Sensitivity to 5-hydroxytryptamine in different afferent subpopulations within mesenteric nerves supplying the rat jejunum

J Physiol. 1998 Jun 15;509 ( Pt 3)(Pt 3):717-27. doi: 10.1111/j.1469-7793.1998.717bm.x.


1. This study was performed to elucidate the type of afferents that mediate the multiple actions of 5-hydroxytryptamine (5-HT) on mesenteric nerve discharge. Electrophysiological recordings were made from mesenteric afferents innervating the mid-jejunum of the urethane-anaesthetized rat. The discharge of single nerves within the whole nerve recording was monitored using waveform discrimination software. 2. Afferents responded to 5-HT in one of two ways: a short latency, transient excitation mediated by 5-HT3 receptors, or a delayed onset, more prolonged effect that was 5-HT2A receptor mediated. Afferents showing the 5-HT3-mediated response did not respond to luminal distension but were sensitive to intraluminal hydrochloric acid (150 mM) in twenty-eight of twenty-nine experiments. In eight experiments, the 5-HT3-mediated response was reversibly abolished by a 2 min exposure to intraluminal application of local anaesthetic (2 % Xylocaine). 3. Mechanosensitive afferents which responded to distension (< 10 cmH2O) did not show a 5-HT3-mediated response (P = 0.92, n = 14), and maintained this mechanosensitivity after luminal anaesthesia. Mechanosensitive afferents did show a secondary response to 5-HT that was significantly attenuated by atropine (100-200 microg kg-1), whereas hexamethonium (8 mg kg-1) had no effect. 4. In animals whose vagal afferent contribution to their mesenteric nerves had been eliminated by chronic truncal vagotomy, the 5-HT3-mediated response was absent in thirty-six of thirty-six nerve bundles. In contrast, mechanosensitivity to distension and the secondary response to 5-HT could still be evoked. 5. These results suggest that 5-HT stimulates mesenteric afferents by a direct action on 5-HT3 receptors that are present on vagal mucosal afferent terminals. The mucosal afferent response to luminal acid, however, was unaffected by treatment with granisetron (0.5 mg kg-1) indicating that endogenous 5-HT from enterochromaffin cells is not essential for transduction of this luminal signal. In contrast, mechanosensitivity in non-vagal afferents was modulated by 5-HT following an intestinal motor response which was influenced by cholinergic tone.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / drug effects
  • Anesthetics, Local / pharmacology
  • Animals
  • Cholinergic Antagonists / pharmacology
  • Electrophysiology
  • Enteric Nervous System / cytology*
  • Enteric Nervous System / drug effects
  • Ganglionic Blockers / pharmacology
  • Hexamethonium / pharmacology
  • Hydrochloric Acid / pharmacology
  • Jejunum / innervation*
  • Lidocaine / pharmacology
  • Male
  • Neurons, Afferent / drug effects*
  • Physical Stimulation
  • Rats
  • Rats, Wistar
  • Serotonin / pharmacology*
  • Stress, Mechanical
  • Vagotomy


  • Anesthetics, Local
  • Cholinergic Antagonists
  • Ganglionic Blockers
  • Serotonin
  • Hexamethonium
  • Lidocaine
  • Hydrochloric Acid