INDUCED changes in the level of daily activity can alter the period of
the mammalian circadian clock. In this report, we examined the period
of the circadian rhythm of wheel-running activity in a transgenic neu
rological mouse mutant, Wocko. Wocko mice display a dominant behaviora
l phenotype that consists of hyperactivity, circling and head tossing.
The period of the circadian rhythm of wheel-running activity in const
ant dark conditions was significantly shorter in mice expressing the W
ocko mutation than in their normal littermates. Total activity, monito
red by the interruption of an array of infrared beams, was significant
ly elevated in Wocko mice. These findings support the view that sponta
neous exercise can modulate the circadian timekeeping system.