Ontogeny of hippocampal corticosteroid receptors: Effects of antenatal glucocorticoids in human and mouse

Prenatal maternal stress programs infant stress regulation

OBJECTIVE

Prenatal exposure to inappropriate levels of glucocorticoids (GCs) and maternal stress are putative mechanisms for the fetal programming of later health outcomes. The current investigation examined the influence of prenatal maternal cortisol and maternal psychosocial stress on infant physiological and behavioral responses to stress.

METHODS

The study sample comprised 116 women and their full term infants. Maternal plasma cortisol and report of stress, anxiety and depression were assessed at 15, 19, 25, 31 and 36 + weeks' gestational age. Infant cortisol and behavioral responses to the painful stress of a heel-stick blood draw were evaluated at 24 hours after birth. The association between prenatal maternal measures and infant cortisol and behavioral stress responses was examined using hierarchical linear growth curve modeling.

RESULTS

A larger infant cortisol response to the heel-stick procedure was associated with exposure to elevated concentrations of maternal cortisol during the late second and third trimesters. Additionally, a slower rate of behavioral recovery from the painful stress of a heel-stick blood draw was predicted by elevated levels of maternal cortisol early in pregnancy as well as prenatal maternal psychosocial stress throughout gestation. These associations could not be explained by mode of delivery, prenatal medical history, socioeconomic status or child race, sex or birth order.

CONCLUSIONS

These data suggest that exposure to maternal cortisol and psychosocial stress exerts programming influences on the developing fetus with consequences for infant stress regulation.

Gender-specific response of brain corticosteroid receptors to stress and fluoxetine

Gender-related differences in dexamethasone binding to corticosteroid receptors (CR) and in glucocorticoid receptor (GR) protein level in the pituitary, hypothalamus, hippocampus and prefrontal cortex were studied before and after antidepressant fluoxetine administration to both unstressed and rats exposed to a chronic social isolation stress. Untreated males, in comparison to females, displayed higher hormone-binding capacity of both GR and mineralocorticoid receptor (MR) in the hippocampal cytosol, as well as higher GR protein level in the pituitary cytosol. In both genders, dexamethasone binding to MR exceeded that to GR. While fluoxetine treatment and social isolation had no effect on GR activity, the influence on MR was gender-specific. Fluoxetine facilitated MR hormone-binding only in females, increasing the MR/GR activity ratio. In contrast, after a 6-week isolation of males, MR binding capacity was diminished and MR/GR ratio inverted in favor of GR. In addition, fluoxetine induced elevation of cytosolic GR protein level in the pituitary and hypothalamus, the latter change being gender-specific. The results point to gender-related differences in the CRs functioning and suggest that both MR and GR may contribute to well-known sexual dimorphism in vulnerability to stress and stress-related disorders and in the outcome of antidepressant treatment.

Effects of antenatal dexamethasone treatment on glucocorticoid receptor and calcyon gene expression in the prefrontal cortex of neonatal and adult common marmoset monkeys

BACKGROUND

Synthetic glucocorticoids such as dexamethasone (DEX) are commonly used to promote fetal lung maturation in at-risk preterm births, but there is emerging evidence of subsequent neurobehavioral abnormalities in these children e.g. problems with inattention/hyperactivity. However, molecular pathways mediating effects of glucocorticoid overexposure on motor and cognitive development are poorly understood.

METHODS

In this study with common marmoset monkeys, we investigated for neonatal and adulthood effects of antenatal DEX treatment on the expression of the corticosteroid receptors and also calcyon, a risk gene for attention-deficit/hyperactivity disorder, in the prefrontal cortex (PFC). Pregnant marmosets were exposed to DEX (5 mg/kg body weight) or vehicle during early (days 42-48) or late (days 90-96) stages of the 144-day pregnancy.

RESULTS

In neonates, relative to controls, glucocorticoid receptor (GR) mRNA levels were significantly reduced after the late DEX treatment in the medial, orbital and dorsal PFC and after the early DEX treatment in the dorsal PFC. The early DEX exposure, specifically, resulted in significant reduction in calcyon mRNA expression in the medial, orbital, dorsal and lateral PFC relative to controls. Mineralocorticoid receptor (MR) mRNA levels were not significantly affected by DEX treatment. In adults, PFC GR, calcyon, and MR mRNA levels were not significantly affected by early or late prenatal DEX treatment.

