Gamma-aminobutyric acid (GABA) interneurons, the principal mediators of intracortical inhibition, are a heterogeneous group that displays marked diversity in morphological and chemical characteristics. The GABA neurons of monkey area 17 are a morphologically and chemically heterogeneous population of interneurons that are normally distributed most densely within the geniculocortical recipient zones of the visual cortex. In adult monkeys, which are deprived of visual input from one eye, the levels of immunoreactivity for GABA and glutamate decarboxylase (GAD) within neurons of these geniculocortical zones are reduced. Similar changes are seen in the levels of proteins that make up the GABAA receptor subtype. The effects of monocular deprivation on other substances suggest that specific types of GABA neurons, such as those in which the tachykinin neuropeptide family and parvalbumin coexist with GABA, are greatly influenced by changes in visual input. The fact that some proteins remain normal within deprived-eye neurons and other proteins are increased indicates that the changes in the GABA cells of the cortex are not the result of a general reduction in protein synthesis.
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