Growth hormone response to clonidine in adversely reared young adult primates: relationship to serial cerebrospinal fluid corticotropin-releasing factor concentrations

Reduced left ventricular dimension and function following early life stress: A thrifty phenotype hypothesis engendering risk for mood and anxiety disorders

Background

Early life stress (ELS) in macaques in the form of insecure maternal attachment putatively induces epigenetic adaptations resulting in a "thrifty phenotype" throughout the life cycle. For instance, ELS induces persistent increases in insulin resistance, hippocampal and corpus callosum atrophy and reduced "behavioral plasticity", which, taken together, engenders an increased risk for mood and anxiety disorders in humans but also a putative sparing of calories. Herein, we test the hypothesis whether a thrifty phenotype induced by ELS is peripherally evident as hypotrophy of cardiac structure and function, raising the possibility that certain mood disorders may represent maladaptive physiological and central thrift adaptations.

Methods

14 adult bonnet macaques (6 males) exposed to the maternal variable foraging demand (VFD) model of ELS were compared to 20 non-VFD adult subjects (6 males). Left ventricle end-diastolic dimension (LVEDD), Left ventricle end-systolic dimension (LVESD) and stroke volume (SV) were calculated using echocardiography. Blood pressure and heart rate were measured only in females. Previously obtained neurobehavioral correlates available only in males were analyzed in the context of cardiac parameters.

Results

Reduced LVESD (p < 0.05) was observed when controlled for age, sex, body weight and crown-rump length whereas ejection fraction (EF) (p = 0.037) was greater in VFD-reared versus non-VFD subjects. Pulse pressure was lower in VFD versus non-VFD females (p < 0.05). Male timidity in response to a human intruder was associated with reduced LVEDD (p < 0.05).

Conclusions

ELS is associated with both structural and functional reductions of left ventricular measures, potentially implying a body-wide thrifty phenotype. Parallel "thrift" adaptations may occur in key brain areas following ELS and may play an unexplored role in mood and anxiety disorder susceptibility.

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.

The neurobiological toll of child abuse and neglect

Exposure to interpersonal violence or abuse affects the physical and emotional well-being of affected individuals. In particular, exposure to trauma during development increases the risk of psychiatric and other medical disorders beyond the risks associated with adult violence exposure. Alterations in the hypothalamic-pituitary-adrenal (HPA) axis, a major mediating pathway of the stress response, contribute to the long-standing effects of early life trauma. Although early life trauma elevates the risk of psychiatric and medical disease, not all exposed individuals demonstrate altered HPA axis physiology, suggesting that genetic variation influences the consequences of trauma exposure. In addition, the effects of abuse may extend beyond the immediate victim into subsequent generations as a consequence of epigenetic effects transmitted directly to offspring and/or behavioral changes in affected individuals. Recognition of the biological consequences and transgenerational impact of violence and abuse has critical importance for both disease research and public health policy.

Risk and resilience: early manipulation of macaque social experience and persistent behavioral and neurophysiological outcomes

OBJECTIVE

To review the contributions of research on nonhuman primates, specifically macaque monkeys, to the understanding of early social stress and its effects on behavior and neurophysiology.

METHOD

Review and synthesis of two bodies of work on macaque monkeys and early social manipulation: peer rearing and variable foraging demands. The literature was searched with Medline using key terms macaque, variable foraging, and peer rearing. The reference lists of these articles were also used to generate potential studies for review.

RESULTS

Nonhuman primate macaques show similarities to humans in their social development and functioning. Peer rearing of young macaques and rearing of young macaques with mothers experiencing variable foraging conditions both result in increased anxious, impulsive, and aggressive temperament and behavior; more reactive stress physiology; altered neurotransmitter functioning; and immune and metabolic changes. Functional variants of specific genes that code for neuromodulators are mediators of these effects.

