beta-Estradiol induces synaptogenesis in the hippocampus by enhancing brain-derived neurotrophic factor release from dentate gyrus granule cells

Long-Term Oral Tamoxifen Administration Decreases Brain-Derived Neurotrophic Factor in the Hippocampus of Female Long-Evans Rats

Tamoxifen, a selective estrogen receptor modulator (SERM), is commonly used as an adjuvant drug therapy for estrogen-receptor-positive breast cancers. Though effective at reducing the rate of cancer recurrence, patients often report unwanted cognitive and affective side effects. Despite this, the impacts of chronic tamoxifen exposure on the brain are poorly understood, and rodent models of tamoxifen exposure do not replicate the chronic oral administration seen in patients. We, therefore, used long-term ad lib consumption of medicated food pellets to model chronic tamoxifen exposure in a clinically relevant way. Adult female Long-Evans Hooded rats consumed tamoxifen-medicated food pellets for approximately 12 weeks, while control animals received standard chow. At the conclusion of the experiment, blood and brain samples were collected for analyses. Blood tamoxifen levels were measured using a novel ultra-performance liquid chromatography-tandem mass spectrometry assay, which found that this administration paradigm produced serum levels of tamoxifen similar to those in human patients. In the brain, brain-derived neurotrophic factor (BDNF) was visualized in the hippocampus using immunohistochemistry. Chronic oral tamoxifen treatment resulted in a decrease in BDNF expression across several regions of the hippocampus. These findings provide a novel method of modeling and measuring chronic oral tamoxifen exposure and suggest a putative mechanism by which tamoxifen may cause cognitive and behavioral changes reported by patients.

Extracellular matrix metalloproteinase-9 (MMP-9) is required in female mice for 17β-estradiol enhancement of hippocampal memory consolidation

Hippocampal plasticity and memory are modulated by the potent estrogen 17β-estradiol (E₂). Research on the molecular mechanisms of hippocampal E₂ signaling has uncovered multiple intracellular pathways that contribute to these effects, but few have questioned the role that extracellular signaling processes may play in E₂ action. Modification of the extracellular matrix (ECM) by proteases like matrix metalloproteinase-9 (MMP-9) is critical for activity-dependent remodeling of synapses, and MMP-9 activity is required for hippocampal learning and memory. Yet little is known about the extent to which E₂ regulates MMP-9 in the hippocampus, and the influence this interaction may have on hippocampal memory. Here, we examined the effects of hippocampal MMP-9 activity on E₂-induced enhancement of spatial and object recognition memory consolidation. Post-training bilateral infusion of an MMP-9 inhibitor into the dorsal hippocampus of ovariectomized female mice blocked the enhancing effects of E₂ on object placement and object recognition memory, supporting a role for MMP-9 in estrogenic regulation of memory consolidation. E₂ also rapidly increased the activity of dorsal hippocampal MMP-9 without influencing its protein expression, providing further insight into hippocampal E₂/MMP-9 interactions. Together, these results provide the first evidence that E₂ regulates MMP-9 to modulate hippocampal memory and highlight the need to further study estrogenic regulation of extracellular modification.

Effects of oral contraceptive pills on mood and magnetic resonance imaging measures of prefrontal cortical thickness

Gonadal hormones influence neuronal organization and plasticity. Yet the consequences of altering their concentrations by administering contraceptive agents, which are used by most reproductive-age women in the United States, are unclear. Cross-sectional studies have found both larger and smaller cortical regions alongside a variety of mood alterations in women who use oral contraceptive pills (OCPs) compared to naturally-cycling women. The goal of this study, therefore, was to determine whether there is an effect of OCPs on MRI measures of prefrontal cortical brain structure that may influence regulation of mood. We performed a double-blind, placebo-controlled, randomized crossover study comparing effects of OCPs (0.15 mg levonorgestrel + 0.30 μg ethinyl estradiol) vs placebo (N = 26) on MRI measures of prefrontal cortical thickness and on mood, as indicated by self-report on the Daily Record of Severity of Problems, which also includes one item related to somatic symptoms. MRI measures that reflect cortical thickness were smaller bilaterally in the pars triangularis and in the pars opercularis and frontal pole of the right hemisphere during the OCP arm vs. placebo. Only the effect in the right pars triangularis survived multiple comparisons correction. Right pars triangularis MRI measures of cortical thickness were not related to mood symptoms, but negatively correlated across conditions with severity of somatic symptoms on the DSRP. The somatic symptoms and MRI measures may be independently related to the actions of steroid hormones in OCPs, with OCPs simultaneously inducing both more effects on MRI measures of cortical thickness and somatic symptoms.

17β-estradiol activation of dorsal hippocampal TrkB is independent of increased mature BDNF expression and is required for enhanced memory consolidation in female mice

The potent estrogen 17β-estradiol (E₂) is known to enhance hippocampal memory and plasticity, however the molecular mechanisms underlying these effects remain unclear. Brain derived neurotrophic factor (BDNF) and its receptor tropomyosin receptor kinase B (TrkB) are regulated by E₂, but the potential mechanistic roles of neurotrophic signaling in E₂-induced enhancement of memory are not well understood. Here, we examined the effects of hippocampal TrkB signaling on E₂-induced enhancement of memory consolidation in the object placement and recognition tasks. Bilateral infusion of the TrkB antagonist ANA-12 into the dorsal hippocampus of ovariectomized female mice blocked E₂-induced enhancement of memory consolidation, supporting a role for TrkB-mediated signaling in estrogenic regulation of memory. Although dorsal hippocampal E₂ infusion increased levels of phospho-TrkB and mature BDNF (mBDNF) in the dorsal hippocampus within 4-6 h, E₂-induced increases in hippocampal mBDNF expression were not required for hippocampal TrkB activation and were not inhibited by TrkB antagonism. Thus, E₂ regulates TrkB signaling to facilitate memory consolidation in a manner independent of mBDNF expression. Together these results provide the first direct evidence that E₂ modulation of hippocampal TrkB signaling is required for its beneficial effects on memory consolidation and provide additional characterization of the ways in which TrkB/BDNF signaling is regulated by E₂ in the hippocampus.

Depression, Estrogens, and Neuroinflammation: A Preclinical Review of Ketamine Treatment for Mood Disorders in Women

Ketamine has been shown to acutely and rapidly ameliorate depression symptoms and suicidality. Given that women suffer from major depression at twice the rate of men, it is important to understand how ketamine works in the female brain. This review explores three themes. First, it examines our current understanding of the etiology of depression in women. Second, it examines preclinical research on ketamine's antidepressant effects at a neurobiological level as well as how ovarian hormones present a unique challenge in interpreting these findings. Lastly, the neuroinflammatory hypothesis of depression is highlighted to help better understand how ovarian hormones might interact with ketamine in the female brain.

Oestradiol as a neuromodulator of learning and memory

Although hormones such as glucocorticoids have been broadly accepted in recent decades as general neuromodulators of memory processes, sex steroid hormones such as the potent oestrogen 17β-oestradiol have been less well recognized by the scientific community in this capacity. The predominance of females in studies of oestradiol and memory and the general (but erroneous) perception that oestrogens are 'female' hormones have probably prevented oestradiol from being more widely considered as a key memory modulator in both sexes. Indeed, although considerable evidence supports a crucial role for oestradiol in regulating learning and memory in females, a growing body of literature indicates a similar role in males. This Review discusses the mechanisms of oestradiol signalling and provides an overview of the effects of oestradiol on spatial, object recognition, social and fear memories. Although the primary focus is on data collected in females, effects of oestradiol on memory in males will be discussed, as will sex differences in the molecular mechanisms that regulate oestrogenic modulation of memory, which may have important implications for the development of future cognitive therapeutics.

