Social subordination and polymorphisms in the gene encoding the serotonin transporter enhance estradiol inhibition of luteinizing hormone secretion in female rhesus monkeys

Improving Reproductive Success in Captive Marmosets Through Active Female Choice

The recent upsurge in the use of common marmosets (Callithrix jacchus) as a desirable model for high-priority biomedical research has challenged local and global suppliers struggling to provide sufficient numbers of marmosets for large-scale projects. In laboratories, random male-female pairings are often unsuccessful, with intervals of several months before attempting alternate pairings. Here we address this challenge through a behavioral task that promotes self-directed female selection of potential mates to increase the efficiency of breeding in captive marmosets. We created a partner preference test in which nulliparous females (n = 12) had the opportunity to select between two eligible males (n = 23) at a time, in a forced choice test. In this test, both males and females displayed sexual solicitations. However, the females displayed a clear preference for one male by directing affiliative behaviors toward him including proceptive tongue-flicking, approach, and grooming. Her preference remained consistent across three consecutive test sessions. This method resulted in a 2.5-fold improvement in breeding success within 90 days compared to random pairings. This cost-effective and straightforward pairing practice can be used to enhance breeding efficiency in both small and large marmoset colonies.

Obesity-Related Hypogonadism in Women

Obesity-related hypogonadotropic hypogonadism is a well-characterized condition in men (termed male obesity-related secondary hypogonadism; MOSH); however, an equivalent condition has not been as clearly described in women. The prevalence of polycystic ovary syndrome (PCOS) is known to increase with obesity, but PCOS is more typically characterized by increased gonadotropin-releasing hormone (GnRH) (and by proxy luteinizing hormone; LH) pulsatility, rather than by the reduced gonadotropin levels observed in MOSH. Notably, LH levels and LH pulse amplitude are reduced with obesity, both in women with and without PCOS, suggesting that an obesity-related secondary hypogonadism may also exist in women akin to MOSH in men. Herein, we examine the evidence for the existence of a putative non-PCOS "female obesity-related secondary hypogonadism" (FOSH). We précis possible underlying mechanisms for the occurrence of hypogonadism in this context and consider how such mechanisms differ from MOSH in men, and from PCOS in women without obesity. In this review, we consider relevant etiological factors that are altered in obesity and that could impact on GnRH pulsatility to ascertain whether they could contribute to obesity-related secondary hypogonadism including: anti-Müllerian hormone, androgen, insulin, fatty acid, adiponectin, and leptin. More precise phenotyping of hypogonadism in women with obesity could provide further validation for non-PCOS FOSH and preface the ability to define/investigate such a condition.

Population Numbers and Reproductive Health

A recent study published in The Lancet predicts a remarkable drop in population numbers following a peak that will be reached by 2064. A unique feature of the upcoming population drop is that it will be almost exclusively caused by decreased reproduction, rather than factors that increase rates of mortality. The reasons for decreased reproduction are also unique, as, unlike previous centuries, limited reproduction today is hardly due to a shortage in resources. In other words, the predicted population drop is almost exclusively due to changes in reproductive behavior and reproductive physiology. Today, global changes in reproductive behavior are mostly explained by social sciences in a framework of demographic transition hypotheses, while changes in reproductive physiology are usually attributed to effects of endocrine-disrupting pollutants. This review outlines a complementary/alternative hypothesis, which connects reproductive trends with population densities. Numerous wildlife and experimental studies of a broad range of animal species have demonstrated that reproductive behavior and reproductive physiology are negatively controlled via endocrine and neural signaling in response to increasing population densities. The causal chain of this control system, although not fully understood, includes suppression of every level of hypothalamic-pituitary-gonadal cascade by hypothalamic-pituitary-adrenal axis, activated in response to increasing stress of social interactions. This paper discusses evidence in support of a hypothesis that current trends in reproductive physiology and behavior may be partly explained by increasing population densities. Better understanding of the causal chain involved in reproduction suppression by population density-related factors may help in developing interventions to treat infertility and other reproductive conditions.

Neuro-pharmacological reinstatement of ovulation and associated neurobiology in a macaque model of functional hypothalamic amenorrhoea

STUDY QUESTION

What is the underlying neuropathology in a cynomolgus macaque model of functional hypothalamic amenorrhoea (FHA) and can it be normalized to restore ovulation?

SUMMARY ANSWER

Anovulatory monkeys exhibited increased hypothalamic norepinephrine (NE), kisspeptin and gonadotropin-releasing hormone (GnRH) in the early follicular phase, but administration of the NE reuptake inhibitor (NRI), reboxetine (REB), restored ovulation during stress and normalized NE, kisspeptin and GnRH.

WHAT IS KNOWN ALREADY

Female cynomolgus macaques, like women, show individual reproductive sensitivity to modest psychosocial and metabolic stress. During stress, resilient females ovulate through two menstrual cycles whereas stress-sensitive (SS) macaques immediately cease ovulation. On Day 5 of a non-stressed menstrual cycle, resilient macaques have less NE synthesizing enzyme [dopamine β-hydroxylase (DBH)], kisspeptin and GnRH innervation of the medial basal hypothalamus but more endogenous serotonin than SS macaques. Stress increased DBH/NE, kisspeptin and GnRH but did not alter serotonin.

STUDY DESIGN, SIZE, DURATION

In a longitudinal design, 27 adult (7-13 years) female cynomolgus macaques (Macaca fascicularis) with three different levels of sensitivity to stress were monitored with daily vaginal swabs and frequent serum progesterone (P) measurements. Three 90-day experimental periods called 'Cycle Sets' were monitored. A Cycle Set consisted of one ovulatory menstrual cycle without stress, and two cycles, or 60 days, with modest stress. Each Cycle Set was followed by a rest period. During a Cycle Set, individuals were either untreated (placebo) or administered escitalopram (CIT) or REB. Ultimately, half of each sensitivity group was euthanized during stress with CIT or REB treatment and the hypothalamus was obtained. Neurobiological endpoints were compared between CIT and REB treatment groups in stress resilient and SS monkeys.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The monkeys were housed at the University of Pittsburgh primate facility for the duration of the experiments. Upon euthanasia, their brains and serum samples were shipped to the Oregon National Primate Research Center. The hypothalamus was examined with immunohistochemistry for the expression of DBH (a marker for NE axons), kisspeptin and GnRH. P was measured in the serum samples by radioimmunoassay.

MAIN RESULTS AND THE ROLE OF CHANCE

Daily administration of REB restored ovulation in 9 of 10 SS animals during stress. Of note, REB significantly increased P secretion during stress in the most sensitive group (P = 0.032), which indicates ovulation. CIT lacked efficacy. REB significantly reduced DBH/NE, kisspeptin and GnRH axon density in the hypothalamus relative to CIT treatment (P = 0.003. 0.018 and 0.0001, respectively) on Day 5 of the menstrual cycle in resilient and sensitive groups.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The US FDA has not approved REB for human use, although it is used in Europe for the treatment of depression/anxiety as EdronaxTR. Whether REB could be useful for the treatment of FHA in women has not been determined.

