Distribution of glycine receptor subunits on primate retinal ganglion cells: a quantitative analysis

This study investigates the distribution of inhibitory neurotransmitter receptors on sensory neurons. Ganglion cells in the retina of a New World monkey, the common marmoset Callithrix jacchus, were injected with Lucifer yellow and Neurobiotin and subsequently processed with antibodies against one (alpha1), or against all subunits, of the glycine receptor, or against the anchoring protein gephyrin. Immunoreactive (IR) puncta representing glycine receptor or gephyrin clusters were found on the proximal and the distal dendrites of all ganglion cell types investigated. For both parasol and midget cells, the density of receptor clusters was greater on distal than proximal dendrites for all antibodies tested. In parasol cells the average density for the alpha1 subunit of the glycine receptor was 0.087 IR puncta/microm of dendrite, and for all subunits it was 0.119 IR puncta/microm of dendrite. Thus, the majority of glycine receptors on parasol cells contain the alpha1 subunit. For parasol cells, we estimated an average of 1.5 glycinergic synapses/100 microm2 dendritic membrane on proximal dendrites and about 9.4 glycinergic synapses/100 microm2 on distal dendrites. The segregation of receptors to the distal dendrites appears to be a common feature of inhibitory neurotransmitter input to parasol and midget cells, and might be associated with the receptive field surround mechanism.