Onset of estrogen replacement has a critical effect on synaptic density of CA1 hippocampus in ovariectomized adult rats

Effects of estrogen and raloxifene on synaptic density in the hippocampal CA1 region of ovariectomized rats

INTRODUCTION

The CA1 region of the hippocampus has an important role in learning and memory. It has been shown that estrogen deficiency may reduce the synaptic density in the region and that hormone replacement therapy may attenuate the reduction.

OBJECTIVES

This study aimed to evaluate the effects of estrogen and raloxifene on the synaptic density profile in the CA1 region of the hippocampus in ovariectomized rats.

METHODS

Sixty ovariectomized three-month-old virgin rats were randomized into six groups (n = 10). Treatments started either three days (early treatment) or sixty days (late treatment) after ovariectomy. The groups received propylene glycol vehicle (0.5 mL/animal/day), equine conjugated estrogens (50 μg/animal/day), or raloxifene (3 mg/kg/day) either early or late after ovariectomy. The drugs were administered orally by gavage for 30 days. At the end of the treatments, the animals were anesthetized and transcardially perfused with ether and saline solution. The brains were removed and prepared for analysis under transmission electron microscopy and later fixed.

RESULTS

Results showed a significant increase in the synaptic density profile of the hippocampal CA1 region in both the early estrogen (0.534 ± 0.026 µ/m2) and the early raloxifene (0.437 ± 0.012 µ/m2) treatment groups compared to the early or late vehicle-treated control groups (0.338 ± 0.038 µ/m2 and 0.277 ± 0.015 µ/m2 respectively).

CONCLUSIONS

The present data suggest that the raloxifene effect may be lower than that of estrogen, even early or late treatment, on synaptic density in the hippocampus.

Dementia risk reduction: why haven't the pharmacological risk reduction trials worked? An in-depth exploration of seven established risk factors

Identifying the leading health and lifestyle factors for the risk of incident dementia and Alzheimer's disease has yet to translate to risk reduction. To understand why, we examined the discrepancies between observational and clinical trial evidence for seven modifiable risk factors: type 2 diabetes, dyslipidemia, hypertension, estrogens, inflammation, omega-3 fatty acids, and hyperhomocysteinemia. Sample heterogeneity and paucity of intervention details (dose, timing, formulation) were common themes. Epidemiological evidence is more mature for some interventions (eg, non-steroidal anti-inflammatory drugs [NSAIDs]) than others. Trial data are promising for anti-hypertensives and B vitamin supplementation. Taken together, these risk factors highlight a future need for more targeted sample selection in clinical trials, a better understanding of interventions, and deeper analysis of existing data.

Perspective: Estrogen and the Risk of Cognitive Decline: A Missing Choline(rgic) Link?

Factors that influence the risk of neurocognitive decline and Alzheimer's disease (AD) may provide insight into therapies for both disease treatment and prevention. While age is the most striking risk factor for AD, it is notable that the prevalence of AD is higher in women, representing two-thirds of cases. To explore potential underlying biological underpinnings of this observation, the intent of this article is to explore the interplay between cognitive aging and sex hormones, the cholinergic system, and novel hypotheses related to the essential nutrient, choline. Mechanistic evidence points toward estrogen's neuroprotective effects being strongly dependent on its interactions with the cholinergic system, a modulator of attentional functioning, learning, and memory. Estrogen has been shown to attenuate anticholinergic-induced impairments in verbal memory and normalize patterns of frontal and occipital cortex activation, resulting in a more "young adult" phenotype. However, similar to estrogen replacement's effect in cardiovascular diseases, its putative protective effects may be restricted to early postmenopausal women only, supportive of the "critical window hypothesis." Estrogen's impact on the cholinergic system may act both locally in the brain but also through peripheral tissues. Estrogen is critical for inducing endogenous choline synthesis via the phosphatidylethanolamine N-methyltransferase (PEMT) pathway of phosphatidylcholine (PC) synthesis. PEMT is dramatically induced in response to estrogen, producing not only a PC molecule and source of choline for the brain but also a key source of the long-chain omega-3 fatty acid, DHA. Herein, we highlight novel hypotheses related to hormone replacement therapy and nutrient metabolism aimed at directing future preclinical and clinical investigation.

