Studies on the relationship between morphine analgesia and the brain catecholamines in mice.

Abstract

The catecholamine content in the mouse brain has been investigated after the administration of an analgesic dose of morphine. A single dose of 7.5 mg/kg produced a significant reduction in brain noradrenaline during a time‐period of maximal analgesic activity. After inhibition of the rate limiting step of catecholamine synthesis a decrease in noradrenaline content was still obtained. Now even a reduction was found in dopamine content, but this appeared later and was more short‐lasting than the change in noradrenaline. By investigating individual differences in analgesia among animals after inhibition of the catecholamine synthesis or inhibition of dopamine β‐hydroxylation respectively with disulfiram further support was obtained for the view that the release of noradrenaline by morphine is correlated with the analgesic activity better than do changes in dopamine. The possibility that morphine analgesia is induced by interference at the storage sites of brain noradrenaline is discussed.