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PubMed1992

The effects of selective glutamate receptor antagonists on synchronized firing bursts in layer III of rat visual cortex.

In the rat visual cortex in vitro, single-shock stimulations applied to the border between layer VI and the white matter evoke synchronized burst-firing by units in layer III. We have examined the effects of glutamate receptor antagonists on this activity, with antagonists applied via the bath to allow correlation of effects with concentrations. All synaptically driven components (recorded extracellularly as field potential 'S2' spikes, dipoles 'W1' and 'W2', and coinciding single-unit spikes) were inhibited by greater than 90% in 1.0 mM kynurenic acid and in 3 or 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, which selectively blocks AMPA/kainate receptors). S2 spike amplitudes were reduced by half in 0.7 microM CNQX. 2-Amino-5-phosphonovalerate (APV), a specific blocker of NMDA receptors, did not prevent S2 spike burst or horizontal spread of bursting within layer III. However, APV reduced the duration of synchronized bursts and the slower potentials which followed. In Mg(2+)-free medium, new components appeared which were APV-sensitive: (1) low amplitude spikes, distributed spatially like S2 spike, but recurring more slowly, and (2) slow potentials, distributed spatially like W1 and W2 potentials, but lasting for hundreds of milliseconds. The amplitudes of these spikes were reduced by half in 3 microM D-APV. Our data imply that: (1) glutamate receptors play a major role in mediating local, excitatory neurotransmission in the supragranular layers of neocortex, with NMDA and AMPA/kainate subtypes each subserving somewhat different functions; (2) AMPA/kainate receptors mediate rapid excitatory transmission between layer III neurons, responsible for driving the first 15 ms of synchronized bursts; (3) currents gated by NMDA receptors determine the duration of coherent firing bursts, and drive asynchronous neuronal firing following bursts; and (4) under conditions which circumvent block by extracellular Mg2+, activation of NMDA receptors greatly enhances and prolongs the response to single-shock stimulations. In vivo, activation of layer III neurons is likely to depend significantly upon currents gated by NMDA receptors whenever repetitively firing excitatory inputs summed over several tens of milliseconds provide enough depolarization to lift block by extracellular Mg2+.

2-Amino-5-phosphonovalerate↗

PubMed1992

Periodic-pattern-selective cells in monkey visual cortex.

To study the visual processing of periodic and aperiodic patterns, we have analyzed neuronal responses in areas V1 and V2 of the visual cortex of alert monkeys during behaviorally induced fixation of gaze. Receptive field eccentricities ranged between 0.5 degrees and 4 degrees. We found cells that responded vigorously to gratings, but weakly or not all to bars and edges. In some cells the aperiodic stimuli even reduced the activity below the spontaneous level. The distribution of a bar-grating response index indicated a discrete population of "grating cells" characterized by more than 10-fold superiority of gratings. We estimated that these cells have a frequency of 4% in V1 and 1.6% in V2, and that about 4 million grafting cells of V1 subserve the central 4 degrees of vision. The converse, cells that responded to isolated bars but not to gratings of any periodicity, was also observed. The grating cells of V1 were mostly (23 of 26) found in layers 2, 3, and 4B. They preferred spatial frequencies between 2.6 and 19 cycles/degree (median, 9.3), with tuning widths at half-amplitude between 0.4 and 1.4 octaves (median, 1.0). Their tunings were narrower, and their preferred frequencies higher, than those of other cells on average. Grating cells were also narrowly tuned for orientation. Those of V2 were similarly selective. The responses of grating cells depended critically on the number of cycles of the gratings. With square waves of optimum periodicity responses required a minimum of 2-6 grating cycles and leveled off at 4-14 (median, 7.5). The corresponding receptive field widths were 0.34-2.4 degrees (median, 0.78 degrees) for V1 and 0.72-2.4 degrees (median, 1.4 degrees) for V2. Grating cells typically gave unmodulated responses to drifting gratings, were unselective for direction of motion, and were strongly activated also by stationary gratings. Half of those of V1 were monocular, the others binocular, some showing strong binocular facilitation and disparity sensitivity. Length summation was usually monotonic, but strong end-inhibition was also observed. In contrast to other cells, grating cells were not activated by harmonic components. Spatial-frequency response curves for sine-wave, square-wave, and line gratings were similar. Square-wave gratings of one-third the preferred frequency failed to excite the cells, while the isolated 3f component (f = the fundamental of the square wave) of these gratings evoked strong responses. In spite of the nonlinear features, grating cells had low contrast thresholds.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1976

Alterations in receptive field properties of superior colliculus cells produced by visual cortex ablation in infant and adult cats.

