GABAC receptors are expressed in GABAergic and non-GABAergic neurons of the rat superior colliculus and visual cortex

Abstract

GABA(C) receptors are enriched in the upper grey layers of the mammalian superior colliculus and contribute to synaptic processing. Electrophysiological data suggested that the GABA(C) receptor ρ subunits are expressed by GABAergic interneurons which represent about half of the neurons in the stratum griseum superficiale (SGS). Combining in situ hybridization for ρ2 receptor mRNA and the glutamic acid decarboxylase GAD-65 mRNA confirmed this assumption. A majority of ρ-labeled neurons in SGS and pretectum are GABAergic. Combining in situ hybridization with immunohistochemistry for the two projection neuron markers calbindin and parvalbumin revealed that a few ρ2 mRNA expressing cells coexpressed calbindin, but not parvalbumin. In visual cortex, ρ2 mRNA was present in pyramidal neurons and parvalbumin-containing interneurons. The results show that in the SGS primarily GABAergic neurons express GABA(C) receptors whereas the majority of tectothalamic calbindin neurons and intrinsically projecting parvalbumin neurons do not.