CONES ARE REQUIRED FOR NORMAL TEMPORAL RESPONSES TO LIGHT OF PHASE SHIFTS AND CLOCK GENE EXPRESSION

• Published in: Chronobiology international Vol. 27; no. 4; pp. 768 - 781
• Main Authors: Dollet, Anna, Albrecht, Urs, Cooper, Howard M., Dkhissi-Benyahya, Ouria
• Format: Journal Article
• Language: English
• Published: England Informa Healthcare 01.05.2010; Taylor & Francis
• Subjects: Animals; Biological Clocks - physiology; Circadian Rhythm - physiology; Circadian system; Clock genes; Gene Expression; Light; Male; Melanopsin; Mice; Mice, Knockout; Period Circadian Proteins - genetics; Period Circadian Proteins - metabolism; Phase shift; Photic Stimulation; Retina; Retinal Cone Photoreceptor Cells - physiology; SCN; Suprachiasmatic Nucleus - physiology; Time Factors
• ISSN: 0742-0528; 1525-6073
• DOI: 10.3109/07420521003695704

In mammals, non-visual responses to light involve intrinsically photosensitive melanopsin-expressing retinal ganglion cells (ipRGCs) that receive synaptic inputs from rod and cone photoreceptors. Several studies have shown that cones also play a role in light entrainment, photic responses of the suprachiasmatic nucleus (SCN), pupil constriction, and sleep induction. These studies suggest that cones are mainly involved in the initial response to light, whereas melanopsin provides a sustained input for non-visual responses during continued light exposure. Based on this idea, we explored the effects of the absence of middle-wavelength (MW)-cones on the temporal responses of circadian behavior and clock gene expression in light. In mice lacking MW-cones, our results show a reduction in behavioral phase shifts in response to light stimulations of short duration at 480 and 530 nm, but no alteration for short-wavelength (360-nm) light exposures. Similarly, induction of the period gene mPer1 and mPer2 mRNAs in the SCN are attenuated in response to light exposures of mid to long wavelengths. Modeling of the photoresponses shows that mice lacking MW-cones have an overall reduction in sensitivity that increases with longer wavelengths. The differences in photic responsiveness are consistent with the idea that cones provide a strong initial phasic input to the circadian system at light-onset and may confer a priming effect on ipRGC responses to sub-threshold light exposures. In summary, the contribution of MW-cones is essential for the normal expression of phase shifts and clock gene induction by light in mammals. (Author correspondence: ouria.benyahya@inserm.fr)