[Evidence for the existence of L-dopa-immunoreactive neurons in the human mesencephalic region]

The existence of L-3,4-dihydroxyphenylalanine (L-DOPA) immunoreactivity is demonstrated for the first time in some neurons in the human mesencephalic region, using an immunohistochemical method with a newly raised, highly specific anti-L-DOPA antiserum. In this study, we have found many L-DOPA-positive/dopamine (DA)-positive neurons. On the other hand, we observed a few L-DOPA-positive/DA-negative cell bodies in the dopaminergic regions in the midbrain. The present results suggest the possibility of the existence of more than one neuronal group in the human mesencephalic ventral tegmental area region. L-DOPA in one group is an intermediate metabolite for decarboxylation to DA and in another group may exist as an end-product. L-DOPA in the latter group could be a neuromodulator and/or neurotransmitter. Thus, we suggest that L-DOPA plays an important role besides being an intermediate of DA in the human mesencephalon.