Dopamine uptake in serotoninergic terminals in vitro: a valuable tool for the histochemical differentiation of catecholaminergic and serotoninergic terminals in rat cerebral structures.

An in vitro method was developed to separately visualize dopaminergic, noradrenergic and serotoninergic terminals in the cerebral, hippocampal and cerebellar cortices of the rat, by means of the glyoxylic histochemical fluorescence method. Animals were pretreated with alpha-methylparatyrosine to deplete catecholamine stores. Thin vibratome sections were made and incubated in the presence of various exogenous amines and inhibitors of the catecholaminergic and serotoninergic transport systems. Experimental conditions insuring the best specificity were determined and the validity of the combined pharmacological and histochemical approach was further tested by using animals in which the cortical dopaminergic, noradrenergic or serotoninergic innervations were destroyed. Under the experimental conditions used, norepinephrine as well as alpha-methyl-norepinephrine were taken up in only noradrenergic and dopaminergic terminals. A separate visualization of the two systems was obtained by using specific uptake inhibitors. Dopamine was taken up not only in catecholaminergic but also in serotominergic terminals. The uptake of DA in serotoninergic fibers was inhibited by a specific inhibitor of the serotoninergic transport system or by the presence of serotonine in the incubating medium. The signification and the implications of thes results are discussed.