Glucocorticoid programming of pituitary-adrenal function: mechanisms and physiological consequences

Early life nutrient restriction affects hypothalamic-pituitary-interrenal axis gene expression in a diet type-specific manner

Stressful experiences in early life can alter phenotypic expression later in life. For instance, in vertebrates, early life nutrient restriction can modify later life activity of the hypothalamic-pituitary-adrenal/interrenal axis (the HPI in amphibians), including the up- and downstream regulatory components of glucocorticoid signaling. Early life nutrient restriction can also influence later life behavior and metabolism (e.g., fat accumulation). Yet, less is known about whether nutrient stress-induced carryover effects on HPA/HPI axis regulation can vary across environmental contexts, such as the type of diet on which nutrient restriction occurs. Here, we experimentally address this question using the plains spadefoot toad (Spea bombifrons), whose larvae develop in ephemeral habitats that impose intense competition over access to two qualitatively distinct diet types: detritus and live shrimp prey. Consistent with diet type-specific carryover effects of early life nutrient restriction on later life HPI axis regulation, we found that temporary nutrient restriction at the larval stage reduced juvenile (i.e., post-metamorphic) brain gene expression of an upstream glucocorticoid regulator (corticotropin-releasing hormone) and two downstream regulators (glucocorticoid and mineralocorticoid receptors) only on the shrimp diet. These patterns are consistent with known diet type-specific effects of larval nutrient restriction on juvenile corticosterone and behavior. Additionally, larval nutrient restriction increased juvenile body fat levels. Our study indicates that HPA/HPI axis regulatory responses to nutrient restriction can vary remarkably across diet types. Such diet type-specific regulation of the HPA/HPI axis might provide a basis for developmental or evolutionary decoupling of stress-induced carryover effects.

Egg-mediated maternal effects in a cooperatively breeding cichlid fish

Mothers can influence offspring phenotype through egg-mediated maternal effects, which can be influenced by cues mothers obtain from their environment during offspring production. Developing embryos use these components but have mechanisms to alter maternal signals. Here we aimed to understand the role of mothers and embryos in how maternal effects might shape offspring social phenotype. In the cooperatively breeding fish Neolamprologus pulcher different social phenotypes develop in large and small social groups differing in predation risk and social complexity. We manipulated the maternal social environment of N. pulcher females during egg laying by allocating them either to a small or a large social group. We compared egg mass and clutch size and the concentration of corticosteroid metabolites between social environments, and between fertilized and unfertilized eggs to investigate how embryos deal with maternal signalling. Mothers in small groups produced larger clutches but neither laid smaller eggs nor bestowed eggs differently with corticosteroids. Fertilized eggs scored lower on a principal component representing three corticosteroid metabolites, namely 11-deoxycortisol, cortisone, and 11-deoxycorticosterone. We did not detect egg-mediated maternal effects induced by the maternal social environment. We discuss that divergent social phenotypes induced by different group sizes may be triggered by own offspring experience.

Early-life manipulation of cortisol and its receptor alters stress axis programming and social competence

In many vertebrate species, early social experience generates long-term effects on later life social behaviour. These effects are accompanied by persistent modifications in the expression of genes implicated in the stress axis. It is unknown, however, whether stress axis programming can affect the development of social competence, and if so, by which mechanism(s). Here, we used pharmacological manipulations to persistently reprogramme the hypothalamic-pituitary-interrenal axis of juvenile cooperatively breeding cichlids, Neolamprologus pulcher. During the first two months of life, juveniles were repeatedly treated with cortisol, mifepristone or control treatments. Three months after the last manipulation, we tested for treatment effects on (i) social competence, (ii) the expression of genes coding for corticotropin-releasing factor ( crf), glucocorticoid receptor ( gr1) and mineralocorticoid receptor ( mr) in the telencephalon and hypothalamus and (iii) cortisol levels. Social competence in a social challenge was reduced in cortisol-treated juveniles, which is in accordance with previous work applying early-life manipulations using different social experiences. During early life, both cortisol and mifepristone treatments induced a persistent downregulation of crf and upregulation of mr in the telencephalon. We suggest that these persistent changes in stress gene expression may represent an effective physiological mechanism for coping with stress. This article is part of the theme issue 'Developing differences: early-life effects and evolutionary medicine'.

Fetal programming and early identification of newborns at high risk of free radical-mediated diseases

Nowadays metabolic syndrome represents a real outbreak affecting society. Paradoxically, pediatricians must feel involved in fighting this condition because of the latest evidences of developmental origins of adult diseases. Fetal programming occurs when the normal fetal development is disrupted by an abnormal insult applied to a critical point in intrauterine life. Placenta assumes a pivotal role in programming the fetal experience in utero due to the adaptive changes in structure and function. Pregnancy complications such as diabetes, intrauterine growth restriction, pre-eclampsia, and hypoxia are associated with placental dysfunction and programming. Many experimental studies have been conducted to explain the phenotypic consequences of fetal-placental perturbations that predispose to the genesis of metabolic syndrome, obesity, diabetes, hyperinsulinemia, hypertension, and cardiovascular disease in adulthood. In recent years, elucidating the mechanisms involved in such kind of process has become the challenge of scientific research. Oxidative stress may be the general underlying mechanism that links altered placental function to fetal programming. Maternal diabetes, prenatal hypoxic/ischaemic events, inflammatory/infective insults are specific triggers for an acute increase in free radicals generation. Early identification of fetuses and newborns at high risk of oxidative damage may be crucial to decrease infant and adult morbidity.

Epigenetic and transgenerational reprogramming of brain development

Neurodevelopmental programming - the implementation of the genetic and epigenetic blueprints that guide and coordinate normal brain development - requires tight regulation of transcriptional processes. During prenatal and postnatal time periods, epigenetic processes fine-tune neurodevelopment towards an end product that determines how an organism interacts with and responds to exposures and experiences throughout life. Epigenetic processes also have the ability to reprogramme the epigenome in response to environmental challenges, such as maternal stress, making the organism more or less adaptive depending on the future challenges presented. Epigenetic marks generated within germ cells as a result of environmental influences throughout life can also shape future generations long before conception occurs.

