A melatonin agonist facilitates circadian resynchronization in old hamsters after abrupt shifts in the light–dark cycle

Age-related changes in the mammalian circadian system may be associated with a decline in circulating melatonin levels. Using ‘jet lag’ paradigms involving abrupt shifts in the light–dark cycle, we showed that a melatonin agonist, S-20098, accelerated by ∼25% resynchronization of the circadian activity rhythm in old hamsters to the new light–dark cycle. It suggests the usefulness of melatonin-related compounds to treat circadian disorders associated with aging.