WIDER IMPLICATIONS FOR THE FINDINGS

The use of an NRI to treat FHA is a novel approach and the potential reinstatement of ovulation could be straightforward compared to current treatment protocols. The underlying neurobiology provides a compelling case for treating the origin of the pathology, i.e. elevated NE, rather than circumventing the hypothalamus altogether with gonadotropins, which have associated risks such as hyperstimulation syndrome or multiple births.

STUDY FUNDING/COMPETING INTEREST(S)

Portions of this study were supported by NIH grant HD062864 to C.L.B., NIH grant HD62618 to J.L.C. and C.L.B. and 1P51 OD011092 for the operation of the Oregon National Primate Research Center. There were no competing interests.

Recovery of menses after functional hypothalamic amenorrhoea: if, when and why

BACKGROUND

Prolonged amenorrhoea occurs as a consequence of functional hypothalamic amenorrhoea (FHA) which is most often induced by weight loss, vigorous exercise or emotional stress. Unfortunately, removal of these triggers does not always result in the return of menses. The prevalence and conditions underlying the timing of return of menses vary strongly and some women report amenorrhoea several years after having achieved and maintained normal weight and/or energy balance. A better understanding of these factors would also allow improved counselling in the context of infertility. Although BMI, percentage body fat and hormonal parameters are known to be involved in the initiation of the menstrual cycle, their role in the physiology of return of menses is currently poorly understood. We summarise here the current knowledge on the epidemiology and physiology of return of menses.

OBJECTIVE AND RATIONALE

The aim of this review was to provide an overview of (i) factors determining the recovery of menses and its timing, (ii) how such factors may exert their physiological effects and (iii) whether there are useful therapeutic options to induce recovery.

SEARCH METHODS

We searched articles published in English, French or German language containing keywords related to return of menses after FHA published in PubMed between 1966 and February 2020. Manuscripts reporting data on either the epidemiology or the physiology of recovery of menses were included and bibliographies were reviewed for further relevant literature. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) criteria served to assess quality of observational studies.

OUTCOMES

Few studies investigate return of menses and most of them have serious qualitative and methodological limitations. These include (i) the lack of precise definitions for FHA or resumption of menses, (ii) the use of short observation periods with unsatisfactory descriptions and (iii) the inclusion of poorly characterised small study groups. The comparison of studies is further hampered by very inhomogeneous study designs. Consequently, the exact prevalence of resumption of menses after FHA is unknown. Also, the timepoint of return of menses varies strongly and reliable prediction models are lacking. While weight, body fat and energy availability are associated with the return of menses, psychological factors also have a strong impact on the menstrual cycle and on behaviour known to increase the risk of FHA. Drug therapies with metreleptin or naltrexone might represent further opportunities to increase the chances of return of menses, but these require further evaluation.

WIDER IMPLICATIONS

Although knowledge on the physiology of return of menses is presently rudimentary, the available data indicate the importance of BMI/weight (gain), energy balance and mental health. The physiological processes and genetics underlying the impact of these factors on the return of menses require further research. Larger prospective studies are necessary to identify clinical parameters for accurate prediction of return of menses as well as reliable therapeutic options.

A Clinician's Guide to Functional Hypothalamic Amenorrhea

Patients and clinicians alike want to know if stress causes infertility. Stress could impair with reproductive function by a variety of mechanisms, including compromise of ovarian function, spermatogenesis, fertilization, endometrial development, implantation, and placentation. Herein we focus on the pathogenesis and treatment of stress-induced anovulation, which is often termed functional hypothalamic amenorrhea (FHA), with the objective of summarizing the actual knowledge as a clinical guide. FHA is a reversible form of anovulation due to slowing of gonadotropin-releasing hormone pulse frequency that results in insufficient pituitary secretion of gonadotropins to support full folliculogenesis. Importantly, FHA heralds a constellation of neuroendocrine alterations with health concomitants. The activity of the hypothalamic-pituitary-adrenal axis is increased in women with FHA and this observation supports the notion that stress is the cause. The extent of reproductive suppression relates to individual endocrinological and physiological sensitivity to stressors, both metabolic and psychogenic, and chronicity.

Social subordination alters estradiol-induced changes in cortico-limbic brain volumes in adult female rhesus monkeys

Women have a higher risk of developing stress-related disorders compared to men and the experience of a stressful life event is a potent risk-factor. The rodent literature suggests that chronic exposure to stressors as well as 17β-estradiol (E2) can result in alterations in neuronal structure in corticolimbic brain regions, however the translation of these data to humans is limited by the nature of the stressor experienced and issues of brain homology. To address these limitations, we used a well-validated rhesus monkey model of social subordination to examine effects of E2 treatment on subordinate (high stress) and dominant (low stress) female brain structure, including regional gray matter and white matter volumes using structural magnetic resonance imaging. Our results show that one month of E2 treatment in ovariectomized females, compared to control (no) treatment, decreased frontal cortex gray matter volume regardless of social status. In contrast, in the cingulate cortex, an area associated with stress-induced emotional processing, E2 decreased grey matter volume in subordinates but increased it in dominant females. Together these data suggest that physiologically relevant levels of E2 alter cortical gray matter volumes in females after only one month of treatment and interact with chronic social stress to modulate these effects on brain structure.

Effects of social subordination and oestradiol on resting-state amygdala functional connectivity in adult female rhesus monkeys

Preclinical studies demonstrate that chronic stress modulates the effects of oestradiol (E2) on behaviour through the modification of the amygdala and the medial prefrontal cortex (mPFC) neuronal structure. Clinical studies suggest that alterations in amygdala functional connectivity (FC) with the mPFC may be associated with stress-related phenotypes, including mood and anxiety disorders. Thus, identifying the effects of stress and E2 on amygdala-mPFC circuits is critical for understanding the neurobiology underpinning the vulnerability to stress-related disorders in women. In the present study, we used a well-validated rhesus monkey model of chronic psychosocial stress (subordinate social rank) to examine effects of E2 on subordinate (SUB) (i.e. high stress) and dominant (DOM) (i.e. low stress) female resting-state amygdala FC with the mPFC and with the whole-brain. In the non-E2 treatment control condition, SUB was associated with stronger left amygdala FC to subgenual cingulate (Brodmann area [BA] 25: BA25), a region implicated in several psychopathologies in people. In SUB females, E2 treatment strengthened right amygdala-BA25 FC, induced a net positive amygdala-visual cortex FC that was positively associated with frequency of submissive behaviours, and weakened positive amygdala-para/hippocampus FC. Our findings show that subordinate social rank alters amygdala FC and the impact of E2 on amygdala FC with BA25 and with regions involved in visual processing and memory encoding.

