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 GlyRalphal {Glml~(spd-ot), 'oscillator' mouse), the GlyRalpha2 (Glra2~(-/-)) and the GlyRalpha3 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-SI, MA-S1/S5, A17, PA-SI, 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, r ~25 ms). Group II cells showed glycinergic sIPSCs and glycine induced currents in wild-type, Glral~(spd-ot) and Glra3~(-/-) mice (t ~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 (t ~50-70ms). We propose that GlyRs of group II cells are dominated by the a2 subunit; GlyRs of ON-starburst amacrine cells appear to be dominated by the alpha4 subunit.
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