[Effect of morphine on the sensitivity of cerebral cortical neurons to acetylcholine]

Sensitivity of sensorimotor cortical neurons to microiontophoretically applied morphine and acetylcholine has been studied in the experiments on unanesthetized rabbits. The predominant reaction to morphine and acetylcholine was decrease and increase in the rate of neuronal impulse activity, respectively. There was no correlation in the responses to morphine and acetylcholine. Atropine failed to influence the morphine effect. When both drugs are simultaneously applied to neurons, morphine decreases both excitatory and inhibitory responses to acetylcholine. This effect of morphine may occur in the case when the drug is applied in doses which do not change spontaneous neuronal activity. On the contrary, excitatory effect of glutamic acid decreased only when morphine was applied in doses causing local anesthetic effect and decreasing background neuronal activity. It is suggested that morphine can exercise a modulating influence on choline receptors of cortical neurons.