Endocrine disruption and cognitive function in adolescent female rhesus monkeys

Estrogen Replacement Reduces Hearing Threshold Shifts and Cochlear Hair Cell Loss After Acoustic Overexposure in Ovariectomized Rats

Objectives.

The relationship of estrogen (the primary female sex hormone) with hearing function has been studied in both humans and animals. However, whether estrogen levels affect hearing remains uncertain. Therefore, in this study, we investigated changes in the vulnerability of hearing to acoustic overexposure in ovariectomized female rats.

Methods.

Eighteen 8-week-old female Sprague-Dawley rats were separated into four groups as follows: sham ovariectomy (OP), OP only, and OP treated with low (10 µg/kg) or high doses (100 µg/kg) of estrogen. Rats in the estrogen replacement groups were given two intraperitoneal injections. Hearing thresholds were measured before noise exposure, and at 1 day and 2 weeks after exposure.

Results.

The hearing thresholds of the sham OP and OP-only groups were not significantly different. However, both estrogen groups showed a lower threshold shift than the OP-only group. Histological immunostaining analyses showed that hair cell loss in the 32 kHz region was more severe in the sham OP group than in the OP-only group. Furthermore, there was little or no hair cell loss in either estrogen replacement group and significantly more hair cell loss in the OP-only group.

Conclusion.

These results suggest that estrogen replacement may reduce the vulnerability of hearing to noise exposure in menopausal women.

N-3 Polyunsatured Fatty Acids in Menopausal Transition: A Systematic Review of Depressive and Cognitive Disorders with Accompanying Vasomotor Symptoms

Depression is one of the most important health problems worldwide. Women are 2.5 times more likely to experience major depression than men. Evidence suggests that some women might experience an increased risk for developing depression during “windows of vulnerability”, i.e., when exposed to intense hormone fluctuations, such as the menopause transition. Indeed, this period is associated with different symptoms, including vasomotor, depressive, and cognitive symptoms, which have all been shown to worsen as women approach menopause. Even though hormonal therapy represents the most effective treatment, side effects have been reported by several studies. Therefore, an increased number of women might prefer the use of alternative medicine for treating menopausal symptoms. N-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs) are included among these alternative treatments. We here provide a review of studies investigating the effects of n-3 LCPUFAs on hot flashes and depressive and cognitive disorders in menopausal women. The reported results are scattered and heterogeneous. In conclusion, a beneficial role of n-3 LCPUFAs in hot flashes, and depressive and cognitive symptoms related to menopausal transition is still far from conclusive.

ZENK induction in the zebra finch brain by song: Relationship to hemisphere, rhythm, oestradiol and sex

Oestradiol is abundant in the zebra finch auditory forebrain and has the capacity to modulate neural responses to auditory stimuli with specificity as a result of both hemisphere and sex. Arrhythmic song induces greater ZENK expression than rhythmic song in the caudomedial nidopallium (NCM), caudomedial mesopallium (CMM) and nucleus taeniae (Tn) of adult zebra finches. The increases in the auditory regions (i.e. NCM and CMM) may result from detection of errors in the arrhythmic song relative to the learned template. In the present study, zebra finches were treated with oestradiol, the aromatase inhibitor fadrozole or a control and then exposed to rhythmic or arrhythmic song to assess the effect of oestradiol availability on neural responses to auditory rhythms. ZENK mRNA was significantly greater in the left hemisphere within the NCM, CMM and Tn. Main effects of sex were detected in both auditory regions, with increased ZENK in males in the NCM and in females in the CMM. In the CMM, an effect of hormone treatment also existed. Although no pairwise comparison was statistically significant, the pattern suggested greater ZENK expression in control compared to both fadrozole- and oestradiol-treated birds. In the NCM, an interaction between sex and hormone treatment suggested that the sex effect was restricted to control animals. An additional interaction in the NCM among sex, stimulus rhythmicity and hemisphere indicated that the strongest effect of laterality was present in males exposed to arrhythmic song. The hormone effects suggest that an optimal level of oestradiol may exist for processing rhythmicity of auditory stimuli. The overall pattern for left lateralisation parallels the left lateralisation of language processing in humans and may suggest that this hemisphere is specialised for processing conspecific vocalisations. The reversed sex differences in the NCM and CMM suggest that males and females differentially rely on components of the auditory forebrain for processing conspecific song.

