HAFEN, T. AND F. WOLLNIK. Effect of lithium carbonate on activity level and circadian period in different strains of rats. PHARMACOL BIOCHEM BEHAV 49(4) [975][976][977][978][979][980][981][982][983] 1994.-Lithium, an important pharmacological agent for the treatment of manic-depressive illness in humans, is known to lengthen the circadian period in a number of different species. Recent experiments, on the other hand, suggest that pharmacological agents may affect the circadian system indirectly through an increase or decrease of activity. To explore the interaction between pharmacological and activity effects on the circadian system, lithium was administered chronically to three different strains of rats (ACI, BH, and LEW) while wheel-running activity was studied quantitatively. Two of these inbred strains (BH and LEW) show profound abnormalities in their circadian activity rhythms, namely, a reduced overall level of activity and bimodal or multimodal activity patterns. Wheel-running activity was monitored for 4 weeks under baseline conditions, followed by 3 weeks with lithium treatment (0.3% Li 2 C0 1 administered with food) and 4 weeks with normal food. Treatment with lithium (average intake per day = 3.6 ± 0.2 mg) consistently decreased both the overall level and the circadian amplitude of the activity rhythm. The free-running period r was slightly lengthened during lithium treatment, while the most dramatic effect on period was observed after lithium withdrawal. Correlation analysis, however, revealed only a small negative correlation between activity level and period length, which proved significant only for animals of the ACI strain. Our data support the traditional interpretation that lithium lengthens circadian period by a direct pharmacological effect on the circadian pacemaker rather than through indirect effects of activity feedback. to the effect that the therapeutic effect of these drugs may be based on their phase delaying effect on the circadian pacemaker. So far, the mechanisms responsible for lithium's chronopharmacological actions are not known. It has been suggested that lithium could lengthen the circadian period by a) slowing of cellular oscillators, b) by altering the coupling between multiple circadian oscillators, or c) by altering light sensitivity (17). The hypothesis that lithium may weaken the mutual interaction between multiple oscillators is especially intriguing because modifications in coupling strength could theoretically account for changes in period, as well as entrained phase, wave form, and amplitude of circadian rhythms.
Circadian rhythmsThe period-lengthening effect of lithium is of special interest with respect to the hypothesis that there may be an association between the pathophysiology of affective disorders and disturbances of circadian rhythms (22,48). Several studies in humans have demonstrated that many circadian rhythms are phase advanced in depressed patients compared to controls [reviewed in (12,44,45)]. Because lithium and a few other antidepressant agents (5,47...