5-HT7 receptor activation inhibits mechanical hypersensitivity secondary to capsaicin sensitization in mice

Pain. 2009 Feb;141(3):239-247. doi: 10.1016/j.pain.2008.11.009. Epub 2008 Dec 31.

Abstract

This work aimed to evaluate the potential role of the 5-HT(7) receptor in nociception secondary to a sensitizing stimulus in mice. For this purpose, the effects of relevant ligands (5-HT(7) receptor agonists: AS-19, MSD-5a, E-55888; 5-HT(7) receptor antagonists: SB-258719, SB-269970; 5-HT(1A) receptor agonist: F-13640; 5-HT(1A) receptor antagonist: WAY-100635) were assessed on capsaicin-induced mechanical hypersensitivity, a pain behavior involving hypersensitivity of dorsal horn neurons (central sensitization). For the 5-HT(7) receptor agonists used, binding profile and intrinsic efficacy to stimulate cAMP formation in HEK-293F cells expressing the human 5-HT(7) receptor were also evaluated. AS-19 and E-55888 were selective for 5-HT(7) receptors. E-55888 was a full agonist whereas AS-19 and MSD-5a behaved as partial agonists, with maximal effects corresponding to 77% and 61%, respectively, of the cAMP response evoked by the full agonist 5-HT. Our in vivo results revealed that systemic administration of 5-HT(7) receptor agonists exerted a clear-cut dose-dependent antinociceptive effect that was prevented by 5-HT(7) receptor antagonists, but not by the 5-HT(1A) receptor antagonist. The order of efficacy (E-55888>AS-19>MSD-5a) matched their in vitro efficacy as 5-HT(7) receptor agonists. Contrary to agonists, a dose-dependent promotion of mechanical hypersensitivity was observed after administration of 5-HT(7) receptor antagonists, substantiating the involvement of the 5-HT(7) receptor in the control of capsaicin-induced mechanical hypersensitivity. These findings suggest that serotonin exerts an inhibitory role in the control of nociception through activation of 5-HT(7) receptors, and point to a new potential therapeutic use of 5-HT(7) receptor agonists in the field of analgesia.

MeSH terms

  • Animals
  • Capsaicin*
  • Cell Line, Transformed
  • Cyclic AMP / metabolism
  • Dose-Response Relationship, Drug
  • Drug Interactions
  • Humans
  • Hyperalgesia / chemically induced*
  • Hyperalgesia / drug therapy
  • Male
  • Mice
  • Pain Measurement
  • Pain Threshold / drug effects*
  • Protein Binding / drug effects
  • Pyrazoles / pharmacology
  • Reaction Time / drug effects
  • Receptors, Serotonin / drug effects
  • Receptors, Serotonin / metabolism*
  • Serotonin Agents / pharmacology

Substances

  • Pyrazoles
  • Receptors, Serotonin
  • Serotonin Agents
  • dimethyl-(2-(3-(1,3,5-trimethyl-1H-pyrazol-4-yl)phenyl)ethyl)amine dihydrochloride
  • serotonin 7 receptor
  • Cyclic AMP
  • Capsaicin