Glycinergic input of widefield, displaced amacrine cells of the mouse retina

Glycine receptors (GlyRs) of displaced amacrine cells of the mouse retina were analysed using whole cell recordings and immunocytochemical staining with subunit-specific antibodies. During the recordings the cells were filled with a fluorescent tracer and 11 different morphological types could be identified. The studies were performed in wild-type mice and in mutant mice deficient in the GlyR alpha 1 (Glra1(spd-ot), 'oscillator' mouse), the GlyR alpha 2 (Glra2(-/-)) and the GlyR alpha 3 subunit (Glra3(-/-)). Based on their responses to the application of exogenous glycine in the retinas of wild-type and mutant mice, the cells were grouped into three major classes: group I cells (comprising the morphological types MA-S5, MA-S1, MA-S1/S5, A17, PA-S1, PA-S5 and WA-S1), group II cells (comprising the morphological types PA-S4, WA-S3 and WA-multi) and ON-starburst cells. For further analysis, spontaneous inhibitory postsynaptic currents (sIPSCs) were measured both in wild-type and mutant mouse retinas. Glycinergic sIPSCs and glycine induced currents of group I cells remained unaltered across wild-type and the three mutant mice (mean decay time constant of sIPSCs, tau similar to 25 ms). Group II cells showed glycinergic sIPSCs and glycine induced currents in wild-type, Glra1(spd-ot) and Glra3(-/-) mice (tau similar to 25 ms); however, glycinergic currents were absent in group II cells of Glra2(-/-) mice. Glycine induced currents and sIPSCs recorded from ON-starburst amacrine cells did not differ significantly between wild-type and the mutant mouse retinas (tau similar to 50-70 ms). We propose that GlyRs of group II cells are dominated by the alpha 2 subunit; GlyRs of ON-starburst amacrine cells appear to be dominated by the alpha 4 subunit.