Ultrastructural Morphometry Of The Vagus Nerve In Rats Submitted To Aerobic Training

The quantitative changes promoted by aerobic training on somatic nerves are well established. There is an increase in the area of myelin sheat and unmyelinated axons and a significant increase in size of myelinated fibers. However, quantitative studies on the beneficial effects of aerobic training on visceral nerves are scarce and these studies are referred especially to functional aspects of the nerves rather than the morphological or quantitative aspects. In this study we have used electron microscopy to check the influence of aerobic training on quantitative aspects from myelinated and unmyelinated fibers of the vagus nerve using the Wistar rat as an animal model. The effects of treadmill training (for 12 wk) on vagus nerve structure were assessed by comparison of two sets of rats: sedentary animals of the same age and rats of the same body weight as the exercised cohort. Fourteen rats of 6 mo of age were divided into two groups: control group, CG (n=8), and aerobic trained group, AT (n=8). Rats of trained group were submitted to a physical activity program which consisted of running on a treadmill five times a week. The maximum speed stipulated in the physical activity protocol corresponded to 60% of the mean maximum intensity achieved by the group in the text of maximum effort. Systolic blood pressure was measured at two time points: at the beginning of the experiment (6 mo of age) and at the moment of the sacrifice (9 mo of age) using the tail-cuff method. The thickness of the left ventricular wall and the left ventricular internal diameter were obtained by measuring the widths of four of uniformly spaced sites along the length of each section using a computerized program. No significant difference was observed in the body weight between the CG and AT groups. The LVW:BW increased 19% in AT group (p < 0.01) compared to the CG group. Twelve weeks of treadmill running resulted in left ventricular hypertrophy in the trained group compared with sedentary controls. The LV wall thickness increased 4% in the AT group when compared with the CG group (p > 0.05) (NS). The LV internal diameter increased 20% in the AT group (p < 0.05) compared with the CG group. There was a significant increase in the area of both, the myelinated and unmyelinated axons and in the area of myelin sheath with training. The average value of the g ratio was 0.6 for CG and 0.7 for TG. The difference was not significant. A unimodal distribution of myelinated fibers was observed, with a significant peak on the 2.0 μm fibers in the control group and on the 2.5 μm fibers in the trained group. The number of neurotubules and neurofilaments in myelinated fibers of aerobic trained group was significantly greater than that for the control group. In all cases, p < 0.05. Aerobic training promoted significant increase in morphometric parameters of the vagus nerve in the same way it affect somatic nerves.

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