Neuroprotective effects of estrogen therapy for cognitive and neurobiological profiles of monkey models of menopause

Altered Sexual Response-Related Functional Connectivity and Morphometric Changes Influenced by Sex Hormones across Menopausal Status

Our study retrospectively investigated differential patterns of the functional connectivity (FC) of core brain regions synchronous with morphometric changes associated with sexual dysfunction in menopausal women, and their correlations with sexual hormones. Twenty-three premenopausal women (mean age: 41.52 ± 7.38 years) and 21 menopausal women (mean age: 55.52 ± 2.80 years) underwent sex hormone level measurements with high-resolution T1 and functional magnetic resonance imaging (MRI) during rest, neutral, and sexual arousal conditions. Analysis of covariance adjusted for age was used to compare the FC and gray matter (GM) volume between the two groups. Menopausal women showed lower GM volumes in the superior frontal gyrus (SFG), superior temporal pole, parahippocampal gyrus (PHG), hippocampus (Hip), amygdala (Amg), and cerebellum (Cb) compared to premenopausal women (p < 0.05). In addition, compared to premenopausal women, menopausal women showed decreased FC of seed regions involved in the SFG, frontal eye fields, and Amg, as well as target regions involved in the PHG, Hip, inferior frontal gyrus, Cb, and vermis (p < 0.005). Furthermore, the FC between the right Amg and right Cb and between the left Amg and right Cb during sexual arousal in both groups was positively correlated with total estrogen and estradiol levels, respectively (p < 0.01). The GM volume values in the right Amg and right Cb were positively correlated with total estrogen and estradiol levels (p < 0.05). Our study demonstrated an association between menopause-related differential FC and GM volume variations and fluctuating sex hormones. Our findings highlight that overlapping brain regions with functional alterations and morphometric changes are closely linked with menopausal symptom-related decreases in sexual arousal and hormone levels.

Sex Differences in the Neurobiology of Stress

This review highlights the existing knowledge and data that explain the physiologic impacts of stress, especially pertaining to neurobiology, and how these impacts differ by sex. Furthermore, this review explains the benefits of interventions aimed at preventing or mitigating the adverse effects of stress, because of both the significant toll of stress on the body and the disproportionate impact of these changes experienced by women.

The Role of Hormonal Replacement Therapy in BRCA Mutated Patients: Lights and Shadows

All cancers develop as a result of mutations in genes. DNA damage induces genomic instability and subsequently increases susceptibility to tumorigenesis. Women who carry mutations of BRCA 1 and BRCA2 genes have an augmented risk of breast and ovarian cancer and a markedly augmented probability of dying because of cancer compared to the general population. As a result, international guidelines recommend that all BRCA1\2 mutation carriers be offered risk-reducing bilateral salpingo-oophorectomy at an early age to reduce the risk of cancer and decrease the mortality rate of this high-risk population. NCCN guidelines recommend risk-reducing bilateral salpingo-oophorectomy in pre-menopausal women, between 35-40 years in BRCA1 mutation carriers and between 40-45 years in BRCA2 mutation carriers. Unfortunately, the well-documented reduction of cancer risk is counterbalanced by early sterility and premature ovarian failure with an early onset of secondary menopausal syndromes such as neuromotor, cardiovascular, cognitive and urogenital deficiency. Hormonal replacement therapy significantly compensates for hormonal deprivation and counteracts menopausal syndrome morbidity and mortality; however, some data suggest a possible correlation between hormonal medications and cancer risk, especially in BRCA1\2 carriers who undergo long-term regimens. Conversely, short-term treatment before the age of natural menopause does not appear to increase the cancer risk in BRCA1 mutation carriers without a personal history of breast cancer after prophylactic surgery. Few data are available on BRCA2 mutation carriers and more well-designed studies are needed. In conclusion, clinicians should propose short-term hormone replacement therapy to BRCA 1 carriers to counteract hormonal deprivation; personalized counselling should be offered to BRCA2 mutation carriers for a balance between the risks and benefits of the treatment.