Linking Stress and Infertility: A Novel Role for Ghrelin

Infertility affects a remarkable one in four couples in developing countries. Psychological stress is a ubiquitous facet of life, and although stress affects us all at some point, prolonged or unmanageable stress may become harmful for some individuals, negatively impacting on their health, including fertility. For instance, women who struggle to conceive are twice as likely to suffer from emotional distress than fertile women. Assisted reproductive technology treatments place an additional physical, emotional, and financial burden of stress, particularly on women, who are often exposed to invasive techniques associated with treatment. Stress-reduction interventions can reduce negative affect and in some cases to improve in vitro fertilization outcomes. Although it has been well-established that stress negatively affects fertility in animal models, human research remains inconsistent due to individual differences and methodological flaws. Attempts to isolate single causal links between stress and infertility have not yet been successful due to their multifaceted etiologies. In this review, we will discuss the current literature in the field of stress-induced reproductive dysfunction based on animal and human models, and introduce a recently unexplored link between stress and infertility, the gut-derived hormone, ghrelin. We also present evidence from recent seminal studies demonstrating that ghrelin has a principal role in the stress response and reward processing, as well as in regulating reproductive function, and that these roles are tightly interlinked. Collectively, these data support the hypothesis that stress may negatively impact upon fertility at least in part by stimulating a dysregulation in ghrelin signaling.

Socially Housed Female Macaques: a Translational Model for the Interaction of Chronic Stress and Estrogen in Aging

PURPOSE OF REVIEW

Estrogen's role in cognitive aging remains unclear. Despite evidence implicating stress in pathological aging, the interaction of stress with estrogen on cognition in older women has received little attention, and few animal models exist with which to examine this interaction.

RECENT FINDINGS

We present evidence that aging socially subordinate female macaques that experience chronic psychosocial stress constitute a suitable model to investigate this. First, we review studies showing that estrogen modulates cognition in animal models, as well as studies demonstrating that estrogen's action on certain types of cognition is impaired by stress. Next, we discuss data showing that middle-aged socially subordinate female macaques exhibit distinct stress-induced phenotypes, and review our investigations indicating that estrogen modulates behavior and physiology differently in subordinate female monkeys. We conclude that socially housed female macaques represent a translational animal model for investigating the interplay of chronic stress and estrogen on cognitive aging in women.

Stress-induced alterations in estradiol sensitivity increase risk for obesity in women

The prevalence of obesity in the United States continues to rise, increasing individual vulnerability to an array of adverse health outcomes. One factor that has been implicated causally in the increased accumulation of fat and excess food intake is the activity of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis in the face of relentless stressor exposure. However, translational and clinical research continues to understudy the effects sex and gonadal hormones and LHPA axis dysfunction in the etiology of obesity even though women continue to be at greater risk than men for stress-induced disorders, including depression, emotional feeding and obesity. The current review will emphasize the need for sex-specific evaluation of the relationship between stress exposure and LHPA axis activity on individual risk for obesity by summarizing data generated by animal models currently being leveraged to determine the etiology of stress-induced alterations in feeding behavior and metabolism. There exists a clear lack of translational models that have been used to study female-specific risk. One translational model of psychosocial stress exposure that has proven fruitful in elucidating potential mechanisms by which females are at increased risk for stress-induced adverse health outcomes is that of social subordination in socially housed female macaque monkeys. Data from subordinate female monkeys suggest that increased risk for emotional eating and the development of obesity in females may be due to LHPA axis-induced changes in the behavioral and physiological sensitivity of estradiol. The lack in understanding of the mechanisms underlying these alterations necessitate the need to account for the effects of sex and gonadal hormones in the rationale, design, implementation, analysis and interpretation of results in our studies of stress axis function in obesity. Doing so may lead to the identification of novel therapeutic targets with which to combat stress-induced obesity exclusively in females.

Diagnostic Biomarkers for Posttraumatic Stress Disorder: Promising Horizons from Translational Neuroscience Research

Posttraumatic stress disorder (PTSD) is a heterogeneous disorder that affects individuals exposed to trauma (e.g., combat, interpersonal violence, and natural disasters). Although its diagnostic features have been recently reclassified with the emergence of the Diagnostic and Statistical Manual for Mental Disorders, Fifth Edition, the disorder remains characterized by hyperarousal, intrusive reminders of the trauma, avoidance of trauma-related cues, and negative cognition and mood. This heterogeneity indicates the presence of multiple neurobiological mechanisms underlying the etiology and maintenance of PTSD. Translational research spanning the past few decades has revealed several potential avenues for the identification of diagnostic biomarkers for PTSD. These include, but are not limited to, monoaminergic transmitter systems, the hypothalamic-pituitary-adrenal axis, metabolic hormonal pathways, inflammatory mechanisms, psychophysiological reactivity, and neural circuits. The current review provides an update to the literature with regard to the most promising putative PTSD biomarkers, with specific emphasis on the interaction between neurobiological influences on disease risk and symptom progression. Such biomarkers will most likely be identified by multi-dimensional models derived from comprehensive descriptions of molecular, neurobiological, behavioral, and clinical phenotypes.

The Antidepressant-like Effects of Estrogen-mediated Ghrelin

Ghrelin, one of the brain-gut peptides, stimulates food-intake. Recently, ghrelin has also shown to play an important role in depression treatment. However, the mechanism of ghrelin's antidepressant-like actions is unknown. On the other hand, sex differences in depression, and the fluctuation of estrogens secretion have been proved to play a key role in depression. It has been reported that women have higher level of ghrelin expression, and ghrelin can stimulate estrogen secretion while estrogen acts as a positive feedback mechanism to up-regulate ghrelin level. Ghrelin may be a potential regulator of reproductive function, and estrogen may have additional effect in ghrelin's antidepressantlike actions. In this review, we summarize antidepressant-like effects of ghrelin and estrogen in basic and clinical studies, and provide new insight on ghrelin's effect in depression.

Social inequalities in health in nonhuman primates

Overall health has been linked to socioeconomic status, with the gap between social strata increasing each year. Studying the impact of social position on health and biological functioning in nonhuman primates has allowed researchers to model the human condition while avoiding ethical complexities or other difficulties characteristic of human studies. Using female cynomolgus macaques (Macaca fascicularis), our lab has examined the link between social status and stress for 30 years. Female nonhuman primates are especially sensitive to social stressors which can deleteriously affect reproductive health, leading to harmful consequences to their overall health. Subordinates have lower progesterone concentrations during the luteal phase of menstrual cycle, which is indicative of absence or impairment of ovulation. Subordinate animals receive more aggression, less affiliative attention, and are more likely to exhibit depressive behaviors. They also express higher stress-related biomarkers such as increased heart rates and lower mean cortisol. While no differences in body weight between dominant and subordinate animals are observed, subordinates have lower bone density and more visceral fat than their dominant counterparts. The latter increases risk for developing inflammatory diseases. Differences are also observed in neurological and autonomic function. A growing body of data suggests that diet composition may amplify or diminish physiological stress responses which have deleterious effects on health. More experimental investigation of the health effects of diet pattern is needed to further elucidate these differences in an ongoing search to find realistic and long-term solutions to the declining health of individuals living across the ever widening socioeconomic spectrum.

