Participation of serotonin in development of morphine dependence in mice and rats.

The effect of compounds inhibiting serotonergic transmission (reserpine, cyproheptadine, LSD) and stimulating it (imipramine, fluoxetine, 5-hydroxytryptophan) on the development of morphine dependence in mice and rats was investigated. Reserpine inhibited the development of morphine dependence in mice and rats. A combined treatment with 5-hydroxytryptophan and reserpine reversed the inhibitory action of reserpine on development of morphine dependence in mice. Cyproheptadine did not affect and LSD potentiated the formation of morphine dependence in mice. Imipramine potentiated the development of dependence in mice and rats and fluoxetine in mice. The results suggest that a decrease in the function of serotonergic system inhibits the development of morphine dependence, while stimulation of this system potentiates the development of the dependence in mice and rats. It seems that the retention of activity of presynaptic serotonin nerve endings is of importance in the development of dependence.