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PubMed1985

[Types of neurons in the visual cortex of the rat, identified in Nissl- and deimpregnated Golgi preparations].

Neuronal types of the rat's visual cortex were identified in Nissl stained and deimpregnated Golgi sections (rapid Golgi method modified by Fairén et al. 1977, Golgi-Bubenaite, Golgi-Kopsch and modified by Braitenberg; deimpregnation after FAIREN et al. 1977 and Braak and Braak 1982, respectively). Cytoplasm and nucleus become visible in deimpregnated neurons and can then be counter-stained with methylene blue or toluidin blue. Somal and nuclear features of Nissl stained and deimpregnated neurons were compared. Provided that these features as well as the specific localization, the relative size and the shape of the soma agree the neurons are identical. We could find that the following neuronal types are identical in Golgi and Nissl stained sections: pyramidal cells of layers II-VI, pyramid-like neurons of layers VI and VII (VIa, b, c) (type C, Werner et al. 1982), multiangular neurons of layer I (type A, Werner et al. 1982), spiny stellate cells of layer IV, sparsely spined neurons with ascending axons (Martinotti cells) (type H, Werner et al. 1982), large and medium-sized spine-free, multipolar neurons (basket cells) (type B, Werner et al. 1982). Bipolar neurons and chandelier cells are identical with neurons poor in cytoplasm (types E, F, G, Werner et al. 1982). Until today two neuronal types could not be identified: type D of L I (Werner et al. 1982) and small, sparsely-spined neurons of layer IV with variable axons (Hedlich and Winkelmann 1982; Hedlich et al. 1984). Characteristics of somata, dendrites and axons of neurons identified in this paper are summarized in table 1. In most cases, these findings confirm earlier suppositions concerning the identity of neuronal types of the rat's visual cortex in Golgi and Nissl stained sections (Werner et al. 1979) and verify the values of their frequency and distribution pattern (Werner et al. 1982).

Animals↗
PubMed1993

Changes of synaptic density in the primary visual cortex of the macaque monkey from fetal to adult stage.

The kinetics of synaptogenesis in the primary visual cortex (Brodmann's area 17) were analyzed by electron microscopy in 33 rhesus monkeys, ranging in age from the 50th embryonic day (E50) to 20 years. A series of overlapping electron micrographs (vertical probes) were examined at each age on sections of the upper bank of the calcarine fissure. Synaptic contacts were first observed in the E50 specimen in the subplate and marginal zone (prospective layer I). In the cortical plate itself, synapses appear between E65 and E89 starting in the prospective layer VI. By E112, after all cortical neurons have assumed their laminar positions, synapses situated predominantly on dendritic shafts were present at a low density throughout the full thickness of the cortical plate. Thereafter, synapses accumulate more rapidly on dendritic spines and by E144 an equal number of contacts are found on both spines and shafts. The density of synapses continues to increase exponentially in all layers and reaches the mean maximum density of about 90 synapses per 100 microns 3 of neuropil by the third postnatal month. During the next 2 postnatal years the density of synaptic contacts decreases only slightly to a mean of 80/100 microns 3 of neuropil. Around the time of puberty, however, synaptic density decreases more rapidly to reach the adult level of about 40-50/100 microns 3 of neuropil. The 40% decrease in the density of synaptic contacts occurring between 2.7 and 5 years represents a loss of about 5000 synapses per second in the primary visual cortex of the two hemispheres, due primarily to the loss of asymmetric synapses situated on dendritic spines. The transient phase of high density of synaptic contacts located on dendrospines is shorter in thalamo-recipient layer IV than in either supra- or intragranular layers and is completed within the first postnatal year. It ends earlier in sublayer IVC than in layers IVAB and II-III, for example, reflecting biochemical and functional maturation of the different visual subsystems.

Aging↗
PubMedDate not supplied

[Functional maturation of the cat visual cortex during prenatal ontogenesis].