To determine if functional alterations in the superior colliculus might account for recovery of visual behaviors following visual cortex removal in infant cats, the receptive field characteristics of single units in the superior colliculus of cats whose visual cortex was removed within the first week of life were compared with those of cats which sustained visual cortex lesions in adulthood and with those of normal cats. In the normal superior colliculus, 90% of all cells responded to moving stimuli irrespective of shape or orientation. Sixty-four percent of these units were directionally selective, responding well to movement in one direction but poorly or not at all to movement in the opposite direction. Ninety percent of units were binocular, the vast majority of these responding equally to stimulation of either eye or showing only slight preference for stimulation of the contralateral eye. Responses to stationary flashes of light were observed in only 33% of all visually activated cells in the normal superior colliculus. After visual cortex ablation in adult cats, only six percent of movement sensitive cells were directionally selective. Binocular preference was shifted following adult visual cortex lesions such that sixty percent of all cells responded exclusively or predominantly to stimulation of the contralateral eye. Seventy-one percent of all visually responsive units responded to stationary lights flashed on or off within their receptive field boundaries. Lesions limited primarily to area 17 had the same effect as larger lesions of visual cortex. Infant visual cortex lesions resulted in receptive field alterations similar to those observed after adult ablation. Only fifteen percent of motion sensitive units were directionally selective. Seventy-one percent responded exclusively or predominantly to stimulation of the contralateral eye. Seventy-six percent of visually responsive cells were activated by stationary light. Lesions largely confined to area 17 produced the same alterations as more extensive lesions of visual cortex. Thus, no evidence was found that the superior colliculus is involved in the functional reorganization presumed to occur following visual cortex ablation in infant cats. Recovery of visual behaviors following neonatal injury may therefore not involve alterations in the receptive fields of single cells.

Animals↗

PubMed1991

Specialized vascularization of the primate visual cortex.

We have analyzed blood vessel distribution in the primary and secondary visual cortices of the squirrel monkey in relation to cortical modules, laminae, and cytoarchitectonic areas. Measurements of microvessel length in tangential sections through the primary visual cortex showed that blobs are more richly vascularized than intervening cortical regions. Thus, the mean total length of microvessel profiles per unit was 42% greater within these cortical modules than within adjacent (interblob) areas. Total microvessel length per unit area in another class of module, the stripes in the secondary visual cortex, was 27% greater than in interstripe regions. Microvessel distribution also varied systematically from layer to layer in the primary visual cortex, being greatest in lamina IVc. Finally, the overall microvessel length per unit area in sections of the primary visual cortex was 26% greater than that in the secondary visual cortex. These observations indicate that the modular, laminar, and regional organization of the primate visual cortex is reflected in the underlying distribution of cortical microvessels. These vascular patterns should be discernable in living animals with vascular contrast agents and appropriate imaging techniques.

Animals↗

PubMed1990

Development of connections to and from the visual cortex in the wallaby (Macropus eugenii).

The time course of the development of connections between the visual cortex and the main subcortical visual structures, as well as intrahemispheric and interhemispheric connections, has been studied in the marsupial wallaby (Macropus eugenii) to compare its development with that of placental mammals. Pouch young are born prior to retinal innervation of the primary visual centers and spend a protracted period of development in the pouch, making them ideal for visual, developmental studies. Horseradish peroxidase conjugated to wheatgerm agglutinin was injected into either the presumptive visual cortex or the superior colliculus in young of varying ages. Thalamocortical projections from the dorsal lateral geniculate and lateral posterior nuclei reach the presumptive visual cortex between 12 and 15 days after birth. Descending cortical connections form later. Corticogeniculate axons are first detected in the geniculate and lateral posterior nucleus at 48 days after birth, while corticocollicular axons first reach the superior colliculus at 71 days and, by 81 days, have innervated the superficial layers. Intrahemispheric and interhemispheric connections form even later. By 99 days intrahemispheric axons from area 17 have accumulated in visual association areas but are yet to invade layers III and IV, their major termination zones in adult, while axons projecting back to area 17 have also reached their target area. At this time interhemispheric axons from area 17 have begun to accumulate in the opposite visual cortex, although they have not invaded the cortical layers. By 111 days cortical cells projecting to the opposite visual cortex are first labelled. These have a more widespread distribution in area 17 at 111 and 122 days compared to the adult, where they are confined to the 17/18 border. The results show that the marsupial wallaby has a timetable of similar sequence, but different relative timing, in the formation of cortical connections compared to that of placental mammals. In the first half of the period between conception and eye opening, the timing in the wallaby precedes considerably that in placental mammals. Ascending connections from the thalamus develop relatively earlier in the wallaby but descending collicular connections are delayed until the same relative time that they appear in placental mammals.