CONCLUSION

These findings indicate that antenatal DEX treatment could lead to short-term alterations in PFC expression of the GR and calcyon genes, with possible neurodevelopmental functional consequences.

Postnatal ontogeny of the glucocorticoid receptor in the hippocampus

Corticosteroid hormones are important intrinsic factors that not only mediate the response to stress but also largely contribute to the main physiological processes. The biological actions of these steroids involve, first of all, the activation of specific receptors, namely mineralocorticoid (MR) and glucocorticoid (GR) receptors. These two receptor types govern a flexible and well-balanced mechanism that leads to the often opposing changes in the cell. The hippocampus is the central part of the extrahypothalamic feedback loop in the control of the hypothalamic-pituitary-adrenal (HPA) axis activity. The coexpression of both MR and GR in the hippocampus serves a coordinated response to corticosteroids in the hippocampal neurons, thereby mediating the neuronal excitability, stress response, and behavioral adaptation. Each receptor type reveals distinct ontogenetic pattern over the postnatal period. This review addresses the issues relating to postnatal development of the HPA axis and especially the hippocampal expression of the GR proteins in intact and prenatally stressed rats.

Vulnerability to stroke: implications of perinatal programming of the hypothalamic-pituitary-adrenal axis

Chronic stress is capable of exacerbating each major, modifiable, endogenous risk factor for cerebrovascular and cardiovascular disease. Indeed, exposure to stress can increase both the incidence and severity of stroke, presumably through activation of the hypothalamic-pituitary-adrenal (HPA) axis. Now that characterization of the mechanisms underlying epigenetic programming of the HPA axis is well underway, there has been renewed interest in examining the role of early environment on the evolution of health conditions across the entire lifespan. Indeed, neonatal manipulations in rodents that reduce stress responsivity, and subsequent life-time exposure to glucocorticoids, are associated with a reduction in the development of neuroendocrine, neuroanatomical, and cognitive dysfunctions that typically progress with age. Although improved day to day regulation of the HPA axis also may be accompanied by a decrease in stroke risk, evidence from rodent studies suggest that an associated cost could be increased susceptibility to inflammation and neuronal death in the event that a stroke does occur and the individual is exposed to persistently elevated corticosteroids. Given its importance in regulation of health and disease states, any long-term modulation of the HPA axis is likely to be associated with both benefits and potential risks. The goals of this review article are to examine (1) the clinical and experimental data suggesting that neonatal experiences can shape HPA axis regulation, (2) the influence of stress and the HPA axis on stroke incidence and severity, and (3) the potential for neonatal programming of the HPA axis to impact adult cerebrovascular health.

Effects of intrauterine exposure to synthetic glucocorticoids on fetal, newborn, and infant hypothalamic-pituitary-adrenal axis function in humans: a systematic review

BACKGROUND

Synthetic glucocorticoids are commonly used in reproductive medicine. Fetal organ systems are highly sensitive to changes in the intrauterine environment, including overexposure to glucocorticoids. Structural and functional alterations resulting from such changes may persist throughout life and have been associated with diverse diseases. One system that could be particularly sensitive to fetal glucocorticoid overexposure is the hypothalamic-pituitary-adrenal (hpa) axis. Many human studies have investigated this possibility, but a systematic review to identify consistent, emergent findings is lacking.

METHODS

We systematically review 49 human studies, assessing the effects of intrauterine exposure to synthetic glucocorticoids on fetal, neonate, and infant hpa function.

RESULTS

Study quality varied considerably, but the main findings held true after restricting the analyses to higher-quality studies: intrauterine exposure to synthetic glucocorticoids reduces offspring hpa activity under unstimulated conditions after pain but not pharmacological challenge. Although reduced unstimulated hpa function appears to recover within the first 2 wk postpartum, blunted hpa reactivity to pain is likely to persist throughout the first 4 months of life. There is some evidence that the magnitude of the effects is correlated with the total amount of glucocorticoids administered and varies with the time interval between glucocorticoid exposure and hpa assessment.

CONCLUSIONS

This systematic review has allowed the demonstration of the way in which intrauterine exposure to various regimens of synthetic glucocorticoids affects various forms of hpa function. As such, it guides future studies in terms of which variables need to be focused on in order to further strengthen the understanding of such therapy, whilst continuing to profit from its clinical benefits.

