Regulation of Mammalian Circadian Behavior by Non-rod, Non-cone, Ocular Photoreceptors

TLDR

Circadian rhythms in mammals are entrained by light to align with the daily solar cycle. The study examined whether retinal rods and cones are necessary for photoentrainment by assessing light‑induced phase shifts in wheel‑running behavior of mice lacking these photoreceptors. Mice lacking cones or both rods and cones displayed normal phase‑shifting responses, whereas enucleation abolished the behavior, indicating that additional ocular photoreceptors mediate circadian photoentrainment.

Abstract

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.