Dysregulation of prostaglandine E2 and BDNF signaling mediated by estrogenic dysfunction induces primary hippocampal neuronal cell death after single and repeated paraquat treatment

Paraquat (PQ) produces hippocampal neuronal cell death and cognitive dysfunctions after unique and continued exposure, but the mechanisms are not understood. Primary hippocampal wildtype or βAPP-Tau silenced cells were co-treated with PQ with or without E2, N-acetylcysteine (NAC), NS-398 (cyclooxygenase-2 inhibitor), MF63 (PGES-1 inhibitor) and/or recombinant brain-derived neurotrophic factor (BDNF) during one- and fourteen-days to studied PQ effect on prostaglandin E2 (PGE2) and BDNF signaling and their involvement in hyperphosphorylated Tau (pTau) and amyloid-beta (Aβ) protein formation, and oxidative stress generation, that lead to neuronal cell loss through estrogenic disruption, as a possible mechanism of cognitive dysfunctions produced by PQ. Our results indicate that PQ overexpressed cyclooxygenase-2 that leads to an increase of PGE2 and alters the expression of EP1-3 receptor subtypes. PQ induced also a decrease of proBDNF and mature BDNF levels and altered P75^NTR and tropomyosin receptor kinase B (TrkB) expression. PQ induced PGE2 and BDNF signaling dysfunction, mediated through estrogenic disruption, leading to Aβ and pTau proteins synthesis, oxidative stress generation and finally to cell death. Our research provides relevant information to explain PQ hippocampal neurotoxic effects, indicating a probable explanation of the cognitive dysfunction observed and suggests new therapeutic strategies to protect against PQ toxic effects.

Sex hormones and proteins involved in brain plasticity

It is well known that peripheral sex steroid hormones cross the blood-brain barrier and control a broad spectrum of reproductive behaviors. However, their role in other essential brain functions was investigated since the 1980s, when the accumulation of pregnenolone and dehydroepiandrosterone in the brain of mammalian species was determined. Since then, numerous studies have demonstrated the participation of sex hormones in brain plasticity processes. Sex hormones through both genomic and non-genomic mechanisms of action are capable of inducing gene transcription or activating signaling cascades that result in the promotion of different physiological and pathological events of brain plasticity, such as remodeling or formation of dendritic spines, neurogenesis, synaptogenesis or myelination. In this chapter, we will present the effects of sex hormones and proteins involved in brain plasticity.

Synaptic effects of estrogen

The concept that estradiol may act as a local neuromodulator in the brain, rapidly affecting connectivity and synaptic function, has been firmly established by research over the last 30 years. De novo synthesis of estradiol within the brain as well as signaling mechanisms mediating responses to the hormone have been demonstrated, along with morphological evidence indicating rapid changes in synaptic input following increases in local estradiol levels. These rapid synaptic effects may play important roles in both physiological and pathophysiological responses to changes in circulating hormone levels, as well as in neurodegenerative disease. How local effects of estradiol on synaptic plasticity are integrated into changes in the overall activity of neural networks in the brain, however, remains a subject that is only incompletely understood.

Timing of menarche and abnormal hippocampal connectivity in youth at clinical-high risk for psychosis

The "estrogen hypothesis" suggests that estrogen is a protective factor against psychotic disorders such as schizophrenia. Although the precise protective mechanisms are still unclear, one potential explanation lies in the role that increased estrogens play in mediating hippocampal plasticity, as this may reduce hippocampal dysconnectivity that is characteristically observed in psychosis. In support of this view, later age at menarche- less available estrogen during critical early adolescent development- is related to earlier onset of psychosis and increased symptom severity. Furthermore, if estrogens have protective effects, then we should see this effect in the psychosis risk period in those at clinical high-risk (CHR) for psychosis - i.e., individuals showing attenuated symptoms at imminent risk for transitioning to a psychotic diagnosis. This study examined whether earlier age at menarche would result in more normative hippocampal connectivity in CHR youth; menarche is an easily assessed, developmental marker associated with the availability of estrogens. Resting-state connectivity was examined in sixty female participants (26 CHR and 34 healthy control; age 12-21) using a cross-sectional approach; hippocampal connectivity was found to relate to age at menarche. Later age at menarche in the CHR group related to increased hippocampal dysconnectivity to the occipital cortex (a region with a neurotrophic response to estrogen) compared to the controls. Results suggest that earlier availability of estrogens may have neuroprotective effects on hippocampal plasticity. Findings have relevance for understanding sex differences and etiology, as well as guiding novel treatments.

Epigenetic intersection of BDNF Val66Met genotype with premenstrual dysphoric disorder transcriptome in a cross-species model of estradiol add-back

Premenstrual dysphoric disorder (PMDD) affects over 5% of women, with symptoms similar to anxiety and major depression, and is associated with differential sensitivity to circulating ovarian hormones. Little is known about the genetic and epigenetic factors that increase the risk to develop PMDD. We report that 17β-estradiol (E2) affects the behavior and the epigenome in a mouse model carrying a single-nucleotide polymorphism of the brain-derived neurotrophic factor gene (BDNF Val66Met), in a way that recapitulates the hallmarks of PMDD. Ovariectomized mice heterozygous for the BDNF Met allele (Het-Met) and their matched wild-type (WT) mice were administered estradiol or vehicle in drinking water for 6 weeks. Using the open field and the splash test, we show that E2 add-back induces anxiety-like and depression-like behavior in Het-Met mice, but not in WT mice. RNA-seq of the ventral hippocampus (vHpc) highlights that E2-dependent gene expression is markedly different between WT mice and Het-Met mice. Through a comparative whole-genome RNA-seq analysis between mouse vHpc and lymphoblastoid cell line cultures from control women and women with PMDD, we discovered common epigenetic biomarkers that transcend species and cell types. Those genes include epigenetic modifiers of the ESC/E(Z) complex, an effector of response to ovarian steroids. Although the BDNF Met genotype intersects the behavioral and transcriptional traits of women with PMDD, we suggest that these similarities speak to the epigenetic factors by which ovarian steroids produce negative behavioral effects.

The role of hippocampal estradiol in synaptic plasticity and memory: A systematic review

The consolidation of long-term memory is influenced by various neuromodulators. One of these is estradiol, a steroid hormone that is synthesized both in peripheral endocrine tissue and in the brain, including the hippocampus. Here, we examine the evidence regarding the role of estradiol in the hippocampus, specifically, in memory formation and its effects on the molecular mechanisms underlying synaptic plasticity. We conclude that estradiol improves memory consolidation and, thereby, long-term memory. Previous studies have shown that it does this in three, interconnected ways: (1) via functional changes in excitatory activity, (2) signaling changes in calcium dynamics, protein phosphorylation and protein expression, and (3) structural changes to synaptic morphology. Through a functional network analysis of proteins affected by estradiol, we identify potential protein-protein interactions that further support a role for estradiol in modulating synaptic plasticity as well as highlight signaling pathways that may be involved in these changes within the hippocampus.

BDNF-Dependent Effects on Amygdala-Cortical Circuitry and Depression Risk in Children and Youth

The brain-derived neurotrophic factor (BDNF) is critical for brain development, and the functional BDNF Val66Met polymorphism is implicated in risk for mood disorders. The objective of this study was to determine how the Val66Met polymorphism influences amygdala-cortical connectivity during neurodevelopment and assess the relevance for mood disorders. Age- and sex-specific effects of the BDNF Val66Met polymorphism on amygdala-cortical connectivity were assessed by examining covariance of amygdala volumes with thickness throughout the cortex in a sample of Caucasian youths ages 8-22 that were part of the Philadelphia Neurodevelopmental Cohort (n = 339). Follow-up analyses assessed corresponding BDNF genotype effects on resting-state functional connectivity (n = 186) and the association between BDNF genotype and major depressive disorder (MDD) (n = 2749). In adolescents, amygdala-cortical covariance was significantly stronger in Met allele carriers compared with Val/Val homozygotes in amygdala-cortical networks implicated in depression; these differences were driven by females. In follow-up analyses, the Met allele was also associated with stronger resting-state functional connectivity in adolescents and increased likelihood of MDD in adolescent females. The BDNF Val66Met polymorphism may confer risk for mood disorders in females through effects on amygdala-cortical connectivity during adolescence, coinciding with a period in the lifespan when onset of depression often occurs, more commonly in females.

