A comparison of the effects of meptazinol and morphine on the release of acetylcholine from slices of mouse cerebral cortex.

Morphine and the new centrally-active analgesic agent, meptazinol, both increased the K+-evoked release of tritium from slices of mouse cortex preloaded with [3H]choline. The effect of both compounds was antagonised by naloxone whereas the response to meptazinol, but not that to morphine, was reduced in the presence of either scopolamine or tetrodotoxin. Oxotremorine produced a concentration-related inhibition of tritium release, presumably via an action on presynaptic muscarinic receptors, which was also blocked by scopolamine. These results suggest that there may be an indirect component in the action of meptazinol which may be related to a previous finding in which the antinociceptive response to meptazinol in the mouse was antagonised by both scopolamine and naloxone.