Changes of auditory event-related potentials in ovariectomized rats injected with d-galactose: Protective role of rosmarinic acid

Rosmarinic acid (RA), which has multiple bioactive properties, might be a useful agent for protecting central nervous system against age related alterations. In this context, the purpose of the present study was to investigate possible protective effects of RA on mismatch negativity (MMN) component of auditory event-related potentials (AERPs) as an indicator of auditory discrimination and echoic memory in the ovariectomized (OVX) rats injected with d-galactose combined with neurochemical and histological analyses. Ninety female Wistar rats were randomly divided into six groups: sham control (S); RA-treated (R); OVX (O); OVX+RA-treated (OR); OVX+d-galactose-treated (OD); OVX+d-galactose+RA-treated (ODR). Eight weeks later, MMN responses were recorded using the oddball condition. An amplitude reduction of some components of AERPs was observed due to ovariectomy with or without d-galactose administiration and these reduction patterns were diverse for different electrode locations. MMN amplitudes were significantly lower over temporal and right frontal locations in the O and OD groups versus the S and R groups, which was accompanied by increased thiobarbituric acid reactive substances (TBARS) and hydroxy-2-nonenal (4-HNE) levels. RA treatment significantly increased AERP/MMN amplitudes and lowered the TBARS/4-HNE levels in the OR and ODR groups versus the O and OD groups, respectively. Our findings support the potential benefit of RA in the prevention of auditory distortion related to the estrogen deficiency and d-galactose administration at least partly by antioxidant actions.

Sleep disturbance as detected by actigraphy in pre-pubertal juvenile monkeys receiving therapeutic doses of fluoxetine

Sleep disturbance is a reported side effect of antidepressant drugs in children. Using a nonhuman primate model of childhood selective serotonin reuptake inhibitor (SSRI) therapy, sleep was studied quantitatively with actigraphy. Two 48-h sessions were recorded in the home cage environment of juvenile male rhesus monkeys at two and three years of age, after one and two years of treatment with a therapeutic dose of the SSRI fluoxetine, and compared to vehicle treated controls. A third session was conducted one year after discontinuation of treatment at four years of age. During treatment, the fluoxetine group demonstrated sleep fragmentation as indexed by a greater number of rest-activity transitions compared to controls. In addition fluoxetine led to more inactivity during the day as indexed by longer duration of rest periods and the reduced activity during these periods. The fluoxetine effect on sleep fragmentation, but not on daytime rest, was modified by the monkey's genotype for polymorphisms of monoamine oxidase A (MAOA), an enzyme that metabolizes serotonin. After treatment, the fluoxetine effect on nighttime rest-activity transitions persisted, but daytime activity was not affected. The demonstration in this nonhuman primate model of sleep disturbance in connection with fluoxetine treatment and specific genetic polymorphisms, and in the absence of diagnosed psychopathology, can help inform use of this drug in children.

Development of a cognitive testing apparatus for socially housed mother-peer-reared infant rhesus monkeys

Though cognitive testing of infant monkeys has been practiced for the past 40 years, these assessments have been limited primarily to nursery-reared infants due to the confounds of separating mother-reared infants for assessments. Here, we describe a pilot study in which we developed a cognitive testing apparatus for socially housed, mother-peer-reared rhesus macaques under 1 year of age (Macaca mulatta) that allowed the infants to freely return to their mothers for contact comfort. Infants aged 151.2 ± 18.3 days (mean ± SEM; n = 5) were trained and tested on an object detour reach task. Infants completed training in 5.0 ± 0.2 days, and completed testing in 6.2 ± 0.9 days. Across 4 days of testing, infants improved to nearly errorless performance (Friedman test: χ(2)  = 13.27, df = 3, p = 0.004) and learned to do the task more quickly (Friedman test: χ(2)  = 11.69, df = 3, p = 0.009). These are the first cognitive data in group-housed, mother-peer-reared rhesus monkeys under 1 year of age, and they underscore the utility of this apparatus for studying cognitive development in a normative population of infant monkeys.