A chicken model of pharmacologically-induced Hirschsprung disease reveals an unexpected role of glucocorticoids in enteric aganglionosis

The enteric nervous system originates from neural crest cells that migrate in chains as they colonize the embryonic gut, eventually forming the myenteric and submucosal plexus. Failure of the neural crest cells to colonize the gut leads to aganglionosis in the terminal gut, a pathological condition called Hirschsprung disease (HSCR) in humans, also known as congenital megacolon or intestinal aganglionosis. One of the characteristics of the human HSCR is its variable penetrance, which may be attributable to the interaction between genetic factors, such as the endothelin-3/endothelin receptor B pathway, and non-genetic modulators, although the role of the latter has not well been established. We have created a novel HSCR model in the chick embryo allowing to test the ability of non-genetic modifiers to alter the HSCR phenotype. Chick embryos treated by phosphoramidon, which blocks the generation of endothelin-3, failed to develop enteric ganglia in the very distal bowel, characteristic of an HSCR-like phenotype. Administration of dexamethasone influenced the phenotype, suggesting that glucocorticoids may be environmental modulators of the penetrance of the aganglionosis in HSCR disease.

Disruption of fetal hormonal programming (prenatal stress) implicates shared risk for sex differences in depression and cardiovascular disease

Comorbidity of major depressive disorder (MDD) and cardiovascular disease (CVD) represents the fourth leading cause of morbidity and mortality worldwide, and women have a two times greater risk than men. Thus understanding the pathophysiology has widespread implications for attenuation and prevention of disease burden. We suggest that sex-dependent MDD-CVD comorbidity may result from alterations in fetal programming consequent to the prenatal maternal environments that produce excess glucocorticoids, which then drive sex-dependent developmental alterations of the fetal hypothalamic-pituitary-adrenal (HPA) axis circuitry impacting mood, stress regulation, autonomic nervous system (ANS), and the vasculature in adulthood. Evidence is consistent with the hypothesis that disruptions of pathways associated with gamma aminobutyric acid (GABA) in neuronal and vascular development and growth factors have critical roles in key developmental periods and adult responses to injury in heart and brain. Understanding the potential fetal origins of these sex differences will contribute to development of novel sex-dependent therapeutics.

Cortisol and depression: three questions for psychiatry

BACKGROUND

Cortisol plays a multifaceted role in major depression disorder (MDD). Diurnal rhythms are disturbed, there is increased resistance to the feedback action of glucocorticoids, excess cortisol may induce MDD, basal levels may be higher and the post-awakening cortisol surge accentuated in those at risk for MDD. Does this suggest new avenues for studying MDD or its clinical management?

METHOD

The relevant literature was reviewed.

RESULTS

Cortisol contributes to genetic variants for the risk for MDD and the way that environmental events amplify risk. The corticoids' influence begins prenatally, but continues into adulthood. The impact of cortisol at each phase depends not only on its interaction with other factors, such as psychological traits and genetic variants, but also on events that have, or have not, occurred previously.

CONCLUSIONS

This review suggests that the time is now right for serious consideration of the role of cortisol in a clinical context. Estimates of cortisol levels and the shape of the diurnal rhythm might well guide the understanding of subtypes of MDD and yield additional indicators for optimal treatment. Patients with disturbed cortisol rhythms might benefit from restitution of those rhythms; they may be distinct from those with more generally elevated levels, who might benefit from cortisol blockade. Higher levels of cortisol are a risk for subsequent depression. Should manipulation of cortisol or its receptors be considered as a preventive measure for some of those at very high risk of future MDD, or to reduce other cortisol-related consequences such as long-term cognitive decline?

Sex and steroid hormones in early brain injury

Brain injury during development can have severe, long-term consequences. Using an array of animal models, we have an understanding of the etiology of perinatal brain injury. However, we have only recently begun to address the consequences of endogenous factors such as genetic sex and developmental steroid hormone milieu. Our limited understanding has sometimes led researchers to make over-generalizing and potentially dangerous statements regarding treatment for brain injury. Therefore this review acts as a cautionary tale, speaking to our need to understand the effects of sex and steroid hormone environment on the response to brain trauma in the neonate.

Sex, hormones, and stress: how they impact development and function of the carotid bodies and related reflexes

Progesterone and corticosterone are key modulators of the respiratory control system. While progesterone is widely recognized as an important respiratory stimulant in adult and newborn animals, much remains to be described regarding the underlying mechanisms. We review the potential implication of nuclear and membrane progesterone receptors in adults and in newborns. This raises intriguing questions regarding the contribution of progesterone as a protective factor against some respiratory control disorders during early life. We then discuss our current understanding of the central integration of stressful stimuli and the responses they elicit. The fact that this system interacts with the respiratory control system, either because both share some common neural pathways in the brainstem and hypothalamus, or because corticosterone directly modulates the function of the respiratory control network, is a fascinating field of research that has emerged over the past few years. Finally, we review the short- and long-term consequences of disruption of stress circuitry during postnatal development on these systems.

Stress, glucocorticoids and liquorice in human pregnancy: programmers of the offspring brain

A suboptimal prenatal environment may induce permanent changes in cells, organs and physiology that alter social, emotional and cognitive functioning, and increase the risk of cardiometabolic and mental disorders in subsequent life ("developmental programming"). Although animal studies have provided a wealth of data on programming and its mechanisms, including on the role of stress and its glucocorticoid mediators, empirical evidence of these mechanisms in humans is still scanty. We review the existing human evidence on the effects of prenatal maternal stress, anxiety and depression, glucocorticoids and intake of liquorice (which inhibits the placental barrier to maternal glucocorticoids) on offspring developmental outcomes including, for instance, alterations in psychophysiological and neurocognitive functioning and mental health. This work lays the foundations for biomarker discovery and affords opportunities for prevention and interventions to ameliorate adverse outcomes in humans.

Reduced expression of MAPK/ERK genes in perinatal arsenic-exposed offspring induced by glucocorticoid receptor deficits

Changes within the glucocorticoid receptor (GR) cellular signaling pathway were evaluated in adolescent mice exposed to 50 ppb arsenic during gestation. Previously, we reported increased basal plasma corticosterone levels, decreased hippocampal GR levels and deficits in learning and memory performance in perinatal arsenic-exposed mice. The biosynthesis of members of the mitogen-activated protein kinase (MAPK) signaling pathway, known to be involved in learning and memory, is modulated by the binding of GR to glucocorticoid response elements (GREs) in the gene promoters. Two genes of the MAPK pathway, Ras and Raf, contain GREs which are activated upon binding of GRs. We evaluated the activity of GRs at Ras and Raf promoters using chromatin immunoprecipitation and real-time PCR and report decreased binding of the GR at these promoters. An ELISA-based GR binding assay was used to explore whether this decreased binding was restricted to in vivo promoters and revealed no differences in binding of native GR to synthetic GREs. The decreased in vivo GR binding coincides with significantly decreased mRNA levels and slight reductions of protein of both H-Ras and Raf-1 in perinatally arsenic-exposed mice. Nuclear activated extracellular-signal regulated kinase (ERK), a downstream target of Ras and Raf, whose transcriptional targets also play an important role in learning and memory, was decreased in the hippocampus of arsenic-exposed animals when compared to controls. GR-mediated transcriptional deficits in the MAPK/ERK pathway could be an underlying cause of previously reported learning deficits and provide the link to arsenic-induced deficiencies in cognitive development.

