Intrinsic exercise capacity in rats influences dopamine neuroplasticity induced by physical training

Abstract

The study evaluates whether the intrinsic capacity for physical exercise influences dopamine neuroplasticity induced by physical training. Male rats were submitted to three 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 for 6 wk. 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, which was 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 with 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. NEW & NOTEWORTHY The findings reported reveal that dopaminergic neuroplasticity in caudate-putamen induced by physical training is influenced by the intrinsic capacity to exercise in rats. To evaluate the dopaminergic neuroplasticity, we analyzed mRNA levels of D1 receptor, D2 receptor, dopamine transporter, tyrosine hydroxylase, glia cell line neurotrophic factor, and brain-derived neurotrophic factor as well as concentrations of dopamine, serotonin, and their metabolites. These results expand our knowledge about the interrelationship between genetic background, physical training, and dopaminergic neuroplasticity.

Rats with higher intrinsic exercise capacities exhibit greater preoptic dopamine levels and greater mechanical and thermoregulatory efficiencies while running

“…The greater ME in HP rats can also be explained by central factors, particularly by parameters associated with dopaminergic neurotransmission. In previous studies, we reported that HP rats exhibited higher dopaminergic activity in the CPu, a brain area related to motor control, in comparison with rats with lower performance (36,37). Thus, this greater dopaminergic activity in the CPu could result in a higher ME during treadmill running, a hypothesis that is also supported by the findings of Balthazar et al (1).…”

“…In the second week, all rats were subjected to three incremental speed exercises until they were fatigued, with a 48-h interval between tests for recovery. Based on the maximal exercise time (TE max) obtained in one of the three tests, rats were ranked by using a previously described criterion (36,37) into different categories of intrinsic exercise capacity [low-performance (LP), standard-performance (SP) and high-performance (HP)]. Briefly, to be included in the LP group, rats needed to have a TE max lower than 24.9 min, whereas the rats with a TEmax between 24.9 and 57.1 min were ranked in the SP group.…”

“…In all familiarization sessions and experimental trials, the treadmill inclination was kept at 5 degrees, and an electrical stimulus was set to 0.28 mA. This light electrical stimulation was applied to encourage animals to run (36,37).…”

“…DOPAC and DA. Concentrations of DOPAC and DA were measured in the POA with high-performance liquid chromatography with electrochemical detection, as previously described in Rabelo et al (36,37).…”

“…Previous experiments have identified that rats exhibit a large intrinsic variation in exercise performance (23)(24)(25) with this heterogeneity being associated with differences in multiple physiological responses (3,19,21,38). In this context, we have previously identified that rats with different intrinsic capacities to exercise show altered monoaminergic responses in the caudateputamen (CPu), also known as the dorsal striatum (36,37). Such neurotransmitter changes might influence mechanical efficiency (ME), metabolic heat production, and the increase in core temperature during exercise (1).…”