Cognition and mood in perimenopause: a systematic review and meta-analysis

OBJECTIVE

It is suggested that declines in estrogen around menopause are associated with declines in cognitive functioning as well as increased risk of depressive symptoms and depressive disorders. Existing studies of objective cognitive function and mood have differed in the criteria used to stage the menopausal transition and in the outcome measures used. The purpose of this review was to synthesize the existing studies of the relationship between menopausal stage and neuropsychological performance and depression.

DESIGN

A search of the literature of observational studies was performed using PubMed. Four cross-sectional studies on menopausal transition stage and cognitive function and four longitudinal studies on menopausal transition stage and risk of depression, as measured by symptom inventories and structured clinical interviews, were selected. For the cognitive outcomes, fixed effects models were used to estimate overall standardized effect sizes. For the depression outcomes, the results of group comparisons were summarized using the log odds ratio and its estimated standard error.

RESULTS

Postmenopausal women performed significantly worse than pre- and perimenopausal women on delayed verbal memory tasks, and significantly worse than perimenopausal women on phonemic verbal fluency tasks. Peri- and postmenopausal women were at significantly increased risk of depression, as measured by standard symptom inventories and structured clinical interviews, than premenopausal women.

CONCLUSIONS

The menopausal transition is a time of increased vulnerability to cognitive declines and increased risk of depressive symptoms and depressive disorders. However, these results cannot necessarily be generalized beyond the studies included in this review. This article is part of a Special Issue entitled 'Menopause'.

Object discrimination and reversal learning in infant and juvenile non-human primates in a non-clinical laboratory

BACKGROUND

Biopharmaceutical development necessitates use of non-human primates in toxicology, leading to adoption of non-traditional methods including cognitive function assessment.

METHODS

A two-object discrimination and reversal test in cynomolgus monkeys (Macaca fascicularis) was performed using a Wisconsin General Testing Apparatus (WGTA). Non-clinical study design and regulatory considerations dictate that infants are raised by their biological mothers until weaning at 6 months. Thirty-four animals (6-21 months of age) were trained to discriminate between two randomly selected stimulus objects to retrieve a reward. Following training, days to first reversal after interchanging the reward were measured.

RESULTS

Both sexes acquired visual discrimination skills at similar rates. Trends in learning and reversals completed were uniform across age groups. Completing training early in some subjects had no impact on subsequent testing phases.

CONCLUSIONS

Weaned cynomolgus monkey infants can be successfully tested for cognitive abilities using the WGTA in a non-clinical laboratory setting.

Reconciling subjective memory complaints with objective memory performance in the menopausal transition

OBJECTIVE

The overall aim of this study was to examine the relationship between subjective memory complaints and objective cognitive performance in perimenopausal women. The specific aims were to determine (1) if subjective complaints of memory problems relate to objective performance on memory tests, (2) if subjective complaints of memory problems relate to other domains of cognitive function, and (3) if subjective memory complaints relate to other noncognitive factors, such as depression, anxiety, and sleep quality.

METHODS

Seventy-five perimenopausal women completed a comprehensive neuropsychological battery, which included measures of attention, working memory, verbal memory, verbal fluency, visuospatial skill, and fine motor dexterity; completed self-report inventories of their perceived memory and menopausal symptoms; and provided serum levels of estradiol and follicle-stimulating hormone.

RESULTS

Memory complaints were not associated with verbal learning or verbal memory but were associated with working memory and complex attention/vigilance. Memory complaints were also associated with symptoms of depression, anxiety, somatic complaints, and sleep disturbance. Regression analyses revealed that memory complaints were best predicted by depressive symptoms, somatic complaints, and working memory performance.

CONCLUSIONS

Memory complaints in the menopausal transition may reflect true difficulties with attentionally mediated cognitive processes. Memory complaints may also be associated with other menopausal-related symptoms.

