Monoamines modulation of morphine action on pain threshold and cortical acetylcholine outflow

Abstract

The effects of morphine (M) on pain threshold and on the Ach outflow from the cerebral cortex of unanaesthetized guinea-pigs were investigated. pCPA pretreatment slightly attenuated M analgesia and significantly reduced Ach release inhibition caused by the drug. α-MT or reserpine pretreatment had little effect on M analgesia, but potentiated and prolonged its anti-release effect. Conversely, amphetamine showed, per se, a clear-cut analgesic effect and acted synergically with M as regards analgesia. On the other hand, the amine fully prevented the inhibition of Ach outflow. These results are discussed in the light of the hypothesis that 5-HT neurones positively co-operate to the entire pattern of M action, whereas DA neurons potentiate analgesia but antagonize M influence on cortical Ach release. © 1979 The Italian Pharmacological Society.