Estrogens, inflammation and cognition

The effects of estrogens are pleiotropic, affecting multiple bodily systems. Changes from the body's natural fluctuating levels of estrogens, through surgical removal of the ovaries, natural menopause, or the administration of exogenous estrogens to menopausal women have been independently linked to an altered immune profile, and changes to cognitive processes. Here, we propose that inflammation may mediate the relationship between low levels of estrogens and cognitive decline. In order to determine what is known about this connection, we review the literature on the cognitive effects of decreased estrogens due to oophorectomy or natural menopause, decreased estrogens' role on inflammation--both peripherally and in the brain--and the relationship between inflammation and cognition. While this review demonstrates that much is unknown about the intersection between estrogens, cognition, inflammation, we propose that there is an important interaction between these literatures.

Estrogen-cholinergic interactions: Implications for cognitive aging

This article is part of a Special Issue "Estradiol and Cognition". While many studies in humans have investigated the effects of estrogen and hormone therapy on cognition, potential neurobiological correlates of these effects have been less well studied. An important site of action for estrogen in the brain is the cholinergic system. Several decades of research support the critical role of CNS cholinergic systems in cognition in humans, particularly in learning and memory formation and attention. In humans, the cholinergic system has been implicated in many aspects of cognition including the partitioning of attentional resources, working memory, inhibition of irrelevant information, and improved performance on effort-demanding tasks. Studies support the hypothesis that estradiol helps to maintain aspects of attention and verbal and visual memory. Such cognitive domains are exactly those modulated by cholinergic systems and extensive basic and preclinical work over the past several decades has clearly shown that basal forebrain cholinergic systems are dependent on estradiol support for adequate functioning. This paper will review recent human studies from our laboratories and others that have extended preclinical research examining estrogen-cholinergic interactions to humans. Studies examined include estradiol and cholinergic antagonist reversal studies in normal older women, examinations of the neural representations of estrogen-cholinergic interactions using functional brain imaging, and studies of the ability of selective estrogen receptor modulators such as tamoxifen to interact with cholinergic-mediated cognitive performance. We also discuss the implications of these studies for the underlying hypotheses of cholinergic-estrogen interactions and cognitive aging, and indications for prophylactic and therapeutic potential that may exploit these effects.

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

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

Effects of long-term treatment with estrogen and medroxyprogesterone acetate on synapse number in the medial prefrontal cortex of aged female rats

OBJECTIVE

The present study investigated the effects of long-term hormone treatment, including the most commonly prescribed progestin, medroxyprogesterone acetate, during aging on synaptophysin-labeled boutons, a marker of synapses, in the medial prefrontal cortex (mPFC) of rats.

METHODS

Female Long Evans hooded rats were ovariectomized at middle age (12-13 mo) and were placed in one of four groups: no replacement (n = 5), 17β-estradiol alone (n = 6), estradiol and progesterone (n = 7), or estradiol and medroxyprogesterone acetate (n = 4). Estradiol was administered in the drinking water and progestogens were administered via subcutaneous pellets that were replaced every 90 days. After 7 months of hormone replacement, the animals were euthanized, and the brains were stained for synaptophysin, a membrane component of synaptic vesicles. The density of synaptophysin-labeled boutons was quantified in the mPFC using unbiased stereology and multiplied by the volume of the mPFC to obtain the total number.

RESULTS

Animals receiving estradiol and medroxyprogesterone acetate had significantly more synaptophysin-labeled boutons in the mPFC than did animals not receiving replacement (P < 0.03) and those receiving estradiol and progesterone (P < 0.02). In addition, there was a nonsignificant trend for animals receiving estradiol alone to have more synapses than those receiving estradiol and progesterone.