Control of central auditory processing by a brain-generated oestrogen

Recent discoveries show that behaviourally relevant sensory experience drives the production of oestradiol - the classic sex steroid oestrogen - in auditory neurons in the adult brain of both males and females. This brain-generated oestrogen markedly enhances the efficiency of the neural coding of acoustic cues and shapes auditory-based behaviours on a timescale that is relevant for sensory processing and congruent with the action of rapid neuromodulators. These findings are re-shaping our current understanding of the mechanistic framework that supports sensory processing and the functional roles of hormones in the brain, and have implications for multiple health issues.

DDT and Other Chlorinated Insecticides

The use of organochlorine insecticides such as DDT, lindane and cyclodieneshas declined markedly worldwide over the last decades. Most are now banned or not used. At an acute toxicity level they have been relatively safe in use for humans. However, the greatest concerns are their persistence in people, wildlife and the environment due to their slow metabolism. Although their carcinogenicity for humans has not been supported by strong epidemiological evidence, their potential to be modulators of endocrine and immune function at levels remaining in the environment or associated with residual spraying of DDT continue to be of concern. At present, DDT is still allowed by the United Nations for combating malaria, with continual monitoring and assessment where possible. The toxicological consequences of exposure of animals and people to DDT is discussed as well as some analogues and other insecticides such as lindane, dieldrin and chlordecone that, although little used, continue to persist in surroundings and people. Because of circumstances of world health brought about by climate change or human activities that have yet to develop, there may come a time when the importance of some may re-emerge.

Organization of Estrogen-Associated Circuits in the Mouse Primary Auditory Cortex

Sex steroid hormones influence the perceptual processing of sensory signals in vertebrates. In particular, decades of research have shown that circulating levels of estrogen correlate with hearing function. The mechanisms and sites of action supporting this sensory-neuroendocrine modulation, however, remain unknown. Here we combined a molecular cloning strategy, fluorescence in-situ hybridization and unbiased quantification methods to show that estrogen-producing and -sensitive neurons heavily populate the adult mouse primary auditory cortex (AI). We also show that auditory experience in freely-behaving animals engages estrogen-producing and -sensitive neurons in AI. These estrogen-associated networks are greatly stable, and do not quantitatively change as a result of acute episodes of sensory experience. We further demonstrate the neurochemical identity of estrogen-producing and estrogen-sensitive neurons in AI and show that these cell populations are phenotypically distinct. Our findings provide the first direct demonstration that estrogen-associated circuits are highly prevalent and engaged by sensory experience in the mouse auditory cortex, and suggest that previous correlations between estrogen levels and hearing function may be related to brain-generated hormone production. Finally, our findings suggest that estrogenic modulation may be a central component of the operational framework of central auditory networks.

Estradiol-dependent modulation of auditory processing and selectivity in songbirds

The steroid hormone estradiol plays an important role in reproductive development and behavior and modulates a wide array of physiological and cognitive processes. Recently, reports from several research groups have converged to show that estradiol also powerfully modulates sensory processing, specifically, the physiology of central auditory circuits in songbirds. These investigators have discovered that (1) behaviorally-relevant auditory experience rapidly increases estradiol levels in the auditory forebrain; (2) estradiol instantaneously enhances the responsiveness and coding efficiency of auditory neurons; (3) these changes are mediated by a non-genomic effect of brain-generated estradiol on the strength of inhibitory neurotransmission; and (4) estradiol regulates biochemical cascades that induce the expression of genes involved in synaptic plasticity. Together, these findings have established estradiol as a central regulator of auditory function and intensified the need to consider brain-based mechanisms, in addition to peripheral organ dysfunction, in hearing pathologies associated with estrogen deficiency.

