title: Entrainment of the circadian activity rhythm of a lizard to melatonin injections.
abstract: The circadian activity rhythms of lizards (Sceloporus occidentalis) can be entrained (synchronized) to a period of 24 hr by melatonin injections given every other day at the same time of day, but not by saline injections. The activity onsets of the entrained lizards exhibited two preferred phase-relationships (approximately 165 degrees and approximately 30 degrees) with the time of melatonin injections with the 30 degree phase only rarely observed. These results suggest that endogenous rhythms of melatonin secretion (i.e., from the pineal organ) may be involved in synchronizing circadian oscillations within the lizard's multioscillator circadian system.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects*; D005260:Female; D008116:Lizards / Q000502:physiology*; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects*
chemical_list: D008550:Melatonin