A beneficial effect of estrogen on working memory in postmenopausal women taking hormone replacement therapy

Prefrontal cortex lesions and sex differences in fear extinction and perseveration

Electrolytic lesions of the medial prefrontal cortex (PFCX) were examined using fear conditioning to assess the recall of fear extinction and performance in the Y-maze, open field, and object location/recognition in male and female Sprague-Dawley rats. Rats were conditioned to seven tone/footshocks, followed by extinction after 1-h and 24-h delays, revealing PFCX effects and sex differences during all phases of fear conditioning. In male rats, PFCX impaired 24-h recall of fear extinction to tone, which required the 1-h delay extinction and was not attributed to nonassociative factors. In contrast, sham and PFCX females increased freezing to tone following a 24-h delay, whether or not 1-h delay tone extinction was presented. Moreover, PFCX females failed to extinguish to tone, contrasting to the robust extinction to tone that was observed for sham females, PFCX, and sham males. Also, sex differences were found during acquisition, with sham females acquiring fear conditioning slower than PFCX females. By the last tone-shock presentation, sham and PFCX females showed a slight but significant reduction in freezing to tone relative to those of sham and PFCX males. Of the other behavioral measures, PFCX females maintained exploration of a novel object during object recognition when sham females habituated. PFCX did not influence other behaviors in the remaining tasks. These findings show important sex differences in PFC function, with the PFC influencing the recall of fear extinction in males and contributing to the acquisition and maintenance of fear extinction memory in females, perhaps through altering perseveration.

Effects of synaptic plasticity regulated by 17beta-estradiol on learning and memory in rats with Alzheimer's disease

OBJECTIVE

To investigate whether estrogen modulates learning and memory and long-term potentiation (LTP) in the hippocampus of rats with Alzheimer's disease (AD).

METHODS

The rats were divided into ovariectomy (OVX) and estrogen replacement therapy (ERT) groups. Rats in the ERT group received OVX, followed by ERT, while rats in the OVX group received only OVX. The rat model of AD was established by injection of 1 microL (10 microg/microL) amyloid-beta peptide 1-40(Abeta1-40) into the hippocampus. The learning and memory ability and LTP were determined by Morris water maze and electrophysiological method, respectively.

RESULTS

The escape latency in Morris water maze significantly decreased in ERT group compared with that in OVX group (P< 0.05). Besides, rats in ERT group exhibited a significant enhancement of the magnitude of LTP at 30 min after high-frequency stimulation (HFS), compared with that in OVX group (P< 0.01).

CONCLUSION

ERT can attenuate the cognitive deficits in the rat model of AD, and estrogen can regulate LTP and synaptic remodeling in AD rats.

Impact of dietary genistein and aging on executive function in rats

Genistein is an estrogenic soy isoflavone widely promoted for healthy aging, but its effects on cognitive function are not well-understood. We examined the cognitive effects of once daily oral genistein treatment at two doses (approximately 162 microg/kg/day low dose and a 323 microg/kg/day high dose) in ovariectomized young (7 month), middle-aged (16 month), and old (22 month) Long-Evans rats. Operant tasks including delayed spatial alternation (DSA), differential reinforcement of low rates of responding (DRL), and reversal learning that tap prefrontal cortical function were used to assess working memory, inhibitory control/timing, and strategy shifting, respectively. At the conclusion of cognitive testing, brains were collected and relative densities of D1 and D2 dopamine receptors and dopamine transporter (DAT) were measured in the prefrontal cortex. On the DSA task, the high dose old group performed worse than both the high dose young and middle-aged groups. On the DRL task, the high dose of genistein resulted in a marginally significant impairment in the ratio of reinforced to non-reinforced lever presses. This effect was present across age groups. Age effects were also found as old rats performed more poorly than the young and middle-aged rats on the DSA overall. In contrast, middle-aged and old rats made fewer lever presses on the DRL than did the young rats, a pattern of behavior associated with better performance on this task. Moreover, while DAT levels overall decreased with age, genistein treatment produced an increase in DAT expression in old rats relative to similarly aged control rats. D1 and D2 densities did not differ between genistein dose groups or by age. These results highlight the fact that aspects of executive function are differentially sensitive to both genistein exposure and aging and suggest that altered prefrontal dopamine function could potentially play a role in mediating these effects.

Characteristics of hormone therapy, cognitive function, and dementia: the prospective 3C Study

OBJECTIVES

To examine the association between hormone therapy (HT) and cognitive performance or dementia, focusing on the duration and type of treatment used, as well as the timing of initiation of HT in relation to the menopause.

METHODS

Women 65 years and older were recruited in France as part of the Three City Study. At baseline and 2- and 4-year follow-up, women were administered a short cognitive test battery and a clinical diagnosis of dementia was made. Detailed information was also gathered relating to current and past HT use. Analysis was adjusted for a number of sociodemographic, behavioral, physical, and mental health variables, as well as APOE epsilon4.

RESULTS

Among 3,130 naturally postmenopausal women, current HT users performed significantly better than never users on verbal fluency, working memory, and psychomotor speed. These associations varied according to the type of treatment and a longer duration of HT appeared to be more beneficial. However, initiation of HT close to the menopause was not associated with better cognition. HT did not significantly reduce dementia risk over 4 years but current treatment diminished the negative effect associated with APOE epsilon4.

CONCLUSIONS

Current hormone therapy (HT) was associated with better performance in certain cognitive domains but these associations are dependent on the duration and type of treatment used. We found no evidence that HT needs to be initiated close to the menopause to have a beneficial effect on cognitive function in later life. Current HT may decrease the risk of dementia associated with the APOE epsilon4 allele.

Soya isoflavone supplementation enhances spatial working memory in men

Females perform better in certain memory-related tasks than males. Sex differences in cognitive performance may be attributable to differences in circulating oestrogen acting on oestrogen beta receptors (ERbeta) which are prevalent in brain regions such as the hippocampus, frontal lobe and cortex that mediate cognitive functions. Since soya isoflavones are known to activate ERbeta, chronic isoflavone supplementation in males may improve cognitive performance in memory-related tasks. A 12-week double-blind, placebo-controlled cross-over trial was conducted in thirty-four healthy men to investigate the effect of isoflavone supplementation on cognitive function. Volunteers were randomised to take four capsules/d containing soya isoflavones (116 mg isoflavone equivalents/d: 68 mg daidzein, 12 mg genistein, 36 mg glycitin) or placebo for 6 weeks, and the alternate treatment during the following 6 weeks. Assessments of memory (verbal episodic, auditory and working), executive function (planning, attention, mental flexibility) and visual-spatial processing were performed at baseline and after each treatment period. Isoflavone supplementation significantly improved spatial working memory (P = 0.01), a test in which females consistently perform better than males. Compared with placebo supplementation, there were 18 % fewer attempts (P = 0.01), 23 % fewer errors (P = 0.02) and 17 % less time (P = 0.03) required to correctly identify the requisite information. Isoflavones did not affect auditory and episodic memory (Paired Associate Learning, Rey's Auditory Verbal Learning Task, Backward Digit Span and Letter-Number Sequencing), executive function (Trail Making and Initial Letter Fluency Task) or visual-spatial processing (Mental Rotation Task). Isoflavone supplementation in healthy males may enhance cognitive processes which appear dependent on oestrogen activation.

