Seasonal change in the temporal organization of wheel-running activity of the European hamster, Cricetus cricetus

Abstract

In this paper we demonstrate that a dramatic annual change in the temporal organization of locomotor activity goes hand in hand with the seasonal cycle of reproduction. Activity levels increased when the animals entered reproductive conditions, which occurs naturally in spring and early summer. During the 2-3 months of reproduction, a well-defined activity rhythm was observed. During the rest of the year, the level of activity was dramatically reduced and almost no rhythmic organization was detected. The question arising from these observations is whether the loss of temporal organization reflects a weakening or arrhythmia of the underlying pacemaker or whether it is due to an uncoupling of the overt activity rhythm from the central clock.