title: Discharge of RVLM vasomotor neurons is not increased in anesthetized angiotensin II-salt hypertensive rats.
abstract: Neurons of the rostral ventrolateral medulla (RVLM) are critical for generating and regulating sympathetic nerve activity (SNA). Systemic administration of ANG II combined with a high-salt diet induces hypertension that is postulated to involve elevated SNA. However, a functional role for RVLM vasomotor neurons in ANG II-salt hypertension has not been established. Here we tested the hypothesis that RVLM vasomotor neurons have exaggerated resting discharge in rats with ANG II-salt hypertension. Rats in the hypertensive (HT) group consumed a high-salt (2% NaCl) diet and received an infusion of ANG II (150 ng·kg(-1)·min(-1) sc) for 14 days. Rats in the normotensive (NT) group consumed a normal salt (0.4% NaCl) diet and were infused with normal saline. Telemetric recordings in conscious rats revealed that mean arterial pressure (MAP) was significantly increased in HT compared with NT rats (P < 0.001). Under anesthesia (urethane/chloralose), MAP remained elevated in HT compared with NT rats (P < 0.01). Extracellular single unit recordings in HT (n = 28) and NT (n = 22) rats revealed that barosensitive RVLM neurons in both groups (HT, 23 cells; NT, 34 cells) had similar cardiac rhythmicity and resting discharge. However, a greater (P < 0.01) increase of MAP was needed to silence discharge of neurons in HT (17 cells, 44 ± 5 mmHg) than in NT (28 cells, 29 ± 3 mmHg) rats. Maximum firing rates during arterial baroreceptor unloading were similar across groups. We conclude that heightened resting discharge of sympathoexcitatory RVLM neurons is not required for maintenance of neurogenic ANG II-salt hypertension.
authors.affiliation: Department of Physiological Science, Universidade Federal de Goiás, Goiânia, Brazil;
authors.forename: Gustavo R
authors.initials: GR
authors.lastname: Pedrino
authors.forename: Alfredo S
authors.initials: AS
authors.lastname: Calderon
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Andrade
authors.forename: Sergio L
authors.initials: SL
authors.lastname: Cravo
authors.forename: Glenn M
authors.initials: GM
authors.lastname: Toney
mesh_terms: D000804:Angiotensin II; D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D006973:Hypertension / Q000139:chemically induced / Q000503:physiopathology*; D008297:Male; D008526:Medulla Oblongata / Q000503:physiopathology*; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017673:Sodium Chloride, Dietary; D013564:Sympathetic Nervous System / Q000503:physiopathology
chemical_list: D017673:Sodium Chloride, Dietary; D000804:Angiotensin II
keywords: angiotensin II; high-salt diet; hypertension; rostral ventrolateral medulla vasomotor neurons; single unit recording; sympathetic nerve activity