Metabolic and reproductive consequences of the serotonin transporter promoter polymorphism (5-HTTLPR) in adult female rhesus monkeys (Macaca mulatta)

Alcohol as an early life stressor: Epigenetics, metabolic, neuroendocrine and neurobehavioral implications

Ethanol exposure during gestation is an early life stressor that profoundly dysregulates structure and functions of the embryonal nervous system, altering the cognitive and behavioral development. Such dysregulation is also achieved by epigenetic mechanisms, which, altering the chromatin structure, redraw the entire pattern of gene expression. In parallel, an oxidative stress response at the cellular level and a global upregulation of neuroendocrine stress response, regulated by the HPA axis, exist and persist in adulthood. This neurobehavioral framework matches those observed in other psychiatric diseases such as mood diseases, depression, autism; those early life stressing events, although probably triggered by specific and different epigenetic mechanisms, give rise to largely overlapping neurobehavioral phenotypes. An early diagnosis of prenatal alcohol exposure, using reliable markers of ethanol intake, together with a deeper understanding of the pathogenic mechanisms, some of them reversible by their nature, can offer a temporal "window" of intervention. Supplementing a mother's diet with protective and antioxidant substances in addition to supportive psychological therapies can protect newborns from being affected.

Glucocorticoid negative feedback as a potential mediator of trade-offs between reproduction and survival

A large increase in glucocorticoid hormones can inhibit or completely shut down breeding in wild animals. Because of its critical role in reducing glucocorticoids after exposure to stressors, hypothalamic-pituitary-adrenal (HPA) negative feedback could be an important mediator of the ecological trade-off between investing limited resources into survival/self vs. reproduction/offspring. Although assessing negative feedback in a standardized way using injections of the synthetic glucocorticoid dexamethasone is a straightforward procedure, we show that several different approaches are used to report negative feedback in the literature, and then demonstrate that this can in turn affect the statistical results and conclusions of a study. We then review six specific predictions about adaptive within- and across-species patterns in glucocorticoids based on the relative costs and benefits of maintaining or abandoning breeding attempts when animals are faced with prolonged strong stressors, and examine evidence for these predictions in the context of HPA negative feedback. Thus far, evidence supporting these predictions for negative feedback is mixed, with the strongest evidence supporting a link between poor body condition and weak negative feedback in breeding animals. However, more research is necessary to assess the importance of changes in HPA negative feedback, especially in reptile, fish, and amphibian species. Furthermore, future research would benefit from reporting negative feedback ability in a standardized way, or at least making raw data available for the computation of alternate measures, to more easily compare studies in this growing area of research.

Association of 5-HTTLPR Polymorphism with the Nursing Diagnoses and the Achievement of Nursing Outcomes in Patients with Major Depression

The aim of this study is to investigate whether a 44-base-pair insertion/deletion polymorphism in the upstream regulatory region of the serotonin transporter gene (5-HTTLPR) is associated with the nursing diagnoses and the achievement of the desired nursing outcomes in inpatients with major depression. Thirty five patients were evaluated. The nursing diagnoses of risk for suicide and imbalanced nutrition are reported less often in homozygotes of the high-expressing gene (L_A). Carriers of the low-expressing genes (L_G or S) have a worse response to interventions which aim to increase low self-esteem, indicating that they may need more intensive care in order to achieve the desired outcome. Genetics in psychiatric nursing could help refine personalized care, however further studies with large sample sizes and multiple gene evaluations are needed.

