Estrogen prevents the loss of CA1 hippocampal neurons in gerbils after ischemic injury

Protection against APOE4 -associated aging phenotypes with the longevity-promoting intervention 17α-estradiol in male mice

The apolipoprotein ε4 allele ( APOE4 ) is associated with decreased longevity, increased vulnerability to age-related declines, and disorders across multiple systems. Interventions that promote healthspan and lifespan represent a promising strategy to attenuate the development of APOE4 -associated aging phenotypes. Here we studied the ability of the longevity-promoting intervention 17α-estradiol (17αE2) to protect against age-related impairments in APOE4 versus the predominant APOE3 genotype using early middle-aged mice with knock-in of human APOE alleles. Beginning at age 10 months, male APOE3 or APOE4 mice were treated for 20 weeks with 17αE2 or vehicle then compared for indices of aging phenotypes body-wide. Across peripheral and neural measures, APOE4 was associated with poorer outcomes. Notably, 17αE2 treatment improved outcomes in a genotype-dependent manner favoring APOE4 mice. These data demonstrate a positive APOE4 bias in 17αE2-mediated healthspan actions, suggesting that longevity-promoting interventions may be useful in mitigating deleterious age-related risks associated with APOE4 genotype.

The modulation of potassium channels by estrogens facilitates neuroprotection

Estrogens, the sex hormones, have the potential to govern multiple cellular functions, such as proliferation, apoptosis, differentiation, and homeostasis, and to exert numerous beneficial influences for the cardiovascular system, nervous system, and bones in genomic and/or non-genomic ways. Converging evidence indicates that estrogens serve a crucial role in counteracting neurodegeneration and ischemic injury; they are thereby being considered as a potent neuroprotectant for preventing neurological diseases such as Alzheimer's disease and stroke. The underlying mechanism of neuroprotective effects conferred by estrogens is thought to be complex and multifactorial, and it remains obscure. It is well established that the K+ channels broadly expressed in a variety of neural subtypes determine the essential physiological features of neuronal excitability, and dysfunction of these channels is closely associated with diverse brain deficits, such as ataxia and epilepsy. A growing body of evidence supports a neuroprotective role of K+ channels in malfunctions of nervous tissues, with the channels even being a therapeutic target in clinical trials. As multitarget steroid hormones, estrogens also regulate the activity of distinct K+ channels to generate varying biological actions, and accumulated data delineate that some aspects of estrogen-mediated neuroprotection may arise from the impact on multiple K+ channels, including Kv, BK, KATP, and K2P channels. The response of these K+ channels after acute or chronic exposure to estrogens may oppose pathological abnormality in nervous cells, which serves to extend our understanding of these phenomena.

Changes in Cyclin D1, cdk4, and Their Associated Molecules in Ischemic Pyramidal Neurons in Gerbil Hippocampus after Transient Ischemia and Neuroprotective Effects of Ischemic Preconditioning by Keeping the Molecules in the Ischemic Neurons

Simple Summary

Cyclin D1 and cyclin-dependent kinase 4 (cdk4) is implicated in neuronal death induced by various pathological conditions. Ischemic preconditioning (IPC) confers neuroprotective effect, but underlying mechanisms have been poorly addressed. In this study, IPC protected pyramidal neurons (cells) in gerbil hippocampus after transient ischemia. Additionally, IPC controlled expressions of cyclin D1, cdk4, phosphorylated retinoblastoma (p-Rb), and E2 promoter binding factor 1 (E2F1). In particular, the expression of p16INK4a was not different by IPC. These findings indicate that cyclin D1/cdk4-related signals may play important roles in events in neurons related to damage/death following ischemic insults. Especially, the preservation of p16INK4a by IPC may be crucial in attenuating neuronal death/damage or protecting neurons after brain ischemic insults.

Abstract

Inadequate activation of cell cycle proteins including cyclin D1 and cdk4 is involved in neuronal cell death induced by diverse pathological stresses, including transient global brain ischemia. The neuroprotective effect of ischemic preconditioning is well-established, but the underlying mechanism is still unknown. In this study, we examined changes in cyclin D1, cdk4, and related molecules in cells or neurons located in Cornu Ammonis 1 (CA1) of gerbil hippocampus after transient ischemia for 5 min (ischemia and reperfusion) and investigated the effects of IPC on these molecules after ischemia. Four groups were used in this study as follows: sham group, ischemia group, IPC plus (+) sham group, and IPC+ischemia group. IPC was developed by inducing 2-min ischemia at 24 h before 5-min ischemia (real ischemia). Most pyramidal cells located in CA1 of the ischemia group died five days after ischemia. CA1 pyramidal cells in the IPC+ischemia group were protected. In the ischemia group, the expressions of cyclin D1, cdk4, phosphorylated retinoblastoma (p-Rb), and E2F1 (a transcription factor regulated by p-Rb) were significantly altered in the pyramidal cells with time after ischemia; in the IPC+ischemia group, they were controlled at the level shown in the sham group. In particular, the expression of p16^INK4a (an endogenous cdk inhibitor) in the ischemia group was reversely altered in the pyramidal cells; in the IPC+TI group, the expression of p16^INK4a was not different from that shown in the sham group. Our current results indicate that cyclin D1/cdk4-related signals may have important roles in events in neurons related to damage/death following ischemia and reperfusion. In particular, the preservation of p16^INK4a by IPC may be crucial in attenuating neuronal death/damage or protecting neurons after brain ischemic insults.

Extending lifespan by modulating the growth hormone/insulin-like growth factor-1 axis: coming of age

Progress made in the years of aging research have allowed the opportunity to explore potential interventions to slow aging and extend healthy lifespan. Studies performed in yeast, worms, flies and mice subjected to genetic and pharmacological interventions have given insight into the cellular and molecular mechanisms associated with longevity. Furthermore, it is now possible to effectively modulate pathways that slow aging at different stages of life (early life or at an adult age). Interestingly, interventions that extend longevity in adult mice have had sex-specific success, suggesting a potential link between particular pathways that modulate aging and sex. For example, reduction of the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis at an adult age extends lifespan preferentially in females. Moreover, several postnatal dietary interventions tested by the 'Intervention Testing Program (ITP)' from the National Institute of Aging (NIA) have shown that while pharmacological interventions like rapamycin affect the IGF-1/insulin pathway and preferentially extend lifespan in females; dietary compounds that target other cellular pathways are effective only in male mice-indicating mutually exclusive sex-specific pathways. Therefore, a combination of interventions that target non-overlapping aging-related pathways appears to be an effective approach to further extend healthy lifespan in both sexes. Here, we review the germline and postnatal mouse lines that target the GH/IGF-1 axis as a mechanism to extend longevity as well as the dietary compounds that tested positive in the NIA program to increase lifespan. We believe that the interventions reviewed in this paper could constitute feasible combinations for an extended healthy lifespan in both male and female mice.

