Studies on the specificity of uptake and release of radiolabelled histamine in rat brain slices.

Previously it has been shown that radiolabelled histamine is taken up by brain slices and may subsequently be released by depolarizing stimuli in a calcium-dependent manner, indicating the involvement of neurons in uptake and release of histamine. The present study demonstrates that after incubation of brain slices with low (nM) concentrations of [(3)H]histamine the amine may be taken up by (and released from) dopaminergic and serotonergic neurons (nerve terminals). Thus 6-hydroxydopamine- and 5,7-dihydroxytryptamine-induced lesions not only reduced the uptake of [(3)H]dopamine (in striatal slices) and [(3)H]serotonin (in hippocampal slices), but also, though to a lesser extent, that of [(3)H]histamine. Immunocytochemical findings revealed that the neurotoxins did not visibly affect histaminergic neurons. Lesioning of noradrenergic neurons appeared not to alter significantly the uptake of [(3)H]histamine. Further, various drugs acting on either catecholamine-, serotonin- or opioid-receptors and known to cause presynaptic inhibition of the release of [(3)H]dopamine or [(3)H]wrotonin from striatal or hippocampal slices also inhibited [(3)H]histamine release. It is concluded that incubation of brain slices with low concentrations of [(3)H]histamine does not result in a selective labelling of histaminergic neurons. The possibility that, unlike other monoamines, histamine is not subject to high-affinity uptake by the nerve terminals from which it was released, is discussed.