Diversity of glycine receptors in the mouse retina: Localization of the α4 subunit

Abstract

Glycine and γ-aminobutyric acid (GABA) are the major inhibitory neurotransmitters in the retina. Approximately half of the amacrine cells release glycine at their synapses with bipolar, other amacrine, and ganglion cells. Whereas the retinal distributions of glycine receptor (GlyR) subunits α1-, α2, and α3 have been mapped, the role of the α4 subunit in retinal circuitry remains unclear. A rabbit polyclonal antiserum was raised against a peptide that comprises the C-terminal 14 amino acids of the mouse GlyR α4 subunit. Using immunocytochemistry, we localized the α4 subunit in the inner plexiform layer (IPL) in brightly fluorescent puncta, which represent postsynaptically clustered GlyRs. This was shown by double-labeling sections for GlyR α4 and synaptic markers (bassoon, gephyrin). Double-labeling sections for GlyR α4 and the other GlyR α subunits shows that they are mostly clustered at different synapses; however, ∼30% of the α4-containing synapses also express the α2 subunit. We also studied the pre- and postsynaptic partners at GlyR α4-containing synapses and found that displaced (ON-) cholinergic amacrine cells prominently expressed the α4 subunit. The density of GlyR α4-expressing synapses in wildtype, Glra1ot/ot, and Glra3-/- mouse retinas did not differ significantly. Thus, there is no apparent compensation of the loss of α1 or α3 subunits by an upregulation of a4 subunit gene expression; however, the α2 subunit is moderately upregulated. © 2006 Wiley-Liss, Inc.