Fluoxetine shortens circadian period for wheel running activity in mice.

Fluoxetine is a potent and specific serotonin re-uptake inhibitor and an effective antidepressant drug. Male mice were treated with either fluoxetine (8 mg/kg body weight per day) or saline. Wheel running activity was monitored for 2 weeks in a 12:12 LD cycle followed by 2 weeks in constant darkness (DD). Fluoxetine significantly shortened free-running circadian period for wheel running activity (23.93 +/- 0.08 h for fluoxetine treated mice versus 24.17 +/- 0.07 h for saline treated mice; p less than 0.03). These results are consistent with a role for serotonin in the regulation of circadian period in mice.