Light and melatonin inhibit in vivo serotonergic phase advances without altering serotonergic-induced decrease of per expression in the hamster suprachiasmatic nucleus.
In the Syrian hamster a serotonergic (5-HTergic) stimulation during daytime acts on the circadian timing system by inducing behavioral phase advances and by decreasing Per1 and Per2 (Period) mRNA levels in the suprachiasmatic nuclei, containing the main circadian clock in mammals. The present study was conducted in Syrian hamsters, housed in constant darkness, to investigate the interactions between light or melatonin with serotonergic stimulation in terms of phase resetting and clock gene expression. Both light exposure and systemic administration of melatonin prior to the injection of a 5-HT(1A/7) receptor agonist, 8-OH-DPAT, in the middle of the day blocked behavioral phase advances. In contrast, neither light nor melatonin treatment during daytime prevented serotonergic-induced down-regulation of Per1 and/or Per2 mRNA levels in the suprachiasmatic nuclei. Taken together, the results show that interactions between afferent cues to the suprachiasmatic nuclei differentially modulate phase adjustment and clock gene expression during daytime.
Caldelas
Ivette
I
Laboratory of Neurobiology of Rhythms, CNRS, Department of Neuroscience, University L. Pasteur, Strasbourg, France.
Challet
Etienne
E
Saboureau
Michel
M
Pevet
Paul
P
D000818:Animals; D001683:Biological Clocks / Q000235:genetics / Q000502:physiology*; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000502:physiology; D006224:Cricetinae; D003624:Darkness; D017403:In Situ Hybridization; D008027:Light; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000378:metabolism*; D008647:Mesocricetus; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D056950:Period Circadian Proteins; D012333:RNA, Messenger / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D012701:Serotonin; D008550:Melatonin