Estrogen receptor α and ß are involved in the activation of lordosis behavior in estradiol-primed rats.

The present study was designed to assess the participation of estrogen receptors alpha (ERα) and beta (ERß) in the short-term facilitation of lordosis behavior in ovariectomized (ovx), estradiol (E2) primed rats. In experiment 1, dose response curves for PPT and DPN (ERα and ERß agonists, respectively) facilitation of lordosis behavior (lordosis quotient and lordosis score) were established by infusing these agonists into the right lateral ventricle (icv) in female rats injected 40h previously with 5µg of E2 benzoate. PPT doses of 0.08 and 0.4ng produced high lordosis quotients starting at 30min and continuing at 120 and 240min post-injection. DPN induced high levels of lordosis behavior at all times tested. However, the intensity of lordosis induced by both agonists was weak. In experiment 2, we tested the involvement of each ER in facilitation of lordosis by icv infusion of MPP (ERα-selective antagonist) or PHTPP (ERß-selective antagonist) prior to infusion of 2ng of free E2. Icv infusion of either MPP or PHTPP 30min before free E2 significantly depressed E2 facilitation of lordosis. The results suggest that both forms of ER are involved in the short-latency facilitation of lordosis behavior in E2-primed rats.

Survivin Is a transcriptional target of STAT3 critical to estradiol neuroprotection in global ischemia.

Transient global ischemia causes selective, delayed death of hippocampal CA1 pyramidal neurons in humans and animals. It is well established that estrogens ameliorate neuronal death in animal models of focal and global ischemia. However, the role of signal transducer and activator of transcription-3 (STAT3) and its target genes in estradiol neuroprotection in global ischemia remains unclear. Here we show that a single intracerebral injection of 17ß-estradiol to ovariectomized female rats immediately after ischemia rescues CA1 neurons destined to die. Ischemia promotes activation of STAT3 signaling, association of STAT3 with the promoters of target genes, and STAT3-dependent mRNA and protein expression of prosurvival proteins in the selectively vulnerable CA1. In animals subjected to ischemia, acute postischemic estradiol further enhances activation and nuclear translocation of STAT3 and STAT3-dependent transcription of target genes. Importantly, we show that STAT3 is critical to estradiol neuroprotection, as evidenced by the ability of STAT3 inhibitor peptide and STAT3 shRNA delivered directly into the CA1 of living animals to abolish neuroprotection. In addition, we identify survivin, a member of the inhibitor-of-apoptosis family of proteins and known gene target of STAT3, as essential to estradiol neuroprotection, as evidenced by the ability of shRNA to survivin to reverse neuroprotection. These findings indicate that ischemia and estradiol act synergistically to promote activation of STAT3 and STAT3-dependent transcription of survivin in insulted CA1 neurons and identify STAT3 and survivin as potentially important therapeutic targets in an in vivo model of global ischemia.

Neuroprotective actions of estradiol and novel estrogen analogs in ischemia: translational implications.

This review highlights our investigations into the neuroprotective efficacy of estradiol and other estrogenic agents in a clinically relevant animal model of transient global ischemia, which causes selective, delayed death of hippocampal CA1 neurons and associated cognitive deficits. We find that estradiol rescues a significant number of CA1 pyramidal neurons that would otherwise die in response to global ischemia, and this is true when hormone is provided as a long-term pretreatment at physiological doses or as an acute treatment at the time of reperfusion. In addition to enhancing neuronal survival, both forms of estradiol treatment induce measurable cognitive benefit in young animals. Moreover, estradiol and estrogen analogs that do not bind classical nuclear estrogen receptors retain their neuroprotective efficacy in middle-aged females deprived of ovarian hormones for a prolonged duration (8weeks). Thus, non-feminizing estrogens may represent a new therapeutic approach for treating the neuronal damage associated with global ischemia.

Src kinase signaling mediates estrous behavior induced by 5ß-reduced progestins, GnRH, prostaglandin E2 and vaginocervical stimulation in estrogen-primed rats.

