title: Pineal melatonin and locomotor activity of rats under gradual illuminance transitions.
abstract: The locomotor activity and pineal melatonin patterns of adult male rats were compared under two different lighting regimes. The animals were kept 8 days under 12/12 h light/dark cycles with abrupt or slowly decreasing and increasing transitions (twilight periods about 2 h). The onsets of high activity and melatonin rise were phase-locked in the two conditions and related to about half-maximal illuminance level of the gradual dusk. The high activity of the control rats stopped 30-60 min before the abrupt light onset and the rats under the gradual lighting transitions ceased the locomotor activity at about 1 hour before the half-maximal illuminance. The melatonin peak levels were found 4 h before the abrupt lights-on time. Under the slow illuminance transitions the average melatonin peak was related to the illuminance level between maximum and minimum in the morning. Thus, both the melatonin rhythm and the rest-activity rhythm under the gradual dawn and dusk were adjusted according to about half-maximal illuminances in the present conditions.
authors.affiliation: Department of Physiology, University of Helsinki, Finland.
authors.forename: M L
authors.initials: ML
authors.lastname: Laakso
authors.forename: L
authors.initials: L
authors.lastname: Leinonen
authors.forename: S L
authors.initials: SL
authors.lastname: Joutsiniemi
authors.forename: T
authors.initials: T
authors.lastname: Porkka-Heiskanen
authors.forename: D
authors.initials: D
authors.lastname: Stenberg
mesh_terms: D000818:Animals; D001143:Arousal / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D008027:Light; D008297:Male; D008550:Melatonin / Q000096:biosynthesis*; D009043:Motor Activity / Q000502:physiology*; D010870:Pineal Gland / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012894:Sleep Stages / Q000502:physiology
chemical_list: D008550:Melatonin