Effects of ovariectomy, social instability and social status on female Macaca fascicularis social behavior

Psychosocial stress increases risk for type 2 diabetes in female cynomolgus macaques consuming a western diet

Chronic psychosocial stress is associated with increased risk of many chronic diseases including type 2 diabetes mellitus. However, it is difficult to establish a causal relationship between stress and diabetes in human studies because stressors often are self-reported and may be distant in time from metabolic consequences. Macaques are useful models of the effects of chronic psychosocial stress on health and may develop obesity and diabetes similar to human beings. Thus, we studied the relationships between social subordination stress - a well-validated psychological stressor in macaques - and body composition and carbohydrate metabolism in socially housed, middle-aged female cynomolgus monkeys (Macaca fascicularis; n = 42). Following an 8-week baseline phase, the monkeys were fed a Western diet for 36 months (about equivalent to 10 human years). Social status was determined based on the outcomes of agonistic interactions (X¯= 33.3 observation hours/monkey). Phenotypes collected included plasma cortisol, body composition, circulating markers of glucose metabolism, activity levels, and heart rate variability measured as RMSSD (root of mean square of successive differences) and SDDN (standard deviation of beat to beat interval) after 1.5- and 3-years on diet. Mixed model analyses of variance revealed that aggression received, submissions sent, and cortisol were higher, and RMSSD and SDNN were lower in subordinates than dominants (social status: p < 0.05). After 3 years of Western diet consumption, fasting triglyceride, glucose and insulin concentrations, calculated insulin resistance (HOMA-IR), body weight and body fat mass increased in all animals (time: all p's < 0.05); however, the increase in fasting glucose and HOMA-IR was significantly greater in subordinates than dominants (time x social status: p's < 0.05). Impaired glucose metabolism, (glucose > 100 mg/dl) incidence was significantly higher in subordinates (23%) than dominants (0%) (Fisher's exact test, p < 0.05). These findings suggest that chronic psychosocial stress, on a Western diet background, significantly increases type 2 diabetes risk in middle-aged female primates.

Laparoscopic salpingectomy in Papio hamadryas for birth control in captivity

OBJECTIVE

To evaluate the feasibility of laparoscopic salpingectomy in baboons (Papio hamadryas). We hypothesized that laparoscopic salpingectomy could be performed in baboon species within a reasonable amount of surgical time, with minor complications occurring at low rates.

STUDY DESIGN

Case series and technique description.

ANIMALS

Sixteen baboons (n = 16).

METHODS

The surgical procedures were performed using the 3-port technique, with 5 mm instruments and a telescope placed at the umbilical and hypogastric regions. A salpinx dissection was performed, using a radiofrequency bipolar vessel sealing device, from the fimbriae to the uterine attachments. We evaluated the surgical duration, learning curve, and intraoperative and early postoperative complications.

RESULTS

Ten adult and 6 subadult baboons with a mean weight of 9.32 kg, a range of 4-14.2 kg, and a standard deviation (SD) of 3.09 kg were included in the study. The total duration of surgery was 28.75 min (range, 16-50 min; SD, 9.60 min). The installation phase was completed in a mean time of 7.68 min (range, 3-15 min; SD, 3.43 min), and the time to complete the salpingectomy of both salpinges was 9.68 min (range, 4-20 min; SD, 3.97 min). No complications were observed in the postoperative period.

CONCLUSION

Laparoscopic salpingectomy in Papio hamadryas was feasible, with an acceptable surgical time, low invasiveness, and only minor technical perioperative complications.

CLINICAL SIGNIFICANCE

Laparoscopic salpingectomy could be a viable and safe therapeutic option in nonhuman primate birth-control programs.

