Circadian adaptations to regular treadmill exercise alter temporal changes in dopamine and serotonin activity in brain areas.

The beneficial effects of regular exercise may be mediated through its regulatory influence on circadian rhythm. Here, we investigated how regular exercise training affects spontaneous locomotor activity (SLA) and body temperature (T-body) rhythms and its influence on temporal changes in brain dopaminergic and serotonergic activity, corticosterone levels, and muscle Per1 and Bmal1 gene expression. The aerobic exercise schedule consisted of five days of training in the light phase (Zeitgeber time = ZT4 to ZT6, with light on at 7:00 h) followed by a two-day recovery period. After 8 weeks, brain, blood, and muscle samples were collected from adult male rats. Dopamine (DA) and serotonin (5-HT) and their respective metabolites, DOPAC and 5-HIAA, were measured in microdissections of the caudate putamen (CP), preoptic area (POA), and the paraventricular nucleus of the hypothalamus (PVN). Exercise increased the SLA at the end of the night, delayed the acrophase, and increased the mesor of the SLA rhythm. No alterations were found in the T-body rhythm and corticosterone blood levels, although hyperthermia was observed after exercise sessions. Exercise increased muscle Per1 expression at ZT0, leading to a non-rhythmic profile in exercised animals. There were no changes in the CP dopaminergic and serotonergic activity, but there was a decrease in POA at ZT6 and an increase in PVN serotonergic activity at ZT0, resulting in a non-rhythmic profile in exercised animals. Thus, regular physical exercise during the light phase with alterations in SLA promotes adjustments in the daily oscillation in monoaminergic activity in areas directly involved in regulating daily T-body and SLA.