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PubMed1984

[Afferent connections of the visual cortex in the albino mouse].

The afferent connections of the visual cortex of the albino mouse have been studied with the aid of the enzyme Horseradish peroxidase (HRP). Ipsilateral HRP-positive cells have been found in areas 17, 18a, 18b and the temporal cortex; in the contralateral cortex, they were located in areas 17, 18a and in the temporal cortex, the greatest number of labeled cells being situated near the 17/18a border. Apart from the Nucleus dorsalis corporis geniculati, more thalamic nuclei project to the visual cortex; the Nucleus lateralis thalami, pars posterior contains regularly positive cells, whereas other nuclei (Nucleus lateralis thalami, Nucleus medialis thalami, pars lateralis, Nucleus ventralis thalami, pars lateralis and pars medialis) only in some cases show labeled cells. Sporadically, a few labeled cells were observed in the Nuclei medialis and lateralis tractus optici, Nucleus praetectalis thalami and the Nucleus centralis medialis. The afferent connections from the brain stem have not always been visualized. The most frequent afferent connections come from the Nucleus dorsalis tegmenti pontis, followed by the Nucleus reticularis tegmenti pontis and the Nucleus Locus coerulei. Occasionally, a few HRP-positive cells were found in the Nucleus ventralis tegmenti, Nucleus raphe dorsalis, Nucleus parabrachialis lateralis and in the Nucleus centralis superior. The morphology of the projecting neurons in different centres was studied and compared after HRP-filling and after Golgi-impregnation.

Animals↗
PubMed1995

Development of basal forebrain projections to visual cortex: DiI studies in rat.

We performed experiments using retrograde and anterograde labeling with DiI to examine the development of basal forebrain (BFB) projections to the visual cortex in postnatal rats. DiI placed in occipital cortex led to retrograde labeling of BFB neurons as early as postnatal day 0 (P0); labeled cells were found mainly in the diagonal band complex but also in the medial septum, globus pallidus, and substantia innominata. The retrogradely labeled BFB cells displayed remarkably well-developed dendritic arbors, even in younger animals, and showed increases in soma size, dendritic arbors, and dendritic spines over the first 2 postnatal weeks. DiI placements in the diagonal band led to anterogradely labeled axons in cortex. At early ages (P0-P1), labeled axons were largely confined to white matter. With increasing age, greater numbers of labeled axons were seen in the white matter and in deep cortical layers, and labeled axons extended into superficial layers. The leading edge of labeled fibers reached layer V of visual cortex by P2 and layer IV by P4 and were found throughout the cortical layers by P6. Numbers and densities of labeled axons in visual cortex were greater in older animals, at least through P14. The time of ingrowth of labeled BFB axons into visual cortex indicates that these afferents grow into particular cortical layers after those layers have differentiated from the cortical plate. These data indicate that basal forebrain projections arrive in occipital cortex after cortical lamination is well underway and after the entry of primary thalamocortical projections.

Animals↗
PubMed1986

A transient pyramidal tract projection from the visual cortex in the hamster and its removal by selective collateral elimination.

During the early postnatal development of the neocortex in rats there is an axonal projection from the occipital cortex (which includes the visual cortex) to the spinal cord which is subsequently completely removed through a process of selective collateral elimination. In order to determine whether a similar phenomenon occurs during the development of the hamster cortex, we have injected the retrogradely transported fluorescent dye Fast Blue (FB) into the pyramidal decussation of hamsters at various ages. In adult hamsters such an injection results in a band of labeled neurons confined to layer V and to about the rostral two-thirds of the neocortex; no labeled cells are seen in the occipital cortex. However, a similar FB injection made during the first postnatal week results after a 4-day survival in a continuous band of FB-labeled layer V neurons spread throughout the tangential extent of the neocortex, including the occipital cortex. A similar continuous band of FB labeled layer V neurons is seen throughout the tangential extent of the neocortex including the occipital region in hamsters injected during the first postnatal week but allowed to survive until the fourth week (i.e., after the restriction of the widespread neonatal pattern has occurred). Injections of the anterograde tracer wheat germ agglutinin conjugated to horseradish peroxidase made into the occipital cortex, or for comparison, into more rostral cortical regions in hamsters ranging in age from neonates to adults, reveal that the extension of pyramidal tract axons is staggered along the anterioposterior axis of the cortex such that axons originating from the posterior regions lag behind those arising from more rostral areas. The transient occipital projection appears to reach a maximum around the end of the first postnatal week: a large number of labeled occipital axons is seen in the medullary pyramidal tract, and some of these can be followed through the pyramidal decussation and into the dorsal funiculus of the spinal cord. Injections into the occipital cortex on P16 label only a few fibers in the medullary pyramidal tract, and none is labeled in hamsters injected as adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

The length summation properties of layer VI cells in the visual cortex and hypercomplex cell end zone inhibition.

