Rapid signaling of estrogen in hypothalamic neurons involves a novel G-protein-coupled estrogen receptor that activates protein kinase C

The membrane actions of estrogens can potentiate their lordosis behavior-facilitating genomic actions

The membrane actions of estrogens can facilitate their genomic actions. To determine whether this facilitation bears on CNS mechanisms for estrogen-dependent behaviors, ovariectomized rats were subjected to a two-pulse treatment of estrogen directly in the hypothalamic ventromedial nucleus. Two days later, each rat was given progesterone and then tested for lordosis behavior, the induction of which requires the genomic actions of estrogen. When estrogen was given in both pulses (15 min to 2 h duration, and 5 h apart) lordosis was induced. Based on results from studies on neuroblastoma cells, we hypothesized that the membrane actions of estrogen in the first pulse would potentiate the genomic actions of estrogen in the second. This hypothesis was confirmed with the use of a membrane-impermeable estrogen. However, surprisingly, the order of the pulses could be reversed and still achieve lordosis behavior induction. Finally, activators of protein kinase A or PKC were effective substitutes for the membrane-limited pulse of estrogen. Thus, estrogen-induced membrane actions in the hypothalamus can potentiate its lordosis-inducing genomic actions on behavior and may be mediated by signaling pathways involving the activation of protein kinase A and PKC.

Critical in vivo roles for classical estrogen receptors in rapid estrogen actions on intracellular signaling in mouse brain

Estrogen exerts classical genomic as well as rapid nongenomic actions on neurons. The mechanisms involved in rapid estrogen signaling are poorly defined, and the roles of the classical estrogen receptors (ERs alpha and beta) are unclear. We examined here the in vivo role of classical ERs in rapid estrogen actions by evaluating the estrogen-induced effects on two major signaling pathways within the brains of alphaER-, betaER-, and double alphabetaER-knockout (ERKO) ovariectomized female mice. Estrogen significantly (P < 0.05) increased the numbers of phospho-cAMP response element binding protein (phospho-CREB)-immunoreactive cells in specific brain regions of wild-type mice in a time-dependent manner beginning within 15 min. In brain areas that express predominantly ERbeta, this response was absent in betaERKO mice, whereas brain regions that express mostly ERalpha displayed no change in alphaERKO mice. In the medial preoptic nucleus (MPN), an area that expresses both ERs, the estrogen-induced phosphorylation of CREB was normal in both alphaERKO and betaERKO mice. However, estrogen had no effect on CREB phosphorylation in the MPN, or any other brain region, in double alphabetaERKO animals. Estrogen was also found to increase MAPK phosphorylation levels in a rapid (<15 min) manner within the MPN. In contrast to CREB signaling, this effect was lost in either alphaERKO or betaERKO mice. These data show that ERalpha and ERbeta play region- and pathway-specific roles in rapid estrogen actions throughout the brain. They further indicate an indispensable role for classical ERs in rapid estrogen actions in vivo and highlight the importance of ERs in coordinating both classical and rapid actions of estrogen.

Estrogen Modulation of G-Protein-Coupled Receptor Activation of Potassium Channels in the Central Nervous System

Estrogen rapidly alters the excitability of hypothalamic neurons that are involved in regulating numerous homeostatic functions including reproduction, stress responses, feeding, and motivated behaviors. Neurosecretory neurons, such as gonadotropin-releasing hormone (GnRH) and dopamine neurons, and local circuitry neurons, such as pro-opiomelanocortin (POMC) and gamma-aminobutyric acid (GABA) neurons, are among those involved. We have identified membrane-initiated, rapid-signaling pathways through which 17beta-estradiol (E(2)) alters synaptic responses in these neurons using whole-cell patch recording in hypothalamic slices from ovariectomized female guinea pigs. E(2) rapidly uncouples micro -opioid and GABA(B) receptors from G-protein-gated inwardly rectifying K(+) (GIRK) channels in POMC and dopamine neurons as manifested by a reduction in the potency of micro -opioid and GABA(B) receptor agonists to activate these channels. These effects are mimicked by the selective E(2) receptor modulators raloxifene and 4OH-tamoxifen, the membrane impermeable E(2)-bovine serum albumin (BSA), but not by 17alpha-estradiol. Furthermore, the anti-estrogen ICI 182,780 antagonizes these rapid effects of E(2). Inhibitors of phospholipase C, protein kinase C, and protein kinase A block the actions of E(2), indicating that the E(2) receptor is G-protein-coupled to activation of this cascade. Conversely, estrogen enhances the efficacy of alpha1-adrenergic receptor agonists to inhibit apamin-sensitive small-conductance, Ca(2+)-activated K(+) (SK) currents in preoptic GABAergic neurons; it does so in both a rapid and sustained fashion. Finally, we observed a direct, steroid-induced hyperpolarization of GnRH neurons. These findings indicate that E(2) can modulate K(+) channels in hypothalamic (POMC, dopamine, GABA, GnRH) neurons that are involved in regulating numerous homeostatic functions through multiple intracellular signaling pathways.