Neurochemical organization and experience-dependent activation of estrogen-associated circuits in the songbird auditory forebrain

The classic steroid hormone estradiol is rapidly produced by central auditory neurons in the songbird brain and instantaneously modulates auditory coding to enhance the neural and behavioral discrimination of acoustic signals. Although recent advances highlight novel roles for estradiol in the regulation of central auditory processing, current knowledge on the functional and neurochemical organization of estrogen-associated circuits, as well as the impact of sensory experience in these auditory forebrain networks, remains very limited. Here we show that both estrogen-producing and -sensitive neurons are highly expressed in the caudomedial nidopallium (NCM), the zebra finch analog of the mammalian auditory association cortex, but not other auditory forebrain areas. We further demonstrate that auditory experience primarily engages estrogen-producing, and to a lesser extent, estrogen-responsive neurons in NCM, that these neuronal populations moderately overlap and that acute episodes of sensory experience do not quantitatively affect these circuits. Finally, we show that whereas estrogen-producing cells are neurochemically heterogeneous, estrogen-sensitive neurons are primarily glutamatergic. These findings reveal the neurochemical and functional organization of estrogen-associated circuits in the auditory forebrain, demonstrate their activation and stability in response to sensory experience in behaving animals, and highlight estrogenic circuits as fundamental components of central networks supporting sensory processing.

Brain-generated estradiol drives long-term optimization of auditory coding to enhance the discrimination of communication signals

Auditory processing and hearing-related pathologies are heavily influenced by steroid hormones in a variety of vertebrate species, including humans. The hormone estradiol has been recently shown to directly modulate the gain of central auditory neurons, in real time, by controlling the strength of inhibitory transmission via a nongenomic mechanism. The functional relevance of this modulation, however, remains unknown. Here we show that estradiol generated in the songbird homolog of the mammalian auditory association cortex, rapidly enhances the effectiveness of the neural coding of complex, learned acoustic signals in awake zebra finches. Specifically, estradiol increases mutual information rates, coding efficiency, and the neural discrimination of songs. These effects are mediated by estradiol's modulation of both the rate and temporal coding of auditory signals. Interference with the local action or production of estradiol in the auditory forebrain of freely behaving animals disrupts behavioral responses to songs, but not to other behaviorally relevant communication signals. Our findings directly show that estradiol is a key regulator of auditory function in the adult vertebrate brain.

Endocrine disruptors targeting ERbeta function

Endocrine disruptive chemicals (EDCs) circulating in the environment constitute a risk to ecosystems, wildlife and human health. Oestrogen receptor (ER) alpha and beta are targeted by various kinds of EDCs but the molecular mechanisms and long-term consequences of exposure are largely unknown. Some biological effects of EDCs are mediated by the aryl hydrocarbon receptor (AhR), which is a key player in the cellular defence against xenobiotic substances. Adding complexity to the picture, there is also accumulating evidence that AhR-ER pathways have an intricate interplay at multiple levels. In this review, we discuss some EDCs that affect the oestrogen pathway by targeting ERbeta. Furthermore, we describe some effects of AhR activities on the oestrogen system. Mechanisms as well as potential adverse effects on human health are discussed.

Regulation of estrogen receptor beta activity and implications in health and disease

Together with the estrogen receptor (ER) alpha, estrogen receptor beta (ER beta ) mediates many of the physiological effects of estrogens. As ER beta is crucially involved in a variety of important physiological processes, its activity should be tightly regulated. ER beta regulation is achieved by hormone binding as well as by posttranslational modifications of the receptor. Furthermore, ER beta expression levels are under circadian control and can be regulated by DNA methylation of the ER beta promoter region. There are also a number of factors that can interfere with ER beta activity, such as phytoestrogens, endocrine disruptive chemicals, and growth factors. In this article, we outline different mechanisms of ER beta regulation and how they are implicated in various diseases. We also discuss how these insights might help to specifically target ER beta in drug design.

Estradiol shapes auditory processing in the adult brain by regulating inhibitory transmission and plasticity-associated gene expression

Estradiol impacts a wide variety of brain processes, including sex differentiation, mood, and learning. Here we show that estradiol regulates auditory processing of acoustic signals in the vertebrate brain, more specifically in the caudomedial nidopallium (NCM), the songbird analog of the mammalian auditory association cortex. Multielectrode recordings coupled with local pharmacological manipulations in awake animals reveal that both exogenous and locally generated estradiol increase auditory-evoked activity in NCM. This enhancement in neuronal responses is mediated by suppression of local inhibitory transmission. Surprisingly, we also found that estradiol is both necessary and sufficient for the induction of multiple mitogen-activated protein kinase (MAPK)-dependent genes thought to be required for synaptic plasticity and memorization of birdsong. Specifically, we show that local blockade of estrogen receptors or aromatase activity in awake birds decrease song-induced MAPK-dependent gene expression. Infusions of estradiol in acoustically isolated birds induce transcriptional activation of these genes to levels comparable with song-stimulated animals. Our results reveal acute and rapid nongenomic functions for estradiol in central auditory physiology and suggest that such roles may be ubiquitously expressed across sensory systems.

