Expression characteristics of the cyp19a1b aromatase gene and its response to 17β-estradiol treatment in largemouth bass (Micropterus salmoides)

To investigate the regulatory role of the cyp19a1b aromatase gene in the sexual differentiation of largemouth bass (Micropterus salmoides, LMB), we obtained the full-length cDNA sequence of cyp19a1b using rapid amplification of cDNA ends technique. Tissue expression characteristics and feedback with 17-β-estradiol (E2) were determined using quantitative real-time PCR (qRT-PCR), while gonad development was assessed through histological section observations. The cDNA sequence of LMB cyp19a1b was found to be1950 base pairs (bp) in length, including a 5' untranslated region of 145 bp, a 3' untranslated region of 278 bp, and an open reading frame encoding a protein consisting of 1527 bp that encoded 508 amino acids. The qRT-PCR results indicated that cyp19a1b abundantly expressed in the brain, followed by the gonads, and its expression in the ovaries was significantly higher than that observed in the testes (P < 0.05). After feeding fish with E2 for 30 days, the expression of cyp19a1b in the pseudo-female gonads (XY-F) was significantly higher than that in males (XY-M) (P < 0.05), whereas expression did not differ significantly between XX-F and XY-F fish (P > 0.05). Although the expression of cyp19a1b in XY-F and XX-F fish was not significantly different after 60 days (P>0.05), both exhibited significantly higher levels than that of XY-M fish (P<0.05). Histological sections analysis showed the presence of oogonia in both XY-F and XX-F fish at 30 days, while spermatogonia were observed in XY-M fish. At 60 days, primary oocytes were abundantly observed in both XY-F and XX-F fish, while a few spermatogonia were visible in XY-M fish. At 90 days, the histological sections' results showed that a large number of oocytes were visible in XY-F and XX-F fish. Additionally, the gonads of XY-M fish contained numerous spermatocytes. These results suggest that cyp19a1b plays a pivotal role in the development of ovaries and nervous system development in LMB.

Sex biology in amyotrophic lateral sclerosis

Although sex differences in amyotrophic lateral sclerosis (ALS) have not been studied systematically, numerous clinical and preclinical studies have shown sex to be influential in disease prognosis. Moreover, with the development of advanced imaging tools, the difference between male and female brain in structure and function and their response to neurodegeneration are more definitive. As discussed in this review, ALS patients exhibit a sex bias pertaining to the features of the disease, and their clinical, pathological, (and pathophysiological) phenotypes. Several epidemiological studies have indicated that this sex disparity stems from various aetiologies, including sex-specific brain structure and neural functioning, genetic predisposition, age, gonadal hormones, susceptibility to traumatic brain injury (TBI)/head trauma and lifestyle factors.

Aging with TBI vs. Aging: 6-month temporal profiles for neuropathology and astrocyte activation converge in behaviorally relevant thalamocortical circuitry of male and female rats

Traumatic brain injury (TBI) manifests late-onset and persisting clinical symptoms with implications for sex differences and increased risk for the development of age-related neurodegenerative diseases. Few studies have evaluated chronic temporal profiles of neuronal and glial pathology that include sex as a biological variable. After experimental diffuse TBI, late-onset and persisting somatosensory hypersensitivity to whisker stimulation develops at one-month post-injury and persists to at least two months post-injury in male rats, providing an in vivo model to evaluate the temporal profile of pathology responsible for morbidity. Whisker somatosensation is dependent on signaling through the thalamocortical relays of the whisker barrel circuit made up of glutamatergic projections between the ventral posteromedial nucleus of the thalamus (VPM) and primary somatosensory barrel cortex (S1BF) with inhibitory (GABA) innervation from the thalamic reticular nucleus (TRN) to the VPM. To evaluate the temporal profiles of pathology, male and female Sprague Dawley rats ( n = 5-6/group) were subjected to sham surgery or midline fluid percussion injury (FPI). At 7-, 56-, and 168-days post-injury (DPI), brains were processed for amino-cupric silver stain and glial fibrillary acidic protein (GFAP) immunoreactivity, where pixel density of staining was quantified to determine the temporal profile of neuropathology and astrocyte activation in the VPM, S1BF, and TRN. FPI induced significant neuropathology in all brain regions at 7 DPI. At 168 DPI, neuropathology remained significantly elevated in the VPM and TRN, but returned to sham levels in the S1BF. GFAP immunoreactivity was increased as a function of FPI and DPI, with an FPI × DPI interaction in all regions and an FPI × Sex interaction in the S1BF. The interactions were driven by increased GFAP immunoreactivity in shams over time in the VPM and TRN. In the S1BF, GFAP immunoreactivity increased at 7 DPI and declined to age-matched sham levels by 168 DPI, while GFAP immunoreactivity in shams significantly increased between 7 and 168 days. The FPI × Sex interaction was driven by an overall greater level of GFAP immunoreactivity in FPI males compared to FPI females. Increased GFAP immunoreactivity was associated with an increased number of GFAP-positive soma, predominantly at 7 DPI. Overall, these findings indicate that FPI, time post-injury, sex, region, and aging with injury differentially contribute to chronic changes in neuronal pathology and astrocyte activation after diffuse brain injury. Thus, our results highlight distinct patterns of pathological alterations associated with the development and persistence of morbidity that supports chronic neuropathology, especially within the thalamus. Further, data indicate a convergence between TBI-induced and age-related pathology where further investigation may reveal a role for divergent astrocytic phenotypes associated with increased risk for neurodegenerative diseases.

Hippocampus-based behavioral, structural, and molecular dynamics across the estrous cycle

The activity of neurons in the rodent hippocampus contributes to diverse behaviors, with the activity of ventral hippocampal neurons affecting behaviors related to anxiety and emotion regulation, and the activity of dorsal hippocampal neurons affecting performance in learning- and memory-related tasks. Hippocampal cells also express receptors for ovarian hormones, estrogen and progesterone, and are therefore affected by physiological fluctuations of those hormones that occur over the rodent estrous cycle. In this review, we discuss the effects of cycling ovarian hormones on hippocampal physiology. Starting with behavior, we explore the role of the estrous cycle in regulating hippocampus-dependent behaviors. We go on to detail the cellular mechanisms through which cycling estrogen and progesterone, through changes in the structural and functional properties of hippocampal neurons, may be eliciting these changes in behavior. Then, providing a basis for these cellular changes, we outline the epigenetic, chromatin regulatory mechanisms through which ovarian hormones, by binding to their receptors, can affect the regulation of behavior- and synaptic plasticity-related genes in hippocampal neurons. We also highlight an unconventional role that chromatin dynamics may have in regulating neuronal function across the estrous cycle, including in sex hormone-driven X chromosome plasticity and hormonally-induced epigenetic priming. Finally, we discuss directions for future studies and the translational value of the rodent estrous cycle for understanding the effects of the human menstrual cycle on hippocampal physiology and brain disease risk.

Sex, aging and immunity in multiple sclerosis and experimental autoimmune encephalomyelitis: An intriguing interaction

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) with a profound neurodegenerative component early in the disease pathogenesis. Age is a factor with a well-described effect on the primary disease phenotype, namely, the relapsing-remitting vs. the primary progressive disease. Moreover, aging is a prominent factor contributing to the transition from relapsing-remitting MS (RRMS) to secondary progressive disease. However, sex also seems to, at least in part, dictate disease phenotype and evolution, as evidenced in humans and in animal models of the disease. Sex-specific gene expression profiles have recently elucidated an association with differential immunological signatures in the context of experimental disease. This review aims to summarize current knowledge stemming from experimental autoimmune encephalomyelitis (EAE) models regarding the effects of sex, either independently or as a factor combined with aging, on disease phenotype, with relevance to the immune system and the CNS.

