Open AccessInfluences of a light–dark profile and the pineal gland on the hypnotic activity of melatonin in mice and rats
Author(s) -
Wang Fang,
Li Jing Cai,
Wu Chun Fu,
Yang Jing Yu,
Zhang Ruo Ming,
Chai Hui Fang
Publication year - 2003
Publication title -
journal of pharmacy and pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 118
eISSN - 2042-7158
pISSN - 0022-3573
DOI - 10.1211/0022357021729
Subject(s) - melatonin , pinealectomy , pineal gland , hypnotic , circadian rhythm , endocrinology , medicine , wakefulness , sleep (system call) , psychology , pharmacology , electroencephalography , neuroscience , computer science , operating system
We have investigated the influences of the light–dark cycle and the pineal gland on the hypnotic activity of melatonin in rats and mice. The results showed that melatonin significantly shortened time to sleep onset and wakefulness time, increased slow wave sleep, paradoxical sleep, and total sleep time in rats during the light phase of a 12‐h light: 12‐h dark cycle, by electroencephalogram recording. However, during the dark phase it had almost no significant sleep‐promoting effect except shortened time to sleep onset. Melatonin exhibited more potent sleep‐promoting effect in rats exposed to constant light compared with rats exposed to 12:12‐h light:dark at 2000 h. Melatonin markedly prolonged sleeping time in the mice exposed to constant illumination. It was found that pinealectomy was an important factor that influenced the hypnotic activity of melatonin. When melatonin was administered to pinealectomized mice, the hypnotic activity of melatonin was more intense compared with sham‐operated mice. These results demonstrated that the hypnotic activity of melatonin displayed a light‐dependence manner. These results suggested that light exposure and the functional state of the pineal gland could substantially impact the hypnotic activity of melatonin at pharmacological dosage.