Afferent Pathways↗

PubMed1991

Flashed pattern-induced activity in the visual system: I. The short latency evoked response recorded from the cat visual cortex.

Previous methods for estimating visual acuity have used the visual evoked response conventionally the late visual evoked response components or the steady-state potential. The present experiments were undertaken to evaluate the possible use of short latency flashed pattern evoked responses in estimating pattern dependent activity in the cat visual system. Recordings were made from the skull bone and the dura above the primary visual cortex and intracortically. The visual evoked responses to patterned (checks) and non-patterned light flashes of high intensity and short duration were recorded. The visual evoked response activity recorded from the cortical surface had an onset latency of 14-15 ms. The initial positive-negative potential sequences of the responses were similar for patterned and non-patterned stimuli, however a difference was recorded from 35-40 ms after stimulus. The smallest check size which separated a pattern from a non-pattern VER was in the order of 10 min of arc. The results indicate that the short-latency cortical VER may be used to estimate visual resolution.

Animals↗

PubMed1991

Lithium reduces ocular dominance plasticity in kitten visual cortex.

Activity-dependent processes within the visual pathway play a crucial role in the expression of ocular dominance plasticity in immature visual cortex. The necessity of non-retinal, modulatory afferents to the regulation of ocular dominance plasticity has been recognized. Among a few chemically defined signaling systems, the noradrenaline-activated beta-adrenoreceptors seem to have a prime role in this matter. The involvement of acetylcholine afferents was also proven. We looked for plausible molecular mechanisms which integrate the contribution of the two neuromodulator systems to ocular dominance plasticity. At the first step, based on the rich literature on psychotropic action of lithium and the recent advancement in understanding of its molecular mechanisms, we physiologically studied visual cortex of kittens which had been repeatedly injected with the lithium solution intraperitoneally or the cortex directly infused with it. We found (1) that ocular dominance plasticity was significantly reduced in lithium-injected kittens, (2) that the decrease was directly correlated with plasma concentrations of lithium (i.e. the higher the lithium concentration, the lower the plasticity), and (3) that the comparable decrease in the plasticity was obtained from kitten visual cortex which had been directly infused with the lithium solution. The present results suggest that lithium-sensitive processes, through most likely reduced production of second messengers, underlie the regulation of ocular dominance plasticity.

Animals↗

PubMed1975

[Reflection of temporal parameters of an optic stimulus in neuronal responses of the senso-motor and visual cortex in cats].

Neuronal extracellular discharges in visual (area 17) and sensory-motor (area 4 and 6) cortical fields to optical stimuli with a duration up to 1000 ms were examined in the chloralozed cats (70 mg/kg). A comparative analysis of neuronal discharge types and of functional shift intervals revealed: 1) an amount of neurons with on--off discharges in the visual cortex is 25% and in the sensory-motor cortex--100%; 2) the functional shift intervals coincide with the on--off discharge time interval for the same neurons; 3) alongside with the common time interval there are specific ranges for each zone (0--200 ms for the visual cortex; 500 ms and more for the sensory-motor cortex); 1) the afterdischarge latency of a neuron is equal to the functional shift interval value of the same neuron. These data are considered as a reflection of the optical signal time parameters by the sensory-motor cortical neurons. Such peculiarities of the sensory-motor area might be important for the time organization of the cortical movement program.

Animals↗

PubMed1991

Regressive changes among corticocortical neurons projecting from the lateral suprasylvian cortex to area 18 of the kitten's visual cortex.