Hormone Therapy in Menopause: Concepts, Controversies, and Approach to Treatment

Hormone therapy (HT) is an effective treatment for menopausal symptoms, including vasomotor symptoms and genitourinary syndrome of menopause. Randomized trials also demonstrate positive effects on bone health, and age-stratified analyses indicate more favorable effects on coronary heart disease and all-cause mortality in younger women (close proximity to menopause) than in women more than a decade past menopause. In the absence of contraindications or other major comorbidities, recently menopausal women with moderate or severe symptoms are appropriate candidates for HT. The Women's Health Initiative (WHI) hormone therapy trials-estrogen and progestin trial and the estrogen-alone trial-clarified the benefits and risks of HT, including how the results differed by age. A key lesson from the WHI trials, which was unfortunately lost in the posttrial cacophony, was that the risk:benefit ratio and safety profile of HT differed markedly by clinical characteristics of the participants, especially age, time since menopause, and comorbidity status. In the present review of the WHI and other recent HT trials, we aim to provide readers with an improved understanding of the importance of the timing of HT initiation, type and route of administration, and of patient-specific considerations that should be weighed when prescribing HT.

Alternative Animal Models of Aging Research

Most research on mechanisms of aging is being conducted in a very limited number of classical model species, i.e., laboratory mouse (Mus musculus), rat (Rattus norvegicus domestica), the common fruit fly (Drosophila melanogaster) and roundworm (Caenorhabditis elegans). The obvious advantages of using these models are access to resources such as strains with known genetic properties, high-quality genomic and transcriptomic sequencing data, versatile experimental manipulation capabilities including well-established genome editing tools, as well as extensive experience in husbandry. However, this approach may introduce interpretation biases due to the specific characteristics of the investigated species, which may lead to inappropriate, or even false, generalization. For example, it is still unclear to what extent knowledge of aging mechanisms gained in short-lived model organisms is transferable to long-lived species such as humans. In addition, other specific adaptations favoring a long and healthy life from the immense evolutionary toolbox may be entirely missed. In this review, we summarize the specific characteristics of emerging animal models that have attracted the attention of gerontologists, we provide an overview of the available data and resources related to these models, and we summarize important insights gained from them in recent years. The models presented include short-lived ones such as killifish (Nothobranchius furzeri), long-lived ones such as primates (Callithrix jacchus, Cebus imitator, Macaca mulatta), bathyergid mole-rats (Heterocephalus glaber, Fukomys spp.), bats (Myotis spp.), birds, olms (Proteus anguinus), turtles, greenland sharks, bivalves (Arctica islandica), and potentially non-aging ones such as Hydra and Planaria.

Longitudinal Effects of Immediate and Delayed Estradiol on Cognitive Performance in a Spatial Maze and Hippocampal Volume in Menopausal Macaques Under an Obesogenic Diet

The consumption of a diet high in fat and refined sugars has several health risks, including the development of cognitive decline and neurodegeneration. For women, menopause carries additional health risks that may interact with a high-fat diet in negative ways. Some symptoms of menopause, including cognitive impairments, can be modulated by hormone replacement therapy (HRT), but the hormonal formulation and the timing of the treatment relative to the onset of menopause are critical factors determining its efficacy. Little is known about how obesogenic, high-fat, high-sugar diets interact with HRT in menopause to affect cognition and neurodegeneration. Given the high prevalence of the consumption of an obesogenic Western-style diet, understanding how the effects of HRT are modulated by an obesogenic diet is critical for developing optimized therapeutic strategies for peri- and post-menopausal women. In this study, we investigated by magnetic resonance imaging (MRI) the effects of either immediate or delayed estradiol hormone therapy on cognition and neuroanatomy following ovo-hysterectomy (OvH) of aged, female rhesus macaques on an obesogenic diet. The macaques were followed for 2.5 years after ovo-hysterectomy, with four time points at which anatomical MRIs were acquired. Analysis of hippocampal volumes revealed an interaction between time point and treatment; hippocampal volumes in the delayed estrogen group, but not the immediate estrogen group, increased over time compared to those in untreated controls. Performance on a hippocampal-dependent spatial maze task showed improved performance in estrogen treated animals compared to OvH macaques given placebo. These results indicate that HRT may contribute to beneficial cognitive outcomes after menopause under an obesogenic diet.

