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

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Abstract

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 (ED 50 = 200 nM) without significant attenuation of the A-type volley below 1 μM. However, 100 μM 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.

Original languageEnglish (US)
Pages (from-to)H632-H640
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume275
Issue number2 44-2
StatePublished - Sep 5 1998

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Keywords

  • Blood pressure
  • Myelinated axons
  • Nonmyelinated axons
  • Sensory afferents

ASJC Scopus subject areas

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

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