Layer VI of the visual cortex has been considered to be dominated by cells with very long receptive fields, typically summing to 8 degrees or more. We have re-examined this issue in a series of experiments in which the length tuning profiles of layer VI cells in the cat visual cortex have been quantitatively determined. Responses were assessed to optimally oriented bars of light of varying length drifted over the receptive field. The lengths were varied on a randomised interleaved sequence. Although our data confirm the presence of long field cells in layer VI, only 24% of a population of 119 cells had fields greater than 6 degrees in length. Fields greater than 8 degrees were only seen in 17% of cells. 61% of the population of cells had fields showing summation to 4 degrees or less with a mean length of 2.8 degrees (+/-0.15 sem). In this "short field" group, 18% had fields of 1 degrees or less. We observed 7 cells with rapid initial spatial summation up to 1 degree, followed by clear end zone inhibition. It has been recently suggested on the basis of localised inactivation experiments, that layer VI cells with long (greater than 8 degrees) fields may provide the drive to inhibitory interneurones in layer IV generating hypercomplex cell end zone inhibition. This observation is difficult to equate with evidence indicating that hypercomplex cell end zone inhibition reflects a mechanism showing maximal summation at lengths in the region of 2.8 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

[Feedback inhibition in microsegments of the visual cortex].

Interaction between 3-4 neighbouring neurons in the visual cortex of awakening cats was examined using a cross-correlation analysis. In some microsystems neurons revealed a tendency towards synchronized activity indicating a shared excitatory input. In other microsystems asymmetrical interaction was observed: neurons with larger spike amplitudes exhibited excitatory effect on neurons with smaller spike amplitudes (latent period about 5 ms) and neurons with small spike amplitudes inhibited neurons with large spike amplitudes (latent period 1-8 ms, duration of inhibition 30-200 ms). Suggestions were made about the existence of recurrent inhibition and inhibitory interneurons in microsystems of the visual cortex.

Animals↗
PubMed1989

Stimulus-specific neuronal oscillations in orientation columns of cat visual cortex.

In areas 17 and 18 of the cat visual cortex the firing probability of neurons, in response to the presentation of optimally aligned light bars within their receptive field, oscillates with a peak frequency near 40 Hz. The neuronal firing pattern is tightly correlated with the phase and amplitude of an oscillatory local field potential recorded through the same electrode. The amplitude of the local field-potential oscillations are maximal in response to stimuli that match the orientation and direction preference of the local cluster of neurons. Single and multiunit recordings from the dorsal lateral geniculate nucleus of the thalamus showed no evidence of oscillations of the neuronal firing probability in the range of 20-70 Hz. The results demonstrate that local neuronal populations in the visual cortex engage in stimulus-specific synchronous oscillations resulting from an intracortical mechanism. The oscillatory responses may provide a general mechanism by which activity patterns in spatially separate regions of the cortex are temporally coordinated.

Animals↗
PubMed1991

Prosencephalic connections of striate and extrastriate areas of rat visual cortex.