Chronic estradiol replacement impairs performance on an operant delayed spatial alternation task in young, middle-aged, and old rats

The current study examined effects of chronic estradiol replacement on a prefrontally-mediated working memory task at different ages in a rodent model. Ovariectomized young, middle-aged, and old Long-Evans rats were given 5% or 10% 17beta-estradiol in cholesterol vehicle via Silastic implants and tested on an operant delayed spatial alternation task (DSA). The two estradiol exposed groups did not perform as well as the vehicle control group did. Deficits were present at all but the longest delay, where all groups including the vehicle control group performed poorly. Surprisingly, there was not a significant effect of age or an age by estradiol interaction, despite the fact that old rats had longer latencies to respond after both correct and incorrect lever presses. These data confirm our earlier finding that chronic estradiol treatment has an impairing effect on working memory as measured on DSA task. However, contrary to expectations, young, middle-aged and old rats were similarly impaired by chronic estradiol treatment; there were no indications of differential effects at different periods of the lifespan. Also contrary to expectations, there were no indications of a decline in DSA performance with advancing age. Overall, the results demonstrate that chronic estradiol exposure causes deficits in the DSA performance of ovariectomized female rats, not only in young adulthood, but also at older ages analogous to those at which hormone replacement therapy is commonly prescribed in humans.

Resveratrol protects spatial learning in middle-aged C57BL/6 mice from effects of ethanol

Spatial learning and memory have been shown to be especially vulnerable to aging and alcohol consumption. However, moderate consumption of wine has been linked to decreases in incidences of dementia. Resveratrol, a phytoestrogen found in wine, has been shown to have neuroprotective effects against the oxidative stress of ethanol. In this study, middle-aged C57BL/6N female mice given a combination of resveratrol (44.2 mg/kg) and a low amount of ethanol (0.71 g/kg) each day for 6 weeks performed better on the Barnes maze task for spatial learning and memory than mice consuming only the low concentration of ethanol. The results suggest that resveratrol may protect hippocampal-dependent spatial learning from the negative effects of ethanol. However, the resveratrol-ethanol combination did not provide any additional benefit to counter aging-related deficits.

Estrogen and cognitive functions

Although the effects of estrogen on sexual behavior in mammals are well known, its role on other types of behavior, including cognition, have only recently been recognized. This review summarizes work conducted in our laboratory and others with the aim of identifying the effects of estrogen on cognitive functions. The first section will briefly describe the neurobiology of estrogen. The second section will discuss the effects of estrogen on cognitive behaviors in mammals, as well as the physiological relevance of these effects and their applicability to human health and disease. The third section will detail the role of estrogen on working memory in humans and nonhuman primates, and in rodents. Finally, the concluding section will briefly describe the relationship between estrogen and the aging brain.

Dorsal hippocampal progesterone infusions enhance object recognition in young female mice

The effects of progesterone on memory are not nearly as well studied as the effects of estrogens. Although progesterone can reportedly enhance spatial and/or object recognition in female rodents when given immediately after training, previous studies have injected progesterone systemically, and therefore, the brain regions mediating this enhancement are not clear. As such, this study was designed to determine the role of the dorsal hippocampus in mediating the beneficial effect of progesterone on object recognition. Young ovariectomized C57BL/6 mice were trained in a hippocampal-dependent object recognition task utilizing two identical objects, and then immediately or 2 h afterwards, received bilateral dorsal hippocampal infusions of vehicle or 0.01, 0.1, or 1.0 microg/microl water-soluble progesterone. Forty-eight hours later, object recognition memory was tested using a previously explored object and a novel object. Relative to the vehicle group, memory for the familiar object was enhanced in all groups receiving immediate infusions of progesterone. Progesterone infusion delayed 2 h after training did not affect object recognition. These data suggest that the dorsal hippocampus may play a critical role in progesterone-induced enhancement of object recognition.

Hormone therapy and cognitive function

BACKGROUND

Clinical trials yield discrepant information about the impact of hormone therapy on verbal memory and executive function. This issue is clinically relevant because declines in verbal memory are the earliest predictor of Alzheimer's disease and declines in executive function are central to some theories of normal, age-related changes in cognition.

METHODS

We conducted a systematic review of randomized clinical trials of hormone therapy (i.e. oral, transdermal, i.m.) and verbal memory, distinguishing studies in younger (i.e. <or=65 years of age; n = 9) versus older (i.e. >65 years; n = 7) women and studies involving estrogen alone versus estrogen plus progestogen. Out of 32 placebo-controlled trials, 17 were included (13 had no verbal memory measures and 2 involved cholinergic manipulations). We also provide a narrative review of 25 studies of executive function (two trials), since there are insufficient clinical trial data for systematic review.

RESULTS

There is some evidence for a beneficial effect of estrogen alone on verbal memory in younger naturally post-menopausal women and more consistent evidence from small-n studies of surgically post-menopausal women. There is stronger evidence of a detrimental effect of conjugated equine estrogen plus medroxyprogesterone acetate on verbal memory in younger and older post-menopausal women. Observational studies and pharmacological models of menopause provide initial evidence of improvements in executive function with hormone therapy.

CONCLUSIONS

Future studies should include measures of executive function and should address pressing clinical questions; including what formulation of combination hormone therapy is cognitively neutral/beneficial, yet effective in treating hot flashes in the early post-menopause.

Mechanisms of action of estrogen in the brain: insights from human neuroimaging and psychopharmacologic studies

Use of estrogen therapy in the perimenopausal and postmenopausal periods has been shown in several clinical trials to help women maintain a premenopausal level of cognitive function. What is not yet fully understood is how the neurobiological effects of estrogen contribute to these cognitive effects. This review explores data from two related bodies of human literature that provide compelling evidence in support of the biological plausibility that estrogen treatment can benefit cognition. The first half of the literature review focuses on studies from the estrogen neuroimaging literature, and the second half focuses on pharmacologic challenge studies assessing estrogen-neurotransmitter interactions. We integrate these two bodies of literature by focusing on the neurophysiologic underpinnings of estrogen effects on cognition and linking these clinical studies to preclinical studies. The focus on verbal memory is important because it is a cognitive function that has been shown to change with estrogen treatment and predict Alzheimer's disease risk but is not addressed by preclinical studies. Overall, we conclude that estrogen interacts with cholinergic and serotonergic systems to affect hippocampal and frontal cortical brain areas and thereby enhance memory, particularly at the retrieval stage.

