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.
Beani, L., Siniscalchi, A., & Sarto, G. (1979). Monoamines modulation of morphine action on pain threshold and cortical acetylcholine outflow. Pharmacological Research Communications, 11(8), 663–680. https://doi.org/10.1016/S0031-6989(79)80057-0