Effects of melatonin and 5-methoxytryptamine on sleep-wake patterns in the male rat.

Melatonin and 5-methoxytryptamine were administered continuously over a period of 1-3 months to adult male rats by means of subcutaneously implanted silastic capsules containing one or the other of these pineal hormones. Polygraphic recordings during several weeks following hormonal application showed an increase in the amount of time spent in both quiet and rapid eye movement sleep, during the light as well as the dark period; however, diurnal sleep-wake rhythmicity was not affected by either treatment. We conclude that pineal hormones have sleep-promoting effects, but that their correlation with the light-dark cycle does not imply that they are causal factors in generating diurnal rhythms of sleep and wakefulness.