GLYCINE RECEPTORS IN THE ROD PATHWAY OF THE MACAQUE MONKEY RETINA

The distribution of glycinergic synapses in macaque monkey retina was investigated. The monoclonal antibody (mAb2b) against the alpha 1 subu nit of the glycine receptor produced a punctate immunoreactivity that was localized to synapses. In central retina about 70% of the alpha 1 subunit-containing synapses were located in strata 1 and 2 of the inne r plexiform layer, about 30% were located in strata 3 and 4, and immun oreactivity was absent in stratum 5. Electron microscopy showed that t he majority of the synapses in strata 1 and 2 were on cone bipolar axo ns. The presynaptic profile always belonged to an amacrine cell. Presy naptic and postsynaptic profiles were further characterized using doub le-label immunofluorescence with cell-type specific antibodies against calcium-binding proteins. An antiserum against calretinin was used to label AII amacrine cells and an antiserum against recoverin was used to label flat midget bipolar cells. In the outer part of the IPL, 75% of the alpha 1-immunoreactive puncta were colocalized with calretinin- immunoreactive AII processes and 61% of the alpha 1-immunoreactive pun cta were colocalized with recoverin-positive midget bipolar axons. The se results suggest that the alpha 1 subunit of the glycine receptor is present at the chemical synapse made by AII amacrine cells with flat midget bipolar cells, thus providing a pathway for rod signals to reac h midget ganglion cells.