ANTIMANIC DRUGS STABILIZE HAMSTER CIRCADIAN-RHYTHMS

The circadian wheel-running rhythm of golden hamsters was monitored du ring chronic oral treatment with four mood-stabilizing drugs in doses relevant for treatment of manic-depressive disorder. Carbamazepine and verapamil shortened the duration of locomotor activity and improved t he stability of the pattern of running activity. At comparable doses, valproate had no clear effect on any rhythm variable tested. None of t hese drugs consistently altered the phase of light-synchronized runnin g rhythms or the period of the rhythm in constant darkness. The result s are compared to data showing that lithium, which delays entrained ph ase and lengthens circadian period in hamsters, also shortens activity duration and increases the stability of wheel-running rhythms. Stabil ization of circadian rhythms may be a key action of clinically effecti ve mood-stabilizing drugs.