The postnatal development of corticocortical neurons projecting from the medial bank of the lateral suprasylvian cortex to area 18 of the kitten's visual cortex was examined using retrograde fluorescent tracers. Area 18 was injected in young kittens aged nine days or less and in older kittens aged 30 days or more. Many of the injected kittens were perfused with fixative four to five days later, but some of the youngest were killed after longer survival periods of 35-50 days (long-survival animals). Labelled neurons in the medial bank of the lateral suprasylvian cortex were densely distributed in both superficial layers (II and III) and deep layers (V and VI) in the kittens injected less than nine days postnatal, irrespective of whether survival was short or long, but they were found almost exclusively in layers V and VI in the old, short-survival animals. Only in the group of old kittens did we find a clear topographical arrangement of projections in the rostrocaudal direction and a correlation between the rostrocaudal lengths of the injection sites and labelled areas. In the other two groups, for a similarly sized injection site, the labelled areas were much longer rostrocaudally than in the old, short-survival kittens, and occupied roughly the posterior two-thirds of the medial bank of the lateral suprasylvian cortex, irrespective of the positions of the injections. In the frontal plane, topography was unclear in all groups. These findings demonstrate that there is considerable postnatal refinement of the projection from the medial bank of the lateral suprasylvian cortex to area 18. This involves a loss of connections originating from superficial layers and a decrease of convergence with the appearance of topography. Our results from long-survival kittens suggest that most of the early exuberant population of corticocortical neurons projecting from the medial bank of the lateral suprasylvian cortex to area 18 survive beyond the first postnatal month but undergo axonal elimination during this period.

Aging↗

PubMed1989

Responses of lateral geniculate neurons that survive long-term visual cortex damage in kittens and adult cats.

Damage to visual cortex (areas 17-19) in kittens or adult cats produces severe retrograde degeneration of neurons in the dorsal lateral geniculate nucleus (LGN). However, some neurons survive in otherwise degenerated portions of the LGN after a visual cortex lesion at any age. Previous studies have shown that there are well-defined differences in potential retinal inputs, soma size, synaptic connections, outputs, and physiological properties of output targets of the surviving LGN cells in cats that received visual cortex damage at different ages. The present experiment investigated the relationships between these differences and the responses of surviving LGN neurons to visual stimulation. Recordings were made from surviving neurons in the degenerated A- and C-layers of the LGN in cats that had received a visual cortex lesion on the day of birth, at 8 weeks of age, or as adults (survival was 11.5-36 months). Normal adult cats were studied for comparison. The visual receptive field was mapped, and tests were carried out to classify each cell as X, Y, or W. In addition, quantitative methods were used to assess response amplitude, strength of receptive-field surround inhibition, spatial-frequency tuning to drifting or counterphased sine-wave gratings, and response to nondominant-eye stimulation for each cell. We found that surviving cells in all LGN layers respond to light, have normal receptive-field organization, and have normal eye dominance following a lesion at any age tested. In addition, gross retinotopic organization of the LGN is normal. However, 2 main abnormalities were observed following a lesion at all 3 ages. First, there is a reduction in the percentage of X cells in the A layers, from 62% in normal LGNs to about 15% in degenerated LGNs. Second, many surviving cells in both the A- and C-layers have abnormally large receptive-field centers. Other differences that were observed between normal A-layer cells and surviving A-layer cells could be attributed to the loss of X cells. These results indicate that cells within a structure that shows severe retrograde degeneration after brain damage can maintain relatively normal function and can take part in potentially important residual neural pathways. Previous studies indicate that these residual pathways can show both anatomical and physiological compensation for the brain damage, and the present findings bear on the consequences and mechanisms of this compensation.

Animals↗

PubMed1991

Temporal interactions in the cat visual system. I. Orientation-selective suppression in the visual cortex.

The perception of a visual contour depends on the spatial and temporal context in which it is viewed. Interactions between visual contours are believed to underlie a wide range of perceptual phenomena, including geometric illusions and aftereffects, contrast adaptation, and visual masking. The physiological mechanisms that might underlie such interactions were studied in the visual cortex of the cat by recording responses of single neurons to pairs of brief stationary stimuli that were separated in time. The results revealed a long-lasting, orientation-selective suppression, termed "paired-pulse suppression," which was strongest at the cell's preferred orientation, but which was more broadly tuned for orientation than the excitatory response of the cell. Although the strength and duration of the suppression varied widely, some degree of response reduction was present in most cells studied. The function of this suppression may be to regulate the gain with which visual inputs are transmitted to cortical neurons, thus preventing response saturation and positive feedback.

Anesthesia↗

PubMed1988

Noradrenergic sprouting and beta-adrenergic receptor binding in the lateral geniculate nucleus of rats after unilateral visual cortex ablation.

