Fluorescence histochemical observations on the distribution of exogenous dihydroisoquinoline in the rat brain

The distribution of fluorescence in the rat brain after i.p. or intracerebral (i.c.) injections of a fluorescent dihydroisoquinoline derivate of dopamine was studied. After low i.p. doses (50 mg/kg of body weight) the fluorescence was totally confined to the capillary endothelial cells in the cerebral cortex, neostriatum, and substantia nigra (Sn). After large i.p. doses (500 mg/kg) fluorescent material was also present in the neuropil of all the regions studied and some cells of the cerebral cortex and SN. Ater injections to the neostriatum or SN fluorescence was observed in the endothelial cells and some small to medium-sized rounded cells in both regions. A conspicious dark area contrasting with the background fluorescence was constantly present around capillaries, and this area was in contact with nonfluorescent multibranched cells of astrocytic type. In fluorescent cells the fluorescence was present both in the cytoplasm and the nucleus.