Intrinsic exercise capacity is related to differential monoaminergic activity in the rat forebrain

Monoamines levels in central nervous system have been associated with exercise performance and fatigue. The present study investigated whether intrinsic exercise capacity is associated with differential activity of monoamines in the caudate-putamen (CPu) and accumbens (ACC) nucleus. Male Wistar rats were subjected to a progressive testing protocol. Based on the maximal time of exercise in the progressive testing protocol (TEPmax), the animals were divided into low-performance (LP), high-performance (HP), and standard-performance (SP) groups. After classification, eight animals in each group were chosen randomly and evaluated in two experimental situations: rest (n=8) or moderate exercise (ME) at 60% of maximal velocity (n=8). The CPu and ACC were dissected for analyses of monoamine levels. At rest, HP rats exhibited higher 3,4-dihydroxyphenylacetic acid (DOPAC)/dopamine (DA) ratio and lower serotonin (5-HT) concentration compared other groups, and lower 5-hydroxyindoleacetic (5-HIAA) compared with the LP rats. The ME resulted in increased DOPAC/DA ratio in the CPu of all experimental groups. In both the CPu and ACC, ME increased 5-HIAA levels in SP and HP rats and 5-HIAA/5-HT ratio only in HP rats. Thus, our findings demonstrate that rats with natural intrinsic differences in performance to exercise exhibit alterations in dopaminergic and serotonergic systems at rest and after ME exercise until fatigue.