EXPRESSION OF GABA RECEPTOR RHO-SUBUNIT IN RAT-BRAIN

The GABA receptor rho 1, rho 2, and rho 3 subunits are expressed in th e retina where they form bicuculline-insensitive GABA(c) receptors. We used northern blot, in situ hybridization, and RT-PCR analysis to stu dy the expression of rho subunits in rat brains. In situ hybridization allowed us to detect rho-subunit expression in the superficial gray l ayer of the superior colliculus and in the cerebellar Purkinje cells. RT-PCR experiments indicated that (a) in retina and in domains that ma y contain functional GABA(c) receptors, rho 2 and rho 1 subunits are e xpressed at similar levels; and (b) in domains and in tissues that are unlikely to contain GABA(c) receptors, rho 2 mRNA is enriched relativ e to rho 1 mRNA. These results suggest that both rho 1 and rho 2 subun its are necessary to form a functional GABA(c) receptor. The use of RT -PCR also showed that, except in the superior colliculus, rho 3 is exp ressed along with rho 1 and rho 2 subunits. We also raised an antibody against a peptide sequence unique to the rho 1 subunit. The use of th is antibody on cerebellum revealed the rat rho 1 subunit in the soma a nd dendrites of Purkinje neurons. The allocation of GABA(c) receptor s ubunits to identified neurons paves the way for future electrophysiolo gical studies.