Local administration of serotonin agonists blocks light-induced phase advances of the circadian activity rhythm in the hamster.
Circadian rhythms in mammals are synchronized to environmental light-dark cycles through a direct retinal projection to the suprachiasmatic nucleus (SCN), a circadian clock. This process is thought to be modulated by other afferents to the SCN, including a dense serotonergic projection from the midbrain raphe. Previous work from this laboratory demonstrated that a systemically administered 5-hydroxytryptamine1A/7 (5-HT1A/7) agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) dose dependently attenuates light-induced phase shifts of the circadian activity rhythm of the Syrian hamster. In this study, we demonstrate that local injections (1-100 microM) of the 5-HT1A/7 agonists 8-OH-DPAT or 5-carboxamidotryptamine into the region of the SCN inhibit light-induced phase advances of the circadian wheel-running rhythm. In addition, the inhibitory effects of systemically administered 8-OH-DPAT were unaffected by either radiofrequency-induced lesions of the intergeniculate leaflet or 5,7-dihydroxytryptamine-induced lesions of serotonergic projections to the SCN. These findings support a modulatory role of serotonin in photic regulation of circadian phase through an action at the level of the SCN.
Weber
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ET
Biological Rhythms and Integrative Neuroscience Research Institute, Brooks AFB, TX 78235, USA.
Gannon
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RL
Rea
M A
MA
D015116:5,7-Dihydroxytryptamine / Q000633:toxicity; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D006224:Cricetinae; D008027:Light; D008297:Male; D008647:Mesocricetus; D008845:Microinjections; D009043:Motor Activity / Q000187:drug effects*; D017440:Photoperiod; D012701:Serotonin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D013493:Suprachiasmatic Nucleus / Q000187:drug effects / Q000473:pathology / Q000502:physiology*
D017366:Serotonin Receptor Agonists; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C047087:5-carboxamidotryptamine