Serotonin antagonists do not attenuate activity-induced phase shifts of circadian rhythms in the Syrian hamster

Brain Res. 1998 Nov 30;813(1):139-49. doi: 10.1016/s0006-8993(98)01048-8.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Circadian Rhythm / drug effects*
  • Cricetinae
  • Male
  • Mesocricetus
  • Metergoline / pharmacology
  • Piperazines / pharmacology
  • Ritanserin / pharmacology
  • Serotonin Antagonists / pharmacology*


  • Piperazines
  • Serotonin Antagonists
  • 1-(2-methoxyphenyl)-4-(4-(2-phthalimido)butyl)piperazine
  • WAY 100135
  • Ritanserin
  • Metergoline