Infralimbic Estradiol Enhances Neuronal Excitability and Facilitates Extinction of Cocaine Seeking in Female Rats via a BDNF/TrkB Mechanism

Women are more susceptible to developing cocaine dependence than men, but paradoxically, are more responsive to treatment. The potent estrogen, 17β-estradiol (E₂), mediates these effects by augmenting cocaine seeking but also promoting extinction of cocaine seeking through E₂'s memory-enhancing functions. Although we have previously shown that E₂ facilitates extinction, the neuroanatomical locus of action and underlying mechanisms are unknown. Here we demonstrate that E₂ infused directly into the infralimbic-medial prefrontal cortex (IL-mPFC), a region critical for extinction consolidation, enhances extinction of cocaine seeking in ovariectomized (OVX) female rats. Using patch-clamp electrophysiology, we show that E₂ may facilitate extinction by potentiating intrinsic excitability of IL-mPFC neurons. Because the mnemonic effects of E₂ are known to be regulated by brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin-related kinase B (TrkB), we examined whether BDNF/TrkB signaling was necessary for E₂-induced enhancement of excitability and extinction. We found that E₂-mediated increases in excitability of IL-mPFC neurons were abolished by Trk receptor blockade. Moreover, blockade of TrkB signaling impaired E₂-facilitated extinction of cocaine seeking in OVX female rats. Thus, E₂ enhances IL-mPFC neuronal excitability in a TrkB-dependent manner to support extinction of cocaine seeking. Our findings suggest that pharmacological enhancement of E₂ or BDNF/TrkB signaling during extinction-based therapies would improve therapeutic outcome in cocaine-addicted women.

Estradiol and the Development of the Cerebral Cortex: An Unexpected Role?

The cerebral cortex undergoes rapid folding in an "inside-outside" manner during embryonic development resulting in the establishment of six discrete cortical layers. This unique cytoarchitecture occurs via the coordinated processes of neurogenesis and cell migration. In addition, these processes are fine-tuned by a number of extracellular cues, which exert their effects by regulating intracellular signaling pathways. Interestingly, multiple brain regions have been shown to develop in a sexually dimorphic manner. In many cases, estrogens have been demonstrated to play an integral role in mediating these sexual dimorphisms in both males and females. Indeed, 17β-estradiol, the main biologically active estrogen, plays a critical organizational role during early brain development and has been shown to be pivotal in the sexually dimorphic development and regulation of the neural circuitry underlying sex-typical and socio-aggressive behaviors in males and females. However, whether and how estrogens, and 17β-estradiol in particular, regulate the development of the cerebral cortex is less well understood. In this review, we outline the evidence that estrogens are not only present but are engaged and regulate molecular machinery required for the fine-tuning of processes central to the cortex. We discuss how estrogens are thought to regulate the function of key molecular players and signaling pathways involved in corticogenesis, and where possible, highlight if these processes are sexually dimorphic. Collectively, we hope this review highlights the need to consider how estrogens may influence the development of brain regions directly involved in the sex-typical and socio-aggressive behaviors as well as development of sexually dimorphic regions such as the cerebral cortex.

Sex matters: females in proestrus show greater diazepam anxiolysis and brain-derived neurotrophin factor- and parvalbumin-positive neurons than males

In humans and animal models, sex differences are reported for anxiety-like behavior and response to anxiogenic stimuli. In the current work, we studied anxiety-like behavior and response to the prototypical anti-anxiety drug, diazepam. We used 6th generation outbred lines of adult Long Evans rats with high and low anxiety-like behavior phenotypes to investigate the impact of proestrus on the baseline and diazepam-induced behavior. At three doses of diazepam (0, 0.1, and 1.0 mg/kg, i.p.), we measured anxiogenic responses on the elevated plus maze of adult male and female rats. We assessed parvalbumin and brain-derived neurotrophin protein levels in forebrain and limbic structures implicated in anxiety/stress using immunohistochemistry. At baseline, we saw significant differences between anxiety lines, with high anxiety lines displaying less time on the open arms of the elevated plus maze, and less open arm entries, regardless of sex. During proestrus, high anxiety females showed less anxiety-like behavior at 0.1 mg/kg, while low anxiety females displayed less anxiety-like behavior at 0.1 and 1.0 doses, relative to males. Brain-derived neurotrophin protein was elevated in females in the medial prefrontal cortex and central amygdala, while parvalbumin-immunoreactive cells were greater in males in the medial prefrontal cortex. Parvalbumin-positive cells in high anxiety females were higher in CA2 and dentate gyrus relative to males from the same line. In sum, when tested in proestrus, females showed greater anxiolytic effects of diazepam relative to males, and this correlated with increases in neurotrophin and parvalbumin neuron density in corticolimbic structures.

A Cohort Study Comparing Women with Autism Spectrum Disorder with and without Generalized Joint Hypermobility

Reports suggest comorbidity between autism spectrum disorder (ASD) and the connective tissue disorder, Ehlers-Danlos syndrome (EDS). People with EDS and the broader spectrum of Generalized Joint Hypermobility (GJH) often present with immune- and endocrine-mediated conditions. Meanwhile, immune/endocrine dysregulation is a popular theme in autism research. We surveyed a group of ASD women with/without GJH to determine differences in immune/endocrine exophenotypes. ASD women 25 years or older were invited to participate in an online survey. Respondents completed a questionnaire concerning diagnoses, immune/endocrine symptom history, experiences with pain, and seizure history. ASD women with GJH (ASD/GJH) reported more immune- and endocrine-mediated conditions than their non-GJH counterparts (p = 0.001). Autoimmune conditions were especially prominent in the ASD/GJH group (p = 0.027). Presence of immune-mediated symptoms often co-occurred with one another (p < 0.001–0.020), as did endocrine-mediated symptoms (p < 0.001–0.045), irrespective of the group. Finally, the numbers of immune- and endocrine-mediated symptoms shared a strong inter-relationship (p < 0.001), suggesting potential system crosstalk. While our results cannot estimate comorbidity, they reinforce concepts of an etiological relationship between ASD and GJH. Meanwhile, women with ASD/GJH have complex immune/endocrine exophenotypes compared to their non-GJH counterparts. Further, we discuss how connective tissue regulates the immune system and how the immune/endocrine systems in turn may modulate collagen synthesis, potentially leading to higher rates of GJH in this subpopulation.

Cognitive Effects of Aromatase and Possible Role in Memory Disorders

Diverse cognitive functions in many vertebrate species are influenced by local conversion of androgens to 17β-estradiol (E2) by aromatase. This enzyme is highly expressed in various brain regions across species, with some inter-species variation in terms of regional brain expression. Since women with breast cancer and men and women with other disorders are often treated with aromatase inhibitors (AI), these populations might be especially vulnerable to cognitive deficits due to low neuroE2 synthesis, i.e., synthesis of E2 directly within the brain. Animal models have been useful in deciphering aromatase effects on cognitive functions. Consequences of AI administration at various life cycle stages have been assessed on auditory, song processing, and spatial memory in birds and various aspects of cognition in rodent models. Additionally, cognitive deficits have been described in aromatase knockout (ArKO) mice that systemically lack this gene throughout their lifespan. This review will consider evidence to date that AI treatment in male and female rodent models, birds, and humans results in cognitive impairments. How brain aromatase regulates cognitive function throughout the lifespan, and gaps in current knowledge will be considered, along with future directions to better define how aromatase might guide learning and memory from early development through the geriatric period. Better understanding the importance of E2 synthesis on neurobehavioral responses at various ages will likely aid in the discovery of therapeutic strategies to prevent potential cognitive deficits, including Alzheimer's Disease, in individuals treated with AI or those possessing CYP19 gene polymorphisms, as well as cognitive effects of normal aging that may be related to changes in brain aromatase activity.

