A chicken model of blindness reveals functional photoreceptors in the inner retina of non-mammalian vertebrates

VALDEZ DJ; NIETO PS; GARBARINO PICO E; GUIDO ME

Destin, Florida

Congreso; XI Meeting Society for Research on Biological Rhythms; 2008

Society for Research on Biological Rhythms

In mammals, photoreceptors (PRs) located in the inner retina convey photic information to the brain via a non-image forming (NIF) circuitry that regulates a number of non-visual functions. In non-mammalian vertebrates, the retina, deep brain PRs and the pineal organ may be photoreceptive; however, the study of the NIF circuitry has not been explored yet. Herein, we investigated light perception in the absence of functional cone and rod PRs by using GUCY1* chickens. These birds carry an autosomal recessive mutation that causes photoreceptor cell degeneration and blindness at hatch since null electroretinograms were obtained after light exposure. However, they showed light responses in both the pupillary light reflex (PLR) and the entrainment of feeding rhythms to a 12:12 h light dark (LD) cycle. Moreover, when the extraretinal photoperception was inhibited by head occlusion, daily rhythms in feeding were tightly entrained to diverse white and blue LD cycles whereas light responses were lost after enucleation. Blind animals displayed consensual PLRs to white and monochromatic light of 400-550 nm. An action spectrum for the PLRs demonstrated that this response is driven by a single opsin/vitamin A2-based photopigment with peak sensitivity around 484 nm. The results represent the first characterization of functional PRs in the chicken inner retina participating in the regulation of NIF activities. Supported by Fundación Florencio Fiorini, FONCyT, CONICET, SeCyT-UNC, and Agencia Córdoba Ciencia.
Keywords: phototransduction, inner retina, feeding activity rhythms, pupillary light responses, extraretinal photoreceptors, vitamin A2-based photopigment.