Short-term changes in endogenous estrogen levels and consumption of soy isoflavones affect working and verbal memory in young adult females

Estrogen is known to modulate certain cognitive functions, most notably improving working memory and verbal memory. Soy foods contain isoflavones, phytoestrogens structurally similar to estrogen that weakly bind to estrogen receptors. We investigated the effects of natural variations in estrogen levels and short-term dietary supplementation with soy isoflavones on cognitive function in 28 young women. Performance was examined across a range of cognitive tasks on three occasions during separate menstrual cycles: during a menses phase (low estrogen), during a luteal phase (highest estrogen), and once during a menses phase after a 3-day phytoestrogen-rich dietary intervention. Soy supplementation during menses led to an improvement in working memory and verbal memory. The menstrual cycle effects were mixed, with high estrogen improving performance on a verbal memory task but not on working memory. Our results suggest that soy phytoestrogens may improve working memory through estrogen-independent mechanisms.

Estrogens and age-related memory decline in rodents: what have we learned and where do we go from here?

The question of whether ovarian hormone therapy can prevent or reduce age-related memory decline in menopausal women has been the subject of much recent debate. Although numerous studies have demonstrated a beneficial effect of estrogen and/or progestin therapy for certain types of memory in menopausal women, recent clinical trials suggest that such therapy actually increases the risk of cognitive decline and dementia. Because rodent models have been frequently used to examine the effects of age and/or ovarian hormone deficiency on mnemonic function, rodent models of age-related hormone and memory decline may be useful in helping to resolve this issue. This review will focus on evidence suggesting that estradiol modulates memory, particularly hippocampal-dependent memory, in young and aging female rats and mice. Various factors affecting the mnemonic response to estradiol in aging females will be highlighted to illustrate the complications inherent to studies of estrogen therapy in aging females. Avenues for future development of estradiol-based therapies will also be discussed, and it is argued that an approach to drug development based on identifying the molecular mechanisms underlying estrogenic modulation of memory may lead to promising future treatments for reducing age-related mnemonic decline.

The effects of acute 17beta-estradiol treatment on gene expression in the young female mouse hippocampus

Previous studies have demonstrated that treatment with 17beta-estradiol (E(2)) improves both spatial and nonspatial memory in young female mice. Still unclear, however, are the molecular mechanisms underlying the beneficial effects of E(2) on memory. We have previously demonstrated that a single post-training intraperitoneal (i.p.) injection of 0.2 mg/kg E(2) can enhance hippocampal-dependent spatial and object memory consolidation (e.g., Gresack & Frick, 2006b). Therefore, in the present study, we performed a microarray analysis on the dorsal hippocampi of 4-month-old female mice injected i.p. with vehicle or 0.2 mg/kg E(2). Genes were considered differentially expressed following E(2) treatment if they showed a greater than 2-fold change in RNA expression levels compared to controls. Overall, out of a total of approximately 25,000 genes represented on the array, 204 genes showed altered mRNA expression levels upon E(2) treatment, with 111 up-regulated and 93 down-regulated. Of these, 17 of the up-regulated and 6 of the down-regulated genes are known to be involved in learning and memory. mRNA expression changes in 5 of the genes were confirmed by real-time quantitative PCR analysis, and protein changes in these same genes were confirmed by Western blot analysis: Hsp70, a heat shock protein known to be estrogen responsive; Igfbp2, an IGF-I binding protein; Actn4, an actin binding protein involved in protein trafficking; Tubb2a, the major component of microtubules; and Snap25, a synaptosome-specific protein required for neurotransmitter release. The types of genes altered indicate that E(2) may induce changes in the structural mechanics of cells within the dorsal hippocampus that could be conducive to promoting memory consolidation.

Effects of chronic estradiol treatment on delayed spatial alternation and differential reinforcement of low rates of responding

Estrogens have been shown to both enhance and impair cognitive function depending on several factors, including regimen of hormone treatment, age of subject, and task attributes. In rodent models, estradiol tends to enhance spatial learning and impair response or cued learning, but effects on executive functions are less well-studied. In this experiment, spatial working memory and response inhibition were tested using delayed spatial alternation (DSA) and differential reinforcement of low rates of responding (DRL) tasks in ovariectomized rats that were given chronic estradiol via Silastic implants resulting in serum estradiol concentrations of 86.2 +/- 8.2 (SEM) pg/ml. Rats were tested for 25 days DSA with variable delays of 0, 3, 6, 9, and 18 seconds between lever presentations, followed by 30 days on a DRL-15s operant schedule. Estradiol-replaced rats showed a significantly lower proportion of correct responses on the DSA task compared to vehicle-implanted ovariectomized animals. On DRL, estradiol-treated rats showed a lower ratio of reinforced to nonreinforced presses. These data suggest that chronic estrogen exposure may impair rats' abilities on measures of executive function including working memory and response inhibition.

Estrogen and comprehension of metaphoric speech in women suffering from schizophrenia: results of a double-blind, placebo-controlled trial

OBJECTIVE

The effects of estrogen on comprehension of metaphoric speech, word fluency, and verbal ability were investigated in women suffering from schizophrenia. The issue of estrogen-dependent neuropsychological performance could be highly relevant because women with schizophrenia frequently suffer from hypoestrogenism.

METHOD

A placebo-controlled, double-blind, crossover study using 17beta-estradiol for replacement therapy and as an adjunct to a naturalistic maintenance antipsychotic treatment was carried out over a period of 8 months. Nineteen women (mean age = 38.0 years, SD = 9.9 years) with schizophrenia were included in the study. Comprehension of metaphoric speech was measured by a lexical decision paradigm, word fluency, and verbal ability by a paper-and-pencil test.

RESULTS

Significant improvement was seen for the activation of metaphoric meaning during estrogen treatment (P = .013); in contrast, no difference was found for the activation of concrete meaning under this condition. Verbal ability and word fluency did not improve under estrogen replacement therapy either.

CONCLUSIONS

This is the very first study based on estrogen intervention instead of the physiological hormone changes to examine the estrogen effects on neuropsychological performance in women with schizophrenia. In addition, it is the first time that the effect of estrogen on metaphoric speech comprehension was investigated in this context. While in a previous study estrogen therapy as adjunct to a naturalistic maintenance treatment with antipsychotics did not show an effect on psychopathology measured by a rating scale, a significant effect of estrogen on the comprehension of metaphoric speech and/or concretism, a main feature of schizophrenic thought and language disturbance, was found in the present study. Because the improvement of formal thought disorders and language disturbances is crucial for social integration of patients with schizophrenia, the results may have implications for the treatment of these individuals.

