Serotonin antagonists do not attenuate activity-induced phase shifts of circadian rhythms in the Syrian hamster.
A variety of observations from several rodent species suggest that a serotonin (5-HT) input to the suprachiasmatic nucleus (SCN) circadian pacemaker may play a role in resetting or entrainment of circadian rhythms by non-photic stimuli such as scheduled wheel running. If 5-HT activity within the SCN is necessary for activity-induced phase shifting, then it should be possible to block or attenuate these phase shifts by reducing 5-HT release or by blocking post-synaptic 5-HT receptors. Animals received one of four serotonergic drugs and were then locked in a novel wheel for 3 h during the mid-rest phase, when novelty-induced activity produces maximal phase advance shifts. Drugs tested at several doses were metergoline (5-HT1/2 antagonist; i.p.), (+)-WAY100135 (5-HT1A postsynaptic antagonist, which may also reduce 5-HT release by an agonist effect at 5-HT1A raphe autoreceptors; i.p.), NAN-190 (5-HT1A postsynaptic antagonist, which also reduces 5-HT release via an agonist effect at 5-HT1A raphe autoreceptors; i.p.) and ritanserin (5-HT2/7 antagonist; i.p. and i.c.v.). Mean and maximal phase shifts to running in novel wheels were not significantly affected by any drug at any dose. These results do not support a hypothesis that 5-HT release or activity at 5HT1, 2 and 7 receptors in the SCN is necessary for the production of activity-induced phase shifts in hamsters.
Antle
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MC
Department of Psychology, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada.
Marchant
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EG
Niel
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Mistlberger
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D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects*; D006224:Cricetinae; D008297:Male; D008647:Mesocricetus; D008711:Metergoline / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D016713:Ritanserin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology*
D010879:Piperazines; D012702:Serotonin Antagonists; C058895:1-(2-methoxyphenyl)-4-(4-(2-phthalimido)butyl)piperazine; C081293:WAY 100135; D016713:Ritanserin; D008711:Metergoline