One and two weeks after unilateral visual cortex (VC) ablation beta-adrenergic receptor binding is increased in the lateral geniculate nucleus (LGN) of both sides. 6 month later beta-receptor binding in the LGN is decreased again and no differences to untreated control animals are detectable. Using the glyoxylic acid fluorescence method for the visualization of amines a transient increase in the density of noradrenergic fibers in the dorsal part of the ipsilateral LGN can be demonstrated with a maximum 2 weeks after VC ablation. With longer survival time noradrenergic fibre density in the ipsilateral dorsal LGN (LGNd) decreases again and one year after the operation only few fluorescent fibres can be observed in the lateral part of the LGN compared to untreated control animals. Histologically an increased gliosis in the ipsilateral LGNd develops following removal of the visual cortex. In addition, degenerative changes in nerve fibers and terminals as well as neuronal degenerative changes are present and are most pronounced in the medial part of the ipsilateral dorsal LGN. Electron microscopically degenerating terminals in the dorsal part of the ipsilateral LGN can be identified as cortical afferents. Using potassium permanganate fixation typical noradrenergic axons with small dense core vesicles can be demonstrated in the LGN. In the denervated LGNd (i.e. the ipsilateral LGNd after visual cortex ablation) axon terminals with dense core vesicles appear exhibiting the structural peculiarities of growth cones seen during ontogenesis. They could be regarded as ultrastructural equivalent of the newly formed noradrenergic sprouts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1975

Behavioral study of the visual cortex of Galago senegalensis.

An ablation study of the visual cortex of Galago senegalensis was undertaken in the hope of finding clues about the evolution of primate visual cortex. Removal of area 17 resulted in a profound sensory loss manifested by, first, the failure to discriminate between simple patterns; second, a deficit in localizing objects; third, a deficiency in tracking moving objects; and fourth, symptoms attributable to a deficiency in depth perception, such as misreaching and inaccurate jumping. Thus, the effects of ablating area 17 are similar in bushbabies and monkeys. In contrast, minimal sensory loss is produced by ablating area 17 in squirrels or tree shrews. This difference between primates and other mammals may depend on differences in the extent of the cortical target of the tecto-pulvinar path; in Galago and perhaps in all primates, more of the extrastriate visual cortex is entirely dependent on area 17. Removal of the ventral temporal cortex resulted in a loss of learned visual discriminations and in retardation in learning new visual discriminations. These symptoms seem related to the inferotemporal syndrome in monkeys.

Animals↗

PubMed1990

Arrangement of ocular dominance columns in human visual cortex.

The arrangement of the ocular dominance columns in the human primary visual cortex was studied by examining cytochrome oxidase activity in autopsy specimens of occipital lobes obtained from two patients who became blind in one eye before death. By artificially flattening the cortex before processing, it was possible to reconstruct the pattern formed by the ocular dominance columns throughout most of the primary visual cortex. The columns form a mosaic of irregular parallel stripes about 500 microns to 1000 microns wide (right eye column plus left eye column measures 1 to 2 mm), oriented at right angles to the boundary of the primary visual cortex. The columns are wider near the boundary of the primary visual cortex and within the representation of the peripheral visual field, the ocular dominance columns of the ipsilateral eye become fragmented until they disappear altogether at the border of the monocular crescent representation. The arrangement of ocular dominance columns in the human visual cortex is very similar to the pattern reported in the macaque monkey, although the columns in humans are wider.

Aged↗

PubMed1989

The development of basal forebrain projections to the rat visual cortex.

The development of the basal forebrain projections to the visual cortex of the rat were studied using retrograde tracer techniques. Injections of wheat germ agglutinin-horseradish peroxidase placed in the visual cortex of newborn animals resulted in labelling of neurons throughout the basal forebrain nuclei. Although at this time the overall distribution of retrogradely labelled cells within the basal forebrain appeared similar to that seen in the adult, cells were smaller and weakly stained. It was only at the end of the second postnatal week that the somata of stained neurons showed sizes and staining intensity comparable to the adult. This precedes or coincides with the reported significant increases in cortical and basal forebrain ChAT activity and the first detection of ChAT-labelled fibres in this cortical area. These data suggest an important developmental point around the end of the second postnatal week that may correspond to the time when a significant number of cholinergic axons first appear within the visual cortex. They also suggest that the cholinergic projections to the visual cortex develop late in comparison with the thalamic and other subcortical afferents in this cortical area.

Aging↗

PubMed1979

The rabbit and the cat: a comparison of some features of response properties of single cells in the primary visual cortex.