Antenatal betamethasone administration alters stress physiology in healthy neonates

OBJECTIVE

To analyze hypothalamic-pituitary-adrenal axis balance in healthy newborns after antenatal betamethasone treatment for lung maturation where delivery could be prolonged until or near term.

METHODS

In a prospective observational study, salivary cortisol and cortisone levels were measured at the fourth day of life during resting conditions and in response to a pain-induced stress event in 23 neonates with antenatal exposure to a single course of betamethasone (2x12 mg) and compared with 40 controls. The mean interval between betamethasone treatment and delivery was 60+/-23 days.

RESULTS

On day 4 of life, neonates in the control group exhibited a significant increase in cortisol and cortisone from baseline levels after the stress induction (1.175-2.4 ng/mL for cortisol and 11.35-18.15 ng/mL for cortisone [both P<.05]), whereas, in betamethasone-exposed neonates, cortisol and cortisone stress response was not significantly different from baseline levels (1.39-1.6 ng/mL for cortisone [P=.76] and 14.8-17.1 ng/mL for cortisol [P=.69]). No influence of gestational age at betamethasone administration (P=.76) or gestational age at delivery (P=.71) on stress response patterns was observed in a multiple stepwise regression.

CONCLUSION

A single course of antenatal betamethasone treatment induces a suppression of stress reactivity in healthy newborns.

Development of glucocorticoid receptor regulation in the rat forebrain: implications for adverse effects of glucocorticoids in preterm infants

Glucocorticoids are the consensus treatment to avoid respiratory distress in preterm infants but there is accumulating evidence that these agents evoke long-term neurobehavioral deficits. Earlier, we showed that the developing rat forebrain is far more sensitive to glucocorticoid-induced disruption in the fetus than in the neonate. Feedback regulation of glucocorticoid receptors (GRs) is an essential homeostatic mechanism and we therefore examined the development of GR downregulation in the perinatal period. Pregnant rats or newborn pups were given dexamethasone daily (gestational days 17-19, postnatal days 1-3, or postnatal days 7-9), ranging from doses below that recommended for use in preterm infants (0.05 mg/kg) to therapeutic doses (0.2 or 0.8 mg/kg). Twenty-four hours after the last injection, we determined forebrain GR protein by Western blotting. Although postnatal dexamethasone treatment downregulated GRs at all doses, the fetal forebrain failed to show any decrement and instead exhibited slight GR upregulation. In controls, forebrain GR levels also showed a large increment over the course from late gestation through the second postnatal week, despite the fact that circulating glucocorticoid levels increase substantially during this period. Our results suggest that GR homeostasis develops primarily postnatally and that fetal inability to downregulate GRs in the face of exogenous glucocorticoid administration plays a role in the vulnerability of key neural circuits to developmental disruption. Since this developmental phase in the rat corresponds to the critical period in which glucocorticoids are used in preterm infants, adverse effects on brain development may be inescapable.

The long-term behavioural consequences of prenatal stress

Maternal distress during pregnancy increases plasma levels of cortisol and corticotrophin releasing hormone in the mother and foetus. These may contribute to insulin resistance and behaviour disorders in their offspring that include attention and learning deficits, generalized anxiety and depression. The changes in behaviour, with or independent of alterations in the function of the hypothalamic pituitary adrenal (HPA) axis, can be induced by prenatal stress in laboratory rodents and non-human primates. The appearance of such changes depends on the timing of the maternal stress, its intensity and duration, gender of the offspring and is associated with structural changes in the hippocampus, frontal cortex, amygdala and nucleus accumbens. The dysregulation of the HPA axis and behaviour changes can be prevented by maternal adrenalectomy. However, only the increased anxiety and alterations in HPA axis are re-instated by maternal injection of corticosterone.

CONCLUSION

Excess circulating maternal stress hormones alter the programming of foetal neurons, and together with genetic factors, the postnatal environment and quality of maternal attention, determine the behaviour of the offspring.

