Role of paraventricular nucleus in exercise training-induced autonomic modulation in conscious rats.

The paraventricular nucleus (PVN) of the hypothalamus is an important site for autonomic regulation, where gamma-aminobutyric acid (GABA) system plays an important role. The central mechanisms underlying modulatory effects of exercise training have yet to be characterized. Our objective was to analyze the effects on the autonomic modulation and hemodynamic parameters after bicuculline or muscimol injections into the PVN of sedentary (control, C) and previously submitted to swimming training (ST) rats. After ST protocol, adult male Wistar rats, instrumented with guide cannulas to PVN and femoral artery and vein catheters were submitted to mean arterial pressure (MAP) recording. The exercise training reduced the LF oscillations in normalized units and increased the HF oscillations in absolute and normalized units. Compared with the C group, muscimol microinjections in the ST group promoted a higher decrease in MAP (C=-14+/-1 vs. ST=-28+/-4 mm Hg). Spectral analysis of HR (pulse interval) showed that the muscimol microinjections also reduced LF and HF oscillations in absolute units in both groups. Bicuculline microinjections increased the systolic arterial pressure (C=155+/-5, ST=164+/-5 mm Hg) in ST compared with the C group. Bicuculline injections also increased the LF oscillations of HR in absolute units in C and ST groups. Meanwhile, in normalized units only the ST group showed an increase in the LF oscillations. Our data showed that PVN has an important role in autonomic modulation after exercise training.