Glucocorticoid receptor gene haplotypes are not associated with birth anthropometry, blood pressure, glucose and insulin concentrations, and body composition in subjects born small for gestational age

OBJECTIVE

Smaller size at birth has been associated with an increased risk of metabolic and cardiovascular disorders in adult life. Fetal programming of the hypothalamic-pituitary-adrenal axis has been suggested as a possible explanation. Fetal glucocorticoid (GC) overexposure has effects that suggest a role of GCs in this programming. The effects of GCs are mediated through the GC receptor (GR or NR3C1). Several functional polymorphisms have been described, which are associated with relative GC resistance or hypersensitivity. Our aim is to compare frequencies of GR haplotypes, characterized by the R23K, N363S, Bcl1, or 9β polymorphisms, in subjects born small for gestational age (SGA) and associate birth anthropometry data, response to GH treatment, blood pressure, glucose and insulin concentrations, and body composition with these haplotypes.

DESIGN

In total, 418 SGA subjects and 697 healthy controls were enrolled in this study. Methods Anthropometry data were obtained, as well as blood samples to determine fasting glucose and insulin concentrations. Dual energy X-ray absorptiometry scans were used to measure the amount of fat and lean mass.

RESULTS

No differences were found between GR haplotype frequencies in SGA children compared with healthy controls. No associations were found between GR haplotypes and birth length and birth weight, growth response during GH treatment, blood pressure, glucose and insulin concentrations, and body composition.

CONCLUSION

GR haplotypes and their effect on GC sensitivity do not seem to play a significant role in GH-induced catch-up growth and the risk factors of developing metabolic and cardiovascular disorders in adult life of SGA children.

Post-natal stress-induced endocrine and metabolic alterations in mice at adulthood involve different pro-opiomelanocortin-derived peptides

In previous investigations we added a physical stress (mild pain) to the "classical" post-natal psychological stress in male mice, and we found that this combination produced a series of dysmetabolic signs very similar to mild human type-2 diabetes. Here, for the first time we demonstrate that within this diabetes model at least two groups of signs depend on the unbalance of two different endogenous systems. Newborn male mice were daily exposed to stressful procedures for 21 days (brief mother separation plus sham injection). Other groups underwent the same procedure, and also received naloxone (Na) to block μ-δ endogenous receptors, or a phosphorothioate antisense oligonucleotide (AS) directed against pro-opiomelanocortin (POMC)-mRNA [to block adrenocorticotropin (ACTH)- and POMC-derived opioid peptides]. Adult mice which received only post-natal stress increased body weight (+7.5%), abdominal overweight (+74%), fasting glycemia (+43%), plasma corticosterone (+110%), plasma (+169%) and pituitary (+153%) ACTH levels. Conversely, hypothalamic ACTH and corticotropin-releasing hormone (CRH) were reduced (-70% and -75%, respectively). Neonatal AS administration reverted all parameters to control values. Neonatal naloxone had little or no influence on glucose, corticosterone, ACTH, CRH levels, whereas it prevented body overweight and abdominal overweight. We conclude that, within this type-2 diabetes model in male mice at least two endocrino-neurohumoral systems are damaged, one concerning the opioid system, and the other concerning HPA hormones. The use of the two drugs was of primary importance to demonstrate this statement, and to demonstrate that these two groups of signs could be defined as "separate entities" following our complex post-natal stress model.

Role of fetal programming in the development of hypertension

Epidemiological studies have suggested that size at birth contributes to increased cardiovascular disease (CVD) risk in later life. Findings from experimental studies are providing insight into the mechanisms linking impaired fetal growth and the increased risk of CVD and hypertension in adulthood. This article summarizes potential mechanisms involved in the fetal programming of hypertension and CVD, including alterations in the organs and regulatory systems critical to long-term control of sodium and volume homeostasis.

Prenatal origins of poor sleep in children

STUDY OBJECTIVES

We examined whether small body size at birth and prenatal tobacco or alcohol exposure predict poor sleep and more sleep disturbances in children.

DESIGN

An epidemiologic cohort study of 289 eight-year-old children born at term.

MEASUREMENTS AND RESULTS

Sleep duration and efficiency were measured by actigraphy for 7 consecutive nights (mean = 7.1, SD = 1.2). We used both continuous measures of poor sleep and binary variables of short sleep and low sleep efficiency ( < or = 10th percentiles). Parents completed the Sleep Disturbance Scale for Children. Lower birth weight and shorter length at birth were associated with lower sleep efficiency. For every 1-SD decrease in weight and length at birth, the odds for low sleep efficiency increased by 1.7 fold (95% confidence interval [CI]: 1.1 to 2.7) and 2.2 fold (95% CI: 1.3 to 3.7), respectively. For every 1-SD decrease in ponderal index at birth, the risk of parent-reported sleep disorders increased by 1.4 fold (95% CI: 1.0 to 2.0). Moreover, children exposed prenatally to alcohol had a 2.9-fold (95% CI: 1.1 to 7.6) and 3.6-fold (95% CI: 1.3 to 10.0) increased risk for having short sleep and low sleep efficiency, respectively. The associations were not confounded by sex, gestational length, prenatal and perinatal complications, body mass index at 8 years, asthma, allergies, or parental socioeconomic status.

CONCLUSIONS

Poor sleep in children may have prenatal origins. Possible mechanisms include alcohol consumption during pregnancy and other conditions associated with small body size at birth.

