Daily exercise normalizes the number of diaphorase (NOS) positive neurons in the hypothalamus of hypertensive rats

Abstract

It is well known that nitric oxide (NO), within the paraventricular nucleus (PVN) of the hypothalamus, mediates sympatho-inhibition via an inhibitory GABA-ergic mechanism. Furthermore, the inhibitory GABA-ergic mechanism is impaired in the spontaneously hypertensive rat (SHR). These data suggest that the NO system, within the PVN, may also be impaired in the SHR. In addition, previous studies have documented that daily exercise attenuates the development of tachycardia, hypertension and blood pressure related cardiovascular disease risk factors in SHR. These data suggest that daily exercise enhances the inhibitory GABA-ergic and/or NO systems. Therefore, this study was designed to test the hypothesis that hypertension, in the SHR, is associated with a lower number of NADPH-diaphorase (a commonly used marker for neuronal NOS activity) positive neurons within the PVN and that daily exercise increases the number of NOS positive neurons. Using a standard histochemical protocol, NOS positive neurons were measured in the PVN, supraoptic nucleus, median preoptic area, lateral hypothalamus, nucleus of the tractus solitarius and rostral ventrolateral medulla. Results document that SHR have significantly fewer NOS-positive neurons in the PVN than their genetic control, the Wistar-Kyoto (WKY) rats (110+/-11 versus 139+/-17). Furthermore, daily exercise increased the number of NOS positive neurons in the SHR to levels seen in the WKY rats. These data demonstrate that hypertension, in the SHR, is associated with a lower number of NOS positive neurons within the PVN and that daily exercise increases the number of NOS positive neurons within the PVN.