CONCLUSIONS

This study is the first to examine the effects of estradiol and medroxyprogesterone acetate during rat aging on cortical synaptic number. Estradiol with medroxyprogesterone acetate, but not progesterone, resulted in a greater number of synapses in the mPFC during aging than did no replacement.

Sex hormones, aging, and Alzheimer's disease

A promising strategy to delay and perhaps prevent Alzheimer's disease (AD) is to identify the age-related changes that put the brain at risk for the disease. A significant normal age change known to result in tissue-specific dysfunction is the depletion of sex hormones. In women, menopause results in a relatively rapid loss of estradiol and progesterone. In men, aging is associated with a comparatively gradual yet significant decrease in testosterone. We review a broad literature that indicates age-related losses of estrogens in women and testosterone in men are risk factors for AD. Both estrogens and androgens exert a wide range of protective actions that improve multiple aspects of neural health, suggesting that hormone therapies have the potential to combat AD pathogenesis. However, translation of experimental findings into effective therapies has proven challenging. One emerging treatment option is the development of novel hormone mimetics termed selective estrogen and androgen receptor modulators. Continued research of sex hormones and their roles in the aging brain is expected to yield valuable approaches to reducing the risk of AD.

Sex hormones, aging, and Alzheimer's disease

A promising strategy to delay and perhaps prevent Alzheimer's disease (AD) is to identify the age-related changes that put the brain at risk for the disease. A significant normal age change known to result in tissue-specific dysfunction is the depletion of sex hormones. In women, menopause results in a relatively rapid loss of estradiol and progesterone. In men, aging is associated with a comparatively gradual yet significant decrease in testosterone. We review a broad literature that indicates age-related losses of estrogens in women and testosterone in men are risk factors for AD. Both estrogens and androgens exert a wide range of protective actions that improve multiple aspects of neural health, suggesting that hormone therapies have the potential to combat AD pathogenesis. However, translation of experimental findings into effective therapies has proven challenging. One emerging treatment option is the development of novel hormone mimetics termed selective estrogen and androgen receptor modulators. Continued research of sex hormones and their roles in the aging brain is expected to yield valuable approaches to reducing the risk of AD.

Early initiation of hormone therapy in menopausal women is associated with increased hippocampal and posterior cingulate cholinergic activity

CONTEXT

The role of ovarian hormones in maintaining neuronal integrity and cognitive function is still debated. This study was undertaken to clarify the potential relationship between postmenopausal hormone use and the cholinergic system.

OBJECTIVE

We hypothesized that early initiated hormone therapy (HT) preserves the cholinergic system and that estrogen therapy (ET) would be associated with higher levels of acetylcholinesterase activity in the posterior cingulate cortex and hippocampus compared to estrogen plus progestin therapy (EPT) or no HT.

DESIGN AND SETTING

We conducted a cross-sectional study at a university teaching hospital.

PATIENTS

Fifty postmenopausal women (age, 65.2 ± 0.7 yr) with early long-term HT (n = 34; 13 ET and 21 EPT) or no HT (n = 16) participated in the study.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

We measured cholinergic activity (acetylcholinesterase) in the hippocampus and posterior cingulate brain regions as measured by N-[(11)C]methylpiperidin-4-yl propionate and positron emission tomography as a marker of cholinergic function.

RESULTS

Significant effects of treatment on cholinergic activity measures were obtained in the left hippocampus (F = 3.56; P = 0.04), right hippocampus (F = 3.42; P = 0.04), and posterior cingulate (F = 3.76; P = 0.03). No significant effects were observed in a cortical control region. Post hoc testing identified greater cholinergic activity in the EPT group compared to the no-HT group in the left hippocampus (P = 0.048) and posterior cingulate (P = 0.045), with a nonstatistically significant trend in the right hippocampus (P = 0.073).

