The contribution of the median preoptic nucleus to renal sympathetic nerveactivity increased by intracerebroventricular injection of hypertonic saline in the rat

The median preoptic nucleus (MnPO) of the hypothalamus is involved in the o smotic control of neurohypophysial hormone release and drinking behavior. A t the same time, renal sympathetic nerves exert multiple effects on renal f unctions such as regulating renal bloodflow and urinary sodium excretion. W e made the hypothesis that the MnPO may also regulate body fluid balance by exerting an influence on renal sympathetic nerve activity (RSNA). In this study we examined the effect of electrical stimulation of the MnPO on RSNA and the contribution of the MnPO to the change of RSNA induced by intracere broventricular injection of hypertonic saline in the male Wistar rat. Elect rical stimulation of the MnPO and the paraventricular nucleus of the hypoth alamus (PVN) elicited an increase in RSNA. This increase of RSNA elicited b y electrical stimulation of the MnPO was reduced by microinjections (100 nl ) of 10% lidocaine or 4 mM cobaltous chloride (a synaptic transmission bloc king agent) bilaterally into the PVN. Both RSNA and the mean arterial press ure (MAP) were increased by the injection of 1.5 M NaCl into the third vent ricle, although heart rate (HR) was not significantly changed. These respon ses of RSNA and MAP were diminished by microinjection of 10% lidocaine (100 nl) into the MnPO. Our results suggest that the MnPO is involved in body f luid regulation not only by controlling vasopressin secretion and water int ake but also by modulating central sympathetic outflow which regulates body fluid balance through an effect on the kidney. (C) 2000 Elsevier Science B .V. All rights reserved.