Pharmacological analysis of certain mechanisms of morphine addiction

The effects of L-Dopa, Methysergid, Diphenhydramine hydrochloride and LSD on the development of morphine dependence and the abstience syndrome after its withdrawal, were tested in experiments on 200 male Wistar albino rats. L-Dopa had no efect on the development of physical morphine dependence, while Methysergid prevented its development. Applied in rats during the abstinence syndrome, LSD intensified their aggressivity with no influence on the analgesic effect of morphine. Diphenhydramine reduced the aggressiveness of the rats during the abstinence syndrome. Biochemical tests show that in morphine-tolerant rats there was an increase in the content of brain serotonin, less of dopamine and no changes in noradrenaline. The significance of the brain levels of serotonin, dopamine and noradrenaline for the development of physical morphine-dependence is discussed. It is pointed out that serotonin and dopamine play an important role both for the origin of the physical morphine dependence, and in the abstinence syndrome after its withdrawal.