MelatoninPineal GlandReceptors, MelatoninCircadian RhythmAcetylserotonin O-MethyltransferaseSleep Phase ChronotherapyReceptor, Melatonin, MT1Arylalkylamine N-AcetyltransferaseReceptor, Melatonin, MT2Environment, ControlledLightPhotoperiodBody TemperatureWakefulnessRadioimmunoassaySheepPlasmaTryptaminesPlasma Cells