Circadian rhythms of melatonin release from individual superfused chicken pineal glands in vitro.

The pineal gland of birds contains one or more circadian oscillators that play a major role in overall temporal organization. We have developed a flow-through culture system for the isolated pineal by which we can measure the release of melatonin continuously from superfused glands over long periods of time. Chicken pineals release melatonin rhythmically, and these rhythms persist in vitro with a circadian oscillation. In light cycles the release of melatonin is strongly rhythmic; however, in constant conditions the amplitude of the rhythm is lower and appears to be damping. Light has at least two effects upon the isolated pineal: cyclic light input synchronizes the rhythm, and acute light exposure at night rapidly inhibits melatonin release. The cultured avian pineal clearly offers great potential as a model system for the study of vertebrate circadian oscillators and may open the way for an analysis of mechanism.