Microinjection of salusin-beta into the nucleus tractus solitarii inhibits cardiovascular function by suppressing presympathetic neurons in rostral ventrolateral medulla in rats.

Salusin-beta is newly identified bioactive peptide of 20 amino acids, which is widely distributed in hematopoietic system, endocrine system, and the central nervous system (CNS). Although salusin-beta extensively expressed in the CNS, the central cardiovascular functions of salusin-beta are unclear. Our main objective was to determine the cardiovascular effect of microinjection of salusin-beta into the nucleus tractus solitarii (NTS) in anesthetized rats. Bilateral or unilateral microinjection of salusin-beta (0.94-94 microg/rat) into the NTS dose-dependently decreased blood pressure and heart rate. Bilateral NTS microinjection of salusin-beta (9.4 microg/rat) did not alter baroreflex sensitivity. Prior application of the glutamate receptor antagonist kynurenic acid (0.19 microg/rat, n=9) into the NTS did not alter the salusin-beta (9.4 microg/rat) induced hypotension and bradycardia. However, pretreatment with the GABA receptor agonist muscimol (0.5 ng/rat) within the rostral ventrolateral medulla (RVLM) completely abolished the hypotension (-14+/-5 vs. -3+/-5 mm Hg, P<0.05) and bradycardia (-22+/-6 vs. -6+/-5 bpm, P<0.05) evoked by intra-NTS salusin-beta (9.4 microg/rat). In addition, we found that vagotomy didn't influence the actions of salusin-beta (9.4 microg/rat) in the NTS. In conclusion, our present study shows that microinjection of salusin-beta into the NTS significantly produces hypotension and bradycardia, presumably by suppressing the activities of presympathetic neurons in the RVLM.