LIGHT AND CIRCADIAN REGULATION OF MELATONIN SYNTHESIS IN CULTURED RETINAL GANGLION CELLS

CONTIN MARIA ANA; VERRA DANIELA MARIANA; GUIDO MARIO EDUARDO

Fort Lauredale, Florida, EEUU.

Congreso; Association for Research in Vision and Ophtalmology (ARVO); 2006

ARVO

Melatonin is synthesized in the pineal gland and the retina of many vertebrate species. In the retina, melatonin appears to play a mayor role in the circadian regulation of retinal physiology. The melatonin synthesis is rhythmic and driven by an endogenous circadian clock, which is also regulated by the interaction of the environmental photic input and the circadian clock. Within the retina, the issue of which cell type(s) are responsible for the melatonin synthesis, it is not totally known yet. Many reports suggest that it takes place in photoreceptors (PRCs), however, we have recently shown that immunopurified retinal ganglion cells from chicken embryos (eRGCs) also synthesize 3H-melatonin from 3H-tryptophan under a circadian bases with higher levels during the first 8 hours indicating that they are autonomous circadian oscillators (Garbarino-Pico et al., 2004). Recently it was found that a subpopulation of mammalian RGCs is intrinsically photosensitive by depolarizing to light (Berson et al., 2002). This RGC subpopulation projects to brain areas that mediate non-visual responses to light. In this work, we show that cultures of eRGCs synchronized to a 12:12 LD cycle for 3 days and released to DD, biosynthesized radiolabeled melatonin in a rhythmic manner with higher levels during the subjective day whereas light exposure significantly inhibits this synthesis. In order to investigate the potential pathway of phototransduction taking place in eRGCs, we used different effectors to modulate the light effect on melatonin synthesis. Preliminary data suggest that an invertebrate-like cascade may be acting in this photic pathway. The results indicate that chicken eRGCs are intrinsically photosensitive as seen in the regulation of melatonin synthesis by light.