The interaction of membrane estradiol receptors and metabotropic glutamate receptors in adaptive and maladaptive estradiol-mediated motivated behaviors in females

Estrogen receptors were initially identified as intracellular, ligand-regulated transcription factors that result in genomic change upon ligand binding. However, rapid estrogen receptor signaling initiated outside of the nucleus was also known to occur via mechanisms that were less clear. Recent studies indicate that these traditional receptors, estrogen receptor α and estrogen receptor β, can also be trafficked to act at the surface membrane. Signaling cascades from these membrane-bound estrogen receptors (mERs) can rapidly alter cellular excitability and gene expression, particularly through the phosphorylation of CREB. A principal mechanism of neuronal mER action has been shown to occur through glutamate-independent transactivation of metabotropic glutamate receptors (mGlu), which elicits multiple signaling outcomes. The interaction of mERs with mGlu has been shown to be important in many diverse functions in females, including driving motivated behaviors. Experimental evidence suggests that a large part of estradiol-induced neuroplasticity and motivated behaviors, both adaptive and maladaptive, occurs through estradiol-dependent mER activation of mGlu. Herein we will review signaling through estrogen receptors, both "classical" nuclear receptors and membrane-bound receptors, as well as estradiol signaling through mGlu. We will focus on how the interactions of these receptors and their downstream signaling cascades are involved in driving motivated behaviors in females, discussing a representative adaptive motivated behavior (reproduction) and maladaptive motivated behavior (addiction).

Allopregnanolone Improves Locomotor Activity and Arousal in the Aged CGG Knock-in Mouse Model of Fragile X-Associated Tremor/Ataxia Syndrome

Carriers of the fragile X premutation (PM) can develop a variety of early neurological symptoms, including depression, anxiety and cognitive impairment as well as being at risk for developing the late-onset fragile X-associated tremor/ataxia syndrome (FXTAS). The absence of effective treatments for FXTAS underscores the importance of developing efficacious therapies to reduce the neurological symptoms in elderly PM carriers and FXTAS patients. A recent preliminary study reported that weekly infusions of Allopregnanolone (Allop) may improve deficits in executive function, learning and memory in FXTAS patients. Based on this study we examined whether Allop would improve neurological function in the aged CGG knock-in (CGG KI) dutch mouse, B6.129P2(Cg)-Fmr1^tm2Cgr/Cgr, that models much of the symptomatology in PM carriers and FXTAS patients. Wild type and CGG KI mice received 10 weekly injections of Allop (10 mg/kg, s.c.), followed by a battery of behavioral tests of motor function, anxiety, and repetitive behavior, and 5-bromo-2'-deoxyuridine (BrdU) labeling to examine adult neurogenesis. The results provided evidence that Allop in CGG KI mice normalized motor performance and reduced thigmotaxis in the open field, normalized repetitive digging behavior in the marble burying test, but did not appear to increase adult neurogenesis in the hippocampus. Considered together, these results support further examination of Allop as a therapeutic strategy in patients with FXTAS.

Role of glial cells in the generation of sex differences in neurodegenerative diseases and brain aging

Diseases and aging-associated alterations of the nervous system often show sex-specific characteristics. Glial cells play a major role in the endogenous homeostatic response of neural tissue, and sex differences in the glial transcriptome and function have been described. Therefore, the possible role of these cells in the generation of sex differences in pathological alterations of the nervous system is reviewed here. Studies have shown that glia react to pathological insults with sex-specific neuroprotective and regenerative effects. At least three factors determine this sex-specific response of glia: sex chromosome genes, gonadal hormones and neuroactive steroid hormone metabolites. The sex chromosome complement determines differences in the transcriptional responses in glia after brain injury, while gonadal hormones and their metabolites activate sex-specific neuroprotective mechanisms in these cells. Since the sex-specific neuroprotective and regenerative activity of glial cells causes sex differences in the pathological alterations of the nervous system, glia may represent a relevant target for sex-specific therapeutic interventions.

Astroglial cells as neuroendocrine targets in forebrain development: Implications for sex differences in psychiatric disease

Astroglial cells are the most abundant cell type in the mammalian brain. They are implicated in almost every aspect of brain physiology, including maintaining homeostasis, building and maintaining the blood brain barrier, and the development and maturation of neuronal networks. Critically, astroglia also express receptors for gonadal sex hormones, respond rapidly to gonadal hormones, and are able to synthesize hormones. Thus, they are positioned to guide and mediate sexual differentiation of the brain, particularly neuronal networks in typical and pathological conditions. In this review, we describe astroglial involvement in the organization and development of the brain, and consider known sex differences in astroglial responses to understand how astroglial cell-mediated organization may play a role in forebrain sexual dimorphisms in human populations. Finally, we consider how sexually dimorphic astroglial responses and functions in development may lead to sex differences in vulnerability for neuropsychiatric disorders.

G Protein-Coupled Estrogen Receptor Immunoreactivity in the Rat Hypothalamus Is Widely Distributed in Neurons, Astrocytes, and Oligodendrocytes, Fluctuates during the Estrous Cycle, and Is Sexually Dimorphic

INTRODUCTION

The membrane-associated G protein-coupled estrogen receptor 1 (GPER) mediates the regulation by estradiol of arginine-vasopressin immunoreactivity in the supraoptic and paraventricular hypothalamic nuclei of female rats and is involved in the estrogenic control of hypothalamic regulated functions, such as food intake, sexual receptivity, and lordosis behavior.

OBJECTIVE

To assess GPER distribution in the rat hypothalamus.

METHODS

GPER immunoreactivity was assessed in different anatomical subdivisions of five selected hypothalamic regions of young adult male and cycling female rats: the arcuate nucleus, the lateral hypothalamus, the paraventricular nucleus, the supraoptic nucleus, and the ventromedial hypothalamic nucleus. GPER immunoreactivity was colocalized with NeuN as a marker of mature neurons, GFAP as a marker of astrocytes, and CC1 as a marker of mature oligodendrocytes.

RESULTS

GPER immunoreactivity was detected in hypothalamic neurons, astrocytes, and oligodendrocytes. Sex and regional differences and changes during the estrous cycle were detected in the total number of GPER-immunoreactive cells and in the proportion of neurons, astrocytes, and oligodendrocytes that were GPER-immunoreactive.

CONCLUSIONS

These findings suggest that estrogenic regulation of hypothalamic function through GPER may be different in males and females and may fluctuate during the estrous cycle in females.

It takes a neural village: Circuit-based approaches for estrogenic regulation of episodic memory

Cognitive behaviors, such as episodic memory formation, are complex processes involving coordinated activity in multiple brain regions. However, much of the research on hormonal regulation of cognition focuses on manipulation of one region at a time or provides a single snapshot of how a systemic treatment affects multiple brain regions without investigating how these regions might interact to mediate hormone effects. Here, we use estrogenic regulation of episodic memory as an example of how circuit-based approaches may be incorporated into future studies of hormones and cognition. We first review basic episodic memory circuitry, rapid mechanisms by which 17β-estradiol can alter circuit activity, and current knowledge about 17β-estradiol's effects on episodic memory. Next, we outline approaches that researchers can employ to consider circuit effects in their estrogen research and provide examples of how these methods have been used to examine hormonal regulation of memory and other behaviors.

Lipotoxicity, neuroinflammation, glial cells and oestrogenic compounds

The high concentrations of free fatty acids as a consequence of obesity and being overweight have become risk factors for the development of different diseases, including neurodegenerative ailments. Free fatty acids are strongly related to inflammatory events, causing cellular and tissue alterations in the brain, including cell death, deficits in neurogenesis and gliogenesis, and cognitive decline. It has been reported that people with a high body mass index have a higher risk of suffering from Alzheimer's disease. Hormones such as oestradiol not only have beneficial effects on brain tissue, but also exert some adverse effects on peripheral tissues, including the ovary and breast. For this reason, some studies have evaluated the protective effect of oestrogen receptor (ER) agonists with more specific tissue activities, such as the neuroactive steroid tibolone. Activation of ERs positively affects the expression of pro-survival factors and cell signalling pathways, thus promoting cell survival. This review aims to discuss the relationship between lipotoxicity and the development of neurodegenerative diseases. We also elaborate on the cellular and molecular mechanisms involved in neuroprotection induced by oestrogens.

[Reactive changes in morphological and morphometric parameters of immunopositive astrocytes of the amygdala in response to hormone level in absence epilepsy]

AIM

To study the changes in the morphological and morphometric parameters of immunopositive astrocytes of the amygdala in absence epilepsy depending on hormonal profile.

MATERIAL AND METHODS

Adult female WAG/Rij rats were used as experimental subjects. The astrocytes were detected on serial sections using a reaction to glial fibrillary acidic protein (GFAP) with pre-stained hematoxylin. Quantitative analysis was carried out for a 204.8´153.6 μm² field of view.