Cognitive effects of Tamoxifen in pre-menopausal women with breast cancer compared to healthy controls

INTRODUCTION

The selective estrogen receptor modulator, Tamoxifen (TAM), is one of the most frequently prescribed drugs for the treatment of breast cancer; however, its effects on the cognition of users have not been adequately studied. Although TAM is an effective anti-estrogen that blocks tumour growth in the breast, it could also influence the activity of other target estrogen sites, including the brain. The exact nature of this interaction is unknown.

METHODS

A cross-sectional design was used to compare cognitive task performance of two treatment groups: 1) women using TAM for the treatment of early breast cancer (n = 23); and 2) age-matched, healthy women not using TAM (n = 23). All participants were pre-menopausal, and recipients of chemotherapy were excluded from the study.

RESULTS

It was found that TAM users scored significantly worse than controls on tasks of immediate and delayed visual memory, verbal fluency, immediate verbal memory, visuo-spatial ability, and processing speed.

DISCUSSIONS/CONCLUSIONS

Although limited by the lack of baseline data and pre-morbid intelligence measures, the results of this exploratory study suggest that at least in pre-menopausal women, TAM may exert a widespread negative influence on cognitive abilities.

IMPLICATIONS FOR CANCER SURVIVORS

Larger, randomized, prospective trials are required to confirm these results; however, TAM use in pre-menopausal breast cancer may be associated with cognitive difficulties. Knowledge and understanding of these complications will be important for professionals in communicating both the benefits and risks of TAM use in breast cancer survivors.

The female advantage in object location memory is robust to verbalizability and mode of presentation of test stimuli

This study extends Duff and Hampson's [Duff, S., & Hampson, E. (2001). A sex difference on a novel spatial working memory task in humans. Brain and Cognition,47, 470-493] finding of a sex-related difference in favor of females for an object location memory task. Twenty female and 20 male undergraduate students performed both manual and computer-generated versions of the task using stimuli that varied in degree of verbalizability. A 2x2x3 ANOVA with Sex as a between-subjects factor, and Presentation (manual or computer) and Stimuli (common objects, common shapes, and novel shapes) as within-subjects repeated measures revealed a significant main effect for Sex. Females made fewer errors than males regardless of presentation and across the three levels of verbalizability (i.e., stimulus types); moreover, the effect size was considered "large" [Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed.). Berlin: Springer]. These findings are interpreted within the context of the current literature that demonstrates a female advantage for object location memory (e.g., [Voyer, D., Postma, A., Brake, B., & Imperato-McGinley, J. (2007). Gender differences in object location memory: A meta-analysis. Psychonomic Bulletin and Review, 14, 23-38]).

Working memory for emotional facial expressions: role of the estrogen in young women

Physiological hormonal fluctuations during the menstrual cycle, postpartum, and menopause have been implicated in the modulation of mood, cognition, and affective disorders. Taking into account that women's performance in memory tasks can also fluctuate with circulating hormones levels across the menstrual cycle, the cognitive performance in a working memory task for emotional facial expressions, using the six basic emotions as stimuli in the delayed matching-to-sample, was evaluated in young women in different phases of the menstrual cycle. Our findings suggest that high levels of estradiol in the follicular phase could have a negative effect on delayed matching-to-sample working memory task, using stimuli with emotional valence. Moreover, in the follicular phase, compared to the menstrual phase, the percent of errors was significantly higher for the emotional facial expressions of sadness and disgust. The evaluation of the response times (time employed to answer) for each facial expression with emotional valence showed a significant difference between follicular and luteal in reference to the emotional facial expression of sadness. Our results show that high levels of estradiol in the follicular phase could impair the performance of working memory. However, this effect is specific to selective facial expressions suggesting that, across the phases of the menstrual cycle, in which conception risk is high, women could give less importance to the recognition of the emotional facial expressions of sadness and disgust. This study is in agreement with research conducted on non-human primates, showing that fluctuations of ovarian hormones across the menstrual cycle influence a variety of social and cognitive behaviors. Moreover, our data could also represent a useful tool for investigating emotional disturbances linked to menstrual cycle phases and menopause in women.

Post-training progesterone dose-dependently enhances object, but not spatial, memory consolidation

The aim of this study was to determine if progesterone modulates object and spatial memory consolidation in young ovariectomized C57BL/6 mice. Object memory was tested in an object recognition task using 24- and 48-h delays. Spatial memory was tested in a 2-day version of the Morris water maze in which retention was tested 24 or 48 h after training. Immediately after training in each task, mice received a single intraperitoneal injection of vehicle or 5, 10, or 20mg/kg water-soluble progesterone. Mice were then tested 24 or 48 h later in the absence of circulating progesterone. Post-training injections of 10 and 20mg/kg progesterone enhanced object recognition, but not memory in the spatial water maze. These findings suggest that object memory consolidation in young female mice is more sensitive to the modulatory effects of progesterone than spatial memory consolidation, at least using the tasks, doses, and delays tested. As such, these findings may have important implications for the design of progesterone therapies intended to reduce age-related memory decline.

A study of visuospatial working memory pre- and post-Gonadotropin Hormone Releasing Hormone agonists (GnRHa) in young women

Gonadotropin Hormone Releasing Hormone agonists (GnRHa) produce an acute decline in ovarian hormone production leading to a 'pseudo' menopause. This is therapeutically useful in the management of a variety of gynaecological conditions but also serves as a powerful model to study the effects of ovarian hormones on cognition. Animal and human behavioral studies report that memory is particularly sensitive to the effects ovarian hormone suppression (e.g. post GnRHa). Further, it has recently been reported that ovariectomy in young women increases the risk of cognitive impairment in later life. However, the underlying brain networks and/or stages of memory processing that might be modulated by acute ovarian hormone suppression remain poorly understood. We used event-related fMRI to examine the effect of GnRHa on visual working memory (VWM). Neuroimaging outcomes from 17 pre-menopausal healthy women were assessed at baseline and 8 weeks after GnRHa treatment. Seventeen matched wait-listed volunteers served as the control group and were assessed at similar intervals during the late follicular phase of the menstrual cycle. We report GnRHa was associated with attenuation of left parahippocampal (BA 35) and middle temporal gyri (BA 21 ,22, 39) activation, with a significant group-by-time interaction at left precuneus (BA 7) and posterior cingulate cortex (PCC) (BA 31) at encoding, and with cerebellar activation at recognition in the context of unimpaired behavioral responses. Our study suggests that acute ovarian hormone withdrawal following GnRHa, and perhaps at other times, (e.g. following surgical menopause and postpartum) alters the neural circuitry underlying performance of VWM.

