Autoradiographic localization of GABAergic and muscarinic cholinergic receptor sites in the visual system of the kitten.

The distribution of binding sites for [3H] muscimol (which binds to GABA, receptor) and [3H] QNB (which binds to muscarinic cholinergic receptor) was studied in visual areas of 5 week-old kittens using contact film autoradiography after incubation in vitro of brain sections. A distinct laminar localization of [3H] muscimol receptor sites was observed in young animals with the highest density in layers II/ III and IV of all cortical areas that were investigated. For [3H] QNB binding a laminar pattern of distribution was also found with labeling in layer V exceeding that in adjacent layers. A small intracortical regional variability was noted, for both of the investigated neuroreceptors. [3H] muscimol labeling of the lateral geniculate nucleus and superior colliculus was weaker in comparison to that found in the cortex. The superficial layers of the superior colliculus revealed a high density of [3H] muscimol and [3H] QNB binding sites. The laminar and regional variations in the distribution of [3H] muscimol and [3H] QNB binding sites observed in young kittens, may be related to the possible role of GABAergic and muscarinic receptors in regulation of plastic changes that occur after visual deprivation.