Brain tumour necrosis factor- modulates neurotransmitters in hypothalamic paraventricular nucleus in heart failure

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Abstract
Increased proinflammatory cytokines after myocardial infarction augment the progression of heart failure (HF) and are of prognostic significance. Recently, we demonstrated that increased proinflammatory cytokines in the brains of HF rats increased paraventricular nucleus (PVN) superoxide and down-regulated neuronal nitric oxide synthase (nNOS), contributing to sympathoexcitation. In this study, we explored the possible roles of brain proinflammatory cytokines and their effects on modulating PVN neurotransmitters in the exaggerated sympathetic activity in HF. Sprague–Dawley rats with HF or sham-operated control (SHAM) rats were treated for 4 weeks with a continuous intracerebroventricular (ICV) infusion of the cytokine blockers—pentoxifylline (PTX, 10 µg/h and 40 µg/h), etanercept (ETN, 5 µg/h and 10 µg/h), or vehicle. Another set of HF and SHAM rats were treated with intraperitoneal (ip) infusion of a similar dose of PTX or ETN. HF rats had increased neuronal excitation accompanied by higher levels of glutamate, norepinephrine (NE), and tyrosine hydroxylase (TH), and lower levels of γ-aminobutyric acid (GABA), nNOS, and 67-kDa isoform of glutamate decarboxylase (GAD67) in the PVN when compared with SHAM rats. Plasma cytokines, NE, epinephrine, angiotensin II, and renal sympathetic nerve activity (RSNA) were also increased in HF rats. ICV treatment with low doses of PTX or ETN attenuated, and high doses prevented, increases in levels of glutamate, NE, and TH, and decreases in levels of GABA, nNOS, and GAD67 in the PVN in HF rats. The same ICV treatments also attenuated the increased RSNA seen in HF rats. IP treatment with similar doses of PTX or ETN did not affect glutamate, NE, TH, GABA, nNOS, and GAD67 in the PVN and had no effect on RSNA of HF rats. This study, for the first time, demonstrates that proinflammatory cytokines modulate neurotransmitters in the PVN and contribute to sympathoexcitation in HF.

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