Loss of Estrogen Efficacy Against Hippocampus Damage in Long-Term OVX Mice Is Related to the Reduction of Hippocampus Local Estrogen Production and Estrogen Receptor Degradation

Postmenopausal women experience a higher risk for neurodegenerative diseases, including cognitive impairment and ischemic stroke. Many preclinical studies have indicated that estrogen replacement therapy (ERT) may provide protective effects against these neurological diseases. However, the results of Women's Health Initiative (WHI) studies have led to the proposal of "critical period hypothesis," which states that there is a precise window of opportunity for administering beneficial hormone therapy following menopause. However, the underlying molecular mechanisms require further characterization. Here, we explored the effects of ERT on cognition decline and global cerebral ischemia (GCI)-induced hippocampal neuronal damage in mice that had experienced both short-term (ovariectomized (OVX) 1 week) and long-term (OVX 10 weeks) estrogen deprivation. We also further explored the concentration of 17β-estradiol (E2) in the circulation and hippocampus and the expression of aromatase and estrogen receptors (ERα, ERα-Ser118, and ERβ). We found that the neuroprotective effectiveness of ERT against hippocampus damage exhibited in OVX1w mice was totally absent in OVX10w mice. Interestingly, the concentration of hippocampal E2 was irreversibly reduced in OVX10w mice, which was related to the decrease of aromatase expression in the hippocampus. In addition, long-term estrogen deprivation (LTED) led to a decrease in estrogen receptor proteins in the hippocampus. Thus, we concluded that the loss of ERT neuroprotection against hippocampus injury in LTED mice was related to the reduction in hippocampus E2 production and estrogen receptor degradation. These results provide several intervention targets to restore the effectiveness of ERT neuroprotection in elderly post-menopausal women.

YES-10, A Combination of Extracts from Clematis mandshurica RUPR. and Erigeron annuus (L.) PERS., Prevents Ischemic Brain Injury in A Gerbil Model of Transient Forebrain Ischemia

: Clematis mandshurica RUPR. (CMR) and Erigeron annuus (L.) PERS. (EALP) have pharmacological effects including anti-inflammatory activity and been used in traditional medicines in Asia. However, neuroprotective effects of CMR and/or EALP extracts against brain ischemic insults have never been addressed. Thus, the aim of this study was to examine neuroprotective effects of YES-10, a combination of extracts from CMR and EALP (combination ratio, 1:1), in the hippocampus following ischemia/reperfusion in gerbils. Protection of neurons was investigated by cresyl violet staining, fluoro-jade B histofluorescence staining and immunohistochemistry for neuronal nuclei. In addition, attenuation of gliosis was studied by immunohistochemistry for astrocytic and microglial markers. Treatments with 50 or 100 mg/kg YES-10 failed to protect neurons in the hippocampus after ischemia/reperfusion injury. However, administration of 200 mg/kg YES-10 protected neurons from ischemia/reperfusion injury and attenuated reactive gliosis. These findings strongly suggest that a combination of extracts from CMR and EALP can be used as a prevention approach/drug against brain ischemic damage.

Improved HCN channels in pyramidal neurons and their new expression levels in pericytes and astrocytes in the gerbil hippocampal CA1 subfield following transient ischemia

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have been known to participate in the regulation of neuronal excitability, synaptic transmission and long-term potentiation in the hippocampus. The present study investigated transient ischemia-induced changes of HCN1 and HCN2 expressions in the Cornu Ammonis 1 (CA1) subfield of the hippocampus in gerbils subjected to 5 min transient global cerebral ischemia (tgCI). Neuronal death was exhibited in pyramidal neurons of the striatum pyramidale in the CA1 subfield 4 days after tgCI. HCN1 and HCN2 immunoreactivities were demonstrated in intact CA1 pyramidal neurons, and were transiently and markedly increased in the CA pyramidal neurons at 6 h after ischemia. Thereafter, they gradually decreased in a time-dependent manner. A total of 4 days after ischemia, HCN1 and HCN2 immunoreactivities were barely detected in the CA1 pyramidal neurons; however, HCN1 and HCN2 were began to be expressed in pericytes and astrocytes at 4 days after ischemia. The results indicated that HCN1 and HCN2 expression levels were apparently changed in the gerbil hippocampal CA1 subfield following tgCI and suggested that ischemia-induced alterations in HCN1 and HCN2 expression levels may be closely associated with the death of CA1 pyramidal neurons following 5 min of tgCI.

GPER agonist G1 suppresses neuronal apoptosis mediated by endoplasmic reticulum stress after cerebral ischemia/reperfusion injury

Studies have confirmed a strong association between activation of the endoplasmic reticulum stress pathway and cerebral ischemia/reperfusion (I/R) injury. In this study, three key proteins in the endoplasmic reticulum stress pathway (glucose-regulated protein 78, caspase-12, and C/EBP homologous protein) were selected to examine the potential mechanism of endoplasmic reticulum stress in the neuroprotective effect of G protein-coupled estrogen receptor. Female Sprague-Dawley rats received ovariectomy (OVX), and then cerebral I/R rat models (OVX + I/R) were established by middle cerebral artery occlusion. Immediately after I/R, rat models were injected with 100 μg/kg E2 (OVX + I/R + E2), or 100 μg/kg G protein-coupled estrogen receptor agonist G1 (OVX + I/R + G1) in the lateral ventricle. Longa scoring was used to detect neurobehavioral changes in each group. Infarct volumes were measured by 2,3,5-triphenyltetrazolium chloride staining. Morphological changes in neurons were observed by Nissl staining. Terminal dexynucleotidyl transferase-mediated nick end-labeling staining revealed that compared with the OVX + I/R group, neurological function was remarkably improved, infarct volume was reduced, number of normal Nissl bodies was dramatically increased, and number of apoptotic neurons in the hippocampus was decreased after E2 and G1 intervention. To detect the expression and distribution of endoplasmic reticulum stress-related proteins in the endoplasmic reticulum, caspase-12 distribution and expression were detected by immunofluorescence, and mRNA and protein levels of glucose-regulated protein 78, caspase-12, and C/EBP homologous protein were determined by polymerase chain reaction and western blot assay. The results showed that compared with the OVX + I/R group, E2 and G1 treatment obviously decreased mRNA and protein expression levels of glucose-regulated protein 78, C/EBP homologous protein, and caspase-12. However, the G protein-coupled estrogen receptor antagonist G15 (OVX + I/R + E2 + G15) could eliminate the effect of E2 on cerebral I/R injury. These results confirm that E2 and G protein-coupled estrogen receptor can inhibit the expression of endoplasmic reticulum stress-related proteins and neuronal apoptosis in the hippocampus, thereby improving dysfunction caused by cerebral I/R injury. Every experimental protocol was approved by the Institutional Ethics Review Board at the First Affiliated Hospital of Shihezi University School of Medicine, China (approval No. SHZ A2017-171) on February 27, 2017.

PELP1: a key mediator of oestrogen signalling and actions in the brain

Proline-, glutamic acid- and leucine-rich protein 1 (PELP1) is an oestrogen receptor (ER) coregulator protein identified by our collaborative group. Work from our laboratory and others has shown that PELP1 is a scaffold protein that interacts with ERs and kinase signalling factors, as well as proteins involved in chromatin remodelling and DNA repair. Its role in mediating 17β-oestradiol (E₂ ) signalling and actions has been studied in detail in cancer cells, although only recently has attention turned to its role in the brain. In this review, we discuss the tissue, cellular and subcellular localisation of PELP1 in the brain. We also discuss recent evidence from PELP1 forebrain-specific knockout mice demonstrating a critical role of PELP1 in mediating both extranuclear and nuclear ER signalling in the brain, as well as E₂ -induced neuroprotection, anti-inflammatory effects and regulation of cognitive function. Finally, the PELP1 interactome and unique gene network regulated by PELP1 in the brain is discussed, especially because it provides new insights into PELP1 biology, protein interactions and mechanisms of action in the brain. As a whole, the findings discussed in the present review indicate that PELP1 functions as a critical ER coregulator in the brain to mediate E₂ signalling and actions.