Modulation of alphaCaMKII signaling by rapid ERalpha action

The estrogen receptor (ER) subtypes, ERalpha and ERbeta, modulate numerous signaling cascades in the brain to result in a variety of cell fates including neuronal differentiation. We report here that 17beta-estradiol (E2) rapidly stimulates the autophosphorylation of alpha-Ca(2+)/calmodulin-dependent kinase II (alphaCaMKII) in immortalized NLT GnRH neurons, primary hippocampal neurons, and Cos7 cells co-transfected with ERalpha and alphaCaMKII. The E2-induced alphaCaMKII autophosphorylation is ERalpha- and Ca(2+)/calmodulin (CaM)-dependent. Interestingly, the hormone-dependent association of ERalpha with alphaCaMKII attenuates the positive effect of E2 on alphaCaMKII autophosphorylation, suggesting that ERalpha plays a complex role in modulating alphaCaMKII activity and may function to fine-tune alphaCaMKII-triggered signaling events. However, it appears as though the activating signal of E2 dominates the negative effect of ER since there is a clear, positive downstream response to E2-activated alphaCaMKII; pharmacological inhibitors and RNAi technology show that targets of ERalpha-mediated alphaCaMKII signaling include extracellular signal-regulated kinase 1/2 (ERK1/2), cAMP response element-binding protein (CREB), and microtubule associated protein 2 (MAP2). These findings suggest a novel model for the modulation of alphaCaMKII signaling by ERalpha, which provides a molecular link as to how E2 might influence brain function.

Role of androgens and the androgen receptor in remodeling of spine synapses in limbic brain areas

Accumulating evidence indicate that structural synaptic plasticity in limbic areas plays a vital role not only in normal brain functions, such as cognition and mood, but also in the development of neurological and mental disorders. We have learned from studies investigating neuronal remodeling that estrogens have an exceptional synaptogenic potential that seems to be specific to limbic areas of the adult female brain. On the other hand, structural synaptic plasticity in the adult male brain and the synaptogenic effect of androgens received relatively little attention. During the last five years, the Leranth laboratory provided conclusive evidence that the hippocampus and prefrontal cortex of adult male rodents and non-human primates retain considerable structural synaptic plasticity similar to the female, and that androgens are capable of inducing spine synapse growth in both the hippocampus and prefrontal cortex similar to estrogens. Our recent work also demonstrates that androgen-induced remodeling of spine synapses in the prefrontal cortex of adult male rats is dependent, at least to some extent, on functional androgen receptors, while being entirely independent of the androgen receptor in the hippocampus. Based on these findings and on their many beneficial effects, we believe that androgens hold a great and undeservingly neglected therapeutic potential that could be employed to reverse synaptic pathology in various neurocognitive and neuropsychiatric disorders.

Testosterone and gonadotropins but not estrogen associated with spatial ability in women suffering from schizophrenia: a double-blind, placebo-controlled study

The aim of this study was to investigate the association between estrogen and spatial ability tasks in women suffering from schizophrenia. For this purpose, a placebo-controlled, double-blind, three-time cross-over study using 17beta-estradiol combined with norethisterone acetate for replacement therapy and as an adjunct to a naturalistic maintenance antipsychotic treatment was carried out over a period of 8 months. Nineteen women (mean age=38.0 years, SD=9.9 years) with schizophrenia hospitalized for the first time or repeatedly were included in the study. Sex hormones - 17beta-estradiol, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, testosterone, and dehydroepiandrosterone sulfate - were measured and the patients completed a neuropsychological test in the last two active drug and/or placebo phases. Three different spatial ability tasks - spatial orientation, spatial visualization, and flexibility of closure - were measured by a paper-and-pencil test. No association between estrogen and spatial ability was found; however, in an additional exploratory data analysis, high levels of testosterone, LH, and FSH correlated significantly with performance in the flexibility of closure task. This is the very first study, based on estrogen intervention instead of physiological hormone changes, to examine the association between estrogen and spatial ability in women with schizophrenia.

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.

No differences in performance on test of working memory and executive functioning between healthy elderly postmenopausal women using or not using hormone therapy

BACKGROUND

On average, ovarian function ceases at the age of 52 years so that estrogen (E) levels are chronically low following the menopause. Numerous studies have found that hormone therapy (HT) helps to protect verbal memory, a hippocampal function. Estrogen receptors are also found in the prefrontal cortex (PFC), suggesting that estrogen may modulate executive and working memory functions, both mediated by the PFC. The possible role of progesterone (P) on executive functions and working memory is unknown.

OBJECTIVE

To examine the relationship between neuropsychological performance, age of initiation of HT, and duration of HT use.

METHOD

In this cross-sectional study, the neuropsychological performance of 37 postmenopausal women (mean age, 65 years) who used either estrogen-only or sequential E + P (E-alone group)(n = 22) or E + P continuously (n = 15) was compared to that of 28 healthy postmenopausal women matched for age and education who had never used HT. It was hypothesized that the E-only users would perform better then the E + P and the never-users on neuropsychological tests of verbal memory, executive function and working memory.

RESULTS

Results showed only minor between-group differences on working memory scores such that the E + P users were slowest to generate a response on the N-Back test of working memory. No group differences on tests of executive functions were found.

CONCLUSION

There was no relationship between neuropsychological performance, age of initiation of HT, or duration of HT use.

Life-long environmental enrichment differentially affects the mnemonic response to estrogen in young, middle-aged, and aged female mice

The present study was designed to examine whether life-long exposure to standard or enriched housing affects the ability of estrogen to improve spatial and object memory throughout the lifespan. Three-week-old female mice were maintained in standard or enriched housing up to and through ovariectomy and behavioral testing at 5, 17, or 22 months of age. Spatial memory was tested in the Morris water maze and object memory was tested using an object recognition task. Immediately after training each day, mice were injected intraperitoneally with vehicle or 0.2 mg/kg 17beta-estradiol. Among young females, object recognition was enhanced by estradiol alone, an effect that was reduced by enrichment. In contrast, spatial water maze performance was impaired by estradiol alone, but improved by the combination of both estradiol and enrichment. At middle-age, object recognition was enhanced by estradiol or enrichment alone, and the combination of both treatments. Spatial memory in the water maze was also improved by both treatments at middle-age, but the beneficial effects of estradiol were limited to standard-housed females. Finally, whereas enrichment in aged females significantly enhanced performance in both tasks, estradiol had no effect at this age in either task. In total, the data indicate that life-long enrichment can significantly alter the extent to which estradiol affects memory in mice throughout the lifespan. Importantly, the interaction between these treatments is highly dependent on age and type of memory tested.

