Intrinsically photosensitive retinal ganglion cells (ipRGCs) combine direct photosensitivity through melanopsin with synaptically mediated drive from classical photoreceptors through bipolar-cell input. Here, we sought to provide a fuller description of the least understood ipRGC type, the M5 cell, and discovered a distinctive functional characteristic—chromatic opponency (ultraviolet excitatory, green inhibitory). Serial electron microscopic reconstructions revealed that M5 cells receive selective UV-opsin drive from Type 9 cone bipolar cells but also mixed cone signals from bipolar Types 6, 7, and 8. Recordings suggest that both excitation and inhibition are driven by the ON channel and that chromatic opponency results from M-cone-driven surround inhibition mediated by wide-field spiking GABAergic amacrine cells. We show that M5 cells send axons to the dLGN and are thus positioned to provide chromatic signals to visual cortex. These findings underscore that melanopsin's influence extends beyond unconscious reflex functions to encompass cortical vision, perhaps including the perception of color. Stabio et al. describe a novel type of output neuron of mouse retina that exhibits both direct, melanopsin-based photosensitivity and center-surround chromatic opponency generated by amacrine-cell inhibition. Their signals are routed toward visual cortex, where they may support color perception.
Bibliographical noteFunding Information:
The authors thank Dianne Boghossian and Kimberly Boghossian for assistance maintaining and genotyping mice; Tom Finger for laboratory support and advice, Sümbül and colleagues for sharing their code for digital flattening of confocal z stacks; Sam Mancuso and Mark Hornsby for statistical advice; and Tiffany Zhao for performing some intraocular injections. This work was funded by NIH Grants F32-EY021994 to M.E.S., R01-EY012793 to D.M.B., NSF Grant I2011104359 to P.M.F., and the Banting Postdoctoral Fellowship of Canada to S.S.
© 2017 Elsevier Inc.
- amacrine cells
- bipolar cells
- color vision
- cone opsins
- ganglion cell photoreceptors
- intrinsically photosensitive retinal ganglion cells
- lateral geniculate nucleus
- retinal ganglion cells