Serotonin increases excitability of rabbit C-fiber neurons by two distinct mechanisms

J Appl Physiol (1985). 1989 Aug;67(2):584-91. doi: 10.1152/jappl.1989.67.2.584.


Serotonin (5-HT) increases impulse activity in visceral afferent C-fibers in vivo. A 5-HT-induced membrane depolarization may partially account for this effect. Here, we examined the potential contribution of an additional mechanism to the 5-HT-mediated increase in impulse activity. Approximately 40% of rabbit visceral C-fiber neurons exhibit a protracted (greater than 3 s) spike afterhyperpolarization (AHPslow) that is a major determinant of repetitive firing properties in these neurons. Intracellular recording methods were applied to rabbit nodose ganglion neurons in vitro to assess whether 5-HT could increase excitability through effects on the AHPslow. Results revealed a concentration-dependent 5-HT-mediated depression of the AHPslow amplitude and duration that was accompanied by decreased accommodation of action potential firing. Experiments with 5-HT receptor antagonists further showed that this autacoid depressed the AHPslow through a different 5-HT receptor subtype than that subserving the 5-HT-induced depolarization. Thus the AHPslow represents a distinct locus where 5-HT can increase the impulse activity of these visceral C-fiber afferents.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Electrophysiology
  • Male
  • Membrane Potentials
  • Methysergide / metabolism
  • Nerve Fibers / physiology
  • Nodose Ganglion / metabolism*
  • Rabbits
  • Serotonin / pharmacology*
  • Tubocurarine / metabolism
  • Vagus Nerve / metabolism*


  • Serotonin
  • Tubocurarine
  • Methysergide