Estrogen abolishes latent inhibition in ovariectomized female rats

Estrogen is frequently prescribed as a method of birth control and as hormone replacement therapy for post-menopausal women with varied effects on cognition. Here the effects of estrogen on attention were examined using the latent inhibition (LI) behavioral paradigm. Ovariectomized (OVX) female rats were given either estrogen benzoate (EB, 10 or 100 microg/ml/kg; SC) or sesame oil vehicle. Males and OVX females receiving vehicle displayed normal LI. In contrast, LI was abolished in OVX females receiving EB. The lack of LI in OVX females receiving EB was a result of low suppression ratios, reflecting strong conditioning between the tone and the shock in these subjects even if they were pre-exposed to the tone. Thus, estrogen impaired the ability of OVX females to ignore irrelevant stimuli. Since different cognitive tasks vary in their required ability to ignore irrelevant stimuli, these results may account for some of the variations in the current literature on estrogen and cognition.

The clinical relevance of the relationship between estrogen and cognition in women

Randomized controlled trials (RCTs) and observational and longitudinal studies provide positive, albeit, inconsistent evidence that estrogen might protect against cognitive decline in postmenopausal women. The fact that the Women's Health Initiative Memory Study (WHIMS), the largest RCT to date, failed to find that estrogen therapy (ET) had a protective effect against cognitive aging led to the formulation of the critical period hypothesis which holds that ET will effectively protect against memory decline when it is initiated around the time of menopause but not when considerable time has elapsed since the menopause. Evidence from basic neuroscience, and from rodent, nonhuman primate, and human studies that supports this theory is presented. Although much work remains to be done on the timing of initiation of treatment, on the most effective hormonal compounds and on their routes of administration, the hope is that, eventually, hormonal treatments may be able to attenuate or prevent the decline in aspects of cognition that occur with normal aging.

Effects of hormone replacement therapy and aging on cognition: evidence for executive dysfunction

The present study was designed to explore whether the frontal lobe hypothesis of cognitive aging may be extended to describe the cognitive effects associated with estrogen use in postmenopausal women. Postmenopausal estrogen-only users, estrogen + progesterone users, and non-users (60-80 years old), as well as young, regularly cycling women (18-30 years old) completed an item and source memory task. Since source memory is thought to rely more on executive processes than item memory, we hypothesized that aging and estrogen effects would be greater for source memory than for item memory. Neuropsychological tests explored whether the effects of aging and estrogen use were revealed on other tests of frontal lobe function. Results from the experimental task revealed greater aging and estrogen effects for source memory than for item memory, and neuropsychological results revealed aging and estrogen effects on a subset of tests of executive function. Women on estrogen + progesterone therapy did not outperform non-users, suggesting that the addition of progesterone to hormone therapy may mitigate the benefits induced by estrogen use alone. Overall, findings support the hypothesis that estrogen use may temper age-related cognitive decline by helping to maintain functions subserved by the frontal lobes.

Administration of an inhibitor of estrogen biosynthesis facilitates working memory acquisition in male rats

Estradiol is known to improve performance of some working memory tasks in female animals and post-menopausal women. In females the main source of estradiol is the ovary. In addition, in both males and females estradiol is synthesized in extragonadal tissues. The role of non-ovarian estradiol synthesis on cognitive abilities has not been adequately explored. In the sent study we have assessed the effect of an inhibitor of aromatase, the enzyme that produces estradiol from testosterone, on egocentric working memory in male rats. Sprague-Dawley adult male rats received the intra-esophageal administration of the aromatase inhibitor letrozole (2.5 mg/kg), or vehicle. Rats treated with the aromatase inhibitor committed less errors than untreated animals or animals treated with vehicle, when tested in a cross-arms maze. Retention and retrieval stages were unaffected by aromatase inhibition. This finding indicates that aromatase activity is involved in egocentric working memory performance. The effect of the aromatase inhibitor on working memory may be due to the increase in testosterone levels resulting from aromatase inhibition or to modifications in the availability of estradiol in the brain.

Neurotrophic and neuroprotective actions of estrogen: basic mechanisms and clinical implications

Estrogen is an important hormone signal that regulates multiple tissues and functions in the body. This review focuses on the neurotrophic and neuroprotective actions of estrogen in the brain, with particular emphasis on estrogen actions in the hippocampus, cerebral cortex and striatum. Sex differences in the risk, onset and severity of neurodegenerative disease such as Alzheimer's disease, Parkinson's disease and stroke are well known, and the potential role of estrogen as a neuroprotective factor is discussed in this context. The review assimilates a complex literature that spans research in humans, non-human primates and rodent animal models and attempts to contrast and compare the findings across species where possible. Current controversies regarding the Women's Health Initiative (WHI) study, its ramifications, concerns and the new studies needed to address these concerns are also addressed. Signaling mechanisms underlying estrogen-induced neuroprotection and synaptic plasticity are reviewed, including the important concepts of genomic versus nongenomic mechanisms, types of estrogen receptor involved and their subcellular targeting, and implicated downstream signaling pathways and mediators. Finally, a multicellular mode of estrogen action in the regulation of neuronal survival and neurotrophism is discussed, as are potential future directions for the field.

Testosterone levels and cognitive functioning in women with polycystic ovary syndrome and in healthy young women

We investigated the possible influence of testosterone (T) on cognitive functioning in women with polycystic ovary syndrome (PCOS), an endocrine disorder associated with elevated levels of free testosterone (free T). Performance on a battery of neuropsychological tests in 29 women with elevated free T levels due to PCOS was compared to the performance of 22 age- and education-matched, healthy control women with free T levels in the normal female range. Women with PCOS had significantly higher levels of free T (estimated by the free androgen index) and demonstrated significantly worse performance on tests of verbal fluency, verbal memory, manual dexterity, and visuospatial working memory than the healthy control women. No differences between the groups were found on tests of mental rotation, spatial visualization, spatial perception, or perceptual speed. These results suggest that, in women, elevations in free T may be associated with poorer performance on cognitive tasks that tend to show a female advantage.

Verified hormone therapy improves episodic memory performance in healthy postmenopausal women

Studies of hormone therapy (HT) and cognition have yielded conflicting results. The aim of this observational study was to examine the effect of estradiol, via serum verified HT (estradiol, estriol, progesterone) and endogenous estradiol, on 108 healthy postmenopausal women's cognitive performance. The results demonstrated that the 43 HT-users performed at a significantly higher level than non-users on episodic memory tasks and on a verbal fluency task, whereas HT-users and non-users did not differ on tasks assessing semantic memory and spatial visualization. In addition, there was a positive relationship between serum estradiol level and episodic memory performance, indicating that postmenopausal HT is associated with enhanced episodic memory and verbal fluency, independent of age and education. These observational results suggest that HT use may be sufficient to exert small, yet positive effects on female sensitive cognitive tasks. Hormone therapy compliance and formulation is discussed as confounding factors in previous research.

