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 neonat ally treated with clomipramine - a serotonin/noradrenaline re-uptake inhibi tor antidepressant) were initially entrained to a 14:10 light:dark cycle, a nd their reentrainment rate after a 6 h phase advance in the photoperiod wa s 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, excep t 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.