Factors determining male introduction success and long-term stability in captive rhesus macaques

The entrance of new males into non-human primate groups bears high social risk, yet migration is necessary to prevent inbreeding. Males are not always accepted in their new group. In the wild, males may increase the likelihood of successful group entry by choosing a new group based on their own and the group's characteristics. Understanding whether these characteristics also determine a male's ability to enter captive groups is crucial to improve introduction management. This study aims to identify which factors determine male introduction success (i.e. male stays in the group for at least 4 weeks) and long-term stability (i.e. the male does not cause considerable behavioural problems after success) after male introductions in captive groups of rhesus macaques (Macaca mulatta), creating one-male groups. We studied 64 male introductions at the breeding colony of the Biomedical Primate Research Centre in Rijswijk, The Netherlands. 49 (77%) introductions were successful, with the male obtaining a long-term stable social position in the group in 38 (59%) introductions. Introductions of males that reached at least prime age, into groups with more adult females, but without pregnant females were most successful. Moreover, long-term stability was highest when males were heavier, were at least 3.5 years old when they were first removed from their natal group, and groups had few matrilines and no pregnant females were present. Males should be introduced at the time they would naturally immigrate, when they are strongest. Moreover, groups should consist of few large matrilines, as observed in the wild, with philoatric females and males that are removed at natural age. Our study highlights the importance of composing naturalistic groups and mimicking natural migration patterns to maintain long-term stable breeding groups in captivity.

Long-term sertraline treatment and depression effects on carotid artery atherosclerosis in premenopausal female primates

OBJECTIVE

Atherosclerosis developed during premenopausal years predicts postmenopausal atherosclerosis burden. Selective serotonin reuptake inhibitor (SSRI) antidepressants, recently approved for hot flushes, have been associated with increased ischemic stroke risk in several observational studies; however, effects on carotid artery atherosclerosis, a strong predictor of future vascular events, are unknown.

METHODS

The effects of chronic administration of a commonly prescribed SSRI, sertraline HCl, on atherosclerosis in the carotid artery was assessed in a placebo-controlled, longitudinal, randomized study of premeonopausal depressed and nondepressed cynomolgus monkeys (Macaca fascicularis; n = 42). Physiologic and behavioral phenotypes were evaluated at baseline and after 18 months of oral sertraline (20 mg/kg, n = 21) or placebo (n = 21). Carotid artery atherosclerosis was measured post mortem via histomorphometry.

RESULTS

Atherosclerosis extent in the right common carotid artery, on average, was 60% greater in sertraline-treated depressed monkeys compared with all other groups (P = 0.028). The results of linear regression analyses suggested that sertraline and depression effects on atherosclerosis were not mediated by their effects on behavioral and physiological risk factors.

CONCLUSIONS

These findings suggest that chronic SSRI treatment is associated with the progression of carotid artery atherosclerosis, which may increase the risk for future vascular events, particularly in depressed women. The underlying mechanism remains to be determined, but does not appear to be related to SSRI effects on traditional cardiovascular risk factors.

Relationships of depressive behavior and sertraline treatment with walking speed and activity in older female nonhuman primates

Depression is the most common mental health problem in aging persons and is a leading risk factor for physical disability, especially in women. Though antidepressant drugs such as serotonin reuptake inhibitors (SSRI) are commonly prescribed, epidemiological evidence reveals mixed effects of long-term antidepressant use on physical function and activity, possibly depending on depressive status. The purpose of this preclinical trial was to determine the relationships of depressive behavior and the potential for an SSRI treatment to modulate walking speed and activity patterns in older adult female cynomolgus monkeys (Macaca fascicularis). We evaluated the effects of depression and a commonly prescribed SSRI, sertraline HCl (20 mg/kg/day p.o.), on (a) walking speed, (b) accelerometry-derived activity (counts) and sedentariness (daytime 60-s sedentary epochs), and (c) observed locomotor and sedentary behaviors (% time) in adult female depressed and nondepressed monkeys (n = 42; 17.2 ± 1.8 years) during an 18 month pre-treatment phase and an 18 month treatment phase using a longitudinal, stratified placebo-control study design. Monkeys that were depressed prior to treatment (19/42) subsequently had slower walking speeds (F _D [1, 38] = 4.14; p ≤ 0.05) and tended to be more sedentary during the daytime (F _D [1, 38] = 3.63; p ≤ 0.06). Sertraline did not affect depressive behaviors, walking speed, accelerometry-derived physical activity or sedentariness, or time observed in total locomotor or sedentary behavior (all p > 0.10). This study provides the first experimental demonstration of relationships between nonhuman primate behavioral depression and walking speed, activity, and sedentariness and provides evidence for a lack of an effect of SSRI treatment on these phenotypes.

