Abstract
The pineal organ of the lizard Anolis carolinensis can be maintained for up to 10 days in superfused organ culture. During this time it synthesizes and releases melatonin into the medium flowing slowly over it. Collection of timed aliquots of medium and subsequent analysis for melatonin by radioimmunoassay reveal circadian rhythms of melatonin output by the isolated pineal. These rhythms persist for many cycles in constant darkness and at several constant ambient temperatures ranging from 22 to 37 degrees C. The period of the rhythm is temperature compensated (Q10 approximately equal to 1.14) and the rhythm is synchronized by light-dark cycles imposed on the cultured gland. This isolated vertebrate organ displays the three major properties of circadian systems and must therefore contain one or more circadian oscillators.