Expression of GABAC receptor ρ1 and ρ2 subunits during development of the mouse retina

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Abstract
Retinal γ-aminobutyric acid type C (GABAC) receptors consist of ρ subunits. Here we report our results from a competitive PCR and patch-clamp electrophysiology study quantifying ρ subunit message and characterizing GABAC receptor-mediated currents at different stages of mouse retinal development. Mouse ρ1 message is first detected at postnatal day 6 (P6), increases significantly until P9 and remains at this level through adulthood, whereas mouse ρ2 message does not appear until P9, peaks at P15 and remains at this level through adulthood. There is an approximate twofold excess of ρ1 compared to ρ2 message at most stages of development, which persists in adulthood. Functional GABAC receptors are detected in acutely dissociated bipolar cells of P9 or older mouse retina. Early in development (P9–10), GABAC receptors are composed solely of ρ1 subunits, but subsequently contain ρ1 and/or ρ2 subunits (by P11 and later). These findings are intriguing because the onset and rapid increase in ρ subunit transcription and functional expression match the initiation and active period of bipolar cell differentiation in retinal development as well as the stage of eye opening and initial visual experience in the rodent. The investigation of mouse ρ subunits here forms a basis for future studies on the role of GABAC receptors in retinal development.