Operantly conditioned running: effects on brain catecholamine concentrations and receptor densities in the rat

It was hypothesized that endurance exercise results in an alteration in the brain monoamine systems. Rats were trained to run for food reinforcement on a variable ratio schedule in running wheels. Yoked control rats were also allowed to run but were not specifically reinforced for running. The animals ran 5 days per week for 8 weeks and were sacrificed 48 hours after the last endurance training session. The brains were assayed for norepinephrine and dopamine concentrations and beta-adrenergic (3H-dihydroalprenolol binding) and dopaminergic (3H-spiroperidol binding) receptor densities. Changes in norepinephrine concentration and beta-adrenergic receptor densities were not significantly different between reinforced running and yoked control groups. Dopamine concentrations were significantly higher while dopamine receptor densities were significantly lower in the reinforced running group. These results suggest that chronic running elevates dopamine secretion and consequently produces a compensatory down-regulation of dopaminergic receptor sites. The relationship of these changes to motor activity and to the antidepressant effects of exercise are discussed.