Expression of GABA(C) receptor rho 1 and rho 2 subunits during developmentof the mouse retina

Retinal gamma-aminobutyric acid type C (GABA(C)) receptors consist of rho s ubunits. Here we report our results from a competitive PCR and patch-clamp electrophysiology study quantifying rho subunit message and characterizing GABA(C) receptor-mediated currents at different stages of mouse retinal dev elopment. Mouse rho 1 message is first detected at postnatal day 6 (P6), in creases significantly until P9 and remains at this level through adulthood, whereas mouse rho 2 message does not appear until P9, peaks at P15 and rem ains at this level through adulthood. There is an approximate twofold exces s of rho 1 compared to rho 2 message at most stages of development, which p ersists in adulthood. Functional GABA(C) receptors are detected in acutely dissociated bipolar cells of P9 or older mouse retina. Early in development (P9-10), GABA(C) receptors are composed solely of rho 1 subunits, but subs equently contain rho 1 and/or rho 2 subunits (by P11 and later). These find ings are intriguing because the onset and rapid increase in rho subunit tra nscription and functional expression match the initiation and active period of bipolar cell differentiation in retinal development as well as the stag e of eye opening and initial visual experience in the rodent. The investiga tion of mouse rho subunits here forms a basis for future studies on the rol e of GABA(C) receptors in retinal development.