The progesterone receptor (PR) is a dual function protein that acts in the nucleus as a transcriptional factor and at the cytoplasm as a scaffold for the Src-MAPK signaling pathway. Several agents lacking affinity for the PR, such as 5ß-reduced progestins, GnRH or prostaglandin E(2) (PGE(2)) facilitate estrous behavior in ovariectomized (ovx), estrogen-primed rats yet their action is blocked by the antiprogestin RU486. We hypothesize that these agents act by using the PR-Src-mitogen activated protein kinase alternative pathway. To test this hypothesis we used PP2, a specific inhibitor of the Src kinase family. Intraventricular infusion of 30 µg of PP2, 30 min before behavioral testing, significantly attenuated estrous behaviors induced in estradiol benzoate (E(2)B)-primed rats by 5ß-dihydroprogesterone (5ß-DHP), 5ß-pregnan-3ß-ol-20-one (5ß,3ß-Pgl), GnRH, PGE(2) and by manual flank/vaginocervical stimulation. These results suggest that the Src signaling system, by activating mitogen-activated protein kinases, participates in the facilitation of estrous behavior in E(2)B-primed rats induced by agents lacking affinity for the PR.

Neuroprotection and estrogen receptors.

This review is intended to assess the state of current knowledge on the role of estrogen receptors (ERs) in the neuroprotective effects of estrogens in models for acute neuronal injury and death. We evaluate the overall evidence that estrogens are neuroprotective in acute injury and critically assess the role of ERα, ERß, GPR 30, and nonreceptor-mediated mechanisms in these robust neuroprotective effects of this ovarian steroid hormone. We conclude that all three receptors, as well as nonreceptor-mediated mechanisms can be involved in neuroprotection, depending on the model used, the level of estrogen administrated, and the mode of administration of the steroid. Also, the signaling pathways used by both ER-dependent and ER-independent mechanisms to exert neuroprotection are considered. Finally, further studies that are needed to parse out the relative contribution of receptor versus nonreceptor-mediated signaling are discussed.

Critical role of STAT3 in leptin's metabolic actions.

Leptin has pleiotropic effects on glucose homeostasis and feeding behavior. Here, we validate the use of a cell-permeable phosphopeptide that blocks STAT3 activation in vivo. The combination of this biochemical approach with stereotaxic surgical techniques allowed us to pinpoint the contribution of hypothalamic STAT3 to the acute effects of leptin on food intake and glucose homeostasis. Leptin's ability to acutely reduce food intake critically depends on intact STAT3 signaling. Likewise, hypothalamic signaling of leptin through STAT3 is required for the acute effects of leptin on liver glucose fluxes. Lifelong obliteration of STAT3 signaling via the leptin receptor in mice (s/s mice) results in severe hepatic insulin resistance that is comparable to that observed in db/db mice, devoid of leptin receptor signaling. Our results demonstrate that the activation of the hypothalamic STAT3 pathway is an absolute requirement for the effects of leptin on food intake and hepatic glucose metabolism.

Estradiol modulation of phenylephrine-induced excitatory responses in ventromedial hypothalamic neurons of female rats.

Estrogens act within the ventromedial nucleus of the hypothalamus (VMN) to facilitate lordosis behavior. Estradiol treatment in vivo induces alpha(1b)-adrenoreceptor mRNA and increases the density of alpha(1B)-adrenoreceptor binding in the hypothalamus. Activation of hypothalamic alpha(1)-adrenoceptors also facilitates estrogen-dependent lordosis. To investigate the cellular mechanisms of adrenergic effects on VMN neurons, whole-cell patch-clamp recordings were carried out on hypothalamic slices from control and estradiol-treated female rats. In control slices, bath application of the alpha(1)-agonist phenylephrine (PHE; 10 microM) depolarized 10 of 25 neurons (40%), hyperpolarized three neurons (12%), and had no effect on 12 neurons (48%). The depolarization was associated with decreased membrane conductance, and this current had a reversal potential close to the K(+) equilibrium potential. The alpha(1b)-receptor antagonist chloroethylclonidine (10 microM) blocked the depolarization produced by PHE in all cells. From estradiol-treated rats, significantly more neurons in slices depolarized (71%) and fewer neurons showed no response (17%) to PHE. PHE-induced depolarizations were significantly attenuated with 4-aminopyridine (5 mM) but unaffected by tetraethylammonium chloride (20 mM) or blockers of Na(+) and Ca(2+) channels. These data indicate that alpha(1)-adrenoceptors depolarize VMN neurons by reducing membrane conductance for K(+). Estradiol amplifies alpha(1b)-adrenergic signaling by increasing the proportion of VMN neurons that respond to stimulation of alpha(1b)-adrenergic receptors, which is expected in turn to promote lordosis.

