Anaphylactic Hypotension Causes Renal And Adrenal Sympathoexcitaion And Induces C-Fos In The Hypothalamus And Medulla Oblongata

We previously reported that sympathetic nerve activity (SNA) to the kidney and the hindlimb increases during anaphylactic hypotension in anaesthetized rats. Based on this evidence, we examined effects of anaphylactic hypotension on SNA to the brown adipose tissue (BAT), and the adrenal gland and kidney in anaesthetized rats. We demonstrated that adrenal and renal SNA, but not BAT-SNA, were stimulated. In addition, the effects of anaphylaxis on neural activities of the hypothalamic and medullary nuclei, which are candidates for relaying efferent SNA to the peripheral organs, were investigated via immunohistochemical staining of c-fos. Anaphylaxis increased c-fos expression in the neurons of the paraventricular nucleus (PVN) of the hypothalamus and in those of the nucleus tractus solitarii (NTS) and rostral ventrolateral medulla (RVLM) of the medulla oblongata; c-fos was expressed in -aminobutyric acid (GABA)-ergic neurons of the NTS and in the catecholaminergic neurons of the RVLM. In addition, c-fos expression in the rostral NTS and mid NTS during anaphylaxis was reduced by sinoaortic baroreceptor denervation; however, increased c-fos expression in the caudal NTS and RVLM or adrenal sympathoexcitation were not affected by sinoaortic baroreceptor denervation. These results indicated that anaphylactic hypotension activates the hypothalamic PVN and the medullary NTS and RVLM independently of the baroreflex pathway. Further, it stimulated efferent SNA to the adrenal gland and kidney to restore blood pressure.