A circadian rhythm in mice that is unaffected by the period mutation at clock

Circadian rhythms of locomotor behavior were induced in mice using chronic d-amphetamine. The periods of the rhythms at various doses of amphetamine were unaffected by a mutation at the clock locus that lengthens circadian period. Amphetamine-induced rhythms were superimposed on the host's natural circadian rhythm that is driven by the pacemaker in the suprachiasmatic nucleus. The results demonstrate the existence of an alternative mechanism for generating circadian rhythms that does not require the activity of canonical clock genes.