Estrogen stimulates brain-derived neurotrophic factor expression in embryonic mouse midbrain neurons through a membrane-mediated and calcium-dependent mechanism

We have provided evidence that 17 beta -estradiol (E) synthesized in the mi dbrain promotes the differentiation of midbrain dopamine neurons through no nclassical steroid action. Because these developmental effects resemble tho se reported for brain-derived neurotrophic factor (BDNF), we hypothesized t hat E influences dopaminergic cell differentiation through a BDNF-dependent mechanism. Competitive RT-PCR and ELISA techniques were employed to study first the developmental pattern of BDNF and trkB expression in the mouse mi dbrain. BDNF protein/mRNA levels peaked postnatally, whereas trkB did not f luctuate perinatally. To prove the hypothesis that E regulates BDNF express ion in vivo, fetuses and newborns were treated with the aromatase antagonis t CGS 16949A. CGS 16949A exposure reduced midbrain BDNF mRNA/protein levels . The coapplication of CGS 16949A and E abolished this effect. Midbrain cul tures from mouse fetuses were used to investigate intracellular signaling m echanisms involved in transmitting E effects. Estrogen increased expression of BDNF but not of other neurotrophins. As concerns the related signaling mechanism, these effects were antagonized by interrupting intracellular Ca2 + signaling with BAPTA and thapsigargin but not by the estrogen receptor an tagonist ICI 182,780. Insofar as E effects on BDNF mRNA expression were inh ibited by cycloheximide, it appears likely that other, not yet characterize d intermediate proteins take part in the estrogenic regulation of BDNF expr ession. We conclude that E exerts its stimulatory effect on the differentia tion of dopaminergic neurons by coordinating BDNF expression. This particul ar E effect appears to be transmitted through Ca2+-dependent signaling casc ades upon activation of putative membrane estrogen receptors. (C) 2001 Wile y-Liss, Inc.