Afferent connections of rat primary visual cortex (area 17 or V1 area) and the rostral and caudal parts of areas 18a and 18b were studied, by placing in each of the areas, small electrophoretic injections of enzyme horseradish peroxidase (HRP) or wheat germ agglutinated-HRP. The results indicate that: 1) each of the areas has a distinct pattern of distribution of afferent neurons in the ipsilateral visual thalamus - area 17 receives its principal thalamic input from the dorsal lateral geniculate nucleus, the caudal parts of areas 18a and 18b receive a major thalamic input from the lateral posterior nucleus and a minor input from the posterior nucleus, while the rostral parts of areas 18a and 18b receive a major input from the posterior nucleus, and a minor projection from the lateral posterior nucleus; 2) the rostral and caudal parts of areas 18a and 18b each receive an associational input from area 17; 3) the rostral parts of areas 18a and 18b each receive associational input from three different extrastriate regions, the caudal part of the same extrastriate area, and the rostral and caudal parts of the other extrastriate area, whereas the caudal parts of areas 18a and 18b receive associational inputs only from one or two extrastriate regions; 4) area 17, area 18b and rostral area 18a each receive a substantial associational input from lamina V of the caudal part of the frontal eye field (FEF) in the motor cortex; however the input from the FEF to caudal area 18a (if present) is very small; 5) The extrastriate areas studied receive associational input from the restrosplenial cingulate area 29d; however, the input from area 29d to area 17 appears to be very small. The distinct patterns of distribution of prosencephalic afferents suggest to us that multiple retinotopically organized areas described previously in the rat cortex (cf Montero 1981; Espinoza and Thomas 1983) represent functionally distinct areas.

Afferent Pathways↗
PubMed1981

Extrageniculate projections to the visual cortex in the macaque monkey: an HRP study.

Extrageniculate projections to the visual cortex were examined in the macaque monkeys by the horseradish peroxidase (HRP) method. Extrageniculate neurons sending fibers to the visual cortex were found in the lateral and inferior pulvinar nuclei, paracentral thalamic nucleus, claustrum, basal nucleus of Meynert, lateral part of the basal amygdaloid nucleus, lateral hypothalamus, locus coeruleus, and dorsomedial and midline regions of the pontine tegmentum.

Animals↗
PubMed1985

Small lesions in the primary visual cortex of rats cause a specific reorganization of associational connections.

Neuroplastic changes in associational connections were investigated 3 weeks after the intrinsic organization of the visual cortex of rats had been partially damaged by small cylindrical lesions (type I). These lesions caused the degeneration of short intracortical connections and associational connections that form patches in the primary and secondary visual areas. The resulting terminal degeneration disappeared within 20 days p.o. after which only some fiber degeneration was evident in the infragranular layers. Patches of terminal degeneration reappeared in the vicinity of the stab wounds, when the associational connections between the retrosplenial and the primary visual cortex had been secondarily interrupted by elongated lesions (type II), which penetrated the paramedian cortex and subcortical white matter. When type-II lesions were made in the intact cortex, patches of degeneration were absent, although in both cases some terminal degeneration was diffusely distributed in the primary visual cortex. Horseradish peroxidase (HRP) was applied to sites similar to those where type-I lesions were applied. In the intact cortex, HRP caused a granular labeling of numerous neurons in various positions including the retrosplenial cortex and patches of the postero-median visual cortex. HRP was also applied to type-I lesions that had been made 3 weeks earlier. In these cases, apparently HRP labeled the same subpopulations of neurons as it did in the intact cortex. However, a fraction of the labeled neurons showed a Golgi-like staining (e.g., 27% of the labeled neurons in the retrosplenial cortex) only when HRP was applied to stab wounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1987

Effects of cholinergic depletion on neuron activities in the cat visual cortex.

1. Unilateral lesions of the nucleus basalis magnocellularis (nBM), a source of cholinergic projection to the cerebral cortex, were produced by injection of kainic acid in the cat. The lesions caused a significant reduction in density of choline acetyltransferase-immunoreactive terminals in the visual cortex ipsilateral to the lesions. 2. In the primary visual cortex ipsilateral to the lesions [acetylcholine (ACh)-depleted cortex], about half of the cells had weak or undetectable visual responses, whereas in the contralateral visual cortex almost all the cells had normal responsivity. The response selectivity, such as orientation and direction selectivities, of cortical cells was not affected by the depletion of ACh. 3. The microionophoretic application of ACh to cells under observation facilitated visual responses in 83% of the cells recorded from the ACh-depleted cortex, whereas it suppressed the responses in only 9%. The application of a muscarinic antagonist, atropine, to cells in the ACh-depleted cortex was ineffective, suggesting no residual ACh activity. 4. The mean current required to induce facilitation in the cortex ipsilateral to the lesion was significantly smaller than that required in the contralateral cortex and the visual cortex of the normal cat, suggesting a supersensitivity of receptors mediating the effect or a reduction in catabolism of exogenous ACh in the ACh-depleted cortex. 5. More than half of the cells that had been unresponsive to visual stimuli became clearly responsive during the ACh application. The response magnitude of cortical cells, as a whole, increased to the same degree as that observed during the ACh application in the normal cat. 6. In addition to the decrease in the average response magnitude, there was a remarkable variability in responses of cells to motion of the slit from sweep to sweep in the ACh-depleted cortex. The application of ACh to cortical cells decreased the variability of responses and consequently made the responses much more consistent. 7. These results suggest that without ACh supplied from the nBM, most of the cortical neurons could not respond briskly and consistently to excitatory inputs and that exogenously applied ACh could reverse such an impairment of cortical neurons through intact or even supersensitive postsynaptic receptors.

