Behavioral effects of melatonin treatment in non-human primates

Melatonin treatment has been shown to induce sleepiness and promote sleep in humans. In order to understand the mechanisms by which melatonin acts on human sleep and behavior, it would be useful to have an animal model in which the physiological nocturnal increase in melatonin secretion correlated with nocturnal sleep, i.e., a diurnal species. In this pilot study the oral administration of melatonin to two Pigtail macaques (Macaca Nemestrina) at different times of the day significantly decreased motor activity and promoted earlier sleep onset, as measured actigraphically. The decline in the animals' motor activity occurred within 25-40 min after melatonin ingestion. The duration of motor inhibition was dose dependent. Administration of a 0.05 mg dose induced serum melatonin levels comparable to the peak physiologic concentrations reported in untreated humans and the non-human primates. These data suggest that melatonin may modulate motor activity and sleep pattern in certain diurnally-active primates.