Glycinergic input of small-field amacrine cells in the retinas of wildtype and glycine receptor deficient mice

Amacrine cells are known to express strychnine-sensitive glycine receptors (GlyRs), however, it is not known which of the four GlyRalpha subunits (alpha1-4) are expressed in this diverse group of cells. Herein, we studied the presence of glycine activated currents and spontaneous inhibitory postsynaptic currents (sIPSCs) of amacrine cells in the mouse retina. By recording glycinergic currents in retinal slices of wildtype mice and of mice deficient in GlyRalpha subunits (Glra1spd-ot, Glra2-/-, Glra3-/-), we could classify AII and narrow-field amacrine cells (NF, Types 5, 6, 7) on the basis of their alpha-subunit composition. Glycinergic sIPSCs of AII cells displayed medium fast kinetics (mean decay time constant tau=11+/-2 ms), which were completely absent in the Glra3-/- mouse, indicating that synaptic GlyRs of AII cells mainly contain the alpha3 subunit. Glycinergic sIPSCs of NF cells had slow kinetics (tau=27+/-6.8 ms) that were significantly prolonged in Glra2-/- mice (tau=69+/-16 ms). These data show that morphologically distinct amacrine cells express different sets of GlyRs.