Sertraline effects on cerebrospinal fluid monoamines and species-typical socioemotional behavior of female cynomolgus monkeys

RATIONALE

Although widely prescribed, little is known about the effects of selective serotonin reuptake inhibitors (SSRIs) on social behavior and cerebrospinal fluid (CSF) monoamines in female primates.

OBJECTIVE

The objective of this study was to determine the effects of sertraline on agonistic and affiliative behavior.

METHODS

Twenty-one adult female cynomolgus monkeys were housed in small, stable social groups, trained to participate in oral dosing, and began a 5-week cumulative dose-response study. Serial doses of 0, 5, 10, 15, and 20 mg/kg of sertraline were administered orally for 1 week each. Behavior was recorded daily during 10-min observations before and 4 h after dosing. On the seventh day of dosing, circulating sertraline/desmethylsertraline and CSF monoamines/metabolites were determined 4 h after the last dose.

RESULTS

At 20 mg/kg, circulating sertraline/desmethylsertraline was in the therapeutic range. CSF 5-hydroxyindole acetic acid decreased by 33 % (p < 0.05). Overall aggression, submission, locomotion, and time alone decreased, whereas affiliative behaviors (body contact, grooming) increased (all p values <0.05). Effects of sertraline on aggression and submission were social status-dependent, reducing aggression in dominants and submission in subordinates.

CONCLUSIONS

A clinically relevant oral dose of sertraline resulted in CSF metabolite changes similar to those observed in patients and altered the socioemotional behavior of female monkeys. Changes in CSF 5-HT and dopamine are novel observations that may be sex-specific. The robust effects of sertraline on aggression and affiliation may explain the efficacy of SSRIs on a range of human behavioral pathologies that share the characteristics of increased aggression and decreased sociality.

Long-term ovariectomy alters social and anxious behaviors in semi-free ranging Japanese macaques

Symptoms of anxiety and depression often occur in young women after complete hysterectomy and in older women during menopause. There are many variables that are hard to control in human population studies, but that are absent to a large extent in stable nonhuman primate troops. However, macaques exhibit depressive and anxious behaviors in response to similar situations as humans such as isolation, stress, instability or aggression. Therefore, we hypothesized that examination of behavior in ovariectomized individuals in a stable macaque troop organized along matriarchal lineages and in which individuals have social support from extended family, would reveal effects that were due to the withdrawal of ovarian steroids without many of the confounds of human society. We also tested the hypothesis that ovariectomy would elicit and increase anxious behavior in a stressful situation such as brief exposure to single caging. Japanese macaques (Macaca fuscata) were ovariectomized (Ovx) or tubal-ligated (intact controls) at 3 years of age and allowed to mature for 3 years in a stable troop of approximately 300 individuals. Behaviors were recorded in the outdoor corral in the third year followed by individual temperament tests in single cages. There was no obvious difference in anxiety-related behaviors such as scratching between Ovx and tubal-ligated animals in the corral. Nonetheless, compared to tubal-ligated animals, Ovx animals exhibited a significant decrease in (1) positive social behavior, (2) initiating dominance behavior, (3) time receiving grooming, (4) locomoting, (5) mounting behavior, and in (6) consort behavior. However, Ovx females exhibited a significant increase in (1) consummatory behavior and (2) object play compared to tubal-ligated controls. In the individual temperament tests, Ovx individuals exhibited an increase in anxiety-related behaviors. There was no difference in adrenal weight/body weight suggesting that neither group was under chronic stress. These data indicate that ovarian hormones enable females to successfully navigate their social situation and may reduce anxiety in novel situations.

Social stress, visceral obesity, and coronary artery atherosclerosis in female primates