Sex differences in brain-derived neurotrophic factor signaling and functions

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family that plays a critical role in numerous neuronal activities. Recent studies have indicated that some functions or action mechanisms of BDNF vary in a sex-dependent manner. In particular, BDNF content in some brain parts and the tendency to develop BDNF deficiency-related diseases such as depression are greater in female animals. With the support of relevant studies, it has been suggested that sex hormones or steroids can modulate the activities of BDNF, which may account for its functional discrepancy in different sexes. Indeed, the cross-talk between BDNF and sex steroids has been detected for decades, and some sex steroids, such as estrogen, have a positive regulatory effect on BDNF expression and signaling. Thus, the sex of animal models that are used in studying the functions of BDNF is critical. This Mini-Review summarizes our current findings on the differences in expression, signaling, and functions of BDNF between sexes. We also discuss the potential mechanisms for mediating these differential responses, with a specific emphasis on sex steroids. By presenting and discussing these findings, we seek to encourage researchers to take sex influences into consideration when designing experiments, interpreting results, and drawing conclusions. © 2016 Wiley Periodicals, Inc.

A sexually dimorphic pre-stressed translational signature in CA3 pyramidal neurons of BDNF Val66Met mice

Males and females use distinct brain circuits to cope with similar challenges. Using RNA sequencing of ribosome-bound mRNA from hippocampal CA3 neurons, we found remarkable sex differences and discovered that female mice displayed greater gene expression activation after acute stress than males. Stress-sensitive BDNF Val66Met mice of both sexes show a pre-stressed translational phenotype in which the same genes that are activated without applied stress are also induced in wild-type mice by an acute stressor. Behaviourally, only heterozygous BDNF Val66Met females exhibit spatial memory impairment, regardless of acute stress. Interestingly, this effect is not observed in ovariectomized heterozygous BDNF Val66Met females, suggesting that circulating ovarian hormones induce cognitive impairment in Met carriers. Cognitive deficits are not observed in males of either genotype. Thus, in a brain region not normally associated with sex differences, this work sheds light on ways that genes, environment and sex interact to affect the transcriptome’s response to a stressor.

Animals’ response to acute stress is known to be influenced by sex and genetics. Here the authors performed RNA-seq on actively translated mRNAs in hippocampal CA3 neurons in mice, and document the effects of sex and genotype (i.e., BDNF Val66Met) on acute stress-induced gene expression.

Platycodon grandiflorus Root Extract Improves Learning and Memory by Enhancing Synaptogenesis in Mice Hippocampus

Platycodon grandiflorus (Jacq.) A.DC. (PG) has long been used as an ingredient of foods and is known to have beneficial effects on cognitive functions as well. The present study examined the effect of each PG extract (PGE) from root, aerial part, and seeds on cognitive functions in mice. Changes in spatial learning and memory using a Y-maze test, and markers of adult hippocampal neurogenesis and synaptogenesis were examined. Moreover, changes in neuritogenesis and activation of the ERK1/2 pathway were investigated. Results indicated that mice administered PGE (root) showed increased spontaneous alternation in the Y-maze test and synaptogenesis in the hippocampus. In addition, PGE (root) and platycodin D, the major bioactive compound from the PG root, significantly stimulated neuritic outgrowth by phosphorylation of the ERK1/2 signaling pathway in vitro. These results indicate that the PGE (root), containing platycodin D, enhances cognitive function through synaptogenesis via activation of the ERK1/2 signaling pathway.

Sex steroids and neurogenesis

The brain has long been known as a dimorphic organ and as a target of sex steroids. It is also a site for their synthesis. Sex steroids in numerous ways can modify cerebral physiology, and along with many processes adult neurogenesis is also modulated by sex steroids. This review will focus on the effects of the main steroids, estrogens, androgens and progestogens, and unveil some aspects of their partly disclosed mechanisms of actions. Gonadal steroids act on different steps of neurogenesis: cell proliferation seems to be increased by estrogens only, while androgens and progestogens favor neuronal renewal by increasing cell survival; differentiation is a common target. Aging is characterized by a cognitive deficiency, paralleled by a decrease in the rate of neuronal renewal and in the levels of circulating gonadal hormones. Therefore, the effects of gonadal hormones on the aging brain are important to consider. The review will also be expanded to related molecules which are agonists to the nuclear receptors. Sex steroids can modify adult neuronal renewal and the extensive knowledge of their actions on neurogenesis is essential, as it can be a leading pathway to therapeutic perspectives.

Selective Oestrogen Receptor Agonists Rescued Hippocampus Parameters in Male Spontaneously Hypertensive Rats

Spontaneously hypertensive rats (SHR) show pronounced hippocampus alterations, including low brain-derived neurotrophic factor (BDNF) expression, reduced neurogenesis, astrogliosis and increased aromatase expression. These changes are reverted by treatment with 17β-oestradiol. To determine which oestradiol receptor (ER) type is involved in these neuroprotective effects, we used agonists of the ERα [propylpyrazole triol (PPT)] and the ERβ [diarylpropionitrite (DPN)] given over 2 weeks to 4-month-old male SHR. Wistar Kyoto normotensive rats served as controls. Using immunocytochemistry, we determined glial fibrillary protein (GFAP)+ astrocytes in the CA1, CA3 and hilus of the dentate gyrus of the hippocampus, aromatase immunostaining in the hilus, and doublecortin (DCX)+ neuronal progenitors in the inner granular zone of the dentate gyrus. Brain-derived neurotrophic factor mRNA was also measured in the hippocampus by the quantitative polymerase chain reaction. In SHR, PPT had no effect on blood pressure, decreased astrogliosis, slightly increased BDNF mRNA, had no effect on the number of DCX+ progenitors, and increased aromatase staining. Treatment with DPN decreased blood pressure, decreased astrogliosis, increased BDNF mRNA and DCX+ progenitors, and did not modify aromatase staining. We hypothesise that, although both receptor types may participate in the previously reported beneficial effects of 17β-oestradiol in SHR, receptor activation with DPN may preferentially facilitate BDNF mRNA expression and neurogenesis. The results of the present study may help in the design of ER-based neuroprotection for the encephalopathy of hypertension.

Reproductive Steroid Regulation of Mood and Behavior

In this article, we examine evidence supporting the role of reproductive steroids in the regulation of mood and behavior in women and the nature of that role. In the first half of the article, we review evidence for the following: (i) the reproductive system is designed to regulate behavior; (ii) from the subcellular to cellular to circuit to behavior, reproductive steroids are powerful neuroregulators; (iii) affective disorders are disorders of behavioral state; and (iv) reproductive steroids affect virtually every system implicated in the pathophysiology of depression. In the second half of the article, we discuss the diagnosis of the three reproductive endocrine-related mood disorders (premenstrual dysphoric disorder, postpartum depression, and perimenopausal depression) and present evidence supporting the relevance of reproductive steroids to these conditions. Existing evidence suggests that changes in reproductive steroid levels during specific reproductive states (i.e., the premenstrual phase of the menstrual cycle, pregnancy, parturition, and the menopause transition) trigger affective dysregulation in susceptible women, thus suggesting the etiopathogenic relevance of these hormonal changes in reproductive mood disorders. Understanding the source of individual susceptibility is critical to both preventing the onset of illness and developing novel, individualized treatments for reproductive-related affective dysregulation. © 2016 American Physiological Society. Compr Physiol 6:1135-1160, 2016e.

Lambda-cyhalothrin disrupts the up-regulation effect of 17β-estradiol on post-synaptic density 95 protein expression via estrogen receptor α-dependent Akt pathway

Lambda-cyhalothrin (LCT), one of the type II pyrethroids, has been widely used throughout the world. The estrogenic effect of LCT to increase cell proliferation has been well established. However, whether the estrogenic effect of LCT will influence neurodevelopment has not been investigated. In addition, 17β-Estradiol (E2) plays a crucial role in neurodevelopment and induces an increase in synaptic proteins. The post-synaptic density 95 (PSD95) protein, which is involved in the development of the structure and function of new spines and localized with estrogen receptor α (ERα) at the post-synaptic density (PSD), was detected in our study by using hippocampal neuron cell line HT22. We found that LCT up-regulated PSD95 and ERα expression, estrogen receptor (ER) antagonist ICI182,780 and phosphatidylinositol-4; 5-bisphosphate 3-kinase (PI3K) inhibitor LY294,002 blocked this effect. In addition, LCT disrupted the promotion effect of E2 on PSD95. To investigate whether the observed changes are caused by ERα-dependent signaling activation, we next detected the effects of LCT on the ERα-mediated PI3K-Protein kinase B (PKB/Akt)-eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1) pathway. There existed an activation of Akt and the downstream factor 4E-BP1 after LCT treatment. In addition, LCT could disrupt the activation effect of E2 on the Akt pathway. However, no changes in cAMP response element-binding protein (CREB) activation and PSD95 messenger ribonucleic acid (mRNA) were observed. Our findings demonstrated that LCT could increase the PSD95 protein level via the ERα-dependent Akt pathway, and LCT might disrupt the up-regulation effect of E2 on PSD95 protein expression via this signaling pathway.

