Aging and substitutive hormonal therapy influence in regional and subcellular distribution of ERα in female rat brain

Oestradiol, threat conditioning and extinction, post-traumatic stress disorder, and prolonged exposure therapy: A common link

The accumulating evidence regarding the impact of estradiol on learning and memory synergized studies to examine its influence on enhancing animal's ability to quell fear and anxiety. In this review, we first provide a foundational platform regarding the impact of oestradiol on cellular mechanisms of learning and memory and we review recent advances from rodent and human data showing that oestrogen enhances extinction learning across species. We then propose clinical application to these data. We discuss the potential role of oestradiol variance on the aetiology, maintenance and treatment for post-traumatic stress disorder. Specifically, we argue that the use of oestradiol as an adjunct to prolonged exposure (PE) therapy for PTSD may provide a new treatment approach for enhancing the efficacy of PE in women with PTSD. This could advance our understanding of the mechanisms of PTSD and help tailor sex-specific treatments for this disorder.

Neuroprotective effect of Asparagus racemosus root extract via the enhancement of brain-derived neurotrophic factor and estrogen receptor in ovariectomized rats

ETHNOPHARMACOLOGICAL RELEVANCE

Asparagus racemosus (AR) is well known as an Ayurvedic rasayana which used traditionally by Ayurvedic practitioners for nervous disorders and prevent aging. In our previous study it was found that ethanol AR root extract can improve learning and memory impairment, induced by an ovariectomy, but the extract's mechanisms as a neuroprotective property are still unknown.

AIM OF THE STUDY

This study aimed to examine the effects and mechanisms of ethanol AR root extract on the alteration of brain-derived neurotrophic factor (BDNF) and estrogen receptor (ER) subtypes in ovariectomized (OVX) rats.

MATERIALS AND METHODS

Adult female Wistar rats were divided into five groups, 4 groups underwent ovariectomy, and one group was designed to be the sham control group. Two groups were gavaged with propylene glycol for sham, and a second group similarly prepared for OVX. Two further groups of OVX rats were gavaged once daily, one group with 100 mg/kg b.w. of ethanol AR root extract and the second group with 1000 mg/kg b.w. of ethanol AR root extract. The fifth group was gavaged once daily with 0.1 mg/kg b.w. of 17α-ethynylestradiol (EE). BDNF, ERα and ERβ expression were evaluated by western blot analysis.

RESULTS

The western blot analysis revealed that the OVX rats showed a significant decrease in BDNF and a down-regulation of ERα and ERβ in the frontal cortex and hippocampus. It was also demonstrated that EE and AR root extract increased BDNF, ERα and ERβ in the frontal cortex and hippocampus of ovariectomized rats.

CONCLUSIONS

Based on these results, the enhancement of BDNF and ERs up-regulation may be involved in the neuroprotective effects of ethanol AR root extract in ovariectomized rat.

Mechanisms of Sex Differences in Fear and Posttraumatic Stress Disorder

Following sexual maturity, females disproportionately have higher rates of posttraumatic stress disorder (PTSD) and experience greater symptom severity and chronicity as compared with males. This observation has led many to examine sex differences in PTSD risk factors. Though relatively few, these studies reveal that the root causes of PTSD sex differences are complex, and partly represent interactions between sex-specific nonbiological and biological risk factors, which differentially shape PTSD vulnerability. Moreover, these studies suggest that sex-specific PTSD vulnerability is partly regulated by sex differences in fear systems. Fear, which represents a highly conserved adaptive response to threatening environmental stimuli, becomes pathological in trauma- and stress-based psychiatric syndromes, such as PTSD. Over the last 30 years, considerable progress has been made in understanding normal and pathological molecular and behavioral fear processes in humans and animal models. Thus, fear mechanisms represent a tractable PTSD biomarker in the study of sex differences in fear. In this review, we discuss studies that examine nonbiological and biological sex differences that contribute to normal and pathological fear behaviors in humans and animal models. This, we hope, will shed greater light on the potential mechanisms that contribute to increased PTSD vulnerability in females.

