Regulation of mammalian circadian behavior by non-rod, non-cone, ocular photoreceptors

Circadian rhythms of mammals are entrained by light to follow the daily sol ar cycle (photoentrainment). To determine whether retinal rods and cones ar e required for this response, the effects of light on the regulation of cir cadian wheel-running behavior were examined in mice lacking these photorece ptors. Mice without cones (cl) or without both rods and cones (rdta/cl) sho wed unattenuated phase-shifting responses to light. Removal of the eyes abo lishes this behavior. Thus, neither rods nor cones are required for photoen trainment, and the murine eye contains additional photoreceptors that regul ate the circadian clock.