Abstract
Abstract: :
Purpose: Glycine, next to GABA, is the major inhibitory transmitter of the mammalian retina. Approximately 50% of all amacrine cells are glycinergic. However, the role of glycine in retinal function and the synaptic details are still poorly understood. Here we studied the molecular diversity of the postsynaptic glycine receptors (GlyRs). Methods: GlyRs are ligand–gated chloride channels composed of α and ß subunits forming the pentameric receptor protein. Molecular cloning has revealed four genes encoding the α subunits (α1, α2, α3, α4) and only one gene encoding the ß subunit. We applied antibodies that specifically recognize the α1, α2 and α3 subunits to sections of the mouse retina and studied the distribution of GlyRs by fluorescence light microscopy. Results: All three subunits were aggregated in brightly fluorescent puncta throughout the inner plexiform layer (IPL), which we interprete as postsynaptic clusters of GlyRs. GlyRα3 clusters were most frequent, followed by GlyRα2, and GlyRα1 clusters. Different α subunits were only rarely colocalized in the same postsynaptic cluster. We also studied the involvement of the different GlyRs in identified neuronal circuits such as the AII to OFF cone bipolar cell synapses. Specific patterns of expression were found which differed both according to the pre– and postsynaptic partners. Conclusions: Glycinergic inhibition in the retina is complex. It involves many different types of glycinergic amacrine cells, and at least three different isoforms of GlyRs are expressed at glycinergic synapses.
Keywords: retinal connections, networks, circuitry • inhibitory neurotransmitters • neurotransmitters/neurotransmitter systems