Psychological stress in aged female mice causes acute hypophagia independent of central serotonin 2C receptor activation

Sex differences exist in the activation of the hypothalamic–pituitary–adrenal axis following exposure to stress, and the stress response is further affected by aging. This study was conducted to elucidate the mechanism of hypophagia in aged female mice exposed to stress. Immediately after a stress load, aged female mice exhibited acute hypophagia and a rise in plasma corticosterone levels. The administration of a serotonin 2C receptor (5-HT_2CR) antagonist suppressed plasma corticosterone but did not affect the reduction in food intake. In contrast, an endogenous ghrelin enhancer, rikkunshito (RKT), significantly inhibited the reduction in food intake. An increase in peripheral acylated ghrelin levels during fasting, which occurs in young mice, was not observed in aged female mice. Moreover, in these mice, significantly increased levels of ghrelin and gastric preproghrelin mRNA expression were observed in the fed status. Moreover, plasma ghrelin levels were elevated by RKT and not by the 5-HT_2CR antagonist. In female mice, the hypothalamic non-edited (INI) and partially edited mRNA 5-HT_2CR isoforms (VNV, VNI, VSV or VSI) decreased with age, while in male mice, the editing isoform was unchanged by aging or stress. Estrogen receptor α (ERα)-positive cell counts in the arcuate nucleus of young male mice exposed to stress and control aged male mice were increased compared with those in young control mice. In aged male mice exposed to stress, the number of ERα-expressing cells in the paraventricular nucleus were significantly increased compared with those in aged control mice; in female mice, there was no increase in the number of ERα-positive cells. Hypophagia in aged female mice exposed to stress may be independent of 5-HT_2CR activation. It seems likely that the mechanisms may be caused by sex dependent, differential regulation in 5-HT_2CR mRNA expression, peripheral acylated ghrelin secretion and/or hypothalamic ERα expression.

Expression of aromatase and estrogen receptors in lumbar motoneurons of mice

Estrogen exerts protective roles in amyotrophic lateral sclerosis (ALS). However, the expression of aromatase (ARO) and estrogen receptors (ERs) in the motoneurons of spinal cord, has not yet been elucidated. By immunohistochemistry, we found that ARO and ERs were present in the ventral horn of adult mice lumbar spinal cord, and colocalized with SMI-32, a motoneuron specific marker. Within motoneurons, we observed that ARO is detected primarily in the cytoplasm, with fewer ARO in the nucleus; ERα and ERβ mainly localized in the nucleus with less in the cytoplasm; while GPR30 is located in soma and processes. In conclusion, we found that ERs and ARO are expressed in the motoneurons of lumbar spinal cord in adult mice. These findings suggest that estrogen may be useful as a promising therapeutic agent for prevention of damage and improvement of locomotor function in ALS.

Aging and estradiol effects on gene expression in the medial preoptic area, bed nucleus of the stria terminalis, and posterodorsal medial amygdala of male rats

Studies on the role of hormones in male reproductive aging have traditionally focused on testosterone, but estradiol (E2) also plays important roles in the control of masculine physiology and behavior. Our goal was to examine the effects of E2 on the expression of genes selected for E2-sensitivity, involvement in behavioral neuroendocrine functions, and impairments with aging. Mature adult (MAT, 5 mo) and aged (AG, 18 mo) Sprague-Dawley male rats were castrated, implanted with either vehicle or E2 subcutaneous capsules, and euthanized one month later. Bilateral punches were taken from the bed nucleus of the stria terminalis (BnST), posterodorsal medial amygdala (MePD) and the preoptic area (POA). RNA was extracted, and expression of 48 genes analyzed by qPCR using Taqman low-density arrays. Results showed that effects of age and E2 were age- and region-specific. In the POA, 5 genes were increased with E2 compared to vehicle, and there were no age effects. By contrast the BnST showed primarily age-related changes, with 6 genes decreasing with age. The MePD had 5 genes that were higher in aged than mature males, and 17 genes with significant interactions between age and E2. Gene families identified in the MePD included nuclear hormone receptors, neurotransmitters and neuropeptides and their receptors. Ten serum hormones were assayed in these same males, with results revealing both age- and E2-effects, in several cases quite profound. These results support the idea that the male brain continues to be highly sensitive to estradiol even with aging, but the nature of the response can be substantially different in mature and aging animals.

