Chronic activation of the cyclic AMP signaling pathway promotes development and long-term survival of mesencephalic dopaminergic neurons.

Abstract

Dibutyryl cyclic AMP (dbcAMP), a permeant analogue of cyclic AMP (cAMP), prevented, for at least 3 weeks, the death of tyrosine hydroxylase (TH)-immunopositive dopaminergic neurons, which occurred spontaneously by apoptosis in mesencephalic cultures. Treatment with the cyclic nucleotide analogue also led to a significant increase in the uptake of [3H] dopamine, attesting that the rescued TH+ neurons were fully functional and differentiated. dbcAMP was most effective when added immediately after plating, but delayed treatment could still arrest the ongoing degenerative process. Trophic/survival effects were long-lasting, declining only progressively after withdrawal of dbcAMP from the culture medium. They were independent of cell density and still detectable in the absence of serum proteins. The effects of dbcAMP were mimicked by depolarizing concentrations of potassium and by agents that increase endogenous production of cAMP, such as forskolin or 3-isobutyl-1-methylxanthine, but not by native cAMP, which cannot cross cell membranes. Elimination of glial cells by arabinoside-C did not reduce the activity of dbcAMP. GABAergic neurons, also present in these cultures, were much less dependent on the cyclic nucleotide analogue for their survival, and serotoninergic cells were not dependent at all. Therefore, cAMP-dependent signaling may be particularly crucial for the maturation and long-term survival of mesencephalic dopaminergic neurons.