Striatal cells containing aromatic l-amino acid decarboxylase: an immunohistochemical comparison with other classes of striatal neurons

Abstract

In a previous study, we described a population of striatal cells in the rat brain containing aromatic l-amino acid decarboxylase, the enzyme involved in the conversion of l-DOPA into dopamine. We have also presented evidence that these cells produce dopamine in the presence of exogenous l-DOPA. In this paper, we further characterize these striatal aromatic l-amino acid decarboxylase-containing cells in order to determine whether they form a subclass of one of the known categories of striatal neurons or if they represent a novel cell type. Using immunohistochemical methods, we compared the morphology and distribution of the aromatic l-amino acid decarboxylase-immunolabeled cells with those of other classes of striatal neurons. Our results show that both the morphology and distribution of aromatic l-amino acid decarboxylase-immunolabeled cells are very distinctive and do not resemble those of cells labeled for other striatal neuronal markers. Double-labeling procedures revealed that aromatic l-amino acid decarboxylase cells do not co-localize somatostatin or parvalbumin, and only a very small percentage of them co-localize calretinin. However, the population of aromatic l-amino acid decarboxylase cells label intensely for GABA. Overall, our results suggest that these aromatic l-amino acid decarboxylase-containing cells represent a class of striatal GABAergic neurons not described previously.