The sublethal effects of high predation risk on both prey behavior and physiology may have long‐term consequences for prey population dynamics. We tested the hypothesis that snowshoe hares during the population decline are chronically stressed because of high predation risk whereas those during the population low are not, and that this has negative effects on both their physiology and demography. Snowshoe hares exhibit 10‐yr population cycles; during declines, virtually every hare that dies is killed by a predator. We assessed the physiological responsiveness of the stress axis and of energy mobilization by subjecting hares during the population decline and low to a hormonal‐challenge protocol. We monitored the population demography through live‐trapping and assessed reproduction through a maternal‐cage technique. During the 1990s' decline in the Yukon, Canada, hares were chronically stressed—as indicated by higher levels of free cortisol, reduced maximum corticosteroid‐binding capacity, reduced testosterone response, reduced index of body condition, reduced leucocyte counts, increased overwinter body‐mass loss, and increased glucose mobilization, relative to hares during the population low. This evidence is consistent with the explanation that predation risk, not high hare density or poor nutritional condition, accounted for the chronic stress and for the marked deterioration of reproduction during the decline. Reproduction and indices of stress physiology did not improve until predation risk declined. These findings may also account for the lag in recovery of hare reproduction after predator densities have declined and thus may implicate the long‐term consequences of predation risk on prey populations beyond the immediate effects of predators on prey behavior and physiology.

We showed previously in neocortical explants, derived from developing wild-type and estrogen receptor (ER)-alpha gene-disrupted (ERKO) mice, that both 17alpha- and 17beta-estradiol elicit the rapid and sustained phosphorylation and activation of the mitogen-activated protein kinase (MAPK) isoforms, the extracellular signal-regulated kinases ERK1 and ERK2. We proposed that the ER mediating activation of the MAPK cascade, a signaling pathway important for cell division, neuronal differentiation, and neuronal survival in the developing brain, is neither ER-alpha nor ER-beta but a novel, plasma membrane-associated, putative ER with unique properties. The data presented here provide further evidence that points strongly to the existence of a high-affinity, saturable, 3H-estradiol binding site (K(d), approximately 1.6 nm) in the plasma membrane. Unlike neocortical ER-alpha, which is intranuclear and developmentally regulated, and neocortical ER-beta, which is intranuclear and expressed throughout life, this functional, plasma membrane-associated ER, which we have designated "ER-X," is enriched in caveolar-like microdomains (CLMs) of postnatal, but not adult, wild-type and ERKO neocortical and uterine plasma membranes. We show further that ER-X is functionally distinct from ER-alpha and ER-beta, and that, like ER-alpha, it is re-expressed in the adult brain, after ischemic stroke injury. We also confirmed in a cell-free system that ER-alpha is an inhibitory regulator of ERK activation, as we showed previously in neocortical cultures. Association with CLM complexes positions ER-X uniquely to interact rapidly with kinases of the MAPK cascade and other signaling pathways, providing a novel mechanism for mediation of the influences of estrogen on neuronal differentiation, survival, and plasticity.

Most patients with the syndrome resistance to thyroid hormone (RTH) express a mutant thyroid hormone receptor beta (TRbeta) with transdominant negative transcriptional effects. Since no patient with a mutant TRalpha has been identified, we introduced a point mutation into the mouse thyroid hormone receptor (TRalpha1) locus originally found in the TRbeta gene, that reduces ligand binding 10-fold. Heterozygous 2- to 3-week- old mice exhibit a severe retardation of post-natal development and growth, but only a minor reduction in serum thyroxine levels. Homozygous mice died before 3 weeks of age. Adult heterozygotes overcome most of these defects except for cardiac function abnormalities, suggesting that other factors compensate for the receptor defect. However, the additional deletion of the TRbeta gene in this mouse strain caused a 10-fold increase in serum thyroxine, restored hormonal regulation of target genes for TRs, and rescued the growth retardation. The data demonstrate a novel array of effects mediated by a dominant negative TRalpha1, and may provide important clues for identification of a potentially unrecognized human disorder and its treatment.

The estrogen 17beta-estradiol has profound effects on the brain throughout life, whereas 17alpha-estradiol, the natural optical isomer, is generally considered less active because it binds less avidly to estrogen receptors. On the contrary, recent studies in the brain document that 17alpha-estradiol elicits rapid and sustained activation of the MAPK/ERK and phosphatidylinositol 3-kinase-Akt signaling pathways; is neuroprotective, after an ischemic stroke and oxidative stress, and in transgenic mice with Alzheimer's disease; and influences spatial memory and hippocampal-dependent synaptic plasticity. The present study measured the endogenous content of 17alpha-estradiol in the brain and further clarified its actions and kinetics. Here we report that: 1) endogenous levels of 17alpha-estradiol and its precursor estrone are significantly elevated in the postnatal and adult mouse brain and adrenal gland of both sexes, as determined by liquid chromatography/tandem mass spectrometry; 2) 17alpha-estradiol and 17beta-estradiol bind estrogen receptors with similar binding affinities; 3) 17alpha-estradiol transactivates an estrogen-responsive reporter gene; and 4) unlike 17beta-estradiol, 17alpha-estradiol does not bind alpha-fetoprotein or SHBG, the estrogen-binding plasma proteins of the developing rodent and primate, respectively. 17alpha-Estradiol was also found in the brains of gonadectomized or gonadectomized/adrenalectomized mice, supporting the hypothesis that 17alpha-estradiol is locally synthesized in the brain. These findings challenge the view that 17alpha-estradiol is without biological significance and suggest that 17alpha-estradiol and its selective receptor, ER-X, are not part of a classical hormone/receptor endocrine system but of a system with important autocrine/paracrine functions in the developing and adult brain. 17alpha-Estradiol may have enormous implications for hormone replacement strategies at the menopause and in the treatment of such neurodegenerative disorders as Alzheimer's disease and ischemic stroke.