RESULTS

In the control group, astrocytes had a relatively regular stellate form and GFAP was moderately expressed in their bodies and processes. The number of astrocytes was 18.20±2.87, and their area was 164±3.29 μm². After ovariectomy, a high expression of the protein, both in the bodies and in the processes of astrocytes, increasing the cell size to 188.85±4.97 μm² (p<0.05) was observed. The astrocytes increased to 34.55±3.03 (p<0.05). In addition, the deformation of the processes and their diffuse defibration were observed. After hormone replacement therapy, a decrease in GFAP expression was detected, the area of astrocytes became smaller in comparison with the group after ovariectomy: 173.54±5.48 μm² (p<0.05). Morphological changes in glial cells were manifested as a decrease in the size of their bodies, the processes became smooth without diffuse sprouting and swelling, which is probably associated with neuroprotective functions of estradiol.

CONCLUSION

Thus, the results of our study demonstrated that the deficiency of female sex hormones led to the increase in both the amount and area of astrocytes in the anterior cortical nucleus of the amygdala, and hormone replacement therapy positively affected the structural and quantitative characteristics of astrocytes due to the endogenous protective role of estradiol.

Chronic Antipsychotic Treatment Modulates Aromatase (CYP19A1) Expression in the Male Rat Brain

Antipsychotic drugs, known as the antagonists of dopaminergic receptors, may also affect a large spectrum of other molecular signaling pathways in the brain. Despite the numerous ongoing studies on neurosteroid action and regulation, there are no reports regarding the influence of extended treatment with typical and atypical neuroleptics on brain aromatase (CYP19A1) expression. In the present study, we assessed for the first time aromatase mRNA and protein levels in the brain of rats chronically (28 days) treated with olanzapine, clozapine, and haloperidol using quantitative real-time PCR, end-point RT-PCR, and Western blotting. Both clozapine and haloperidol, but not olanzapine treatment, led to an increase of aromatase mRNA expression in the rat brain. On the other hand, aromatase protein level remained unchanged after drug administration. These results cast a new light on the pharmacology of examined antipsychotics and contribute to a better understanding of the mechanisms responsible for their action. The present report also underlines the complex nature of potential interactions between neuroleptic pharmacological effects and physiology of brain neurosteroid pathways.

Norepinephrine control of ventromedial hypothalamic nucleus glucoregulatory neurotransmitter expression in the female rat: Role of monocarboxylate transporter function

The ventromedial hypothalamic nucleus (VMN) is a critical component of the neural circuitry that regulates glucostasis. Astrocyte glycogen is a vital reserve of glucose and its oxidizable metabolite L-lactate. In hypoglycemic female rats, estradiol-dependent augmentation of VMN glycogen phosphorylase (GP) protein requires hindbrain catecholamine input. Research here investigated the premise that norepinephrine (NE) regulation of VMN astrocyte metabolism shapes local glucoregulatory neurotransmitter signaling in this sex. Estradiol-implanted ovariectomized rats were pretreated by intra-VMN administration of the monocarboxylate transporter inhibitor alpha-cyano-4-hydroxy-cinnamic acid (4CIN) or vehicle before NE delivery to that site. NE caused 4CIN-reversible reduction or augmentation of VMN glycogen synthase and phosphorylase expression. 4CIN prevented NE stimulation of gluco-inhibitory (glutamate decarboxylase65/67) and suppression of gluco-stimulatory (neuronal nitric oxide synthase) neuron marker proteins. These outcomes imply that effects of noradrenergic stimulation of VMN astrocyte glycogen depletion on glucoregulatory transmitter signaling may be mediated, in part, by glycogen-derived substrate fuel provision. NE control of astrocyte glycogen metabolism may involve down-regulated adrenoreceptor (AR), e.g. alpha1 and alpha2, alongside amplified beta1 AR and estrogen receptor-beta signaling. Noradrenergic hypoglycemia was refractory to 4CIN, implying that additional NE-sensitive VMN glucoregulatory neurochemicals may be insensitive to monocarboxylate uptake. Augmentation of circulating free fatty acids by combinatory NE and 4CIN, but not NE alone implies that acute hypoglycemia induced here is an insufficient stimulus for mobilization of these fuels, but is adequate when paired with diminished brain monocarboxylate fuel availability.

Norepinephrine regulation of ventromedial hypothalamic nucleus metabolic transmitter biomarker and astrocyte enzyme and receptor expression: Impact of 5' AMP-activated protein kinase

The ventromedial hypothalamic energy sensor AMP-activated protein kinase (AMPK) maintains glucostasis via neurotransmitter signals that diminish [γ-aminobutyric acid] or enhance [nitric oxide] counter-regulation. Ventromedial hypothalamic nucleus (VMN) 'fuel-inhibited' neurons are sensitive to astrocyte-generated metabolic substrate stream. Norepinephrine (NE) regulates astrocyte glycogen metabolism in vitro, and hypoglycemia intensifies VMN NE activity in vivo. Current research investigated the premise that NE elicits AMPK-dependent adjustments in VMN astrocyte glycogen metabolic enzyme [glycogen synthase (GS); glycogen phosphorylase (GP)] and gluco-regulatory neuron biomarker [glutamate decarboxylase_65/67 (GAD); neuronal nitric oxide synthase (nNOS); SF-1] protein expression in male rats. We also examined whether VMN astrocytes are directly receptive to NE and if noradrenergic input regulates cellular sensitivity to the neuro-protective steroid estradiol. Intra-VMN NE correspondingly augmented or reduced VMN tissue GAD and nNOS protein despite no change in circulating glucose, data that imply that short-term exposure to NE promotes persistent improvement in VMN nerve cell energy stability. The AMPK inhibitor Compound C (Cc) normalized VMN nNOS, GS, and GP expression in NE-treated animals. NE caused AMPK-independent down-regulation of alpha₂-, alongside Cc-reversible augmentation of beta₁-adrenergic receptor protein profiles in laser-microdissected astrocytes. NE elicited divergent adjustments in astrocyte estrogen receptor-beta (AMPK-unrelated reduction) and GPR-30 (Cc-revocable increase) proteins. Outcomes implicate AMPK in noradrenergic diminution of VMN nitrergic metabolic-deficit signaling and astrocyte glycogen shunt activity. Differentiating NE effects on VMN astrocyte adrenergic and estrogen receptor variant expression suggest that noradrenergic regulation of glycogen metabolism may be mediated, in part, by one or more receptors characterized here by sensitivity to this catecholamine.

Reactivity of microglia and astrocytes after an excitotoxic injury induced by kainic acid in the rat spinal cord

After injury of the nervous system glial cells react according to the stimuli by modifying their morphology and function. Glia activation was reported in different kainic acid (KA)-induced neurodegeneration models. Here, we describe glial morphometric changes occurring in an excitotoxic KA-induced cervical spinal cord injury model. Concomitant degenerative and apoptotic processes are also reported. Male rats injected at the spinal cord C5 segment either with KA or saline were euthanized at post-injection (PI) days 1, 2, 3 or 7. Anti-IBA-1 and anti-GFAP antibodies were used to identify microglia and activated astrocytes, respectively, and to morphometrically characterized them. Fluoro-Jade B staining and TUNEL reaction were used to determine neuronal and glial degeneration and apoptosis. KA-injected group showed a significant increase in microglia number at the ipsilateral side by PI day 3. Different microglia reactive phenotypes were observed. Reactive microglia was still present by PI day 7. Astrocytes in KA-injected group showed a biphasic increase in number at PI days 1 and 3. Degenerative and apoptotic events were only observed in KA-injected animals, increasing mainly by PI day 1. Understanding the compromise of glia in different neurodegenerative processes may help to define possible common or specific therapeutic approaches directed towards neurorestorative strategies.

Profiling changes in cortical astroglial cells following chronic stress

Recent studies have suggested that cortical astroglia play an important role in depressive-like behaviors. Potential astroglial contributions have been proposed based on their known neuroplastic functions, such as glutamate recycling and synaptic plasticity. However, the specific mechanisms by which astroglial cells may contribute or protect against a depressive phenotype remain unknown. To delineate astroglial changes that accompany depressive-like behavior, we used astroglial-specific bacTRAP mice exposed to chronic variable stress (CVS) and profiled the astroglial translatome using translating ribosome affinity purification (TRAP) in conjunction with RNAseq. As expected, CVS significantly increased anxiety- and depressive-like behaviors and corticosterone levels and decreased GFAP expression in astroglia, although this did not reflect a change in the total number of astroglial cells. TRAPseq results showed that CVS decreased genes associated with astroglial plasticity: RhoGTPases, growth factor signaling, and transcription regulation, and increased genes associated with the formation of extracellular matrices such as perineuronal nets (PNNs). PNNs inhibit neuroplasticity and astroglia contribute to the formation, organization, and maintenance of PNNs. To validate our TRAPseq findings, we showed an increase in PNNs following CVS. Degradation of PNNs in the prefrontal cortex of mice exposed to CVS reversed the CVS-induced behavioral phenotype in the forced swim test. These data lend further support to the neuroplasticity hypothesis of depressive behaviors and, in particular, extend this hypothesis beyond neuronal plasticity to include an overall decrease in genes associated with cortical astroglial plasticity following CVS. Further studies will be needed to assess the antidepressant potential of directly targeting astroglial cell function in models of depression.