Our previous work in cynomolgus monkeys demonstrated significant relationships between (i) social reorganization stress and visceral fat deposition, and (ii) central fat deposition and coronary artery atherosclerosis (CAA). Nevertheless, direct relationships between CAA and visceral fat have not been demonstrated in people or animals, nor have relationships among stress, visceral obesity, and CAA been observed within a single study. Here, we examine the hypothesis that visceral obesity provides a link between social stress and CAA. Subjects were 41 socially housed females that consumed an atherogenic diet for 32 months. Social behavior and ovarian function were continuously recorded; dexamethasone suppression tests, telemetered overnight heart rate, BMI, visceral (VAT) and subcutaneous abdominal (SAT) adipose tissue were measured before necropsy. Females with high VAT:SAT were relatively subordinate, socially isolated, received more aggression and less grooming, desensitized to circulating glucocorticoids, had impaired ovarian function, higher heart rates late in the day, and more CAA than low VAT:SAT females. High-BMI females had higher heart rates than low-BMI females. Poor ovarian function in high VAT:SAT females is a novel observation suggesting the need for studies of fat distribution and ovarian function in women. The results of this study are the first to demonstrate a relationship between CAA and visceral obesity, and suggest that social stress may exacerbate CAA in part by increasing the ratio of visceral:subcutaneous fat mass in selected individuals susceptible to diet-induced CAA. Further studies are needed to understand the complex and multifactorial temporal relationship among relative visceral obesity, physiological stress responses, and CAA.

Regional obesity and coronary artery atherosclerosis in females: a non-human primate model

The relationships between regional obesity, atherosclerosis and atherosclerosis risk factors were studied in female cynomolgus monkeys (Macaca fascicularis). In a retrospective necropsy study it was found that females with relatively high central: peripheral fat deposition had three times more extensive coronary artery atherosclerosis. In a second experiment it was found that females with high central fat ratios and females with high levels of whole body obesity were relatively hyperglycemic. In a third experiment it was found that females with relatively high whole body obesity, and females with relatively central fat deposition had higher blood pressures. Females with relatively central fat deposition had higher total and lower high density lipoprotein plasma cholesterol concentrations, and exacerbated coronary artery atherosclerosis. Social subordinates were more likely to exhibit a central fat deposition pattern than dominants. These findings suggest that female cynomolgus macaques may be a potential animal model of the health impact of regional obesity.

Behavioral and neurobiological characteristics influencing social hierarchy formation in female cynomolgus monkeys

Socially housed monkeys have been used as a model to study human diseases. The present study examined behavioral, physiological and neurochemical measures as predictors of social rank in 16 experimentally naïve, individually housed female cynomolgus monkeys (Macaca fascicularis). The two behavioral measures examined were novel object reactivity (NOR), as determined by latency to touch an opaque acrylic box placed in the home cage, and locomotor activity assessed in a novel open-field apparatus. Serum cortisol concentrations were evaluated three times per week for four consecutive weeks, and stress reactivity was assessed on one occasion by evaluating the cortisol response to adrenocorticotropic hormone (ACTH) following dexamethasone suppression. Measures of serotonin (5-HT) function included whole blood 5-HT (WBS) concentrations, cerebrospinal fluid (CSF) concentrations of the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) and brain 5-HT transporter (SERT) availability obtained using positron emission tomography (PET). After baseline measures were obtained, monkeys were assigned to four social groups of four monkeys per group. The two measures that correlated with eventual social rank were CSF 5-HIAA concentrations, which were significantly higher in the animals who eventually became subordinate, and latency to touch the novel object, which was significantly lower in eventual subordinate monkeys. Measures of 5-HT function did not change as a consequence of social rank. These data suggest that levels of central 5-HIAA and measures of novel object reactivity may be trait markers that influence eventual social rank in female macaques.

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.

Hormone therapy effects on social behavior and activity levels of surgically postmenopausal cynomolgus monkeys

The purpose of the experiments reported here was to investigate central nervous system effects of commonly prescribed postmenopausal hormone therapies in a primate model, the cynomolgus monkey (Macaca fascicularis). The results of two experiments are reported. In the first, ovariectomized adult cynomolgus monkeys were treated for eight weeks each with oral micronized 17beta-estradiol (E2) (n=23), E2+medroxyprogesterone acetate (MPA) (n=23), E2+progesterone (P4) (n=23), and placebo (n=23) using a crossover design. In the second, ovariectomized adult cynomolgus monkeys were treated for eight weeks with oral micronized E2+oral micronized P4 (n=10), or E2+intravaginal micronized P4 delivered via a Silastic ring (n=8), or oral placebo and intravaginal placebo (n=5), using a parallel arm design. Behavior was recorded during weeks two through four. Cerebrospinal fluid (CSF) and blood were sampled, and 24h heart rate recorded by telemetry during weeks five through seven. Monoaminergic metabolites were assayed in CSF, and cortisol was assayed in serum. There were no significant effects of treatment on CSF monoaminergic metabolites or heart rate. E2+MPA increased cortisol concentrations. While there were some differences in effects between experiments, both progestogens and both routes of administration increased time spent resting, particularly resting in body contact, resulting in increased passive affiliative interaction. Thus, synthetic progestogens appear to be as sedating as progesterone, and the ring delivery system does not appear to protect the central nervous system from effects of progestogens. Further research is needed to explore social context as an important feature of behavioral response to steroid hormone regimens and to verify and extend knowledge of systemic effects of vaginal ring-delivered progestogens.