Neurite outgrowth promoting effect of 17-β estradiol is mediated through estrogen receptor alpha in an olfactory epithelium culture

Olfactory deficits are observed early in the course of chronic neurological disorders including Alzheimer's disease (AD). Estrogen treatment in post-menopausal women reduced the incidence of olfactory dysfunction, raising the possibility that estrogen treatment can cure olfactory deficits in preclinical stages of AD. In this study, we examined the estradiol׳s effects on neurite outgrowth in explant cultures of mouse olfactory epithelium (OE). We found that neurons in OE cultures treated with 100 pM 17-β estradiol (estradiol) had significantly longer neurite outgrowth than cultures treated with ethanol alone (vehicle). The OE neurons expressed estrogen receptors alpha (ERα) and ER beta (ERβ). Estrogen treatment upregulated both ERα and ERβ expression in OE culture. Treatment of OE cultures with propyl pyrazole triol (PPT), a selective agonist for ERα increased neurite outgrowth to comparable extent as estradiol treatment. In contrast, 2,3-bis-4-hydroxyphenyl (DPN), a specific agonist for ERβ, had no effect on neurite outgrowth. Furthermore, estradiol treatment increased neurite outgrowth in OE cultures derived from ERβ-deficient/knockout mice and wild-type littermates, but not in ERα-deficient/knockout mice. These data suggest that ERα mediates the neurite outgrowth promoting effects of estradiol in OE cultures. We propose that olfactory dysfunction in chronic neurological disorders, where estrogen deficiency is a risk factor, is an indicator of compromised axonal regeneration of olfactory sensory neurons.

Reprint of "GPR30 mediates estrogen rapid signaling and neuroprotection"

G-protein-coupled estrogen receptor-30 (GPR30), also known as G-protein estrogen receptor-1 (GPER1), is a putative extranuclear estrogen receptor whose precise functions in the brain are poorly understood. Studies using exogenous administration of the GPR30 agonist, G1 suggests that GPR30 may have a neuroprotective role in cerebral ischemia. However, the physiological role of GPR30 in mediating estrogen (E2)-induced neuroprotection in cerebral ischemia remains unclear. Also unclear is whether GPR30 has a role in mediating rapid signaling by E2 after cerebral ischemia, which is thought to underlie its neuroprotective actions. To address these deficits in our knowledge, the current study examined the effect of antisense oligonucleotide (AS) knockdown of GPR30 in the hippocampal CA1 region upon E2-BSA-induced neuroprotection and rapid kinase signaling in a rat model of global cerebral ischemia (GCI). Immunohistochemistry demonstrated that GPR30 is strongly expressed in the hippocampal CA1 region and dentate gyrus, with less expression in the CA3 region. E2-BSA exerted robust neuroprotection of hippocampal CA1 neurons against GCI, an effect abrogated by AS knockdown of GPR30. Missense control oligonucleotides had no effect upon E2-BSA-induced neuroprotection, indicating specificity of the effect. The GPR30 agonist, G1 also exerted significant neuroprotection against GCI. E2-BSA and G1 also rapidly enhanced activation of the prosurvival kinases, Akt and ERK, while decreasing proapototic JNK activation. Importantly, AS knockdown of GPR30 markedly attenuated these rapid kinase signaling effects of E2-BSA. As a whole, the studies provide evidence of an important role of GPR30 in mediating the rapid signaling and neuroprotective actions of E2 in the hippocampus.

Brain-derived estrogen exerts anti-inflammatory and neuroprotective actions in the rat hippocampus

17β-estradiol (E2) has been implicated to play a critical role in neuroprotection, synaptic plasticity, and cognitive function. Classically, the role of gonadal-derived E2 in these events is well established, but the role of brain-derived E2 is less clear. To address this issue, we investigated the expression, localization, and modulation of aromatase and local E2 levels in the hippocampus following global cerebral ischemia (GCI) in adult ovariectomized rats. Immunohistochemistry (IHC) revealed that the hippocampal regions CA1, CA3 and dentate gyrus (DG) exhibited high levels of immunoreactive aromatase staining, with aromatase being co-localized primarily in neurons in non-ischemic animals. Following GCI, aromatase became highly expressed in GFAP-positive astrocytes in the hippocampal CA1 region at 2-3 days post GCI reperfusion. An ELISA for E2 and IHC for E2 confirmed the GCI-induced elevation of local E2 in the CA1 region and that the increase in local E2 occurred in astrocytes. Furthermore, central administration of aromatase antisense (AS) oligonucleotides, but not missense (MS) oligonucleotides, blocked the increase in aromatase and local E2 in astrocytes after GCI, and resulted in a significant increase in GCI-induced hippocampal CA1 region neuronal cell death and neuroinflammation. As a whole, these results suggest that brain-derived E2 exerts important neuroprotective and anti-inflammatory actions in the hippocampal CA1 region following GCI.

GPR30 mediates estrogen rapid signaling and neuroprotection

G-protein-coupled estrogen receptor-30 (GPR30), also known as G-protein estrogen receptor-1 (GPER1), is a putative extranuclear estrogen receptor whose precise functions in the brain are poorly understood. Studies using exogenous administration of the GPR30 agonist, G1 suggests that GPR30 may have a neuroprotective role in cerebral ischemia. However, the physiological role of GPR30 in mediating estrogen (E2)-induced neuroprotection in cerebral ischemia remains unclear. Also unclear is whether GPR30 has a role in mediating rapid signaling by E2 after cerebral ischemia, which is thought to underlie its neuroprotective actions. To address these deficits in our knowledge, the current study examined the effect of antisense oligonucleotide (AS) knockdown of GPR30 in the hippocampal CA1 region upon E2-BSA-induced neuroprotection and rapid kinase signaling in a rat model of global cerebral ischemia (GCI). Immunohistochemistry demonstrated that GPR30 is strongly expressed in the hippocampal CA1 region and dentate gyrus, with less expression in the CA3 region. E2-BSA exerted robust neuroprotection of hippocampal CA1 neurons against GCI, an effect abrogated by AS knockdown of GPR30. Missense control oligonucleotides had no effect upon E2-BSA-induced neuroprotection, indicating specificity of the effect. The GPR30 agonist, G1 also exerted significant neuroprotection against GCI. E2-BSA and G1 also rapidly enhanced activation of the prosurvival kinases, Akt and ERK, while decreasing proapototic JNK activation. Importantly, AS knockdown of GPR30 markedly attenuated these rapid kinase signaling effects of E2-BSA. As a whole, the studies provide evidence of an important role of GPR30 in mediating the rapid signaling and neuroprotective actions of E2 in the hippocampus.

Neuroprotection with non-feminizing estrogen analogues: an overlooked possible therapeutic strategy

Although many of the effects of estrogens on the brain are mediated through estrogen receptors (ERs), there is evidence that neuroprotective activity of estrogens can be mediated by non-ER mechanisms. Herein, we review the substantial evidence that estrogens neuroprotection is in large part non-ER mediated and describe in vitro and in vivo studies that support this conclusion. Also, we described our drug discovery strategy for capitalizing on enhancement in neuroprotection while at the same time, reducing ER binding of a group of synthetic non-feminizing estrogens. Finally, we offer evidence that part of the neuroprotection of these non-feminizing estrogens is due to enhancement in redox potential of the synthesized compounds.

Is basic research providing answers if adjuvant anti-estrogen treatment of breast cancer can induce cognitive impairment?