Sexual dimorphism in cognitive disorders in a murine model of neuropathic pain

BACKGROUND

A sex-difference in susceptibility to chronic pain is well-known. Although recent studies have begun to reveal the sex-dependent mechanisms of nerve injury-induced pain sensitization, sex differences in the affective and cognitive brain dysfunctions associated with chronic pain have not been investigated. Therefore, we tested whether chronic pain leads to affective and cognitive disorders in a mouse neuropathic pain model and whether those disorders are sexually dimorphic.

METHODS

Chronic neuropathic pain was induced in male and female mice by L5 spinal nerve transection (SNT) injury. Pain sensitivity was measured with the von Frey test. Affective behaviors such as depression and anxiety were assessed by the forced swim, tail suspension, and open field tests. Cognitive brain function was assessed with the Morris water maze and the novel object location and novel object recognition tests.

RESULTS

Mechanical allodynia was induced and maintained for up to 8 weeks after SNT in both male and female mice. Depressive- and anxiety-like behaviors were observed 8 weeks post-SNT injury regardless of sex. Chronic pain-induced cognitive deficits measured with the Morris water maze and novel object location test were seen only in male mice, not in female mice.

CONCLUSIONS

Chronic neuropathic pain is accompanied by anxiety- and depressive-like behaviors in a mouse model regardless of sex, and male mice are more vulnerable than female mice to chronic pain-associated cognitive deficits.

Hormonal Influences on Cognitive Function

This article examines how hormonal changes may affect the neuronal networking and mechanisms of cognitive function. Hormones are the chemical regulators of the human body and function critically to maintain various processes, such as growth, emotions and even cognition. Numerous studies have examined the relationship between hormonal effects and cognitive function; these studies have investigated different factors, such as aging, pregnancy, post-natal states, emotions and stress. Different types of hormones produce different outcomes for the human body and mind. Hormones may also contribute to both positive and negative outcomes, depending on whether the hormone levels are too low or too high. To investigate the hormonal effects on cognitive function, the sources of localisation must be localised, so that the neuronal network can be realised. Furthermore, cognitive function does not rely on a specific brain region but is determined by the neuronal network interactions. Thus, it is worthwhile to know the neural mechanisms behind cognitive functions that are affected by hormones.

Neuroimaging the Menstrual Cycle and Premenstrual Dysphoric Disorder

Knowledge of gonadal hormone-related influences on human brain anatomy, function, and chemistry is scarce. The present review scrutinized organizational and functional neuroimaging correlates of the menstrual cycle and premenstrual dysphoric disorder (PMDD). Supportive evidence of cyclic short-term structural and functional brain plasticity in response to gonadal hormonal modulation is provided. The paucity of studies, sparsity and discordance of findings, and weaknesses in study design at present hinder the drawing of firm conclusions. Ideal study designs should comprise high-resolution multimodal neuroimaging (e.g., MRI, DTI, rs-fMRI, fMRI, PET), hormones, genetic, and behavioral longitudinal assessments of healthy women and PMDD patients at critical time points of the menstrual cycle phase (i.e., early follicular phase, late follicular phase, mid-luteal phase) in a counter-balanced setup. Studies integrating large-scale brain network structural, functional, and molecular neuroimaging, as well as treatment data, will deepen the understanding of neural state, disorder, and treatment markers.

