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

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Abstract
The pineal gland of birds contains 1 or more circadian oscillators that play a major role in overall temporal organization. A flow-through culture system was developed for the isolated pineal by which the release of melatonin can be measured 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, melatonin release is strongly rhythmic; however, in constant conditions, the amplitude of the rhythm is lower and appears to be damping. Light has at least 2 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.