Circadian control of the pupillary light responses in an avian model of blindness, the GUCY1 chickens

The vertebrate inner retina has a subset of intrinsically photosensitive retinal ganglion cells (ipRGCs) that express the nonvisual photopigment melanopsin. The intrinsically photosensitive retinal ganglion cells send light information from the environment to the brain to control, among other parameters, the amount of energy entering the eyes through the pupillary light reflex (PLR). A daily variation in the PLR in both mice and humans has recently been shown, indicating circadian control of this response. In a previous work involving the sensitivity spectra for the PLR, we showed that blind chickens (GUCY1*) display the highest sensitivity to light of 480 nm. The aim of the present study was to evaluate the potential circadian control of PLRs in blind birds under scotopic conditions. Circadian PLR was performed on GUCY1* chickens with lights of different wavelengths (white or blue light of 475 nm) under scotopic conditions. We found a significant daily variation in the PLRs of chickens exposed to white or blue light of 475 nm, with increased sensitivity at circadian time 6 during the subjective day. Our observations clearly point to circadian control of PLRs even in blindness, strongly indicating that both the entry of light into the eyes and its quality are differentially regulated during the day in diurnal animals.