title: Phase shift of the circannual reproductive rhythm in European hamsters by 2 days of long photoperiod.
abstract: OBJECTIVE
  In European hamsters a circannual clock drives the seasonal changes in the reproductive state. Its resetting by photoperiod is clearly phase dependent. In mid subjective winter a 1-month pulse of long photoperiod (LP) advances the onset of the reproductive phase of animals maintained in constant short photoperiod (SP) by up to 1.5 months. The present study investigated whether shorter pulses, i.e. 8, 4 or 2 days LP-pulses are still effective to phase shift the circannual rhythm.
  
  
  RESULTS
  All pulses induced gonadal development after a similar time relative to the offset of the pulse and earlier than in the control group. Thus, they all shared a similar effectiveness.
  
  
  CONCLUSIONS
  In European hamsters a very brief LP-pulse can phase shift the reproductive rhythm but its strength is not determined by its duration at least not in the tested range.
authors.affiliation: Institut des Neurosciences Cellulaires et Intégratives, Neurobiologie des Rythmes, Université de Strasbourg, France. stefanie.monecke@inci-cnrs.unistra.fr
authors.forename: Stefanie
authors.initials: S
authors.lastname: Monecke
authors.forename: André
authors.initials: A
authors.lastname: Malan
authors.forename: Michel
authors.initials: M
authors.lastname: Saboureau
authors.forename: Paul
authors.initials: P
authors.lastname: Pévet
mesh_terms: D000818:Animals; D057906:Circadian Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D006224:Cricetinae; D008297:Male; D017440:Photoperiod; D012098:Reproduction / Q000502:physiology*; D012621:Seasons; D013997:Time Factors