Receptive field characteristics of single cells in primary visual cortex of rabbit were studied. Seventy-two percent of cells were found to be orientation selective, and the remainder had concentric, uniform, movement selective or pure direction selective receptive fields. Single cells were also recorded from primary visual cortex of cat to permit a comparison of visual cortical organization in cats and rabbits. Laminar organization of receptive field types was observed in rabbits which was similar in most respects to that described in the cat. Although the major categories of orientation selective cells (simple, complex, hypercomplex) were similar for both cat and rabbit, many differences emerged: (I) tuning of orientation selectivity was narrower in cats than in rabbits; (II) units which preferred oblique orientations were less frequently represented in rabbits than in cats; (III) orientation preferences appeared to be arranged in clusters in rabbit cortex; in rabbits we found no evidence of the columnar organization of orientation selectivity which characterizes cat visual cortex. A comparison of our data with those previously reported for mouse, rat, hamster and opossum visual cortex suggest that mammals in which a significant proportion of visual cortical cells are not orientation selective have in common certain patterns of cortical organization involving a less precise and less specilized representation of stimulus orientation.

Animals↗

PubMed1991

Isochronic transplantation of neonatal grafts in the visual cortex of cats: responsiveness, ocular dominance and specificity of cortical cells to visual stimulation.

The visual cortex of adult cats was studied physiologically following neonatal isochronic transplantation of grafts from areas 17,18, which were placed homotopically, in order to reveal their functional integration and thus possible repairing of damaged cortical neuronal circuits. Three homograft cats, in which transplantation was carried out between siblings (228 cortical cells) were compared to 4 animals receiving reimplanted autografts of the equivalent size (131 cells) as well as 3 animals with analogous sectioning of the visual cortex (162 cells) (pseudograft controls). The location of the boundaries between the transplant region and the host were determined using the Nissl's method for staining histological cross sections. Extracellular unit recording revealed typical waveform of the action potentials in the transplanted region and in the surrounding host tissue of all groups of cats. Visual responsiveness in the homograft cats was 17.5% in the transplanted region and 80.4% in the unoperated hemisphere; the corresponding results were 40.3% for the transplanted region and 82.2% for the unoperated hemisphere in the autografts and 23.1% and 73.4% in the pseudografts. The specificity of the cells to visual stimulation as expressed by their orientation and direction specificity, indicated preservation of these properties in the transplanted cats. While all responsive cells in the transplanted region of the homografts were orientation specific, their proportion was 60% in the autografts and 55.5% in the analogous region in the pseudograft controls. As to the direction specific cells, their performance in the grafted region of the grafted cats was even much higher than that of the pseudograft controls. The ocular dominance distribution of the cells showed preservation of binocularity in the transplanted region (90.0% binocular cells) of the homografts; it was however smaller in the equivalent region of the autografts (65.0%) and remarkably reduced (20.0%) in the pseudografts. It was concluded that despite the deafferentation induced during the transplantation procedure, a remarkable visual responsiveness was found in the transplanted region, indicating postoperative recovery. However, the cells there were mainly affected in their activity and less in their specificity to visual stimulation.

Animals↗

PubMed1987

Effects of neonatal monocular and binocular enucleation on transient acetylcholinesterase activity in developing rat visual cortex.

Geniculo-recipient layers of visual cortical area 17 in the laboratory rat display a transient pattern of acetylcholinesterase (AChE) activity during the second and third postnatal weeks of life. The appearance of the AChE histochemical reaction product and its distribution in thalamic recipient layers of cortical area 17 suggest that this transient AChE serves as a marker for the region of geniculocortical axon terminals. In the present study, infant rats were enucleated monocularly or binocularly on the day of birth. Animals were sacrificed at postnatal days 5-21. Frozen sections cut in either the transverse plane or parallel to the pial surface were processed for AChE histochemistry. Neonatal monocular enucleation resulted in a marked reduction of transient AChE activity in thalamic recipient layers of the medial part of area 17 contralateral to the enucleated orbit, i.e., the monocular segment of area 17. No loss of AChE was observed in area 17 ipsilateral to the enucleation. Pigmented and albino strains of rats did not differ significantly in the extent to which monocular enucleation reduced the transient AChE in contralateral visual cortex. Neonatal binocular enucleation resulted in an almost complete loss of AChE histochemical staining in thalamic recipient layers throughout cortical area 17, without loss of AChE in other cortical regions. These data support the hypothesis that transient AChE serves as a marker for the region of geniculocortical axon terminals, and also demonstrate that the transient expression of AChE in visual cortex depends upon normal innervation or activity of the geniculocortical neurons.

Acetylcholinesterase↗