EFFECTS OF DIBUTYRYL-CYCLIC-AMP AND RETINOIC ACID ON THE DIFFERENTIATION OF DOPAMINE NEURONS - PREVENTION OF CELL-DEATH BY DIBUTYRYL-CYCLIC-AMP

Immature neurons, including fetal and tumoral cells, are used for inve stigating neuronal differentiation in vitro. The human neuroblastoma c ell line NB69 could be induced to differentiate to dopamine or acetylc holine neurons by different compounds, including neurotrophins and act ivators of the protein kinases. In these NB69 cells dibutyryl cyclic A MP (dbcAMP) at 2 mM reduced the division rate and increased the levels of catecholamines, tyrosine hydroxylase (TH) activity, and monoamine oxidase activity. The dbcAMP also increased cell size, dendritic arbor ization, density of the sites for high-affinity dopamine uptake, and a ctivity of choline acetyltransferase, In fetal rat midbrain neurons tr eatment with dbcAMP increased the levels of dopamine and the number of TH-immunoreactive neurons in the culture. When embryonic day 14 fetal midbrain neurons, previously exposed to 1 mu M retinoic acid (a compo und that severely reduces the number of fetal midbrain dopamine neuron s), were treated with dbcAMP, the levels of dopamine and the number of TH-immunoreactive cells returned to normal levels. This suggests that dbcAMP induces the differentiation to dopamine neurons of quiescent p rogenitor or facilitates expression of the dopamine phenotype in immat ure neurons. Therefore, dbcAMP not only differentiates uncommitted imm ature dopamine neurons, but also reverses the antidopaminergic effects of retinoic acid, These properties of dbcAMP could be of therapeutic value in Parkinson's disease.