Morphological Identification of Melanopsin-Expressing Retinal Ganglion Cell Subtypes in Mice.

Melanopsin-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs) are a relatively recently discovered class of photoreceptor. ipRGCs can be subdivided into at least five subtypes (M1-M5), each of which has a distinct complement of morphological and physiological properties. ipRGC subtypes can be identified morphologically based on a combination of dendritic morphology and immunostaining for a cell-type specific marker. In this chapter, we describe methods for conclusively identifying each of the five ipRGC subtypes through a combination of patch clamp electrophysiology, Neurobiotin filling, visualization of ipRGC dendrites, and immunostaining for the marker SMI-32.