Wheel running as a function of varying effort requirements in rats

These experiments explore a wheel running work-response function with the goal of paralleling the drug magnitude-response (dose-response) function, as a way of measuring the value of running for rats. Friction levels were manipulated by varying the amount of weight applied to running wheels. Experiment 1 examined how male running patterns changed in response to weights applied on alternate days and calculated the work-response scores for each weight. Experiment 2 explored how male running changed when weights were applied for only a portion of the night, on an alternate night schedule. Experiments 3 and 4 replicated the procedures used in Experiments 1 and 2 with females. The results demonstrated that, whereas baseline running gradually decreased over days, it decreased further as the weights were increased for both males and females. However, the actual work expended running first increased then decreased as the weights increased. When the weights were applied and increased during the first few hours of the night, running decreased. After the weights were removed, male rats compensated by running more during the remaining friction-free hours of the night, however female rats did not show the same compensatory response pattern as the males. It is suggested that in males, the total distance traveled in the wheel rather than the total amount of work expended may more accurately represent what male rats regulate in their wheel running, which does not appear to be the case in females. It is suggested that the females\u27 estrous cycles may have confounded the results