Acetylcholine↗
PubMed1991

[Neurons in the visual cortex of Microtus brandti].

Neurons were described in the visual Cortex of Microtus brandti, a Mongolian harmful rodent living in day-activity. We find following types of neurons in our Golgi-material: 1. spiny neurons: pyramidal and stellate neurons. 2. smooth or sparsely spined neurons: smooth, large neurons, sparsely spined small neurons with descending axons, sparsely spined neurons with ascending axons. Double-bouquet-, chandelier and neuroglioforme cells are not impregnated. There are no bipolare neurons (Martinotti cells) among the neurons with ascending axons. The small, sparsely spined neurons are not only in lamina IV - like in other species - but they can also be found in laminae II to IV. Their distribution of spines on the distal parts of dendrites seems to be characteristical for rodents. The lamination of the visual cortex of Microtus brandti is the same like in the rat. All cells are of large size in relation to the body mass of the animal.

Animals↗
PubMed1992

Postnatal development of dye-coupling among astrocytes in rat visual cortex.

Intercellular coupling among astrocytes was studied in rat visual cortex slices from animals aged 1 week to 4 months. Cell coupling via gap junctions was determined by the dye spread of the low molecular weight dye Lucifer Yellow CH injected into electrophysiologically identified cells to adjacent cells. Coupling among glial cells was first detected at postnatal day 11 and was thereafter consistently observed until adulthood. Dye spread was observed up to 300 microns radially from the injected cell covering multiple cortical layers. Following dye injection into a single cell up to several hundred Lucifer Yellow-positive cells could be observed. Quantitative analysis revealed a similar extent of dye spread at different developmental stages including a quite constant number of dye-coupled astrocytes from the end of the second postnatal week to adulthood. Double labelling of Lucifer Yellow-filled cells with an antiserum against the glial fibrillary acidic protein confirmed the astrocytic nature of the injected and coupled cells. Comparison of the density of dye-coupled cells in a given area and the total number of astrocytes as revealed by immunocytochemical staining suggests that dye-coupling includes the entire local astrocytic population. It is concluded that coupling among astrocytes via gap junctions in rat visual cortex occurs shortly after birth and reflects one of the first steps in astroglial maturation.

Animals↗
PubMed1991

Magnetic stimuli applied over motor and visual cortex: influence of coil position and field polarity on motor responses, phosphenes, and eye movements.

Transcranial magnetic stimulation was performed over the motor and visual cortex with the Novametrix 12-cm diameter stimulation coil. The influence of coil position on the size of electromyographic responses and on the intensity and position of phosphenes in the binocular visual field was studied. Furthermore, it was investigated whether stimulation over the visual cortex or over the frontal eye field evoked or disturbed eye movements. Coil position was recorded by constructing grids on the skull surface using extracranial bony landmarks, and was then related individually to underlying cerebral sulci by analysis of magnetic resonance images of the brain. Motor responses. Excitatory effects were maximal when the coil windings in the middle of the coil ring lay over the particular motor representation field of area 4. The response size depended on the direction of the coil currents passing over the motor cortex. For example, coil currents passing over the lateral part of the precentral gyrus from the front and transversely to the central sulcus elicited maximal responses in hand muscles. With the currents passing over the same area in the opposite direction, response amplitudes were much smaller, suggesting activation of different inputs to cortical motoneurons. Phosphenes. Fields of fixed, white and unstructured phosphens occurred in the lower half of the visual field when the coil center was placed about 7 cm anterior to the inion on the inion-nasion line. Counterclockwise or clockwise coil currents elicited phosphenes within the left or right lower quadrant of the binocular visual field, respectively, which could be attributed to an activation of the right or left primary visual cortex (area 17). The 'cortical' phosphenes moved with voluntary eye movements, but not during caloric and optokinetic nystagmus. Phosphenes resulting from an excitation of the optic nerve rather than the retina could be evoked by stimulation over frontal parts of the skull. Eye movements. The application of single magnetic field pulses over the frontal eye field or over the visual cortex did not elicit eye movements except for small vertical eye movements as part of a magnetically elicited blink.

