Midline medullary depressor responses are mediated by inhibition of RVLM sympathoexcitatory neurons in rats

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 1999-04, Vol.276 (4), p.1054-R1062
• Main Authors: Verberne, Anthony J. M, Sartor, Daniela M, Berke, Ayse
• Format: Article
• Language: English
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.1999.276.4.r1054

University of Melbourne, Clinical Pharmacology and Therapeutics Unit, Austin and Repatriation Medical Centre, Heidelberg, Victoria 3084, Australia Mechanisms underlying the depressor and sympathoinhibitory responses evoked from the caudal medullary raphe (MR) region were investigated in pentobarbital sodium-anesthetized, paralyzed rats. Intermittent electrical stimulation (0.5 Hz, 0.5-ms pulses, 200   µA) of the MR elicited a mixed sympathetic response that consisted of a long-latency sympathoexcitatory (SE) peak (onset = 146 ±   7 ms) superimposed on an inhibitory phase (onset = 59 ± 10 ms). Chemical stimulation of the MR (glutamate; Glu) most frequently elicited depressor responses accompanied by inhibition of sympathetic nerve discharge. Occasionally, these responses were preceded by transient pressor and SE responses. We examined the influence of intermittent electrical stimulation (0.5 Hz, 0.5-ms pulses, 25-200 µA) and Glu stimulation of the MR on the discharge of rostral ventrolateral medulla (RVLM) premotor SE neurons. Peristimulus-time histograms of RVLM unit discharge featured a prominent inhibitory phase in response to MR stimulation (onset = 20 ± 2 ms; duration   = 42 ± 4 ms; n  = 12 units). Glu stimulation of the MR reduced blood pressure ( 37 ± 2 mmHg, n  = 19) and inhibited the discharge of RVLM SE neurons (15 of 19 neurons). Depressor and sympathoinhibitory responses elicited by chemical and electrical stimulation of the MR region are mediated by inhibition of RVLM premotor SE neurons and withdrawal of sympathetic vasomotor discharge. blood pressure; sympathoinhibitory neurons Deceased 12 May 1998.   The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked " advertisement " in accordance with 18 U.S.C. §1734 solely to indicate this fact.