The Association of 5-HTTLPR XLL Genotype with Higher Cortisol Levels in African Americans

Genetic variants of the human serotonin transporter (SERT) may contribute to HPA axis dysregulation. SERT has two promoter region polymorphisms (5-HTTLPR: VNTR and SNP: rs25531), which may alter levels of SERT protein and its function. Combining these polymorphisms creates a functional polymorphism (FN) which may modulate mRNA expression. This study examines the relationship between these genetic variants and morning and evening salivary samples of both cortisol and dehydroepiandrosterone sulfate (DHEAS) concentrations in 269 African American (AA) adults. Resultant allele frequencies for the VNTR, SNP, and FN genotypes were 70% L (2% XLL), 84% A, and 54% LA (2% XLLA), respectively. The XLL genotype was associated with significantly higher concentrations of cortisol (~3X) and DHEAS (~2X) for both VNTR and FN polymorphisms. No significant differences were found for SNP genotypes. Conclusions were that persons with VNTR and FN XLL polymorphisms had significantly higher cortisol and DHEAS concentrations than other genotypes. AAs also appear to have a higher frequency of the rare XL allele than Caucasians. Whether the XLL genotype predisposes AAs to greater health challenges will require further research to determine the implications of these findings.

Co-administration of paroxetine and pravastatin causes deregulation of glucose homeostasis in diabetic rats via enhanced paroxetine exposure

AIM

Clinical evidence shows that co-administration of pravastatin and paroxetine deregulates glucose homeostasis in diabetic patients. The aim of this study was to verify this phenomenon in diabetic rats and to elucidate the underlying mechanisms.

METHODS

Diabetes mellitus was induced in male SD rats by a high-fat diet combined with a low-dose streptozotocin injection. The rats were orally administered paroxetine (10 mg/kg) and pravastatin (10 mg/d) or both the drugs daily for 28 d. The pharmacokinetics of paroxetine and pravastatin were examined on d 1 and d 28. Biochemical parameters including serum insulin, glucose and lipids were monitored during the treatments. An insulin-secreting cell line (INS-1) was used for measuring insulin secretion.

RESULTS

In diabetic rats, co-administration of paroxetine and pravastatin markedly increased the concentrations of both the drugs compared with administration of each drug alone. Furthermore, co-administration severely impaired glucose homeostasis in diabetic rats, as demonstrated by significantly increased serum glucose level, decreased serum and pancreatic insulin levels, and decreased pancreatic Insulin-2 mRNA and tryptophan hydroxylase-1 (Tph-1) mRNA levels. Treatment of INS-1 cells with paroxetine (5 and 10 μmol/L) significantly inhibited insulin secretion, decreased the intracellular insulin, 5-HT, Insulin-2 mRNA and Tph-1 mRNA levels. Treatment of the cells with pravastatin (10 μmol/L) significantly stimulated insulin secretion, which was weakened by co-treatment with paroxetine.

CONCLUSION

Paroxetine inhibits insulin secretion at least via decreasing intracellular 5-HT and insulin biosynthesis. The deregulation of glucose homeostasis by co-administration of paroxetine and pravastatin in diabetic rats can be attributed to enhanced paroxetine exposure.

The evolutionary history of SLC6A4 and the role of plasticity in Macaca

Serotonin has been repeatedly indicated as a biological marker of behavior. In particular, the serotonin transporter gene, SLC6A4, has been the focus of a large body of research. Interestingly, both rhesus macaques (Macaca mulatta) and humans have independently evolved a number of shared polymorphisms for this gene, which is indicative of parallel evolution between the two species. However, little is known about the evolution of this gene, particularly within macaques. Although there are several hypotheses as to the adaptive values of various polymorphisms, few authors have gone beyond theoretical discussion. Here, we examined the genetic variation in SLC6A4 within and between several species of macaques and investigate whether selection has played a significant role in its evolutionary history. In addition, we assayed the promoter region polymorphism, 5-HTTLPR, which is known to play a significant role in regulating both serotonin turnover and behavior. In examining the distribution of the 5-HTTLPR polymorphism, we identified significant differences between Indian and Chinese populations of Macaca mulatta; furthermore, we discovered its presence in Macaca cyclopis, which has not been described before. In regard to the evolutionary history of SLC6A4, we found little evidence for selection and conclude that SLC6A4 largely evolved through neutral processes, possibly due to its potential role in regulating behavioral plasticity. However, we also found very low levels of linkage between the coding regions and 5-HTTLPR. Because we limited evolutionary analyses to the coding regions, it is possible that the promoter region shows a distinct evolutionary history from SLC6A4.