Antagonism of corticotrophin-releasing factor type 1 receptors attenuates caloric intake of free feeding subordinate female rhesus monkeys in a rich dietary environment

Social subordination in macaque females is a known chronic stressor and previous studies have shown that socially subordinate female rhesus monkeys consume fewer kilocalories than dominant animals when a typical laboratory chow diet is available. However, in a rich dietary environment that provides access to chow in combination with a more palatable diet (i.e. high in fat and refined sugar), subordinate animals consume significantly more daily kilocalories than dominant conspecifics. Substantial literature is available supporting the role of stress hormone signals in shaping dietary preferences and promoting the consumption of palatable, energy-dense foods. The present study was conducted using stable groups of adult female rhesus monkeys to test the hypothesis that pharmacological treatment with a brain penetrable corticotrophin-releasing factor type 1 receptor (CRF1) antagonist would attenuate the stress-induced consumption of a palatable diet among subordinate animals in a rich dietary environment but would be without effect in dominant females. The results show that administration of the CRF1 receptor antagonist significantly reduced daily caloric intake of both available diets among subordinate females compared to dominant females. Importantly, multiple regression analyses showed that the attenuation in caloric intake in response to Antalarmin (Sigma-Aldrich, St Louis, MO, USA) was significantly predicted by the frequency of submissive and aggressive behaviour emitted by females, independent of social status. Taken together, the findings support the involvement of activation of CRF1 receptors in the stress-induced consumption of excess calories in a rich dietary environment and also support the growing literature concerning the importance of CRF for sustaining emotional feeding.

Oestradiol alters central 5-HT1A receptor binding potential differences related to psychosocial stress but not differences related to 5-HTTLPR genotype in female rhesus monkeys

Social subordination in female macaques represents a well-described model of chronic psychosocial stress. Additionally, a length polymorphism (5-HTTLPR) in the regulatory region of the serotonin (5-HT) transporter (5-HTT) gene (SLC6A4) is present in rhesus macaques, which has been linked to adverse outcomes similar to that described in humans with an analogous 5-HTTLPR polymorphism. The present study determined the effects of social status and the 5-HTTLPR genotype on 5-HT1A receptor binding potential (5-HT1A BP(ND)) in brain regions implicated in emotional regulation and stress reactivity in ovariectomised female monkeys, and then assessed how these effects were altered by 17β-oestradiol (E(2)) treatment. Areas analysed included the prefrontal cortex [anterior cingulate (ACC); medial prefrontal cortex (mPFC); dorsolateral prefrontal cortex; orbitofrontal prefrontal cortex], amygdala, hippocampus, hypothalamus and raphe nucleui. Positron emission tomography using p-[(18) F]MPPF was performed to determine the levels of 5-HT1A BP(ND) under a non-E(2) and a 3-week E(2) treatment condition. The short variant (s-variant) 5-HTTLPR genotype produced a significant reduction in 5-HT1A BP(ND) in the mPFC regardless of social status, and subordinate s-variant females showed a reduction in 5-HT1A BP(ND) within the ACC. Both these effects of 5-HTTLPR were unaffected by E(2). Additionally, E(2) reduced 5-HT1A BP(ND) in the dorsal raphe of all females irrespective of psychosocial stress or 5-HTTLPR genotype. Hippocampal 5-HT1A BP(ND) was attenuated in subordinate females regardless of 5-HTTLPR genotype during the non-E(2) condition, an effect that was normalised with E(2). Similarly, 5-HT1A BP(ND) in the hypothalamus was significantly lower in subordinate females regardless of 5-HTTLPR genotype, an effect reversed with E(2). Taken together, the data indicate that the effect of E(2) on modulation of central 5HT1A BP(ND) may only occur in brain regions that show no 5-HTTLPR genotype-linked control of 5-HT1A binding.

Social subordination stress and serotonin transporter polymorphisms: associations with brain white matter tract integrity and behavior in juvenile female macaques

We examined the relationship between social rank and brain white matter (WM) microstructure, and socioemotional behavior, and its modulation by serotonin (5HT) transporter (5HTT) polymorphisms in prepubertal female macaques. Using diffusion tensor imaging and tract-based spatial statistics, social status differences were found in medial prefrontal cortex (mPFC) WM and cortico-thalamic tracts, with subordinates showing higher WM structural integrity (measured as fractional anisotropy, FA) than dominant animals. 5HTT genotype-related differences were detected in the posterior limb of the internal capsule, where s-variants had higher FA than l/l animals. Status by 5HTT interaction effects were found in (1) external capsule (middle longitudinal fasciculus), (2) parietal WM, and (3) short-range PFC tracts, with opposite effects in dominant and subordinate animals. In most regions showing FA differences, opposite differences were detected in radial diffusivity, but none in axial diffusivity, suggesting that differences in tract integrity likely involve differences in myelin. These findings highlight that differences in social rank are associated with differences in WM structural integrity in juveniles, particularly in tracts connecting prefrontal, sensory processing, motor and association regions, sometimes modulated by 5HTT genotype. Differences in these tracts were associated with increased emotional reactivity in subordinates, particularly with higher submissive and fear behaviors.

CRH receptor antagonism reverses the effect of social subordination upon central GABAA receptor binding in estradiol-treated ovariectomized female rhesus monkeys

Persistent exposure to environmental stressors causes dysregulation of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis and alters GABAA receptor (GABAAR) levels throughout the brain. Social subordination in socially housed female rhesus results in distinctive stress-related physiological and behavioral phenotypes that are dependent on the ovarian hormone estradiol (E2). In the present study, we utilized ovariectomized adult female rhesus monkeys undergoing hormone replacement with E2 to test the hypothesis that the chronic psychosocial stress of subordination alters GABAAR binding potential (GABAAR BPND) in limbic regions implicated in emotional processing including the prefrontal cortex, temporal lobe (amygdala and hippocampus), and hypothalamus. Furthermore, we tested the hypothesis that peripheral administration of a corticotropin-releasing hormone (CRH) receptor antagonist (astressin B) would reverse the alterations in GABAAR binding within these regions in subordinate females. After subjects received astressin B or saline for three consecutive days, GABAAR BPND was determined by positron emission tomography (PET) using (18)F-flumazenil as a radioligand. T1-weighted structural magnetic resonance imaging scans were also acquired for PET scan co-registration, in order to perform a region of interest analysis using the pons as a reference region. Compared to socially dominant females, subordinate females exhibited increased GABAAR BPND in the prefrontal cortex but not in the temporal lobe or the hypothalamus. Administration of astressin B eliminated the status difference in GABAAR BPND in the prefrontal cortex, suggesting that the chronic stressor of social subordination modulates GABAergic tone via effects on CRH and the LHPA axis, at least in prefrontal regions.

