UV- and midwave-sensitive cone-driven retinal responses of the mouse: A possible phenotype for coexpression of cone photopigments

Molecular biological, histological and flicker electroretinographic results have established that mice have two cone photopigments, one peaking near 3 50 nm (UV-cone pigment) and a second near 510 nm [midwave (M)-cone pigment] . The goal of this investigation was to measure the action spectra and abso lute sensitivities of the UV-cone- and M-cone-driven b-wave responses of C5 7BL/6 mice. To achieve this goal, we suppressed rod-driven signals with ste ady or flashed backgrounds and obtained intensity-response relations for co ne-driven b-waves elicited by narrowband flashes between 340 and 600 nm. Th e derived cone action spectra can be described as retinal, pigments with pe aks at 355 and 508 nm. The UV peak had an absolute sensitivity of similar t o 8 nV/(photon mu m(2)) at the cornea, approximately fourfold higher than t he M peak. In an attempt to isolate UV-cone-driven responses, it was discov ered that an orange conditioning flash (lambda > 530 nm) completely suppres sed ERG signals driven by both M pigment- and UV pigment-containing cones. Analysis showed that the orange flash could not have produced a detectable response in the UV-cone pathway were their no linkage between M pigment- an d UV pigment-generated signals. Because cones containing predominantly the UV and M pigments have been shown to be located largely in separate parts o f the mouse retina (Szel et al., 1992), the most probable linkage is coexpr ession of M pigment in cones primarily expressing UV pigment. New histologi cal evidence supports this interpretation (Gloesman and Ahnelt, 1998). Our data are consistent with an upper bound of similar to 3% coexpression of M pigment in the cones that express mostly the UV pigment.