Effects of Narcotic Analgesics on Serotonin Metabolism in Brain of Rats and Mice

Abstract

The effects of narcotic analgesics on the brain 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels of rats and mice were investigated in relation to our preceding data on the effect of humoral modulators on morphineinduced changes in locomotor activity and body temperature of rodents. The results suggest that morphine accelerates the release of brain 5-HT both in rats and mice, and that neither methadone nor pethidine alters the brain 5-HT and 5-HIAA levels in rats. The morphine-induced increase in brain 5-HT turnover is likely to be involved in the morphine-induced decrease in locomotor activity and hypothermia in rats. The activity-decreasing effects of methadone or pethidine, on the other hand, are mediated by mechanisms different from those which mediate the effects of morphine. In contrast, an increase in brain 5-HT turnover in mice apparently does not play an important role on activity-increasing effects of morphine but rather participates in other pharmacological effects of morphine.