Dietary variety is associated with larger meals in female rhesus monkeys

The complex, interacting influences on eating behavior and energy expenditure prevent elucidation of the causal role of any single factor in the current obesity epidemic. However, greater variety in the food supply, particularly in the form of highly palatable, energy-dense foods, has likely made a contribution. This study was undertaken to test the hypothesis that greater dietary variety is associated with greater caloric intake within individual meals consumed by free-feeding, socially-housed female rhesus monkeys. Meal patterns were assessed during two, two-week dietary phases. One phase consisted of a choice between a standard chow diet and a highly palatable diet (HPD). The other phase consisted of access to the chow only. Food intake for each subject was recorded continuously using previously validated, automated feeders, and a meal was defined based on a minimum kilocalorie requirement and a minimum inter-meal interval. During the choice condition, animals electively consumed mixed meals that incorporated both diets as well as other meals that consisted exclusively of a single diet - chow-only or HPD-only. Animals consumed the most calories per meal when the meal was comprised of both the chow and HPD, which differed in caloric density, flavor, and texture. Interestingly, however, there was no significant difference in the amount of calories consumed as HPD-only meals in the choice condition compared to meals in the chow-only, no choice condition, suggesting consumption of a single food during a meal, regardless of palatability, provides a constant sensory experience that may lead to more rapid habituation and subsequent meal cessation. Additionally, during the dietary choice condition, animals consumed fewer calories in the form of chow-only meals. Thus, the present results suggest that limiting dietary variety, regardless of palatability, may be a useful strategy for weight loss in overweight and obese individuals by reducing caloric intake within individual meals.

Social stress and the polymorphic region of the serotonin reuptake transporter gene modify oestradiol-induced changes on central monoamine concentrations in female rhesus monkeys

Psychosocial stress exposure is linked to the disruption of emotional regulation that can manifest as anxiety and depression. Women are more likely to suffer from such psychopathologies than men, indicating that sex-based differences in gonadal steroids may be a key factor in the aetiology of stress-induced adverse health outcomes. Oestradiol (E2 ) positively influences mood and cognition in females, an effect likely related to the ability of E2 to modulate the serotonin and dopamine neurotransmitter systems. Furthermore, genetic variation as a result of the polymorphism in the promoter region of the gene (SLC6A4) encoding the serotonin transporter (5HTTLPR) also can influence the ability of E2 to modulate behaviour and physiology. However, it remains uncertain whether exposure to social stress interacts with the 5HTTLPR to influence E2 -induced changes in behaviour and physiology. The present study used ovariectomised adult female rhesus monkeys to investigate acute and chronic effects of E2 on central monoamine metabolite concentrations using cerobrospinal fluid sampling. We further assessed how E2 -induced changes in monoamine metabolite levels are modified by the unpredictable stress of social subordination and the 5HTTLPR polymorphism. Levels of the serotonin metabolite 5-hydroxyindoleacetic acid decreased significantly during chronic E2 treatment only in dominant females with the long promoter length of SLC6A4. Chronic administration of E2 decreased levels of the dopamine metabolite dihydrophenylacetic acid in a manner independent of the social status, 5HTTLPR genotype, or their interactions. Overall levels of dopamine and serotonin metabolites were increased in subordinate females, although this effect of social stress was not influenced by 5HTTLPR genotype. Together, these data emphasise how E2 can modulate central neurotransmitter systems and indicate that social subordination in female monkeys is a valid model for examining how chronic psychosocial stress alters sensitivity to E2 . Future studies are necessary to elaborate how changes in central neurotransmitter metabolism affect behaviour and physiology as a result of E2 and prolonged exposure to stress.

Neuroendocrine recovery initiated by cognitive behavioral therapy in women with functional hypothalamic amenorrhea: a randomized, controlled trial

OBJECTIVE

To determine whether cognitive behavior therapy (CBT), which we had shown in a previous study to restore ovarian function in women with functional hypothalamic amenorrhea (FHA), could also ameliorate hypercortisolemia and improve other neuroendocrine and metabolic concomitants of in FHA.

DESIGN

Randomized controlled trial.

SETTING

Clinical research center at an academic medical university.

PATIENT(S)

Seventeen women with FHA were randomized either to CBT or observation.

INTERVENTION(S)

CBT versus observation.

MAIN OUTCOME MEASURE(S)

Circulatory concentrations of cortisol, leptin, thyroid-stimulating hormone (TSH), total and free thyronine (T(3)), and total and free thyroxine (T(4)) before and immediately after completion of CBT or observation. (Each woman served as her own control.)

RESULT(S)

Cognitive behavior therapy but not observation reduced cortisol levels in women with FHA. There were no changes in cortisol, leptin, TSH, T(3), or T(4) levels in women randomized to observation. Women treated with CBT showed increased levels of leptin and TSH, but their levels of T(3) and T(4) remained unchanged.

CONCLUSION(S)

In women with FHA, CBT ameliorated hypercortisolism and improved the neuroendocrine and metabolic concomitants of FHA while observation did not. We conclude that a cognitive, nonpharmacologic approach aimed at alleviating problematic attitudes not only can restore ovarian activity but also improve neuroendocrine and metabolic function in women with FHA.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01674426.

Social and emotional predictors of the tempo of puberty in female rhesus monkeys

A cascade of neuroendocrine events regulates the initiation and progression of female puberty. However, the factors that determine the timing of these events across individuals are still uncertain. While the consequences of puberty on subsequent emotional development and adult behavior have received significant attention, what is less understood are the social and environmental factors that actually alter the initiation and progression of puberty. In order to more fully understand what factors influence pubertal timing in females, the present study quantified social and emotional behavior; stress physiology; and growth and activity measures in juvenile female rhesus monkeys to determine what best predicts eventual puberty. Based on previous reports, we hypothesized that increased agonistic behavior resulting from subordinate status in their natal group, in combination with slowed growth, reduced prosocial behavior, and increased emotional reactivity would predict delayed puberty. The analyses were restricted to behavioral and physiological measures obtained prior to the onset of puberty, defined as menarche. Together, our findings indicate that higher rates of aggression but lower rates of submission received from group mates; slower weight gain; and greater emotional reactivity, evidenced by higher anxiety, distress and appeasing behaviors, and lower cortisol responsivity in response to a potentially threatening situation, predicts delayed puberty. Together the combination of these variables accounted for 58% of the variance in the age of menarche, 71% in age at first ovulation, and 45% in the duration of adolescent sterility. While early puberty may be more advantageous for the individual from a fertility standpoint, it presents significant health risks, including increased risk for a number of estrogen dependent cancers and as well as the emergence of mood disorders during adulthood. On the other hand, it is possible that increased emotional reactivity associated with delayed puberty could persist, increasing the risk for emotional dysregulation to socially challenging situations. The data argue for prospective studies that will determine how emotional reactivity shown to be important for pubertal timing is affected by early social experience and temperament, and how these stress-related variables contribute to body weight accumulation, affecting the neuroendocrine regulation of puberty.

