Effects of running wheel activity on circulating free fatty acid levels and subsequent bar press behavior

Abstract

Two experiments designed to investigate running as a behavioral regulatory system for food motivated behavior are reported. The first experiment examined some of the variables involved in the modification of scrum free fatty acid (FFA) levels of rats, as a function of food deprivation of 0, 10, and 20 percent body weight, and comparable food deprivation followed by activity wheel experience. Serum FFA levels increased with deprivation, but the serum FFA levels of subjects which lost 20 percent of their body weights were lower than the serum FFA levels of the subjects deprived of 10 percent of their body weights. FFA mobilization rates also increased with food deprivation, but there was no difference between subjects which lost 10 and 20 percent of their body weights. Total body fat decreased across all levels of deprivation. A possible explanation of these findings is that the rise in serum FFA levels observed in subjects deprived of 10 percent of their body weights was a result of the increased, FFA mobilization associated with this deprivation level, while the serum FFA levels of the subjects deprived of 20 percent of their body weights was a result of the reduced body fat observed at this deprivation level. Subjects given activity wheel experience following deprivation were compared with equally deprived subjects not given activity wheel experience. Only the subjects deprived of 10 percent of their body weights exhibited a reduction in serum FFA levels as a function of the running wheel experience. Rate of FFA mobilization was not altered, but total body fat was reduced at each of the deprivation levels, as a function of activity wheel experience. This reduction in total body fat, following running wheel activity, was an unexpected finding, and since serum FFA concentrations are partially determined by total body fat, the use of the nonactive subjects as controls for active subjects in comparing serum FFA concentrations was questioned. If running has a behavioral regulatory effect on food motivated behavior, then following activity wheel experience, food deprived rats should work less for food than equally deprived subjects not given activity wheel experience. The second experiment revealed that subjects deprived of 10 and 20 percent of their body weights, allowed to run in activity wheels immediately preceding a test session in a small rodent test chamber, pressed a bar less frequently than comparably deprived rats not allowed to run in the wheels. The adequacy of nonactive subjects as controls for active subjects was discussed.