Hormone treatment gives no benefit against cognitive changes caused by acute sleep deprivation in postmenopausal women

The objective was to evaluate whether hormone therapy (HT) gives any benefit against the possible impairment of cognitive performance when challenged by acute sleep deprivation. Twenty postmenopausal women volunteered (age range 59-72 years, mean=64.4 years, SD=4.4): 10 HT users and 10 nonusers. Eleven young women served as a control group for the cognitive age effect (age range 20-26 years, mean age 23.1 years, SD=1.6). The subjects spent four consecutive nights at the sleep laboratory and were exposed to acute sleep deprivation of 40 h. Measures of attention (reaction speed and vigilance), alertness, and mood were administered every 2 h during the daytime and every hour during the sleep deprivation night. Postmenopausal women performed slower than young controls, whereas young controls made more errors. In HT users, the recovery night did not fully restore the performance in the simple and two-choice reaction time tasks, but in nonusers it did so. Sleep deprivation had a detrimental, yet reversible effect on vigilance in all groups. In all groups, sleepiness started to increase after 15 h of sleep deprivation and remained elevated in the morning after the recovery night. Prolonged wakefulness or HT had no effect on mood. In conclusion, sleep deprivation impaired cognitive performance in postmenopausal as well as young women. Postmenopausal women kept up their performance at the expense of reaction speed and young women at the expense of accuracy. One night was not enough for HT users to recover from sleep deprivation. Thus, HT gave no benefit in maintaining the attention and alertness during sleep deprivation.

Effects of continuous and intermittent estrogen treatments on memory in aging female mice

The manner in which hormone therapy is given to postmenopausal women may significantly influence its ability to reduce age-associated memory loss. To test the hypothesis that a regimen that approximates the timing of estrogen surges in the natural cycle is more beneficial for memory than a regimen that provides continuous levels of estrogen, we examined the effects of continuous and intermittent estrogen regimens on spatial and object memory in aging female mice. Mice (18 months) were treated with 0.2 mg/kg 17beta-estradiol (E(2)) or vehicle (VEH) for 3 months following ovariectomy. A fast-acting water-soluble cyclodextrin-encapsulated E(2) was used to ensure metabolism within 24 h. Vehicle-treated mice received daily injections of 2-hydroxypropyl-beta-cyclodextrin vehicle. The continuous estradiol group (Contin E(2)) was injected daily with estradiol. The intermittent group (Twice/wk E(2)) received estradiol every 4 days and vehicle on all other days. Mice (21 months) were tested in water-escape motivated 8-arm radial arm maze (WRAM) and object recognition tasks. During WRAM acquisition, the Twice/wk E(2) group committed significantly more reference memory errors than VEH and Contin E(2) groups, and tended to make more working memory errors than the VEH group. The Contin E(2) group did not differ from VEH on either WRAM measure. Additionally, the Twice/wk E(2) group tended to exhibit impaired object recognition. Thus, neither treatment improved spatial or object memory. Indeed, intermittent estradiol was detrimental to both types of memory. These results suggest that the timing of administration may play an important role in the mnemonic response of aging females to estrogen.

Post-training estrogen enhances spatial and object memory consolidation in female mice

The present study was designed to determine if post-training injections of a water-soluble form of 17beta-estradiol could enhance spatial and object memory consolidation in young female mice. Young ovariectomized female mice were trained in Morris water maze and object recognition tasks, injected with 0.1, 0.2, or 0.4 mg/kg cyclodextrin-encapsulated 17beta-estradiol or cyclodextrin-conjugated vehicle, and then re-tested after a delay. In the water maze, mice were trained in eight consecutive trials, injected, and memory for the platform location was re-tested after 24 h. All mice learned to find the platform on Day 1, but only mice receiving 0.2 mg/kg estradiol remembered the platform location on Day 2. In the object recognition task, mice were first presented with two identical objects, injected, and then presented with a familiar and novel object after a 24- or 48-h delay. For both delays, the 0.2 and 0.4 mg/kg doses enhanced memory for the familiar object. These data demonstrate that a 0.2 mg/kg dose of estradiol can enhance multiple types of memory consolidation in female mice, and suggest a narrower effective dose range for spatial memory than for object memory.

Effects of estrogen and progesterone on spatial memory consolidation in aged females

Interpretation of data illustrating that estrogen, with or without progestin, is detrimental to memory in post-menopausal women is complicated by the fact that little is known about the effects of progestins on memory. The present study examined if estrogen, alone or with progesterone, affects spatial memory consolidation in ovariectomized aged female mice. Mice received eight training trials in a spatial Morris water maze followed immediately by injection of water-soluble 17beta-estradiol (E(2); 0.2 mg/kg) or vehicle. Mice were re-tested 24 h later. All mice learned to find the platform on Day 1. On Day 2, the performance of control, but not E(2) mice, deteriorated, suggesting that E(2) enhanced memory for the platform location. In a second experiment, mice were injected with E(2) and 10 or 20 mg/kg water-soluble progesterone. The 10 mg/kg dose of progesterone did not affect estrogen's ability to enhance spatial memory consolidation, but 20 mg/kg blocked this effect. These data indicate that estrogen can improve spatial memory consolidation in aged females and that this effect can be attenuated by progesterone.

Hormone replacement therapy and cognitive performance in postmenopausal women—a review by cognitive domain

Laboratory, animal and neuroimaging evidences suggest that hormone replacement therapy (HRT) may be beneficial to human cognition. This systematic review includes 26 studies on the association between HRT and cognition and 17 studies on HRT and risk of dementia. It was hypothesised that HRT would have a positive association with cognitive speed and verbal memory and possibly visual memory but not with executive functioning, and would be associated with a decreased risk of dementia. Evidence for HRT's neuroenhancing and neuroprotective properties was also evaluated. There was significant statistical and clinical heterogeneity among studies precluding meta-analysis. Results showed no consistent relationship between HRT and performance in any cognitive domain. Cross-sectional studies tended to report more positive results than longitudinal studies and randomised-controlled trials, particularly in the areas of verbal memory and executive functioning. HRT was associated with decreased risk of dementia in observational studies, but with increased risk in one randomised-controlled trial. Cognitive improvement or maintenance are not secondary benefits of HRT.