Sex steroid hormones as neuroprotective elements in ischemia models

Among sex steroid hormones, progesterone and estradiol have a wide diversity of physiological activities that target the nervous system. Not only are they carried by the blood stream, but also they are locally synthesized in the brain and for this reason, estradiol and progesterone are considered 'neurosteroids'. The physiological actions of both hormones range from brain development and neurotransmission to aging, illustrating the importance of a deep understanding of their mechanisms of action. In this review, we summarize key roles that estradiol and progesterone play in the brain. As numerous reports have confirmed a substantial neuroprotective role for estradiol in models of neurodegenerative disease, we focus this review on traumatic brain injury and stroke models. We describe updated data from receptor and signaling events triggered by both hormones, with an emphasis on the mechanisms that have been reported as 'rapid' or 'cytoplasmic actions'. Data showing the therapeutic effects of the hormones, used alone or in combination, are also summarized, with a focus on rodent models of middle cerebral artery occlusion (MCAO). Finally, we draw attention to evidence that neuroprotection by both hormones might be due to a combination of 'cytoplasmic' and 'nuclear' signaling.

Reduced astrocyte density underlying brain volume reduction in activity-based anorexia rats

OBJECTIVES

Severe grey and white matter volume reductions were found in patients with anorexia nervosa (AN) that were linked to neuropsychological deficits while their underlying pathophysiology remains unclear. For the first time, we analysed the cellular basis of brain volume changes in an animal model (activity-based anorexia, ABA).

METHODS

Female rats had 24 h/day running wheel access and received reduced food intake until a 25% weight reduction was reached and maintained for 2 weeks.

RESULTS

In ABA rats, the volumes of the cerebral cortex and corpus callosum were significantly reduced compared to controls by 6% and 9%, respectively. The number of GFAP-positive astrocytes in these regions decreased by 39% and 23%, total astrocyte-covered area by 83% and 63%. In neurons no changes were observed. The findings were complemented by a 60% and 49% reduction in astrocyte (GFAP) mRNA expression.

CONCLUSIONS

Volumetric brain changes in ABA animals mirror those in human AN patients. These alterations are associated with a reduction of GFAP-positive astrocytes as well as GFAP expression. Reduced astrocyte functioning could help explain neuronal dysfunctions leading to symptoms of rigidity and impaired learning. Astrocyte loss could constitute a new research target for understanding and treating semi-starvation and AN.

Reciprocal interactions between prostaglandin E2- and estradiol-dependent signaling pathways in the injured zebra finch brain

Background

Astrocytic aromatization and consequent increases in estradiol are neuroprotective in the injured brain. In zebra finches, cyclooxygenase-activity is necessary for injury-induced aromatase expression, and increased central estradiol lowers neuroinflammation. The mechanisms underlying these influences are unknown. Here, we document injury-induced, cyclooxygenase-dependent increases in glial aromatase expression and replicate previous work in our lab showing increases in central prostaglandin E2 and estradiol following brain damage. Further, we describe injury-dependent changes in E-prostanoid and estrogen receptor expression and reveal the necessity of E-prostanoid and estrogen receptors in the injury-dependent, reciprocal interactions of neuroinflammatory and neurosteroidogenic pathways.

Methods

Adult male and female birds were shams or received bilateral injections of the appropriate drug or vehicle into contralateral telencephalic lobes.

Results

Injuries sustained in the presence of indomethacin (a cyclooxygenase inhibitor) had fewer aromatase-expressing reactive astrocytes relative to injuries injected with vehicle suggesting that cyclooxygenase activity is necessary for the induction of glial aromatase around the site of damage. Injured hemispheres had higher prostaglandin E2 and estradiol content relative to shams. Importantly, injured hemispheres injected with E-prostanoid- or estrogen receptor-antagonists showed elevated prostaglandin E2 and estradiol, respectively, but lower prostaglandin E2 or estradiol-dependent downstream activity (protein kinase A or phosphoinositide-3-kinase mRNA) suggesting that receptor antagonism did not affect injury-induced prostaglandin E2 or estradiol, but inhibited the effects of these ligands. Antagonism of E-prostanoid receptors 3 or 4 prevented injury-induced increases in neural estradiol in males and females, respectively, albeit this apparent sex-difference needs to be tested more stringently. Further, estrogen receptor-α, but not estrogen receptor-β antagonism, exaggerated neural prostaglandin E2 levels relative to the contralateral lobe in both sexes.

Conclusion

These data suggest injury-induced, sex-specific prostaglandin E2-dependent estradiol synthesis, and estrogen receptor-α dependent decreases in neuroinflammation in the vertebrate brain.

Methylation dictates PI.f-specific CYP19 transcription in human glial cells

CYP19 is the single copy gene encoding for the estrogen synthetic enzyme aromatase. Alternate splicing of the promoter is the regulatory mechanism of this gene. In the brain, estrogen is synthesized in neuronal and glial cells and the gene is mainly regulated by the alternate promoter PI.f. The hormone produced in this vicinity has been associated with maintaining normal brain functions. Previously, epigenetic regulation has been shown in the promoters PII and I.3 of CYP19 in adipocytes. In the present study, the methylation of PI.f in CYP19 was examined in glial cells. Treatment of the hypomethylating agent 5-aza-2'deoxycytidine increased CYP19 mRNA species in U87 MG cells while little changes were observed in the other glia cell lines. As PI.f is also chiefly used in T98G cells with high expression of CYP19, the methylation statuses of the promoter in these two cell models were compared. Our results showed that treating U87 MG cells with 10 μM 5-aza-2'deoxycytidine significantly induced a ∼10-fold increase in CYP19 transcription and ∼80% increase in aromatase activity. In contrast, the same treatment did not change either endpoint in T98G cells. Further investigation illustrated the CpGs in PI.f were differentially methylated in the two cell lines; 63% and 37% of the 14 CpG sites were methylated in U87 MG and T98G cells respectively. In conclusion, this study illustrated that the brain-specific PI.f derived CYP19 expression can be regulated by DNA methylation.

Estrogen-Induced Hypothalamic Synaptic Plasticity and Pituitary Sensitization in the Control of the Estrogen-Induced Gonadotrophin Surge

Proper gonadal function requires coordinated (feedback) interactions between the gonads, adenohypophysis, and brain: the gonads elaborate sex steroids (progestins, androgens, and estrogens) and proteins (inhibin-activin family) during gamete development. In both sexes, the brain-pituitary gonadotrophin-regulating interaction is coordinated by estradiol through its opposing actions on pituitary gonadotrophs (sensitization of the response to gonadotrophin-releasing hormone [GnRH]) versus hypothalamic neurons (inhibition of GnRH secretion). This dynamic tension between the gonadotrophs and the GnRH cells in the brain regulates the circulating gonadotrophins and is termed reciprocal/negative feedback. In females, reciprocal/negative feedback dominates approximately 90% of the ovarian cycle. In a spectacular exception, the dynamic tension is broken during the surge of circulating estrogen that marks follicle and oocyte(s) maturation. The cause is an estradiol-induced disinhibition of the GnRH neurons that releases GnRH secretion to the highly sensitized pituitary gonadotrophs that in turn release the gonadotrophin surge (the estrogen-induced gonadotrophin surge [EIGS], also known as positive feedback). Studies during the past 4 decades have shown this disinhibition to result from estrogen-induced synaptic plasticity (EISP), including a reversible approximately 50% loss in arcuate nucleus synapses. The disinhibited GnRH secretion occurs during maximal gonadotroph sensitization and results in the EIGS. Specific immunoneutralization of estradiol blocks the EISP and EIGS. The EISP is accompanied by increases in insulinlike growth factor 1, polysialylated neural cell adhesion molecule, and ezrin, 3 proteins that the authors believe are the links between estrogen-induced astroglial extension and the EISP that releases GnRH secretion at the moment of maximal sensitization of the pituitary gonadotrophs. The result is the paradoxical surge of gonadotrophins at the peak of ovarian estrogen secretion and the triggering of ovulation. This enhanced understanding of the mechanics of gonadotrophin control clarifies elements of the involved feedback loops and opens the way to a better understanding of the neurobiology of reproduction.

