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PubMed1985

Effects of intraocular tetrodotoxin on dendritic spines in the developing rat visual cortex: a Golgi analysis.

The effect of tetrodotoxin (TTX)-induced monocular impulse blockade on the growth of dendritic spines in the developing rat primary visual cortex was analysed by quantitative Golgi techniques. Between 5 and 21 days postnatal (dpn), rats were injected with TTX every 2 days into the right eye to chronically eliminate optic impulses. Effectiveness of TTX was monitored by loss of the pupillary light reflex. At 21 dpn, the number of spines located on the portion of the apical dendrite within layers III, IV and the superficial region of layer V was reduced by approximately 26%. These decreases were found on the apical dendrites of both large and medium sized pyramidal cells. TTX also reduced the number of spines on the proximal portion of oblique dendrites in layer IV by 16%, yet did not change the number of spines on basilar dendrites. No evidence of transneuronal degeneration was seen following long-term TTX treatment. These data indicate that dendritic spine development in the visual cortex is sensitive to the loss of optic impulses and that the decrease in spine population is principally due to a reduction in spine growth.

Animals↗
PubMed1999

Differential regulation of brain-derived neurotrophic factor messenger RNA cellular expression in the adult rat visual cortex.

In this study, we report a comparative analysis of the distribution of brain-derived neurotrophic factor messenger RNA in the binocular primary visual cortex of rats analysed at the end of the critical period for monocular deprivation (postnatal day 35) and during adulthood (postnatal day 90). High-resolution non-isotopic in situ hybridization coupled with Nissl staining allowed to determine the relative number of neurons expressing brain-derived neurotrophic factor messenger RNA. In postnatal day 90 rats, the relative number of neurons positive for brain-derived neurotrophic factor messenger RNA significantly decreases in layer II/III with respect to postnatal day 35 animals, being constant in all the other cortical layers. Moreover, we demonstrate that dark rearing for 22 days, starting from postnatal day 90, determines: (i) a decrease of the overall level of brain-derived neurotrophic factor messenger RNA with a consequent reduction of labelling intensity in all cells throughout cortical layers II-VI; (ii) an increase of cell numbers expressing brain-derived neurotrophic factor messenger RNA in layers IV and V; and (iii) a decreased intensity of staining for brain-derived neurotrophic factor messenger RNA in dendrites after dark rearing. A re-exposure to light for 2 h after the period of darkness almost restores the number of brain-derived neurotrophic factor RNA-positive neurons. We conclude that the maturation of brain-derived neurotrophic factor messenger RNA in neurons of layer II/III goes beyond postnatal days 35-40, which can be considered the end of the critical period [Fagiolini M. et al. (1994) Vis. Res., 34, 709-720]. Moreover, we show that the cellular expression of brain-derived neurotrophic factor messenger RNA is regulated by light in adult rats as well as during development.

Animals↗
PubMed1991

[Orientation tuning of the visual cortex neurons in the cat before and after nembutal injection].

In acute experiments on immobilized cats orientation tuning of 40 neurons in the primary visual cortex (field 17) has been studied before and after nembutal injection. It was found that the preferred orientation (PO) of half of neurons remained constant after injection, while another half of neurons revealed a reliable shift of PO (by 53.6 +/- 8.0 degrees on the average) during 1 min-3 hours. Neurons with constant PO preferred horizontal and vertical orientations more often, while neurons with unstable PO had wider distribution of their POs. "Stable" neurons had more narrow and selective orientation tuning before and after narcotization than the "unstable" ones. After injection of nembutal, the width of orientation tuning changed in a half of neurons; this was more often expressed in "unstable" neurons (68%), than in the "stable" ones (38%). After narcotization the mean background discharge frequency decreased 5.5 times on the average in all neurons, while the evoked frequency of discharges--1.5 times.

Animals↗
PubMed1995

Tempo of neurogenesis and synaptogenesis in the primate cingulate mesocortex: comparison with the neocortex.