CONCLUSIONS

A differential effect of postmenopausal ET and EPT on cholinergic neuronal integrity was identified in postmenopausal women. The findings are consistent with a preservation of cholinergic neuronal integrity in the EPT group.

Chronic stress and a cyclic regimen of estradiol administration separately facilitate spatial memory: relationship with hippocampal CA1 spine density and dendritic complexity

This study investigated the effects of chronic restraint stress and repeated cyclic estradiol pulses on hippocampal CA3 and CA1 dendritic and/or spine morphology and spatial memory in female rats. Sprague-Dawley adult female rats were ovariectomized and then injected over 2 days with 17β-estradiol (10 μg, s.c.), which was repeated every 4-5 days. While all rats received similar estradiol injection histories, half of the rats were chronically restrained and/or given a final cyclic pulse of estradiol prior to testing on a hippocampal-dependent object placement (OP) task to assess spatial memory. OP testing was performed 2 days after the last restraint session, as well as when the last 2 estradiol pulses best captured the maximal effect on hippocampal CA1 spine density. The data revealed several novel findings: (a) chronic stress or estradiol separately facilitated spatial memory, but did not have the same effects when coadministered, (b) CA1 spine densities negatively correlated with spatial memory, and (c) repeated estradiol pulses failed to prevent stress-induced CA3 dendritic retraction. We also corroborated previous studies showing increased CA1 spine density following estradiol, chronic stress, and behavioral manipulations. The present study uniquely combined chronic stress, repeated estradiol pulses, hippocampal morphology, and behavior within the same animals, allowing for correlational analyses to be performed between CA1 spine morphology and spatial memory. We demonstrate novel findings that chronic stress or estradiol pulses independently facilitate spatial memory, but not when coadministered, and that these effects may involve a balance of CA1 apical spine expression that is independent of CA3 dendritic complexity.

Perimenopausal use of hormone therapy is associated with enhanced memory and hippocampal function later in life

Evidence suggests that initiation of some forms of hormone therapy (HT) early in the perimenopausal or postmenopausal stage might confer benefit to verbal memory and the neural systems underlying memory, whereas late-life initiation confers no benefit or harm. This "critical window hypothesis" remains a topic of debate. Using functional magnetic resonance imaging (fMRI), we examined the long-term impact of perimenopausal HT use on brain function during performance of verbal and figural memory tasks. Participants were 34 postmenopausal women (mean age 60 years) from the Melbourne Women's Midlife Health Project and included 17 early (perimenopausal) and continuous users of HT and 17 never users matched on age, education, and verbal knowledge. Continuous HT use from the perimenopausal stage versus no use was validated with prospective daily diary records and study visit data. The primary outcome was patterns of brain activation in an a priori region of interest in the medial temporal lobe during verbal encoding and recognition of words. Results indicated that perimenopausal HT users performed better than nonusers on the imaging verbal memory task (p<.05). During verbal recognition, perimenopausal HT users showed increased activation in the left hippocampus and decreased activation in the parahippocampal gyrus bilaterally compared with never users. Each of these patterns of activation was associated with better memory performance on the imaging memory task. These results suggest that perimenopausal use of HT might confer long-term benefits to verbal memory and the brain systems underlying verbal memory. More generally, the results support the critical window hypothesis.

Assessment of estradiol influence on spatial tasks and hippocampal CA1 spines: evidence that the duration of hormone deprivation after ovariectomy compromises 17beta-estradiol effectiveness in altering CA1 spines

