Abstract
We have demonstrated that the central nNOS neuronal system in normotensive Dahl rats was downregulatd compared with normotensive Sprague-Dawley (SD) rats. In accordance with development of hypertension, the above system especially in the brainstem became upregulated to the level in SD rats, although the nNOS activity in the diencephalon remained downregulated. Since tissue blocks used in the enzyme assay might be too large to discern alterations in nNOS in small populations of cells if they were present, in this study we tried to compare the number of nNOS neurons within the diencephalon between Dahl rats and SD rats. The Dahl salt-sensitive (DSS) and salt-resistant (DSR) rats were fed 8% NaCl (DSS8% and DSR8%) or 0.4% NaCl (DSS0.4% and DSR0.4%). SD rats were fed only 0.4% NaCl foods (SD0.4%). Immunohistochemical staining using anti-nNOS antibody revealed that the distribution of nNOS neurons in the hypothalamus is highly localized in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). The number of nNOS neurons in the SON was higher in DSS8% and SD0.4% than the other normotensive rat groups (DSS0.4%, DSR8% and DSR0.4%). While that in the PVN was higher in SD0.4% than all Dahl rat groups. These results indicated that in hypertensive DSS rats, downregulation of nNOS neuronal system in the PVN could not be normalized, although that system in the brainstem was upregulated to compensate high blood pressure. Thus, overall NO-mediated sympathoinhibition might not be enough to normalize high blood pressure. [J Physiol Sci. 2007;57 Suppl:S241]