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Expression of the nuclear receptor interacting factor 3 (NRIF3) coregulator in a wide variety of breast cancer cells selectively leads to rapid caspase-2–dependent apoptotic cell death. A novel death domain (DD1) was mapped to a 30– amino acid region of NRIF3. Because the cytotoxicity of NRIF3 and DD1 seems to be cell type–specific, these studies suggest that breast cancer cells contain a novel “death switch” that can be specifically modulated by NRIF3 or DD1. Using an MCF-7 cell cDNA library in a yeast two-hybrid screen, we cloned a factor that mediates apoptosis by DD1 and refer to this factor as DD1-interacting factor-1 (DIF-1). DIF-1 is a transcriptional repressor that mediates its effect through SirT1, and this repression is attenuated by the binding of NRIF3/DD1. DIF-1 expression rescues breast cancer cells from NRIF3/DD1-induced apoptosis. Small interfering RNA (siRNA) knockdown of DIF-1 selectively leads to apoptosis of breast cancer cells, further suggesting that DIF-1 plays a key role in NRIF3/DD1-mediated apoptosis. A protein kinase A inhibitor (H89) also elicits apoptosis of breast cancer cells but not of the other cell types examined, and DIF-1 also protects these cells from H89-mediated apoptosis. In addition, H89 incubation results in a rapid increase in NRIF3 levels and siRNA knockdown of NRIF3 protects breast cancer cells from H89-mediated apoptosis. Our results indicate that DIF-1 plays a key role in breast cancer cell survival and further characterizing this pathway may provide important insights into developing novel therapies to selec tively target breast cancer cells for apoptosis.

Responses of serum corticosterone (B) and corticosteroid-binding globulin (CBG) to ether anesthesia (a "classic" acute stress) and to a number of stressors influencing metabolic homeostasis--fasting, physical exercise, cold exposure, and water deprivation--were studied in male and female rats. Metabolic stressors included placing in an ice bath, physical exercise (swimming), fasting for 2 d, swimming after fasting for 2 d, cold-room (4 degrees C) exposure for 2 d, fasting in combination with cold-room exposure for 1 d, and water deprivation for 2 d. The study demonstrated clear differences between males and females in basal B levels and B responses to some stressors. Only ether anesthesia and fasting resulted in similar B levels in males and females whereas in control and all other groups serum B levels were higher in females. Serum CBG was considerably higher in females. In females, ether, swimming, swimming after fasting, fasting, and fasting during cold exposure resulted in a decrease in circulating CBG. Ice bathing and cold exposure did not influence CBG, and water deprivation elevated serum CBG. In males, animals subjected to fasting and fasting during cold exposure had CBG levels lower than control animals. Other groups did not differ from the control. Higher CBG levels in females counterbalanced higher total B in setting circulating free B: significant sex differences in free B were observed only after swimming or fasting during cold exposure. Stress-responsive changes in CBG levels seem to contribute little to changes in free B; the main contributing factor is the rise in total B. However, CBG may play a special role, independent of the functions of corticosteroids. It is proposed that the need for substantial mobilization of spare fuel (as it takes place during physical exercise or fasting) is critical in involving CBG in the stress response.

This article is available online at http://www.jlr.org surface to the circulating blood, and releases vasoactive substances involved in the regulation of vascular tone ( 1, 2 ). Besides, it selectively permits the movement of molecules into and out of the bloodstream, and this semipermeable capacity of the endothelial monolayer depends majorly on cell-to-cell connections, namely adherens junctions (AJs), tight junctions (TJs), and gap junctions ( 3, 4 ). Disruption of these junctions leads to a leaky endothelial barrier, which allows the traffi cking of leukocytes through the blood vessels into the interstitial space and initiates infl ammation ( 2, 4 ). A large body of evidence indicates that TJs of endothelium play a pivotal role in modulating its barrier permeability, and dysfunctional endothelium often manifests increased barrier permeability ( 5, 6 ). Many studies suggest that oxidative stress is one of the underlying factors in endothelial dysfunction and atherosclerosis ( 7,8 ). NADPH oxidase, a major source of reactive oxygen species (ROS) production ( 9 ), has been reported to increase EC barrier permeability ( 10, 11 ). Xanthine oxidase (XO), a purine-catabolizing enzyme, was also found as another major source of cellular ROS production ( 12 ). XO results from sulfhydryl oxidation or proteolytic conversion of xanthine dehydrogenase (XDH) ( 13,14 ). Although both XDH and XO convert hypoxanthine and xanthine to uric acid, XO preferentially converts molecular oxygen to superoxide anion and hydrogen peroxide ( 12 ). However, under the reduced state, XDH can also react with molecular oxygen and generate ROS ( 15 ). Although the physiological signifi cance of XDH conversion to XO is not clear, XO was found to be abundantly present in several tissues, including in the luminal surface of the microvascular endothelium, and is thought to be involved in the pathogenesis of various diseases such as infl ammation and Endothelium, which is constituted by a monolayer of endothelial cells (ECs), is the inner most lining of the blood vessels, provides nonplatelet adherent nonthrombotic Abstract To understand the mechanisms of 15(S)-HETEinduced endothelial cell (EC) barrier dysfunction, we examined the role of xanthine oxidase (XO). 15(S)-HETE induced