Adjuvant treatment of cancer by chemotherapy is associated with cognitive impairment in some cancer survivors. Breast cancer patients are frequently also receiving endocrine therapy with selective estrogen receptor modulators (SERMs) and/or aromatase inhibitors (AIs) to suppress the growth of estradiol sensitive breast tumors. Estrogens are well-known, however, to target brain areas involved in the regulation of cognitive behavior. In this review clinical and basic preclinical research is reviewed on the actions of estradiol, SERMs and AIs on brain and cognitive functioning to see if endocrine therapy potentially induces cognitive impairment and in that respect may contribute to the detrimental effects of chemotherapy on cognitive performance in breast cancer patients. Although many clinical studies may be underpowered to detect changes in cognitive function, current basic and clinical reports suggest that there is little evidence that AIs may have a lasting detrimental effect on cognitive performance in breast cancer patients. The clinical data on SERMs are not conclusive, but some studies do suggest that tamoxifen administration may form a risk for cognitive functioning particularly in older women. An explanation may come from basic preclinical research which indicates that tamoxifen often acts agonistic in the absence of estradiol but antagonistic in the presence of endogenous estradiol. It could be hypothesized that the negative effects of tamoxifen in older women is related to the so-called window of opportunity for estrogen. Administration of SERMs beyond this so-called window of opportunity may not be effective or might even have detrimental effects similar to estradiol.

Brain-derived neurotrophic factor Val⁶⁶Met polymorphism affects resting regional cerebral blood flow and functional connectivity differentially in women versus men

The human Val⁶⁶Met single nucleotide polymorphism in the brain-derived neurotrophic factor (BDNF) gene impacts BDNF signaling at the cellular level. At the neural-systems level, it is associated with differences in prefrontal cortex (PFC) and hippocampal function during performance of cognitive and affective tasks. Because the impact of this variant on basal prefrontal and hippocampal activity is not known but may be relevant to understanding the function of this gene in health and disease, we studied 94 healthy individuals with H₂ ¹⁵O PET to assess regional cerebral blood flow (rCBF) during rest and tested for between-genotype differences. Because BDNF and gonadal steroid hormones conjointly influence neuronal growth, survival, and plasticity in hippocampus and PFC, we also tested for sex × genotype interactions. Finally, in light of the known impact of BDNF on plasticity and dendritic arborization, we complimented direct rCBF comparisons with connectivity analyses to determine how activity in hippocampal and prefrontal regions showing between-genotype group differences covaries with rCBF in other nodes throughout the brain in a genotype- or sex-dependent manner. Compared with Val homozygotes, Met carriers had higher rCBF in prefrontal (BA25 extending into BA10) and hippocampal/parahippocampal regions. Moreover, there were significant sex × genotype interactions in regions (including frontal, parahippocampal, and lateral temporal cortex) in which Val homozygotes showed higher rCBF in females than males, but Met carriers showed the opposite relationship. Functional connectivity analysis demonstrated that correlations of BA25, hippocampus, and parahippocampus with frontal and temporal networks were positive for Val homozygotes and negative for Met carriers. In addition, sex × genotype analysis of functional connectivity revealed that genotype affected directionality of the inter-regional correlations differentially in men versus women. Our data indicate that BDNF allelic variation and sex interactively affect basal prefrontal and hippocampal function.

Estrone is neuroprotective in rats after traumatic brain injury

In various animal and human studies, early administration of 17β-estradiol, a strong antioxidant, anti-inflammatory, and anti-apoptotic agent, significantly decreases the severity of injury in the brain associated with cell death. Estrone, the predominant estrogen in postmenopausal women, has been shown to be a promising neuroprotective agent. The overall goal of this project was to determine if estrone mitigates secondary injury following traumatic brain injury (TBI) in rats. Male rats were given either placebo (corn oil) or estrone (0.5 mg/kg) at 30 min after severe TBI. Using a controlled cortical impact device in rats that underwent a craniotomy, the right parietal cortex was injured using the impactor tip. Non-injured control and sham animals were also included. At 72 h following injury, the animals were perfused intracardially with 0.9% saline followed by 10% phosphate-buffered formalin. The whole brain was removed, sliced, and stained for TUNEL-positive cells. Estrone decreased cortical lesion volume (p<0.01) and neuronal injury (p<0.001), and it reduced cerebral cortical levels of TUNEL-positive staining (p<0.0001), and decreased numbers of TUNEL-positive cells in the corpus callosum (p<0.03). We assessed the levels of β-amyloid in the injured animals and found that estrone significantly decreased the cortical levels of β-amyloid after brain injury. Cortical levels of phospho-ERK1/2 were significantly (p<0.01) increased by estrone. This increase was associated with an increase in phospho-CREB levels (p<0.021), and brain-derived neurotrophic factor (BDNF) expression (p<0.0006). In conclusion, estrone given acutely after injury increases the signaling of protective pathways such as the ERK1/2 and BDNF pathways, decreases ischemic secondary injury, and decreases apoptotic-mediated cell death. These results suggest that estrone may afford protection to those suffering from TBI.

Estrogen neuroprotection and the critical period hypothesis

17β-Estradiol (estradiol or E2) is implicated as a neuroprotective factor in a variety of neurodegenerative disorders. This review focuses on the mechanisms underlying E2 neuroprotection in cerebral ischemia, as well as emerging evidence from basic science and clinical studies, which suggests that there is a "critical period" for estradiol's beneficial effect in the brain. Potential mechanisms underlying the critical period are discussed, as are the neurological consequences of long-term E2 deprivation (LTED) in animals and in humans after natural menopause or surgical menopause. We also summarize the major clinical trials concerning postmenopausal hormone therapy (HT), comparing their outcomes with respect to cardiovascular and neurological disease and discussing their relevance to the critical period hypothesis. Finally, potential caveats, controversies and future directions for the field are highlighted and discussed throughout the review.

Investigations of transcript expression in fathead minnow (Pimephales promelas) brain tissue reveal toxicological impacts of RDX exposure

Production, usage and disposal of the munitions constituent (MC) cyclotrimethylenetrinitramine (RDX) has led to environmental releases on military facilities. The chemical attributes of RDX are conducive for leaching to surface water which may put aquatic organisms at risk of exposure. Because RDX has been observed to cause aberrant neuromuscular effects across a wide range of animal phyla, we assessed the effects of RDX on central nervous system (CNS) functions in the representative aquatic ecotoxicological model species, fathead minnow (Pimephales promelas). We developed a fathead minnow brain-tissue cDNA library enriched for transcripts differentially expressed in response to RDX and trinitrotoluene (TNT) exposure. All 4,128 cDNAs were sequenced, quality filtered and assembled yielding 2230 unique sequences and 945 significant blastx matches (E ≤10(-5)). The cDNA library was leveraged to create custom-spotted microarrays for use in transcript expression assays. The impact of RDX on transcript expression in brain tissue was examined in fathead minnows exposed to RDX at 0.625, 2.5, 5, 10mg/L or an acetone-spike control for 10 days. Overt toxicity of RDX in fathead minnow occurred only at the highest exposure concentration resulting in 50% mortality and weight loss. Conversely, Bayesian analysis of microarray data indicated significant changes in transcript expression at concentrations as low as 0.625 mg/L. In total, 154 cDNAs representing 44 unique transcripts were differentially expressed in RDX exposures, the majority of which were validated by reverse transcriptase-quantitative PCR (RT-qPCR). Investigation of molecular pathways, gene ontology (GO) and individual gene functions affected by RDX exposures indicated changes in metabolic processes involved in: oxygen transport, neurological function, calcium binding/signaling, energy metabolism, cell growth/division, oxidative stress and ubiquitination. In total, our study indicated that RDX exposure affected molecular processes critical to CNS function in fathead minnow.