In the neocortex, the onset of the rapid phase (phase 3) of synaptogenesis occurs after the end of neurogenesis. However, we still do not know whether or not these two developmental events are causally related. The present study compares the time-course and tempo of neurogenesis and synaptogenesis in the anterior cingulate cortex (area 24 of Brodmann) and in the primary visual cortex (area 17) in a series of pre- and postnatal rhesus monkeys. Autoradiographic analysis of animals fetally injected with 3H-thymidine showed that all neurons destined for area 24 are generated by embryonic day 70, which is 30 days earlier than in area 17. The rapid phase of synaptogenesis in area 24 starts during the third embryonic month and continues at the same rate through the remainder of gestation and the first 2 months after birth, as has been seen in neocortical areas examined previously. Statistical analysis of the linear portions of the rapid phase indicates that, although neurogenesis in area 24 is completed 1 month earlier than in area 17, the rapid phase of synaptogenesis occurs 41 days later. Moreover, the tempo of synaptic accretion was remarkably similar to that in motor, somatosensory, visual, or associational areas. All were grouped within the same time window of about 40 days, centered at birth. After the second postnatal month, synaptic density in area 24 remains at a high level until sexual maturity. This work shows that the rapid phase of synaptogenesis in the cingulate mesocortex is not linked temporally to the end of neurogenesis. We suggest that it is regulated by the same genetic or humoral factors that control synaptogenesis in the phylogenetically newer neocortical areas.

Animals↗
PubMed1984

Distribution of the cells of origin of the corpus callosum and anterior commissure in the marmoset monkey.

The neurons of origin of the great cerebral commissures of the marmoset monkey were identified by horseradish peroxidase histochemistry and their distribution was studied. Six adult marmosets were used. Three were normal: the others were subjected to section of the corpus callosum (CC), sparing the anterior commissure (AC). All six were injected with horseradish peroxidase throughout one cerebral hemisphere. The three normals provide information on the origins of both the CC and AC, whereas the three callosotomized monkeys allow study of the origins of the AC alone. All CC and AC neurons in the marmoset are pyramidal cells. Except for layer I, all cortical layers possess commissural cells; their laminar organization varies according to cortical area. There exists a progression in predominance from supra- to infragranular commissural neurons proceeding from temporal through occipital to parietal and finally to frontal cortex. Major acallosal zones are found in the primary visual cortex and the fore- and hindlimb representations of the somatosensory cortex. Correlations between commissural neuron distribution and cytoarchitectonic areas are not always obvious. Commissural neurons were not organized in columnar fashion.

Animals↗
PubMed2003

Braille alexia during visual hallucination in a blind man with selective calcarine atrophy.

The case of a 56-year-old man who has been blind for 25 years due to retinal degeneration is herein described. The patient complained of elementary visual hallucination, during which it was difficult for him to read Braille. Brain magnetic resonance imaging showed marked atrophy of the bilateral striate cortex. Visual hallucination as a release phenomenon of the primary visual cortex has never been reported to cause alexia for Braille. The present case supports the results of recent functional imaging studies of the recruitment of striate and prestriate cortex for Braille reading.

Atrophy↗
PubMed2005

Location coding by the human visual system: multiple topological adaptations in a case of strabismic amblyopia.

Amblyopia, a major cause of vision loss, is a developmental disorder of visual perception commonly associated with strabismus (squint). Although defined by a reduction in visual acuity, severe distortions of perceived visual location are common in strabismic amblyopia. These distortions can help us understand the cortical coding of visual location and its development in normal vision, as well as in amblyopia. The history of retinotopic mapping in the visual cortex highlights the potential impact of amblyopia. Theories of amblyopia include topological disarray of receptors in primary visual cortex, undersampling from the amblyopic eye compared with normal eyes, and the presence of anomalous retinal correspondence or multiple cortical representations of the strabismic fovea. We examined the distortions in a strabismic amblyope, using a pop-out localization task, in which normal observers made errors dependent on the visual context of the stimulus. The localization errors of the strabismic amblyope were abnormal. We found that none of the available theories could fully explain this one patient's localization performance. Instead, the observed behavior suggests that multiple adaptations of the underlying cortical topology are possible simultaneously in different parts of the visual field.

Adult↗
PubMed1995

Ketamine activates psychosis and alters limbic blood flow in schizophrenia.

The non-competitive NMDA antagonist ketamine, given to schizophrenic individuals in subanesthetic doses, produced a short-lived, discrete activation of their psychotic symptoms, which had striking similarities to symptoms of their usual psychotic episodes. To further study this psychotomimetic property of ketamine, we administered 0.3 mg kg-1 of the drug to schizophrenic individuals during a [15O] water cerebral blood flow study. Regional cerebral blood flow (rCBF) was measured using H2(15)O and positron emission tomography (PET) before and after ketamine administration to identify regions of flow change, rCBF was increased in anterior cingulate cortex and was reduced in the hippocampus and primary visual cortex (lingual and fusiform gyri). These data encourage further consideration of altered glutamatergic transmission in schizophrenic and PCP-induced psychoses.

