Properties of the melatonin-generating system of the sailfin molly, Poecilia velifera.

The properties of the melatonin-generating system of a tropical teleost, the sailfin molly (Poecilia velifera), were investigated in vitro in a series of experiments using static or perifusion culture techniques. The properties examined included photic entrainment, circadian rhythmicity under continuous light (LL) and continuous darkness (DD), functionality of the melatonin-generating system at birth, and presence of multiple circadian oscillators in the molly pineal. Pineal glands or skull caps with the pineal gland firmly attached were dissected from adult and new-born fishes, respectively, and placed into static or perifusion culture at constant temperature (27 degrees C) depending upon the experiment. Melatonin release in samples was quantified by RIA. Rhythmic melatonin release was observed from isolated adult pineals under 12L:12D and 14L:10D, with low amounts of melatonin released during the light and high amounts during the dark. Melatonin release was inhibited by LL. However, under DD, melatonin release was robust and rhythmic with a circadian period (Tau) that ranged between 21.3 and 27.0 h (n = 21). Pineals from new-born (1-day old) mollies released melatonin rhythmically under a light:dark cycle and DD in both static and perifusion culture. Melatonin release from half and quarter pineals of adult mollies under DD was robust and rhythmic with circadian periods that ranged between 22.5 and 29.0 h (n = 19). Taken together, these data show that the molly pineal is photosensitive, fully functional from birth, and contains multiple circadian oscillators (at least four) regulating melatonin production.