Steroid modulation of neurogenesis: Focus on radial glial cells in zebrafish

Estrogens are known as steroid hormones affecting the brain in many different ways and a wealth of data now document effects on neurogenesis. Estrogens are provided by the periphery but can also be locally produced within the brain itself due to local aromatization of circulating androgens. Adult neurogenesis is described in all vertebrate species examined so far, but comparative investigations have brought to light differences between vertebrate groups. In teleost fishes, the neurogenic activity is spectacular and adult stem cells maintain their mitogenic activity in many proliferative areas within the brain. Fish are also quite unique because brain aromatase expression is limited to radial glia cells, the progenitor cells of adult fish brain. The zebrafish has emerged as an interesting vertebrate model to elucidate the cellular and molecular mechanisms of adult neurogenesis, and notably its modulation by steroids. The main objective of this review is to summarize data related to the functional link between estrogens production in the brain and neurogenesis in fish. First, we will demonstrate that the brain of zebrafish is an endogenous source of steroids and is directly targeted by local and/or peripheral steroids. Then, we will present data demonstrating the progenitor nature of radial glial cells in the brain of adult fish. Next, we will emphasize the role of estrogens in constitutive neurogenesis and its potential contribution to the regenerative neurogenesis. Finally, the negative impacts on neurogenesis of synthetic hormones used in contraceptive pills production and released in the aquatic environment will be discussed.

Sex and laterality differences in medial amygdala neurons and astrocytes of adult mice

The posterodorsal aspect of the medial amygdala (MePD) in rats is sexually dimorphic, being larger and containing more and larger neurons in males than in females. It is also highly lateralized, with the right MePD larger than the left in both sexes, but with the smaller left MePD actually containing more and larger neurons than the larger right. Astrocytes are also strikingly sexually differentiated, with male-biased numbers and lateralized favoring the right in the rat MePD. However, comparable information is scant for mice where genetic tools offer greater experimental power. Hence, we examined the MePD from adult male and female C57Bl/6(J) mice. We now report that the MePD is larger in males than in females, with the MePD in males containing more astrocytes and neurons than in females. However, we did not find sex differences in astrocyte complexity or overall glial number nor effects of laterality in either measure. While the mouse MePD is generally less lateralized than in rats, we did find that the sex difference in astrocyte number is only on the right because of a significant lateralization in females, with significantly fewer astrocytes on the right than the left but only in females. A sex difference in neuronal soma size favoring males was also evident, but only on the left. Sex differences in the number of neurons and astrocytes common to both rodent species may represent core morphological features that critically underlie the expression of sex-specific behaviors that depend on the MePD. J. Comp. Neurol. 524:2492-2502, 2016. © 2016 Wiley Periodicals, Inc.

Trajectories and phenotypes with estrogen exposures across the lifespan: What does Goldilocks have to do with it?

This article is part of a Special Issue "Estradiol and cognition". Estrogens impact the organization and activation of the mammalian brain in both sexes, with sex-specific critical windows. Throughout the female lifespan estrogens activate brain substrates previously organized by estrogens, and estrogens can induce non-transient brain and behavior changes into adulthood. Therefore, from early life through the transition to reproductive senescence and beyond, estrogens are potent modulators of the brain and behavior. Organizational, reorganizational, and activational hormone events likely impact the trajectory of brain profiles during aging. A "brain profile," or quantitative brain measurement for research purposes, is typically a snapshot in time, but in life a brain profile is anything but static--it is in flux, variable, and dynamic. Akin to this, the only thing continuous and consistent about hormone exposures across a female's lifespan is that they are noncontinuous and inconsistent, building and rebuilding on past exposures to create a present brain and behavioral landscape. Thus, hormone variation is especially rich in females, and is likely the destiny for maximal responsiveness in the female brain. The magnitude and direction of estrogenic effects on the brain and its functions depend on a myriad of factors; a "Goldilocks" phenomenon exists for estrogens, whereby if the timing, dose, and regimen for an individual are just right, markedly efficacious effects present. Data indicate that exogenously-administered estrogens can bestow beneficial cognitive effects in some circumstances, especially when initiated in a window of opportunity such as the menopause transition. Could it be that the age-related reduction in efficacy of estrogens reflects the closure of a late-in-life critical window occurring around the menopause transition? Information from classic and contemporary works studying organizational/activational estrogen actions, in combination with acknowledging the tendency for maximal responsiveness to cyclicity, will elucidate ways to extend sensitivity and efficacy into post-menopause.

Aromatase, estrogen receptors and brain development in fish and amphibians

Estrogens affect brain development of vertebrates, not only by impacting activity and morphology of existing circuits, but also by modulating embryonic and adult neurogenesis. The issue is complex as estrogens can not only originate from peripheral tissues, but also be locally produced within the brain itself due to local aromatization of androgens. In this respect, teleost fishes are quite unique because aromatase is expressed exclusively in radial glial cells, which represent pluripotent cells in the brain of all vertebrates. Expression of aromatase in the brain of fish is also strongly stimulated by estrogens and some androgens. This creates a very intriguing positive auto-regulatory loop leading to dramatic aromatase expression in sexually mature fish with elevated levels of circulating steroids. Looking at the effects of estrogens or anti-estrogens in the brain of adult zebrafish showed that estrogens inhibit rather than stimulate cell proliferation and newborn cell migration. The functional meaning of these observations is still unclear, but these data suggest that the brain of fish is experiencing constant remodeling under the influence of circulating steroids and brain-derived neurosteroids, possibly permitting a diversification of sexual strategies, notably hermaphroditism. Recent data in frogs indicate that aromatase expression is limited to neurons and do not concern radial glial cells. Thus, until now, there is no other example of vertebrates in which radial progenitors express aromatase. This raises the question of when and why these new features were gained and what are their adaptive benefits. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

Astrocyte-derived growth factors and estrogen neuroprotection: role of transforming growth factor-α in estrogen-induced upregulation of glutamate transporters in astrocytes

Extensive studies from the past decade have completely revolutionized our understanding about the role of astrocytes in the brain from merely supportive cells to an active role in various physiological functions including synaptic transmission via cross-talk with neurons and neuroprotection via releasing neurotrophic factors. Particularly, numerous studies have reported that astrocytes mediate the neuroprotective effects of 17β-estradiol (E2) and selective estrogen receptor modulators (SERMs) in various clinical and experimental models of neuronal injury. Astrocytes contain two main glutamate transporters, glutamate aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1), that play a key role in preventing excitotoxic neuronal death, a process associated with most neurodegenerative diseases. E2 has been shown to increase expression of both GLAST and GLT-1 mRNA and protein and glutamate uptake in astrocytes. Growth factors such as transforming growth factor-α (TGF-α) appear to mediate E2-induced enhancement of these transporters. These findings suggest that E2 exerts neuroprotection against excitotoxic neuronal injuries, at least in part, by enhancing astrocytic glutamate transporter levels and function. Therefore, the present review will discuss proposed mechanisms involved in astrocyte-mediated E2 neuroprotection, with a focus on glutamate transporters.

Role of astrocytes in the neuroprotective actions of 17β-estradiol and selective estrogen receptor modulators

Neuroprotective actions of 17β-estradiol (estradiol) are in part mediated by direct actions on neurons. Astrocytes, which play an essential role in the maintenance of the homeostasis of neural tissue, express estrogen receptors and are also involved in the neuroprotective actions of estradiol in the brain. Estradiol controls gliosis and regulates neuroinflammation, edema and glutamate transport acting on astrocytes. In addition, the hormone regulates the release of neurotrophic factors and other neuroprotective molecules by astrocytes. In addition, reactive astrocytes are a local source of neuroprotective estradiol for the injured brain. Since estradiol therapy is not free from peripheral risks, alternatives for the hormone have been explored. Some selective estrogen receptor modulators (SERMs), which are already in use in clinical practice for the treatment of breast cancer, osteoporosis or menopausal symptoms, exert similar actions to estradiol on astrocytes. Therefore, SERMs represent therapeutic alternatives to estradiol for the activation of astroglia-mediated neuroprotective mechanisms.

