Light and circadian regulation of melatonin synthesis in cultured retinal ganglion cells

CONTIN MARIA ANA; VERRA DANIELA MARIANA; GUIDO MARIO EDUARDO

Pinamar, Buenos Aires Argentina

Congreso; Sociedad Argentina de Neuroquimica (SAN); 2005

SAN

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, many reports suggest that the melatonin synthesis takes place in photoreceptors (PRCs), however, we have recently shown that retinal ganglion cells from chicken embryos (eRGCs) also synthesize 3H-melatonin under a circadian bases, 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). 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.