Intrinsically photosensitive ganglion cells of the primate retina express distinct combinations of inhibitory neurotransmitter receptors.

Intrinsically-photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin and function as irradiance detectors, responsible for crucial non-image forming visual functions. In addition to their intrinsic photosensitivity, ipRGCs are also activated by synaptic inputs originating at the classical photoreceptors, rods and cones. Little is known about inhibition through these retinal pathways, despite ipRGCs receiving massive synaptic inputs from inhibitory amacrine interneurons. We performed a wide anatomical screening for neurotransmitter receptors possibly involved in the inhibitory modulation of ipRGCs in the macaque retina. We investigated both subtypes of primate ipRGCs described so far and report that outer-stratifying (M1) cells possess mainly GlyR α2 and GABA(A)R α3 subunits, while inner-stratifying (M2) cells are overall subject to less inhibitory modulation. Our results suggest that M1 and M2 ipRGC subtypes are modulated via distinct inhibitory intraretinal circuits.