[Reactivity of perineuronal astrocytes in the prefrontal cortex in schizophrenia: an ultrastructural morphometric study]

OBJECTIVE

Previously the ultrastructural alterations of astrocytes have been reported in schizophrenia. Reduced dendritic arborization of the neurons in layer 5 of the prefrontal cortex has been found in schizophrenia. Authors hypothesized that the abnormalities in perineuronal astrocytes (PA) might contribute to these neuronal changes. It was aimed to study the ultrastructure of PA in the prefrontal cortex in schizophrenia.

MATERIAL AND METHODS

Postmortem electron microscopic morphometric study of PA was performed in layer 5, area 10 of the prefrontal cortex in 39 cases of schizophrenia and 37 controls.

RESULTS

No significant group differences were found in areas of cell, nucleus, cytoplasm, volume fraction (Vv) of lipofuscin granules and areal density of PA. However, in the subgroup of women with schizophrenia, the areal density of PA was significantly lower and the area of PA was significantly higher as compared to the subgroup of healthy women (-52%, p<0,01; +32%, p<0.05 respectively) and to the subgroup of men with schizophrenia (-56%, p<0,01; +23%, p<0,05 respectively). The area of PA nucleus was negatively correlated with the duration of disease (r= -0.37, p=0.02) and positively with the age of disease onset (ADO) (r=0,47, p<0,01). Areas of PA and of PA nucleus were significantly lower in early ADO (<21 y.o.) as compared to the adult ADO (>21 y.o.) (-24%, p<0.05). Vv of lypofuscin granules was correlated with the age in control group (r=0.52, p=0.001), but not in schizophrenia group (r=0.13, p=0.4).

CONCLUSION

Significant differences in PA reactivity in the prefrontal cortex in the schizophrenia are associated with gender and age at onset of the disease.

Estrogen, astrocytes and the neuroendocrine control of metabolism

Obesity, and its associated comorbidities such as type 2 diabetes, cardiovascular diseases, and certain cancers, represent major health challenges. Importantly, there is a sexual dimorphism with respect to the prevalence of obesity and its associated metabolic diseases, implicating a role for gonadal hormones. Specifically, estrogens have been demonstrated to regulate metabolism perhaps by acting as a leptin mimetic in the central nervous system (CNS). CNS estrogen receptors (ERs) include ER alpha (ERα) and ER beta (ERβ), which are found in nuclear, cytoplasmic and membrane sites throughout the brain. Additionally, estrogens can bind to and activate a G protein-coupled estrogen receptor (GPER), which is a membrane-associated ER. ERs are expressed on neurons as well as glia, which are known to play a major role in providing nutrient supply for neurons and have recently received increasing attention for their potentially important involvement in the CNS regulation of systemic metabolism and energy balance. This brief overview summarizes data focusing on the potential role of astrocytic estrogen action as a key component of estrogenic modulation responsible for mediating the sexual dimorphism in body weight regulation and obesity.

Induced synthesis of oestrogens by glia in the songbird brain

Studies on birds have long provided landmarks and touchstones in the fields of neuroendocrinology, immunology and neuroplasticity. The passerine brain is an excellent model for studying the actions of hormones, including steroids, on a diversity of behavioural endpoints. Oestrogens, for example, have profound effects on avian neuroanatomy and neurophysiology throughout life and, importantly, are synthesised at high levels within neurones of the songbird brain. More recently, aromatisation in another set of neural cells has been identified. Specifically, aromatase expression is induced in astrocytes and radial glia following disruption of the neuropil by multiple forms of perturbation. The avian brain, therefore, can be provided with high levels of oestrogens constitutively or via induction, by aromatisation in neurones and glia, respectively. In this review, we begin with the initial discovery of aromatisation by non-neuronal cells and discuss the mechanisms underlying the induction of aromatase expression in glial cells. We then focus on the emerging interactions between the neuroendocrine and neuroimmune systems with respect to brain injury. Next, we briefly review the extensive literature on the influence of glial aromatisation on neuroplasticity, and end with some recent data on sex differences in the induction of glial aromatase in the zebra finch. Throughout this review, we consider the unanswered questions and future studies that may emerge from these findings.

CYP19 expression is induced by 2,3,7,8-tetrachloro-dibenzo-para-dioxin in human glioma cells

Dioxins are the most concerned environmental pollutants. Recent studies have shown that these compounds could disrupt the proper functioning of our endocrine system. Estrogen is synthesized in glial cells of the brain. The hormone has been linked to the maintenance of normal brain operation, ranging from neurotransmission to synapse formation. Aromatase or CYP19 is the enzyme responsible for estrogen synthesis. In the present study, we demonstrated that 2,3,7,8-tetrachloro-dibenzo-para-dioxin (TCDD) stimulated the enzyme activity in human brain cells as low as 1pM. Increased brain-specific CYP19 mRNA species was also observed in these cells. Since the brain-specific promoter I.f of CYP19 contains two binding motifs for CCAAT/enhancer binding protein, electrophoretic mobility shift assay was performed to validate the activation. We further traced the triggering signal and found that the mitogen-activated protein kinases ERK-1/2 were activated. In summary, TCDD could induce CYP19 transcription in brain cells. Exposure to the pollutant might perturb the hormonal balance in the brain.

Temporal changes of cytochrome P450 (Cyp) and eicosanoid-related gene expression in the rat brain after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) induces arachidonic acid (ArA) release from cell membranes. ArA metabolites form a class of over 50 bioactive eicosanoids that can induce both adaptive and/or maladaptive brain responses. The dynamic metabolism of ArA to eicosanoids, and how they affect the injured brain, is poorly understood due to their diverse activities, trace levels, and short half-lives. The eicosanoids produced in the brain postinjury depend upon the enzymes present locally at any given time. Eicosanoids are synthesized by heme-containing enzymes, including cyclooxygenases, lipoxygenases, and arachidonate monoxygenases. The latter comprise a subset of the cytochrome P450 "Cyp" gene family that metabolize fatty acids, steroids, as well as endogenous and exogenous toxicants. However, for many of these genes neither baseline neuroanatomical nor injury-related temporal expression have been studied in the brain.In a rat model of parietal cortex TBI, Cyp and eicosanoid-related mRNA levels were determined at 6 h, 24 h, 3d, and 7d postinjury in parietal cortex and hippocampus, where dynamic changes in eicosanoids have been observed. Quantitative real-time polymerase chain reaction with low density arrays were used to assay 62 rat Cyps, 37 of which metabolize ArA or other unsaturated fatty acids; 16 eicosanoid-related enzymes that metabolize ArA or its metabolites; 8 eicosanoid receptors; 5 other inflammatory- and recovery-related genes, plus 2 mouse Cyps as negative controls and 3 highly expressed "housekeeping" genes.

RESULTS

Sixteen arachidonate monoxygenases, 17 eicosanoid-related genes, and 12 other Cyps were regulated in the brain postinjury (p < 0.05, Tukey HSD). Discrete tissue levels and distinct postinjury temporal patterns of gene expression were observed in hippocampus and parietal cortex.

CONCLUSIONS

The results suggest complex regulation of ArA and other lipid metabolism after TBI. Due to the temporal nature of brain injury-induced Cyp gene induction, manipulation of each gene (or its products) at a given time after TBI will be required to assess their contributions to secondary injury and/or recovery. Moreover, a better understanding of brain region localization and cell type-specific expression may be necessary to deduce the role of these eicosanoid-related genes in the healthy and injured brain.

Window of opportunity: estrogen as a treatment for ischemic stroke

The neuroprotection research in the last 2 decades has witnessed a growing interest in the functions of estrogens as neuroprotectants against neurodegenerative diseases including stroke. The neuroprotective action of estrogens has been well demonstrated in both in vitro and in vivo models of ischemic stroke. However, the major conducted clinical trials so far have raised concern for the protective effect of estrogen replacement therapy in postmenopausal women. The discrepancy could be partly due to the mistranslation between the experimental stroke research and clinical trials. While predominant experimental studies tested the protective action of estrogens on ischemic stroke using acute treatment paradigm, the clinical trials have mainly focused on the effect of estrogen replacement therapy on the primary and secondary stroke prevention which has not been adequately addressed in the experimental stroke study. Although the major conducted clinical trials have indicated that estrogen replacement therapy has an adverse effect and raise concern for long term estrogen replacement therapy for stroke prevention, these are not appropriate for assessing the potential effects of acute estrogen treatment on stroke protection. The well established action of estrogen in the neurovascular unit and its potential interaction with recombinant tissue Plasminogen Activator (rtPA) makes it a candidate for the combined therapy with rtPA for the acute treatment of ischemic stroke. On the other hand, the "critical period" and newly emerged "biomarkers window" hypotheses have indicated that many clinical relevant factors have been underestimated in the experimental ischemic stroke research. The development and application of ischemic stroke models that replicate the clinical condition is essential for further evaluation of acute estrogen treatment on ischemic stroke which might provide critical information for future clinical trials. This article is part of a Special Issue entitled Hormone Therapy.

