This study was designed to investigate the effect of acute and chronic high-intensity treadmill exercise on changes in plasma lactate and brain neuropeptide (NPY), leucine-enkephalin (L-ENK), and dynorphin A(1-13) (DYN A(1-13)). Avidin-biotin complex (ABC) immunohistochemistry and image pattern analysis were used to observe the effect of chronic (total 7 weeks) and acute treadmill exercise (an initial speed of 15 m min(-1) gradually increased to 35 m min(-1) with 0 degrees, 20-25 min per day duration) on the changes of NPY, L-ENK, and DYN A(1-13) in different areas of rat brain. Plasma lactate was also measured in response to such exercise. Compared with preexercise control (P < 0.01), plasma lactate concentration significantly increased in the immediate postexercise; but it returned to the normal level soon after the 30 min postexercise. The content of NPY in paraventricular (PVN), dorsomedial (DMN), and ventromedial (VMN) hypothalamic nuclei continued to increase in 0, 30, and 180 min postexercise compared with preexercise control (P < 0.01). The content of L-ENK in caudate-putamen (CPu) significantly increased in the immediate postexercise compared with preexercise control (P < 0.01), but it gradually returned to the normal level after the 180 min postexercise. However, the content of DYN A(1-13) in PVN rose substantially only in 30 min postexercise in comparison with the preexercise control (P < 0.01). Thus, different changes of NPY, L-ENK, and DYN A(1-13) in response to such high-intensity exercise depend on the brain region and the time examined, especially, the contents of NPY in different brain regions continuously remain at a high level after such high-intensity exercise. And this high level might reduce energy expenditure and thus contribute to the stimulation of brain NPY neurons.