Role of nitric oxide in the control of the heart rate within the nucleus ambiguus of rats

The aim of this study was to determine whether NO plays a role in the contr ol of heart rate (HR) within the nucleus ambiguus (NA). Experiments were pe rformed in 29 male Wistar rats anaesthetized with urethane. Microinjections of the NO-donor sodium nitroprusside (SNP; 5 mmol) as well as of L-arginin e (L-arg; 50 mmol) into functionally identified cardioinhibitory sites with in the NA significantly decreased HR (-57.7 +/- 8.4 and -53.8 +/- 3.2 bpm, respectively), whereas the NO-synthase inhibitor N-omega-nitro-L-arginine m ethyl ester (L-NAME) significantly increased HR (+40 +/- 2.7 bpm). Bilatera l vagotomy and i.v. injection of atropine (0.5 mg/kg) always abolished the: HR decrease induced by SNP and L-arg, whereas propranolol did not affect t he HR responses. These results demonstrated that NO mechanisms within the N A play a role in the parasympathetic control of the HR. NeuroReport 11:481- 485 (C) 2000 Lippincott Williams & Wilkins.