Estradiol signaling in the regulation of reproduction and energy balance

Our knowledge of membrane estrogenic signaling mechanisms and their interactions that regulate physiology and behavior has grown rapidly over the past three decades. The discovery of novel membrane estrogen receptors and their signaling mechanisms has started to reveal the complex timing and interactions of these various signaling mechanisms with classical genomic steroid actions within the nervous system to regulate physiology and behavior. The activation of the various estrogenic signaling mechanisms is site specific and differs across the estrous cycle acting through both classical genomic mechanisms and rapid membrane-initiated signaling to coordinate reproductive behavior and physiology. This review focuses on our current understanding of estrogenic signaling mechanisms to promote: (1) sexual receptivity within the arcuate nucleus of the hypothalamus, (2) estrogen positive feedback that stimulates de novo neuroprogesterone synthesis to trigger the luteinizing hormone surge important for ovulation and estrous cyclicity, and (3) alterations in energy balance.

Neurosteroids, trigger of the LH surge

Recent experiments from our laboratory are consistent with the idea that hypothalamic astrocytes are critical components of the central nervous system (CNS) mediated estrogen positive feedback mechanism. The "astrocrine hypothesis" maintains that ovarian estradiol rapidly increases free cytoplasmic calcium concentrations ([Ca(2+)](i)) that facilitate progesterone synthesis in astrocytes. This hypothalamic neuroprogesterone along with the elevated estrogen from the ovaries allows for the surge release of gonadotropin-releasing hormone (GnRH) that triggers the pituitary luteinizing hormone (LH) surge. A narrow range of estradiol stimulated progesterone production supports an "off-on-off" mechanism regulating the transition from estrogen negative feedback to estrogen positive feedback, and back again. The rapidity of the [Ca(2+)](i) response and progesterone synthesis support a non-genomic, membrane-initiated signaling mechanism. In hypothalamic astrocytes, membrane-associated estrogen receptors (mERs) signal through transactivation of the metabotropic glutamate receptor type 1a (mGluR1a), implying that astrocytic function is influenced by surrounding glutamatergic nerve terminals. Although other putative mERs, such as mERβ, STX-activated mER-Gα(q), and G protein-coupled receptor 30 (GPR30), are present and participate in membrane-mediated signaling, their influence in reproduction is still obscure since female reproduction be it estrogen positive feedback or lordosis behavior requires mERα. The astrocrine hypothesis is also consistent with the well-known sexual dimorphism of estrogen positive feedback. In rodents, only post-pubertal females exhibit this positive feedback. Hypothalamic astrocytes cultured from females, but not males, responded to estradiol by increasing progesterone synthesis. Estrogen autoregulates its own signaling by regulating levels of mERα in the plasma membrane of female astrocytes. In male astrocytes, the estradiol-induced increase in mERα was attenuated, suggesting that membrane-initiated estradiol signaling (MIES) would also be blunted. Indeed, estradiol induced [Ca(2+)](i) release in male astrocytes, but not to levels required to stimulate progesterone synthesis. Investigation of this sexual differentiation was performed using hypothalamic astrocytes from post-pubertal four core genotype (FCG) mice. In this model, genetic sex is uncoupled from gonadal sex. We demonstrated that animals that developed testes (XYM and XXM) lacked estrogen positive feedback, strongly suggesting that the sexual differentiation of progesterone synthesis is driven by the sex steroid environment during early development. This article is part of a Special Issue entitled 'Neurosteroids'.

Estrogen-regulated synaptogenesis in the hippocampus: sexual dimorphism in vivo but not in vitro

Hippocampal neurons are capable of synthesizing estradiol de novo. Estradiol synthesis can be suppressed by aromatase inhibitors and by knock-down of steroid acute regulatory protein (StAR), whereas elevated levels of substrates of steroidogenesis enhance estradiol synthesis. In rat hippocampal cultures, the expression of estrogen receptors (ERs) and synaptic proteins, as well as synapse density, correlated positively with aromatase activity, regardless of whether the cultures originated from males or females. All effects induced by the inhibition of aromatase activity were rescued by application of estradiol to the cultures. In vivo, however, systemic application of letrozole, an aromatase inhibitor, induced synapse loss in female rats, but not in males. Furthermore, in the female hippocampus, density of spines and spine synapses varied with the estrus cycle. In addressing this in vivo-in vitro discrepancy, we found that gonadotropin-releasing hormone (GnRH) regulated estradiol synthesis via an aromatase-mediated mechanism and consistently regulated spine synapse density and the expression of synaptic proteins. Along these lines, GnRH receptor density was higher in the hippocampus than in the cortex and hypothalamus, and estrus cyclicity of spinogenesis was found in the hippocampus, but not in the cortex. Since GnRH receptor expression also varies with the estrus cycle, the sexual dimorphism in estrogen-regulated spine synapse density in the hippocampus very likely results from differences in the GnRH responsiveness of the male and the female hippocampus. This article is part of a Special Issue entitled 'Neurosteroids'.

Differential acute and chronic effects of leptin on hypothalamic astrocyte morphology and synaptic protein levels

Astrocytes participate in neuroendocrine functions partially through modulation of synaptic input density in the hypothalamus. Indeed, glial ensheathing of neurons is modified by specific hormones, thus determining the availability of neuronal membrane space for synaptic inputs, with the loss of this plasticity possibly being involved in pathological processes. Leptin modulates synaptic inputs in the hypothalamus, but whether astrocytes participate in this action is unknown. Here we report that astrocyte structural proteins, such as glial fibrillary acidic protein (GFAP) and vimentin, are induced and astrocyte morphology modified by chronic leptin administration (intracerebroventricular, 2 wk), with these changes being inversely related to modifications in synaptic protein densities. Similar changes in glial structural proteins were observed in adult male rats that had increased body weight and circulating leptin levels due to neonatal overnutrition (overnutrition: four pups/litter vs. control: 12 pups/litter). However, acute leptin treatment reduced hypothalamic GFAP levels and induced synaptic protein levels 1 h after administration, with no effect on vimentin. In primary hypothalamic astrocyte cultures leptin also reduced GFAP levels at 1 h, with an induction at 24 h, indicating a possible direct effect of leptin. Hence, one mechanism by which leptin may affect metabolism is by modifying hypothalamic astrocyte morphology, which in turn could alter synaptic inputs to hypothalamic neurons. Furthermore, the responses to acute and chronic leptin exposure are inverse, raising the possibility that increased glial activation in response to chronic leptin exposure could be involved in central leptin resistance.

Aromatase is increased in astrocytes in the presence of elevated pressure

After traumatic brain injury (TBI), a progressive injury and death of neurons and glia leads to decreased brain function. Endogenous and exogenous estrogens may protect these vulnerable cells. In this study, we hypothesized that increased pressure leads to an increase in aromatase expression and estrogen production in astrocytes. In this study, we subjected rat glioma (C6) cells and primary cortical astrocytes to increased pressure (25 mm Hg) for 1, 3, 6, 12, 24, 48, and 72 h. Total aromatase protein and RNA levels were measured using Western analysis and RT-PCR, respectively. In addition, we measured aromatase activity by assaying estrone levels after administration of its precursor, androstenedione. We found that increased pressure applied to the C6 cells and primary cortical astrocytes resulted in a significant increase in both aromatase RNA and protein. To extend these findings, we also analyzed aromatase activity in the primary astrocytes during increased pressure. We found that increased pressure resulted in a significant (P < 0.01) increase in the conversion of androstenedione to estrone. In conclusion, we propose that after TBI, astrocytes sense increased pressure, leading to an increase in aromatase production and activity in the brain. These results may suggest mechanisms of brain estrogen production after increases in pressure as seen in TBI patients.