Cell-cell signaling drives the evolution of complex traits: introduction-lung evo-devo

Physiology integrates biology with the environment through cell–cell interactions at multiple levels. The evolution of the respiratory system has been “deconvoluted” (Torday and Rehan in Am J Respir Cell Mol Biol 31:8–12, 2004) through Gene Regulatory Networks (GRNs) applied to cell–cell communication for all aspects of lung biology development, homeostasis, regeneration, and aging. Using this approach, we have predicted the phenotypic consequences of failed signaling for lung development, homeostasis, and regeneration based on evolutionary principles. This cell–cell communication model predicts other aspects of vertebrate physiology as adaptational responses. For example, the oxygen-induced differentiation of alveolar myocytes into alveolar adipocytes was critical for the evolution of the lung in land dwelling animals adapting to fluctuating Phanarezoic oxygen levels over the past 500 million years. Adipocytes prevent lung injury due to oxygen radicals and facilitate the rise of endothermy. In addition, they produce the class I cytokine leptin, which augments pulmonary surfactant activity and alveolar surface area, increasing selection pressure for both respiratory oxygenation and metabolic demand initially constrained by high-systemic vascular pressure, but subsequently compensated by the evolution of the adrenomedullary beta-adrenergic receptor mechanism. Conserted positive selection for the lung and adrenals created further selection pressure for the heart, which becomes progressively more complex phylogenetically in tandem with the lung. Developmentally, increasing heart complexity and size impinges precociously on the gut mesoderm to induce the liver. That evolutionary-developmental interaction is significant because the liver provides regulated sources of glucose and glycogen to the evolving physiologic system, which is necessary for the evolution of the neocortex. Evolution of neocortical control furthers integration of physiologic systems. Such an evolutionary vertical integration of cell-to-tissue-to-organ-to-physiology of intrinsic cell–cell signaling and extrinsic factors is the reverse of the “top-down” conventional way in which physiologic systems are usually regarded. This novel mechanistic approach, incorporating a “middle-out” cell–cell signaling component, will lead to a readily available algorithm for integrating genes and phenotypes. This symposium surveyed the phylogenetic origins of such vertically integrated mechanisms for the evolution of cell–cell communication as the basis for complex physiologic traits, from sponges to man.

Prenatal stress or high-fat diet increases susceptibility to diet-induced obesity in rat offspring

OBJECTIVE

Perturbations to the prenatal environment have been associated with the development of adult chronic disease, findings that gave rise to the "Barker Hypothesis" or the "developmental origins of adult disease" concept. In this study, we used an animal model to determine the metabolic consequences of maternal prenatal stress and high-fat feeding on the developing offspring.

RESEARCH DESIGN AND METHODS

Pregnant female Sprague-Dawley rats were maintained on standard chow or 60% high-fat diet throughout gestation and lactation. Half of each group were exposed to a novel variable stress paradigm during the 3rd week of gestation, whereas control dams were left undisturbed. Body weight, body composition, glucose tolerance, and endocrine parameters were measured in offspring through early adulthood.

RESULTS

Male and female pups from dams that experienced prenatal stress and/or were on a high-fat diet weighed more beginning on postnatal day 7 compared with standard chow-control pups. Access to high-fat diet at weaning increased the body weight effect through early adulthood and was attributable to greater adiposity. Pups weaned onto standard chow diet showed no significant difference in glucose clearance or insulin secretion. However, pups weaned onto high-fat diet had impaired glucose tolerance if their dams were on a high-fat diet, experienced prenatal stress, or both.

CONCLUSIONS

Our data demonstrate that prenatal stress and/or high-fat diet during the intrauterine or postnatal environment affects offspring in a manner that increases their susceptibility to diet-induced obesity and leads to secondary adverse metabolic consequences.

Programming neuroendocrine stress axis activity by exposure to glucocorticoids during postembryonic development of the frog, Xenopus laevis

Exposure to elevated glucocorticoids during early mammalian development can have profound, long-term consequences for health and disease. However, it is not known whether such actions occur in nonmammalian species, and if they do, whether the molecular physiological mechanisms are evolutionarily conserved. We investigated the effects of dietary restriction, which elevates endogenous corticosterone (CORT), or exposure to exogenous CORT added to the aquarium water of Xenopus laevis tadpoles on later-life measures of growth, feeding behavior, and neuroendocrine stress axis activity. Dietary restriction of prometamorphic tadpoles reduced body size at metamorphosis, but juvenile frogs increased food intake, showed catch-up growth through 21 d after metamorphosis, and had elevated whole-body CORT content compared with controls. Dietary restriction causes increased CORT in tadpoles, so to mimic this increase, we treated tadpoles with 100 nm CORT or vehicle for 5 or 10 d and then reared juvenile frogs to 2 months after metamorphosis. Treatment with CORT decreased body weight at metamorphosis, but juvenile frogs showed catch-up growth and had elevated basal plasma (CORT). Immunohistochemical analysis showed that CORT exposure as a tadpole led to decreased glucocorticoid receptor immunoreactivity in brain regions involved with stress axis regulation and in the anterior pituitary gland of juvenile frogs. The elevated CORT in juvenile frogs, which could result from decreased negative feedback owing to down-regulation of glucocorticoid receptor, may drive the hyperphagic response. Taken together, our findings suggest that long-term, stable phenotypic changes in response to elevated glucocorticoids early in life are an ancient and conserved feature of the vertebrate lineage.

Dysfunctional nurturing behavior in rat dams with limited access to nesting material: a clinically relevant model for early-life stress

BACKGROUND

Early-life emotional stress may be associated with affective and cognitive disorders later in life, yet satisfactory animal models for studying the underlying mechanisms are limited. Because maternal presence and behavior critically influence molecular and behavioral stress responses in offspring, we sought to create a model of dysfunctional, fragmented maternal nurturing behavior that would, in turn, provoke chronic early-life stress in the offspring.

METHODS

Sprague-Dawley rat dams' nursing and nurturing behaviors were altered by limiting their ability to create satisfactory nests during postpartum days 2-9. Maternal behavior was observed throughout the diurnal cycle, and the frequency and duration of nurturing behaviors were scored. In addition, potential stress and anxiety of the dams were assessed using behavioral, molecular and hormonal measures.

RESULTS

Both the quantity and the quality of dams' care of their pups were profoundly influenced by restriction of nesting materials in their cages: licking/grooming activities decreased and the frequency of leaving the pups increased, resulting in fragmented interactions between the dams and pups. The abnormal activity patterns of the dams were accompanied by increased anxiety-like behavior in the open field, but not in the elevated plus maze tests. Additionally, dams' plasma corticosterone levels and adrenal weights were augmented, suggesting chronic stress of these dams. By the end of the limited-nesting, stress-inducing period, hypothalamic corticotropin releasing hormone (CRH) mRNA expression was reduced in the limited-nesting dams, while arginine-vasopressin (AVP) mRNA levels were not significantly affected.