Neurocognitive effects of estrogens across the adult lifespan in nonhuman primates: State of knowledge and new perspectives

This article is part of a Special Issue "Estradiol and cognition". This review discusses the unique contribution of nonhuman primate research to our understanding of the neurocognitive effects of estrogens throughout the adult lifespan in females. Mounting evidence indicates that estrogens affect many aspects of hippocampal, prefrontal and cholinergic function in the primate brain and the underlying mechanisms are beginning to be elucidated. In addition, estrogens may also influence cognitive function indirectly, via the modulation of other systems that impact cognition. We will focus on the effects of estrogens on sleep and emphasize the need for primate models to better understand these complex interactions. Continued research with nonhuman primates is essential for the development of therapies that are optimal for the maintenance of women's cognitive health throughout the lifespan.

Effects of Age and Estradiol on Gene Expression in the Rhesus Macaque Hypothalamus

BACKGROUND

The hypothalamus plays a key role in mediating the effects of estrogen on many physiological functions, including reproduction, metabolism, and thermoregulation. We have previously observed marked estrogen-dependent gene expression changes within the hypothalamus of rhesus macaques during aging, especially in the KNDy neurons of the arcuate-median eminence (ARC-ME) that produce kisspeptin, neurokinin B, and dynorphin A. Little is known, however, about the mechanisms involved in mediating the feedback from estrogen onto these neurons.

METHODS

We used quantitative real-time PCR to profile age- and estrogen-dependent gene expression changes in the rhesus macaque hypothalamus. Our focus was on genes that encode steroid receptors (ESR1, ESR2, PGR, and AR) and on enzymes that contribute to the local synthesis of 17β-estradiol (E2; STS, HSD3B1/2, HSD17B5, and CYP19A). In addition, we used RT(2) Profiler™ PCR Arrays to profile a larger set of genes that are integral to hypothalamic function.

RESULTS

KISS1, KISS1R, TAC3, and NPY2R mRNA levels increased in surgically menopausal (ovariectomized) old females relative to age-matched ovariectomized animals that received E2 hormone therapy. In contrast, PGR, HSD17B, GNRH2, SLC6A3, KISS1, TAC3, and NPY2R mRNA levels increased after E2 supplementation.

CONCLUSION

The rhesus macaque ARC-ME expresses many genes that are responsive to changes in circulating estrogen levels, even during old age, and these may contribute to causing the normal and pathophysiological changes that occur during menopause.

Functional and molecular neuroimaging of menopause and hormone replacement therapy

The level of gonadal hormones to which the female brain is exposed considerably changes across the menopausal transition, which in turn, is likely to be of great relevance for neurodegenerative diseases and psychiatric disorders. However, the neurobiological consequences of these hormone fluctuations and of hormone replacement therapy in the menopause have only begun to be understood. The present review summarizes the findings of thirty-five studies of human brain function, including functional magnetic resonance imaging, positron and single-photon computed emission tomography studies, in peri- and postmenopausal women treated with estrogen, or estrogen-progestagen replacement therapy. Seven studies using gonadotropin-releasing hormone agonist intervention as a model of hormonal withdrawal are also included. Cognitive paradigms are employed by the majority of studies evaluating the effect of unopposed estrogen or estrogen-progestagen treatment on peri- and postmenopausal women's brain. In randomized-controlled trials, estrogen treatment enhances activation of fronto-cingulate regions during cognitive functioning, though in many cases no difference in cognitive performance was present. Progestagens seems to counteract the effects of estrogens. Findings on cognitive functioning during acute ovarian hormone withdrawal suggest a decrease in activation of the left inferior frontal gyrus, thus essentially corroborating the findings in postmenopausal women. Studies of the cholinergic and serotonergic systems indicate these systems as biological mediators of hormonal influences on the brain. More, hormonal replacement appears to increase cerebral blood flow in several cortical regions. On the other hand, studies on emotion processing in postmenopausal women are lacking. These results call for well-powered randomized-controlled multi-modal prospective neuroimaging studies as well as investigation on the related molecular mechanisms of effects of menopausal hormonal variations on the brain.