Sex Steroids Influence Brain-Derived Neurotropic Factor Secretion From Human Airway Smooth Muscle Cells

Brain derived neurotropic factor (BDNF) is emerging as an important player in airway inflammation, remodeling, and hyperreactivity. Separately, there is increasing evidence that sex hormones contribute to pathophysiology in the lung. BDNF and sex steroid signaling are thought to be intricately linked in the brain. There is currently little information on BDNF and sex steroid interactions in the airway but is relevant to understanding growth factor signaling in the context of asthma in men versus women. In this study, we assessed the effect of sex steroids on BDNF expression and secretion in human airway smooth muscle (ASM). Human ASM was treated with estrogen (E2 ) or testosterone (T, 10 nM each) and intracellular BDNF and secreted BDNF measured. E2 and T significantly reduced secretion of BDNF; effects prevented by estrogen and androgen receptor inhibitor, ICI 182,780 (1 μM), and flutamide (10 μM), respectively. Interestingly, no significant changes were observed in intracellular BDNF mRNA or protein expression. High affinity BDNF receptor, TrkB, was not altered by E2 or T. E2 (but not T) significantly increased intracellular cyclic AMP levels. Notably, Epac1 and Epac2 expression were significantly reduced by E2 and T. Furthermore, SNARE complex protein SNAP25 was decreased. Overall, these novel data suggest that physiologically relevant concentrations of E2 or T inhibit BDNF secretion in human ASM, suggesting a potential interaction of sex steroids with BDNF in the airway that is different from brain. The relevance of sex steroid-BDNF interactions may lie in their overall contribution to airway diseases such as asthma.

A novel form of synaptic plasticity in field CA3 of hippocampus requires GPER1 activation and BDNF release

Estrogen gates metabotropic glutamate receptor–dependent long-term depression at mossy fiber–CA3 synapses through a mechanism involving GPER1-mediated BDNF release, mTOR-dependent protein synthesis, and proteasome activity.

Estrogen is an important modulator of hippocampal synaptic plasticity and memory consolidation through its rapid action on membrane-associated receptors. Here, we found that both estradiol and the G-protein–coupled estrogen receptor 1 (GPER1) specific agonist G1 rapidly induce brain-derived neurotrophic factor (BDNF) release, leading to transient stimulation of activity-regulated cytoskeleton-associated (Arc) protein translation and GluA1-containing AMPA receptor internalization in field CA3 of hippocampus. We also show that type-I metabotropic glutamate receptor (mGluR) activation does not induce Arc translation nor long-term depression (LTD) at the mossy fiber pathway, as opposed to its effects in CA1, and it only triggers LTD after GPER1 stimulation. Furthermore, this form of mGluR-dependent LTD is associated with ubiquitination and proteasome-mediated degradation of GluA1, and is prevented by proteasome inhibition. Overall, our study identifies a novel mechanism by which estrogen and BDNF regulate hippocampal synaptic plasticity in the adult brain.

Signaling mechanisms mediating the regulation of synaptic plasticity and memory by estradiol

This article is part of a Special Issue "Estradiol and Cognition". Estradiol participates in the regulation of the function and plasticity of synaptic circuits in key cognitive brain regions, such as the prefrontal cortex and the hippocampus. The mechanisms elicited by estradiol are mediated by the regulation of transcriptional activity by nuclear estrogen receptors and by intracellular signaling cascades activated by estrogen receptors associated with the plasma membrane. In addition, the mechanisms include the interaction of estradiol with the signaling of other factors involved in the regulation of cognition, such as brain derived neurotrophic factor, insulin-like growth factor-1 and Wnt. Modifications in these signaling pathways by aging or by a long-lasting ovarian hormone deprivation after menopause may impair the enhancing effects of estradiol on synaptic plasticity and cognition.

The effects of estradiol on mood and behavior in human female adolescents: a systematic review

Mood disorders and health risk behaviors increase in adolescence. Puberty is considered to contribute to these events. However, the precise impact of pubertal hormone changes to the emergence of mood disorders and risk behaviors is relatively unclear. It is important that inappropriate attribution is not made. Our aim was to determine what is known about the effect of endogenous estradiol on human adolescent girls' mood and behavior. The databases searched were MEDLINE, Embase, PsycINFO, Education Resources Information Center (ERIC), Pre-MEDLINE, Web of Science, and Scopus for all dates to October 2014. For inclusion, contemporaneous hormone and mood or behavioral assessment was required. Data were extracted following a template created by the authors. Fourteen studies met our inclusion criteria. There was some consistency in findings for mood and estradiol levels, with associations between estradiol and depression and emotional tone and risk taking. Results were less consistent for studies assessing other mood and behavioral outcomes. Most studies were cross-sectional in design; assay methodologies used in older studies may lack the precision to detect early pubertal hormone levels.

CONCLUSION

Three longitudinal and several cross-sectional studies indicate potential associations between estradiol and certain mood or affective states, especially depression and mood variability though there are insufficient data to confirm that the rise in estradiol during puberty is causative. We believe that it is important for health professionals to take care when attributing adolescent psychopathology to puberty hormones, as the current data supporting these assertions are limited.

Estrogens are neuroprotective factors for hypertensive encephalopathy

Estrogens are neuroprotective factors for brain diseases, including hypertensive encephalopathy. In particular, the hippocampus is highly damaged by high blood pressure, with several hippocampus functions being altered in humans and animal models of hypertension. Working with a genetic model of primary hypertension, the spontaneously hypertensive rat (SHR), we have shown that SHR present decreased dentate gyrus neurogenesis, astrogliosis, low expression of brain derived neurotrophic factor (BDNF), decreased number of neurons in the hilus of the dentate gyrus, increased basal levels of the estrogen-synthesizing enzyme aromatase, and atrophic dendritic arbor with low spine density in the CA1 region compared to normotensive Wistar Kyoto (WKY) ratsl. Changes also occur in the hypothalamus of SHR, with increased expression of the hypertensinogenic peptide arginine vasopressin (AVP) and its V1b receptor. Following chronic estradiol treatment, SHR show decreased blood pressure, enhanced hippocampus neurogenesis, decreased the reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus, increased neuronal number in the hilus of the dentate gyrus, further increased the hyperexpression of aromatase and replaced spine number with remodeling of the dendritic arbor of the CA1 region. We have detected by qPCR the estradiol receptors ERα and ERβ in hippocampus from both SHR and WKY rats, suggesting direct effects of estradiol on brain cells. We hypothesize that a combination of exogenously given estrogens plus those locally synthesized by estradiol-stimulated aromatase may better alleviate the hippocampal and hypothalamic encephalopathy of SHR. This article is part of a Special Issue entitled "Sex steroids and brain disorders".

Molecular signature of rapid estrogen regulation of synaptic connectivity and cognition

There is now a growing appreciation that estrogens are capable of rapidly activating a number of signaling cascades within the central nervous system. In addition, there are an increasing number of studies reporting that 17β-estradiol, the major biologically active estrogen, can modulate cognition within a rapid time frame. Here we review recent studies that have begun to uncover the molecular and cellular framework which contributes to estrogens ability to rapidly modulate cognition. We first describe the mechanisms by which estrogen receptors (ERs) can couple to intracellular signaling cascades, either directly, or via the transactivation of other receptors. Subsequently, we review the evidence that estrogen can rapidly modulate both neuronal function and structure in the hippocampus and the cortex. Finally, we will discuss how estrogens may influence cognitive function through the modulation of neuronal structure, and the implications this may have on the treatment of a range of brain disorders.

