Effects of an activity-correlated feeding regime on circadian locomotor activity rhythms in LEW/Ztm rats.
The aim of the present study was to examine the possible feedback effect of activity on the circadian system in rats. The animals were housed in running wheel cages equipped with food dispensers and were forced to run for their food during parts of the study. Overall level and free-running period tau of wheel-running activity were recorded continuously to quantify the relationship between tau and the level of activity. Surprisingly, the activity-dependent feeding regime failed to increase the level of wheel-running activity and did not affect the activity pattern. Nevertheless, the period of wheel-running activity was shortened in 50% of the animals subjected to food dispensers and in 38% of the animals fed only once a day at irregular times, indicating that subtle environmental differences can affect the circadian pacemaker system without changing the level or the pattern of activity. In addition, 26% of the animals showed a shortening of tau after 3 weeks, i.e., before any change in the experimental setup. This shortening was probably caused by the access to the running wheel at the beginning of the experiment. The present results suggest that the effect on the circadian pacemaker common to both of these experimental manipulations is a change in the physiological or emotional state of the animal rather than an increase of the overall level of activity.
Kohler
M
M
Institute of Biology, University of Stuttgart, Germany. Markus.Kohler@po.uni-stuffgart.de
Wollnik
F
F
D000818:Animals; D001143:Arousal; D001245:Association Learning; D002940:Circadian Rhythm; D005247:Feeding Behavior; D005260:Female; D008297:Male; D009043:Motor Activity; D051381:Rats; D011917:Rats, Inbred Lew