DEVELOPMENT OF RHYTHMIC MELATONIN SYNTHESIS IN CULTURED PINEAL GLANDSAND PINEAL CELLS ISOLATED FROM CHICK-EMBRYO

The chick pineal gland exhibits circadian rhythms in melatonin synthes is under in vivo and in vitro conditions. A daily rhythm of melatonin production was first detectable in pineal glands isolated from chick e mbryos at embryonic day 16 and incubated under a LD cycle. All pineal glands isolated from 17-day-old and older embryos were rhythmic while no gland isolated at embryonic day 14 and 15 exhibited a daily rhythm in melatonin synthesis. Melatonin production in static cultures of emb ryonic pineal cells was rhythmic over 45 h if the cells were kept unde r a LD cycle. When embryonic pineal cells were incubated in constant d arkness the rhythm in melatonin production was damped within 48 h. The se results suggest that chick pineal cells from embryonic day 16 onwar ds are photosensitive but that the endogenous component of the melaton in rhythm is not completely developed at that age. A soluble analogue of cAMP stimulated and norepinephrine inhibited melatonin synthesis in cultured embryonic pineal cells. These findings indicate that the sti mulatory and inhibitory pathways controlling melatonin synthesis in th e mature pineal gland are effective in pineal cells isolated from chic k embryos at least 2 days before hatching.