CONCLUSIONS

Disrupted social relations during macaque rearing contribute to the risk for developing emotional and neurophysiological disturbance. In the face of such disruption, certain genotypes contribute to resilience. This can be alternately stated that, for animals of high-risk genotypes, resilience is conferred by quality relationships during rearing. This interaction of genetics with early social environment also applies to child mental health, implicating biological mediators identified in macaques as contributing to more complex outcomes in humans.

Epigenetic mechanisms and the transgenerational effects of maternal care

The transmission of traits across generations has typically been attributed to the inheritance by offspring of genomic information from parental generations. However, recent evidence suggests that epigenetic mechanisms are capable of mediating this type of transmission. In the case of maternal care, there is evidence for the behavioral transmission of postpartum behavior from mothers to female offspring. The neuroendocrine and molecular mediators of this transmission have been explored in rats and implicate estrogen-oxytocin interactions and the differential methylation of hypothalamic estrogen receptors. These maternal effects can influence multiple aspects of neurobiology and behavior of offspring and this particular mode of inheritance is dynamic in response to environmental variation. In this review, evidence for the generational transmission of maternal care and the mechanisms underlying this transmission will be discussed as will the implications of this inheritance system for offspring development and for the transmission of environmental information from parents to offspring.

Epigenetic mechanisms mediating the long-term effects of maternal care on development

The long-term consequences of early environmental experiences for development have been explored extensively in animal models to better understand the mechanisms mediating risk of psychopathology in individuals exposed to childhood adversity. One common feature of these models is disruption of the mother-infant relationship which is associated with impairments in stress responsivity and maternal behavior in adult offspring. These behavioral and physiological characteristics are associated with stable changes in gene expression which emerge in infancy and are sustained into adulthood. Recent evidence suggests that these long-term effects may be mediated by epigenetic modification to the promoter regions of steroid receptor genes. In particular, DNA methylation may be critical to maternal effects on gene expression and thus generate phenotypic differentiation of offspring and, through effects on maternal behavior of offspring, mediate the transmission of these effects across generations. In this review we explore evidence for the influence of mother-infant interactions on the epigenome and consider evidence for and the implications of such epigenetic effects for human mental health.

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.

Early-life stress and the development of obesity and insulin resistance in juvenile bonnet macaques

Stress is a risk factor for chronic illnesses such as obesity, type 2 diabetes, and hypertension and has been postulated to cause the metabolic syndrome via perturbation of the hypothalamo-pituitary-adrenal (HPA) axis. In our model of early-life stress (variable foraging demand [VFD]), food insecurity is imposed on monkey mothers for 16 weeks beginning when their nursing offspring are 3-5 months of age. Under VFD, food availability is never restricted, and the infant's growth is unaffected. VFD rearing does, however, cause a range of neurobiological abnormalities, including dysregulation of the HPA axis, manifested in abnormal cerebrospinal fluid cortisol and corticotropin-releasing factor levels. We previously reported spontaneous occurrence of metabolic syndrome in 14% of normally reared peripubertal bonnet macaques given ad libitum access to standard monkey chow. Here, we show that compared with normally reared monkeys, peripubertal VFD juveniles exhibit greater weight, BMI, abdominal circumference, and glucagon-like peptide-1 and decreased glucose disposal rates during hyperinsulinemic-euglycemic clamps. Our data suggest that early-life stress during a critical period of neuro development can result in the peripubertal emergence of obesity and insulin resistance.

The impact of early adverse care on HPA axis development: nonhuman primate models

This review presents supporting evidence that early disruptions in mother-infant relationship in primates, including infant maltreatment, are important risk factors for the development of psychopathology and pathophysiology during childhood and adolescence. Current research in this field is trying to identify important aspects of early adverse experiences such as the timing, frequency, duration, "perceived" intensity of the stressful or traumatic events, the role of social support (e.g., nurturing caregiver) in buffering the deleterious outcomes of early adversity, as well as the role of sex and genetic factors on individual variability in vulnerability. The use of nonhuman primate models of early adverse caregiving is helping to put the pieces of the puzzle together to fully understand the causes and consequences of similar experiences in humans. These models are essential to characterize the time course of biobehavioral alterations throughout development, using prospective, longitudinal studies performed under controlled experimental conditions and using invasive approaches that are unrealistic and unethical when studying human populations.