Development of the perceiving function of the visual cortex was studied on the foeti of cats in the second stage of antenatal development with intact placental blood circulation. It has been found that functional maturing of the cortical end of the visual analyser starts at the beginning of the second half of antenatal life. At this period EPs to stimulation of the optic nerve are recorded throughout the dorsal cortex of the contralateral hemisphere. At first they appear as slow three-phase (positive-negative-positive) oscillations of a small amplitude. As the foetus develops, the EP amplitude increases, and the EP configuration in the striate zone of the cortex becomes complex. Two weaks before birth, a short-latency negative wave appears against the background of the primary positive oscillation. In the last week of antenatal development of the foeti and in the first few days of the kittens life, EPs are represented in the specific zone of the visual cortex (g. lateralis) as two negative oscillations, and in the so-called associative zone (the middle part of the suprasylvian gyrus) by one long-latency high-amplitude negative oscillation which corresponds by latency to the second negative EP component in the striate cortex.

Animals↗
PubMed2000

Neuronal activity in human primary visual cortex correlates with perception during binocular rivalry.

During binocular rivalry, two incompatible monocular images compete for perceptual dominance, with one pattern temporarily suppressed from conscious awareness. We measured fMRI signals in early visual cortex while subjects viewed rival dichoptic images of two different contrasts; the contrast difference served as a 'tag' for the neuronal representations of the two monocular images. Activity in primary visual cortex (V1) increased when subjects perceived the higher contrast pattern and decreased when subjects perceived the lower contrast pattern. These fluctuations in V1 activity during rivalry were about 55% as large as those evoked by alternately presenting the two monocular images without rivalry. The rivalry-related fluctuations in V1 activity were roughly equal to those observed in other visual areas (V2, V3, V3a and V4v). These results challenge the view that the neuronal mechanisms responsible for binocular rivalry occur primarily in later visual areas.

Algorithms↗
PubMed1994

Non-linear dynamics of columns of cat visual cortex revealed by simulation and experiment.

Correlation images were derived from simultaneous recordings of 12 signals representing the synaptic activity at different layers of a column in cat visual cortex (area 18) and 12 signals representing the local average spiking activity at the same locations. Because the ongoing activity and the activity evoked by stroboscopic flashes yielded the same correlation image, ongoing activity is caused by an input to a column similar to flash-evoked activity and is thus not endogenous. Moving bar stimuli evoked bursts of oscillations (25-75 Hz band) in the correlation image. The rhythm of these oscillations was not related to any frequency component in the stimulus. In all correlation images we observed that synaptic activity in one layer resulted in simultaneous spiking activity in all layers with latency differences smaller than 2 ms (the sample interval used). Similar behaviour was observed in a simulation experiment where we 'realistically' modelled one column of visual cortex with 1000 three-compartmental neurons in 11 functional layers. When such a model column was tuned to yield a stable and excitable system with low ongoing activity, activation of any of the layers caused simultaneous activity in all 11 layers. Both the simulation and the experimental results suggest that a column can be regarded as a basic processing element sending the same information over all its outputs to other columns within the same cortical region, other visual areas and subcortical structures.

Animals↗
PubMed2003

Figure-ground activity in primary visual cortex (V1) of the monkey matches the speed of behavioral response.

To look at an object its position in the visual scene has to be localized and subsequently appropriate oculo-motor behavior needs to be initiated. This kind of behavior is largely controlled by the cortical executive system, such as the frontal eye field. In this report, we analyzed neural activity in the visual cortex in relation to oculo-motor behavior. We show that in a figure-ground detection task, the strength of late modulated activity in the primary visual cortex correlates with the saccade latency. We propose that this may indicate that the variability of reaction times in the detection of a visual stimulus is reflected in low-level visual areas as well as in high-level areas.

Animals↗
PubMed1992

Critical period for monocular deprivation in the cat visual cortex.