Corticosteroid receptor-gene variants: modulators of the stress-response and implications for mental health

The stress-response, including autonomic and hypothalamic-pituitary-adrenal (HPA) axis reactivity, is essential for maintaining homeostasis during a challenge. Brain mineralocorticoid receptors and glucocorticoid receptors operate in balance to coordinate the stress-response. Genetic variants in both the human mineralocorticoid and glucocorticoid receptor-genes have been functionally characterized. In vitro effects of these genetic variants on transactivation and mRNA stability have been described. In vivo, two mineralocorticoid receptor-gene SNPs (-2 G/C (allele frequency: 50%), MR I180V (11%)) and four glucocorticoid receptor-gene SNPs (ER22/23EK (3%), N363S (4%), BclI (37%), A3669G (15%)) are associated with changes in hypothalamic-pituitary-adrenal (HPA) axis reactivity. Importantly, the two mineralocorticoid receptor-gene variants (but none of the glucocorticoid receptor-gene variants) also associate with changes in autonomic output as measured as increased heart beat following a psychosocial stress (TSST). Moreover, several of these mineralocorticorticoid receptor- and glucocorticoid receptor variants have been found associated with stress-related disorders, including depression. These data indicate that dysregulation of mineralocorticoid- and glucocorticoid receptor are causative in the pathogenesis of depression. Moreover, these mineralocorticoid- and glucocorticoid receptor-gene variants constitute part of the genetic make up that determines individual stress-responsiveness inducing vulnerability to disease. Furthermore, mineralocorticoid- and glucocorticoid receptors are drug targets, thereby aiming at the underlying mechanisms of stress-related disorders.

Corticosteroid receptor polymorphisms: determinants of vulnerability and resilience

Why some individuals thrive and others break down under similar adverse conditions, is a central question in the neuroendocrinology of stress related psychopathology. The brain mineralocorticoid (MR) and glucocorticoid receptors (GR) operate in balance to coordinate behavioural, autonomic and neuroendocrine response patterns involved in homeostasis and health. Genetic variants of both the MR and GR have been functionally characterized. The four GR-gene single nucleotide polymorphisms (SNPs) (ER22/23EK (allele frequency: 3%), N363S (4%), BclI (37%), A3669G (15%)) and the two MR-gene SNPs (-2 G/C (50%), MR-I180V (11%)) showed in vitro changes in transactivational capacity, or affect stability of the mRNA (GR exon 9beta A3669G). All of these MR-and GR-SNPs change the regulation of the hypothalamus-pituitary-adrenal (HPA) axis at different levels including basal level (-2 G/C), dexamethasone induced negative feedback (ER22/23EK, N363S, BclI, 9beta A3669G) or following a psychosocial stress test (Trier Social Stress Test (TSST); all of the MR-and GR-SNPs). Importantly, the MR-I180V increased autonomic output and enhanced cortisol secretion during the TSST. Recently, several of these MR-and GR-variants have been found associated with psychopathology (depression, bipolar disorder). These data provide evidence that dysregulation of MR and GR are causative in the pathogenesis of depression and that these MR-and GR-gene variants are part of the genetic make up that determines individual stress-responsivity and coping style, affecting vulnerability to disease.

Fetal programming of hypothalamic-pituitary-adrenal (HPA) axis function and behavior by synthetic glucocorticoids

Reduced fetal growth has been closely associated with an increased risk for the development of chronic disease in later life. Accumulating evidence indicates that fetal exposure to excess glucocorticoids represents a critical mechanism underlying this association. Approximately 7% of pregnant women are at risk of preterm delivery and these women are routinely treated with synthetic glucocorticoids (sGC) between 24 and 34 of weeks gestation to improve neonatal outcome. Animal studies have demonstrated that maternally administered sGC crosses the placenta, affecting fetal hypothalamic-pituitary-adrenal (HPA) development, resulting in changes in HPA axis function that persist throughout life. These changes appear to be modulated at the level of glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) in the brain and pituitary. As the HPA axis interacts with many other physiological pathways, the changes in endocrine function are also sex-specific and age-dependent. Alterations in behavior, particularly locomotion, in animals exposed to sGC in utero have also been demonstrated. Consistent with the finding in animal models, emerging human data are indicating attention deficit-hyperactivity disorder (ADHD)-like symptoms in children exposed to repeated courses of sGC in utero. This behavioral phenotype is likely linked to alterations in dopamine (DA) signaling, suggesting that sGC are able to permanently modify or 'program' this system. Finally, it is emerging that changes in HPA axis function and behavior following antenatal exposure to sGC are transgenerational and likely involve epigenetic mechanisms. A comprehensive understanding of the acute and long-term impact of sGC exposure in utero is necessary to begin to develop recommendations and treatment options for pregnant women at risk of preterm delivery.