Social stress-associated depression in adult female cynomolgus monkeys (Macaca fascicularis)

This paper describes a behavior pattern in adult female cynomolgus monkeys that has several behavioral and physiological characteristics in common with human depression including reduced body fat, low levels of activity, high heart rate, hypothalamic-pituitary-adrenal (HPA) axis disturbances, and increased mortality. Under certain circumstances, this depressive behavior appears more common in socially stressed subordinate, than dominant, females. This is the first animal model of social stress-related depression in females and the first primate model of adult depression. It is important to have a female animal model of depression because women are more likely to experience a clinically significant depression than men, and depression in women is often associated with changes in reproductive system function. This model is particularly useful because these monkeys have menstrual cycles that are similar to those of women, and those that exhibit depressive behavior have relatively low levels of ovarian steroids. These monkeys may be a useful model of reproductive system-associated mood disorders in females.

Effects of social status and moderate alcohol consumption on mammary gland and endometrium of surgically postmenopausal monkeys

OBJECTIVE

To evaluate the effects of social subordination stress and chronic moderate alcohol consumption on indices of breast and endometrial cancer risk.

DESIGN

Forty-six adult, ovariectomized, cynomolgus monkeys (Macaca fascicularis) were trained to voluntarily drink a placebo or a two-drink/day equivalent of ethanol (0.5 g/kg), 5 days a week for 26 months, the latter resulting in average blood alcohol levels of 42 mg/100 mL. Indices of cell proliferation and sex steroid receptor abundance were measured.

RESULTS

Compared with dominants, socially subordinate females had increased cell proliferation and proportions of glandular (P < 0.02) and epithelial tissue (P = 0.009) and less stroma (P < 0.02) in endometrium, and increased tissue thickness in breast (P < 0.05). There was no evidence of increased risk of breast or endometrial cancer with chronic moderate alcohol consumption, as indicated by markers of cell proliferation and sex steroid receptor abundance. Chronic moderate alcohol consumption did not effect circulating sex steroid concentrations (all P > 0.10). The adipocyte hormones leptin and adiponectin were correlated with indices of cell proliferation and sex steroid receptor abundance.

CONCLUSIONS

These observations suggest that social status was more important than chronic moderate alcohol consumption in endometrial and breast biology of surgically postmenopausal females. Endogenous sex steroid metabolism was not significantly affected by chronic moderate alcohol exposure consistent with the lack of estrogen-like effects on breast and endometrium. Social subordination stress was associated with initial cellular changes that may increase endometrial cancer risk. Ovariectomized cynomolgus monkeys may be a useful model for the study of effects of social factors and obesity on breast and endometrial cancer risk.

Triphasic oral contraceptive treatment alters the behavior and neurobiology of female cynomolgus monkeys

Oral contraceptives (OCs) are the most widely prescribed and effective of the reversible contraceptive methods. In addition to inhibiting ovulation, OCs alter central nervous system function in women; however, methodological problems have prevented clear human studies. Thus, in this experiment we investigated the effects of OC treatment on behavior, hypothalamic- pituitary-adrenal axis function and the central nervous system in 75 adult female cynomolgus monkeys (Macaca fascicularis) housed in social groups of four to five monkeys per pen. Monkey social groups were randomly divided into either a control or an OC treatment group which was administered a clinically prescribed OC (Triphasil(R), levonorgestrel and ethinyl estradiol tablets) for 2 years. OC treatment increased the frequency of contact aggression received, time spent in locomotion, and sitting close to another animal, and decreased time spent fearfully scanning. OC treatment decreased heart rate, increased activity levels, and increased baseline cortisol concentrations and the cortisol response to adrenocorticotropin compared to control animals. OC treatment decreased the prolactin response to fenfluramine suggesting decreased serotonergic activity. These results suggest that this triphasic OC disrupts social behavior, hypothalamic-pituitary-adrenal axis regulation and the underlying central nervous system function.