Two pulses of 17beta-estradiol (10 microg) are commonly used to increase hippocampal CA1 apical dendritic spine density and alter spatial performance in ovariectomized (OVX) female rats, but rarely are the measures combined. The goal of this study was to use this two-pulse injection protocol repeatedly with intervening wash-out periods in the same rats to: 1) measure spatial ability using different tasks that require hippocampal function and 2) determine whether ovarian hormone depletion for an extended 10-week period reduces 17beta-estradiol's effectiveness in elevating CA1 apical dendritic spine density. Results showed that two injections of 10 microg 17beta-estradiol (72 and 48 h prior to testing and timed to maximize CA1 apical spine density at behavioral assessment) corresponded to improved spatial memory performance on object placement. In contrast, two injections of 5 microg 17beta-estradiol facilitated spatial learning on the water maze compared to rats given two injections of 10 microg 17beta-estradiol or the sesame oil vehicle. Neither 17beta-estradiol dose altered Y-maze performance. As expected, the intermittent two-pulse injection protocol increased CA1 apical spine density, but 10 weeks of OVX without estradiol treatment decreased the effectiveness of 10 microg 17beta-estradiol to increase CA1 apical spine density. Moreover, two pulses of 5 microg 17beta-estradiol injected intermittently failed to alter CA1 apical spine density and decreased basal spine density. These results demonstrate that extended time without ovarian hormones reduces 17beta-estradiol's effectiveness to increase CA1 apical spine density. Collectively, these findings highlight the complex interactions among estradiol, CA1 spine density/morphology, and task requirements, all of which contribute to behavioral outcomes.

Brain aging modulates the neuroprotective effects of estrogen on selective aspects of cognition in women: a critical review

Although there is now a substantial literature on the putative neuroprotective effects of estrogen on cognitive functioning in postmenopausal women, it is replete with inconsistencies. The critical period hypothesis, posited several years ago, attempts to account for the discrepancies in this literature by positing that estrogen treatment (ET) will protect aspects of cognition in older women only when treatment is initiated soon after the menopause. Indeed, evidence from basic neuroscience and from the animal and human literature reviewed herein provides compelling support for the critical period hypothesis. Although it is not known with certainty why estrogen does not protect cognition and may even cause harm when administered to women over the age of 65years, it is likely that the events that characterize brain aging, such as a reduction in brain volume and in neuronal size, alterations in neurotransmitter systems, and a decrease in dendritic spine numbers, form an unfavorable background that precludes a neuroprotective effects of exogenous estrogen on the brain. Other factors that have likely contributed to the discrepancies in the estrogen-cognition literature include differences in the estrogen compounds used, their route of administration, cyclic versus continuous regimens, and the concomitant use of progestins. This critical analysis attempts to define conditions under which ET may protect aspects of cognition in aging women while also considering the cost/benefit ratio for the treatment of women aged 50-59years. Suggestions for specific future research questions are also addressed.

Hot flashes and estrogen therapy do not influence cognition in early menopausal women

OBJECTIVE

To examine how menopausal symptoms and estrogen therapy (ET)-induced symptom relief affect cognition in early menopause.

DESIGN

There were two components. Part 1 was a cross-sectional study of 37 healthy, recently postmenopausal women with diverse menopausal symptoms. Women were categorized as having low (n=20) or high symptoms (n=17) based on a validated symptom questionnaire. Women completed mood and sleep questionnaires and underwent cognitive testing, which included verbal memory, visual memory, emotional memory, and verbal fluency. Thirty-two of these women went on to part 2 of the study. Fourteen were randomly assigned to receive ET and 18 to receive placebo for 8 weeks. Before treatment and at 4 and 8 weeks, women completed the same measures as in part 1 of the study.

RESULTS

High symptom women had more negative mood (P=0.01) and lower quality sleep (P<0.001) than low symptom women. Despite suffering from more menopausal symptoms, worse mood, and poorer sleep, women in the high symptom group performed the same on cognitive testing as women in the low symptom group. Women receiving ET had greater improvements in menopausal symptoms and sleep compared with those receiving the placebo (P<or=0.05). ET did not improve mood compared with placebo. Women receiving ET did not have any improvement in cognitive performance compared with those receiving the placebo.

CONCLUSIONS

Menopausal symptoms do not impair cognition. ET does not improve cognition despite alleviating symptoms and improving sleep in recently naturally menopausal women with diverse menopausal symptoms.