Twenty-four hour growth hormone secretion in patients with panic disorder

BACKGROUND

Patients with panic disorder have blunted growth hormone (GH) responses to clonidine, suggesting subsensitivity of post-synaptic alpha(2)-adrenoreceptors, presumably in response to excessive central noradrenergic outflow. However, basal levels of GH release over a full circadian cycle have not been examined in panic. Reduced basal GH release would suggest an overall hypo-active GH system rather than a specific alpha-adrenergic abnormality.

METHODS

To determine whether panic patients show reduced basal GH secretion, 20 patients and 12 healthy controls were studied. Blood samples were drawn every 15 min for 24 h and plasma was assayed for GH. Patients were restudied during successful treatment with alprazolam. Groups were compared on overnight and daytime GH secretion and circadian patterns of release.

RESULTS

Patients showed normal levels on all measures of GH release. Treatment may have reduced nocturnal GH release slightly, but treated patients still did not differ from controls. The normal predominance of sleep over waking GH secretion was seen in both groups.

CONCLUSIONS

Panic patients, in contrast to depressed patients, have normal somatotrophic axis activity when measured in a resting state over a full circadian cycle. GH dysregulation may only be evident in these patients in activation paradigms and has been most consistently demonstrated by challenges with the alpha(2)-noradrenergic agonist, clonidine.

A magnetic resonance spectroscopic imaging study of adult nonhuman primates exposed to early-life stressors

BACKGROUND

Long-term behavioral, immunologic, and neurochemical alterations have been found in primates exposed to adverse early rearing.

METHODS

Bonnet macaque (Macaca radiata) mother-infant dyads were exposed to uncertain requirements for food procurement (variable foraging demand, VFD) for a few months. Ten years later, these offspring and age- and gender-matched control subjects were studied using proton magnetic resonance spectroscopic imaging (MRSI).

RESULTS

In anterior cingulate, VFD-reared subjects displayed significantly decreased N-acetylaspartate (NAA) resonance and significantly increased glutamate-glutamine-gamma-aminobutyric acid (Glx) resonance relative to the stable neurometabolite creatine (Cr). Across all subjects, NAA/Cr and Glx/Cr ratios in the anterior cingulate were negatively correlated (r = -.638, p =.014). In the medial temporal lobe, the ratio of choline-containing compounds to Cr was significantly increased in VFD subjects.

CONCLUSIONS

These findings indicate that adverse early rearing in primates has an enduring impact on adult MRSI measures considered reflective of neuronal integrity and metabolism, membrane structure and glial function, and cerebral glutamate content, and that these alterations occur in the same brain regions implicated in trauma-related psychiatric disorders.

Persistent central nervous system effects of an adverse early environment: clinical and preclinical studies

In the search for the underlying biological causes of psychiatric disorders, primary roles for both genetics and environment have been clearly established. A family history of mood or anxiety disorders, representing the genetic component, clearly increases the risk for developing these illnesses in adulthood. The pivotal role of early environmental influences in the pathogenesis of these disorders is also supported by an abundance of both clinical and preclinical data. This review will highlight some of the preclinical and clinical literature that suggests early adverse experience may sensitize corticotropin-releasing factor (CRF) circuitry. The neurobiology of depression highlighting the pathophysiological role of CRF is reviewed. Next, some of the preclinical models of early life stress are discussed; along with a review of the relevant clinical literature that suggests that the functional dysregulation of CRF circuitry in response to early life trauma may contribute to adulthood depression. The discussion will be framed in regards to a stress-diathesis model in which early adverse events result in a sensitized stress axis that predisposes individuals to develop mood disorders.