Estrogen and cognitive aging in women

Although several randomized controlled trials of surgically menopausal women have provided evidence that estrogen protects aspects of memory, many cross-sectional and longitudinal studies, including those from the Women's Health Initiative Memory Study, have failed to confirm these findings. One critical difference between studies that found a protective effect of estrogen on memory and those that did not is that, in the former studies, treatment with estrogen began at the time of menopause and in the latter studies, it was first administered many years after the menopause had occurred. Recent evidence from rodent, nonhuman primate, and human studies consistently suggests that the timing of the initiation of estrogen treatment with regard to the menopause may be critical to our understanding of the estrogenic effect on memory. Results of these animal and human studies indicate that the initiation of estrogen treatment at the time of menopause, or soon after ovariectomy, provides a window of opportunity for the protection of memory in females whereas the administration of the hormone following a considerable delay in time after ovariectomy or following a natural menopause has little or no beneficial effect on cognition.

Estrogen receptor alpha and beta immunoreactive neurons in normal adult and aged female rat hippocampus: a qualitative and quantitative study

We have studied the distribution pattern and levels of expression of two estrogen receptor (ER) subtypes, ERalpha and ERbeta, in the normal adult (n = 10) and the aged (n = 10) female rat hippocampus with the objective to establish baseline data and the changes that occur during aging. Techniques including immunohistochemical localization, co-localization with double immunofluorescence and confocal microscopy, image analysis including neuronal counts/mm(2) area and measurements of optical density (OD) of immunoreactivity in immunoreactive neurons and Western blot analysis have been used. The results revealed ERalpha and ERbeta positive neurons in all subfields of the hippocampus with maximum presence in the stratum pyramidale of CA3. Some stained neurons in CA3 exhibited pyramidal neuron like morphological characteristics; such neurons were not found in CA1. All other immunoreactive neurons showed non-pyramidal neuron like morphological characteristics. Neuronal counts revealed a significant decrease in the number of immunoreactive neurons in CA3-CA1 of aged hippocampus. The percent decrease in counts of the immunoreactive neurons/mm(2) area in the aged rat (compared to the adult) was 78% for the ERalpha and 88% for the ERbeta (P < 0.001) in CA3. In CA1, it was 56% (P < 0.001) and 41% (P < 0.01) respectively. The OD of immunoreactivity was significantly decreased (P < 0.01) in CA3 but increased (P < 0.01) in the CA1 immunoreactive neurons. Western blot analysis also showed a significant decline (P < 0.01) in the levels of the ERalpha and ERbeta proteins in the aged hippocampus. Co-localization revealed that the two ER subtypes do co-exist in the same hippocampal neurons.

Selective and persistent effect of foetal sex on cognition in pregnant women

Despite widespread anecdotal complaints of impairment, systematic research addressing cognition in gestating women has yielded equivocal results. One way that ambiguous findings could arise is if male and female foetuses affect maternal cognition in different ways. Using a longitudinal within-participants design, we tracked women's cognitive performance from early pregnancy through to postnatal resumption of menstruation. On several cognitive tests, the sex of the foetus was unrelated to maternal performance. But specifically on difficult tests of working memory and spatial ability, a large and enduring effect of foetal sex was evident: women pregnant with boys consistently outperformed women pregnant with girls. A foetal-derived factor that differs in type or concentration between male and female foetuses may thus influence mothers' cognition.

Age-related cognitive decline in the menopause: effects of hormone replacement therapy on cognitive event-related potentials

OBJECTIVE

Although epidemiological and clinical studies suggest that hormone replacement therapy (HRT) may protect against cognitive disorders and neurodegenerative diseases, the relation between estrogen and cognition in postmenopausal women remains controversial.

METHODS

In a double-blind placebo-controlled, parallel group design study the effects of HRT with the estrogen-progestogen combination Presomen 1.25 compositum((R)) (1.25mg equine conjugated estrogens administered for 21 days plus the progestogen 5mg medrogeston given for 11 days) on event-related potentials (ERPs) in postmenopausal patients with age-related cognitive decline (DSM-IV code 780.9, ICD-10 code R 41.8) were investigated. After a pre-drug comparison with age-matched normal postmenopausal controls, 48 psychotropic drug-free patients aged 60 +/- 6 years were randomized to receive either placebo or verum for 4 months. ERPs were recorded before as well as on the 91-92 days of the study, which thus fell into the estrogen phase of the treatment during the fourth cycle.

RESULTS

At baseline, patients showed a lengthening of P300 latency and an attenuation of P300 amplitudes as compared with normal controls. After HRT with Presomen, a significant shortening of P300 latency as compared with placebo was observed.

CONCLUSIONS

The baseline P300 differences suggest that in the patient group the aging process was advanced, while after HRT with Presomen a significant improvement and normalization of information processing as indexed by P300 was observed.

Strategies and methods for research on sex differences in brain and behavior

Female and male brains differ. Differences begin early during development due to a combination of genetic and hormonal events and continue throughout the lifespan of an individual. Although researchers from a myriad of disciplines are beginning to appreciate the importance of considering sex differences in the design and interpretation of their studies, this is an area that is full of potential pitfalls. A female's reproductive status and ovarian cycle have to be taken into account when studying sex differences in health and disease susceptibility, in the pharmacological effects of drugs, and in the study of brain and behavior. To investigate sex differences in brain and behavior there is a logical series of questions that should be answered in a comprehensive investigation of any trait. First, it is important to determine that there is a sex difference in the trait in intact males and females, taking into consideration the reproductive cycle of the female. Then, one must consider whether the sex difference is attributable to the actions of gonadal steroids at the time of testing and/or is sexually differentiated permanently by the action of gonadal steroids during development. To answer these questions requires knowledge of how to assess and/or manipulate the hormonal condition of the subjects in the experiment appropriately. This article describes methods and procedures to assist scientists new to the field in designing and conducting experiments to investigate sex differences in research involving both laboratory animals and humans.

Inhibitory avoidance task reveals differences in ectonucleotidase activities between male and female rats

Studies demonstrated that endogenous levels of estrogen affect the long-term potentiation (LTP) and long-term depression (LTD). ATP and adenosine may play a role in the modulation of LTP. Our laboratory observed in previous studies that inhibitory avoidance task is associated with a decrease in hippocampal ectonucleotidase activities in adult male rats. To explore if ectonucleotidases are modulated in memory formation in female rats, as observed in males, we evaluated the effect of inhibitory avoidance training on synaptosomal NTP Dase and 5'-nucleotidase activities in rat hippocampus from both sexes. The results demonstrated a decrease in ATP, ADP and AMP hydrolysis (37%, 38% and 32%, respectively) immediately after training and a significant inhibition only in ATP hydrolysis (36%) 30 min post-training in male rats. There were no changes in ectonucleotidase activities from female rats. These findings provide support for the view that could exist biochemical differences in ectonucleotidase activities between males and females.