Morphine analgesia and its modification by drugs altering serotonin (5-HT) and dopamine levels in the brain.

Morphine analgesia in mice was significantly potentiated by pretreatment with 5-hydroxytryptophan (5-HTP), especially with higher dose of morphine. Morphine analgesia was antagonised by reserpine. With l-dopa it was antogonised when the dose of morphine was minimal but with increased dosage of morphine, there was no significant effect.