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

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 t his paper, we further characterize these striatal aromatic L-amino acid dec arboxylase-containing cells in order to determine whether they form a subcl ass of one of the known categories of striatal neurons or if they represent a novel cell type. Using immunohistochemical methods, we compared the morp hology and distribution of the aromatic L-amino acid decarboxylase-immunola beled cells with those of other classes of striatal neurons. Our results sh ow that both the morphology and distribution of aromatic L-amino acid decar boxylase-immunolabeled cells are very distinctive and do not resemble those of cells labeled for other striatal neuronal markers. Double-labeling proc edures revealed that aromatic L-amino acid decarboxylase cells do not co-lo calize somatostatin or parvalbumin, and only a very small percentage of the m 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 descr ibed previously. (C) 2000 IBRO. Published by Elsevier Science Ltd. All righ ts reserved.