COUPLING EFFECT OF LOCOMOTOR-ACTIVITY ON THE RATS CIRCADIAN SYSTEM

Exercise is recognized to affect circadian rhythmicity in a variety of ways. It masks the expression of other behavioral and physiological r hythms, entrains the master pacemaker, and influences the free-running period of other rhythms. In this paper we study the influence of exer cise on the organization of the timing system by analyzing the effect of voluntary locomotor activity on the circadian feeding behavior of r ats subjected to different lighting conditions. The availability of wh eel running prevented loss of feeding circadian rhythmicity under cons tant bright light (LL) but did not elicit any circadian pattern in rat s showing a previous arrhythmic pattern. Under dim red light (DR), the rhythm was more pronounced in exercising than in sedentary rats, whil e wheel-running availability accelerated the emergence of circadian rh ythmicity in arrhythmic animals that were moved from LL to DR. These r esults can be explained by the existence of a positive feedback loop b etween physical exercise and its pacemaker and also suggest that exerc ise changes the functioning of the circadian system to facilitate the emergence of circadian rhythms in previously arrhythmic animals.