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.

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.

miR-15a and miR-16 regulate serotonin transporter expression in human placental and rat brain raphe cells

The serotonin transporter (SERT) is a key regulatory molecule in serotonergic transmission implicated in numerous biological processes relevant to human disorders. Recently, it was shown that SERT expression is controlled by miR-16 in mouse brain. Here, we show that SERT expression is regulated additionally by miR-15a as well as miR-16 in human and rat tissues. This post-transcriptional regulation was observed and characterized in reporter assays and likewise when endogenous SERT expression was evaluated in human placental choriocarcinoma JAR cells and rat brain raphe RN46A cells - two cell lines that endogenously express SERT. Similar effects for miR-16 to those of miR-15a were found in both human and rat cell lines. The effects of miR-15a and miR-16 were comparable in extent to those originally reported for miR-16 in mice. These findings represent a novel layer of complexity for SERT expression regulation exerted by the mir-15a/16 cluster, whose genes are adjacently located at human chromosome 13q14.3.

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.

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.

Estradiol and progesterone modify the effects of the serotonin reuptake transporter polymorphism on serotonergic responsivity to citalopram

Individual vulnerability to psychopathologies is linked to a number of genetic polymorphisms including the serotonin transporter (5HTT) promoter polymorphic region (5HTTLPR). A single copy of the short variant (s-variant) allele of 5HTTLPR confers increased susceptibility to anxiety disorders and depression and decreased efficacy of serotonin-releasing agents in pharmacotherapy compared to the homozygous long 5HTTLPR variant (l/L). The data suggesting that the 5HTTLPR polymorphism modulates the efficacy of serotonin-releasing agents in pharmacotherapy is inconsistent. Other factors such as age, gender, and hormonal status could interact with 5HTTLPR genotype to affect individual physiological and behavioral responses to serotonin reuptake inhibitors such as citalopram. Indeed, estradiol and progesterone, the primary female steroid hormones, exert an array of effects on the serotonergic system, including 5HTT expression. The present study used ovariectomized female rhesus monkeys to determine the interaction between the 5HTTLPR polymorphism and the effects of midfollicular levels of estradiol and luteal levels of progesterone on serotonergic responsivity to acute citalopram administration. The increase in serum prolactin, a surrogate measure of serotonin activity, following citalopram administration was significantly larger in l/L females than in s-variant females over the course of two hours during concurrent estradiol and progesterone hormone replacement only. These data suggest that ovarian function and the 5HTTLPR polymorphism interact to gate serotonergic reactivity in females, suggesting that clinicians should be aware of the ovarian status and 5HTTLPR genotype of women when considering serotonergic pharmacotherapy in women.

Val1483Ile polymorphism in the fatty acid synthase gene was associated with depressive symptoms under the influence of psychological stress

BACKGROUND

To study the association between lipid-metabolism and depressive symptoms, genetic polymorphisms in serotonin transporter linked promoter region (5-HTTLPR) and fatty acid synthase gene (FASN) were investigated.

METHOD

A cross-sectional study was conducted on 177 women (n = 166) and men (n = 15) recruited from workers in a hospital and nursing homes in Japan. Depressive symptoms were assessed by the Center for Epidemiologic Studies Depression (CES-D) scale and perceived psychological stress was measured using visual analogue scale (VAS). The genotypes of 5-HTTLPR (insertion/deletion; L/S), and FASN (Val1483Ile) were determined by the PCR methods. Linear regression analysis was performed, in which CES-D scores served as a dependent variable, and VAS scores, gene polymorphism, and confounders as independent variables.