CONCLUSION

Limiting dams' ability to construct a nest for their pups leads to an abnormal repertoire of nurturing behaviors, possibly as a result of chronic stress and mild anxiety of the dams. Because the fragmented and aberrant maternal behavior provoked chronic stress in the pups, the limited-nesting paradigm provides a useful tool for studying the mechanisms and consequences of such early-life stress experience in the offspring.

Early life programming of obesity and metabolic disease

It is becoming increasingly apparent that conditions experienced in early life play an important role in the long-term health of individuals. Alterations in development due to impaired, excessive or imbalanced growth, both in utero and during critical periods of relative plasticity beyond birth, can lead to the permanent programming of physiological systems. The regulation of energy balance is one area that is receiving particular attention, as rates of obesity and associated metabolic and cardiovascular disease continue to rise. Over recent decades, much progress has been made toward understanding the way in which metabolic tissues and physiological systems develop, and the impact of early life events and nutrition on these processes. It is apparent within human populations that some individuals are better able to maintain an appropriate body weight in the face of an obesogenic environment. Animal models have been widely used for the investigation of differential susceptibility to diet-induced obesity (DIO) and impaired energy balance regulation, and are shedding light on key pathways that may be involved. Alterations in pathways mediating energy homeostasis, outlined below, are likely candidates for programming effects following disturbed growth in early life.

Increased hypothalamic-pituitary-adrenal axis activity and hepatic insulin resistance in low-birth-weight rats

Individuals born with a low birth weight (LBW) have an increased prevalence of type 2 diabetes, but the mechanisms responsible for this association are unknown. Given the important role of insulin resistance in the pathogenesis of type 2 diabetes, we examined insulin sensitivity in a rat model of LBW due to intrauterine fetal stress. During the last 7 days of gestation, rat dams were treated with dexamethasone and insulin sensitivity was assessed in the LBW offspring by a hyperinsulinemic euglycemic clamp. The LBW group had liver-specific insulin resistance associated with increased levels of PEPCK expression. These changes were associated with pituitary hyperplasia of the ACTH-secreting cells, increased morning plasma ACTH concentrations, elevated corticosterone secretion during restraint stress, and an approximately 70% increase in 24-h urine corticosterone excretion. These data support the hypothesis that prenatal stress can result in chronic hyperactivity of the hypothalamic-pituitary-adrenal axis, resulting in increased plasma corticosterone concentrations, upregulation of hepatic gluconeogenesis, and hepatic insulin resistance.

Prenatal dexamethasone exposure induces changes in nonhuman primate offspring cardiometabolic and hypothalamic-pituitary-adrenal axis function

Prenatal stress or glucocorticoid administration has persisting "programming" effects on offspring in rodents and other model species. Multiple doses of glucocorticoids are in widespread use in obstetric practice. To examine the clinical relevance of glucocorticoid programming, we gave 50, 120, or 200 microg/kg/d of dexamethasone (dex50, dex120, or dex200) orally from mid-term to a singleton-bearing nonhuman primate, Chlorocebus aethiops (African vervet). Dexamethasone dose-dependently reduced maternal cortisol levels without effecting maternal blood pressure, glucose, electrolytes, or weight gain. Birth weight was unaffected by any dexamethasone dose, although postnatal growth was attenuated after dex120 and dex200. At 8 months of age, dex120 and dex200 offspring showed impaired glucose tolerance and hyperinsulinemia, with reduced (approximately 25%) pancreatic beta cell number at 12 months. Dex120 and dex200 offspring had increased systolic and diastolic blood pressures at 12 months. Mild stress produced an exaggerated cortisol response in dex200 offspring, implying hypothalamic-pituitary-adrenal axis programming. The data are compatible with the extrapolation of the glucocorticoid programming hypothesis to primates and indicate that repeated glucocorticoid therapy and perhaps chronic stress in humans may have long-term effects.

Fetal programming of temperamental negative affectivity among children born healthy at term

The fetal programming hypothesis suggests that an adverse in utero environment, reflected in small body size at birth, has life-long effects on different physiological systems that may affect both health and behavior. We explored whether fetal growth was associated with biologically based temperamental outcomes (negative affectivity scales, the CBQ) among 5(1/2)-year-old children (n = 416) born healthy at term (gestational weeks 37-42). In line with the hypotheses, small body size at birth (thinness measured by ponderal index, kg/m(3)) was related to increased negative affectivity and its subscales: anger-, discomfort-, and sadness-proneness in childhood. Longer length at birth was predictive of higher levels of child anger- and sadness-proneness. Length of gestation moderated the associations of weight and length at birth with negative affectivity. The results suggest that the biological basis of temperament may be subjected to antenatal environmental influences, and that the mechanisms, proposed to be related to fetal glucocorticoid environment, may operate even within the normal range of term birth.

Early life events and their consequences for later disease: a life history and evolutionary perspective

Biomedical science has little considered the relevance of life history theory and evolutionary and ecological developmental biology to clinical medicine. However, the observations that early life influences can alter later disease risk--the "developmental origins of health and disease" (DOHaD) paradigm--have led to a recognition that these perspectives can inform our understanding of human biology. We propose that the DOHaD phenomenon can be considered as a subset of the broader processes of developmental plasticity by which organisms adapt to their environment during their life course. Such adaptive processes allow genotypic variation to be preserved through transient environmental changes. Cues for plasticity operate particularly during early development; they may affect a single organ or system, but generally they induce integrated adjustments in the mature phenotype, a process underpinned by epigenetic mechanisms and influenced by prediction of the mature environment. In mammals, an adverse intrauterine environment results in an integrated suite of responses, suggesting the involvement of a few key regulatory genes, that resets the developmental trajectory in expectation of poor postnatal conditions. Mismatch between the anticipated and the actual mature environment exposes the organism to risk of adverse consequences-the greater the mismatch, the greater the risk. For humans, prediction is inaccurate for many individuals because of changes in the postnatal environment toward energy-dense nutrition and low energy expenditure, contributing to the epidemic of chronic noncommunicable disease. This view of human disease from the perspectives of life history biology and evolutionary theory offers new approaches to prevention, diagnosis and intervention.

