title: Photoperiod differentially modulates photic and nonphotic phase response curves of hamsters.
abstract: Circadian pacemakers respond to light pulses with phase adjustments that allow for daily synchronization to 24-h light-dark cycles. In Syrian hamsters, Mesocricetus auratus, light-induced phase shifts are larger after entrainment to short daylengths (e.g., 10 h light:14 h dark) vs. long daylengths (e.g., 14 h light:10 h dark). The present study assessed whether photoperiodic modulation of phase resetting magnitude extends to nonphotic perturbations of the circadian rhythm and, if so, whether the relationship parallels that of photic responses. Male Syrian hamsters, entrained for 31 days to either short or long daylengths, were transferred to novel wheel running cages for 2 h at times spanning the entire circadian cycle. Phase shifts induced by this stimulus varied with the circadian time of exposure, but the amplitude of the resulting phase response curve was not markedly influenced by photoperiod. Previously reported photoperiodic effects on photic phase resetting were verified under the current paradigm using 15-min light pulses. Photoperiodic modulation of phase resetting magnitude is input specific and may reflect alterations in the transmission of photic stimuli.
authors.affiliation: Department of Psychology, University of California, San Diego, La Jolla, California 92093, USA. jaevans@ucsd.edu
authors.forename: J A
authors.initials: JA
authors.lastname: Evans
authors.forename: J A
authors.initials: JA
authors.lastname: Elliott
authors.forename: M R
authors.initials: MR
authors.lastname: Gorman
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D006224:Cricetinae; D008297:Male; D008647:Mesocricetus; D009043:Motor Activity / Q000502:physiology*; D009919:Orchiectomy; D010775:Photic Stimulation; D017440:Photoperiod; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone