Our laboratory has recently been involved in investigating factors which influence plasticity of neurotransmitter phenotypic expression both in vivo and in culture. Our previous studies have shown that precursor neuroblasts are pluripotential with respect to neurotransmitter phenotype and respond differentially to microenvironmental signals. In the present study, we examined phenotypic expression in neuroblastoma cells, P2 clone, using the activities of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) as neuronal markers for the cholinergic and catecholaminergic phenotypes, respectively. Cells were plated and grown for 4 days in culture, harvested and frozen for assay of ChAT and TH. Basal activity of ChAT was 2.47 +/- 0.22 nmoles Ach formed /h/mg protein and that of TH was 5.23 +/- 0.41 pmoles CO2 formed /h/mg protein in control cultures. When intracellular cAMP levels were increased by addition to the growth medium of 10 micrograms/ml prostaglandin E1 (PGE1; a receptor-mediated enhancer of adenylate cyclase activity) or 200 micrograms/ml RO20-1724 (an inhibitor of cyclic nucleotide phosphodiesterase) the activity of TH was increased 340- and 423-fold, respectively. In marked contrast, the activity of ChAT was not affected by either agent. Double staining immunocytochemical examination demonstrated that both ChAT and TH were colocalized in the same cell. The molecular mechanism whereby catecholaminergic expression exclusively is affected in this cell model is currently under investigation. We conclude that (1) P2 neuroblastoma is a pluripotential cell line, (2) phenotypic expression in a homogenous cell population, such as P2 neuroblastoma, is differentially regulated. Moreover, this cell line is a unique model for studying the molecular mechanisms of phenotypic expression and neuronal plasticity.