Oestradiol modulation of cognition in adult female marmosets (Callithrix jacchus)

The common marmoset (Callithrix jacchus) provides many advantages over traditional rodent and macaque species as a model for human ageing and may be very useful for studying the effects of sex steroids on cognitive and brain ageing. We present the first study examining the effects of oestrogens on cognitive function in female marmosets. Adult monkeys (3-5 years of age) were trained to a specific learning criterion on a battery of cognitive tasks preoperatively (object discrimination, delayed response with increasing delays and detour reaching with opaque box) and were tested on different versions of these tasks (object reversals, delayed response with randomised delays and detour reaching with clear box) after ovariectomy and simultaneous implantation with 17β-oestradiol (E2 ) (n = 6) or blank (n = 6) Silastic capsules. Acquisition of a delayed matching-to-position task with a 1-s delay was also administered after completion of these tests. E2 -treated monkeys were significantly impaired on the second reversal and showed an increase in perseverative responding from reversals 1-3. Their performance also tended to be worse than that of control monkeys on the delayed response task. Performance acquisition on the delayed matching-to-position tended to be better in E2 -treated relative to control monkeys, although the group difference did not reach statistical significance. No effect of treatment was detected for detour reaching or affiliative behaviours. Overall, the findings indicate that E2 compromises performance on prefrontally-mediated tasks. The suggestion that E2 may improve acquisition on tasks dependent on the hippocampus will require further validation. These results are discussed in the context of dopaminergic and serotonergic signalling. We conclude that the marmoset is a useful new primate model for examining the effects of oestrogens on cognitive function.

Delayed response task performance as a function of age in cynomolgus monkeys (Macaca fascicularis)

We compared delayed response task performance in young, middle-aged, and old cynomolgus monkeys using three memory tests that have been used with non-human primates. Eighteen cynomolgus monkeys—6 young (4–9 years), 6 middle-aged (10–19 years), and 6 old (above 20 years)—were tested. In general, the old monkeys scored significantly worse than did the animals in the two other age groups. Longer delays between stimulus presentation and response increased the performance differences between the old and younger monkeys. The old monkeys in particular showed signs of impaired visuo-spatial memory and deteriorated memory consolidation and executive functioning. These results add to the body of evidence supporting the utility of Macaca fascicularis in studies of cognition and as a potential translational model for age-associated memory impairment/dementia-related disorders.

Ovarian hormones promote recovery from sleep deprivation by increasing sleep intensity in middle-aged ovariectomized rats

Sleep disturbances are commonly associated with menopause. Hormone replacement therapy is often used to treat various menopausal symptoms, but its efficacy for improving sleep is a matter of debate. We addressed this question by using a rodent model of ovarian hormone loss and replacement in midlife. Middle-aged female rats were ovariectomized and implanted with capsules containing estradiol with or without progesterone, or oil. After two weeks, sleep/wake states were recorded polygraphically during a 24-h baseline period, followed by 6h of sleep deprivation in the second half of the light phase, and a 24-h recovery period. During the baseline dark phase, hormone treatments increased wakefulness, and decreased non-rapid eye movement sleep (NREMS) by shortening NREMS episodes; however, NREMS EEG delta power or energy (cumulative power) was unaffected by combined hormones. Following sleep deprivation, all the groups showed NREMS and rapid eye movement sleep (REMS) rebounds, with similar relative increases from respective baseline levels. The increases in NREMS EEG delta power/energy during recovery were enhanced by combined hormones. These results from middle-aged ovariectomized rats indicate that replacement with estrogen with or without progesterone reduces baseline NREMS without affecting sleep intensity, particularly during the dark (active) phase, whereas following sleep deprivation the same hormone treatments do not affect the ability to increase NREMS or REMS, but treatment with both hormones, in particular, enhances the intensity of recovery sleep. These results support the usefulness of ovariectomized middle-aged rats as a model system to study the biological effects of hormone replacement on sleep regulation.

