Role of GABA A and GABA B receptors in GABA-induced inhibition of rat red nucleus neurons.

We investigated GABA receptor subtypes mediating GABA-induced inhibition of red nucleus (RN) neuronal firing recorded extracellularly from anaesthetized rats. GABA response was mimicked by the GABA(A) agonists muscimol and isoguvacine in all cases and was partially blocked by the GABA(A) antagonist bicuculline. The GABA(B) agonist baclofen induced a long-lasting inhibition in 84% of cells. Neurons responding to either GABA(A) or GABA(B) agonists were equally distributed within the RN. The GABA(C) receptor agonist cis-amino-crotonic acid (CACA) did not modify RN neuronal firing; at high doses CACA occasionally induced inhibition abolished by bicuculline and thus mediated by GABA(A) receptors. We conclude that the inhibitory effects of GABA in the RN are mediated by both GABA(A) and GABA(B) receptors, whereas GABA(C) receptors are not involved.