Identification of L‐DOPA‐dopamine and L‐DOPA cell bodies in the rat mesencephalic dopaminergic cell systems

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Abstract
An immunocytochemical technique for simultaneously visualizing two different antigens, dihydroxyphenylalanine (L‐DOPA) and dopamine (DA), has been used to investigate the presence of cell bodies containing both compounds L‐DOPA and DA and those having only L‐DOPA in rat mesencephalon areas. The brain slices were processed with a double peroxidase‐antiperoxidase method using simultaneously an incubation of a rabbit anti‐L‐DOPA serum and a monoclonal anti‐DA antibody raised in mouse. Both antigens were revealed by the peroxidase reaction but with different chromogens that are easily distinguishable. In this staining procedure, the first antigen, conjugated DA was stained using the 3,3′‐diaminobenzidine (DAB)‐Nickel complex; while the second antigen, conjugated L‐DOPA, was localized using DAB. The yellow‐brown color due to DAB was masked by that of DAB‐nickel. The possible existence of both single and double labelings could be worked. We have found many L‐DOPA‐positive/DA‐positive and a few L‐DOPA‐positive/DA‐negative cell bodies in dopaminergic regions in the rat midbrain: substantia nigra, ventral tegmental area, and raphe nuclei. In the locus coeruleus, we noted only L‐DOPA‐positive/DA‐positive cell bodies. These results confirm those previously described for rat and cat hypothalamus, where both immunoreactive‐cell body types have been detected: L‐DOPA positive/DA positive and L‐DOPA positive/DA negative. The existence of neuronal cells containing only L‐DOPA is a new neuroanatomic finding, accounting better for the heterogeneity of dopamine systems with respect to physiologic, pharmacologic, and molecular data.