Melatonin affects circadian rhythmicity in lizards

Summary Subcutaneous Silastic capsules which continuously released melatonin at low rates (10 g/day) either (i) lengthened the period of the freerunning activity rhythm in two iguanid lizard species (Sceloporus occidentalis andS. olivaceus) exposed to either continuous illumination or continuous darkness or (ii) induced arrhythmicity inS. olivaceus exposed to continuous illumination. These results and previous observations that two melatonin synthesizing sites in lizards, the pineal organ and lateral eyes, are involved in circadian rhythmicity suggest that melatonin may be a chemical messenger between the pineal or eyes and other elements of the circadian system.