RESULTS

Under the influence of perceived stress, S/S carriers of the 5-HTTLPR gene showed significantly higher CES-D scores in comparison with L/L+L/S carriers (F = 8.2, standardised β = 0.15, p < 0.05). Regression analysis also confirmed that CES-D scores in participants with Ile/Ile+Val/Ile genotypes of the FASN gene were significantly higher than those with Val/Val genotype (F = 8.4, standardised β = 0.16, p<0.05). In relation to physical features, BMI among participants with S/S genotype of 5-HTTLPR was significantly lower compared with those with L/L+L/S genotypes.

CONCLUSIONS

The Val1483Ile polymorphism in the FASN was associated with depressive symptoms under the influence of psychological stress. The S variant of 5-HTTLPR was related with less obese.

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.

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.

Further exploration of the possible influence of polymorphisms in HTR2C and 5HTT on body weight

Receptors of the 5-HT2C subtype are of importance for the influence of serotonin on food intake, and 2 single nucleotide polymorphisms in this gene (HTR2C)--Cys23Ser (rs6318) and -759C>T (rs3813929)--have been reported to be associated with weight and/or antipsychotic-induced weight gain. The present study aimed to replicate these associations; in addition, the 5-HTTLPR polymorphism in the promoter region of the serotonin transporter gene (SLC6A4) was assessed. The polymorphisms were genotyped in subjects recruited from the normal population (n = 510), and possible associations between genotype and body mass index (BMI) were assessed. The Ser23 allele was more common in underweight subjects (BMI <20) than in normal- and overweight (BMI > or =20) subjects (P = .006). The T allele of the -759C/T polymorphism was less common in the overweight group (BMI > or =25) (P = .007). Homozygosity for the short allele of 5-HTTLPR was more frequent in underweight subjects (P = .015). Our results are in agreement with previous studies, suggesting polymorphisms in HTR2C to be associated with body weight, particularly in women; and they also suggest that 5-HTTLPR may influence this phenotype. Further studies on the importance of the investigated genes for eating disorders and drug-induced weight gain are warranted.

Alteration of serotonin transporter messenger RNA level in the peripheral blood mononuclear cells from simian/human immunodeficiency virus infected Chinese rhesus macaques (Macaca mulatta)

Serotonin transporter (SERT, 5-HTT) is a key element in the serotonergic system which is probably involved in the psychiatric disorders commonly observed in people living with HIV/AIDS. However, no information is available about the effects of HIV infection on SERT expression. In this study, a TaqMan real-time RT-PCR method was established, levels of SERT mRNA in the peripheral blood mononuclear cells (PBMCs) and various tissues from normal Chinese rhesus macaques, in PBMCs from 32 SHIV-sf162p4 infected rhesus macaques and from 8 rhesus macaques before and 7, 14, 21, 28 and 196 days after SHIV-sf162p4 infection, and in PBMCs before and after in vitro phytohemagglutinin (PHA) stimulation were examined. It was found that SERT mRNA was widely distributed in lymphoid tissues; the level of SERT mRNA was significantly reduced in PBMCs from SHIV infected rhesus macaques and in PBMCs stimulated with PHA. The most evident decrease (to about one-tenth) in SERT mRNA level was observed at day 7 after SHIV infection. Difference in PBMC SERT mRNA level between 5-HTTLPR genotypes was not statistically significant. These data indicated that, in addition to previously observed abnormality in serotonin metabolism, SERT expression might be affected in HIV/AIDS, which might be associated with depression and other psychiatric disorders in HIV/AIDS. Besides, this study provided a basis for quantitative analysis of SERT gene expression under effects of host and environmental factors, such as 5-HTTLPR genotypes, SERT targeting drugs or other infectious agents.