Environmental factors and puberty timing: expert panel research needs

Serono Symposia International convened an expert panel to review the impact of environmental influences on the regulation of pubertal onset and progression while identifying critical data gaps and future research priorities. An expert panel reviewed the literature on endocrine-disrupting chemicals, body size, and puberty. The panel concluded that available experimental animal and human data support a possible role of endocrine-disrupting chemicals and body size in relation to alterations in pubertal onset and progression in boys and girls. Critical data gaps prioritized for future research initiatives include (1) etiologic research that focus on environmentally relevant levels of endocrine-disrupting chemicals and body size in relation to normal puberty as well as its variants, (2) exposure assessment of relevant endocrine-disrupting chemicals during critical windows of human development, and (3) basic research to identify the primary signal(s) for the onset of gonadotropin-releasing hormone-dependent/central puberty and gonadotropin-releasing hormone-independent/peripheral puberty. Prospective studies of couples who are planning pregnancies or pregnant women are needed to capture the continuum of exposures at critical windows while assessing a spectrum of pubertal markers as outcomes. Coupled with comparative species studies, such research may provide insight regarding the causal ordering of events that underlie pubertal onset and progression and their role in the pathway of adult-onset disease.

Methoxychlor suppresses the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible CYP1A1 expression in murine Hepa-1c1c7 cells

Methoxychlor (MXC) is a pesticide that was developed as a replacement for dichlorodiphenyltrichloroethane (DDT). The influence of MXC on CYP1A1 expression or the functions of mouse hepatoma Hepa-1clc7 remain unclear. Cultured Hepa-1c1c7 cells were treated with MXC with or without 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to assess the role of MXC on CYP1A1 expression. MXC alone did not affect CYP1A1-specific 7-ethoxyresorufin O-deethylase (EROD) activity. In contrast, TCDD-inducible EROD activities were markedly reduced upon concomitant treatment with TCDD and MXC in a concentration-dependent manner. Treatment with ICI 182.780, an estrogen-receptor antagonist, did not affect the suppressive effects of MXC on TCDD-inducible EROD activity. TCDD-inducible CYP1A1 mRNA levels were markedly suppressed upon treatment with TCDD and MXC, and this is consistent with their effects on EROD activity. A transient transfection assay using dioxin-response element (DRE)-linked luciferase and an electrophoretic mobility shift assay revealed that MXC reduced the transformation of the aryl hydrocarbons (Ah) receptor to a form capable of specifically binding to the DRE sequence in the promoter region of the CYP1A1 gene. These results suggest that the downregulation of CYP1A1 gene expression by MXC in Hepa-1c1c7 cells might be an antagonism of the DRE binding potential of the nuclear Ah receptor but is not mediated through the estradiol receptor.

Interactive effects of fitness and hormone treatment on brain health in postmenopausal women

Recent research in rodents suggests that extended and chronic hormone therapy can exacerbate memory impairments and irreversibly damage cells. However, aerobic fitness regimens have been shown to spare brain tissue and cognitive function. In addition, interactions between estrogen treatment and exercise have been reported in rodents. However, whether aerobic fitness and hormone treatments show interactive effects on human brain tissue and cognition has yet to be determined. Here we report two unique and important results: (a) HRT treatment up to 10 years in duration spares gray matter in prefrontal cortex and is associated with better performance on measures of executive function, whereas HRT treatment beyond 10 years in duration increases the degree of prefrontal deterioration and amplifies the decline on measures of executive functioning (b) higher fitness levels augment the effects of shorter durations of hormone treatment and ameliorate the declines associated with prolonged hormone treatment.