Clinically relevant hormone treatments fail to induce spinogenesis in prefrontal cortex of aged female rhesus monkeys

Preclinical animal models have provided strong evidence that estrogen (E) therapy (ET) enhances cognition and induces spinogenesis in neuronal circuits. However, clinical studies have been inconsistent, with some studies revealing adverse effects of ET, including an increased risk of dementia. In an effort to bridge this disconnect between the preclinical and clinical data, we have developed a nonhuman primate (NHP) model of ET combined with high-resolution dendritic spine analysis of dorsolateral prefrontal cortical (dlPFC) neurons. Previously, we reported cyclic ET in aged, ovariectomized NHPs increased spine density on dlPFC neurons. Here, we report that monkeys treated with cyclic E treatment paired with cyclic progesterone (P), continuous E combined with P (either cyclic or continuous), or unopposed continuous E failed to increase spines on dlPFC neurons. Given that the most prevalent form of ET prescribed to women is a combined and continuous E and P, these data bring into convergence the human neuropsychological findings and preclinical neurobiological evidence that standard hormone therapy in women is unlikely to yield the synaptic benefit presumed to underlie the cognitive enhancement reported in animal models.

Effects of a Chinese medicinal plant Radix astragali on the ovariectomized female rats

Perimenopausal syndrome occurs during the transition to menopause. Complementary and alternative medicine, especially Chinese medicinal plants, has manifested significant effects in alleviating perimenopausal symptoms. However, little research has been focused on the effects of Chinese medicinal plant on the immune function of the perimenopausal women. The present study aimed to explore the effects of Radix Astragali (RA) on the sex hormone levels and the interleukins of the ovariectomized female rats. 24 female Sprague-Dawley (SD) rats were randomly divided into model control group (MOD group), sham-operation group (SHAM group), RA group and estrogen group (EST group). After all the treatment ended, the serum levels of estradiol (E2), follicle stimulating hormone (FSH), luteinizing hormone (LH), interleukin-2 (IL-2), and interleukin-8 (IL-8) were measured using enzyme-linked immune-sorbent assay (ELISA) and the uterus was removed and weighed after blood exsanguinations immediately. In the MOD group, the serum levels of E2 were significantly lower, and the serum levels of FSH and LH were markedly higher than those of the RA group, EST group and SHAM group (P<0.05). In the RA group, the serum levels of E2 were significantly lower, and the serum levels of FSH were markedly higher than those of the SHAM group and EST group, respectively. In the MOD group, the serum levels of IL-2 and IL-8 were significantly lower than those of the RA group, EST group and SHAM group (P<0.05), and no marked differences existed among RA group, EST group and SHAM group in the serum levels of IL-2 and IL-8 (P>0.05). The uterine weight of the rats in the RA group, EST group and SHAM group were significantly higher than those of the rats in MOD group (P<0.05). There were no marked differences among the rats from RA group, EST group and SHAM group on the uterine weight (P>0.05). It is concluded that RA can significantly improve the immune functions of the ovariectomized female rats, although it cannot change the sex hormones levels as significantly as estrogen.

Hormone replacement therapy and risk for neurodegenerative diseases

Over the past two decades, there has been a significant amount of research investigating the risks and benefits of hormone replacement therapy (HRT) with regards to neurodegenerative disease. Here, we review basic science studies, randomized clinical trials, and epidemiological studies, and discuss the putative neuroprotective effects of HRT in the context of Alzheimer's disease, Parkinson's disease, frontotemporal dementia, and HIV-associated neurocognitive disorder. Findings to date suggest a reduced risk of Alzheimer's disease and improved cognitive functioning of postmenopausal women who use 17β-estradiol. With regards to Parkinson's disease, there is consistent evidence from basic science studies for a neuroprotective effect of 17β-estradiol; however, results of clinical and epidemiological studies are inconclusive at this time, and there is a paucity of research examining the association between HRT and Parkinson's-related neurocognitive impairment. Even less understood are the effects of HRT on risk for frontotemporal dementia and HIV-associated neurocognitive disorder. Limits to the existing research are discussed, along with proposed future directions for the investigation of HRT and neurodegenerative diseases.