Effects of estrogen on beta-amyloid-induced cholinergic cell death in the nucleus basalis magnocellularis

Alzheimer disease is characterized by accumulation of β-amyloid (Aβ) and cognitive dysfunctions linked to early loss of cholinergic neurons. As estrogen-based hormone replacement therapy has beneficial effects on cognition of demented patients, and it may prevent memory impairments, we investigated the effect of estrogen-pretreatment on Aβ-induced cholinergic neurodegeneration in the nucleus basalis magnocellularis (NBM). We tested which Aβ species induces the more pronounced cholinotoxic effect in vivo. We injected different Aβ assemblies in the NBM of mice, and measured cholinergic cell and cortical fiber loss. Spherical Aβ oligomers had the most toxic effect. Pretreatment of ovariectomized mice with estrogen before Aβ injection decreased cholinergic neuron loss and partly prevented fiber degeneration. By using proteomics, we searched for proteins involved in estrogen-mediated protection and in Aβ toxicity 24 h following injection. The change in expression of, e.g., DJ-1, NADH ubiquinone oxidoreductase, ATP synthase, phosphatidylethanolamine-binding protein 1, protein phosphatase 2A and dimethylarginine dimethylaminohydrolase 1 support our hypothesis that Aβ induces mitochondrial dysfunction, decreases MAPK signaling, and increases NOS activation in NBM. On the other hand, altered expression of, e.g., MAP kinase kinase 1 and 2, protein phosphatase 1 and 2A by Aβ might increase MAPK suppression and NOS signaling in the cortical target area. Estrogen pretreatment reversed most of the changes in the proteome in both areas. Our experiments suggest that regulation of the MAPK pathway, mitochondrial pH and NO production may all contribute to Aβ toxicity, and their regulation can be prevented partly by estrogen pretreatment.

Effects of estrogens and endocrine-disrupting chemicals on cell differentiation-survival-proliferation in brain: contributions of neuronal cell lines

Estrogens and estrogen receptors (ER) are key actors in the control of differentiation and survival and act on extrareproductive tissues such as brain. Thus, estrogens may display neuritogenic effects during development and neuroprotective effects in the pathophysiological context of brain ischemia and neurodegenerative pathologies like Alzheimer's disease or Parkinson's disease. Some of these effects require classical transcriptional "genomic" mechanisms through ER, whereas other effects appear to rely clearly on "membrane-initiated mechanisms" through cytoplasmic signal transduction pathways. Disturbances of these mechanisms by endocrine-disrupting chemicals (EDC) may exert adverse effects on brain. Some EDC may act via ER-independent mechanisms but might cross-react with endogenous estrogen. Other EDC may act through ER-dependent mechanisms and display agonistic/antagonistic estrogenic properties. Because of these potential effects of EDC, it is necessary to establish sensitive cell-based assays to determine EDC effects on brain. In the present review, some effects of estrogens and EDC are described with focus on ER-mediated effects in neuronal cells. Particular attention is given to PC12 cells, an interesting model to study the mechanisms underlying ER-mediated differentiating and neuroprotective effects of estrogens.

The assessment of non-feminizing estrogens for use in neuroprotection

Menopause is associated with a precipitous decline in circulating estrogens and a resulting loss of the neuroprotective actions of this steroid hormone. In view of the results of the Women's Health Initiative and the preceding knowledge that orally administered estrogens has a variety of adverse side effects, likely through actions on peripheral estrogen receptor alpha (ERα), we initiated a program of research to synthesis and assess a group of non-feminizing estrogens that lack ability to interact with ERs but retain much of the neuroprotective action of feminizing estrogens. This program of research is aimed at the identification of compounds which do not stimulate ERs but are potentially neuroprotective in vitro and in animal models of neuronal cell death. We discovered that the most effective non-feminizing estrogens were those with large bulky groups in the 2 and/or 4 carbon of the phenolic A ring of the steroid. These compounds were 8- to 114-fold more potent than 17 β-estradiol (βE2), but lacked ER binding capacity in vitro and feminizing effects in vivo. The success of this program of research suggests that strategies to optimize non-feminizing estrogens for use in postmenopausal women can be successful.

Premarin improves outcomes of spinal cord injury in male rats through stimulating both angiogenesis and neurogenesis

OBJECTIVE

To ascertain whether Premarin improves spinal cord injury outcomes in male rats by stimulating both angiogenesis and neurogenesis.

DESIGN

Chi Mei Medical Center research laboratory.

SUBJECTS

Male Sprague-Dawley rats 240-258 g.

INTERVENTIONS

Anesthetized rats, after the onset of spinal cord injury, were divided into two groups and given the vehicle solution (1 mL/kg of body weight) or Premarin (1 mg/kg of body weight). Saline or Premarin solutions were administered intravenously and immediately after spinal cord injury.

MEASUREMENTS AND MAIN RESULTS

Premarin (an estrogen sulfate) causes attenuation of spinal cord injury-induced spinal cord infarction and hind limb locomotor dysfunction. Spinal cord injury-induced apoptosis as well as activated inflammation was also significantly Premarin-reduced. In injured spinal cord, angiogenesis, neurogenesis, and production of an antiinflammatory cytokine were all Premarin therapy-promoted.

CONCLUSIONS

Our results indicate that Premarin therapy may protect against spinal cord apoptosis after spinal cord injury through mechanisms stimulating both angiogenesis and neurogenesis in male rats.

Experimental models of vascular dementia and vascular cognitive impairment: a systematic review

Vascular cognitive impairment (VCI) encompasses vascular dementia and is the second most common cause of dementing illness after Alzheimer's disease. The main causes of VCI are: cerebral small vessel disease; multi-infarct dementia; strategic infarct (i.e. located in a functionally-critical brain area); haemorrhage/microbleed; angiopathy (including cerebral amyloid angiopathy); severe hypoperfusion (e.g. cardiac arrhythmia); and hereditary vasculopathy (e.g. cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, CADASIL). In this systematic analysis, we aimed to relate cognitive and neuropathological features of experimental models to clinical VCI. We extracted data from 107 studies covering 16 models. These included: brief global ischaemic insults (in rats, mice or gerbils); chronic global hypoperfusion (rats, mice, gerbils); chronic hypertension (in primates or stroke-prone, spontaneously-hypertensive rats); multiple ischaemic lesions because of intra-vascular emboli (in rodents, rabbits or primates); strategic ischaemic lesions (in rats or mini-pigs); generalised vasculopathies, because of mutant Notch3, hyperhomocysteinaemia, experimental diabetes mellitus or lack of cerebral vasodilator M(5) receptors (rats or mice). Most cognitive testing showed deficits in working and reference memory. The lesions observed were microinfarcts, diffuse white matter lesions, hippocampal neuronal death, focal ischaemic lesions and micro-haemorrhages. The most-used model was bilateral carotid artery occlusion in rats, leading to chronic hypoperfusion and white matter injury.