Transgenerational transmission of cortisol and PTSD risk

Parental posttraumatic stress disorder (PTSD) appears to be a relevant risk factor for the development of PTSD, as evidenced by a greater prevalence of PTSD, but not trauma exposure, in adult offspring of Holocaust survivors with PTSD, compared to children of Holocaust-exposed parents without PTSD. This paper summarizes recent neuroendocrine studies in offspring of parents with PTSD. Offspring of trauma survivors with PTSD show significantly lower 24-h mean urinary cortisol excretion and salivary cortisol levels as well as enhanced plasma cortisol suppression in response to low dose dexamethasone administration than offspring of survivors without PTSD. In all cases, neuroendocrine measures were negatively correlated with severity of parental PTSD symptoms, even after controlling for PTSD and even other symptoms in offspring. Though the majority of our work has focused on adult offspring of Holocaust survivors, recent observations in infants born to mothers who were pregnant on 9/11 demonstrate that low cortisol in relation to parental PTSD appears to be present early in the course of development and may be influenced by in utero factors such as glucocorticoid programming. Since low cortisol levels are particularly associated with the presence of maternal PTSD the findings suggest the involvement of epigenetic mechanisms.

Perinatal maternal undernutrition programs the offspring hypothalamo-pituitary-adrenal (HPA) axis

There is now compelling evidence, coming both from animal and human studies that an early exposure to undernutrition is frequently associated with low birth weight and programs HPA axis alterations throughout the lifespan. Although animal models have reported conflicting findings arising from differences in experimental paradigms and species, they have clearly demonstrated that such programming not only affects the brain but also the pituitary corticotrophs and the adrenal cortex. In fetuses, maternal undernutrition reduces HPA axis function and implicates a reduction of placental 11beta-HSD2 activity and a greater transplacental transfer of glucocorticoids (GRs). In young adults, usually only fine HPA axis alterations were observed, whereas in older ones, maternal undernutrition was frequently associated with chronic hyperactivity of this neuroendocrine axis. In humans, evidence of HPA axis dysregulation in people who were small at birth has recently emerged. Thus, we suggest that such alterations in adults may be implicated in the aetiology of several disorders related to the metabolic syndrome as well as to immune or inflammatory diseases. To reverse such programming, recent experimental reports have shown that postnatal environmental interventions, dietary modifications and the use of agents modulating the epigenomic state could partly restore physiological functions and thus open new therapeutic strategies.

A relative resistance of T cells to dexamethasone in bipolar disorder

OBJECTIVE

A relative resistance of immune cells to steroids has been established in patients with major depression (MD). In this study, we investigated the in vitro responsiveness of T cells to dexamethasone (DEX) of patients with bipolar disorder (BD).

METHODS

T cells of outpatients with DSM-IV BD (n = 54) and of healthy control subjects (HC; n = 29) were isolated, cultured and stimulated with phytohemagglutinin (PHA) for 72 h. The suppressive effect of graded concentrations of DEX (5 x 10(-9)-10(-5) M) on PHA-induced CD25 (IL-2R) expression was measured by fluorescence-activated cell sorting (FACS) analysis. Data were correlated to the T-cell activation status in the peripheral blood of the same patients and to their diagnosis, current mood state, ultradian cycling pattern and current use of medication, including lithium.

RESULTS

T cells of patients with BD were less sensitive to DEX-induced suppressive effects as compared with T cells of HC. These data were particularly evident at 10(-7) M DEX (mean % suppression +/- SEM BD: 18.9% +/- 3.5 versus HC: 35.8% +/- 4.7, p = 0.001). We found no correlations of this relative in vitro DEX resistance of T cells neither with the previously mentioned clinical characteristics nor with the actual activation status of the T cells in the BD patients.

CONCLUSION

A relative T-cell resistance to steroids, as has been observed in MD previously, may be a trait phenomenon of BD, independent of mood state.

Adiposity in children born small for gestational age

Epidemiological studies indicate that children born small for gestational age (SGA) have an increased risk of metabolic and cardiovascular disorders as adults. This suggests that foetal undernutrition leads to permanent metabolic alterations, which predispose to metabolic abnormalities upon exposure to environmental factors such as low physical activity and/or high-energy intake in later life (thrifty phenotype hypothesis). However, this relationship is not restricted to foetal undernutrition or intrauterine growth retardation, but is also found for children born premature, or for high birth weight children. Furthermore, early post-natal nutrition, and more specifically catch-up growth, appear to modulate cardiovascular risk as well. Intrauterine growth retardation can be induced in animal models by energy/protein restriction, or ligation of uterine arteries. In such models, altered glucose homeostasis, including low beta-cell mass, low insulin secretion and insulin resistance is observed after a few weeks of age. In humans, several studies have confirmed that children born SGA have insulin resistance as adolescents and young adults. Alterations of glucose homeostasis and increased lipid oxidation can indeed be observed already in non-diabetic children born SGA at early pubertal stages. These children also have alterations of stature and changes in body composition (increased fat mass), which may contribute to the pathogenesis of insulin resistance. Permanent metabolic changes induced by foetal/early neonatal nutrition (metabolic inprinting) may involve modulation of gene expression through DNA methylation, or alterations of organ structure. It is also possible that events occurring during foetal/neonatal development lead to long-lasting alterations of the hypothalamo-pituitary-adrenal axis or the hypothalamo-pituitary-insulin-like growth factor-1 axis.

Administration of antisense oligonucleotide against pro-opiomelanocortin prevents enduring hormonal alterations induced by neonatal handling in male mice

Early life events have been implicated in the programming of adult chronic diseases. Several investigations suggest that the role of early environment in influencing development mainly involves the hypothalamic-pituitary-adrenal axis. Therefore, we examined whether 1) daily neonatal handling, applied from birth to weaning induces HPA hormones alterations in mice lasting up to the adult age; and 2) if the administration of an antisense oligodeoxynucleotide versus pro-opiomelanocortin (As-POMC) prevents hormonal alterations observed in previously handled mice (Handled). In the adult phase (90 days), Handled are overweight and have higher basal plasma immuno-reactive (ir)-corticosterone and adrenocorticotropin (ir-ACTH), and higher pituitary ir-ACTH; while they have lower hypothalamic ir-ACTH and corticotropin-releasing hormone (ir-CRH) in comparison with the non-handled mice. As-POMC (0.05-0.1 nmol/g body weight per day) administered during the same period dose-dependently prevents the increase in body weight, in plasma ir-corticosterone, ir-ACTH, and pituitary ir-ACTH, also preventing the decrease in hypothalamic ir-CRH and ir-ACTH; while the mismatch oligonucleotide is nearly inactive. This data indicates that pharmacological treatment in neonatal life may have enduring effects, reducing the alterations in hormonal homeostatic programming mechanisms induced by early repeated handling.

