RESUMEN
The paraventricular nucleus (PVN) of the hypothalamus is an important site for autonomic and neuroendocrine regulation. Experiments in anesthetized animals and in vitro indicate an interaction among gamma-aminobutyric acid (GABA), nitric oxide (NO), and glutamate in the PVN. The cardiovascular role of the PVN and interactions of these neurotransmitters in conscious animals have not been evaluated fully. In chronically instrumented conscious rats, mean arterial pressure (MAP) and heart rate (HR) responses to microinjections (100 nl) in the region of the PVN were tested. Bilateral blockade of ionotropic excitatory amino acid (EAA) receptors (kynurenic acid, Kyn) in the PVN produced small but significant decreases in MAP and HR. GABA(A) receptor blockade (bicuculline, Bic), and inhibition of NO synthase [(NOS), N-(G)-monomethyl-L-arginine, L-NMMA] each increased MAP and HR. The NO donor sodium nitroprusside (SNP) produced depressor responses that were attenuated by Bic. NOS inhibition potentiated both pressor responses to the selective EAA agonist, N-methyl-D-aspartic acid (NMDA), and depressor responses to Kyn. Increases in MAP and HR due to Bic were blunted by prior blockade of EAA receptors. Thus, pressor responses to GABA blockade require EAA receptors and GABA neurotransmission contributes to NO inhibition. Tonic excitatory effects of glutamate in the PVN are tonically attenuated by NO. These data demonstrate that, in the PVN of conscious rats, GABA, glutamate, and NO interact in a complex fashion to regulate arterial pressure and HR under normal conditions.
RESUMEN
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.