Endogenous L-dopa, its immunoreactivity in neurons of midbrain and its projection fields in the cat.

L-DOPA (L-3,4-dihydroxyphenylalanine) immunoreactivity was demonstrated in neurons of the cat ventral midbrain and its projection areas, using an immunohistochemical method in conjunction with a newly developed highly specific anti-L-DOPA serum. L-DOPA-immunoreactive (IR) neurons were found in the substantia nigra, retrorubral area and ventral tegmental area of Tsai. L-DOPA-labeled fibers and terminals were hardly detectable in the nigrostriatal pathway and in the caudate nucleus which showed very intense dopamine-immunoreactivity. In contrast, many short labeled processes were detectable in the central amygdala and, although very few in number, in the entorhinal cortex.