NOV/CCN3 upregulates CCL2 and CXCL1 expression in astrocytes through beta1 and beta5 integrins

Increasing evidence suggests that CCN matricellular proteins play important roles in inflammation. One of the major cell types that handle inflammation in the brain is the astrocyte, which, upon activation, dramatically increases its production of cytokines and chemokines. Here, we report that NOV/CCN3, added to primary cultured rat brain astrocytes, markedly increased the expression of CCL2 and CXCL1 chemokines, as indicated by ELISA and RT-qPCR assays. This effect was selective, as the production of thirteen other cytokines and chemokines was not affected by NOV. NOV expression by astrocytes was demonstrated by immunocytochemistry and Western blot analysis, and astrocyte transfection with NOV small interfering RNA (siRNA) markedly decreased CXCL1 and CCL2 production, indicating that endogenous NOV played a major role in the control of astrocytic chemokine synthesis. NOV was shown to mediate several of its actions through integrins. Here, we observed that siRNAs against integrins beta1 and beta5 decreased basal and abrogated NOV-stimulated astrocyte expression of CCL2 and CXCL1, respectively. Using a panel of kinase inhibitors, we demonstrated that NOV action on CCL2 and CXCL1 production involved a Rho/ROCK/JNK/NF-kappaB and a Rho/qROCK/p38/NF-kappaB pathway, respectively. Thus, distinct integrins and signaling mechanisms are involved in NOV-induced production of CCL2 and CXCL1 in astrocytes. Finally, astrocytic expression of NOV was detected in rat brain tissue sections, and NOV intracerebral injection increased CCL2 and CXCL1 brain levels in vivo. Altogether, our data shed light on the signaling pathways operated by NOV and strongly suggest that NOV mediates astrocyte activation and, therefore, might play a role in neuroinflammation.

Differential distribution of tight junction proteins suggests a role for tanycytes in blood-hypothalamus barrier regulation in the adult mouse brain

The median eminence is one of the seven so-called circumventricular organs. It is located in the basal hypothalamus, ventral to the third ventricle and adjacent to the arcuate nucleus. This structure characteristically contains a rich capillary plexus and features a fenestrated endothelium, making it a direct target of blood-borne molecules. The median eminence also contains highly specialized ependymal cells called tanycytes, which line the floor of the third ventricle. It has been hypothesized that one of the functions of these cells is to create a barrier that prevents substances in the portal capillary spaces from entering the brain. In this paper, we utilize immunohistochemistry to study the expression of tight junction proteins in the cells that compose the median eminence in adult mice. Our results indicate that tanycytes of the median eminence express occludin, ZO-1, and claudin 1 and 5, but not claudin 3. Remarkably, these molecules are organized as a continuous belt around the cell bodies of the tanycytes that line the ventral part of the third ventricle. In contrast, the tanycytes at the periphery of the arcuate nucleus do not express claudin 1 and instead exhibit a disorganized expression pattern of occludin, ZO-1, and claudin 5. Consistent with these observations, permeability studies using peripheral or central injections of Evans blue dye show that only the tanycytes of the median eminence are joined at their apices by functional tight junctions, whereas tanycytes located at the level of the arcuate nucleus form a permeable layer. In conclusion, this study reveals a unique expression pattern of tight junction proteins in hypothalamic tanycytes, which yields new insights into their barrier properties.

Role of estradiol in the dynamic control of tanycyte plasticity mediated by vascular endothelial cells in the median eminence

In the ever-changing physiological context of the neuroendocrine brain, the mechanisms by which cellular events involving neurons, astroglia, and vascular cells are coordinated to bring forth the appropriate neuronal signaling is not yet known but is amenable to examination. In the median eminence of the hypothalamus, endothelial cells are key players in the plasticity of tanycytes (specialized astroglia) and neuroendocrine synapse efficacy. Here we report that estradiol acts on both purified endothelial cells and isolated tanycytes to trigger endothelial-to-glial communication that leads to a sudden and massive retraction of tanycyte processes. The blockade of endothelial nitric oxide synthase by in vitro adenoviral-mediated gene transfer of a dominant-negative form of endothelial nitric oxide synthase abrogates the estradiol-induced tanycyte plasticity mediated by endothelial cells. In parallel, increases in prostaglandin-E(2) (PGE(2)) due to changes in cyclooxygenase (COX)-1 and COX-2 expression induced by the exposure of tanycytes to estradiol promote acute tanycyte plasticity. We also demonstrate by electron microscopy that the administration of PGE(2) to median eminence explants induces rapid neuroglial plasticity at the neurovascular junction of neurons that release GnRH (the neuropeptide controlling reproduction). Conversely, preventing local PGE(2) synthesis in the median eminence of adult female rats with the COX inhibitor indomethacin impairs the ovarian cycle, a process that requires a pulsatile, coordinated delivery of GnRH into the hypothalamo-hypophyseal portal system. Taken together, our findings show that estradiol controls the dialog between endothelial cells and astroglia to regulate neuroglial plasticity in the neuroendocrine brain.

The design of barriers in the hypothalamus allows the median eminence and the arcuate nucleus to enjoy private milieus: the former opens to the portal blood and the latter to the cerebrospinal fluid

The blood-brain barrier (BBB) is a single uninterrupted barrier that in the brain capillaries is located at the endothelial cells and in the circumventricular organs, such as the choroid plexuses (CP) and median eminence (ME), is displaced to specialized ependymal cells. How do hypothalamic hormones reach the portal circulation without making the BBB leaky? The ME milieu is open to the portal vessels, while it is closed to the cerebrospinal fluid (CSF) and to the arcuate nucleus. The cell body and most of the axons of neurons projecting to the ME are localized in areas protected by the BBB, while the axon terminals are localized in the BBB-free area of the ME. This design implies a complex organization of the intercellular space of the median basal hypothalamus. The privacy of the ME milieu implies that those neurons projecting to this area would not be under the influence of compounds leaking from the portal capillaries, unless receptors for such compounds are located at the axon terminal. Amazingly, the arcuate nucleus also has its private milieu that is closed to all adjacent neural structures and open to the infundibular recess. The absence of multiciliated cells in this recess should result in a slow CSF flow at this level. This whole arrangement should facilitate the arrival of CSF signal to the arcuate nucleus. This review will show how peripheral hormones can reach hypothalamic targets without making the BBB leaky.

Interactions of estradiol and insulin-like growth factor-I signalling in the nervous system: new advances

Estradiol and insulin-like growth factor-I (IGF-I) interact in the brain to regulate a variety of developmental and neuroplastic events. Some of these interactions are involved in the control of hormonal homeostasis and reproduction. However, the interactions may also potentially impact on affection and cognition by the regulation of adult neurogenesis in the hippocampus and by promoting neuroprotection under neurodegenerative conditions. Recent studies suggest that the interaction of estradiol and IGF-I is also relevant for the control of cholesterol homeostasis in neural cells. The molecular mechanisms involved in the interaction of estradiol and IGF-I include the cross-regulation of the expression of estrogen and IGF-I receptors, the regulation of estrogen receptor-mediated transcription by IGF-I and the regulation of IGF-I receptor signalling by estradiol. Current investigations are evidencing the role exerted by key signalling molecules, such as glycogen synthase kinase 3 and beta-catenin, in the cross-talk of estrogen receptors and IGF-I receptors in neural cells.

Headache endocrinological aspects

In this chapter we review the current understanding of how hormones, neurohormones, and neurotransmitters participate in the pain modulation of primary headaches. Stressful conditions and hormones intimately implicated in headache neurobiology are also discussed. With the recent progress in neuroimaging techniques and the development of animal models to study headache mechanisms, the physiopathology of several of the primary headaches is starting to be better understood. Various clinical characteristics of the primary headaches, such as pain, autonomic disturbances, and behavioral changes, are linked to hypothalamic brainstem activation and hormonal influence. Headache is greatly influenced by the circadian circle. Over the millennia the nervous system has evolved to meet changing environmental conditions, including the light-dark cycle, in order to ensure survival and reproduction. The main elements for synchronization between internal biological events and the external environment are the pineal gland and its main secretory product, melatonin. Melatonin is believed to be a significant element in migraine and in other headache disorders, which has implications for treatment. A potential therapeutic use of melatonin has been considered in several headache syndromes. In short, primary headaches are strongly influenced by physiological hormonal fluctuations, when nociceptive and non-nociceptive pathways are differentially activated to modulate the perception of pain.