Effects of acute and chronic methadone treatment of the uptake of 3H-5-hydroxytryptamine in rat hypothalamus slices.

Effects of in vitro methadone and several other narcotics were investigated on 3H-5-HT uptake in rat hypothalamus slices. The results indicated that d, l-methadone and levorphanol had slightly greater inhibitory action on the uptake than the isomers, d-methadone and dextrorphan, respectively. Morphine, diacetylmorphine and the narcotic antagonist naloxone produced a considerably weaker inhibitory effect. After an acute injection of methadone, but not morphine, the uptake of 5-HT by hypothalamic slices of treated animals was inhibited. The chronic treatment of rats with methadone for 18 days had no significant effect on the uptake, but following the withdrawal of this treatment for 2 weeks the 5-HT uptake was significantly elevated. The inhibitory effects of in vitro methadone in the hypothalamus slices were not modified by the chronic drug treatment.