Non-ovarian aromatization is required to activate female sexual motivation in testosterone-treated ovariectomized quail

Although aromatase is expressed in both male and female brains, its functional significance in females remains poorly understood. In female quail, sexual receptivity is activated by estrogens. However it is not known whether sexual motivation is similarly estrogen-dependent and whether estrogens locally produced in the brain contribute to these behavioral responses. Four main experiments were designed to address these questions. In Experiment 1 chronic treatment of females with the anti-estrogen tamoxifen decreased their receptivity, confirming that this response is under the control of estrogens. In Experiment 2 chronic treatment with tamoxifen significantly decreased sexual motivation as treated females no longer approached a sexual partner. In Experiment 3 (a) ovariectomy (OVX) induced a significant decrease of time spent near the male and a significantly decreased receptivity compared to gonadally intact females, (b) treatment with testosterone (OVX+T) partially restored these responses and (c) this effect of T was prevented when estradiol synthesis was inhibited by the potent aromatase inhibitor Vorozole (OVX+T+VOR). Serum estradiol concentration was significantly higher in OVX+T than in OVX or OVX+T+VOR females. Together these data demonstrate that treatment of OVX females with T increases sexual motivation and that these effects are mediated at least in part by non-gonadal aromatization of the androgen. Finally, assays of aromatase activity on brain and peripheral tissues (Experiment 4) strongly suggest that brain aromatization contributes to behavioral effects observed here following T treatment but alternative sources of estrogens (e.g. liver) should also be considered.

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.

Pomegranate seed hydroalcoholic extract improves memory deficits in ovariectomized rats with permanent cerebral hypoperfusion /ischemia

OBJECTIVES

Estrogen deficit following menopause results in cognitive behaviors impairment. This study aimed to evaluate the effects of pomegranate seed extract (PGSE) on avoidance memories after permanent bilateral common carotid arteries occlusion (2CCAO) in ovariectomized (OVX) rats.

MATERIALS AND METHODS

Adult female Wistar rats were divided randomly into eight groups with 8 rats in each group: 1) Sham-operated for ovaries and 2CCAO (ShO); 2) OVX and sham operated for ischemia (OShI); 3-7) OVX with 2CCAO (OI) received PGSE (100, 200, 400 and 800 mg/2ml/kg or normal saline, orally) for 14 days (OI+E100, 200, 400, 800 or OI+Veh); 8) OShI received most effective dose of PGSE (200 and 400 mg/kg for passive and active avoidance memories respectively). Active and passive avoidance tasks were measured in Y-maze and two-way shuttle box respectively. Data were analyzed with one-way and RM-ANOVA followed by HSD post-hoc test.

RESULTS

Sensorimotor impaired in OShI+Veh and OI+Veh (P<0.001 vs. ShO). PGSE improved it significantly in dose dependently manner (P<0.001 vs. OI+Veh). Both types of memories were significantly impaired in OVX rats before and after 2CCAO (P<0.001). PGSE treatment significantly improved memories in OI groups (P<0.05, P<0.01 and P<0.001) compared with OI+Veh. No toxicity was observed with PGSE consumption (800 mg/kg, 2 weeks, orally).

CONCLUSION

PGSE exhibits therapeutic potential for avoidance memories, which is most likely related at least in part to its phytoestrogenic and also antioxidative actions.

Oestrogen, ocular function and low-level vision: a review

Over the past 10 years, a literature has emerged concerning the sex steroid hormone oestrogen and its role in human vision. Herein, we review evidence that oestrogen (oestradiol) levels may significantly affect ocular function and low-level vision, particularly in older females. In doing so, we have examined a number of vision-related disorders including dry eye, cataract, increased intraocular pressure, glaucoma, age-related macular degeneration and Leber's hereditary optic neuropathy. In each case, we have found oestrogen, or lack thereof, to have a role. We have also included discussion of how oestrogen-related pharmacological treatments for menopause and breast cancer can impact the pathology of the eye and a number of psychophysical aspects of vision. Finally, we have reviewed oestrogen's pharmacology and suggest potential mechanisms underlying its beneficial effects, with particular emphasis on anti-apoptotic and vascular effects.