Reproductive age modulates the impact of focal ischemia on the forebrain as well as the effects of estrogen treatment in female rats

While human observational studies and animal studies report a neuroprotective role for estrogen therapy in stroke, the multicenter placebo-controlled Women's Health Initiative (WHI) study concluded that hormone therapy increased the risk for stroke in postmenopausal women. The present study therefore tested the hypothesis that estrogen replacement would increase the severity of a stroke-like injury in females when this replacement occurs after a prolonged hypoestrogenic period, such as the menopause or reproductive senescence, but not when given to females that were normally cycling immediately prior to the hormone replacement. Two groups of female rats were used: multiparous females with normal but lengthened estrus cycles (mature adults), and older multiparous females currently in a persistent acyclic state (reproductive senescent). Animals were either used intact, or were bilaterally ovariectomized and immediately replaced with a 17beta-estradiol pellet or control pellet. Animals were subject to a forelimb placing test (a test for sensorimotor deficit) and thereafter to middle cerebral artery occlusion (MCAo) by stereotaxic injection of the vasoconstrictive peptide endothelin-1, adjacent to the MCA. One week after stroke, behavioral tests were performed again. Cortical and striatal infarct volume, measured from brain slices, was significantly greater in intact reproductive senescent females as compared to intact mature adults. Furthermore, estrogen treatment to ovariectomized mature adult females significantly reduced the cortical infarct volume. Paradoxically, estrogen treatment to ovariectomized reproductive senescent females significantly increased cortical and striatal infarct volumes as compared to control pellet replaced senescent females. Significant post-stroke behavioral deficit was observed in all groups on the side contralateral to the lesion, while senescent females also exhibited deficits on the ipsilateral side, in the cross-midline forelimb placement test. Using an animal model that approximates the natural ovarian aging process, these findings strongly support the hypothesis that the effectiveness of estrogen therapy in protecting brain health may depend critically on the time of initiation with respect to a female's reproductive status.

Hormone therapy in postmenopausal women affects hemispheric asymmetries in fine motor coordination

Evidence exists that the functional differences between the left and right cerebral hemispheres are affected by age. One prominent hypothesis proposes that frontal activity during cognitive task performance tends to be less lateralized in older than in younger adults, a pattern that has also been reported for motor functioning. Moreover, functional cerebral asymmetries (FCAs) have been shown to be affected by sex hormonal manipulations via hormone therapy (HT) in older women. Here, we investigate whether FCAs in fine motor coordination, as reflected by manual asymmetries (MAs), are susceptible to HT in older women. Therefore, sixty-two postmenopausal women who received hormone therapy either with estrogen (E) alone (n=15), an E-gestagen combination (n=21) or without HT (control group, n=26) were tested. Saliva levels of free estradiol and progesterone (P) were analyzed using chemiluminescence assays. MAs were measured with a finger tapping paradigm consisting of two different tapping conditions. As expected, postmenopausal controls without HT showed reduced MAs in simple (repetitive) finger tapping. In a more demanding sequential condition involving four fingers, however, they revealed enhanced MAs in favour of the dominant hand. This finding suggests an insufficient recruitment of critical motor brain areas (especially when the nondominant hand is used), probably as a result of age-related changes in corticocortical connectivity between motor areas. In contrast, both HT groups revealed reduced MAs in sequential finger tapping but an asymmetrical tapping performance related to estradiol levels in simple finger tapping. A similar pattern has previously been found in younger participants. The results suggest that, HT, and E exposure in particular, exerts positive effects on the motor system thereby counteracting an age-related reorganization.

Development of novel microsatellite DNA markers by cross-amplification and analysis of genetic variation in gerbils

The objectives of this study are to establish microsatellite loci for the Mongolian gerbil based on mouse microsatellite DNA sequences and to investigate genetic variation in the laboratory gerbil (Capital Medical University, CMU) and 2 wild gerbil populations (from Yin Chuan city [YIN] and the Hohehot Municipality [HOH]). In total, 536 mouse microsatellite markers were chosen to identify polymorphic dinucleotide repeat loci in the gerbil by cross-amplification. Of these markers, 313 (58.39%) have been discretely amplified from the CMU laboratory gerbil and been sequenced. Of the 313 sequenced markers, 130 were confirmed as simple sequence repeat (SSR) loci in the gerbil. In total, 6 of those newly identified loci plus 6 identified in previous reports were used to estimate the genetic polymorphism for 30 laboratory gerbils and 54 wild gerbils (27 each of the HOH and YIN groups). A total of 29 alleles were observed in the 3 populations, and 11 of 12 loci (91.67%) are polymorphic markers. Nei's standard genetic distances of 0.0592 (CMU vs. HOH) and 0.1033 (CMU vs. YIN) were observed. The averages of observed versus expected heterozygosity are 0.5231/0.4008, 0.5051/0.3882, and 0.4825/0.3665 for the YIN, HOH, and CMU populations, respectively. These results show that cross-amplification using mouse microsatellite primers is an efficient way to identify gerbil SSR loci. By using these 12 selected markers, we have demonstrated that genetic variation level within the CMU population is higher than that has been reported previously and are comparable with the levels found in 2 wild populations.

Extranuclear estrogen receptors mediate the neuroprotective effects of estrogen in the rat hippocampus

Background

17β-estradiol (E2) has been implicated to exert neuroprotective effects in the brain following cerebral ischemia. Classically, E2 is thought to exert its effects via genomic signaling mediated by interaction with nuclear estrogen receptors. However, the role and contribution of extranuclear estrogen receptors (ER) is unclear and was the subject of the current study.

Methodology/Principal Findings

To accomplish this goal, we employed two E2 conjugates (E2 dendrimer, EDC, and E2-BSA) that can interact with extranuclear ER and exert rapid nongenomic signaling, but lack the ability to interact with nuclear ER due to their inability to enter the nucleus. EDC or E2-BSA (10 µM) was injected icv 60 min prior to global cerebral ischemia (GCI). FITC-tagged EDC or E2-BSA revealed high uptake in the hippocampal CA1 region after icv injection, with a membrane (extranuclear) localization pattern in cells. Both EDC and E2-BSA exerted robust neuroprotection in the CA1 against GCI, and the effect was blocked by the ER antagonist, ICI182,780. EDC and E2-BSA both rapidly enhanced activation of the prosurvival kinases, ERK and Akt, while attenuating activation of the proapoptotic kinase, JNK following GCI, effects that were blocked by ICI182,780. Administration of an MEK or PI3K inhibitor blocked the neuroprotective effects of EDC and E2-BSA. Further studies showed that EDC increased p-CREB and BDNF in the CA1 region in an ERK- and Akt-dependent manner, and that cognitive outcome after GCI was preserved by EDC in an ER-dependent manner.

Conclusions/Significance

In conclusion, the current study demonstrates that activation of extranuclear ER results in induction of ERK-Akt-CREB-BDNF signaling in the hippocampal CA1 region, which significantly reduces ischemic neuronal injury and preserves cognitive function following GCI. The study adds to a growing literature that suggests that extranuclear ER can have important actions in the brain.

Complexities of oestrogen in stroke

Evidence exists for the potential protective effects of circulating ovarian hormones in stroke, and oestrogen reduces brain damage in animal ischaemia models. However, a recent clinical trial indicated that HRT (hormone-replacement therapy) increased the incidence of stroke in post-menopausal women, and detrimental effects of oestrogen on stroke outcome have been identified in a meta-analysis of HRT trials and in pre-clinical research studies. Therefore oestrogen is not an agent that can be promoted as a potential stroke therapy. Many published reviews have reported the neuroprotective effects of oestrogen in stroke, but have failed to include information on the detrimental effects. This issue is addressed in the present review, along with potential mechanisms of action, and the translational capacity of pre-clinical research.

