Baroreflex frequency-response characteristics to aortic depressor and carotid sinus nerve stimulation in rats

Wei Fan, Patrick J. Reynolds, Michael C. Andresen

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

Dynamic cardiovascular regulation depends on baroreflexes and the processing of sensory information. We evaluated the influence of choice of anesthetic on the frequency-response characteristics of the baroreflex of rats by electrical stimulation of two major baroreceptor-containing nerves, the carotid sinus (CSN) and aortic depressor nerves (ADN). The ADN contains baroreceptors alone, and the CSN has both chemoreceptors and baroreceptors. Most studies were performed under pentobarbital sodium (PB; 65 mg/kg) anesthesia. We compared this to a combination of α-chloralose (80 mg/kg) and urethan (800 mg/kg) (CU). Stimulus trains were fixed at 60-s periods(0.1-ms shocks, supramaximal intensities, 1-200 Hz) and delivered in steady and burst patterns. Unilateral steady-frequency ADN stimulation in PB-anesthestized rats evoked reflex decreases in mean arterial pressure and heart rate that increased with frequencies between 1 and ~10 Hz before reaching a maximum. From 10 to 200 Hz, PB ADN reflex responses were sustained at these maximal levels. Cutting the opposite ADN or both CSNs did not alter ADN baroreflex relationships. Heart rate and mean arterial pressure depressor responses evoked by CSN stimulation in PB-anesthetized rats were smaller compared with ADN stimulation and were biphasic, with small pressor responses at 1 Hz. Maximal CSN depressor responses in PB-anesthetized rats occurred at ~20 Hz and were sustained at 20-200 Hz. Baroreflex responses for ADN stimulation in CU-anesthetized rats were similar to those in PB-anesthetized rats. In contrast, in CU-anesthetized rats, maximal CSN responses occurred at 20 Hz but declined at 50-200 Hz. Constant- and burst-stimulation responses were equivalent. The results suggest that rat aortic baroreflex responses are sustained even at very high input frequencies (>100 Hz). The sustained high- frequency baroreflex responses seem to present a paradox in understanding central integration because other studies show substantial depression of sensory transmission at the first synapse in the nucleus tractus solitarius at frequencies as low as 10 Hz.

Original languageEnglish (US)
Pages (from-to)H2218-H2227
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume271
Issue number6 40-6
StatePublished - Dec 1 1996

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Keywords

  • baroreceptors
  • blood pressure
  • chloralose-urethan
  • heart rate

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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