Regional specific regulation of steroid receptor coactivator-1 immunoreactivity by orchidectomy in the brain of adult male mice

Androgens including testosterone and dihydrotestosterone play important roles on brain structure and function, either directly through androgen receptor or indirectly through estrogen receptors, which need coactivators for their transcription activation. Steroid receptor coactivator-1 (SRC-1) has been shown to be multifunctional potentials in the brain, but how it is regulated by androgens in the brain remains unclear. In this study, we explored the effect of orchidectomy (ORX) on the expression of SRC-1 in the adult male mice using nickel-intensified immunohistochemistry. The results showed that ORX induced dramatic decrease of SRC-1 immunoreactivity in the olfactory tubercle, piriform cortex, ventral pallidum, most parts of the septal area, hippocampus, substantia nigra (compact part), pontine nuclei and nucleus of the trapezoid body (p<0.01). Significant decrease of SRC-1 was noticed in the dorsal and lateral septal nucleus, medial preoptical area, dorsomedial and ventromedial hypothalamic nucleus and superior paraolivary nucleus (p<0.05). Whereas in other regions examined, levels of SRC-1 immunoreactivity were not obviously changed by ORX (p>0.05). The above results demonstrated ORX downregulation of SRC-1 in specific regions that have been involved in sense of smell, learning and memory, cognition, neuroendocrine, reproduction and motor control, indicating that SRC-1 play pivotal role in the mediating circulating androgenic regulation on these important brain functions. It also indicates that SRC-1 may serve as a novel target for the central disorders caused by the age-related decrease of circulating androgens.

Mechanisms of estradiol in fear circuitry: implications for sex differences in psychopathology

Over the past two decades, substantial knowledge has been attained about the mechanisms underlying the acquisition and subsequent extinction of conditioned fear. Knowledge gained on the biological basis of Pavlovian conditioning has led to the general acceptance that fear extinction may be a useful model in understanding the underlying mechanisms in the pathophysiology of anxiety disorders and may also be a good model for current therapies treating these disorders. Lacking in the current knowledge is how men and women may or may not differ in the biology of fear and its extinction. It is also unclear how the neural correlates of fear extinction may mediate sex differences in the etiology, maintenance, and prevalence of psychiatric disorders. In this review, we begin by highlighting the epidemiological differences in incidence rate. We then discuss how estradiol (E2), a primary gonadal hormone, may modulate the mechanisms of fear extinction and mediate some of the sex differences observed in psychiatric disorders.

Estrogen-dependent changes in estrogen receptor-β mRNA expression in middle-aged female rat brain

During aging, estrogen production and circulating levels of estrogen are markedly decreased in females. Although several differences exist in the process of reproductive aging between women and female rats, the results of many studies suggest that the female rat, especially the middle-aged or aged ovariectomized female, is an important animal model of hormone loss in women. In target tissues including the brain, the actions of estrogen are mediated mainly via the alpha and beta subtypes of the estrogen receptor (ER-α and ER-β). Estrogen treatment is known to change the expression of ER-α mRNA and protein in specific regions of the brain in middle-aged female rodents. In contrast, we do not know if estrogen regulates the expression of ER-β in the brain at this stage of life. In the present study, we performed in situ hybridization on brain sections of ovariectomized and estrogen-treated middle-aged female rats to reveal the effects of estrogen on the expression of ER-β throughout the brain. Our results showed that estrogen treatment decreased the number of ER-β mRNA-positive cells in the mitral cell and external plexiform layers of the olfactory bulb, central amygdaloid nucleus, medial geniculate nucleus, posterior hypothalamic nucleus, suprachiasmatic nucleus, and reticular part of the substantia nigra. As compared to the results of previous studies of young females, our data revealed that the regions in which expression of ER-β mRNA expression is affected by estrogen differ in middle age. These results suggest that the effects of estrogen on ER-β expression change with age.