Differential Regulation of Arylalkylamine N-Acetyltransferase Activity in Chicken Retinal Ganglion Cells by Light and the Circadian Clock

DIEGO J. VALDEZ; EDUARDO GARBARINO-PICO; NICOLAS M. DIAZ; MARIO E. GUIDO

CHRONOBIOLOGY INTERNATIONAL

TAYLOR & FRANCIS INC

Lugar: Londres; Año: 2012 vol. 29 p. 1011 - 1020

0742-0528

Retinal ganglion cells (RGCs) contain circadian clocks driving melatonin synthesis during the day, a subset of these cells acting as non-visual photoreceptors sending photic information to the brain. In this work, we investigated the temporal and light regulation of arylalkylamine N-acetyltransferase (AA-NAT) activity, a key enzyme in melatonin synthesis. We first examined this activity in RGCs of wild-type chickens and compared it to that in photoreceptor cells (PRs) from animals maintained 48 h in constant dark (DD), light (LL), or a regular 12:12 h light/dark (LD) cycle. AA-NAT activity in RGCs displays a circadian rhythmicity with the highest levels during the subjective day in both DD and LL as well as in the light phase of a LD cycle. By contrast, AA-NAT activity in PRs exhibits the typical nocturnal peak in DD and LD but no detectable oscillation was observed under LL, under which conditions the levels were basal at all times examined. A light pulse of 30-60 min significantly decreased AA-NAT activity in PRs during the subjective night but had no effect on RGCs during the day or night. Intraocular injection of dopamine (50 nmol/eye) during the night to mimic the effect of light presented a significant inhibition of AA-NAT activity in PRs compared to controls but had no effect on RGCs. The results clearly demonstrate that the regulation of the diurnal increase in AA-NAT activity in RGCs undergoes a different control mechanism from that observed in PRs in which the endogenous clock, light and dopamine exhibited differential effects.