Anaphylactic hypotension causes renal and adrenal sympathoexcitaion and induces c-fos in the hypothalamus and medulla oblongata

New Findings

• What is the central question of this study?

  Whether anaphylaxis affects sympathetic outflows to the brown adipose tissue (BAT) and adrenal grand is not known. Moreover, it is unknown whether anaphylaxis affects some brain areas in association with sympathetic regulation.

• What is the main finding and its importance?

  We showed that sympathoexcitatory responses to anaphylaxis regionally occurred in the kidney and adrenal grand, but not in the thermogenesis-related BAT. Further, anaphylactic hypotension also caused increase in c-fos immunoreactivity in the hypothalamic and medullary areas. Moreover, catecholaminergic neurons of the brain stem causes adrenal sympathoexcitation in a baroreceptor-independent manner.

Abstract

We previously reported that sympathetic nerve activity (SNA) to the kidney and the hind limb increases during anaphylactic hypotension in anesthetized 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 anesthetized 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 solitarius (NTS) and rostral ventrolateral medulla (RVLM) of the medulla oblongata; c-fos was expressed in gamma-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 were 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 grand and kidney to restore blood pressure.

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