Administration of human leptin differentially affects parameters of cortisol secretion in socially housed female rhesus monkeys

Chronic exposure to psychosocial stress may lead to a dysregulation of the limbic-hypothalamic-pituitary-adrenal axis that results in a number of adverse health outcomes. The fat-derived hormone leptin has been indicated as a potential key component to maintaining homeostasis by enhancing glucocorticoid negative feedback. Using an established model of nonhuman primate social stress, notably social subordination, this study examined the effects of continuous leptin administration on cortisol secretion in female rhesus monkeys. The 20 subjects were maintained in stable five-member social groups with established dominance hierarchies. All females were ovariectomized but received estradiol throughout the study to maintain serum concentrations at early follicular phase levels. Three parameters of cortisol secretion were examined in dominant and subordinate females during control and leptin-treatment conditions: diurnal cortisol secretion; response to a dexamethasone suppression test; and response to a brief separation from their social group. We hypothesized that leptin supplementation would attenuate the hypercortisolemia characteristic of subordinate females. During baseline conditions, subordinate female rhesus monkeys had significantly lower levels of serum leptin compared with more dominant monkeys and were less sensitive to glucocorticoid negative feedback. Exogenous administration of leptin improved glucocorticoid negative feedback in subordinate females and decreased morning cortisol in all animals. However, there were no status differences in response to a social separation test and diurnal rhythm in cortisol during baseline conditions. However, leptin administration did not attenuate the increase in cortisol in response to a social separation. The data presented in this study demonstrate that leptin can attenuate several parameters of cortisol secretion in female rhesus monkeys and thus may play a role in the response of the adrenal glands to socio-environmental stimuli.

The relationship between social status and atherosclerosis in male and female monkeys as revealed by meta-analysis

More than 25 years ago our laboratory reported sex-dependent relationships between social status and coronary artery atherosclerosis among cholesterol-fed cynomolgus monkeys (Macaca fascicularis) maintained in social groups of four to six animals each. Dominant males developed more atherosclerosis than subordinates, but only if housed in recurrently reorganized social groups. In contrast, dominant females developed significantly less atherosclerosis than subordinates, irrespective of social setting. Although we have continued to study these associations, no confirmatory investigations have been reported by other laboratories or using other atherosclerosis-susceptible monkey species. Accordingly, we conducted a meta-analysis of all relevant data sources developed in our laboratory since 1982 to determine whether the originally reported relationships between social status and atherosclerosis reflected robust associations. The sentinel (first) studies were composed of 16 females and 27 males. The current meta-analysis encompassed 419 animals (200 females and 219 males) derived from 11 separate investigations. The results confirmed that, among males, dominant individuals developed more extensive atherosclerosis than subordinates when housed in recurrently reorganized (unstable) social groups in which an estrogen-implanted female was also present. Dominant males in stable social groups tended to have less atherosclerosis than similarly housed subordinates, but this effect was not significant. On the contrary, we found that dominant females developed reliably less atherosclerosis than subordinates.

Serum antimüllerian hormone predicts ovarian reserve in a monkey model

OBJECTIVE

A monkey model of the menopausal transition (perimenopause) would facilitate efforts to understand better the effect of hormonal fluctuations during this life phase on the initiation of chronic diseases associated with the postmenopausal years. Antimüllerian hormone (AMH) is a promising marker of ovarian reserve (primordial follicle number) in women. Here, we describe the relationship between AMH and ovarian reserve in cynomolgus monkeys (Macaca fascicularis) estimated to be 12 to 15 years of age (approximately 36-45 y in women).

