Estradiol-Mediated Axogenesis of Hypothalamic Neurons Requires ERK1/2 and Ryanodine Receptors-Dependent Intracellular Ca Rise in Male Rats.

17β-estradiol (E2) induces axonal growth through extracellular signal-regulated kinase 1 and 2 (ERK1/2)-MAPK cascade in hypothalamic neurons of male rat embryos , but the mechanism that initiates these events is poorly understood. This study reports the intracellular Ca increase that participates in the activation of ERK1/2 and axogenesis induced by E2. Hypothalamic neuron cultures were established from 16-day-old male rat embryos and fed with astroglia-conditioned media for 48 h. E2-induced ERK phosphorylation was completely abolished by a ryanodine receptor (RyR) inhibitor (ryanodine) and partially attenuated by an L-type voltage-gated Ca channel (L-VGCC) blocker (nifedipine), an inositol-1,4,5-trisphosphate receptor (IPR) inhibitor (2-APB), and a phospholipase C (PLC) inhibitor (U-73122). We also conducted Ca imaging recording using primary cultured neurons. The results show that E2 rapidly induces an increase in cytosolic Ca, which often occurs in repetitive Ca oscillations. This response was not observed in the absence of extracellular Ca or with inhibitory ryanodine and was markedly reduced by nifedipine. E2-induced axonal growth was completely inhibited by ryanodine. In summary, the results suggest that Ca mobilization from extracellular space as well as from the endoplasmic reticulum is necessary for E2-induced ERK1/2 activation and axogenesis. Understanding the mechanisms of brain estrogenic actions might contribute to develop novel estrogen-based therapies for neurodegenerative diseases.