Soy and social stress affect serotonin neurotransmission in primates

Stress and sex steroidal milieu can each influence mood in women. The purpose of this study was to compare the effect of long-term conjugated equine estrogen (CEE), soy phytoestrogen (SPE), and social subordination stress on dorsal raphe serotonin neurotransmission of ovariectomized cynomolgus monkeys. Tryptophan hydroxylase (TPH) and serotonin reuptake transporter (SERT) protein content were determined, and the in vitro degradation of macaque SERT protein was examined in the presence and absence of protease inhibitors, serotonin (5-HT), and citalopram. Like CEE, SPE increased TPH protein levels. Social subordinates had markedly lower TPH protein levels than dominants regardless of hormone replacement. Therefore, these two variables had independent and additive effects. CEE and SPE increased SERT, and social status had no effect. Thus, the hormone-induced increase in SERT was accompanied by increased 5-HT synthesis and neuronal firing, which appears biologically reasonable as 5-HT prevented SERT degradation in vitro.

Behavioral responses to ovariectomy and chronic anabolic steroid treatment in female cynomolgus macaques

A pilot study was conducted to investigate the effects of ovariectomy on rates of aggressive and affiliative behavior, as well as body size, in 38 young adult female cynomolgus monkeys (Macaca fascicularis) living in isosexual social groups of four to five animals. In addition, we assessed the effects of nandrolone decanoate (an anabolic steroid used for postmenopausal hormone replacement therapy) on indices of aggression, submission, and body size. Animals were randomized into three experimental conditions: 1) sham ovariectomized, untreated (SHAM); 2) ovariectomized, untreated (OVX); and, 3) ovariectomized, treated with nandrolone decanoate for 24 months (NAN). Each individual was observed for 10 min, one to two times per month, and all instances of agonistic and affiliative behavior were recorded by means of focal animal sampling. Ovariectomized, untreated animals exhibited a two- to threefold increase in aggression compared to SHAM or NAN animals; F(2, 32) = 4.09, p = 0.026; however, the expression of prosocial or affiliative behaviors as measured by rates of grooming and initiating friendly behavior was unaffected. At an i.m. dose of 25 mg every 2 weeks, nandrolone decanoate caused a 60% increase in body weight of the animals compared to untreated intact and ovariectomized animals, F(2, 31) = 161.57, p < 0.0001.

Social subordination stress, behavior, and central monoaminergic function in female cynomolgus monkeys

BACKGROUND

Social subordination in female cynomolgus monkeys is stressful and activates the hypothalamic-pituitary-adrenal axis. In a previous experiment behavioral depression was observed in a subset of subordinates.

METHODS

In the experiment reported here behavioral and physiological indicators of stress were evaluated in dominant and subordinate female cynomolgus monkeys, and brain dopaminergic activity was assessed, as reflected in the prolactin response to haloperidol, a dopamine2 (D2) receptor antagonist.

RESULTS

Subordinates were aggressed more, spent more time in fearful scanning of the social environment, spent less time as the recipients of the active affiliative behavior of being groomed, had more variable heart rates in response to a novel environment, and were hypercortisolemic compared to dominants. Prolactin responses to haloperidol challenge were lower in subordinates than dominants, an observation consistent with the hypothesis that subordinate females have decreased D2 receptor function.

CONCLUSIONS

These observations suggest that social subordination is stressful and may alter brain dopaminergic function in primates. The neurophysiological characteristics of social subordinates may contribute to their susceptibility to depression.

Behavioral and neurobiological effects of estrogen replacement therapy and a history of triphasic oral contraceptive exposure

The effects of contraceptive steroids and estrogen replacement therapy on behavior and neuroendocrine function were evaluated in adult female cynomolgus monkeys. During the 'premenopausal' phase of the experiment, the animals were assigned to either treatment with a triphasic oral contraceptive (OC) for 24 months or the untreated control group. The monkeys were then ovariectomized and half of each of the premenopausal groups were randomly assigned to either treatment with conjugated equine estrogens (ERT) or the untreated control group for 12 months (the 'postmenopausal' phase). All evaluations were completed during the postmenopausal phase of the experiment. Both types of exogenous steroid treatments appeared to increase cardiovascular and hypothalamic-pituitary-adrenal responses to stress in socially dominant but not socially subordinate females. A history of triphasic OC administration increased contact aggression received, and reduced the prolactin response to fenfluramine, suggesting reduced serotonergic activity, for at least a year following the cessation of triphasic OC treatment.