The Effect of 3-Year Treatment with 0.25 mg/day of Micronized 17β-Estradiol on Cognitive Function in Older Postmenopausal Women

OBJECTIVES

To evaluate the effect of ultra-low-dose (0.25 mg/d) micronized 17beta-estradiol on cognitive function in older postmenopausal women.

DESIGN

Randomized, placebo-controlled trial conducted for 3 years.

SETTING

Academic health center in greater Hartford, Connecticut.

PARTICIPANTS

Fifty-seven healthy, community-dwelling, older postmenopausal women.

INTERVENTION

Women received 0.25 mg/d of micronized 17beta-estradiol (estrogen therapy (ET), n=32) or placebo (n=25); all women who had not had a hysterectomy received 100 mg/d of oral micronized progesterone for 2-week periods every 6 months.

MEASUREMENTS

Neuropsychological measures of memory, language, mood, and executive function were collected at baseline, 3 months, and 36 months. Measures of executive function included the Controlled Oral Word Association Test, the Trail Making Test, and the Wisconsin Card Sorting Test. The Boston Naming Test was used to measure language skills. The Symbol Digit Modalities Test was used as a measure of sustained attention. Measures of memory included the Complex Figure Test, Fuld Object Memory Test, and a selected subtest from the Wechsler Memory Scale. Scores from the Geriatric Depression Scale and the Beck Anxiety Inventory were used to assess symptoms of depression.

RESULTS

No differences were found between ET and placebo on any of the neurocognitive measures or depression instruments, nor were there any differences when the groups were stratified according to age.

CONCLUSION

This small study, which had adequate power to detect change in some but not all domains of cognition tested, revealed that low-dose estrogen neither benefits nor harms cognitive function in older women after 3 years of treatment, but confirmation is needed from larger trials.

The critical period hypothesis: can it explain discrepancies in the oestrogen-cognition literature?

Although there is compelling evidence from small randomised controlled trials and cross-sectional studies indicating that oestrogen helps to protect against cognitive ageing in women, the findings of the large, Women's Health Initiative Memory Study failed to support the earlier findings. The attempt to resolve these discrepancies led to the formulation of the Critical Period Hypothesis which holds that oestrogen has maximal protective benefits on cognition in women when it is initiated closely in time to a natural or surgical menopause but not when treatment is begun decades after the menopause. This article reviews the evidence from basic neuroendocrinology, from animal behavioural studies and from human studies that supports the critical period hypothesis. In view of the promise of this hypothesis and its considerable clinical implications, a direct test of its validity is warranted.

Estrogen receptor alpha and its splice variants in the hippocampus in aging and Alzheimer's disease

Clinical and experimental studies show that estrogens can have beneficial effects on hippocampus-dependent cognitive functions that may be mediated by estrogen receptor (ER)alpha. We investigated whether menopause and Alzheimer's disease (AD) cause changes in this ER subtype. Immunocytochemical staining of ERalpha, aromatase and Golgi complex (GC) was performed on paraffin embedded hippocampal tissue from women of the pre-, peri- and postmenopausal age. Canonical ERalpha mRNA amplicons, ERalpha splice variants (del.2, del.4, del.7, MB1) and aromatase transcripts were measured by Q-PCR in frozen hippocampal samples of AD and matched control cases. Nuclear ERalpha, aromatase and the GC enhanced during aging in women indicating availability of locally synthesized estrogens that may up-regulate ERalpha by which neuronal metabolism can be augmented in the hippocampus after the menopause. In AD cases canonical and alternatively spliced ERalpha mRNA, and aromatase gene expression were down-regulated suggesting a deficit in local estrogen levels and diminished signalling through ERalpha. The major ERalpha splice variants in the hippocampus were found to be MB1 and del.4. A novel ERalpha isoform TADDI was isolated and sequenced from two female patients. It lacks 31 bp at the junction between exons 3 and 4 with an insertion of 13 nucleotides from the middle of the exon 2.

