EFFECTS OF MELATONIN ON SLEEP AND NEUROCHEMISTRY IN THE RAT

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Abstract
1 The effects of intraperitoneally administered melatonin on sleep and brain neurochemistry in the rat were studied by use of EEG recording and standard fluorescence techniques. 2 Melatonin, 10 mg/kg, reduced time to sleep onset and time spent awake but increased both slow wave and paradoxical sleep. Qualitatively similar but smaller effects were produced by a dose of 2.5 mg/kg. 3 Neither dose of melatonin altered normal EEG patterns or disrupted normal sleep behaviour. 4 Melatonin, 20 mg/kg, did not significantly alter concentrations of tryptophan, 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, noradrenaline or dopamine in any part of the brain. 5 It is concluded that the sleep promoting activity of melatonin cannot be related to gross changes in brain indoleamine and catecholamine levels.