Effects of chronic social separation on cardiovascular disease risk factors in female cynomolgus monkeys

A lack of social support is associated with increased risk of coronary heart disease morbidity and mortality in human beings. Similarly, chronic social separation (single cage housing) potentiates atherosclerosis in female monkeys. Under the hypothesis that autonomic arousal and/or ovarian impairment may mediate this effect (as both are associated with increased atherosclerosis), heart rate and luteal phase plasma progesterone concentrations were measured in 12 female cynomolgus monkeys that were first socially housed, then individually housed, and finally returned to their original social groups. Afternoon heart rates increased during social separation compared to the social groupings (P < 0.001). Increased heart rates could not be explained by activity levels, which were lower during social separation than in social groupings (P < 0.001). Ovarian function (i.e. luteal-phase progesterone concentrations) was not influenced by housing condition. Single caging reduced the extent of social signaling, even though animals were in visual and auditory contact. Rates of affiliative behaviors increased and time spent alone decreased in post-reunion social groups compared to pre-separation social groups (P's < 0.01). The results indicate that chronic social separation in this group-living species may exacerbate atherosclerosis via altered autonomic activity, as evidenced by higher heart rates during social separation.

Behavior and physiology of social stress and depression in female cynomolgus monkeys

The hypothesis that social subordination is stressful, and results in a depressive response in some individuals, was examined in socially housed female cynomolgus monkeys. Social status was manipulated such that half of the previously subordinate females became dominant and half of the previously dominant females became subordinate. Current subordinates hypersecreted cortisol, were insensitive to negative feedback, and had suppressed reproductive function. Current subordinates received more aggression, engaged in less affiliation, and spent more time alone than dominants. Furthermore, they spent more time fearfully scanning the social environment and displayed more behavioral depression than dominants. Current subordinates with a history of social subordination were preferentially susceptible to a behavioral depression response. The results of this experiment suggest that the stress of social subordination causes hypothalamic-pituitary-adrenal and ovarian dysfunction, and support the hypothesis that chronic, low-intensity social stress may result in depression in susceptible individuals.

Psychosocial factors, sex differences, and atherosclerosis: lessons from animal models

OBJECTIVE

Premenopausal women, compared with men, are relatively spared from coronary heart disease and the underlying atherosclerosis. Our purpose has been to elucidate the reason for this difference and to explore the role of behavioral factors in this phenomenon.

METHODS

Studies employed socially housed cynomolgus macaques (Macaca fascicularis) fed an atherogenic diet and subjected to behavioral observations. Ovariectomy, with or without hormone replacement, was used to test specific hypotheses about estrogen's role in the protection of females from atherosclerosis and coronary heart disease.

RESULTS

Female macaques, like women, are resistant to atherosclerosis. However, this resistance is modified by social status-dominant monkeys develop little atherosclerosis, whereas subordinates resemble males in the amount of lesion that occurs. Subordinate females also are characterized by hypercortisolemia, behavioral dysfunction, and impaired ovarian function; the resulting low concentrations of circulating estrogen perhaps explain their accelerated atherosclerosis. Notably, atherosclerosis is exacerbated in ovariectomized monkeys but is suppressed in association with pregnancy, a hyperestrogenic state. Moreover, exogenous estrogen (an oral contraceptive) inhibits atherosclerosis in premenopausal social subordinates.

CONCLUSIONS

To the extent that our results apply to women, they highlight the potential importance of behavioral stressors and their effects on estrogen activity in the premenopausal development of atherosclerosis. The triad of hypercortisolism, ovarian impairment, and psychiatric morbidity found in monkeys also occurs in women and may represent a high-risk state for disorders of the cardiovascular system and perhaps, other estrogen-sensitive tissues.