Brain-derived neurotrophic factor and addiction: Pathological versus therapeutic effects on drug seeking

Many abused drugs lead to changes in endogenous brain-derived neurotrophic factor (BDNF) expression in neural circuits responsible for addictive behaviors. BDNF is a known molecular mediator of memory consolidation processes, evident at both behavioral and neurophysiological levels. Specific neural circuits are responsible for storing and executing drug-procuring motor programs, whereas other neural circuits are responsible for the active suppression of these "seeking" systems. These seeking-circuits are established as associations are formed between drug-associated cues and the conditioned responses they elicit. Such conditioned responses (e.g. drug seeking) can be diminished either through a passive weakening of seeking- circuits or an active suppression of those circuits through extinction. Extinction learning occurs when the association between cues and drug are violated, for example, by cue exposure without the drug present. Cue exposure therapy has been proposed as a therapeutic avenue for the treatment of addictions. Here we explore the role of BDNF in extinction circuits, compared to seeking-circuits that "incubate" over prolonged withdrawal periods. We begin by discussing the role of BDNF in extinction memory for fear and cocaine-seeking behaviors, where extinction circuits overlap in infralimbic prefrontal cortex (PFC). We highlight the ability of estrogen to promote BDNF-like effects in hippocampal-prefrontal circuits and consider the role of sex differences in extinction and incubation of drug-seeking behaviors. Finally, we examine how opiates and alcohol "break the mold" in terms of BDNF function in extinction circuits.

Estrogenic mediation of serotonergic and neurotrophic systems: implications for female mood disorders

Clinical research has demonstrated a significant sex difference in the occurrence of depressive disorders. Beginning at pubertal onset, women report a higher incidence of depression than men. Women are also vulnerable to the development of depressive disorders such as premenstrual dysphoric disorder, postpartum depression, and perimenopausal depression. These disorders are associated with reproductive stages involving changes in gonadal hormone levels. Specifically, female depression and female affective behaviors are influenced by estradiol levels. This review argues two major mechanisms by which estrogens influence depression and depressive-like behavior: through interactions with neurotrophic factors and through an influence on the serotonergic system. In particular, estradiol increases brain derived neurotrophic factor (BDNF) levels within the brain, and alters serotonergic expression in a receptor subtype-specific manner. We will take a regional approach, examining these effects of estrogens in the major brain areas implicated in depression. Finally, we will discuss the gaps in our current knowledge of the effects of estrogens on female depression, and the potential utility for estrogen receptor modulators in treatment for this disorder.

An organotypic brain slice preparation from adult patients with temporal lobe epilepsy

BACKGROUND

A long-term in vitro preparation of diseased brain tissue would facilitate work on human pathologies. Organotypic tissue cultures retain an appropriate neuronal form, spatial arrangement, connectivity and electrical activity over several weeks. However, they are typically prepared with tissue from immature animals. In work using tissue from adult animals or humans, survival times longer than a few days have not been reported and it is not clear that pathological neuronal activities are retained.

NEW METHOD

We modified tissue preparation procedures and used a defined culture medium to make organotypic cultures of temporal lobe tissue obtained after operations on adult patients with pharmaco-resistant mesial temporal lobe epilepsies.

RESULTS

Organototypic culture preparation and maintenance techniques were judged on criteria of morphology and the generation of epileptiform activities. Short-duration (30-100 ms) interictal-like population activities were initiated spontaneously in either the subiculum, dentate gyrus or the CA2/CA3 region, but not the cortex, for up to 3-4 weeks in culture. Ictal-like discharges, of duration greater than 10s, were induced by convulsants. Epileptiform activities were modulated by both glutamatergic and GABAergic receptor antagonists.

COMPARISON WITH EXISTING METHODS

Our methods now permit the maintenance in organotypic culture of epileptic adult human tissue, generating appropriate epileptiform activity over 3-4 weeks.

CONCLUSIONS

We have shown that characteristic morphology and pathological activities are maintained in organotypic cultures of adult human tissue. These cultures should permit studies on the effects of prolonged drug treatments and long-term procedures such as viral transduction.

17β-Estradiol regulates histone alterations associated with memory consolidation and increases Bdnf promoter acetylation in middle-aged female mice

Histone acetylation is essential for hippocampal memory formation in young adult rodents. Although dysfunctional histone acetylation has been associated with age-related memory decline in male rodents, little is known about whether histone acetylation is altered by aging in female rodents. In young female mice, the ability of 17β-estradiol (E₂) to enhance object recognition memory consolidation requires histone H3 acetylation in the dorsal hippocampus. However, the extent to which histone acetylation is regulated by E₂ in middle-aged females is unknown. The mnemonic benefits of E₂ in aging females appear to be greatest in middle age, and so pinpointing the molecular mechanisms through which E₂ enhances memory at this age could lead to the development of safer and more effective treatments for maintaining memory function without the side effects of current therapies. Here, we show that dorsal hippocampal infusion of E₂ rapidly enhanced object recognition and spatial memory, and increased histone H3 acetylation in the dorsal hippocampus, while also significantly reducing levels of histone deacetylase (HDAC2 and HDAC3) proteins. E₂ specifically increased histone H3 acetylation at Bdnf promoters pII and pIV in the dorsal hippocampus of both young and middle-aged mice, despite age-related decreases in pI and pIV acetylation. Furthermore, levels of mature BDNF and pro-BDNF proteins in the dorsal hippocampus were increased by E₂ in middle-aged females. Together, these data suggest that the middle-aged female dorsal hippocampus remains epigenetically responsive to E₂, and that E₂ may enhance memory in middle-aged females via epigenetic regulation of Bdnf.

Regulation of object recognition and object placement by ovarian sex steroid hormones

The ovarian hormones 17β-estradiol (E2) and progesterone (P4) are potent modulators of hippocampal memory formation. Both hormones have been demonstrated to enhance hippocampal memory by regulating the cellular and molecular mechanisms thought to underlie memory formation. Behavioral neuroendocrinologists have increasingly used the object recognition and object placement (object location) tasks to investigate the role of E2 and P4 in regulating hippocampal memory formation in rodents. These one-trial learning tasks are ideal for studying acute effects of hormone treatments on different phases of memory because they can be administered during acquisition (pre-training), consolidation (post-training), or retrieval (pre-testing). This review synthesizes the rodent literature testing the effects of E2 and P4 on object recognition (OR) and object placement (OP), and the molecular mechanisms in the hippocampus supporting memory formation in these tasks. Some general trends emerge from the data. Among gonadally intact females, object memory tends to be best when E2 and P4 levels are elevated during the estrous cycle, pregnancy, and in middle age. In ovariectomized females, E2 given before or immediately after testing generally enhances OR and OP in young and middle-aged rats and mice, although effects are mixed in aged rodents. Effects of E2 treatment on OR and OP memory consolidation can be mediated by both classical estrogen receptors (ERα and ERβ), and depend on glutamate receptors (NMDA, mGluR1) and activation of numerous cell signaling cascades (e.g., ERK, PI3K/Akt, mTOR) and epigenetic processes (e.g., histone acetylation, DNA methylation). Acute P4 treatment given immediately after training also enhances OR and OP in young and middle-aged ovariectomized females by activating similar cell signaling pathways as E2 (e.g., ERK, mTOR). The few studies that have administered both hormones in combination suggest that treatment can enhance OR and OP, but that effects are highly dependent on factors such as dose and timing of administration. In addition to providing more detail on these general conclusions, this review will discuss directions for future avenues of research into the hormonal regulation of object memory.

