CIRCADIAN-RHYTHMS IN MICE CAN BE REGULATED BY PHOTORECEPTORS WITH CONE-LIKE CHARACTERISTICS

In this report we have characterized the photopigments mediating circa dian phase shifts in retinal degenerate (rd) mice. In aged rd/rd mice, which lack detectable opsin, high performance liquid chromatography ( HPLC) was used to quantify the photopigment chromophore 11-cis-retinal dehyde. This chromophore was photoisomerized in whole eyes, suggesting the presence of a functional opsin-based photopigment system. We also analyzed the spectral sensitivity of phase shifting circadian locomot or rhythms. Our data implicate a photopigment that is consistent with the involvement of the middle wavelength-sensitive cone photoreceptors (M-cones; lambda(max) = 511 nm) found in the mouse retina. In additio n, discrete near-ultraviolet (UV-A) pulses were capable of eliciting l arge phase shifts in circadian locomotor activity rhythms. This result is consistent with the involvement of the short wavelength-sensitive cone photoreceptors (UV-cones; lambda(max) = 359 nm) in photoentrainme nt. Collectively, these data suggest that both cone classes of the mou se may mediate the photic regulation of circadian rhythms. If this is the case, circadian sensitivity can be maintained by very few degenera te cones. Alternatively, an unknown class of ocular photoreceptor may fulfill this function.