Estrogen-containing hormone therapy and Alzheimer’s disease risk: Understanding discrepant inferences from observational and experimental research

Estrogen has the potential to influence brain processes implicated in Alzheimer's disease pathogenesis. With the loss of ovarian estrogen production after menopause, estrogen-containing hormone therapy might be expected to influence the risk of Alzheimer's disease. Observational data link use of hormone therapy to reductions in Alzheimer risk, but experimental evidence from the Women's Health Initiative Memory Study trial demonstrates that oral estrogen, with or without a progestin, increases the incidence of dementia for postmenopausal women age 65 years or older. Mechanisms of harm in this setting are unknown. Bias and unrecognized confounding in observational research are leading candidates for discrepant results between observational studies and the Women's Health Initiative Memory Study trial. Studies are also distinguished by differences in outcome measures, hormone therapy formulations, prevalence of menopausal symptoms among study participants, and participant age. Finally, Women's Health Initiative Memory Study findings may not generalize to estrogen use by relatively young women during the menopausal transition or early postmenopause, a class of women who were ineligible for the Women's Health Initiative Memory Study trial. In observational studies, hormone therapy exposure often included use by younger women for menopausal vasomotor symptoms. Although there is no clinical trial evidence that hormone therapy at any age protects against Alzheimer's disease, it remains to be determined whether the age at which hormone exposure occurs or the timing of hormone therapy initiation in relation to the menopause (the critical window hypothesis) modifies treatment outcomes on dementia risk.

Morphometric evaluation of effects of two sex steroids on mammary gland of female rats

OBJECTIVE

The purpose of this study was to evaluate the effects of two sex hormones on normal mammary gland of female rats.

METHODS

Forty 250-day-old female rats, 20 of them with offspring and 20 not, were ovariectomized and, divided into 4 subgroups in order to receive one of the following subcutaneous treatment: estradiol benzoate (EB), medroxyprogesterone (MPA), EB+MPA or placebo, for 10 weeks. After treatment, mammary glands were studied with optical microscope. Whole gland, lobule, ductule and lumen compartments were evaluated by morphometric methods. Also a qualitative evaluation were performed seeking for secretion, microcalcification and trophic status.

RESULTS

It was found that (a) MPA-only and placebo were similar for all parameters; (b) the same between EB and EB+MPA; (c) EB and EB+MPA increased lobule, ductule and lumen compartments significantly compared to MPA-only or placebo; (d) EB increased epithelium but without significance and EB+MPA increased it significantly compared to placebo or MPA; (e) EB and EB+MPA incremented secretion.

CONCLUSIONS

In normal mammary gland of female rats: progestin action depends on estrogen presence. MPA does not revert estrogen-dependent proliferation, but it magnifies estradiol effect. Both EB and EB+MPA stimulate differentiation. Rats without offspring presented a greater epithelial proliferation under treatment with these sex hormones.

Ovariectomy-induced disruption of long-term synaptic depression in the hippocampal CA1 region in vivo is attenuated with chronic estrogen replacement

Endogenous cyclical changes in the levels of estrogen can have marked effects on hippocampal synaptic plasticity. In two experiments, we examined the effect of chronic estrogen loss and replacement following ovariectomy on the induction of bidirectional changes in synaptic plasticity in the CA1 region in vivo. In Experiment 1, ovariectomy carried out either 5 days or 5 weeks before testing impaired the induction of long-term depression (LTD) and but not long-term potentiation (LTP). In Experiment 2, chronic estrogen replacement (0.2 ml of 10 microg injection of 17beta-estradiol every 48 h) over the course of 5 weeks enhanced the magnitude of paired-pulse-induced LTD in the CA1 region but had no effect on the induction of LTP. The results demonstrate that acute and chronic estrogen deprivation disrupted dynamic synaptic plasticity processes in the hippocampal CA1 region and that this disruption was ameliorated by chronic estrogen replacement. The findings are discussed with reference to: (1) the contribution of Ca(2+) regulated synaptic signalling pathways in the CA1 region to estradiol modulation of LTP and LTD and (2) the potential functional significance of ovariectomy-induced changes in synaptic plasticity for learning and memory processes.

