Simultaneous ultrastructural localization of cholecystokinin- and tyrosine hydroxylase-like immunoreactivity in nerve fibers of the rat nucleus accumbens.

Ultrathin frozen sections were used to study the localization of cholecystokinin (CCK) in dopaminergic systems in the rat nucleus accumbens. Antibodies against CCK and tyrosine hydroxylase (TH), a synthetic enzyme of dopamine, were differentially visualized using protein A conjugated to colloidal gold particles of different sizes. Nerve processes were observed to be immunocytochemically labelled for either CCK or TH but also in some cases for both CCK and TH. CCK-like immunoreactivity was localized in vesicles with a diameter of 70-160 nm, whereas TH-like immunoreactivity was primarily localized in the axoplasm. Most of the double-labelled nerve processes did not show pre- or postsynaptic specializations and most likely represent preterminal elements.