EFFECT OF VARIABLE TEMPERATURES, DARKNESS AND LIGHT ON THE SECRETION OF MELATONIN BY PINEAL EXPLANTS IN THE GECKO, CHRISTINUS-MARMORATUS

This study examined the combined effect of thermocycles with either va riable or constant photic conditions on melatonin production by pineal organs in vitro in the gecko, Christinus marmoratus. A 30 degrees C:1 5 degrees C thermocycle elicited a rhythm of melatonin production unde r conditions of 12L:12D, constant light or constant darkness when the cryophase coincided with the dark phase of the photocycle or with the subjective night. A 6 h advance of the thermocycle with respect to the photocycle produced an advance in the onset and offset of melatonin p roduction in subsequent nights. When the thermocycle was 180 degrees o ut of phase with the photoperiod, the rhythm of melatonin production w as disrupted, suggesting a differential pattern of sensitivity to phot othermal stimuli. It was concluded that both light and temperature are important modulators of pineal function although their combined effec ts on pineal melatonin production is complex and unclear.