Adolescent↗
PubMed1984

Synaptic characteristics of identified pyramidal and multipolar non-pyramidal neurons in the visual cortex of young and adult rabbits. A quantitative Golgi-electron microscope study.

The visual cortex of 20 day old rats and rabbits has been considered as mature on the basis of the observations that the dendritic arborization and the overall synaptic population have almost reached their adult stage in these animals. In the present study we have investigated the visual cortex of 20 day and 7 month old (adult) rabbits in order to determine whether this apparent adult appearance also holds for the synaptic organization of individual neurons. Neurons mainly located in layers III and IV of the primary visual cortex (area 17) were Golgi-impregnated, gold toned and deimpregnated and were then, after embedding in plastic, sectioned serially. The number and length of synaptic profiles, and the length of the neuronal boundaries were analysed in every tenth section. From these counts and measurements the size distribution of the synaptic discs, the number of synapses per 100 micron2 neuronal surface and the receptive surface expressed as the percentage of the total neuronal surface covered with synaptic contacts were estimated using stereological methods. At both ages studied, the density of synapses was significantly higher for the non-pyramidal neurons than for the pyramidal neurons. Differences in the amount of receptive surface were parallel to the differences observed for the number of synapses per 100 micron2. At day 20 the receptive surface of the non-pyramidal neurons was significantly larger than that of the pyramidal neurons. The receptive surface of the non-pyramidal neurons in the adult stage was not only larger than that of the pyramidal neurons in the adults, but also larger than that of the day 20 non-pyramidal neurons. From our results the following conclusions can be drawn: (1) The synaptic input received by the pyramidal neurons is mainly established at day 20 of postnatal life, i.e. prior to the establishment of adult visual behaviour. (2) The non-pyramidal neurons complete their maturation in a later stage than the pyramidal neurons. (3) Medium to large sized synaptic contacts are newly formed after day 20 and are mainly added to the synaptic population on dendrites of non-pyramidal neurons. (4) The specific increase in the number of synapses on non-pyramidal neurons is discussed in relation to intracortical inhibition which is thought to be important for the fine regulation of visual function during development.

Animals↗
PubMed1991

Cortisol reduces plasticity in the kitten visual cortex.

We investigated the effect of elevated levels of cortisol on plasticity in the visual cortex of the cat. Animals were given daily injections of cortisol i.m. for 20 days starting around 35 days of age. After 10 days they were monocularly deprived, and after an additional 10 days recordings were made from the visual cortex to construct an ocular dominance histogram. The results were compared with those from normal animals of the same age, and with animals monocularly deprived for the same period but not treated with cortisol. Cortisol reduced the ocular dominance shift in a dose-dependent manner, but did not totally abolish it even at the highest doses used. Two other series of animals were recorded, one slightly later in the critical period and one slightly earlier, with care taken to give cortisol before the animals were exposed to light in the morning. In both cases, cortisol reduced the ocular dominance shift but did not abolish it. To interpret these results, we measured levels of plasma cortisol in normal cats of various ages. Average levels were fairly constant between birth and 12 months of age (0.5-1 microgram/dl), and increased slightly after that, but there was a large variation between animals. Thus elevated levels of cortisol can have a substantial effect on plasticity in the visual cortex of the cat, but the decline of the critical period for plasticity between 6 weeks and 3-5 months of age does not seem to be due to a rise in cortisol levels during this time.

2-Amino-5-phosphonovalerate↗
PubMedDate not supplied

Influence of pulse stimulation of the visual cortex on the function of the superior colliculus of the awake rabbit.

