Meeting Abstract
Distinct populations of retinal ganglion cells (RGCs) drive image forming and non-image forming vision. Intrinsically photosensitive (ip)RGCs express the photopigment melanopsin and drive non-image forming functions such as circadian photoentrainment and the pupillary light reflex. Ablation of ipRGCs results in loss of non-image forming behaviors but intact rod/cone dependent image forming vision. These findings have led to the conclusion that ipRGCs are simple photoreceptors that convey brightness information to mediate non-image forming vision, while conventional RGCs mediate image formation via relay of more complex features of the visual scene. Contradictory to this prevailing view, we find that a conventional RGC type, the ON alpha RGC, is intrinsically photosensitive. Furthermore, we find that melanopsin allows ON alpha RGCs to signal both lighting history and changes in environmental luminance over long periods of time. Consistent with the high contrast sensitivity of alpha RGCs, animals lacking melanopsin or completely lacking ON alpha RGCs have a clear deficit in visual contrast sensitivity as assayed by optokinetic tracking, demonstrating that melanopsin plays an unexpected role in contrast detection. Furthermore, this phenomenon is not specific to mice as the ON alpha-like RGCs of the ground squirrel are also intrinsically photosensitive. These findings suggest that melanopsin functions in the image-forming visual system to influence physiology and behavior.