A role for Src kinase in progestin facilitation of estrous behavior in estradiol-primed female rats.

This study tested the hypothesis that the Src/Raf/MAPK signaling pathway is involved in the facilitation of the lordosis and proceptive behaviors induced by progesterone (P) and its ring A-reduced metabolites in ovariectomized, estradiol-primed rats. Intraventricular (icv) infusion of PP2 (7.5, 15 and 30 microg), a Src kinase inhibitor, significantly depressed P-dependent estrous behavior (lordosis and proceptivity) in estradiol-primed rats. Icv infusion of 30 microg of PP2 also significantly attenuated estrous behavior induced by the ring A-reduced P metabolites 5 alpha-dihydroprogesterone (5 alpha-DHP) and 5 alpha-pregnan-3alpha-ol-20-one (allopregnanolone). PP2 did not inhibit estrous behavior induced by administration of high doses of estradiol alone to ovariectomized rats. We also assessed if the ventromedial hypothalamus (VMH) is one of the neural sites at which progestins activate Src signaling to facilitate estrous behavior. Bilateral administration of 15 microg of PP2 into the VMH inhibited the stimulation of both lordosis and proceptive behaviors elicited by subcutaneous P administration to estradiol-primed rats. These results suggest that progestins act through Src/Raf/MAPK signaling to initiate estrous behaviors in estrogen-primed rats. This event is one component of the cellular pathways leading to the display of estrous behaviors induced by P and its ring A-reduced metabolites in female rats.

Developing and communicating responsible data management policies to trainees and colleagues.

The basic components of data management including data ownership, collection, selection, recording, analysis, storage, retention, destruction, and sharing. A number of important principles underlie best practices for each of these components; these include recording details such that another can repeat the experiment, keeping the data safe, managing storage in such a way as to facilitate easy retrieval for the period of time required by regulatory agencies and establishing data sharing principles with colleagues before collaborations begin. Experience as practicing scientists and teachers has aided in developing helpful strategies and approaches for communicating these principles, policies and practices to trainees and colleagues. We recommend didactic instruction focused by discipline, combined with the use of "teachable moments" in a student's career, as well as teaching principles versus rules, because changing methods of data collection and storage have implications for data management practices.

Estradiol rescues neurons from global ischemia-induced cell death: multiple cellular pathways of neuroprotection.

The potential neuroprotective role of sex hormones in chronic neurodegenerative disorders and acute brain ischemia following cardiac arrest and stroke is of a great therapeutic interest. Long-term pretreatment with estradiol and other estrogens affords robust neuroprotection in male and female rodents subjected to focal and global ischemia. However, the receptors (e.g., cell surface or nuclear), intracellular signaling pathways and networks of estrogen-regulated genes that intervene in neuronal apoptosis are as yet unclear. We have shown that estradiol administered at physiological levels for two weeks before ischemia rescues neurons destined to die in the hippocampal CA1 and ameliorates ischemia-induced cognitive deficits in ovariectomized female rats. This regimen of estradiol treatment involves classical intracellular estrogen receptors, transactivation of IGF-1 receptors and stimulation of the ERK/MAPK signaling pathway, which in turn maintains CREB activity in the ischemic CA1. We also find that a single, acute injection of estradiol administrated into the brain ventricle immediately after an ischemic event reduces both neuronal death and cognitive deficits. Because these findings suggest that hormones could be used to treat patients when given after brain ischemia, it is critical to determine whether the same or different pathways mediate this form of neuroprotection. We find that an agonist of the membrane estrogen receptor GPR30 mimics short latency estradiol facilitation of synaptic transmission in the hippocampus. Therefore, we are testing the hypothesis that GPR30 may act together with intracellular estrogen receptors to activate cell signaling pathways to promote neuron survival after global ischemia.