1. Cats were monocularly deprived for 3 mo starting at 8-9 mo, 12 mo, 15 mo, and several years of age. Single cells were recorded in both visual cortexes of each cat, and the ocular dominance and layer determined for each cell. Ocular dominance histograms were then constructed for layers II/III, IV, and V/VI for each group of animals. 2. There was a statistically significant shift in the ocular dominance for cells in layers II/III and V/VI for the animals deprived between 8-9 and 11-12 mo of age. There was a small but not statistically significant shift for cells in layer IV from the animals deprived between 8-9 and 11-12 mo of age, and for cells in layers V/VI from the animals deprived between 15 and 18 mo of age. There was no noticeable shift in ocular dominance for any other layers in any other group of animals. 3. We conclude that the critical period for monocular deprivation is finally over at approximately 1 yr of age for extragranular layers (layers II, III, V, and VI) in visual cortex of the cat.

Aging↗
PubMed2006

Cellular and subcellular localization of alpha-1 adrenoceptors in the rat visual cortex.

Noradrenaline is thought to play modulatory roles in a number of physiological, behavioral, and cellular processes. Although many of these modulatory effects are mediated through alpha-1 adrenoceptors, basic knowledge of the cellular and subcellular distributions of these receptors is limited. We investigated the laminar distribution pattern of alpha-1 adrenoceptors in rat visual cortex, using immunohistochemistry at both light and electron microscopic levels. Affinity-purified anti-alpha-1 antibody was confirmed to react only with a single band of about 70-80 kDa in total proteins prepared from rat visual cortex. Alpha-1 adrenoceptors were widely distributed though all cortical layers, but relatively high in density in layers I, II/III, and V. Immunoreactivity was observed in both neuronal perikarya and processes including apical dendrites. In double-labeling experiments with anti-microtubule-associated protein 2, anti-neurofilament, anti-glial fibrillary acidic protein, anti-glutamic acid decarboxylase 65/67, anti-2-3-cyclic nucleotide 3-phosphodiesterase, and anti-tyrosine hydroxylase antibodies, alpha-1 adrenoceptors were found mainly in dendrites and somata of microtubule-associated protein 2-immunopositive neurons. About 20% of alpha-1 adrenoceptors were in GABAergic neurons. A small number of alpha-1 adrenoceptors were also distributed in axons of excitatory neurons, astrocytes, oligodendrocytes and noradrenergic fibers. Using an immunoelectron microscopic technique, numerous regions of alpha-1 adrenoceptor immunoreactivity were found in cell somata, on membranes of dendrites, and in postsynaptic regions. Moreover, a small number of immunoreaction products were also detected in axons and presynaptic sites. These findings provide the first quantitative evidence regarding the cellular and subcellular localization of alpha-1 adrenoceptor immunoreactivity in visual cortex. Moreover, the ultrastructural distribution of alpha-1 adrenoceptor immunoreactivity suggests that alpha-1 adrenoceptors are transported mainly into dendrites and that they exert effects at postsynaptic sites of neurons.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1994

Long-range horizontal connections between supragranular pyramidal cells in the extrastriate visual cortex of the rat.

In this study, we examined the morphological structure and synaptic physiology of long-range axon projections among supragranular pyramidal cells in the extrastriate visual cortex of the rat. Intra- and extracellular recordings from layer II/III pyramidal cells were performed in brain slices of area 18a following extracellular stimulation of either the underlying white matter or within layer II/III. Neurons were injected with biocytin for two-dimensional reconstruction of their axon arborizations. The conduction velocity of afferent fibers (0.58 m/s) was twice as high as that of intracortical tangential fibers (0.28 m/s). Layer II/III cells were mainly di- or polysynaptically driven by afferent activation, but predominantly monosynaptically driven from intracortical stimulation sites. The afferent as well as intracortically evoked postsynaptic potentials showed a very similar time course and shape. From both stimulation sites, suprathreshold action potentials could be elicited. The current threshold for a postsynaptic response and the slope and width of excitatory postsynaptic potentials (EPSPs) increased with the distance of lateral stimulation. The morphological properties of layer II/III pyramidal cell axon collaterals closely corresponded to the electrophysiological results. Long-range intraareal axon collaterals could be followed up to 1 mm within the supragranular layers. Their length-distance distribution showed an inverse relationship to the threshold currents of EPSPs. Pyramidal cells exhibited regularly spaced patches of horizontal axon collaterals with an interpatch distance of about 250 microns. We concluded that the supragranular horizontal network in the extrastriate visual cortex of the rat is qualitatively very similar to that of cats and monkeys. However, quantitative differences exist in its spatial extent and physiological characteristics.

