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The phospholipase C-IP3 pathway is involved in muscarinic antinociception

Nicoletta Galeotti1, Alessandro Bartolini, Carla Ghelardini

  • 1Department of Preclinical and Clinical Pharmacology, University of Florence, Viale G. Pieraccini 6, I-10539 Florence, Italy.

Neuropsychopharmacology : Official Publication of the American College of Neuropsychopharmacology
|May 9, 2003
PubMed

Insights

Central muscarinic analgesia in mice involves the phospholipase C (PLC) pathway, not protein kinase C (PKC) activation. Inhibiting PLC or its downstream targets blocks pain relief, while activating PKC reduces analgesic effects.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Pain Research

Background:

  • Muscarinic receptor activation is known to induce analgesia, but the precise intracellular signaling pathways involved remain incompletely understood.
  • Previous studies suggest a role for G protein-coupled receptors in mediating analgesic effects, yet specific downstream effectors require elucidation.

Purpose of the Study:

  • To investigate the cellular mechanisms underlying central muscarinic analgesia in a mouse model.
  • To determine the involvement of the phospholipase C (PLC) pathway and protein kinase C (PKC) in mediating or modulating muscarinic-induced antinociception.

Main Methods:

  • Utilized the hot-plate test in mice to assess antinociceptive effects of cholinomimetic drugs.
  • Employed intracerebroventricular (i.c.v.) administration of antisense oligonucleotides (aODNs) against G(q)/G(11) alpha subunits and PLCbeta(1).
  • Administered pharmacological inhibitors (U-73122, LiCl, heparin, TMB-8, calphostin C) and activators (PMA, PDBu) of key signaling molecules.
  • Assessed behavioral effects using rota-rod and hole-board tests to rule out motor or general behavioral impairments.

Main Results:

  • Antisense oligonucleotides against G(q)/G(11) alpha subunits and PLCbeta(1) blocked physostigmine- and oxotremorine-induced analgesia.
  • Inhibition of PLC, phosphatidylinositol synthesis (LiCl), IP(3) receptor (heparin), and intracellular Ca(2+) release (TMB-8) antagonized muscarinic analgesia.
  • Coadministration of Ca(2+) restored analgesia in mice pretreated with LiCl, heparin, or TMB-8.
  • Selective protein kinase C (PKC) inhibition enhanced analgesia, while PKC activation (PMA, PDBu) dose-dependently prevented it.

Conclusions:

  • The phospholipase C-IP(3) pathway plays a critical role in central muscarinic analgesia in mice.
  • Activation of PKC by cholinomimetic drugs appears to negatively modulate muscarinic antinociception, acting as a feedback mechanism.
  • The findings elucidate key intracellular signaling events contributing to central pain control via muscarinic pathways.

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