Short-term testosterone manipulations modulate visual recognition memory and some aspects of emotional reactivity in male rhesus monkeys

The role of testosterone (T) in modulating cognitive function and emotion in men remains unclear. The paucity of animal studies has likely contributed to the slow progress in this area. In particular, studies in nonhuman primates have been lacking. Our laboratory has begun to address this issue by pharmacologically manipulating T levels in intact male rhesus monkeys, using blind, placebo-controlled, crossover designs. We previously found that T-suppressed monkeys receiving supraphysiological T for 4 weeks had lower visual recognition memory for long delays and enhanced attention to videos of negative social stimuli (Lacreuse et al., 2009, 2010) compared to when treated with oil. To further delineate the conditions under which T affects cognition and emotion, the present study focused on the short-term effects of physiological T. Six intact males were treated with the gonadotropin-releasing hormone antagonist degarelix (3 mg/kg) for 7 days and received one injection of T enanthate (5 mg/kg) followed by one injection of oil vehicle 7 days later (n=3), or the reverse treatment (n=3). Performance on two computerized tasks, the Delayed-non-matching-to-sample (DNMS) with random delays and the object-Delayed Recognition Span test (object-DRST) and one task of emotional reactivity, an approach/avoidance task of negative, familiar and novel objects, was examined at baseline and 3-5 days after treatment. DNMS performance was significantly better when monkeys were treated with T compared to oil, independently of the delay duration or the nature (emotional or neutral) of the stimuli. Performance on the object-DRST was unaffected. Interestingly, subtle changes in emotional reactivity were also observed: T administration was associated with fewer object contacts, especially on negative objects, without overt changes in anxious behaviors. These results may reflect increased vigilance and alertness with high T. Altogether, the data suggest that changes in general arousal may underlie the beneficial effects of T on DNMS performance. This hypothesis will require further study with objective measures of physiological arousal.

Cognitive response to estradiol in postmenopausal women is modified by high cortisol

Estradiol has potent favorable effects on brain function and behavior in animals while in human trials, the results are inconsistent. A number of potential mediating variables influencing response to estradiol have been proposed to account for this variability, 1 of which includes stress. We conducted a placebo-controlled study to examine joint and independent effects of estradiol and elevated levels of the stress hormone cortisol on cognition and biomarkers of aging and neurodegenerative disease. Thirty-nine healthy postmenopausal women (56-84 years) received 0.10 mg/dL of transdermal 17β-estradiol (E2) or placebo for 8 weeks. During the last 4 days of the trial, subjects also received 90 mg/day (30 mg 3×/day) of oral hydrocortisone (CORT) to induce stress-level elevations in cortisol, or a matched placebo. The 4 groups thus included placebo (placebo patch/placebo pill), CORT-alone (placebo patch/hydrocortisone), E2-alone (estradiol patch/placebo pill), and E2+CORT (estradiol patch/hydrocortisone). Eight weeks of E2 increased plasma estradiol by 167%, and 4 days of CORT increased plasma cortisol by 119%. Overall, E2 had favorable effects on verbal memory (p = 0.03), working memory (p = 0.02), and selective attention (p = 0.04), and the magnitude of these effects was attenuated for E2+CORT. E2-alone and E2+CORT had opposing effects on plasma levels of the amyloid-β (Aβ) biomarker (Aβ40/42 ratio, p < 0.05), with the more favorable response observed for E2-alone. CORT-induced increases in insulin-like growth factor-1 were blunted by E2 coadministration. Our findings indicate that cognitive and physiological responses to estradiol are adversely affected by elevated stress hormone levels of cortisol in healthy postmenopausal women.