Animals↗
PubMed1987

Importance of the visual cortex for postural stabilization: inferences from pigeon and frog data.

Optokinetically induced self-motion with its consequences for postural balance is based upon visual-vestibular convergence. It is a matter for speculation which visual pathways--subcortical accessory optic tract and/or cortical striate projection--convey optokinetic information to the central vestibular system. The functional significance of the visual cortex was tested by a behavioral approach in two animals, selected for their different evolutionary stage: frog (midbrain visual center); pigeon (primitive neocortical center). Lateral postural sway during optokinetic stimulation in roll served as a measurement for induced rollvection and apparent body tilt. Roll motion elicits a tonic 'compensatory' postural adjustment towards the direction of pattern motion in pigeon as in man but not in frog. From the lack of this reaction we infer that the frog does not perceive rollvection because it has no visual cortex. This agrees with the absence of visual-vestibular convergence in the frogs vestibular nuclei neurons as well as the absence of a nystagmus velocity storage in the brainstem. The animal experiments fit human data in hemianopic patients who also only experience rollvection when stimulated in the unaffected hemifield.

Animals↗
PubMed1988

Pharmacological induction of use-dependent receptive field modifications in the visual cortex.

Lasting modifications of the receptive fields of neurons in the visual cortex can be induced by pairing visual stimuli with iontophoretic application of the neuromodulators acetylcholine and noradrenaline or the excitatory amino acids N-methyl-D-aspartate (NMDA) and L-glutamate. The modifications are obtained in less than 1 hour and persist for more than 40 minutes. Thus, acetylcholine and norepinephrine have a permissive role in use-dependent neuronal plasticity. These results support the notion of a postsynaptic threshold for neuronal malleability that differs from that of sodium-dependent action potentials.

Acetylcholine↗
PubMed1986

The laminar distributions and postnatal development of neurotransmitter and neuromodulator receptors in cat visual cortex.

We review efforts to further understand the development and nature of sensory processing mechanisms in the cat visual cortex. In vitro autoradiographic and homogenate assay techniques have been employed to determine the laminar distribution and characteristics of various neurotransmitter and neuromodulator receptor populations during postnatal development. Each receptor population shows a distinct laminar-specific pattern of binding, which, in most cases, is age-dependent. Changes in receptor number and affinity are also observed during postnatal development. These findings indicate that major alterations in the basic chemical circuitry of cat visual cortex are a normal feature of postnatal maturation and may play a role in plasticity mechanisms.

Aging↗
PubMed1996

Tissue compartments in laminae II-V of rabbit visual cortex--three-dimensional arrangement, size and developmental changes.