Prenatal exposure to interleukin-6 results in hypertension and alterations in the renin-angiotensin system of the rat

Cytokines are emerging as important in developmental processes. They may induce alterations in normal gene expression patterns, activate angiotensinogen transcription, or alter expression of the renin-angiotensin system (RAS). To determine whether prenatal exposure to interleukin-6 (IL-6) influences gene expression of the intrarenal RAS and contributes to renal dysfunction and hypertension in adulthood, we exposed female rats to IL-6 early (EIL-6 females) and late (LIL-6 females) in pregnancy and analysed blood pressure in the offspring at 5-20 weeks of age. Renal fluid and electrolyte excretion was assessed in clearance experiments, mRNA expression by real-time PCR, and protein levels by Western blot. Systolic pressure was increased at 5 weeks in IL-6 females and at 11 weeks in males. Circulatory RAS levels were increased in all IL-6 females, but angiotensin-1-converting enzyme (ACE) activity was increased only in LIL-6 females. LIL-6 males and IL-6 females showed decreased urinary flow rate and urinary sodium and potassium excretion. Dopamine excretion was decreased IL-6 females. In adult renal cortex, renin expression was increased in all IL-6 females, but angiotensinogen mRNA was increased only in LIL-6 females; AT(1) receptor (AT(1)-R) mRNA and protein levels were increased in LIL-6 females, whereas AT(2) receptor (AT(2)-R) levels were decreased in LIL-6 females and EIL-6 males. In adult renal medulla, AT(1)-R protein levels were increased in LIL-6 females, and AT(2)-R mRNA and protein levels were decreased in EIL-6 males and LIL-6 females. Prenatal IL-6 exposure may cause hypertension by altering the renal and circulatory RAS and renal fluid and electrolyte excretion, especially in females.

Activation of the hypothalamic-pituitary-adrenal axis and autonomic nervous system during inflammation and altered programming of the neuroendocrine-immune axis during fetal and neonatal development: lessons learned from the model inflammagen, lipopolysaccharide

The hypothalamic-pituitary-adrenal axis (HPAA) and autonomic nervous system (ANS) are both activated during inflammation as an elaborate multi-directional communication pathway designed to restore homeostasis, in part, by regulating the inflammatory and subsequent immune response. During fetal and neonatal development programming of the HPAA, ANS and possibly the immune system is influenced by signals from the surrounding environment, as part of an adaptive mechanism to enhance the survival of the offspring. It is currently hypothesized that if this programming is either misguided, or the individual's environment is drastically altered such that neuroendocrine programming becomes maladaptive, it may contribute to the pathogenesis of certain diseases. Current research, suggests that exposure to inflammatory signals during critical windows of early life development may influence the programming of various genes within the neuroendocrine-immune axis. This review will provide, (1) an overview of the HPAA and ANS pathways that are activated during inflammation, highlighting studies that have used lipopolysaccharide as a model inflammagen and, (2) evidence to support the hypothesis that inflammatory stress during fetal and neonatal development can alter programming of the neuroendocrine-immune axis, influencing stress and immune responsiveness, and possibly disease resistance later in life.

Glucocorticoid exposure in preterm babies predicts saliva cortisol response to immunization at 4 months

Preterm babies are exposed to multiple stressors and this may have long-term effects. In particular, high levels of endogenous cortisol might have a programming effect on the hypothalamic-pituitary-adrenal axis as may administered glucocorticoids. In this study, we aimed to test the hypothesis that the level of endogenous and exogenous glucocorticoid exposure during the neonatal period predicts the saliva cortisol response to immunization at 4 mo of age. We followed 45 babies born below 32 wk gestation. We showed that their concentration of plasma cortisol during the first 4 wk was 358, 314, 231, and 195 nmol/L cortisol, respectively (geometric mean). This is four to seven times higher than fetal levels at the same gestational age range. We used routine immunization at 4 mo and 12 mo as a stressor and measured the change in saliva cortisol as the stress response. Mean circulating cortisol in the first 4 wk predicted the cortisol response at 4 but not at 12 mo. Path analysis showed that birthweight for gestational age, therapeutic antenatal steroids, and therapeutic postnatal steroids also contributed to the magnitude of the saliva cortisol response at 4 mo. This provides evidence that the magnitude of glucocorticoid exposure, both endogenous and exogenous, may have an effect on later stress responses.

Neonatal maternal separation and early life programming of the hypoxic ventilatory response in rats

The neonatal period is critical for central nervous system (CNS) development. Recent studies have shown that this basic neurobiological principle also applies to the neural circuits regulating respiratory activity as exposure to excessive or insufficient chemosensory stimuli during early life can have long-lasting consequences on the performance of this vital system. Although the tactile, olfactory, and auditory stimuli that the mother provides to her offspring during the neonatal period are not directly relevant to respiratory homeostasis, they likely contribute to respiratory control development. This review outlines the rationale for the link between maternal stimuli and programming of the hypoxic ventilatory response during early life, and presents recent results obtained in rats indicating that experimental disruption of mother-pup interaction during this critical period elicits significant phenotypic plasticity of the hypoxic ventilatory response.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

Fetal plasma testosterone correlates positively with cortisol

BACKGROUND

Fetal exposure to testosterone has been implicated in programming childhood behaviour, but little is known about the determinants of fetal testosterone concentrations.

AIMS

To investigate the relation between fetal testosterone and maternal and fetal cortisol.

METHODS

Clinically indicated blood samples taken from 44 human fetuses (mean gestational age 27 weeks, range 15-38), together with paired maternal samples, were analysed for testosterone and cortisol concentrations.

RESULTS

Male fetuses had significantly higher concentrations of testosterone than females. Female but not male fetal concentrations rose significantly with gestational age. Fetal testosterone correlated positively with both fetal cortisol and maternal testosterone concentrations. Multiple regression showed that maternal testosterone and fetal cortisol were independently correlated with fetal plasma testosterone in both sexes.

