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S. Majumdar, H. Wassle; Glycinergic Synaptic Inputs of Two Ganglion Cell Types of the Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3102.
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Glycine and GABA are the major inhibitory neurotransmitters of the mammalian retina. Retinal ganglion cells receive glycinergic inputs from various narrow field amacrine cells. In this study, we have evaluated the spontaneous glycinergic inputs to the Alpha (A) and Bistratified (D) ganglion cells of the mouse retina (Sun et al., 2002. J. Comp. Neurol. 451:115–126.).
Patch–clamp recordings were performed from wholemounts of wildtype, Glrα1(–/–) and Glrα3(–/–) mice. During the recordings, cells were filled with Alexa568, helping recovery of the cell morphology after the experiments. The glycinergic spontaneous inhibitory post synaptic currents (sIPSCs) were recorded in the presence of GABA receptor blockers and the decay time constants (τdecay) of sIPSCs of wildtype and knockout mice were compared.
Large glycine induced currents were found in both A and D cells. Whilst A cells have glycinergic sIPSCs with very fast τdecay, D cells were found to have a mixture of fast and slow τdecay. In A cells of the Glrα1(–/–) mice, a reduction of the amplitude of glycinergic currents was observed and the frequency of sIPSCs substantially reduced. This suggests that A cells predominantly express α1 subunits. In contrast, no difference was observed for D cells in Glrα1(–/–) mice. In A cells of the Glrα3(–/–) mice, glycine evoked currents and glycinergic sIPSCs are indistinguishable from wild type mice. However, in D cells of Glrα3(–/–) mice, a group of slow glycinergic sIPSCs was missing. Hence, D cells express α3 subunits at some inhibitory synapses. In addition, the faster and slower glycinergic sIPSCs of D cells may be contributed from synapses expressing the α4 and α2 subunits, respectively.
A predominant expression of the fast conducting α1 subunit at their inhibitory input might shape the transient light responses of A cells. D2 cells are known to be the direction selective (DS) cells. The presence of both fast and slow GlyRs at their inhibitory input modulates their light responses, however, it is not responsible for DS light responses which are based on GABAergic inhibition (Wyatt and Daw, 1975. J. Neurophysiol. 38:613–626).
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