The neuropil in laminae II/III and IV of the mature rabbit visual cortex is subdivided into (a) dendrite bundles consisting of apical dendrites of pyramidal cells and associated axons and glial processes, (b) bundles of myelinated axons ascending vertically from the white matter up to lamina IV and (c) neuropil between bundles comprising mainly thin unmyelinated axons, small dendrites and associated glial processes. In this investigation the three-dimensional structure of these compartments was analysed. In addition, the volume fractions of the three neuropil compartments, perikarya and blood vessels in the different laminae and their quantitative changes from the late fetal period up to young adulthood and in a group of aged animals were determined. Serial 1-micron epoxy sections were analysed. Dendrite bundles are more numerous and more intensively intertwined in lamina II/III than in lamina IV. At 28 days after conception the tissue in laminae II-V consists of approximately equal amounts, i.e. between 40 and 50%, of perikarya and neuropil. The volume fraction of blood vessels is about 4% and does not change much during development. During the first 16 days after birth the volume fraction of the neuropil increases to more than 70%, and conversely the volume fraction of nerve cells decreases to about 20%. Later, significant changes are seen only when the volume fractions of the three neuropil compartments are considered separately. The volume fraction of the neuropil between bundles increases throughout all laminae investigated, whereas the volume fraction of dendrite bundles is found to decrease. After 1 month, in lamina IV further increase of the neuropil between bundles is less marked, because here the bundles of myelinated axons become visible as an additional compartment. In young adult animals, the volume fractions of dendrite bundles are about 28% in the upper half, 16% in the lower half of lamina II/III and 7% in lamina IV. The neuropil between bundles comprises about 52% in the upper half, 65% in the lower half of lamina II/III and 62% in lamina IV. In lamina IV 14% is occupied by bundles of myelinated axons. In aged animals, the volume fraction of the neuropil between bundles decreases significantly in all laminae investigated. From previous ultrastructural studies, the extracellular space is known to be about 30% larger in the neuropil between bundles than in the dendrite bundles. Moreover, due to the prevalence of thin cell processes, the degree of tortuosity is larger in the neuropil between bundles than in the dendrite bundles. The present results together with these previous data are an indication of lamina-specific differences in the structure of the extracellular space. This may help to explain the electrical conductivity in the respective laminae of the cerebral cortex. The time course of postnatal changes of the neuropil compartments coincides with fundamental steps of structural and functional maturation of the rabbit visual cortex that are documented in the literature, and thus may be a valid parameter to investigate the degree of maturation or aging by morphological means.

Aging↗
PubMed1993

Monocular deprivation effects in the rat visual cortex and lateral geniculate nucleus are prevented by nerve growth factor (NGF). II. Lateral geniculate nucleus.

In the preceding paper (Berardi et al. Proc. R. Soc. Lond. B 251, 17 (1993)), it has been shown that nerve growth factor (NGF) prevents the functional and anatomical alterations induced by monocular deprivation (MD) at the level of the visual cortex. Here we report that an exogenous supply of NGF prevents the shrinkage of neurons in the deprived laminae of lateral geniculate nucleus (LGN). The soma size distribution for the deprived ipsilateral laminae of MD rats is shifted towards smaller sizes (mean percentage of shrinkage with respect to the ipsilateral undeprived lamina = 21%, s.d. = 2%). As in other mammals, MD affects LGN relay neurons and spares LGN neurons projecting to the monocular portion of primary visual cortex. In NGF-treated animals we found that the soma size distributions for the deprived and undeprived ipsilateral laminae extensively overlap. The results of the two papers show that an exogenous supply of NGF prevents MD effects at both levels, visual cortex and LGN, and suggest a role for NGF in the plasticity of the geniculo-cortical pathway.

Animals↗
PubMed1983

A quantitative study of visual cortex synapses during the postnatal development of dark-reared rats.

