Relationship between wheel running, feeding, drinking, and body weight in male rats

The amount of wheel running varies widely between rats. Wheel introduction and running also have profound effects on the animal's energy balance. We explored the effects of ad lib wheel access and running levels on feeding, drinking, and body weight in 30 young adult male rats with wheel access and in 30 rats without wheel access. The initial running period (Days 1-8) and a time of stable running [Days 29-32 (DEnd)] were analyzed using both between- and within-group approaches. Initially, wheel access suppressed feeding (by about 25% over the 8 days) but not drinking. There were no significant correlations between the amount of wheel running and the other behaviors. The degree of feeding suppression was also not correlated to the amount of running. When running had stabilized (animal ran from 841 to 13,124 wheel turns per day), food intake was increased by about 0.75 g per 1000 wheel turns. Running at this time correlated positively with feeding and drinking and negatively with body weight and weight gain. In animals without wheel access, feeding and drinking were positively correlated with weight and weight gain, but in animals with wheel access, these correlations were close to zero. Only early running predicted later levels of running but accounted for only 23% of the variance in running. Wheel access has profound but very different immediate and long-term effects on the rats' energy balance.