Serotonin increases excitability of rabbit C-fiber neurons by two distinct mechanisms.
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.
Christian
E P
EP
Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore 21201.
Taylor
G E
GE
Weinreich
D
D
D000818:Animals; D004594:Electrophysiology; D008297:Male; D008564:Membrane Potentials; D008784:Methysergide / Q000378:metabolism; D009412:Nerve Fibers / Q000502:physiology; D009620:Nodose Ganglion / Q000378:metabolism*; D011817:Rabbits; D012701:Serotonin / Q000494:pharmacology*; D014403:Tubocurarine / Q000378:metabolism; D014630:Vagus Nerve / Q000378:metabolism*
D012701:Serotonin; D014403:Tubocurarine; D008784:Methysergide