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

VALDEZ, DIE GO JAVIER; NIETO PAULA SOFIA; DELLA COSTA NATALIA; GUIDO MARIO EDUARDO

Mendoza

Simposio; XII Latin American Symposium on Chronobiology; 2013

The vertebrate retina is a photosensitive tissue including cones and rods photoreceptors (PRs) that expresses 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 (Guido et al 2010). In mammals, the melanopsin-associated photosensitivity is fundamental for non-image-forming responses (photoentrainment of daily rhythms, pupil constriction, etc) (Lucas et al 2003; Freedman et al 1999). 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 (Valdez et al 2009).  Other studies showed that melanopsin mRNA expression in the chicken retina displays a circadian rhythmicity (Chaurasia et al 2005). Taking into account these evidences, we hypothesize that the PLR in chickens could display a circadian regulation.