Central muscarinic activation elicits compulsive drinking behaviour in the rat.

Injection of bethanechol into the lateral cerebral ventricle of the rat induces a marked increase in drinking, within 30 min from administration. The response is dose-related, maximal water intake (6.1 +/- 0.55 mL; mean +/- s.e.) occurring at 10 micrograms of bethanechol. Peripheral administration of the agonist (up to 3 mg kg-1 i.p.) fails to elicit drinking. Among several specific antagonists only antimuscarinic drugs produced a significant inhibition of the response, suggesting that the compulsive drinking behaviour in the rat is caused by activation of central muscarinic receptors. The drinking behaviour emerges as a reliable test to assess central muscarinic activity of both agonists and antagonists.