Effects of prenatal dexamethasone on spatial learning and response to stress is influenced by maternal factors

Harshness is not stress

We must differentiate between stressful and harsh environments to understand animals' resilience to global change. Harshness is not stress. Stressful environments activate the physiological stress response to increase energy availability, while harsh environments inhibit the physiological stress response to save energy.

Towards an Evolutionary Theory of Stress Responses

All organisms have a stress response system to cope with environmental threats, yet its precise form varies hugely within and across individuals, populations, and species. While the physiological mechanisms are increasingly understood, how stress responses have evolved remains elusive. Here, we show that important insights can be gained from models that incorporate physiological mechanisms within an evolutionary optimality analysis (the 'evo-mecho' approach). Our approach reveals environmental predictability and physiological constraints as key factors shaping stress response evolution, generating testable predictions about variation across species and contexts. We call for an integrated research programme combining theory, experimental evolution, and comparative analysis to advance scientific understanding of how this core physiological system has evolved.

Long-term neuropathological and/or neurobehavioral effects of antenatal corticosteroid therapy in animal models: a systematic review

BACKGROUND

Antenatal corticosteroids (ACSs) are recommended to all women at risk for preterm delivery; currently, there is controversy about the subsequent long-term neurocognitive sequelae. This systematic review summarizes the long-term neurodevelopmental outcomes after ACS therapy in animal models.

METHODS

An electronic search strategy incorporating MeSH and keywords was performed using all known literature databases and in accordance with PRISMA guidance (PROSPERO CRD42019119663).

RESULTS

Of the 669 studies identified, eventually 64 were included. The majority of studies utilized dexamethasone at relative high dosages and primarily involved rodents. There was a high risk of bias, mostly due to lack of randomization, allocation concealment, and blinding. The main outcomes reported on was neuropathological, particularly glucocorticoid receptor expression and neuron densities, and neurobehavior. Overall there was an upregulation of glucocorticoid receptors with lower neuron densities and a dysregulation of the dopaminergic and serotonergic systems. This coincided with various adverse neurobehavioral outcomes.

CONCLUSIONS

In animal models, ACSs consistently lead to deleterious long-term neurocognitive effects. This may be due to the specific agents, i.e., dexamethasone, or the repetitive/higher total dosing used. ACS administration varied significantly between studies and there was a high risk of bias. Future research should be standardized in well-characterized models.

Prenatal maternal cortisol measures predict learning and short-term memory performance in 3- but not 5-month-old infants

Little is known about relations between maternal prenatal stress and specific cognitive processes-learning and memory-in infants. A modified crib-mobile task was employed in a longitudinal design to test relations between maternal prenatal cortisol, prenatal subjective stress and anxiety, psychosocial variables, and learning and memory in 3- and 5-month-old infants. Results revealed that maternal prenatal cortisol was affected by particular psychosocial variables (e.g., maternal age, whether or not the infant's grandmother provided childcare, financial status), but was unrelated to measures of maternal depression, anxiety, and stress. Although maternal prenatal cortisol was not predictive of learning or memory performance in 5-month-old infants, higher levels of basal maternal cortisol and reduced prenatal cortisol response was predictive of some learning and short-term memory measures in 3-month-old infants. These results suggest an influence of maternal neuroendocrine functioning on fetal neurological development, and the importance of separate examination of subjective and biological measures of stress.

Effects of Neonatal Dexamethasone Exposure on Adult Neuropsychiatric Traits in Rats

The effects of early life stress in utero or in neonates has long-term consequences on hypothalamic-pituitary-adrenal (HPA) stress axis function and neurodevelopment. These effects extend into adulthood and may underpin a variety of mental illnesses and be related to various developmental and cognitive changes. We examined the potential role of neonatal HPA axis activation on adult psychopathology and dopamine sensitivity in the mature rat using neonatal exposure to the synthetic glucocorticoid receptor agonist and stress hormone, dexamethasone. We utilized a comprehensive battery of assessments for behaviour, brain function and gene expression to determine if elevated early life HPA activation is associated with adult-onset neuropsychiatric traits. Dexamethasone exposure increased startle reactivity under all conditions tested, but decreased sensitivity of sensorimotor gating to dopaminergic disruption–contrasting with what is observed in several neuropsychiatric diseases. Under certain conditions there also appeared to be mild long-term changes in stress and anxiety-related behaviours with neonatal dexamethasone exposure. Electrophysiology revealed that there were no consistent neuropsychiatric abnormalities in auditory processing or resting state brain function with dexamethasone exposure. However, neonatal dexamethasone altered auditory cortex glucocorticoid activation, and auditory cortex synchronization. Our results indicate that neonatal HPA axis activation by dexamethasone alters several aspects of adult brain function and behaviour and may induce long-term changes in emotional stress-reactivity. However, neonatal dexamethasone exposure is not specifically related to any particular neuropsychiatric disease.