Nitric oxide and ERK/MAPK mediation of estrous behavior induced by GnRH, PGE2 and db-cAMP in rats.

We tested the hypothesis that GnRH, PGE2 and db-cAMP act via the nitric oxide (NO)-cGMP and MAPK pathways to facilitate estrous behavior (lordosis and proceptivity) in estradiol-primed female rats. Estradiol-primed rats received intracerebroventricular (icv) infusions of pharmacological antagonists of NO synthase (L-NAME), NO-dependent soluble guanylyl cyclase (ODQ), protein kinase G (KT5823), or the ERK1/2 inhibitor PD98059 15 min before icv administration of 50 ng of GnRH, 1 microg of PGE2 or 1 microg of db-cAMP. Icv infusions of GnRH, PGE2 and db-cAMP enhanced estrous behavior at 1 and 2 h after drug administration. Both L-NAME and ODQ blocked the estrous behavior induced by GnRH, PGE2 and db-cAMP at some of the times tested. The protein kinase G inhibitor KT5823 reduced PGE2 and db-cAMP facilitation of estrous behavior but did not affect the behavioral response to GnRH. In contrast, PD98059 blocked the estrous behavior induced by all three compounds. These data support the hypothesis that the NO-cGMP and ERK/MAPK pathways are involved in the lordosis and proceptive behaviors induced by GnRH, PGE2 and db-cAMP. However, cGMP mediation of GnRH-facilitated estrous behavior is independent of protein kinase G.

Protein kinase inhibitors infused intraventricularly or into the ventromedial hypothalamus block short latency facilitation of lordosis by oestradiol.

An injection of unesterified oestradiol (E2 ) facilitates receptive behaviour in E2 benzoate (EB)-primed, ovariectomised female rats when it is administered i.c.v. or systemically. The present study tested the hypothesis that inhibitors of protein kinase A (PKA), protein kinase G (PKG) or the Src/mitogen-activated protein kinase (MAPK) complex interfere with E2 facilitation of receptive behaviour. In Experiment 1, lordosis induced by i.c.v. infusion of E2 was significantly reduced by i.c.v. administration of Rp-cAMPS, a PKA inhibitor, KT5823, a PKG inhibitor, and PP2 and PD98059, Src and MAPK inhibitors, respectively, between 30 and 240 minutes after infusion. In Experiment 2, we determined whether the ventromedial hypothalamus (VMH) is one of the neural sites at which those intracellular pathways participate in lordosis behaviour induced by E2 . Administration of each of the four protein kinase inhibitors into the VMH blocked facilitation of lordosis induced by infusion of E2 also into the VMH. These data support the hypothesis that activation of several protein kinase pathways is involved in the facilitation of lordosis by E2 in EB-primed rats.

GnRH mediates estrous behavior induced by ring A reduced progestins and vaginocervical stimulation.

