Localization of GABA receptor rho 2 and rho 3 subunits in rat brain and functional expression of homooligomeric rho 3 receptors and heterooligomeric rho 2 rho 3 receptors

Ionotropic GABA receptors that are composed of rho subunits act to gate bic uculline-insensitive Cl- currents. Reverse transcription-polymerase chain r eaction analysis revealed that the expression of rho 2 mRNA in adult rat br ain was approximately eight times higher than mRNA in the rat brain at embr yonic day 16, while that of rho 3 in the embryonic brain was approximately six times higher than in the adult brain. In the adult rat brain the rho 3 mRNA was present in the mesencephalon, hippocampus, cerebellum, thalamus an d basal ganglia. In situ hybridization has been used to demonstrate the pre sence of rho 2 mRNA in the hippocampal CA1 region of the 8-day-old rat, and in the CA1 region of the hippocampus, lateral geniculate nucleus, superfic ial gray layer of the superior colliculus and the pars compacta of the subs tantia nigra of the adult rat. When the homooligomeric rho 3 receptors were expressed in Xenopus oocytes, applications of agonists induced ionic curre nts, The order of potency of the agonists was muscimol > GABA is approximat ely equal to trans-4-aminocrotonic acid > cis-4-aminocrotonic acid. The ion ic currents induced by GABA were blocked by picrotoxinin and Zn2+ in dose-d ependent manner. In heterooligomeric rho 2 rho 3 receptors, picrotoxinin se nsitivity was significantly reduced.