The effect of monoamines reuptake inhibitors on aerobic exercise performance in bank voles from a selection...

Exercise performance depends on both physiological abilities (e.g., muscle strength) and behavioral characteristics (e.g., motivation). We tested the hypothesis that evolution of increased aerobic exercise performance can be facilitated by evolution of neuropsychological mechanisms responsible for motivation to undertake physical activity. We used a unique model system: lines of bank voles Myodes glareolus selected for high swim-induced aerobic metabolism ("aerobic" A lines). In generation 21, voles from the 4 A lines achieved a 57% higher "voluntary maximum" swim-induced aerobic metabolism (VO₂swim) than voles from 4 unselected, "control" C lines. In C lines, VO₂swim was 9% lower than the maximum forced-exercise aerobic metabolism (VO₂run; P = 0.007), while in A lines it was even higher than VO₂run, although not significantly (4%, P = 0.15). Thus, we hypothesized that selection changed both the aerobic capacity and the neuronal mechanisms behind motivation to undertake activity. We investigated the influence of reuptake inhibitors of dopamine (DARI), serotonin (SSRI), and norepinephrine (NERI) on VO₂swim. The drugs decreased VO₂swim both in C and A lines (% decrease compared with saline: DARI 8%, P < 0.001; SSRI 6%, P < 0.001; NERI 8%, P < 0.001), but the proportional response differed between selection directions only for NERI (stronger effect in C lines: P = 0.008) and the difference was marginally non-significant for SSRI (P = 0.07) and DARI (P = 0.06). Thus, the results suggest that all the 3 monoamines are involved in signaling pathways controlling the motivation to be active and that norepinephrine could have played a role in the evolution of increased aerobic exercise performance in our animal model.