The present study was designed to assess the participation of gonadotropin-releasing hormone (GnRH) in the display of estrous behavior induced by application of vaginal-cervical stimulation (VCS) and by the intracerebroventricular (icv) administration of progesterone and its ring A-reduced metabolites to ovariectomized (ovx), estradiol benzoate (E2B) primed rats. Icv injection of Antide, a GnRH-1 receptor antagonist, significantly depressed lordosis behavior in ovx, E2B-primed rats treated with icv GnRH. Application of VCS to ovx, E2B-primed rats facilitated both lordosis and proceptivity. These behavioral responses were significantly depressed by the icv administration of Antide. Similarly, icv Antide blocked the stimulatory effect on both lordosis and proceptive behaviors elicited by progesterone and its ring A-reduced metabolites: 5alpha-pregnandione (5alpha-DHP), 5alpha-pregnan-3alpha-ol-20-one (5alpha,3alpha-Pgl) and 5beta-pregnan-3beta-hydroxy-20-one (5beta,3beta-Pgl) in ovx, E2B-primed rats. By contrast, icv injection of Antide failed to interfere with the facilitatory effect of the synthetic progestin megestrol acetate on lordosis and proceptive behaviors. This progestin is not reduced in ring A. The results suggest that GnRH release is an important process in the chain of events leading to the display of estrous behavior in response to progesterone, its ring A-reduced metabolites, and VCS in female rats.

MAPK signaling is critical to estradiol protection of CA1 neurons in global ischemia.

The importance of hormone therapy in affording protection against the sequelae of global ischemia in postmenopausal women remains controversial. Global ischemia arising during cardiac arrest or cardiac surgery causes highly selective, delayed death of hippocampal CA1 neurons. Exogenous estradiol ameliorates global ischemia-induced neuronal death and cognitive impairment in male and female rodents. However, the molecular mechanisms by which estrogens intervene in global ischemia-induced apoptotic cell death are unclear. Here we show that estradiol acts via the classical estrogen receptors, the IGF-I receptor, and the ERK/MAPK signaling cascade to protect CA1 neurons in ovariectomized female rats and gerbils. We demonstrate that global ischemia promotes early dephosphorylation and inactivation of ERK1 and the transcription factor cAMP-response element binding protein (CREB), subsequent down-regulation of the antiapoptotic protein Bcl-2, a known gene target of estradiol and CREB, and activation of caspase-3. Estradiol treatment increases basal phosphorylation of both ERK1 and ERK2 in hippocampal CA1 and prevents ischemia-induced dephosphorylation and inactivation of ERK1 and CREB, down-regulation of Bcl-2 and activation of the caspase death cascade. Whereas ERK/MAPK signaling is critical to CREB activation and neuronal survival, the impact of estradiol on Bcl-2 levels is ERK independent. These findings support a model whereby estradiol acts via the classical estrogen receptors and IGF-I receptors, which converge on activation of ERK/MAPK signaling and CREB to promote neuronal survival in the face of global ischemia.

Facilitation of estrous behavior by vaginal cervical stimulation in female rats involves alpha1-adrenergic receptor activation of the nitric oxide pathway.

In estrogen-primed female rats, vaginal cervical stimulation (VCS) provided by male intromissions or by an experimenter enhances estrous behaviors exhibited by females during subsequent mating with a male. We tested the hypothesis that alpha(1)-adrenergic receptors, acting via the nitric oxide-cGMP-protein kinase G pathway, mediate VCS-induced facilitation of female reproductive behaviors. Ovariectomized, estradiol-primed rats received intracerebroventricular (icv) infusions of vehicle or pharmacological antagonists 15 or 60min before VCS. Estrous behaviors (lordosis and proceptivity) in the presence of a male were recorded immediately (0min), and 120min following VCS. First we verified that VCS, but not manual flank stimulation alone, enhanced estrous behaviors when females received icv infusion of the vehicles used to administer drugs. Increased estrous behavior was apparent immediately following VCS and persisted for 120min. We then infused prazosin, phenoxybenzamine (alpha(1)-adrenergic receptor antagonists), yohimbine, idaxozan (alpha(2)-adrenergic receptor antagonists), or propranolol (beta-adrenergic receptor antagonist) 15min prior to the application of VCS in females primed with 5mug estradiol benzoate. Only alpha(1)-adrenergic antagonists inhibited VCS facilitation of estrous behavior, apparent 120min after VCS. Finally, we administered specific inhibitors of soluble guanylyl cyclase, nitric oxide synthase or protein kinase G icv 15 or 60min before VCS. All three agents significantly attenuated VCS facilitation of estrous behavior. These data support the hypothesis that endogenously released norepinephrine, acting via alpha(1)-adrenergic receptors, mediates the facilitation of lordosis by VCS, and are consistent with a mechanism involving alpha(1)-adrenergic activation of the nitric oxide/cGMP/protein kinase G pathway.