Estrogen and hearing: a summary of recent investigations

Is the female sex steroid estrogen the key to preserved hearing in the aging human? This question remains unanswered, but hearing loss is more profound in elderly males than females. There are also well-known sex differences in the auditory brainstem response (ABR), i.e. women have shorter latencies than men. Moreover, menopausal women who are administered hormone replacement therapy have slightly better hearing than those who are not, and women with Turner's syndrome (45,X), who are biologically estrogen-deficient, show longer ABR latencies and early presbyacusis. These findings are also supported by animal experiments. When boosted with estrogen or testosterone the non-reproductive female midshipman fish alters its inner ear auditory mechanism so that it can hear the male's hum-like call. If estrogen receptor beta is knocked out in mice, severe progressive hearing loss occurs, leading to early deafness. In apparent contradiction to these findings, there have been case reports suggesting that hormone replacement therapy and oral contraceptive use can lead to hearing loss, but of another type, namely acute sudden deafness. Such contradictory aspects of the action of estrogen are commonly found and may spring from the fact that there are two estrogen receptors, alpha and beta, both of which are present in the inner ear of mice, rats and humans. Knowing how sex steroids can alter hearing ability may give important clues as to how estrogen can preserve hearing in humans. In this review we present a summary of current knowledge about hearing and estrogen.

Neurobehavioral evaluation of rhesus monkey infants fed cow's milk formula, soy formula, or soy formula with added manganese

The possible neurobehavioral effects of excess manganese in soy formula were studied. Male rhesus monkeys (n=8/group) were fed a commercial cow's milk based formula (Control), a commercial soy protein based formula (Soy), or the soy formula with added manganese (Soy+Mn) from birth to 4 months of age. Soy formulas naturally have higher manganese (Mn) content than cow's milk formulas. Monkeys received behavioral evaluations, growth measurements, and cerebrospinal fluid (CSF) sampling from birth to 18 months of age. Soy and Soy+Mn groups engaged in less play behavior and more affiliative clinging in social dyadic interactions. These groups also had shorter wake cycles and shorter periods of daytime inactivity than controls. An impulsivity test was sensitive to the Soy group diet. The Soy+Mn group also had a blunted response to the dopamine agonist apomorphine. Groups did not differ significantly in CSF dopamine and serotonin metabolite concentrations, but these concentrations were correlated with several tasks affected by experimental formula. This experiment suggests that components of soy formula, including Mn, may influence brain development as reflected in behavioral measures.

Gestational dexamethasone treatment elicits sex-dependent alterations in locomotor activity, reward-based memory and hippocampal cholinergic function in adolescent and adult rats

Glucocorticoids are the consensus treatment for preventing respiratory distress syndrome in preterm infants but there is emerging evidence of subsequent neurobehavioral abnormalities, independent of somatic growth effects. Pregnant rats were given 0.2 mg/kg of dexamethasone, a dose commensurate with clinical use, on gestational days 17-19 and behavioral evaluations were made on the offspring in adolescence and adulthood. The dexamethasone groups had the same body weights as the controls but nevertheless displayed long-term, sex-selective alterations in locomotor and cognitive behaviors. In the figure-8 activity apparatus, dexamethasone treatment ablated the normal sex differences in locomotor activity by reducing values in females to the lower level typical of males; habituation of activity similarly was impaired in females, reducing the profile to match that of control males, while male rats in the dexamethasone group showed a partially feminized pattern of habituation. In the 8-arm radial maze, control rats displayed typical sex differences, with male rats performing more accurately than females. Dexamethasone treatment eliminated this normal dichotomy, delaying learning in males while improving performance in females to the level normally seen in control males. Finally, we assessed hippocampal [3H]hemicholinium-3 binding as a biomarker for cholinergic synaptic activity, and again found loss of sex differences in the dexamethasone group: values in males were increased to the higher levels typical of females. These results indicate that gestational treatment with dexamethasone obtunds the normal sex differences in neurochemistry and behavior that are typically seen in adolescence in adulthood, thus producing sex-selective alterations in activity, learning, and memory.