Behavior↗
PubMed2004

Time-dependent changes in the expression of the MEF2 transcription factor family during topographic map reorganization in mammalian visual cortex.

Removal of retinal input from a restricted region of adult mammalian visual cortex leads to a substantial reorganization of the retinotopy within the lesion projection zone (LPZ) of primary visual cortex (area 17). Little is known about the molecular mechanisms underlying such cortical plasticity. We investigated whether small but homonymous central retinal lesions induced differences in gene expression patterns between central area 17, the LPZ, vs. peripheral area 17 of the adult cat. Systematic differential mRNA display screening revealed higher levels for the mRNA encoding the transcription factor MEF2A in the LPZ. Semi-quantitative PCR confirmed this dependency of mef2A mRNA expression on visual eccentricity in area 17 of animals with retinal lesions in contrast to normal animals. Western blotting experiments extended these data to the protein level and to two other members of the MEF2 transcription factor family, i.e. MEF2C and MEF2D. Quantitative analysis of the Western blotting experiments further revealed a post-lesion survival time-dependent change in expression for all three MEF2 family members. The lesion effect was maximal at 3 days and 1 month post-lesion, but only minor at 2 weeks post-lesion. Interestingly, complete removal of retinal input from area 17 by surgery did not significantly alter the expression of the MEF2 transcription factors, excluding a definite correlation between neuronal activity and MEF2A expression levels. MEF2A immunocytochemistry confirmed both qualitatively and quantitatively the Western blotting observations in all animal models. Together, our findings identified a brain plasticity-related expression pattern for the MEF2 transcription factor family in adult mammalian neocortex.

Animals↗
PubMed1994

Cytoarchitecture and staining for acetylcholinesterase and zinc in the visual cortex of the Parma wallaby (Macropus parma).

Cytoarchitecture and distributions of acetylcholinesterase-containing fibers and zinc-containing neuropil are described in the primary visual cortex of a metatherian, the Parma wallaby (Macropus parma). Although some cytoarchitectural features of layer III suggest that a subdivision and a corresponding layer IIIa-c terminology may be employed, neurochemistry is more concisely described using a simple layer I-VI terminology. Horizontal acetylcholinesterase-containing fibers in layer I take on a vertical course as they pass through layer II to form a reticulate pattern in upper layer III. Fibers gather into vertical groups in lower layer III and, markedly, in layer IV. No dominant orientation is seen in layer V, whereas an horizontal course is often seen in layer VI. Zinc-containing neuropil is very dense layers I, II and upper III, where particles are homogeneously distributed. Particles begin to form strands in lower layer III and form conspicuous vertical clusters in an otherwise almost unstained layer IV. There is a sharp transition to a densely and homogeneously stained layer V, a decrease in staining intensity in layer VI, and a further decrease within layer VI towards the white matter. The distribution of acetylcholinesterase-containing fibers in M. parma, a metatherian representative, adds to the number of species-specific patterns observed in eutherians. The distribution of zinc-containing neuropil in M. parma resembles the consistent pattern seen in eutherian species. Thus, pathways incorporating zinc, as a putative neuromodulator of excitatory amino acid receptor responses, may be organized similarly in the cortex of meta- and eutherians.

Acetylcholinesterase↗
PubMed1999

The critical period for ocular dominance plasticity in the Ferret's visual cortex.

Microelectrode recordings and optical imaging of intrinsic signals were used to define the critical period for susceptibility to monocular deprivation (MD) in the primary visual cortex of the ferret. Ferrets were monocularly deprived for 2, 7 or >14 d, beginning between postnatal day 19 (P19) and P110. The responses of visual cortical neurons to stimulation of the two eyes were used to gauge the onset, peak, and decline of the critical period. MDs ending before P32 produced little or no loss of response to the deprived eye. MDs of 7 d or more beginning around P42 produced the greatest effects. A rapid decline in cortical susceptibility to MD was observed after the seventh week of life, such that MDs beginning between P50 and P65 were approximately half as effective as those beginning on P42; MDs beginning after P100 did not reduce the response to the deprived eye below that to the nondeprived eye. At all ages, 2 d deprivations were 55-85% as effective as 7 d of MD. Maps of intrinsic optical responses from the deprived eye were weaker and less well tuned for orientation than those from the nondeprived eye, with the weakest maps seen in the hemisphere ipsilateral to the deprived eye. Analysis of the effects of 7 d and longer deprivations revealed a second period of plasticity in cortical responses in which MD induced an effect like that of strabismus. After P70, MD caused a marked loss of binocular responses with little or no overall loss of response to the deprived eye. The critical period measured here is compared to other features of development in ferret and cat.