Prenatal glucocorticoid exposure in rats: programming effects on stress reactivity and cognition in adult offspring

Human epidemiological studies have provided compelling evidence that prenatal exposure to stress is associated with significantly increased risks of developing psychiatric disorders in adulthood. Exposure to excessive maternal glucocorticoids may underlie this fetal programming effect. In the current study, we assessed how prenatal dexamethasone administration during the last week of gestation affects stress reactivity and cognition in adult offspring. Stress reactivity was assessed by evaluating anxiety-like behavior on an elevated plus maze and in an open field. In addition, to characterize the long-term cognitive outcomes of prenatal exposure to glucocorticoids, animals were assessed on two cognitive tasks, a spatial reference memory task with reversal learning and a delayed matching to position (DMTP) task. Our results suggest that prenatal exposure to dexamethasone had no observable effect on anxiety-like behavior, but affected cognition in the adult offspring. Prenatally dexamethasone-exposed animals showed a transient deficit in the spatial reference memory task and a trend to faster acquisition during the reversal-learning phase. Furthermore, prenatally dexamethasone-treated animals also showed faster learning of new platform positions in the DMTP task. These results suggest that fetal overexposure to glucocorticoids programs a phenotype characterized by cognitive flexibility and adaptability to frequent changes in environmental circumstances. This can be viewed as an attempt to increase the fitness of survival in a potentially hazardous postnatal environment, as predicted by intrauterine adversity. Collectively, our data suggest that prenatal exposure to dexamethasone in rats could be used as an animal model for studying some cognitive components of related psychiatric disorders.

Neuropeptide Y and peptide YY protect from weight loss caused by Bacille Calmette-Guérin in mice

Background and Purpose

Immune challenge of mice with Bacille Calmette–Guérin (BCG) has been reported to cause transient weight loss and a behavioural sickness response. Although BCG-induced depression involves the kynurenine pathway, weight loss occurs independently of this factor. Because neuropeptide Y (NPY) and peptide YY (PYY) are involved in the regulation of food intake, we hypothesized that they play a role in the BCG-induced weight loss.

Experimental Approach

Male wild-type, PYY knockout (PYY−/−), NPY knockout (NPY−/−) and NPY−/−;PYY−/− double knockout mice were injected with vehicle or BCG (approximately 10⁸ colony-forming units per mouse), and their weight, locomotion, exploration and ingestion were recorded for 2 weeks post-treatment.

Key Results

Deletion of PYY and NPY aggravated the BCG-induced loss of body weight, which was most pronounced in NPY−/−;PYY−/− mice (maximum loss: 15%). The weight loss in NPY−/−;PYY−/− mice did not normalize during the 2 week observation period. BCG suppressed the circadian pattern of locomotion, exploration and food intake. However, these changes took a different time course than the prolonged weight loss caused by BCG in NPY−/−;PYY−/− mice. The effect of BCG to increase circulating IL-6 (measured 16 days post-treatment) remained unaltered by knockout of PYY, NPY or NPY plus PYY.

Conclusions and Implications

These data show that NPY and PYY are both required to protect from the action of BCG-evoked immune challenge to cause prolonged weight loss and disturb energy balance. The findings attest to an important role of NPY and PYY in orchestrating homeostatic reactions to infection and immune stimulation.

Chronic high-fat diet increases acute neuroendocrine stress response independently of prenatal dexamethasone treatment in male rats

OBJECTIVE

Intrauterine growth restriction (IUGR) has been associated with metabolic disorders later in life such as obesity and diabetes as well as psychiatric disorders such as depression and schizophrenia. Therefore, we wanted to investigate whether behavioural, metabolic or neuroendocrine abnormalities could be provoked or exacerbated by a high-fat diet (HFD) in an experimental model of IUGR.

METHODS

Pregnant dams were exposed to dexamethasone (DEX) in the third gestational week to induce IUGR. Late adolescent male offspring of DEX- and vehicle-treated dams were then fed a HFD or standard chow for 8 weeks and subjected to a variety of assessments.

RESULTS

Only diet affected the hypothalamus-pituitary-adrenal (HPA) axis stress response, as HFD doubled the observed corticosterone levels following acute restraint. HFD and prenatal DEX exposure concomitantly exacerbated depressive-like behaviour in the forced swim test, even though no interaction was seen. Prenatal DEX treatment tended to increase the basal acoustic startle response (ASR), while an interaction between HFD and DEX was present in the ASR pre-pulse inhibition suggestive of fundamental changes in neuronal gating mechanisms. Metabolic parameters were only affected by diet, as HFD increased fasting glucose and insulin levels.

CONCLUSION

We conclude that chronic HFD may be more important in programming of the HPA axis stress responsiveness than an adverse foetal environment and therefore potentially implies an increased risk for developing psychiatric and metabolic disease.