Neuroprotective actions of sex steroids in Parkinson's disease

The sex difference in Parkinson's disease, with a higher susceptibility in men, suggests a modulatory effect of sex steroids in the brain. Numerous studies highlight that sex steroids have neuroprotective properties against various brain injuries. This paper reviews the protective effects of sex hormones, particularly estradiol, progesterone and androgens, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease as compared to methamphetamine toxicity. The molecular mechanisms underlying beneficial actions of sex steroids on the brain have been investigated showing steroid, dose, timing and duration specificities and presently focus is on the dopamine signaling pathways, the next frontier. Both genomic and non-genomic actions of estrogen converge to promote survival factors and show sex differences. Neuroprotection by estrogen involves activation of signaling molecules such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. Interaction with growth factors, such as insulin-like growth factor 1, also contributes to protective actions of estrogen.

Premarin can act via estrogen receptors to rescue mice from heatstroke-induced lethality

The present study was conducted to assess whether Premarin, a water-soluble estrogen sulfate, can act via estrogen receptors (ERs) to rescue mice from heat-induced lethality. Unanesthetized, unrestrained mice were exposed to ambient temperature of 42.4 degrees C to induce heatstroke (HS). Another group of mice was exposed to room temperature (24 degrees C) and used as normothermic controls. They were given isotonic sodium chloride solution, Premarin (0.1 - 1.0 mg/kg of body weight, i.p.), or Premarin (1 mg/kg of body weight, i.p.) plus the nonselective ER antagonist ICI 182, 780 (0.25 mg/kg of body weight, i.p.) 1 h after the termination of heat stress. Their physiologic and biochemical parameters were continuously monitored. Mice that survived on day 4 of heat treatment were considered survivors. When the vehicle-treated mice underwent heat, the fraction survival and core temperature at +4 h of body heating were found to be 0 of 12 and 34.4 degrees C +/- 3 degrees C, respectively. Administration of Premarin (1 mg/kg) 1 h after the cessation of heat stress rescued the mice from heat-induced death (fraction survival, 12/12) and reduced the hypothermia (core temperature, 37.3 degrees C). The beneficial effects of Premarin in ameliorating lethality and hypothermia can be abolished by simultaneous administration of ICI 182, 780. Both IL-10 (an anti-inflammatory cytokine) and estradiol in the serum were increased significantly in heat-stressed mice administered Premarin compared with vehicle-treated HS group. Heat-induced apoptosis, as indicated by terminal deoxynucleotidyl-transferase-mediated alpha UDP-biotin nick end-labeling staining, in the spleen, liver, and kidney were significantly reduced by Premarin. The increased levels of cellular ischemia (e.g., glutamate, lactate-to-pyruvate ratio, and nitrite) and damage (e.g., glycerol) markers and iNOS expression in the hypothalamus during HS were decreased significantly by Premarin therapy. The levels of proinflammatory cytokines (e.g., IL-1 beta and TNF-alpha) and renal and hepatic dysfunction markers in plasma that are up-regulated in heat stressed mice were significantly lower in Premarin-administered mice. The data indicate that Premarin may act via ERs to rescue mice form HS-induced lethality.

Chronic estradiol treatment increases CA1 cell survival but does not improve visual or spatial recognition memory after global ischemia in middle-aged female rats

Transient global ischemia induces selective, delayed neuronal death in the hippocampal CA1 and cognitive deficits. Physiological levels of 17beta-estradiol ameliorate ischemia-induced neuronal death and cognitive impairments in young animals. In view of concerns regarding hormone therapy in postmenopausal women, we investigated whether chronic estradiol treatment initiated 14 days prior to ischemia attenuates ischemia-induced CA1 cell loss and impairments in visual and spatial memory, in ovariohysterectomized (OVX), middle-aged (9-11 months) female rats. To determine whether the duration of hormone withdrawal affects the efficacy of estradiol treatment, hormone treatment was initiated immediately (0 week), 1 week, or 8 weeks after OVX. Age-matched, OVX and gonadally intact females were studied at each OVX interval. Ischemia was induced 1 week after animals were pretested on a variety of behavioral tasks. Global ischemia produced significant neuronal loss in the CA1 and impaired performance on visual and spatial recognition. Chronic estradiol modestly but significantly increased the number of surviving CA1 neurons in animals at all OVX durations. However, in contrast with previous results in young females, estradiol did not preserve visual or spatial memory performance in middle-aged females. All animals displayed normal locomotion, spontaneous alternation and social preference, indicating the absence of global behavioral impairments. Therefore, the neuroprotective effects of estradiol are different in middle-aged than in young rats. These findings highlight the importance of using older animals in studies assessing potential treatments for focal and global ischemia.

Estrogen therapy affects right hemisphere functioning in postmenopausal women

It has been suggested that hormone therapy (HT) in postmenopausal women differentially affects verbal and visuo-spatial abilities which mainly rely on left hemisphere (LH) and right hemisphere (RH) functioning, respectively. Thus, it seems likely that HT-related effects on cognition are driven by associated hormonal changes and their impact on functional brain organization, and functional cerebral asymmetries (FCAs) in particular. The present study investigated HT-related effects on FCAs in sixty-seven postmenopausal women who received hormone therapy either with estrogen (E) alone (n=14), an E-gestagen combination (n=22) or without HT (control group, n=31). Saliva levels of free E and progesterone (P) were analyzed using chemiluminescence assays. FCAs were measured with the visual half-field (VHF) technique using a word matching and a figural comparison task. In agreement with previous results, a postmenopausal control group showed a left hemisphere (LH) advantage in the verbal task and a right hemisphere (RH) advantage in visuo-spatial processing. In contrast, both HT groups revealed significantly reduced FCAs in the figural comparison task as a result of an E-related decrease in RH performance. The findings suggest that E-therapy in postmenopausal women can affect visuo-spatial abilities by modulating the functional brain organization and RH functioning in particular.

The injured nervous system: a Darwinian perspective

Much of the permanent damage that occurs in response to nervous system damage (trauma, infection, ischemia, etc.) is mediated by endogenous secondary processes that can contribute to cell death and tissue damage (excitotoxicity, oxidative damage and inflammation). For humans to evolve mechanisms to minimize secondary pathophysiological events following CNS injuries, selection must occur for individuals who survive such insults. Two major factors limit the selection for beneficial responses to CNS insults: for many CNS disease states the principal risk factor is advanced, post-reproductive age and virtually all severe CNS traumas are fatal in the absence of modern medical intervention. An alternative hypothesis for the persistence of apparently maladaptive responses to CNS damage is that the secondary exacerbation of damage is the result of unavoidable evolutionary constraints. That is, the nervous system could not function under normal conditions if the mechanisms that caused secondary damage (e.g., excitotoxicity) in response to injury were decreased or eliminated. However, some vertebrate species normally inhabit environments (e.g., hypoxia in underground burrows) that could potentially damage their nervous systems. Yet, neuroprotective mechanisms have evolved in these animals indicating that natural selection can occur for traits that protect animals from nervous system damage. Many of the secondary processes and regeneration-inhibitory factors that exacerbate injuries likely persist because they have been adaptive over evolutionary time in the healthy nervous system. Therefore, it remains important that researchers consider the role of the processes in the healthy or developing nervous system to understand how they become dysregulated following injury.

