Chromatic Coding from Cone-type Unselective Circuits in the Mouse Retina

Retinal specializations such as cone-photoreceptor opsin-expression gradients, as found in several vertebrate species, are intuitively considered detrimental to color vision. In mice, the majority of cones coexpress both "blue" and "green" opsin. The coexpression ratio changes along the dorsoventral axis, resulting in a "green"-dominant dorsal and a "blue"-dominant ventral retina. Here, we asked how these specializations affect chromatic processing, especially with respect to the opsin transitional zone, the band where opsin coexpression shifts from "green" to "blue." Using electrophysiology, modeling, and calcium imaging, we found that "alpha-like" retinal ganglion cells, which previously have not been implicated in chromatic processing, display color-opponent responses when located in the vicinity of the opsin transitional zone. Moreover, direction-selective ganglion cells within this zone respond differentially to color sequences. Our data suggest that the dorsoventral opsin distribution, in combination with conventional spatiotemporal processing, renders mouse ganglion cell responses color-opponent without requiring cone-type selective connectivity.