Circadian rhythms of house sparrows are phase-shifted by pharmacological manipulation of brain serotonin

Fluoxetine, a specific serotonergic reuptake blocker and indirect agonist, and 5,6-dihydroxytryptamine, a serotonergic neurotoxin, affect the free-running locomotor rhythms of house sparrows, Passer domesticus. Both compounds caused phase-shifts in the circadian system that times locomotor activity of the birds. The magnitude and direction of the phase-shifts were dependent on the circadian phase of the drug administration, suggesting that serotonergic activity can modulate the circadian pacemaker of the house sparrow.