Circadian rhythms of mammals are entrained by light to follow the daily solar cycle (photoentrainment). To determine whether retinal rods and cones are required for this response, the effects of light on the regulation of circadian wheel-running behavior were examined in mice lacking these photoreceptors. Mice without cones (cl) or without both rods and cones (rdta/cl) showed unattenuated phase-shifting responses to light. Removal of the eyes abolishes this behavior. Thus, neither rods nor cones are required for photoentrainment, and the murine eye contains additional photoreceptors that regulate the circadian clock.

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The atrophied subcutaneous eyes of Spalax ehrenbergi (the blind mole rat) express a long wavelength sensitive (LWS) cone opsin. Our data provide strong evidence that this photopigment is spectrally tuned to enhance photon capture in the red light environment of the eye. Furthermore, novel mechanisms appear partially responsible for this sensory finetuning. These data support the hypothesis that the LWS opsin of Spalax acts as a functional photopigment and that it is not à residue' of the pre-subterranean visual system. As the eye of Spalax has only one known function, the entrainment of circadian rhythms to environmental light, the LWS photopigment is implicated in this task. These results, together with our recent findings that rod and cone photopigments are not required for murine photoentrainment, suggest that multiple photopigments (classical and novel) mediate the effects of light on the mammalian circadian system. z 1999 Federation of European Biochemical Societies.