The development of small primate models for aging research

Nonhuman primate (NHP) aging research has traditionally relied mainly on the rhesus macaque. But the long lifespan, low reproductive rate, and relatively large body size of macaques and related Old World monkeys make them less than ideal models for aging research. Manifold advantages would attend the use of smaller, more rapidly developing, shorter-lived NHP species in aging studies, not the least of which are lower cost and the ability to do shorter research projects. Arbitrarily defining "small" primates as those weighing less than 500 g, we assess small, relatively short-lived species among the prosimians and callitrichids for suitability as models for human aging research. Using the criteria of availability, knowledge about (and ease of) maintenance, the possibility of genetic manipulation (a hallmark of 21st century biology), and similarities to humans in the physiology of age-related changes, we suggest three species--two prosimians (Microcebus murinus and Galago senegalensis) and one New World monkey (Callithrix jacchus)--that deserve scrutiny for development as major NHP models for aging studies. We discuss one other New World monkey group, Cebus spp., that might also be an effective NHP model of aging as these species are longer-lived for their body size than any primate except humans.

The impact of age-related ovarian hormone loss on cognitive and neural function

On average, women now live one-third of their lives after menopause. Because menopause has been associated with an elevated risk of dementia, an increasing body of research has studied the effects of reproductive senescence on cognitive function. Compelling evidence from humans, nonhuman primates, and rodents suggests that ovarian sex-steroid hormones can have rapid and profound effects on memory, attention, and executive function, and on regions of the brain that mediate these processes, such as the hippocampus and prefrontal cortex. This chapter will provide an overview of studies in humans, nonhuman primates, and rodents that examine the effects of ovarian hormone loss and hormone replacement on cognitive functions mediated by the hippocampus and prefrontal cortex. For humans and each animal model, we outline the effects of aging on reproductive function, describe how ovarian hormones (primarily estrogens) modulate hippocampal and prefrontal physiology, and discuss the effects of both reproductive aging and hormone treatment on cognitive function. Although this review will show that much has been learned about the effects of reproductive senescence on cognition, many critical questions remain for future investigation.

Long-term effects of conjugated equine estrogen therapies on domain-specific cognitive function: results from the Women's Health Initiative study of cognitive aging extension

OBJECTIVES

To determine whether small decrements in global cognitive function that conjugated equine estrogen (CEE) therapies have been shown to produce in older women persist after cessation and extend to specific cognitive domains.

DESIGN

Randomized controlled clinical trial.

SETTING

Fourteen clinical centers of the Women's Health Initiative.

PARTICIPANTS

Two thousand three hundred four women aged 65 to 80 free of probable dementia at enrollment.

INTERVENTION

CEE 0.625 mg/d with or without medroxyprogesterone acetate (MPA, 10 mg/d) and matching placebos.

MEASUREMENTS

Annual administrations of a battery of cognitive tests during and after the trial.

RESULTS

Assignment to CEE-based therapies was associated with small mean relative decrements in global cognitive function and several domain-specific cognitive functions during the trial, which largely persisted through up to 4 years after the trial. The strongest statistical evidence was for global cognitive function (0.07-standard deviation decrements during (P=.007) and after (P=.01) the trial. For domain-specific scores, the mean decrements were slightly smaller, were less significant, and tended to be larger for CEE-alone therapy.

CONCLUSION

CEE-based therapies, when initiated after the age of 65, produce a small broad-based decrement in cognitive function that persists after their use is stopped, but the differences in cognitive function are small and would not be detectable or have clinical significance for an individual woman. Differences in effects between cognitive domains suggest that more than one mechanism may be involved.

Immune senescence in aged nonhuman primates

Aging is accompanied by a general dysregulation in immune system function, commonly referred to as 'immune senescence'. This progressive deterioration affects both innate and adaptive immunity, although accumulating evidence indicates that the adaptive arm of the immune system may exhibit more profound changes. Most of our current understanding of immune senescence stems from clinical and rodent studies. More recently, the use of nonhuman primates (NHPs) to investigate immune senescence and test interventions aimed at delaying/reversing age-related changes in immune function has dramatically increased. These studies have been greatly facilitated by several key advances in our understanding of the immune system of old world monkeys, specifically the rhesus macaques. In this review we describe the hallmarks of immune senescence in this species and compare them to those described in humans. We also discuss the impact of immune senescence on the response to vaccination and the efficacy of immuno-restorative interventions investigated in this model system.