Insulin and glucose: relationships with hassles, anger, and hostility in nondiabetic older adults

Relationships of psychosocial factors (anger, hostility, hassles, and caregiving) with fasting insulin and glucose levels were examined. Samples included two groups of nondiabetic adults (mean age = 69.4 years): spouse caregivers (CG) of individuals with diagnoses of Alzheimer's disease (AD) (N = 78) and spouses of nondemented controls (CO) (N = 72) matched for age and gender. The groups were assessed twice with a 15-to 18-month hiatus. To obtain more stable assessments, all biopsychosocial measures were averaged over time. Psychosocial factors were associated with insulin and glucose, even after controlling for significant health variables: obesity, lipids, and cardiovascular disease. As hypothesized, CG with high anger-out/hostility (AOHO) had significantly higher glucose levels than all other group combinations. The glucose levels for subjects with high hassles or high AOHO were significantly higher than those for subjects who were low on both of these factors. For insulin, a three-way interaction occurred among AOHO, hassles, and gender-hormone replacement therapy (HRT); in women taking HRT, no relationships occurred between insulin with AOHO and hassles. In women not taking HRT, those with high AOHO and high hassles had significantly higher insulin levels than the other three combinations, whereas in men, those with either high AOHO or high hassles had significantly higher insulin levels than men who were low on both of these factors. Given these results, future research should examine the degree to which interactions between metabolic processes with psychosocial variables, gender, and HRT have long term health consequences in nondiabetics.

Dominant social status and contraceptive hormone treatment inhibit atherogenesis in premenopausal monkeys

The stress of social subordination is associated with exacerbation of coronary artery atherosclerosis in premenopausal cynomolgus monkeys, possibly as a result of the ovarian dysfunction that reliably accompanies subordinate social status. The primary objective of the current study was to determine whether treatment with an oral contraceptive (OC) provides relative protection from development of atherosclerotic plaques, especially among animals made vulnerable to atherosclerosis by social subordination. In the present study, 193 adult female monkeys (Macaca fascicularis) were placed in social groups of 5 or 6 animals each. Half of the animals were then fed an atherogenic diet to which had been added a triphasic OC, while the remainder received only the atherogenic diet. At the end of 26 months, atherosclerosis was measured in an iliac artery biopsy taken from each monkey. The results demonstrated that among untreated animals subordinate individuals developed significantly more atherosclerosis than did their dominant counterparts (P < .01); however, OC treatment inhibited atherosclerosis in subordinate animals (P < .05) and eliminated the difference between dominant and subordinate animals that was observed in the untreated condition. Subordinate social status and OC treatment were both associated with reduced plasma concentrations of HDL cholesterol (P < .01 for both), and subordinate monkeys also had elevations in LDL cholesterol plus VLDL cholesterol (P < .01). Nonetheless, the interaction between social status and OC treatment remained significant even after covariance adjustment for variation in plasma lipids. Taken together, these results suggest that social subordination worsens, whereas OC treatment inhibits, atherosclerosis, and that these effects are independent of concomitant variability in plasma lipids.

Social status and coronary artery atherosclerosis in female monkeys

While coronary heart disease is the leading cause of death in women in the United States, research in the area is lacking, especially concerning psychosocial risk factors. The purpose of this experiment was to study the effect of a known psychosocial risk factor in female monkeys, social status, and the effect of alteration of social status on coronary artery atherosclerosis. In previous experiments it has been demonstrated that social status is an enduring characteristic of the individual and that socially subordinate female monkeys have poor ovarian function and exacerbated coronary artery atherosclerosis. In the present experiment, adult female monkeys were fed an atherogenic diet and housed in small social groups, and social status was altered in half of the animals (subordinates became dominant and dominants became subordinate). The manipulation of social status had minimal effects on risk factors but significantly affected coronary artery atherosclerosis, supporting the hypothesis that social status affects atherogenesis in these females. However, all animals that changed social positions had worsened coronary artery atherosclerosis whether they became dominant or became subordinate, and this effect was independent of ovarian function. Subordinates that became dominant had 44% more and dominants that became subordinate had 500% more atherosclerosis than their counterparts that did not change social status. Thus, modification of this psychosocial risk factor was not effective in reducing coronary artery atherosclerosis. The manipulation of social status may have deleteriously altered a complex interaction between individuals and their psychosocial environment.