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B.A. Ekesten, P. Gouras; Identification of rod and cone signals in murine retinal ganglion cells . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4271.
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Purpose: Because of behavioral evidence of color vision in mice in the presence of significant co–expression of both cone pigments in the same cones as well as a different spatial distribution of M–and UV–cones in murine retina, we are trying to determine whether signals transmitted by murine ganglion cells are compatible with color vision processing and/or co–expression of opsins in all cones. Methods: Responses of single impulse producing neurons are detected with a metal electrode into the intact eye of an anesthetized mouse. The position of the electrode on the retina can be seen through a dilated pupil with a thin cover slip on the cornea. The eye is proptosed and the extra–ocular muscles are cut to reduce eye movements and the head fixed to minimize respiratory movements. Photoreceptor responses are identified by comparing the responses of each ganglion cell to two wavelengths of stimulation (360 and 520 nm) at different energies of stimulation in the absence and presence of selective chromatic adaptation. A rod response is identified by its absence in the presence of a dim adapting field. M–cone responses are identified by significant response weakening in the presence of a strong yellow adapting field. UV–cone responses are identified by tolerance of the latter adapting field. The stimulus is a full field xenon strobe flash before the eye and filtered by narrow band filters. Results: Five classes of ganglion cells have been found: on–cells with only UV cone inputs; on–cells with rod and weak UV cone inputs; on–cells with rod and weak M–cone inputs; off–cells with rod and weak UV cone inputs; off–cells with rod and strong UV inputs. The latter cells are unusual because the UV cone off response is much quicker than the rod off–response. Some cells with low sensitivity cannot be classified. Classic color opponent cells have not been found yet. Conclusions:Some ganglion cells receive inputs from only UV cones. Co–expression of opsins cannot be complete. Strong inputs from M–cones are not as easy to detect. Color vision remains a possibility.
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