Actions of acetylcholine and atropine on cerebral cortical neurons in chronically morphine-treated rats

In rats receiving a daily injection of increasing doses of morphine for 25–29 days, the sensitivity of cerebral cortical neurons to acetylcholine (ACh) and the ability of atropine to antagonize ACh effects were examined. While the responses of neurons to ACh were qualitatively and quantitatively similar between morphinized and control animals there was a marked reduction in the efficacy of atropine in blocking ACh effects in the morphine-treated rats.