Non-Visual Phototransduction in Blind Birds
Diego J. Valdez1, Paula S. Nieto1, Eduardo Garbarino-Pico1, Lucia B. Avalle2, Hugo Díaz-Fajreldines3, Clemar Schurrer2, Kimberly M. Cheng4 and Mario E. Guido1?
1CIQUIBIC-Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, 5000 Córdoba, Argentina;
2Facultad de Matemáticas, Astronomía y Física, Universidad Nacional de Córdoba, 5000 Córdoba, Argentina;
3Instituto de Neurociencias Córdoba, 5000
4Avian
In mammals, photoreceptors located in the inner retina convey photic information to the brain[GDC1] , regulating diverse non-image forming tasks such as pupillary light reflexes and photic synchronization (entrainment) of daily activity rhythms. In non-mammalian vertebrates, the retina, deep brain photoreceptors, and the pineal organ may be photoreceptive. Here we investigated light perception in the absence of functional cone and rod photoreceptors [GDC2] using GUCY1* chickens, birds carrying a null mutation that causes blindness at hatch. They showed light responses in both the pupillary light reflex and the entrainment of feeding rhythms to a h light dark cycle. Light responses persisted even when the extra-retinal photoperception was abolished, but they were lost after enucleation; this strongly indicates the essential role played by the inner retina. An action spectrum study for the pupillary reflex that combined pupil responses to different monochromatic lights of various intensities demonstrated that a single opsin/vitamin A-based photopigment peaking at 484 nm drives photic responses; the best fit (lowest sum of squares, R2 = 0.9622) was attained with an opsin:vitamin A2 template. The results are the first characterization of functional inner retinal photoreceptors participating in the regulation of non-image forming activities in non-mammalian vertebrates.
Keywords: phototransduction, inner retina, feeding activity rhythms, pupillary light responses, extra-retinal photoreceptors, vitamin A-based photopigment.