The method of Aghajanian and Bloom (1967) was applied to the visual cortex of normal and neonatally visually deprived rats. The rats were kept with their mothers in total darkness since birth, in a ventilated and temperature-controlled animal quarter. Controls were rats from the same stock, maintained in a regular 12-h-light/12-h-dark rhythm. The animals were killed at 15, 23, 40, and 65 days of age, and the visual cortices fixed in 4% glutaraldehyde and processed for electron micrography with ethanol-phosphotungstic acid. A total of 6249 synaptic profiles were counted and their numerical density (DS) determined in both conditions. Features of the presynaptic grid were used for classifying the synaptic profiles in: type A [with one presynaptic dense projection (PsDP)]; type B (with two or three PsDPS); and type C (with four or more PsDPS). In the visually deprived rats the DS increases with a rate similar to controls, but the values for each age are slightly lower (P less than 0.01). Type B synapses predominate in the visually deprived group while types A and C are scarcer. The differences found between types were maximal at 65 days of age and the results were highly significant (P less than 0.001). It is concluded that major effects of dark-rearing are manifested when the individual features of the presynaptic grid are considered. It seems that a selected population of synapses is affected by the alteration of the normal epigenetic influence of early visual experience.

Animals↗
PubMed2002

Rapid eye movement sleep deprivation modifies expression of long-term potentiation in visual cortex of immature rats.

During rapid eye movement (REM) sleep, activity of non-retinal origin is propagated into central visual-system pathways in a manner similar, in pattern and intensity, to central visual-system activity that is exogenously generated in waking. It has been hypothesized that REM sleep, which is more abundantly represented early in life than later, functions to provide adjunct 'afferent' input for shaping synaptic connectivity during brain maturation. Here we present data that support this proposal. Recent studies have described a developmentally regulated form of in vitro long-term potentiation (LTP) in the visual cortex that is experience- and age-dependent. In immature rats, suppression of retinal activation of the visual system by removal of visual experience (dark rearing) extends the age when the developmentally regulated form of LTP can be produced. This study tests whether suppression of REM-state activation of the visual system also lengthens the developmental period in which this specific form of LTP can be elicited. Young rats were deprived of REM sleep by the multiple-small-platforms-over-water method during the typically latest week for induction of such LTP in slices of visual cortex. After this week, we could still induce LTP in slices from nearly all the REM-sleep-deprived rats (8/9) but not from age-matched rats that had not lost REM sleep (0/5). The control rats had been housed on large platforms that allow the animals to obtain REM sleep. Only body weights and the concentration of thyrotrophin-releasing hormone in the hypothalamus distinguished home-caged, normal-sleeping controls from both groups of platform animals. On all measures, stress levels were not dissimilar in the two platforms groups. After 7 days of behavioral suppression of REM sleep in immature rats, and consequent reduction of the intense, extra-retinal activity endogenously generated during this sleep state, we found that the period was extended in which developmentally regulated synaptic plasticity (LTP) could be elicited in slices of visual neocortex. These studies support the role of REM sleep and its associated neuronal activity in brain maturation.

Aging↗
PubMed1979

Anatomical organization of the primary visual cortex (area 17) of the cat. A comparison with area 17 of the macaque monkey.

Golgi and axonal transport techniques have been used to examine the organization of neurons within primary visual cortex, area 17, of the cat. This organization has been compared to that of the primate cortical area 17 as described in previous studies and it is discussed in relationship to the distribution of afferents from the dorsal lateral geniculate nucleus (dLGN). The visual cortex of the cat and monkey show strong similarities in the laminar positions of neurons projecting extrinsically and also in the restriction of spiny stellate neurons to a central lamina (lamina 4) receiving input from the dLGN. However, lamina 4B in the monkey, which contains spiny stellate neurons but does not receive direct input from the dLGN, has no direct counterpart in cat area 17. Axon projections of spiny stellate neurons in the other divisions of lamina 4 differ in cat and monkey: the small, closely packed neurons in the lowermost division of lamina 4 (4B in the cat, 4Cbeta in the monkey) project chiefly within lamina 4 in the cat whereas in the monkey they have a strong projection to lamina 3. In the cat, spiny stellate neurons of lamina 4A project upon lamina 3 whereas in the monkey those in the apparently equivalent zone, 4Calpha, project upon lamina 4B. Most non-spiny stellate neurons examined have precisely organized interlaminar axonal projections which differ from the axon trajectories of neighboring spiny neurons.

Animals↗