Star-crossed? The association of the 5-HTTLPR s allele with season of birth in a healthy female population, and possible consequences for temperament, depression and suicide

BACKGROUND

Birth season has well-known effects on neuropsychiatric disorders, and may also influence genotype distribution by possibly influencing chance of conception via parental idiosyncratic conception patterns or survival of foetuses or infants. The 5-HTTLPR is associated with phenomena including affective temperaments or suicide which are also associated with birth season. Our aim was to investigate the association of 5-HTTLPR genotype and birth season in a healthy female population.

METHODS

Birth date and 5-HTTLPR genotype was determined for 327 psychiatrically healthy women. The association between presence of s allele and time of birth was analysed using generalized linear models.

RESULTS

A significant association between s allele frequency and time of birth was detected. S allele carrier frequency was marginally significantly higher in July borns and significantly lower in autumn borns.

LIMITATIONS

We investigated an adult sample so genotype frequency data do not reflect birth frequencies. Our sample consisted exclusively of females.

CONCLUSIONS

There is no clear explanation for the observed association, although idiosyncratic parental conception patterns, the association of 5-HTTLPR with sudden infant/intrauterine death, or other s allele-mediated behaviours may play a role. Our results are strikingly parallel with earlier data reporting a higher risk of completed suicide in July borns, and higher scores of July borns and lower scores of autumn borns on certain affective temperament scales, both of which are also associated with the s allele of 5-HTTLPR. Thus our results may add to the growing body of evidence regarding the etiological background of affective disorders.

Small changes in meal patterns lead to significant changes in total caloric intake. Effects of diet and social status on food intake in female rhesus monkeys

Social subordination in macaques is a well-established model to study the adverse effects of psychosocial stress on a number of health outcomes, including stress-induced eating. The present analysis was conducted to empirically define a meal among free-feeding female rhesus monkeys and to examine the roles of meal patterning (e.g., meal size, meal frequency, and snacking patterns) in findings from a previous study demonstrating that psychosocial stress increases overall caloric intake among subordinate animals with access to a highly palatable diet. Results indicate that all animals, regardless of social status, consumed more frequent meals, larger meals, and more calories in the form of snacks when a highly palatable diet was available. Additional findings suggest that subordinate animals consumed significantly larger meals compared to their dominant counterparts regardless of the dietary environment. Additionally, subordinate females with a history of exposure to the palatable diet consumed significantly more snack calories than both dominant and subordinate animals without previous exposure to the palatable diet when these females were returned to a standard laboratory diet. These findings illustrate how small changes in meal patterns can lead to significant increases in total caloric intake, which if prolonged, could promote the emergence of an obese phenotype.

Social status modifies estradiol activation of sociosexual behavior in female rhesus monkeys

Estrogen (E2) has activational effects on sexual motivation and mitigating effects on anxiety-like behaviors that can be attenuated with chronic exposure to psychosocial stress. Some studies suggest that this attenuation can be overcome by higher doses of E2, while others show that chronic psychosocial stress may alter the mechanisms of E2 function, thus reducing any positive benefit from higher doses of E2. To determine the interaction between psychosocial stress and E2 dose on behavior, we examined the scope of attenuation across a suite of socioemotional behaviors, including reproduction, affiliation, aggression, submission, and anxiety-like behaviors on 36 ovariectomized female rhesus monkeys. Females were exposed to graded psychosocial stress, established by an intrinsic female dominance hierarchy, where subordinate animals receive high amounts of harassment. Our data show that E2 dose-dependently increased sexual motivation and male-affiliation in dominant (e.g. low-stress) females, while subordinate females showed no positive effects of E2, even at higher doses. In addition, contact aggression was attenuated in dominant females, while non-contact aggression was attenuated in both dominant and middle-ranking females. These results suggest that the stress-induced attenuation of E2's activational effects on sexual behavior and affiliation with males may not be overcome with higher doses of E2. Furthermore, the observed behavioral consequences of psychosocial stress and E2 dose may be dependent on the behaviors of all the females in the social-group, and better resolution on these effects depends on isolating treatment to individuals within the group to minimize alterations in social-group interactions.

The relation of developmental changes in brain serotonin transporter (5HTT) and 5HT1A receptor binding to emotional behavior in female rhesus monkeys: effects of social status and 5HTT genotype

The goal of the present study was to examine how social subordination stress and 5HTT polymorphisms affect the development of brain serotonin (5HT) systems during the pubertal transition in female rhesus monkeys. We also examined associations with developmental changes in emotional reactivity in response to a standardized behavioral test, the Human Intruder (HI). Our findings provide the first longitudinal evidence of developmental increases in 5HT1A receptor and 5HTT binding in the brain of female primates from pre- to peripuberty. The increase in 5HT1A BP(ND) in these socially housed female rhesus monkeys is a robust finding, occurring across all groups, regardless of social status or 5HTT genotype, and occurring in the left and right hemispheres of all prefrontal regions studied, as well as the amygdala, hippocampus, hypothalamus, and raphe nuclei. 5HTT BP(ND) also showed an increase with age in raphe, anterior cingulate cortex, and dorsolateral prefrontal cortex. These changes in brain 5HT systems take place as females establish more adult-like patterns of social behavior, as well as during the HI paradigm. Indeed, the main developmental changes in behavior during the HI (increase in freezing and decrease in submission/appeasement) were related to neurodevelopmental increases in 5HT1A receptors and 5HTT, because the associations between these behaviors and 5HT endpoints emerge at peripuberty. We detected an effect of social status on 5HT1A BP(ND) in the hypothalamus and on 5HTT BP(ND) in the orbitofrontal cortex, with subordinates showing higher BP(ND) than dominants in both cases during the pubertal transition. No main effects of 5HTT genotype were observed for 5HT1A or 5HTT BP(ND). Our findings indicate that adolescence in female rhesus monkeys is a period of central 5HT reorganization, partly influenced by exposure to the social stress of subordination, that likely functions to integrate adrenal and gonadal systems and shape the behavioral response to emotionally challenging social situations.

Social stress interacts with diet history to promote emotional feeding in females

Stress-induced eating disorders cause significant health problems and are often co-morbid with mood disorders. Emotional feeding, particularly in women, may be important for the development of obesity and failed attempts to lose weight. However, prospective studies assessing the effect of chronic psychosocial stress on appetite in different dietary environments in females are lacking. The present study tested the hypothesis that chronic psychosocial stress would increase consumption of high caloric diet and this emotional feeding would persist even when a healthier diet was available. Socially housed female rhesus monkeys were studied to address whether subordination increases caloric intake when a high fat and sugar diet (HFSD) was available concurrently with a low fat, high fiber diet (LCD). Cortisol responsivity and food intake were quantified during this choice phase and when only the LCD was available. The order of diet condition was counterbalanced to assess whether a history of HFSD would affect appetite. All females preferred the HFSD but subordinates consumed significantly more calories during the choice phase. The increased calorie intake was maintained in subordinate monkeys even after withdrawal of the HFSD. Subordinate females demonstrated reduced glucocorticoid negative feedback, with post dexamethasone serum cortisol levels significantly predicting intake of the HFSD but not the LCD during the choice condition. The cortisol response to an acute stressor significantly predicted subsequent intake of a HFSD in all females. Continual exposure to the psychosocial stress of subordination in female monkeys results in excess caloric intake of foods that mimic a western dietary environment. In addition, this social stressor interacts with a history of HFSD intake to promote increased feeding even in a healthy dietary environment.