17α-Oestradiol-induced neuroprotection in the brain of spontaneously hypertensive rats

17β-oestradiol is a powerful neuroprotective factor for the brain abnormalities of spontaneously hypertensive rats (SHR). 17α-Oestradiol, a nonfeminising isomer showing low affinity for oestrogen receptors, is also endowed with neuroprotective effects in vivo and in vitro. We therefore investigated whether treatment with 17α-oestradiol prevented pathological changes of the hippocampus and hypothalamus of SHR. We used 20-week-old male SHR with a blood pressure of approximately 170 mmHg receiving s.c. a single 800 μg pellet of 17α-oestradiol dissolved in cholesterol or vehicle only for 2 weeks Normotensive Wistar-Kyoto (WKY) rats were used as controls. 17α-Oestradiol did not modify blood pressure, serum prolactin, 17β-oestradiol levels or the weight of the testis and pituitary of SHR. In the brain, we analysed steroid effects on hippocampus Ki67+ proliferating cells, doublecortin (DCX) positive neuroblasts, glial fibrillary acidic protein (GFAP)+ astrocyte density, aromatase immunostaining and brain-derived neurotrophic factor (BDNF) mRNA. In the hypothalamus, we determined arginine vasopressin (AVP) mRNA. Treatment of SHR with 17α-oestradiol enhanced the number of Ki67+ in the subgranular zone and DCX+ cells in the inner granule cell layer of the dentate gyrus, increased BDNF mRNA in the CA1 region and gyrus dentatus, decreased GFAP+ astrogliosis in the CA1 subfield, and decreased hypothalamic AVP mRNA. Aromatase expression was unmodified. By contrast to SHR, normotensive WKY rats were unresponsive to 17α-oestradiol. These data indicate a role for 17α-oestradiol as a protective factor for the treatment of hypertensive encephalopathy. Furthermore, 17α-oestradiol is weakly oestrogenic in the periphery and can be used in males.

Dynorphin up-regulation in the dentate granule cell mossy fiber pathway following chronic inhibition of GluN2B-containing NMDAR is associated with increased CREB (Ser 133) phosphorylation, but is independent of BDNF/TrkB signaling pathways

Emerging evidence suggests that neuronal responses to N-methyl-d-aspartate (NMDAR) activation/inactivation are influenced by subunit composition. For example, activation of synaptic NMDAR (comprised of GluN2A>GluN2B) phosphorylates cAMP-response-element-binding protein (CREB) at Ser 133, induces BDNF expression and promotes neuronal survival. Activation of extrasynaptic NMDAR (comprised of GluN2B>GluN2) dephosphorylates CREB (Ser 133), reduces BDNF expression and triggers neuronal death. These results led us to hypothesize that chronic inhibition of GluN2B-containing NMDAR would increase CREB (Ser 133) phosphorylation, increase BDNF levels and subsequently alter downstream dynorphin (DYN) and neuropeptide Y (NPY) expression. We focused on DYN and NPY because these neuropeptides can decrease excitatory neurotransmission and seizure occurrence and we reported previously that seizure-like events are reduced following chronic treatment with GluN2B antagonists. Consistent with our hypothesis, chronic treatment (17-21days) of hippocampal slice cultures with the GluN2B-selective antagonists ifenprodil or Ro25,6981 increased both CREB (Ser 133) phosphorylation and granule cell mossy fiber pathway DYN expression. Similar treatment with the non-subtype-selective NMDAR antagonists d-APV or memantine had no significant effect on either CREB (Ser 133) phosphorylation or DYN expression. In contrast to our hypothesis, BDNF levels were decreased following chronic treatment with Ro25,6981, but not ifenprodil, d-APV or memantine. Blockade of BDNF actions and TrkB activation did not significantly augment hilar DYN expression in vehicle-treated cultures and had no effect in Ro25,6981 treated cultures. These findings suggest that chronic exposure to GluN2B-selective NMDAR antagonists increased DYN expression through a putatively pCREB-dependent, but BDNF/TrkB-independent mechanism.

Sex differences and the modulating effects of gonadal hormones on basal and the stressor-decreased newly proliferative cells and neuroblasts in dentate gyrus

This study was undertaken to assess sex differences and the modulating effects of gonad intactness and the estrous phase on basal and the stressor-decreased cell proliferation and early differentiation in Balb/C mouse dentate gyrus (DG). Besides, we compared the stress-reversing effects exerted by the presence of male and female Balb/C mouse odors in stressed male and female mouse DG in this regard. Female mice had lower baselines in the number of newly proliferated cells and neuroblasts than male mice. Although the stressor induced decreases in the number of newly proliferative cells and neuroblasts in both male and female DG, an obvious decrease in neuronal lineage commitment was observed in female DG. Moreover, ovariectomy induced decreases in baselines in the number of proliferative cells and neuroblasts but did not affect the stressor-induced decrease in neuronal lineage commitment in female DG. Interestingly, pro-estrous mice exhibited the stressor-decreased neuronal lineage commitment, while estrous and diestrous mice did not display such a decrease. Furthermore, orchidectomy did not affect basal or the stressor-decreased newly proliferative cells or neuroblasts in male DG. Finally, male odors were less effective than female odors in abolishing the stressor-decreased neuronal lineage commitment in female mice, while male and female odors were comparable in reversing the stressor-decreased newly proliferated cells and neuroblasts in male mice. The protective effects of mouse odors' company in the stressed male mouse DG were associated with local BDNF and NGF replenishment. Taken together, sexual differences in baselines in the number of newly proliferative cells, neuroblasts, and the sensitivity to stress-altered neuronal lineage commitment in the DG could be, in part, due to gonadal hormone differences between the two sexes. Mouse odors may reverse stressor-decreased newly proliferative cells and neuroblasts in male, but not in female, mouse DG by restoring BDNF and NGF levels.

Isoflurane exposure in newborn rats induces long-term cognitive dysfunction in males but not females

Volatile anesthetics are used widely for achieving a state of unconsciousness, yet these agents are incompletely understood in their mechanisms of action and effects on neural development. There is mounting evidence that children exposed to anesthetic agents sustain lasting effects on learning and memory. The explanation for these behavioral changes remains elusive, although acute neuronal death after anesthesia is commonly believed to be a principal cause. Rodent models have shown that isoflurane exposure in newborns induces acute neuroapoptosis and long-term cognitive impairment. However, the assessment of predisposing factors is lacking. We investigated the role of sex by delivering isoflurane to postnatal day (P)7 male and female Sprague Dawley rats for 4 h. Brain cell death was assessed 12 h later using FluoroJade C staining in the thalamus, CA1-3 regions of hippocampus, and dentate gyrus. Behavior was assessed separately using a series of object recognition tasks and a test of social memory beginning at P38. We found that isoflurane exposure significantly increased neuronal death in each brain region with no difference between sexes. Behavioral outcome was also equivalent in simple novel object recognition. However, only males were impaired in the recognition of objects in different locations and contexts. Males also exhibited deficient social memory while females were intact. The profound behavioral impairment in males relative to females, in spite of comparable cell death, suggests that males are more susceptible to long-term cognitive effects and this outcome may not be exclusively attributed to neuronal death.

Sex differences in stress reactivity of hippocampal BDNF in mice are associated with the female preponderance of decreased locomotor activity in response to restraint stress

The incidence and prevalence of depression is higher in women than in men, but the cause of this sex discrepancy remains unknown. Brain-derived neurotrophic factor (BDNF) is a key protein for maintaining neuronal integrity. The purpose of this study was to investigate the female preponderance in behavioral responsivity to restraint stress focusing on the stress reactivity of BDNF in the hippocampus. Male and female ICR mice were exposed to a 3-h session of restraint stress. Plasma corticosterone was measured by high-performance liquid chromatography. BDNF mRNA expression in the whole hippocampus was measured by quantitative real-time reverse transcription-polymerase chain reaction. Wheel-running activity was monitored during the dark period. In response to restraint stress, the increase in levels of serum corticosterone was higher in female than in male mice. Restraint stress resulted in decreased voluntary wheel-running behavior that was greater in female than male animals. In addition to these sex differences in stress reactivity, we found a significant sex difference in BDNF levels in the hippocampus of restraint-stressed mice; total BDNF levels significantly decreased in female mice, but not in male mice in response to the stress. Furthermore, BDNF exon I and IV mRNA expression also showed the same tendency. These data indicate that the reduction in levels of voluntary wheel-running activity in response to stress can be significantly influenced by sex. Moreover, our findings suggest a link between the sex differences in this behavioral response to stress and differential stress reactivity in the production of BDNF in the hippocampus.

