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Methoctramine, a selective M2 alpha muscarinic receptor antagonist, does not inhibit carbachol-induced drinking in

M Massi1, C Polidori, C Melchiorre

  • 1Institute of Pharmacology and Pharmacognosy, University of Camerino, Bologna, Italy.

European Journal of Pharmacology
|April 25, 1989
PubMed

Insights

Methoctramine, a selective M2 alpha muscarinic receptor antagonist, did not inhibit carbachol-induced drinking in rats. This suggests M2 alpha receptors are not involved in this drinking response.

Area of Science:

  • Neuroscience
  • Pharmacology

Background:

  • Cholinergic pathways regulate drinking behavior in rats.
  • Muscarinic receptors, specifically M1 and M2 subtypes, are implicated in various physiological processes.

Purpose of the Study:

  • To investigate the role of M2 alpha muscarinic receptors in carbachol-induced drinking in rats.
  • To determine if selective M2 alpha muscarinic receptor antagonism can inhibit this drinking behavior.

Main Methods:

  • Intracerebroventricular administration of methoctramine, a selective M2 alpha muscarinic receptor antagonist, in rats.
  • Testing other muscarinic receptor antagonists (4-DAMP, pirenzepine, hexahydrosiladifenidol) and an M1 agonist (McN-A-343).
  • Observing the effects on carbachol-induced drinking behavior.

Main Results:

  • Methoctramine did not inhibit carbachol-induced drinking at non-toxic doses.
  • Higher doses of methoctramine exhibited toxicity.
  • The potency order of other tested antagonists correlated with their M1 receptor affinity, suggesting M1 receptor involvement.

Conclusions:

  • M2 alpha muscarinic receptors do not appear to mediate cholinergic drinking in the rat.
  • The involvement of M1 or M2 beta muscarinic receptors in this response remains undetermined.

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