METHODS AND RESULTS

The results of daily vaginal swabbing (to detect menses) and thrice weekly blood sampling for 12 weeks indicate that AMH is relatively stable across the menstrual cycle (intraclass correlation, approximately 0.80), with a slight although significant (P < 0.02) reduction (approximately 1.4-fold) on days 2 to 5 postovulation. Substantial interindividual variation in AMH concentrations were observed between monkeys, with values ranging from 4.46 +/- 0.17 to 18.80 +/- 0.71 ng/mL (mean +/- SE). Antimüllerian hormone concentrations were reduced by approximately 63% after the removal of one ovary (7.6 +/- 0.77 vs 2.75 +/- 0.37 ng/mL; P < 0.001; n = 19) and were below the level of detection after the removal of both ovaries (5.8 +/- 0.42 to <0.05 ng/mL; P < 0.001; n = 84), suggesting that the ovary is likely to be either the major or the sole source of AMH in the monkey. Finally, we examined the association between AMH and primordial, primary, and secondary follicles in 29 monkeys and found significant associations with all follicle types (r = 0.78, r = 0.66, and r = 0.80, respectively; P < 0.01).

CONCLUSIONS

The relationship between AMH and ovarian reserve in the monkey is similar to that in women, suggesting that monkeys may be a useful model for studying hormonal fluctuations across the menopausal transition.

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

Psychosocial factors, particularly social stress, may compromise reproduction. However, some individuals may be more susceptible to socially induced infertility. The present study used group-housed, adult, ovariectomized rhesus monkeys to test the hypothesis that exposure to psychosocial stress, imposed by social subordination, would enhance estradiol (E2)-negative feedback inhibition of LH. Because polymorphisms in the gene encoding the serotonin transporter (SLC6A4) may contribute to individual differences in response to adverse environments, we determined whether subordinate females with the short-promoter-length allele (s-variant) would show greater suppression of LH. Subordinate females, particularly those with the s-variant SLC6A4 genotype, received significantly higher rates of noncontact aggression from more dominant cage mates and had consistently lower body weights. Serum LH was not influenced by social status in the absence of E2. In contrast, subordinate females were hypersensitive to E2-negative feedback inhibition of LH. Furthermore, serum LH in subordinate females with s-variant SLC6A4 genotype was maximally suppressed by Day 4 of treatment, whereas nadir concentrations were not reached until later in treatment in other females. Finally, pharmacological elevation of serum cortisol potentiated E2-negative feedback inhibition in all females. The current data suggest that infertility induced by psychosocial stressors may be mediated by hypersensitivity to E2-negative feedback and that polymorphisms in the SLC6A4 gene may contribute to differences in reproductive compromise in response to chronic stress.

T-cell phenotypic and functional changes associated with social subordination and gene polymorphisms in the serotonin reuptake transporter in female rhesus monkeys

Increased vulnerability to psychosocial stressors likely predisposes individuals to decreased immune function and inability to control pathogens. While many factors influence the susceptibility to psychosocial stress, genetic polymorphisms may modify individual reactivity to environmental stressors. The present study evaluated how immune function was altered by the interaction of in polymorphisms in the gene that encodes the serotonin reuptake transporter (5HTT) and the psychosocial stress imposed by social subordination in adult female rhesus monkeys. Subjects were dominant and subordinate females that carried both alleles of the long promoter variant (l/l) of the 5HTT gene, and dominant and subordinate that had at least one allele for the short promoter length variant (l/s or s/s, s-variant). Plasma cortisol was higher in subordinate females in response to a social separation paradigm, confirming their increased reactivity to psychosocial stressors. Subordinate females exhibited increased T-cell activation and proliferation regardless of genotype. Despite these higher levels of T-cell proliferation and activation, subordinate females showed significantly lower frequency of T-cells. This latter finding may be due to an increased susceptibility to cell death, as indicated by higher levels of annexin-V+ CD4+ and CD8+ T-cells in s-variant subordinate compared to dominant females. These findings indicate that subordinate rhesus monkeys with the s-variant 5HTT genotype exhibit decreased T-cell numbers perhaps compromising their ability to mount an immune response to pathogens. These data underscore the importance for considering gene polymorphisms that influence emotional reactivity to better understand susceptibility to disease.

