Intrinsic Exercise Capacity in Rats Influences Dopamine Neuroplasticity Induced by Physical Training

The study evaluates whether the intrinsic capacity for physical exercise influences dopamine neuroplasticity induced by physical training. Male rats were submitted to 3 progressive tests until fatigue. Based on the maximal time of exercise (TE), rats were considered as low-performance (LP), standard-performance (SP) or high-performance (HP) to exercise. Eight animals from each group (LP, SP and HP) were randomly subdivided in sedentary (SED) or trained (TR). Physical training was performed during six weeks. After that, concentrations of dopamine (DA), serotonin (5-HT) and their metabolites and mRNA levels of D1 receptor (Drd1), D2 receptor (Drd2), dopamine transporter (Dat), tyrosine hydroxylase (Th), glia cell line-neurotrophic factor (Gdnf) and brain-derived neurotrophic factor (Bdnf) were determined in the caudate-putamen (CPu). TE was increased with training in all performance groups. However, the relative increase was markedly higher in LP rats and this was associated with a training-induced increase in dopaminergic activity in the CPu, determined by the 3,4-dihydroxyphenylacetic acid (DOPAC)/DA ratio. An opposite monoamine response was found in HP-TR rats, in which physical training decreased the DOPAC/DA ratio in the CPu. Moreover, LP-SED rats displayed higher levels of Drd2 in the CPu compared to the other SED groups, and this higher expression was decreased by physical training. Physical training also decreased Dat and increased Gdnf in the CPu of LP rats. Physical training decreased Bdnf in the CPu only in HP rats. Thus, we provide evidence that the intrinsic capacity to exercise affects the neuroplasticity of the dopaminergic system in response to physical training.

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