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

This study investigates the distribution of inhibitory neurotransmitter rec eptors on sensory neurons. Ganglion cells in the retina of a New World monk ey, the common marmoset Callithrix jacchus, were injected with Lucifer yell ow and Neurobiotin and subsequently processed with antibodies against one ( alpha1), or against all subunits, of the glycine receptor, or against the a nchoring protein gephyrin. Immunoreactive (IR) puncta representing glycine receptor or gephyrin clusters were found on the proximal and the distal den drites of all ganglion cell types investigated. For both parasol and midget cells, the density of receptor clusters was greater on distal than proxima l dendrites for all antibodies tested. In parasol cells the average density for the alpha1 subunit of the glycine receptor was 0.087 IR puncta/mum of dendrite, and for all subunits it was 0.119 IR puncta/mum of dendrite. Thus , the majority of glycine receptors on parasol cells contain the alpha1 sub unit. For parasol cells, we estimated an average of 1.5 glycinergic synapse s/100 mum(2) dendritic membrane on proximal dendrites and about 9.4 glycine rgic synapses/100 mum(2) on distal dendrites. The segregation of receptors to the distal dendrites appears to be a common feature of inhibitory neurot ransmitter input to parasol and midget cells, and might be associated with the receptive field surround mechanism.