Aging↗
PubMed1995

Projections from visual areas of the cerebral cortex to pretectal nuclear complex, terminal accessory optic nuclei, and superior colliculus in macaque monkey.

The purpose of this study was to analyze the projections from visually related areas of the cerebral cortex of rhesus monkey to subcortical nuclei involved in eye-movement control; i.e., the pretectal nuclear complex, the terminal nuclei of the accessory optic system (AOS), and the superior colliculus (SC). The anterograde tracer 3H-leucine was pressure injected bilaterally into the cortex of six monkeys (for a total of 12 cases) involving the primary visual cortex (area 17); the medial prestriate cortex (medial 18/19); dorsomedial area 19; the caudal portion of the cortex of the superior temporal sulcus, upper bank (cytoarchitectural area OAa) and lower bank (area PGa); the lower bank of the caudal lateral intraparietal sulcus (area POa); and the inferior parietal lobule (area 7). The results revealed that the pretectal nucleus of the optic tract received inputs from medial prestriate cortex, dorsomedial part of area 19, OAa, and PGa. The posterior pretectal nucleus received sparse projections from area 7 and the cortex lining the intraparietal sulcus (dorsomedial part of area 19 and POa). The pretectal olivary nucleus was targeted by neurons in cortex of dorsomedial area 19, and the anterior pretectal nucleus was targeted by neurons in both dorsomedial 19 and area 7. The nuclei of the AOS (dorsal terminal; lateral terminal; and interstitial nuclei of the superior fasciculus, posterior and medial fibers) received projections exclusively from areas OAa and PGa. Furthermore, in one case with PGa injection, the medial terminal nucleus, dorsal portion, was also labeled. The visual cortical areas studied projected differentially upon the SC laminae. The primary visual area 17 projected only to the superficial laminae, i.e., stratum zonale (SZ), stratum griseum superficiale (SGS), and stratum opticum (SO). On the other hand, the medial portion of the prestriate cortex and caudal OAa and PGa targeted the superficial and intermediate laminae, i.e., SZ, SGS, SO, and stratum griseum intermediale (SGI), whereas caudal area POa projected primarily to the intermediate layer SGI. Rostral area 7 (mainly 7b) neurons terminated in the stratum album intermediale (SAI); no SC terminals were found in a case in which caudal area 7 (mainly 7a) was injected.

Animals↗
PubMed1996

Different balance of excitation and inhibition in forward and feedback circuits of rat visual cortex.

Different cortical areas are linked reciprocally via forward and feedback connections. Forward connections are involved in the representation of retinal images, whereas feedback pathways may play a role in the selection and interpretation of visual information. To examine the synaptic mechanisms of forward and feedback connections between primary and secondary visual cortical areas directly, we have performed intracellular recordings in slices of rat visual cortex. Irrespective of stimulus intensity and membrane potential, 78% (45/58) of the cells in striate cortex activated by feedback input showed monosynaptic responses that were depolarizing only, and inhibitory inputs were evident merely as a slight acceleration in the decay of EPSPs. In contrast, in 89% (17/19) of the cells, stimulation of forward input evoked monosynaptic excitatory postsynaptic potentials (EPSPs), followed by disynaptic, hyperpolarizing inhibitory postsynaptic potentials (IPSPs). EPSPs followed by IPSPs also were recorded after stimulation of local connections within primary visual cortex (92%, 12/13) and after activation of thalamocortical input (91%, 10/11). These results suggest that the synaptic organization of feedback connections are distinct from forward, local, and thalamocortical circuits. The findings further indicate that intracortical back projections exert modulatory influences via synaptic mechanisms in which weak inhibitory input is strongly dominated by excitation.

Animals↗
PubMed1995

Relation between oscillatory activity and long-range synchronization in cat visual cortex.

