PERSISTENT RHYTHMS OF PINEAL AND SERUM MELATONIN IN COCKERELS IN CONTINUOUS DARKNESS

Abstract

SUMMARY The melatonin ( N -acetyl-5-methoxytryptamine) content of the pineal body and serum of White Leghorn cockerels ( Gallus domesticus ) appears to vary cyclically, with a higher level of both found at the mid-point of the dark period than at the mid-point of the light period when the animals were kept in a diurnal light cycle. These rhythmic variations persisted, although with an apparently lower amplitude, when the animals were maintained in continuous darkness for 2 weeks. The oscillations appeared to be free-running, circadian rhythms and to be phase-locked with the locomotor activity rhythms of the individual birds studied.