Differential frequency-dependent reflex integration of myelinated and nonmyelinated rat aortic baroreceptors

Am J Physiol. 1998 Aug;275(2):H632-40. doi: 10.1152/ajpheart.1998.275.2.H632.


Electrical activation of myelinated (A type) and nonmyelinated (C type) baroreceptor axons (BR) in aortic depressor nerve (ADN) evoked baroreflex changes in mean arterial pressure (MAP) in chloralose-urethan-anesthetized rats. Low stimulation intensities (<3 V) activated only A-type BR electroneurograms (ENG). A-type selective stimulus trains required minimum frequencies >10 Hz to evoke reflex MAP decreases, and the largest MAP responses occurred at 50 Hz and higher. In contrast, high stimulation intensities (18-20 V) maximally activated two volleys in ADN ENG corresponding to A- and C-type BR volleys. High-intensity trains decreased MAP at low frequency (1 Hz) and largest reflex responses at >/=5 Hz. Capsaicin (Cap) applied periaxonally to ADN selectively blocked C-type ENG volleys but not A-type volleys. Reflex curves with supramaximal intensity during Cap were indistinguishable from the pre-Cap, low-intensity baroreflexes. In comparison, vagus ENG showed graded Cap block of the C-fiber volley (ED50 = 200 nM) without significant attenuation of the A-type volley below 1 microM. However, 100 microM Cap blocked conduction in all myelinated vagal axons as well as C-type axons. Thus Cap is selective for sensory C-type axons only at low micromolar concentrations. Myelinated and nonmyelinated arterial BR evoke characteristically different frequency-response reflex relations that suggest distinct differences in sensory information processing mechanisms.

MeSH terms

  • Action Potentials
  • Animals
  • Aorta / innervation*
  • Aorta / physiology
  • Axons / drug effects
  • Axons / physiology*
  • Baroreflex / drug effects
  • Baroreflex / physiology*
  • Blood Pressure / physiology*
  • Capsaicin / pharmacology
  • Electric Stimulation
  • Electrophysiology / methods
  • Femoral Artery / physiology
  • Male
  • Muscle, Smooth, Vascular / innervation
  • Muscle, Smooth, Vascular / physiology
  • Nerve Fibers, Myelinated / drug effects
  • Nerve Fibers, Myelinated / physiology*
  • Pressoreceptors / drug effects
  • Pressoreceptors / physiology*
  • Rats
  • Rats, Sprague-Dawley
  • Vagus Nerve / physiology


  • Capsaicin