Social subordination impairs hypothalamic-pituitary-adrenal function in female rhesus monkeys

Linear dominance hierarchies organize and maintain stability in female rhesus macaque (Macaca mulatta) social groups regardless of group size. As a consequence of their low social status, subordinate females suffer from an array of adverse outcomes including reproductive compromise, impaired immune function, and poor cardiovascular health. However, data that differentiate limbic-hypothalamic-pituitary-adrenal axis (LHPA) parameters between dominant from subordinate female monkeys are inconsistent, bringing into question whether social subordination alters the LHPA axis in female macaques. One difficulty in examining LHPA function in macaques may be the confounding effects of cycling ovarian steroids that are known to modulate LHPA activity. The current study used ovariectomized dominant and subordinate female rhesus monkeys to examine the effect that social subordination has on LHPA function by measuring morning and diurnal serum cortisol levels, dexamethasone (Dex) suppression of cortisol, metabolic clearance of Dex, and ACTH stimulation of adrenal cortisol release and cortisol response following exposure to acute social isolation. Compared to dominant females, subordinate females showed diminished morning peak cortisol secretion, weakened glucocorticoid negative feedback, and decreased adrenal cortisol response to an ACTH challenge as well as a restrained cortisol response following social isolation. However, the metabolism of Dex did not account for differences in Dex suppression between dominant and subordinate females. These results indicate that the ability to mount and limit glucocorticoid release is significantly reduced by psychosocial stress in female rhesus macaques, suggesting a hyporesponsive LHPA phenotype which resembles that observed in several human psychopathologies.

Social subordination produces distinct stress-related phenotypes in female rhesus monkeys

Social subordination in female macaques is imposed by harassment and the threat of aggression and produces reduced control over one's social and physical environment and a dysregulation of the limbic-hypothalamic-pituitary-adrenal axis resembling that observed in people suffering from psychopathologies. These effects support the contention that this particular animal model is an ethologically relevant paradigm in which to investigate the etiology of stress-induced psychological illness related to women. Here, we sought to expand this model by performing a discriminate analysis (DA) on 33 variables within three domains; behavioral, metabolic/anthropomorphic, and neuroendocrine, collected from socially housed female rhesus monkeys in order to assess whether exposure to social subordination produces a distinct phenotype. A receiver operating characteristic (ROC) curve was also calculated to determine each domain's classification accuracy. DA found significant markers within each domain that differentiated dominant and subordinate females. Subordinate females received more aggression, showed more submissive behavior, and received less of affiliation from others than did dominant females. Metabolic differences included increased leptin, and reduced adiponectin in dominant compared to subordinate females. Dominant females exhibited increased sensitivity to hormonal stimulation with higher serum LH in response to estradiol, cortisol in response to ACTH, and increased glucocorticoid negative feedback. Serum oxytocin, CSF DOPAC and serum PACAP were all significantly higher in dominant females. ROC curve analysis accurately predicted social status in all three domains. Results suggest that socially house rhesus monkeys represent a cogent animal model in which to study the physiology and behavioral consequences of chronic psychosocial stress in humans.

Behavioral and neurobiological characteristics of social stress versus depression in nonhuman primates

The focus of the review is on the behavioral and physiological manifestations of stress versus depression. The purpose of the review is to evaluate the conceptual approach of using stress models as surrogates for depression. Social stress and depression have many characteristics in common and promote each other. Both have adverse effects on social relationships and the quality of life, and increase risk of other diseases. However, they are not the same constructs. In human and nonhuman primates, the behavior and neurobiology of stressed individuals differ from that of depressed individuals. Some similarities in stress physiology in socially stressed and depressed individuals have been used to support the use of stressed animals as models of depression, and much has been learned from stress models of depression. However, the studies reviewed here also suggest that the depressed state also has different characteristics than the stressed state, and studying the differences may be important to furthering our understanding of each of these constructs as well as their mutual relationship.

Estradiol effects on behavior and serum oxytocin are modified by social status and polymorphisms in the serotonin transporter gene in female rhesus monkeys

Despite the well-documented relation between estradiol (E2) and behavior, exposure to stressors may modify sensitivity to E2. The effects of E2 on behavior are, in part, likely related to their modulation of the serotonin (5HT) and oxytocin systems. The short allele (s-variant) polymorphism found in the promoter region of the SLC6A4 gene that encodes the 5HT transporter (5HTT) modulates responsivity to stressors. The current study used ovariectomized adult female rhesus monkeys to evaluate how exposure to the psychosocial stressor of social subordination and polymorphisms in the gene encoding 5HTT influence the behavioral effects of E2 and immunoreactive serum oxytocin. Dominant females had higher levels of oxytocin than subordinate animals even though E2 increased immunoreactive serum oxytocin in all females. E2 increased affiliative behaviors in all animals, with even more of these prosocial behaviors directed at dominant females. S-variant females, regardless of social status, were more aggressive toward more subordinate cage mates and these behaviors too were increased by E2. Subordinate s-variant females are most often involved in agonistic behavior, less affiliative behavior, and were less responsive to the anxiolytic action of E2. The results show that the short allele of the 5HTT gene synergizes with psychosocial stress exposure to affect the behavioral efficacy of E2 while confirming the actions of E2 for producing generalized behavioral arousal in females. Whether differences in the central action of 5HT and/or oxytocin are responsible for this effect requires further study.

Fetal and maternal factors associated with infant mortality in vervet monkeys

BACKGROUND

Causes of infant death remain unknown in significant proportions of human and non-human primate pregnancies.

METHODS

A closed breeding colony with high rates of infant mortality had pregnancies assessed (n=153) by fetal measurements and maternal characteristics. Infant outcome was classified as neonatal death (stillborn or died <48 hours from birth), postnatal death (died 2-30 days) or surviving (alive after 30 days).

RESULTS

Fetal size did not predict outcome. Poor maternal glycemic control and low social ranking increased odds for adverse outcome (OR=3.72, P=0.01 and 2.27, P=0.04, respectively). Male sex was over-represented in stillbirths (P=0.04), and many were macrosomic, but size did not associate with maternal glycemic control measured as glycated hemoglobin A1c. Postnatally dead infants were smaller (P<0.01), which associated with behavioral factors and glycemic control.

CONCLUSIONS

Fetal growth estimates predicted gestational age but not fetal outcome. Maternal social status and metabolic health, particularly glycemic control, increased risks of adverse pregnancy outcome.