Developmental exposure to pentachlorophenol affects the expression of thyroid hormone receptor beta1 and synapsin I in brain, resulting in thyroid function vulnerability in rats

Pentachlorophenol (PCP), a component of biocides and a contaminant in diverse tissue samples from humans from various geographic areas, disrupts regulatory effects of thyroid hormones. Here we examined the effects of developmental exposure of rats to PCP on various aspects of brain development, male reproductive function, and adrenal function, all of which are under thyroid hormones regulation. PCP was administered to dams and their offspring via drinking water (6.6 mg l(-1)) during gestation and lactation. Tissue samples were obtained from dams, 3-week-old weanling pups, and 12-week-old pups. Gene expressions of thyroid hormone receptor beta1 and synapsin I, factors that promote brain growth, was increased in the cerebral cortex of PCP-treated weanling females, whereas plasma concentrations of total thyroxine were decreased in dams and weanling pups, and plasma thyroid-stimulating hormone concentrations were higher in PCP-treated weanling males. PCP caused a decrease in plasma corticosterone concentrations in 12-week-old female rats, but not in male rats or weanling females. PCP-treated male pups had significantly increased testis weight at 12 week of age. No overt signs of toxicity were noted throughout this study. Our results show that PCP exposure during development causes thyroid function vulnerability, testicular hypertrophy in adults, and aberrations of brain gene expression.

The selective oestrogen receptor modulator, LY362321, is not neuroprotective in a rat model of transient focal ischaemia

Selective oestrogen receptor modulators (SERMs) may offer improved alternatives to oestrogen as neuroprotectants in experimental stroke. The present study investigated the role of a novel SERM, LY362321, in a rat model of transient middle cerebral artery occlusion (MCAO). Female Sprague-Dawley rats were ovariectomised and began receiving daily s.c. injections of either 1 mg/kg (n = 13), 10 mg/kg (n = 14) of LY362321, or vehicle (n = 13). The left MCA was temporarily occluded (90 min), with cortical blood flow monitoring, at 12 days post ovariectomy. Sensorimotor function was assessed using a neurological score prior to the MCAO and daily for 3 days following the MCAO. Tissue was processed for infarct volume assessment using 2,3,5-triphenyltetra-zolium chloride staining. The results indicated that there were no significant differences amongst groups in cortical blood flow during the MCAO. Furthermore, there was no significant difference in infarct size amongst vehicle, 1, and 10 mg/kg treated animals: 22.9 +/- 5.0, 16.7 +/- 4.2, and 21.1 +/- 4.1, respectively, one-way anova [F(2,32) = 0.542, P = 0.587]. The MCAO induced a significant decline in neurological score in the vehicle group (from 14 to 7 at 24 h post-MCAO) but this was not significantly affected by LY362321 at either dose. In conclusion, pretreatment with a low or high dose of the novel SERM LY362321 did not significantly influence cerebral blood flow, infarct volume, or sensorimotor function in rats exposed to transient MCAO.

More than a decade of estrogen neuroprotection

Considerable evidence has emerged through more than a decade of research supporting the neuroprotective and cognition-preserving effects of estrogens. Such basic research coupled with various epidemiological studies led quickly to the assessment of Premarin for the treatment of mild to moderate Alzheimer's disease (AD), initiated by the Alzheimer's Disease Cooperative Study Group and headed by Dr. Leon Thal. While this and subsequent trials with Premarin (Wyeth Research, Monmouth Junction, New Jersey) and PremPro (Wyeth Research), a conjugated equine estrogen preparation plus medoxyprogresterone acetate, have not supported the use of estrogens in treating advanced AD, considerable inferences have been made from these placebo controlled trials of estrogens. Here, we aimed to put these AD trials of estrogens in perspective by considering the potential mechanisms of these potent neuroprotective estrogens, the role of estrogens in other neurodegenerative conditions, such as cerebral ischemia, and based on our current understanding of estrogen neurobiology, offer insight into the design of future clinical trails of estrogens for neuronal protection.

Endogenous estrogen is not associated with cognitive performance before, during, or after menopause

OBJECTIVE

In a population-based sample of women (45, 50, or 55 years old), behavioral data and blood serum were collected concurrently, enabling us (1) to investigate cognitive differences among premenopausal, perimenopausal, and postmenopausal groups of women and (2) to evaluate the relationship between blood estrogen levels and cognitive performance.

DESIGN

Groups of premenopausal (n = 129), perimenopausal (n = 58), and postmenopausal (n = 55) women were tested on tasks assessing episodic and semantic memory, verbal fluency, visuospatial performance, and face recognition. Blood serum was collected concurrently for analyses of estrogen levels.

RESULTS

With inclusion of controls for age and education, results showed that there were no differences in cognitive performance among premenopausal, perimenopausal, and postmenopausal groups of women. In addition, there were no associations between blood estrogen levels and cognitive performance.

CONCLUSIONS

These results do not support the hypothesis that estrogen or menopausal status affects cognitive performance in middle-aged women.

Neurotrophic and neuroprotective actions of estrogen: basic mechanisms and clinical implications

Estrogen is an important hormone signal that regulates multiple tissues and functions in the body. This review focuses on the neurotrophic and neuroprotective actions of estrogen in the brain, with particular emphasis on estrogen actions in the hippocampus, cerebral cortex and striatum. Sex differences in the risk, onset and severity of neurodegenerative disease such as Alzheimer's disease, Parkinson's disease and stroke are well known, and the potential role of estrogen as a neuroprotective factor is discussed in this context. The review assimilates a complex literature that spans research in humans, non-human primates and rodent animal models and attempts to contrast and compare the findings across species where possible. Current controversies regarding the Women's Health Initiative (WHI) study, its ramifications, concerns and the new studies needed to address these concerns are also addressed. Signaling mechanisms underlying estrogen-induced neuroprotection and synaptic plasticity are reviewed, including the important concepts of genomic versus nongenomic mechanisms, types of estrogen receptor involved and their subcellular targeting, and implicated downstream signaling pathways and mediators. Finally, a multicellular mode of estrogen action in the regulation of neuronal survival and neurotrophism is discussed, as are potential future directions for the field.

Estrogen receptor alpha (ESR1) PvuII and XbaI gene polymorphisms in ischemic stroke in a Hungarian population

BACKGROUND

Ischemic stroke is a multifactorial disorder with genetic and environmental components. The aim of our study was to investigate whether two polymorphisms of the estrogen receptor alpha (ESR1) gene (ESR1 c.454-397T>C and c.454-351A>G) are associated with ischemic stroke in a Caucasian population from Hungary.

METHODS

One hundred and ninety-eight patients with ischemic stroke and 180 control subjects were enrolled in this case-control study. Ischemic stroke subtypes were categorized according to the Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification as large-artery atherosclerosis, small-artery occlusion, cardioembolism or stroke of other determined etiology. The ESR1 PvuII and XbaI genotypes were determined using the PCR-RFLP method.

RESULTS

There were no significant differences in the genotype, allele and haplotype frequencies of PvuII and XbaI polymorphisms between the group of patients with ischemic stroke and the control group. Furthermore, ESR1 PvuII and XbaI genotypes, alleles and haplotypes were not associated with any subtype of ischemic stroke.

CONCLUSIONS

We did not observe an association between ESR1 PvuII and XbaI gene polymorphisms and ischemic stroke or any subtype of ischemic stroke. However, further studies are needed to explore the complex interaction between environmental factors and ESR1 gene polymorphisms in the risk of ischemic stroke, particularly in ethnically different populations.

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.