High-performing Rats Research Articles

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 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.

Intrinsic exercise capacity is related to differential monoaminergic activity in the rat forebrain.

Monoamines levels in central nervous system have been associated with exercise performance and fatigue. The present study investigated whether intrinsic exercise capacity is associated with differential activity of monoamines in the caudate-putamen (CPu) and accumbens (ACC) nucleus. Male Wistar rats were subjected to a progressive testing protocol. Based on the maximal time of exercise in the progressive testing protocol (TEPmax), the animals were divided into low-performance (LP), high-performance (HP), and standard-performance (SP) groups. After classification, eight animals in each group were chosen randomly and evaluated in two experimental situations: rest (n=8) or moderate exercise (ME) at 60% of maximal velocity (n=8). The CPu and ACC were dissected for analyses of monoamine levels. At rest, HP rats exhibited higher 3,4-dihydroxyphenylacetic acid (DOPAC)/dopamine (DA) ratio and lower serotonin (5-HT) concentration compared other groups, and lower 5-hydroxyindoleacetic (5-HIAA) compared with the LP rats. The ME resulted in increased DOPAC/DA ratio in the CPu of all experimental groups. In both the CPu and ACC, ME increased 5-HIAA levels in SP and HP rats and 5-HIAA/5-HT ratio only in HP rats. Thus, our findings demonstrate that rats with natural intrinsic differences in performance to exercise exhibit alterations in dopaminergic and serotonergic systems at rest and after ME exercise until fatigue.

Exercise capacity is related to calcium transients in ventricular cardiomyocytes

The aim of the present study was to evaluate the Ca2+ handling and contractility properties of cardiomyocytes isolated from rats with high intrinsic aerobic exercise capacity. Standard-performance (SP) and high-performance (HP) rats were categorized with a treadmill progressive exercise test according to the exercise time to fatigue (TTF). The SP group included rats with TTF between 16.63 and 46.57 min, and the HP group included rats with TTF>46.57 min. Isolated ventricular cardiomyocytes were dissociated from the hearts of SP and HP rats, and intracellular global Ca2+ ([Ca2+]i) transients were measured. The [Ca2+]i transient peak was increased in the HP group relative to the SP group (5.54+/-0.31 vs. 4.18+/-0.12 F/F0; P<or=0.05) and was positively correlated with the TTF attained during the progressive test (r=0.81). We also performed contractility measurements in isolated cardiomyocytes and found higher amplitude of contraction in the HP group compared with the SP group (6.7+/-0.2 vs. 6.0+/-0.3% resting cell length; P<or=0.05). To reinforce the intrinsic differences between SP and HP rats, we performed Western blot experiments and observed increased expression of sarco(endo)plasmic reticulum Ca2+-ATPase type 2a (1.30+/-0.07 vs. 1.74+/-0.18 arbitrary units; P<or=0.05) and ryanodine receptor type 2 (1.86+/-0.13 vs. 3.57+/-0.12 arbitrary units; P<or=0.05) in HP rats. In summary, our data showed important intrinsic differences in cardiomyocyte properties that could explain some of the divergence observed in rats with high intrinsic aerobic exercise capacity.

Equivalent performance in the water maze by rats with an inborn high or low learning capacity in a shuttle box paradigm

The learning capacity of rats with an inborn high performance (HP) and low performance (LP) in an avoidance shuttle box paradigm, was evaluated in the Morris water maze. Escape latencies evaluated in HP and LP rats indicate that acquisition and retention of spatial information were not different from control animals. When a free swim trial was carried out, all groups showed a significant preference towards the target quadrant. Our results suggest that the altered hippocampal physiology described in HP and LP rats does not influence the performance of a spatial task such as the Morris water maze.

Differential threshold for long-term potentiation in the hippocampus of rats with inborn high or low learning capacity

Threshold of stimulation frequency in the perforant path to induce long-term potentiation (LTP) in dentate gyrus was determined in hippocampal slices obtained from two different lines of rats inbred for 30 generations according to their performance in an avoidance escape test in a shuttle box. High-performance (HP) rats were defined as those giving at least 70% conditioned responses (CRs) and low-performance (LP) rats as those giving less than 15% CRs. LTP was defined as a 30% or more increase in the amplitude of the evoked population spike (PS), lasting at least 20 min. Stimulation frequency threshold was determined by stimulating with a train of pulses of 0.5 ms duration during 1 s. The same slice was stimulated with trains of increasing frequency from 5 to 400 Hz, each train separated by an interval of at least 20 min. HP rats showed a lower threshold (13±4 Hz) than LP rats (92±42 Hz) for the induction of LTP; there were no differences in the magnitude of LTP. The greater learning ability of HP rats may be related to the plasticity of hippocampal synaptic transmission.