Estrogenic stimulation of neurite growth in midbrain dopaminergic neurons depends on cAMP/protein kinase A signalling

Previous work from this laboratory indicates that the differentiation of mo use midbrain dopaminergic neurons is influenced by estrogen. These effects may be transmitted either through classical nuclear receptors or via "nonge nomic" mechanisms, including the interaction with hypothetical membrane rec eptors coupled to distinct intracellular signalling pathways. The latter me chanism seems to be of particular interest for the observed interactions of estrogen with developing dopaminergic neurons, insofar as estrogen has bee n shown to increase intracellular calcium levels within seconds. This study focuses on signal transduction cascades that might be activated by estroge n during differentiation of dopaminergic cells. Treatment with 17 beta-estr adiol or a membrane-impermeable estrogen-BSA construct (E-BSA) increased ne urite growth and arborization of dopaminergic neurons. This effect was inhi bited by antagonists of cAMP/protein kinase A (PKA) and calcium signalling pathways but not by the estrogen receptor antagonist ICI. In addition, estr ogen exposure stimulated the phosphorylation of CREB in midbrain dopaminerg ic cells as studied by quantitative double-labelling immunocytochemistry an d gel shift assay. Again, this effect was antagonized only by the simultane ous treatment with inhibitors of the cAMP/PKA or calcium pathways and not b y ICI pretreatment. These data together with our previous findings demonstr ate that estrogen can interact with membrane binding sites on dopaminergic neurons, thereby stimulating the cAMP/PKA/phosphorylated cAMP-responsive el ement binding protein (CREB) signalling cascade, most likely through the ac tivation of calcium-dependent kinases. In conclusion, rapid "nongenomic" es trogen signalling represents another mechanism, in addition to the activati on of classical nuclear estrogen receptors, that is capable of influencing neuronal differentiation in the mammalian brain. (C) 2000 Wiley-Liss, Inc.