Daily rhythms in the pupillary light reflex in blind GUCY1* chickens

VALDEZ, D. J.; NIETO, P.S.; DELLA COSTA, N.S.; SCHURRER, C; GUIDO, M. E.

Tunuyan

Simposio; XII Latin American Symposium on Chronobiology; 2013

The vertebrate retina is a photosensitive tissue including cones and rods photoreceptors (PRs) that express classical photopigments involved in day/night vision respectively and a subset of retinal ganglion cells (RGCs) shown to be intrinsically photosensitive (ipRGCs) expressing the non-visual photopigment melanopsin. In mammals, the melanopsin-associated photosensitivity is fundamental for non-image-forming responses (photoentrainment of daily rhythms, pupil constriction, etc). These responses persist in blind animals but are abolished by bilateral enucleation. Previous studies involving pupillary light reflexes (PLR) suggested that both the melanopsin- and the classical PR systems are complementary and provide together the full dynamic range of normal PLR. We have previously demonstrated that blind chickens lacking PRs (GUCY1*) do express melanopsin in the RGCs and exhibit PLR with a maximum sensitivity at 480 nm. Other studies showed that melanopsin mRNA expression in the chicken retina displays a circadian rhythmicity. Taking into account these evidences, we hypothesize that the PLR in chickens could display a circadian regulation. To test this, we have measured the PLR in GUCY1* birds at different circadian times (CT) during 24 h after stimulation with white, violet (430 nm) or blue (475 nm) lights. We found that GUCY1* chickens exhibit a daily variation in PLRs after white light exposure (p