A dopamine and noradrenaline reuptake inhibitor （bupropion） does not alter exercise performance of bank voles

Physical performance is determined both by biophysical and physiological limitations and behav- ioral characteristic, specifically motivation. We applied an experimental evolution approach com- bined with pharmacological manipulation to test the hypothesis that evolution of increased aerobic exercise performance can be triggered by evolution of motivation to undertake physical activity. We used a unique model system： bank voles from A lines, selected for high swim-induced aerobic metabolism （VO2swim）, which achieved a 61% higher mass-adjusted VO2swim than those from un- selected C lines. Because the voles could float on the water surface with only a minimum activity, the maximum rate of metabolism achieved in that test depended not only on their aerobic capacity, but also on motivation to undertake intensive activity. Therefore, we hypothesized that signaling of neurotransmitters putatively involved in regulating physical activity （dopamine and noradrenaline） had changed in response to selection. We measured VO2swim after intraperitoneal injections of sa- line or the norepinephrine and dopamine reuptake inhibitor bupropion （20 mg/kg or 30 mg/kg）. Additionally, we measured forced-exercise VO2 （VO2max）. In C lines, VO2swim （mass-adjusted mean ± standard error （SE）： 4.0 ± 0.1 mLO2/min） was lower than VO2max （5.0 ± 0.1 mLO2/min）, but in A lines VO2swim （6.0 ± 0.1 mLO2/min） was as high as VO2max （6.0 ± 0.1 mLO2/min）. Thus, the selection effectively changed both the physiological-physical performance limit and mechanisms responsible for the willingness to undertake vigorous locomotor activity. Surprisingly, the drug had no effect on the achieved level of VO2swim. Thus, the results did not allow firm conclusions concerning involvement of these neurotransmitters in evolution of increased aerobic exercise performance in the experimental evolution model system.

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

Exercise performance depends on both physiological abilities (e.g., muscle strength) and behavioral characteristics (e.g., motivati on). We tested the hypothesis that evoluti on of in creased aerobic exercise performanee 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 gen eration 21, voles from the 4 A lines achieved a 57% higher /y voluntary maximum" swiminduced aerobic metabolism (V02swim) than voles from 4 unselected,"control" C lines. In C lines, V02swim 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 behi nd motivation to un dertake activity. We investigated the influe nee of reuptake in hibitors of dopamine (DARI), serotonin (SSRI), and norepinephrine (NERI) on VOaSwim. The drugs decreased V02swim 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.