Long-term behavioral consequences of brief, repeated neonatal isolation.

Rats subjected to stressful stimuli during the stress hyporesponsive period exhibit varied neuroendocrine and behavioral changes as neonates, adolescents and adults. The current work examined the effects of neonatal isolation stress, using a within-litter design, on adult anxiety-related behavior and endocrine stress reactivity. Neonatal rats were isolated daily for 1 h from postnatal day (P) 4 to 9, a manipulation previously shown to induce hypothalamic-pituitary-adrenal (HPA) responses on P9 (Knuth, E.D., Etgen, A.M. (2005) Corticosterone secretion induced by chronic isolation in neonatal rats is sexually dimorphic and accompanied by elevated ACTH. Horm Behav 47:65-75.). Control animals were either handled briefly or left undisturbed (with-dam). Adult rats were tested for anxiety-related behavior using the elevated plus maze and open field, and for endocrine responses following restraint stress. Neonatal isolation decreased center exploration of the open field following 1 h restraint, including decreased time in the center compared to with-dam or handled controls and decreased center entries and distance traveled in the center compared to with-dam controls. It also decreased time in and entries into the open arms of the elevated plus maze compared to handled controls, suggesting enhanced anxiety-related behavior. Neonatal isolation had no effect on basal or restraint-induced levels of ACTH or corticosterone. These findings indicate that neonatal isolation may enhance anxiety-related behaviors, especially in response to stress, without altering HPA function.

Failure of estradiol to ameliorate global ischemia-induced CA1 sector injury in middle-aged female gerbils.

Global forebrain ischemia arising from brief occlusion of the carotid arteries in gerbils produces selective hippocampal CA1 neuronal loss. Pre-treatment with 17beta-estradiol ameliorates, in part, ischemia-induced damage in young animals. Because stroke and cardiac arrest are more likely to occur among elderly individuals, neuroprotective studies in older animals have compelling clinical relevance. We investigated whether estradiol would attenuate ischemia-induced hippocampal neuronal injury in middle-aged (12-14 months) male, intact female, ovariectomized (OVX) female and OVX females treated for 14 days with estradiol. Core temperature telemetry probes were also implanted at the time that estradiol was initiated. Ischemia was induced by bilateral occlusion of the common carotid arteries (5 min), during which time skull temperature was maintained under normothermic conditions. Estradiol blocked the modest spontaneous hyperthermia that normally follows ischemia. However, all four groups exhibited substantial neuronal cell loss in the CA1, assessed at 7 after ischemia. These findings indicate that estradiol pre-treatment under conditions that produce neuroprotection in young animals does not protect against ischemia-induced CA1 cell loss in middle-aged female gerbils.

Effects of estradiol on cognition and hippocampal pathology after lateral fluid percussion brain injury in female rats.

Studies involving animal models of acute central nervous system (CNS) stroke and trauma strongly indicate that sex and/or hormonal status are important determinants of outcome after brain injury. The present study was undertaken to examine the ability of estradiol to protect hippocampal neurons from lateral fluid percussion brain injury. Sprague-Dawley female rats (211-285 g; n = 119) were ovariectomized, and a subset (n = 66) were implanted with 17beta-estradiol pellets to provide near physiological levels of estradiol. Animals were subjected to lateral fluid percussion brain injury or sham injury 1 week later. Activation of caspase-3 (n = 26) and TUNEL staining (n = 21) were assessed at 3 and 12 h after injury, respectively, in surviving control and estradiol-treated animals. Memory retention was examined using a Morris water maze test in a separate subset of animals (n = 43) at 8 days after injury. Activated caspase-3 and TUNEL staining were observed in the dentate hilus, granule cell layer, and CA3 regions in all injured rats, indicative of selective hippocampal cell apoptosis in the acute posttraumatic period. Estradiol did not significantly alter the number of hippocampal neurons exhibiting caspase-3 activity or TUNEL staining. Brain injury impaired cognitive ability, assessed at 1 week post-injury (p < 0.001). However, estradiol at physiological levels did not significantly alter injury-induced loss of memory. These data indicate that estradiol at physiological levels does not ameliorate trauma-induced hippocampal injury or cognitive deficits in ovariectomized female rats.

