Quantitative comparisons of gamma-aminobutyric acid neurons and receptors in the visual cortex of normal and dark-reared cats.

Physiological studies suggest that the function of the visual cortical gamma-aminobutyric acid (GABA) system is abnormal in cats reared in total darkness. The present study asked whether visual input is necessary for the normal postnatal anatomical development of the GABA system by comparing GABA neurons and receptors in the visual cortex of normal and dark-reared cats. Immunohistochemical techniques (anti-GABA) were used to localize GABA neurons. In both rearing conditions, GABA neurons were stained rather uniformly in all cortical layers. Counts of GABA cells indicated a marked increase in density in dark-reared compared to normal cats. Counts of total cellular density in cresyl-stained sections, however, indicated a comparable increase in dark-reared cats. When corrected for total cellular density, there were no differences between dark-reared and normal cats in the density of GABA cells per layer, or the relative proportion of GABA cells across cortical layers. In vitro receptor binding of 3H-muscimol was used to compare GABAA receptors in the two rearing conditions. When corrected for total cellular density, saturation kinetics indicated no difference in the total number or affinity of receptors. Similarly, autoradiographic histology indicated no difference in the laminar distribution of receptors across cortical layers between dark-reared and normal cats. These results indicate that the postnatal development of GABA neurons and receptors occurs normally in the absence of visual input.