Hormone therapy and Alzheimer’s disease: benefit or harm?

Alzheimer's disease (AD) is the most common cause of dementia. After menopause, circulating levels of oestrogens decline markedly and oestrogen influences several brain processes predicted to modify AD risk. For example, oestrogen reduces the formation of beta-amyloid, a biochemical hallmark of AD. Oestrogen effects on oxidative stress and some effects on inflammation and the cerebral vasculature might also be expected to ameliorate risk. However, AD pathogenesis is incompletely understood and other oestrogen actions could be deleterious. Limited clinical trial evidence suggests that oestrogen therapy, begun after the onset of AD symptoms, is without substantial benefit or harm. Observational studies have associated oestrogen-containing hormone therapy with reduced AD risk. However, in the Women's Health Initiative Memory Study - a randomised, placebo-controlled trial of women 65 - 79 years of age - oral oestrogen plus progestin doubled the rate of dementia, with heightened risk appearing soon after treatment was initiated. Based on current evidence, hormone therapy is thus not indicated for the prevention of AD. Discrepancies between observational studies and the Women's Health Initiative clinical trial may reflect biases and unrecognised confounding factors in observational reports. Other explanations for divergent findings should be considered in future research, including effects of unopposed oestrogen or different hormone therapy preparations and the intriguing theoretical possibility that effects of hormone therapy on AD risk may be modified by the timing of use (e.g., initiation during the menopausal transition or early postmenopause versus initiation during the late postmenopause).

Estrogen replacement therapy, Alzheimer's disease, and mild cognitive impairment

This article highlights the latest findings regarding estrogen replacement therapy in the treatment and prevention of Alzheimer's disease (AD) and mild cognitive impairment in women. Despite considerable evidence from observational studies, recent randomized clinical trials of conjugated equine estrogens, alone and in combination with progestin, have shown no benefit for either the treatment of established AD or for the short-term prevention of AD, mild cognitive impairment, or cognitive decline. Based on the evidence, there is no role at present for estrogen replacement therapy in the treatment or prevention of AD or cognitive decline, despite intriguing results from the laboratory and from observational studies. However, numerous questions remain about the biologic effects of estrogens on brain structure and function. Additional basic and clinical investigations are necessary to examine different forms and dosages of estrogens, other populations, and the relevance of timing and duration of exposure.

Cognition, mood disorders, and sex hormones

Macaques (Macaca spp.) are useful models to evaluate effects of ovarian sex steroids and selective estrogen receptor modulators (SERMs) on mood and cognitive function due to similarities to women in their reproductive and central nervous systems. The results of nonhuman primate studies support the hypothesis that estrogen mediates specific aspects of attention and memory, yet much work is needed to understand which cognitive processes are affected, whether natural versus surgical menopause effects are different, and the interaction of age and ovarian senescence on cognitive function. This knowledge is necessary to determine whether to support the cognitive function of women in the menopausal phase of life and, if so, to determine efficacious therapeutic interventions. Mood disorders are prevalent in women and are associated with reproductive function in women and macaques. Exogenous steroid therapies, including oral contraceptives and postmenopausal hormone replacement therapies, have behavioral effects in women and appear to affect the behavior and underlying neural substrates of monkeys. Additional research is necessary to confirm and extend these observations. Ovarian steroids have multiple effects on serotonin synthesis, reuptake, and degradation, on neural activity that drives serotonin release, and on receptor activation in primates. This system modulates cognitive function and mood and is the target of a broad class of antidepressant therapies. Understanding the effects of ovarian steroids on the neural serotonergic system is necessary to understand depression in women. These studies are best carried out in primate models, which are more similar to humans in neural serotonergic function than other animal models.