Differentiating depressed adolescent 24 h cortisol secretion in light of their adult clinical outcome

A clinical follow-up study was performed of adolescent major depressives and normal control subjects approximately 10 years after the subjects had undergone serial cortisol measurements over a 24-h period. In light of their young adulthood clinical status, our objective was to ascertain whether there were any premorbid cortisol abnormalities associated with depressive course of illness. In all, 77 young adults who had received a diagnosis of adolescent major depressive disorder, or were determined to be normal volunteers free of psychiatric diagnosis at index period and during follow-up, were studied. When subjects were adolescents, blood samples were collected for cortisol at 20-min intervals during the 24-h period coinciding with the third consecutive night of sleep EEG. The subjects, in young adulthood at the time of follow-up, were reinterviewed regarding longitudinal course of illness, and the original adolescent cortisol data were analyzed in the light of information obtained. Of the subjects who had experienced at least one lifetime major depressive episode during the follow-up period, the subgroup who would go on to make suicide attempts during the follow-up period secreted significantly greater levels of cortisol in the 4, 6, and 12 h prior to sleep onset. Conversely, this same subgroup exhibited reduced cortisol levels 2-4 h following sleep onset. Adolescents who are at risk to make suicide attempts appear to display significant elevations of cortisol prior to sleep onset, a time when the hypothalamic-pituitary-adrenal (HPA) axis is normally most quiescent. Dysregulation of the HPA axis, combined with dysfunction of sleep-onset mechanisms previously reported in this same cohort, might serve as premorbid biological substrates that predict suicide attempts during follow-up.

Crossroads of corticotropin releasing hormone, corticosteroids and monoamines. About a biological interface between stress and depression

Mental disorders are frequently preceded by stressful events or situations. Depression is a typical case in point. This raises the question, is depression - or possibly better: are certain forms of depression - caused by stress? Can stress be a true pathogenic factor? Phrased differently: can stress destabilize neuronal systems in the central nervous system to such an extent that depressive symptoms are generated? This question is discussed with the corticotrophin releasing hormone (CRH) and MA systems and hypothalamic-pituitary-adrenal (HPA) axis as major foci. The following issues are explored: the effect of antidepressants on corticosteroid receptor gene expression; the behavioral sequellae of CRH administration; CRH disturbances in depression; the impact of early life adversity on the development of the CRH system and on stress reactivity; the interrelationships of stress hormones and monoaminergic (MA ergic) transmission and finally the therapeutic potential of CRH and cortisol antagonists. The available data suggest that CRH overdrive and cortisol overproduction may play a pathogenic role in the occurrence of certain types of depression, directly and/or indirectly, i.e. by induction or exacerbation of disturbances in MA ergic transmission. Stress should, thus, become a major focus of biological depression research.

Variable foraging demand rearing: sustained elevations in cisternal cerebrospinal fluid corticotropin-releasing factor concentrations in adult primates

BACKGROUND

The authors previously reported elevated cerebrospinal fluid (CSF) corticotropin-releasing factor (CRF) concentrations in juvenile primates nursed by mothers undergoing experimentally imposed unpredictable foraging conditions in comparison to normally reared controls. The purpose of the present study was to determine if these changes would endure into young adulthood.

METHODS

Cisternal CSF samples were obtained from those unpredictably reared young adult primates who had been previously studied as juveniles and age-matched ad libitum normally reared controls. Samples were assayed for CSF CRF.

RESULTS

Concentrations of CSF CRF were significantly elevated in the unpredictably reared sample in comparison to the ad libitum-reared control group. A significant positive correlation was noted between juvenile and young adult CSF CRF values within the unpredictably reared cohort.

CONCLUSIONS

Disturbances of maternal-infant attachment processes have an enduring impact on primate CRF function into young adulthood. The CRF elevations following unpredictable maternal foraging conditions appear traitlike in nature.

