Circadian phototransduction and the regulation of biological rhythms in an animal model of blindness. Mario E. Guido1, Diego J. Valdez,1 Paula S. Nieto,1 Eduardo Garbarino-Pico,1 Lucia B. Avalle,2 Hugo Díaz-Fajreldines,3 Kimberley Cheng,4. 1CIQUIBIC-Dpto de Química Biológica, Facultad de Ciencias Químicas, Univ. Nac. de Córdoba, Córdoba, Argentina; 2 Facultad de Matemáticas, Astronomía y Física, Univ. Nac. de Córdoba, Córdoba, Argentina; 3 Instituto de Neurociencias, Córdoba, Argentina; 4 Univ. British Columbia, Vancouver, Canada.
In mammals, a non-image forming (NIF) circuitry conveys photic information from the retina to the brain regulating a number of non-visual functions. In birds, the retina and pineal gland are photoreceptive. GUCY1* chickens that suffer photoreceptor cell (PRC) degeneration and blindness at hatch, constitute an useful model to study light perception without functional PRCs. In these birds, we assessed the consensual pupillary light reflex (PLR) to different monochromatic lights and the synchronization of feeding rhythms to various 12:12 h light-dark (LD) cycles with white and blue light of different irradiances. GUCY1* chickens are clinically blind as null electroretinogram recordings were obtained in response to bright light. However, they displayed detectable light responses in both the PLR and the entrainment of feeding rhythms. Birds bearing the occlusion of their pineal gland and deep brain, exhibited strong daily rhythms in food intake which were tightly entrained to diverse LD cycle schedules as sighted controls. Under scotopic conditions, GUCY1* chicks displayed measurable PLRs to white and monochromatic light of 430, 480 and 500 nm, but no responses were seen at 600 nm. Remarkably, only at 480 nm, low light intensity levels (100 lux) elicited a PLR similar to that at maximal irradiance (5000 lux), resembling a vitamin A-based melanopsin-like photopigment. The results indicate that in birds, photoperception occurs even in the absence of classical PRCs, and pineal gland/encephalic occlusion, through a mechanism involving the inner retina and the NIF pathway.