Recent theoretical studies have suggested that oscillatory firing patterns with frequencies in the gamma band (30-70 Hz) may be instrumental for the establishment of synchrony among widely distributed neurons if synchrony is to be achieved by reciprocal connections. We have now investigated the relationship between synchrony and oscillations in cat visual cortex. Our results show that when synchronization of neuronal activity occurs over distances of > 2 mm in primary visual cortex, or occurs between the two hemispheres, it is almost always associated with oscillatory firing patterns, whereas synchronization over short distances occurs also in the absence of oscillations. Furthermore, our results indicate that short-range interactions affect both the firing rate of the respective neurons and the timing of their discharges, whereas only the latter is influenced by long-range interactions. These data support the hypothesis that oscillatory activity can contribute to the establishment of long-range synchrony in a network of reciprocally coupled neurons.

Animals↗
PubMed1987

A current source density analysis of field potentials evoked in slices of visual cortex.

The method of one-dimensional current source density (CSD) analysis was applied to field potentials recorded from 350 microns thick slices of the primary visual cortex of rats and cats. Field potentials were elicited by stimulation of the white matter and recorded along trajectories perpendicular to the cortical layers at spatial intervals of 25 to 50 microns. The resulting CSD distributions resembled closely those recorded from the cat visual cortex "in vivo". The responses with the shortest latency were distinct sinks in layers IV and VI probably reflecting monosynaptic EPSP's from specific thalamic afferents. From layer IV activity was relayed along three major routes: 1. to the supragranular layers via strong local connections to layer III and from there via both short and long range connections to layer II, 2. to targets within layer IV, and 3. to layer V. The source distributions suggest that the projections to layers III and II terminate on the proximal and distal segments, respectively, of apical dendrites of layer III pyramidal cells while the projection to layer V contacts the apical dendrites of layer VI pyramidal cells. These results indicate that all the excitatory pathways that are detectable with the CSD technique in the "in vivo" preparation remain intact in 350 micron thick cortical slices. However, in the slice paired pulse stimulation did not lead to a depression of the response to the second stimulus while this is the case "in vivo". This might be due to reduced inhibition in the slice which has been reported by several authors.

Age Factors↗
PubMed1994

Broad-tuned chromatic inputs to color-selective neurons in the monkey visual cortex.

1. Input mechanisms of 21 color-selective cells in cytochrome oxidase-rich blobs in layer II/III of the anesthetized and paralyzed monkey primary visual cortex were studied by an iontophoretic administration of the GABAergic receptor antagonist bicuculline methiodide (BMI). 2. Color-selective blob cells become responsive to originally nonresponsive colors of stimuli or brightness contrast stimuli during removal of intracortical inhibition. 3. The magnitudes of the cells' responses to color stimuli during BMI administration were larger than the expected value of response calculated from the previously reported color tuning of color-selective geniculate cells and emission spectra of color stimulus. 4. These results suggest that color-selective blob cells receive a convergence of different types of chromatic inputs and that intracortical inhibition confers selectivity for a given color on them.

Animals↗
PubMedDate not supplied

[Simulation model of the tuning mechanism in the visual cortex neuron for the perception of Y-shape images].

We performed an imitation simulation of receptive fields (RF) of cat cortical neurons in the primary visual cortex, which were able to detect symmetrical and asymmetrical Y-like figures. We investigated the models of the receptive fields of neurons sensitive to Y-like figures through either the convergence from half-bar detectors or disinhibition mechanism. The model of an of the receptive fields of neurons sensitive to Y-like figures through either the convergence from half-bar detectors or disinhibition mechanism. The model of an-like figure detector on the basis of convergence from the angle and orientation detectors was advanced. Tuning of the simulated receptive fields to Y-like figures was compared with their tuning to cross-like figures. It was shown that the detectors of asymmetric Y-like figures are also detectors of a cross, whereas the detectors of symmetric Y-like figures are more sensitive to Y-like figures than to crosses. The features of the model critical for sensitivity to Y-like figures (the shape, localization, and weight of the RF zones) were specified.

Animals↗
PubMed1982

[Noradrenaline and plasticity of the visual cortex of the kitten: a reexamination].

We have undertaken a study of the role of the noradrenergic system in the functional modifications, observed in the primary visual cortex of the Kitten, following monocular deprivation. The lids of one eye were sutured in 5 week old Kittens for a period of 1 or 2 weeks. Noradrenergic depletion was obtained by 6-OHDA injection, either intraventricular or localized in the coeruleus complex. Our results indicate that disappearance of noradrenaline in area 17 does not prevent the loss of binocularity of cortical cells, but appears to limit ocular dominance shifts at a stage equivalent to that observed in the intact Kitten after 6 days of monocular deprivation.

Animals↗