title: Melatonin injections affect circadian behavior and SCN neurophysiology in Djungarian hamsters.
abstract: We investigated the effects of daily melatonin (MEL) injection on phase angle of entrainment, duration of wheel-running activity (alpha), and frequency of suprachiasmatic nuclei (SCN) neuronal discharge in the photo-nonresponsive phenotype of the Djungarian hamster, Phodopus sungorus. Photo-nonresponsiveness is characterized by an absence of physiological adjustments to short days (SD). With respect to wheel-running activity, photo-nonresponsive hamsters have a large negative phase angle of entrainment and a compressed alpha under SD. These hamsters also have a delayed nocturnal MEL pulse. These circadian differences are correlated with the daily profile of SCN neuronal activity. In the present experiments, daily MEL injections to photo-nonresponsive hamsters resulted in molt, gonadal regression, and expansion in alpha until entrainment to lights off. Vehicle-injected controls did not exhibit any of these responses. SCN neuronal activity patterns recorded from MEL-injected photo-nonresponders, but not vehicle-injected controls, resembled electrical activity profiles of photoresponsive hamsters. These results demonstrate that MEL induces "photoresponsiveness" in previously photo-nonresponsive hamsters, that MEL modifies circadian behavior to resemble that of photoresponders, and that MEL injections affect the circadian rhythm of SCN neuronal firing.
authors.affiliation: Department of Biology, Wesleyan University, Middletown, Connecticut 06459.
authors.forename: R R
authors.initials: RR
authors.lastname: Margraf
authors.forename: G R
authors.initials: GR
authors.lastname: Lynch
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects*; D006224:Cricetinae; D004594:Electrophysiology; D008550:Melatonin / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D017111:Phodopus; D017440:Photoperiod; D013493:Suprachiasmatic Nucleus / Q000187:drug effects / Q000502:physiology*
chemical_list: D008550:Melatonin