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

Abstract 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 endproduct. 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.