Identification of L-dopa immunoreactivity in some neurons in the human mesencephalic region: a novel dopa neuron group?

The presence of L-3,4-dihydroxyphenylalanine (L-DOPA) immunoreactivity is reported 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. We have found many L-DOPA-positive/dopamine (DA)-positive and a few L-DOPA-positive/DA-negative cell bodies in dopaminergic regions in the midbrain. The present results suggest the existence of more than one neuronal group of L-DOPA in the human mesencephalon. 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 neurons 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.