Gene-environment interactions, not neonatal growth hormone deficiency, time puberty in female rhesus monkeys

The factors that influence the timing of puberty and the onset of adult fertility are poorly understood. While focus on the juvenile period has provided insights into how growth-related cues affect pubertal timing, growth velocity during infancy that is sustained into the juvenile period may be important. On the other hand, social factors, specifically exposure to psychosocial stressors, can delay sexual maturation, possibly by altering growth velocities during development. Using female rhesus monkeys, the present study used a prospective analysis to determine how neonatal growth hormone (GH) inhibition with a sandostatin analog or suppression of the pituitary-gonadal axis with a GnRH analog affected growth and sexual maturation. A separate retrospective analysis was done assessing the effects of social dominance status during development on pubertal timing. Because a specific polymorphism in the gene encoding the serotonin (5HT) reuptake transporter increases vulnerability to psychosocial stressors, females were also genotyped and were then classified as socially dominant, having both alleles for the long promoter variant or having at least one allele for the short promoter variant, or as socially subordinate, having the long variant or having the short variant. Neonatal treatments were not balanced for social status or genotype, so analyses were performed separately. Although the neonatal treatments reduced GH secretion postnatally and through the juvenile period, neither growth nor sexual maturation was affected. In contrast, the retrospective analysis showed sexual maturation was delayed significantly in subordinate females carrying at least one allele of the short promoter variant in the gene encoding the 5HT reuptake transporter, and this delay was associated with reduced GH and leptin secretion during the juvenile phase but not with differences in growth velocities from birth. These data suggest that decreased neonatal GH secretion does not adversely affect sexual maturation, but that polymorphisms in the gene encoding the 5HT transporter modulate the adverse consequences of social subordination on the timing of puberty in female rhesus monkeys.

Polymorphisms in the serotonin reuptake transporter gene modify the consequences of social status on metabolic health in female rhesus monkeys

Individuals vary substantially in their vulnerability to physical and psychosocial stressors. The causes of such variation in susceptibility to stress are poorly understood, but are thought to relate in part to genetic factors. The present study evaluated the extent to which polymorphisms in the gene encoding the serotonin reuptake transporter (5HTTLPR or SERT) modulated physiologic responses to the imposition of psychosocial stress (social reorganization and subordinate social status) in female rhesus monkeys. Forty females, drawn from the middle ranking genealogies of several large social groups, were reorganized into eight groups containing 5 monkeys each; four groups were comprised entirely of animals homogeneous for the long promoter variant in the SERT gene (l/l), while the other four groups had monkeys with at least one allele of the short promoter variant (l/s or s/s). Females were sequentially introduced into these new groups in random order and dominance ranks were established within several days. During the ensuing 6 weeks, dominant monkeys exhibited elevated rates of aggression while subordinates displayed high rates of submission. Notably, females with the s-variant SERT genotype, collapsed across social status positions, exhibited the highest overall rates of both aggression and submission. Although neither social status nor SERT genotype influenced morning cortisol concentrations, glucocorticoid negative feedback was reduced significantly in subordinate compared to dominant females irrespective of genotype. All animals lost weight and abdominal fat across the experiment. However, decreases were greatest in subordinates, regardless of genotype, and least in dominant females with the l/l genotype. Serum concentrations of insulin, glucose, and ghrelin decreased significantly during the group formation process, effects that were independent of genotype or social status. In contrast, social status and genotype interacted to influence changes in serum concentrations of leptin and triiodothyronine (T3), as dominant, l/l females had the highest levels while subordinate s-variant females had the lowest levels. The order in which a female was introduced to her group generally predicted her eventual social rank. However, rank was additionally predicted by pre-experimental T3 and abdominal fat values, but only in the l/l animals. While these findings must be replicated with a larger sample size, the data suggest that the s-variant SERT genotype confers increased vulnerability to the adverse effects of psychosocial stress associated with subordinate status while the l/l genotype benefits the most from the absence of stress conferred by dominant social status. These findings suggest that genetic factors modify the responses of monkeys to social subordination and perhaps other psychosocial stressors.