Hypothalamic-pituitary-adrenal axis function and the metabolic syndrome X of obesity

Obesity has negative health consequences related to fat distribution, particularly the central or visceral accumulation of fat. The major complications associated with visceral obesity, termed the "Metabolic Syndrome of Obesity," or "Syndrome X," are type II diabetes, hypertension, and dyslipidemia. As with certain mood disorders, the syndrome may be a consequence of neuroendocrine perturbations typically associated with chronic stress. Our work with bonnet macaque monkeys provides an animal model for the relationship between early stress, behavioral and hypothalamic-pituitary-adrenal (HPA) axis dysregulation, and Syndrome X. During their infant's first half-year, mothers face a variable foraging demand (VFD), in which ample food varies unpredictably in the difficulty of its acquisition, and the offspring show persistent abnormalities in systems known to modulate stress and affective regulation. Early work on the bonnet macaque noted the emergence of a sample of spontaneously obese subjects as they matured. Using the VFD model, the current study showed that there was a clear relationship between early cerebrospinal fluid corticotropin-releasing factor levels and subsequently measured body mass index, supporting the hypotheses regarding the interactive roles of early experience and HPA axis dysregulation in the ontogeny of both metabolic and mood disorders.

The role of childhood trauma in the neurobiology of mood and anxiety disorders: preclinical and clinical studies

Epidemiologic studies indicate that children exposed to early adverse experiences are at increased risk for the development of depression, anxiety disorders, or both. Persistent sensitization of central nervous system (CNS) circuits as a consequence of early life stress, which are integrally involved in the regulation of stress and emotion, may represent the underlying biological substrate of an increased vulnerability to subsequent stress as well as to the development of depression and anxiety. A number of preclinical studies suggest that early life stress induces long-lived hyper(re)activity of corticotropin-releasing factor (CRF) systems as well as alterations in other neurotransmitter systems, resulting in increased stress responsiveness. Many of the findings from these preclinical studies are comparable to findings in adult patients with mood and anxiety disorders. Emerging evidence from clinical studies suggests that exposure to early life stress is associated with neurobiological changes in children and adults, which may underlie the increased risk of psychopathology. Current research is focused on strategies to prevent or reverse the detrimental effects of early life stress on the CNS. The identification of the neurobiological substrates of early adverse experience is of paramount importance for the development of novel treatments for children, adolescents, and adults.

Corticotropin-releasing hormone and animal models of anxiety: gene-environment interactions

The study of the neural substrates underlying stress and anxiety has in recent years been enriched by a burgeoning pool of genetic information gathered from rodent studies. Two general approaches have been used to characterize the interaction of genetic and environmental factors in stress regulation: the evaluation of stress-related behavioral and endocrine responses in animals with targeted deletion or overexpression of specific genes and the evaluation of changes in central nervous system gene expression in response to environmental perturbations. We review recent studies that have used molecular biology and genetic engineering techniques such as in situ hybridization, transgenic animal, and antisense oligonucleotide gene-targeting methodologies to characterize the function of corticotropin-releasing hormone (CRH) system genes in stress. The effects of genetic manipulations of each element of the CRH system (CRH, its two receptors, and its binding protein) on stress-related responses are summarized. In addition, the effects of stress (acute, repeated, or developmental) on CRH system gene expression are described. The results from these studies indicate that experimentally engineered or stress-induced dysregulation of gene expression within the CRH system is associated with aberrant responses to environmental contingencies. These results are discussed in the context of how CRH system dysfunction might contribute to stress-related psychopathology and are presented in conjunction with clinical findings of CRH system dysregulation in psychiatric illness. Finally, future research strategies (i.e., high-throughput gene screening and novel gene-targeting methodologies) that may be used to gain a fuller understanding of how CRH system gene expression affects stress-related functioning are discussed.