally selective, almost all in layer 6, a layer receiving direct input from the dorsal lateral geniculate nucleus (LGN). Cone opponency was widespread but almost absent from layer 6. Median optimal spatial frequency tuning was 0.21 cycles/ degrees . Median optimal temporal frequency a high 5.3 Hz. Layer 4 had the highest percentage of simple cells and shortest latency (26 ms). Layers 2/3 had the lowest spontaneous activity and highest temporal frequency tuning. Layer 5 had the broadest spatial frequency tuning and most spontaneous activity. At the layer 4/5 border were sustained cells with high cone opponency. Simple cells, determined by modulation to drifting sinusoidal gratings, responded with shorter latencies, were more selective for orientation and direction, and were tuned to lower spatial frequencies. A comparison with other mammals shows that although the laminar organization of orientation selectivity is variable, the cortical input layers contain more linear cells in most mammals. Nocturnal mammals appear to have more orientation-selective neurons in V1 than diurnal mammals of similar size.

Animals↗
PubMed1991

Developmental gradients of vasoactive intestinal polypeptide (VIP)-containing neurons in the rat visual cortex detected by image analysis.

The postnatal development of vasoactive intestinal polypeptide-immunoreactive (VIP-IR) neurons was followed by computer-assisted image analysis in the rat visual cortex. The laminar distribution of all VIP-IR structures was measured. These structures were subdivided into cell somata, dendritic profiles and axonal boutons and measured separately. VIP-IR neurons were first seen on postnatal day 1, mostly in the upper half of the presumptive visual cortex. A localization of cell bodies similar to that in the adult is reached between days 12 and 16. VIP-IR dendrites have a protracted growth period as compared to perikarya, involving a developmental gradient from an even distribution to a concentration in the upper cortical layers. This is due to the formation of dendritic terminal arbors after the second postnatal week. Scattered VIP-IT axonal boutons appear on day 3 in the midportion of the presumptive visual cortex. Their typical laminar distribution in layers II, IV and lower VI was observed after day 12. Our results suggest that the biochemically detected sharp increase in VIP levels after the second postnatal week is due to the maturation of cell processes as a morphological basis of neuronal connectivity.

Aging↗
PubMed1995

Magnification factors, receptive field images and point-image size in the superior colliculus of flying foxes: comparison with the primary visual cortex.

The magnification factor (MF) of the stratum griseum superficiale (SGS) of the superior colliculus (SC) was calculated based on visual receptive fields recorded from anaesthetised and paralysed flying foxes (Pteropus spp.). In areal terms, the MF at the representation of central vision was 4-6 times larger than that in the peripheral representation. This variation is less marked than that observed in the primary visual area (V1), but is roughly that expected if the retinotopic map in the SC was defined by the distribution of ganglion cells in the retina. Two measures of the functional spread of activity in the SC, the receptive field images and the point-image size, were calculated. Receptive field images are remarkably similar throughout the SC. As in V1, the point-image size in the SGS of flying foxes is 0.5-0.6 mm and varies little with eccentricity. Bilateral ablation of the visual cortex results in a reduction of the mean receptive field size of neurones in the SGS, and the point-image size is reduced by half. However, the shape of the point-image function is not affected. These results demonstrate that the spread of activity in the SC is nearly constant throughout the retinotopic map and that this is primarily a result of the direct retinal projection. Although the visual cortex has an expanded central representation in comparison with the SC, the corticotectal pathway does not exert a preferential influence on the central representation of the SC.

Anesthesia↗
PubMedDate not supplied

[Effect of light deprivation on enzymic activity of synaptosomes and mitochondria of rabbit cortex visual region].

The specific activity of markers-enzymes in the subcellular fractions of the rabbit visual analyzer cortical end, the synaptosomes and mitochondria of nerve cells, changed under the effect of early long deprivation. For cytochromoxidase and Na+, K+-ATPase it lowers considerably in all subfractions, for monoaminoxidase and Mg2+-ATPase it rises mainly in synaptosomes; the activity of acetyl cholinesterase lowers per 1 g of tissue. In the light two weeks later a tendency is observed to normalization of the studied indexes. The specific activity of cytochrome oxidase (except for free mitochondria) and Na+, K+-ATPase reaches the control, that of monoaminoxidase also partially normalizes, but not competely; Mg2+ATPase in all the subfractions is more inhibited than in the control. This evidences for the effect of light deprivation on the activity of the enzymes associated with different cycles of metabolic processes, first of all, of oxidation and ion transport. These changes are reversible when visual impulsation is recovered. Disturbances in chemism at the subcellular level are specific for different enzymic systems and are not the same in certain subfractions of great hemispheres.

Acetylcholinesterase↗