It has been demonstrated in awake rabbits that stimulation of the visual cortex by a solitary pulse of electrical current leads to the formation of a short-latency response in the superior colliculus. The formation of this response is suppressed when a light stimulus precedes it. At the same time, a conditioning solitary electrostimulation of the visual cortex induces a short inhibition of the formation of the response to the test light stimulus. This fact suggests that the influences of the visual cortex on the functioning of the superior colliculus may be biphasic in character. When the adrenergic apparatus of the reticular formation is blocked this inhibitory influence bears a more pronounced and prolonged character. The stimulation of the reticular formation, on the other hand, by means of anodic polarization leads to the diametrically opposite effect: the inhibitory character of the influence of the cortex is replaced by a facilitatory one. The inference is drawn that the character and the directionality of the influence of the visual cortex on the functioning of the superior colliculus is determined to a significant degree by the initial functional state of nonspecific brain systems.

Animals↗
PubMed1988

Enigmatic bipolar cell of rat visual cortex.

Our earlier Golgi-electron microscopic study of bipolar cells in the rat visual cortex showed the axons of these neurons as forming asymmetric synapses (Peters and Kimerer; J. Neurocytol, 10:921-946, '81) in which the most common postsynaptic elements were dendritic spines. This result was unexpected, since Parnavelas (Parnavelas, Sullivan, Lieberman, and Webster: Cell Tissue Res. 183:499-517, '77) had earlier shown a bipolar cell from the same cortex to have an axon forming symmetric synapses with dendritic shafts. Here then was an enigma, strengthened by examination of neuronal components labelled by antibodies to two compounds in particular--namely, vasoactive intestinal polypeptide (VIP) and choline acetyltransferase (ChAT). Antibodies to these compounds preferentially label bipolar cells in the rat cerebral cortex, and the labelled axon terminals form symmetric synapses. Against this background the present study was performed, and it has been shown that the resolution to the enigma is that there are two different populations of bipolar cells in the rat visual cortex. Thus some Golgi-impregnated bipolar cells examined by electron microscopy after gold toning have been found to possess axons forming asymmetric synapses, and others have been found to have axons forming symmetric synapses. The axons of the bipolar cells forming asymmetric synapses most commonly synapse with dendritic spines (67%), although other terminals synapse with dendritic shafts (33%). In contrast, the bipolar cells with axons forming symmetric synapses preferentially synapse with dendritic shafts (100%). The population of bipolar cells that form symmetric synapses includes the ones that label with antibodies to vasoactive intestinal polypeptide (VIP), for the axons of VIP-labelled bipolar cells have been traced to labelled terminals forming symmetric synapses. However, examination of the population of VIP-labelled axon terminals shows that in addition to dendritic shafts, some of the labelled terminals synapse with the cell bodies of pyramidal and nonpyramidal cells. This includes bipolar cells, some of which receive large numbers of VIP-labelled axon terminals. It is also shown that some VIP-positive bipolar cells have myelinated axons. Analysis of tissue labelled with VIP antibody reveals that about 50% of the total population of bipolar cells in the rat visual cortex is VIP positive. These results are discussed in the light of information about labelling of bipolar cells with antibodies to gamma-aminobutyric acid (GABA) and to other peptides, and it is suggested that most VIP-positive bipolar cells also contain GABA.

Animals↗
PubMed1988

Evidence for a nicotinic component to the actions of acetylcholine in cat visual cortex.

Radioligand binding assays, receptor autoradiography and iontophoresis have been used to look for evidence of a nicotinic component to the actions of acetylcholine in cat visual cortex. [3H]Nicotine bound to a uniform population of high affinity binding sites in cat primary visual cortex. This binding was inhibited by nicotine agonists and antagonists but not muscarinic antagonists. The concentration of nicotinic binding sites was about 10% of that of muscarinic binding sites measured with [3H]N-methylscopolamine. The muscarinic sites were resolved into M1 and M2 subtypes. Quantitative receptor autoradiography showed that there were muscarinic sites in all layers, although they were least abundant in layer IV of area 17. In contrast, the nicotinic sites were most concentrated in layer IV in area 17. The concentration of this labelling was reduced at the 17/18 border and also at the 18/19 border. Layer I of the cingulate and suprasylvian gyri were also labelled. Electrolytic lesions of the lateral geniculate nucleus (LGN) led to a loss of nicotinic binding sites in layer IV of area 17, indicating that these sites are most likely located on the LGN terminals. Iontophoresis of mecamylamine, a nicotinic antagonist, decreased evoked responses in visual cortex, providing evidence that the [3H]nicotine binding sites are functional receptors and suggesting that the release of acetylcholine onto these receptors on the LGN terminals facilitates the input of visual information into visual cortex.

Animals↗