Reentrainment in Golden Hamsters: Effect of Melatonin, Age and Neonatal Clomipramine Treatment

Golden hamsters (young: 3 month-old; old: more than 12 month-old; or neonatally treated with clomipramine - a serotonin/noradrenaline re-uptake inhibitor antidepressant) were initially entrained to a 14:10 light:dark cycle, and their reentrainment rate after a 6 h phase advance in the photoperiod was determined. Animals took between 6 and 9 days to reentrain. Melatonin (1 mg/kg, i.p.) accelerated reentrainment to the LD cycle in all groups, except for the clomipramine-treated hamsters. These results support an important accelerating effect of the pineal hormone melatonin on resynchronization, no longer observed in clomipramine-treated hamsters.