Functional interactions between estrogen and insulin-like growth factor-I in the regulation of alpha 1B-adrenoceptors and female reproductive function.

The ovarian hormone estradiol (E(2)) and insulin-like growth factor-I (IGF-I) interact in the CNS to regulate neuroendocrine function and synaptic remodeling. Previously, our laboratory showed that 2 d E(2) treatment induces alpha(1B)-adrenoceptor expression and promotes IGF-I enhancement of alpha(1)-adrenoceptor potentiation of cAMP accumulation in the preoptic area (POA) and hypothalamus (HYP). This study examined the hypothesis that E(2)-dependent aspects of female reproductive function, including alpha(1B)-adrenoceptor expression and function in the POA and HYP, are mediated by brain IGF-I receptors (IGF-IRs) in female rats. Ovariohysterectomized rats were implanted with a guide cannula aimed at the third ventricle and treated in vivo with vehicle or E(2) daily for 2 d before experimentation. Intracerebroventricular infusions of JB-1, a selective IGF-IR antagonist, were administered every 12 hr beginning 1 hr before the first E(2) injection. Administration of JB-1 during E(2) priming completely blocks hormone-induced luteinizing hormone release and partially inhibits hormone-dependent reproductive behavior. Reproductive behavior is restored by intracerebroventricular infusion of 8-bromo-cGMP, the second messenger implicated in alpha(1)-adrenergic facilitation of lordosis. In addition, blockade of IGF-IRs during E(2) priming prevents E(2)-induced increases in alpha(1B)-adenoceptor binding density and abolishes acute IGF-I enhancement of NE-stimulated cAMP accumulation in HYP and POA slices. These data document the existence of a novel mechanism by which IGF-I participates in the remodeling of noradrenergic receptor signaling in the HYP and POA after E(2) treatment. These events may help coordinate the timing of ovulation with the expression of sexual receptivity.

Estrogen protects against global ischemia-induced neuronal death and prevents activation of apoptotic signaling cascades in the hippocampal CA1.

The importance of postmenopausal estrogen replacement therapy in affording protection against the selective and delayed neuronal death associated with cardiac arrest or cardiac surgery in women remains controversial. Here we report that exogenous estrogen at levels that are physiological for hormone replacement in postmenopausal women affords protection against global ischemia-induced neuronal death and prevents activation of apoptotic signaling cascades in the hippocampal CA1 of male gerbils. Global ischemia induced a marked increase in activated caspase-3 in CA1, evident at 6 hr after ischemia. Global ischemia induced a marked upregulation of the proapoptotic neurotrophin receptor p75(NTR) in CA1, evident at 48 hr. p75(NTR) expression was induced primarily in terminal deoxynucleotidyl transferase-mediated UTP nick-end labeling-positive cells, indicating expression in neurons undergoing apoptosis. Global ischemia also induced a marked downregulation of mRNA encoding the AMPA receptor GluR2 subunit in CA1. Caspase-3, p75(NTR), and GluR2 were not significantly changed in CA3 and dentate gyrus, indicating that the ischemia-induced changes in gene expression were cell specific. Exogenous estrogen attenuated the ischemia-induced increases in activated caspase-3 and blocked the increase in p75(NTR) in post-ischemic CA1 neurons but did not prevent ischemia-induced downregulation of GluR2. These findings demonstrate that long-term estrogen at physiological levels ameliorates ischemia-induced hippocampal injury and indicate that estrogen intervenes at the level of apoptotic signaling cascades to prevent onset of death in neurons otherwise "destined to die."