Sex hormones and biomarkers of neuroprotection and neurodegeneration: implications for female reproductive events in bipolar disorder

OBJECTIVES

Previous studies have suggested that women with bipolar disorder are at higher risk for mood episodes during periods of intense hormonal fluctuation (e.g., premenstrual, postpartum, perimenopause). There is converging literature showing that estrogen and progesterone can modulate neurotransmitter systems and intracellular signaling pathways known to be affected by mood stabilizing agents. Here, we critically review clinical aspects of reproductive cycle events in women with bipolar disorder and preclinical studies, with a focus on the functional interactions between sex hormones and biomarkers of neuroprotection and neurodegeneration that are thought to be involved in the neurobiology of bipolar disorder: brain-derived neurotrophic factor, oxidative stress, and inflammation.

METHODS

A MedLine search using estrogen, progesterone, brain-derived neurotrophic factor, oxidative stress, and inflammation as key words was conducted.

RESULTS

Data showed that estrogen and progesterone closely interact with brain-derived neurotrophic factor, oxidative stress, and inflammation pathways.

CONCLUSIONS

This relationship between sex hormones and the pathways of neuroprotection/neurodegeneration may be relevant to the psychopathological aspects of bipolar disorder in women.

Estrogen Regulates Protein Synthesis and Actin Polymerization in Hippocampal Neurons through Different Molecular Mechanisms

Estrogen rapidly modulates hippocampal synaptic plasticity by activating selective membrane-associated receptors. Reorganization of the actin cytoskeleton and stimulation of mammalian target of rapamycin (mTOR)-mediated protein synthesis are two major events required for the consolidation of hippocampal long-term potentiation and memory. Estradiol regulates synaptic plasticity by interacting with both processes, but the underlying molecular mechanisms are not yet fully understood. Here, we used acute rat hippocampal slices to analyze the mechanisms underlying rapid changes in mTOR activity and actin polymerization elicited by estradiol. Estradiol-induced mTOR phosphorylation was preceded by rapid and transient activation of both extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) and by phosphatase and tensin homolog (PTEN) degradation. These effects were prevented by calpain and ERK inhibitors. Estradiol-induced mTOR stimulation did not require activation of classical estrogen receptors (ER), as specific ERα and ERβ agonists (PPT and DPN, respectively) failed to mimic this effect, and ER antagonists could not block it. Estradiol rapidly activated both RhoA and p21-activated kinase (PAK). Furthermore, a specific inhibitor of RhoA kinase (ROCK), H1152, and a potent and specific PAK inhibitor, PF-3758309, blocked estradiol-induced cofilin phosphorylation and actin polymerization. ER antagonists also blocked these effects of estrogen. Consistently, both PPT and DPN stimulated PAK and cofilin phosphorylation as well as actin polymerization. Finally, the effects of estradiol on actin polymerization were insensitive to protein synthesis inhibitors, but its stimulation of mTOR activity was impaired by latrunculin A, a drug that disrupts actin filaments. Taken together, our results indicate that estradiol regulates local protein synthesis and cytoskeletal reorganization via different molecular mechanisms and signaling pathways.

Rapid effects of oestrogen on synaptic plasticity: interactions with actin and its signalling proteins

Oestrogen rapidly enhances fast excitatory postsynaptic potentials, facilitates long-term potentiation (LTP) and increases spine numbers. Each effect likely contributes to the influence of the steroid on cognition and memory. In the present review, we first describe a model for the substrates of LTP that includes an outline of the synaptic events occurring during induction, expression and consolidation. Briefly, critical signalling pathways involving the small GTPases RhoA and Rac/Cdc42 are activated by theta burst-induced calcium influx and initiate actin filament assembly via phosphorylation (inactivation) of cofilin. Reorganisation of the actin cytoskeleton changes spine and synapse morphology, resulting in increased concentrations of AMPA receptors at stimulated contacts. We then use the synaptic model to develop a specific hypothesis about how oestrogen affects both baseline transmission and plasticity. Brief infusions of 17β-oestradiol (E2 ) reversibly stimulate the RhoA, cofilin phosphorylation and actin polymerisation cascade of the LTP machinery; blocking this eliminates the effects of the steroid on transmission. We accordingly propose that E2 induces a weak form of LTP and thereby increases synaptic responses, a hypothesis that also accounts for how it markedly enhances theta burst induced potentiation. Although the effects of E2 on the cytoskeleton could be a result of the direct activation of small GTPases by oestrogen receptors on the synaptic membrane, the hormone also activates tropomyosin-related kinase B receptors for brain-derived neurotrophic factor, a neurotrophin that engages the RhoA-cofilin sequence and promotes LTP. The latter observations raise the possibility that E2 produces its effects on synaptic physiology via transactivation of neighbouring receptors that have prominent roles in the management of spine actin, synaptic physiology and plasticity.

The influence of stress at puberty on mood and learning: role of the α4βδ GABAA receptor

It is well-known that the onset of puberty is associated with changes in mood as well as cognition. Stress can have an impact on these outcomes, which in many cases, can be more influential in females, suggesting that gender differences exist. The adolescent period is a vulnerable time for the onset of certain psychopathologies, including anxiety disorders, depression and eating disorders, which are also more prevalent in females. One factor which may contribute to stress-triggered anxiety at puberty is the GABAA receptor (GABAR), which is known to play a pivotal role in anxiety. Expression of α4βδ GABARs increases on the dendrites of CA1 pyramidal cells at the onset of puberty in the hippocampus, part of the limbic circuitry which governs emotion. This receptor is a sensitive target for the stress steroid 3α-OH-5[α]β-pregnan-20-one or [allo]pregnanolone, which paradoxically reduces inhibition and increases anxiety during the pubertal period (post-natal day ∼35-44) of female mice in contrast to its usual effect to enhance inhibition and reduce anxiety. Spatial learning and synaptic plasticity are also adversely impacted at puberty, likely a result of increased expression of α4βδ GABARs on the dendritic spines of CA1 hippocampal pyramidal cells, which are essential for consolidation of memory. This review will focus on the role of these receptors in mediating behavioral changes at puberty. Stress-mediated changes in mood and cognition in early adolescence may have relevance for the expression of psychopathologies in adulthood.

α4βδ GABAA receptors and tonic inhibitory current during adolescence: effects on mood and synaptic plasticity

The onset of puberty is associated with alterations in mood as well as changes in cognitive function, which can be more pronounced in females. Puberty onset in female mice is associated with increased expression of α4βδ γ-amino-butyric acid-A (GABAA) receptors (GABARs) in CA1 hippocampus. These receptors, which normally have low expression in this central nervous system (CNS) site, emerge along the apical dendrites as well as on the dendritic spines of pyramidal neurons, adjacent to excitatory synapses where they underlie a tonic inhibition that shunts excitatory current and impairs activation of N-methyl-D-aspartate (NMDA) receptors, the trigger for synaptic plasticity. As would be expected, α4βδ expression at puberty also prevents long-term potentiation (LTP), an in vitro model of learning which is a function of network activity, induced by theta burst stimulation of the Schaffer collaterals to the CA1 hippocampus. The expression of these receptors also impairs spatial learning in a hippocampal-dependent task. These impairments are not seen in δ knock-out (-/-) mice, implicating α4βδ GABARs. α4βδ GABARs are also a sensitive target for steroids such as THP ([allo]pregnanolone or 3α-OH-5α[β]-pregnan-20-one), which are dependent upon the polarity of GABAergic current. It is well-known that THP can increase depolarizing current gated by α4βδ GABARs, but more recent data suggest that THP can reduce hyperpolarizing current by accelerating receptor desensitization. At puberty, THP reduces the hyperpolarizing GABAergic current, which removes the shunting inhibition that impairs synaptic plasticity and learning at this time. However, THP, a stress steroid, also increases anxiety, via its action at α4βδ GABARs because it is not seen in δ(-/-) mice. These findings will be discussed as well as their relevance to changes in mood and cognition at puberty, which can be a critical period for certain types of learning and when anxiety disorders and mood swings can emerge.