STUDIES ON THE MECHANISM OF HISTAMINE-INDUCED RELEASE OF NORADRENALINE AND 5-HYDROXYTRYPTAMINE FROM SLICES OF RAT CEREBRAL-CORTEX

The effect of histamine on the release of endogenous noradrenaline and 5-hydroxytryptamine (5-HT) has been examined in slices of rat cerebral cortex. Histamine was found to produce a marked release of both amines from rat cerebral cortex at concentrations btween 0.1 and 1 mM. The response to histamine was relatively resistant to removal of calcium ions from the incubation medium when compared to the release evoked by depolarising potassium stimuli. The response to 1 mM histamine was not. However, significantly inhibited by the H1-antagonist mepyramine (1 .mu.M) or the H2-antagonist cimetidine (100 .mu.M). Furthermore, impromidine which is both a potent H2-agonist and a potent H3-antagonist was without effect on the basal and histamine-stimulated release of endogenous noradrenaline and 5-HT. The response to histamine was, however, significantly attenuated by nisoxetine, fluoxetine and imipramine which are inhibitors of the amine uptake systems. The results of this study show that high concentraitons (0.1 to 1 mM) of histamine can produce a marked increase in the release of endogenous 5-HT and noradrenaline from rat cerebral cortex, apparently via a non-receptor mechanism. The effect will need to be borne in mind in interpreting biochemical and behavioural responses to histamine in this concentration range.