Body weight decreases induced by estradiol in female rhesus monkeys are dependent upon social status

Gonadal steroids regulate appetite and thus body weight. In addition, continuous exposure to stressors negatively influences appetite through circuits likely distinct from those of gonadal steroids. The occurrence of adverse metabolic consequences due to chronic exposure to psychosocial stressors is twice as frequent in women as men, implicating a role for ovarian hormones, estradiol (E2) and progesterone (P4), in modulating stress-induced changes in appetite. Using social subordination in female macaques as a model of social stress, the current study tested the hypothesis that subordinate females would lose more weight during E2 treatment and gain less weight during P4 administration than dominant females. Because polymorphisms in the gene encoding the serotonin transporter (5HTT; SCL6A4) are known to alter responsivity to stress, we hypothesized that weight loss during E2 administration would be greatest in females with the short variant (s-variant) allele of 5HTT. Dominant females were significantly heavier than subordinate animals throughout the study, a result consistent with previous accounts of food intake when animals are fed a low-fat, high-fiber diet. Females with the s-variant 5HTT genotype weighed significantly less than l/l animals. Dominant animals lost significantly more weight than subordinate animals during E2 treatment. Administration of P4 blocked the weight-reducing effects of E2 in all females, regardless of social status. These data provide evidence that social subordination modulates the influence of ovarian steroid hormones on body weight in female rhesus monkeys independent of 5HTT genotype. Given the prosocial effects of these steroids, future studies are necessary to determine whether status differences in E2-induced weight loss are due to diminished food intake and or increases in energy expenditure and how the change in energy availability during E2 treatments relates to a female's motivation to interact with conspecifics.

Impairment of ovarian function and associated health-related abnormalities are attributable to low social status in premenopausal monkeys and not mitigated by a high-isoflavone soy diet

BACKGROUND

Psychological stress may impair premenopausal ovarian function and contribute to risk for chronic disease. Soy isoflavones may also influence ovarian function and affect health. Here, we report the effects of a psychological stressor (subordinate social status) and dietary soy on reproductive function and related health indices in female monkeys. We hypothesized that reproductive compromise and adverse health outcomes would be induced in subordinate when compared with dominant monkeys and be mitigated by exposure to soy.

METHODS

Subjects were 95 adult cynomolgus monkeys (Macaca fascicularis) housed in social groups of five or six. Animals consumed a soy-free, animal protein-based diet during an 8-month Baseline phase and then, during a 32-month Treatment phase, consumed either the baseline diet or an identical diet that substituted high-isoflavone soy protein for animal protein.

RESULTS

Across more than 1200 menstrual cycles, subordinate monkeys consistently exhibited ovarian impairment [increased cycle length (P < 0.02) and variability (P < 0.02) and reduced levels of progesterone (P < 0.04) and estradiol (P < 0.04)]. Subordinate status was confirmed behaviorally and was associated with elevated cortisol (P < 0.04) and relative osteopenia (P < 0.05). Consumption of the soy diet had no significant effects.

CONCLUSIONS

(i) Psychological stress adversely affects ovarian function and related health indices in a well-accepted animal model of women's health; (ii) Similar effects may extend to women experiencing reproductive impairment of psychogenic origin; (iii) soy protein and isoflavones neither exacerbate nor mitigate the effects of an adverse psychosocial environment; and (iv) this study was limited by an inability to investigate the genetic and developmental determinants of social status.

Increased ghrelin sensitivity and calorie consumption in subordinate monkeys is affected by short-term astressin B administration

Animals chronically exposed to stressors with access to diets high in fat and sugar consume and prefer these diets, a result consistent with the association between stress and comfort food ingestion in humans. As social subordination in rhesus monkeys provides an ethologically relevant translational model of psychosocial stress, we tested the hypothesis that differences in food intake between dominant and subordinate female monkeys are due to corticotropin-releasing hormone-(CRH) induced alteration in sensitivity to ghrelin, a potent orexigenic signal. We assessed food intake of animals given a choice between a low (LCD) and high calorie diet (HCD) in response to 4-day treatment with the CRH receptor antagonist, astressin B, and to an acute treatment of ghrelin. Ghrelin stimulated intake of LCD in subordinates but did not further increase consumption of HCD, whereas ghrelin decreased LCD consumption without affecting HCD intake in dominant females. Astressin B decreased cortisol levels and increased preference for and intake of the HCD in subordinates and decreased calorie intake and HCD preference in dominant animals. These results suggest that increased caloric intake by subordinates may, in part, be explained by a greater sensitivity to postprandial increases in ghrelin and that CRH receptor antagonism leading to a decrease in cortisol has mixed effects on food choice depending on an individual's stress background.

Diet choice, cortisol reactivity, and emotional feeding in socially housed rhesus monkeys

Chronic psychosocial stress produces an array of adverse health consequences that are highly comorbid, including emotional eating, affective disorders, and metabolic syndrome. The consumption of high caloric diets (HCDs) is thought to provide comfort in the face of unrelenting psychosocial stress. Using social subordination in female rhesus monkeys as a model of continual exposure to daily stressors in women, we tested the hypothesis that subordinate females would consume significantly more calories from a HCD compared to dominant females, and this pattern of food intake would be associated with reduced cortisol release and reduced frequency of anxiety-like behaviors. Food intake, parameters of cortisol secretion, and socio-emotional behavior were assessed for 3 weeks during a no choice phase when only a low caloric diet (LCD) was available and during a choice condition when both a LCD and HCD were available. While all animals preferred the HCD, subordinate females consumed significantly more of the HCD than did dominant females. A flattening of the diurnal cortisol rhythm and a greater increase in serum cortisol to an acute social separation occurred during the diet choice condition in all females. Furthermore, the rate of anxiety-like behavior progressively declined during the 3-week choice condition in subordinate but not dominant females. These data provide support for the hypothesis that daily exposure to psychosocial stress increases consumption of calorically dense foods. Furthermore, consumption of HCDs may be a metabolic stressor that synergizes with the psychosocial stress of subordination to further increase the consumption of these diets.

Genetic, epigenetic and environmental impact on sex differences in social behavior

The field of behavioral neuroendocrinology has generated thousands of studies that indicate differences in brain structure and reactivity to gonadal steroids that produce sex-specific patterns of social behavior. However, rapidly emerging evidence shows that genetic polymorphisms and resulting differences in the expression of neuroactive peptides and receptors as well as early-life experience and epigenetic changes are important modifiers of social behavior. Furthermore, due to its inherent complexity, the neurochemical mechanisms underlying sex differences in social behavior are usually studied in a tightly regulated laboratory setting rather than in complex environments. Importantly, specific hormones may elicit a range of different behaviors depending on the cues present in these environments. For example, individuals exposed to a psychosocial stressor may respond differently to the effects of a gonadal steroid than those not exposed to chronic stress. The objective of this review is not to re-examine the activational effects of hormones on sex differences in social behavior but rather to consider how genetic and environmental factors modify the effects of hormones on behavior. We will focus on estrogen and its receptors but consideration is also given to the role of androgens. Furthermore, we have limited our discussions to the importance of oxytocin and vasopressin as targets of gonadal steroids and how these effects are modified by genetic and experiential situations. Taken together, the data clearly underscore the need to expand research initiatives to consider gene-environment interactions for better understanding of the neurobiology of sex differences in social behavior.