A Non-Mammalian Vertebrate Model of Blindness Reveals Functional Photoreceptors in the Inner Retina

D. J. VALDEZ, P. S. NIETO, E. GARBARINO-PICO, L. B. AVALLE, H. DÍAZ-FAJRELDINES, C. SCHRURER, K. CHENG, AND M. E. GUIDO

FASEB JOURNAL

The Federation of American Societies for Experimental Biology

Año: 2008 vol. 23 p. 1186 - 1195

0892-6638

In mammals, photoreceptors located in the inner retina convey photic information to the brain 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  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 12:12 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. A sensitivity 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.