CONCLUSION

Unlike the norm in the adult, where testosterone production is often inhibited by cortisol, in the fetus there is a positive link between the two.

The Embryo and Its Future1

The preimplantation mammalian embryo from different species appears sensitive to the environment in which it develops, either in vitro or in vivo, for example, in response to culture conditions or maternal diet. This sensitivity may lead to long-term alterations in the characteristics of fetal and/or postnatal growth and phenotype, which have implications for clinical health and biotechnological applications. We review the breadth of environmental influences that may affect early embryos and their responses to such conditions along epigenetic, metabolic, cellular, and physiological directions. In addition, we evaluate how embryo environmental responses may influence developmental potential and phenotype during later gestation. We conclude that a complex of different mechanisms may operate to associate early embryo environment with future health.

Programming of the hypothalamo-pituitary-adrenal axis: serotonergic involvement

The ability of the early environment to programme the developing hypothalamo-pituitary-adrenal (HPA) axis has been reported in several animal species. There is considerable evidence that a similar process can occur in the human, and that long-term alterations in HPA function are associated with altered susceptibility to disease in later life. The phenotype of HPA function following early manipulation depends on the timing and intensity of the manipulation as well as the gender of the fetus/neonate. There is considerable interplay between the developing HPA and the reproductive axes and emerging evidence indicates that this interaction is modified by early environmental manipulation. Studies are rapidly unravelling the mechanisms that underlie developmental programming of the HPA axis. In this context, the serotonergic system has been identified as a primary system involved in this process. Understanding the mechanisms involved in neuroendocrine programming will facilitate the development of interventions aimed at reversing or ameliorating the impact of an adverse intrauterine environment.

Neonatal maternal separation and sex-specific plasticity of the hypoxic ventilatory response in awake rat

We tested the hypothesis that neonatal maternal separation (NMS), a form of stress that affects hypothalamo-pituitary-adrenal axis (HPA) function in adult rats, alters development of the respiratory control system. Pups subjected to NMS were placed in a temperature and humidity controlled incubator 3 h per day for 10 consecutive days (P3 to P12). Control pups were undisturbed. Once they reached adulthood (8-10 weeks old), rats were placed in a plethysmography chamber for measurement of ventilatory and cardiovascular parameters under normoxic and hypoxic conditions. Measurement of c-fos mRNA expression in the paraventricular nucleus of the hypothalamus (PVH) combined with plasma ACTH and corticosterone levels confirmed that NMS effectively disrupted HPA axis function in males. In males, baseline minute ventilation was not affected by NMS. In contrast, NMS females show a greater resting minute ventilation due to a larger tidal volume. The hypoxic ventilatory response of male NMS rats was 25% greater than controls, owing mainly to an increase in tidal volume response. This augmentation of the hypoxic ventilatory response was sex-specific also because NMS females show an attenuated minute ventilation increase. Baseline mean arterial blood pressure of male NMS rats was 20% higher than controls. NMS-related hypertension was not significant in females. The mechanisms underlying sex-specific disruption of cardio-respiratory control in NMS rats are unknown but may be a consequence of the neuroendocrine disruption associated with NMS. These data indicate that exposure to a non-respiratory stress during early life elicits significant plasticity of these homeostatic functions which persists until adulthood.

Society for Reproductive Biology Founders' Lecture 2003.The making of an embryo: short-term goals and long-term implications

During early development, the eutherian mammalian embryo forms a blastocyst comprising an outer trophectoderm epithelium and enclosed inner cell mass (ICM). The short-term goal of blastocyst morphogenesis, including epithelial differentiation and segregation of the ICM, is mainly regulated autonomously and comprises a combination of temporally controlled gene expression, cell polarisation, differentiative cell divisions and cell–cell interactions. This aspect of blastocyst biogenesis is reviewed, focusing, in particular, on the maturation and role of cell adhesion systems. Early embryos are also sensitive to their environment, which can affect their developmental potential in diverse ways and may lead to long-term consequences relating to fetal or postnatal growth and physiology. Some current concepts of embryo–environment interactions, which may impact on future health, are also reviewed.

Sexually dimorphic effects of maternal alcohol intake and adrenalectomy on left ventricular hypertrophy in rat offspring

In humans, low birth weight and increased placental weight can be associated with cardiovascular disease in adulthood. Low birth weight and increased placental size are known to occur after fetal alcohol exposure or prenatal glucocorticoid administration. Thus the effects of removing the alcohol-induced increase in maternal corticosterone by maternal adrenalectomy on predictors of cardiovascular disease in adulthood were examined in rats. Alcohol exposure of dams during the last 2 wk of gestation resulted in significantly decreased fetal weight and increased placental weight on gestational day 21. Adult female, but not male, offspring of alcohol-consuming mothers exhibited left ventricular hypertrophy. Placental 11beta-hydroxysteroid dehydrogenase-2 (11beta-HSD-2) mRNA levels, measured by Northern blot, were decreased in females but not males. Adrenalectomy of alcohol-consuming dams reversed the increase in placental weight and the decrease in female placental 11beta-HSD-2 expression and eliminated the left ventricular hypertrophy of adult female offspring. These data suggest that alcohol-induced changes in placental 11beta-HSD-2 mRNA levels and left ventricular weight are coupled in female offspring only and depend on maternal adrenal status.

Dynorphin and the hypothalamo-pituitary-adrenal axis during fetal development

Although dynorphin has long been considered an endogenous opioid peptide with high affinity for the kappa-opioid receptor, its biological function remains uncertain. The high concentration of dynorphin peptides and kappa-opioid receptors in the hypothalamus suggest a possible role for dynorphin in neuroendocrine regulation. This review will summarize evidence that support a role for dynorphin in regulation of the developing hypothalamo-pituitary-adrenal (HPA) axis. Dynorphin can exert dual actions on adrenocorticotropin (ACTH) release: (i) via activation of hypothalamic kappa-opioid receptors leading to release of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and (ii) via a non-opioid mechanism that involves N-methyl-D-aspartate (NMDA) receptors and prostaglandins, and which is not dependent on CRH or AVP. The primary site of action of dynorphin and NMDA appears to be the fetal hypothalamus or a supra-hypothalamic site. The non-opioid mechanism does not mature until a few days prior to parturition and is active for only the brief perinatal period. In contrast, the opioid mechanism behaves as a constitutive system with sustained activity from prenatal to postnatal life. It is likely that the two mechanisms may respond to different stress stimuli and play a different role during development.