Hypothalamic paraventricular nucleus inhibition decreases renal sympathetic nerve activity in hypertensive and normotensive rats

Activity of the hypothalamic paraventricular nucleus (PVN) is essential for the maintenance of vasomotor sympathetic nerve discharge (SND) and blood pressure even in the anesthetized rat. Inactivation of the paraventricular nucleus results in a large depressor and sympathoinhibitory response. The current study was designed to examine the regulation of renal sympathetic nerve activity by the paraventricular nucleus in both hypertensive and normotensive rats. Experiments were performed in anesthetized, artificially ventilated spontaneously hypertensive (SH) and Wistar–Kyoto (WKY) rats. Renal sympathetic nerve activity, blood pressure and heart rate were recorded. Bilateral microinjections of the GABAA receptor agonist, muscimol (1 nmol in 100 nl), were made into the paraventricular nucleus. Decreases in blood pressure (SHR: from 111±3 to 54±4 mm Hg; WKY: 84±2 to 48±3 mm Hg), heart rate (SHR: 336±8 to 289±12 bpm; WKY 309±7 to 258±13 bpm) and renal sympathetic nerve activity (to 46±11% and 33±7% of control in the WKY and SHR, respectively) were observed. The renal nerve response to inactivation of the paraventricular nucleus was not different between the strains, indicating that modulation of renal sympathetic nerve activity by the paraventricular nucleus is similar in these rat strains. This is different from the previously reported effect of paraventricular nucleus inhibition on lumbar sympathetic nerve activity [Hypertension 39 (2002) 275]. Overall, we demonstrate that the paraventricular nucleus plays a critical role in the regulation of renal SND even under basal conditions in anesthetized animals.