Rapid estrogen signaling in the brain

Estrogen has multiple actions in the brain to modulate homeostasis, synaptic plasticity/cognition and neuroprotection. While many of these actions undoubtedly involve mediation via the classical genomic mechanism of regulation of transcription of genes via estrogen nuclear receptors, there has been growing interest in the rapid nongenomic effects of estrogen and the role they may play in the neural actions of estrogen. In this review, we will focus on these rapid nongenomic actions of estrogen in the brain and discuss the potential physiological significance of these actions. The evidence for rapid estrogen regulation of cell signaling pathways, including calcium, ion channel and kinase signaling pathways in the brain will be reviewed, as will evidence derived from plasma-membrane impermeable estrogen-peptide conjugates in the regulation of these cell signaling pathways. Evidence supporting classical and nonclassical estrogen receptor localization to the plasma membrane of neurons will also be reviewed, including the putative new membrane estrogen G-protein-coupled receptor, GPR30. Precisely how membrane estrogen receptors couple to kinase signaling pathways is unclear, but we will discuss the latest findings on estrogen receptor-interacting scaffold proteins, such as MNAR/PELP1, striatin and p130Cas, which are capable of linking estrogen receptors and kinases such as Src and PI3K, to potentially mediate estrogen-induced kinase signaling. Finally, we will review the growing evidence that rapid membrane-mediated effects of estrogen play an important physiological role in the neural actions of estrogen in the brain, including estrogen feedback control and modulation of homeostasis, regulation of synaptic plasticity/cognition, and estrogen-mediated neuroprotection.