Developmental methamphetamine exposure results in short- and long-term alterations in hypothalamic-pituitary-adrenal-axis-associated proteins

Developmental exposure to methamphetamine (MA) causes long-term behavioral and cognitive deficits. One pathway through which MA might induce these deficits is by elevating glucocorticoid levels. Glucocorticoid overexposure during brain development can lead to long-term disruptions in the hypothalamic-pituitary-adrenal (HPA) axis. These disruptions affect the regulation of stress responses and may contribute to behavioral and cognitive deficits reported following developmental MA exposure. Furthermore, alterations in proteins associated with the HPA axis, including vasopressin, oxytocin, and glucocorticoid receptors (GR), are correlated with disruptions in mood and cognition. We therefore hypothesized that early MA exposure will result in short- and long-term alterations in the expression of HPA axis-associated proteins. Male mice were treated with MA (5 mg/kg daily) or saline from postnatal day (P) 11 to P20. At P20 and P90, mice were perfused and their brains processed for vasopressin, oxytocin, and GR immunoreactivity within HPA axis-associated regions. At P20, there was a significant decrease in the number of vasopressin-immunoreactive cells and the area occupied by vasopressin immunoreactivity in the paraventricular nucleus (PVN) of MA-treated mice, but no difference in oxytocin immunoreactivity in the PVN, or GR immunoreactivity in the hippocampus or PVN. In the central nucleus of the amygdala, the area occupied by GR immunoreactivity was decreased by MA. At P90, the number of vasopressin-immunoreactive cells was still decreased, but the area occupied by vasopressin immunoreactivity no longer differed from saline controls. No effects of MA were found on oxytocin or GR immunoreactivity at P90. Thus developmental MA exposure has short- and long-term effects on vasopressin immunoreactivity and short-term effects on GR immunoreactivity.

The effects of prenatal and postnatal environmental interaction: prenatal environmental adaptation hypothesis

Adverse antenatal maternal environments during pregnancy influence fetal development that consequently increases risks of mental health problems including psychiatric disorders in offspring. Therefore, behavioral and brain alterations caused by adverse prenatal environmental conditions are generally considered as deficits. In this article, we propose a novel hypothesis, along with summarizing a body of literatures supporting it, that fetal neurodevelopmental alterations, particularly synaptic network changes occurring in the prefrontal cortex, associated with adverse prenatal environmental conditions may be adaptation to cope with expected severe postnatal environments, and therefore, psychiatric disorders may be able to be understood as adaptive strategies against severe environmental conditions through evolution. It is hoped that the hypothesis presented in this article stimulates and opens a new venue on research toward understanding of biological mechanisms and therapeutic treatments of psychiatric disorders.

Early handling modulates outcome of neonatal dexamethasone exposure

Synthetic glucocorticoids such as dexamethasone (DEX) are used to prevent or treat respiratory disorders in prematurely born infants. Besides the short-term benefit on lung development, numerous human and animal studies have reported adverse neurodevelopmental side effects. In contrast, maternal care is known to exert a positive influence on neurodevelopmental outcome in rodents. The aim of the current study was therefore to investigate whether neonatal handling (days 1-21), known to induce maternal care, might serve as an intervention strategy modulating the adverse effects of DEX treatment (days 1-3). For this purpose we have measured the outcome of these early-life manipulations on development as well as adult endocrine and behavioral phenotype of male rats. Maternal care was observed during the first week of life and indeed enhanced in response to handling. Eye opening was accelerated and body weight reduced in DEX-treated animals. In adulthood, we report that handling ameliorated impaired spatial learning observed in DEX treated non-handled animals in the T-maze. Additionally, handling reduced susceptibility to the impact of DEX treatment in the water maze. Although DEX treatment and handling both resulted in enhanced negative feedback of the stress-induced corticosterone response and both reduced startle reactivity, the acquisition of fear was only reduced by handling, without effect of DEX. Interestingly, handling had a beneficial effect on pre-pulse inhibition, which was diminished after DEX treatment. In conclusion, these findings indicate that handling of the neonate enhances maternal care and attenuates specific DEX-induced alterations in the adult behavioral phenotype.

Dexamethasone induces apoptosis in the developing rat amygdala in an age-, region-, and sex-specific manner

Exposure to glucocorticoids (GCs) in early development can lead to long-term changes in brain function and behavior, although little is known about the underlying neural mechanisms. Perinatal exposure to GCs alters adult anxiety and neuroendocrine responses to stress. Therefore, we investigated the effects of either late gestational or neonatal exposure to the GC receptor agonist dexamethasone (DEX), on apoptosis within the amygdala, a region critical for emotional regulation. DEX was administered to timed-pregnant rat dams from gestational day 18 until parturition, or postnatal day 4-6. Offspring were sacrificed the day following the last DEX treatment, and tissue was processed for immunohistochemical detection of cleaved caspase-3, a marker for apoptotic cells. Prenatal DEX treatment significantly increased the number of cleaved caspase-3-positive cells in the amygdala of both sexes, largely due to increases within the medial and basomedial subregions. Postnatal DEX treatment also increased cleaved caspase-3 immunoreactivity within the amygdala, although effects reached significance only in the central nucleus of females. Overall, DEX induction of cleaved caspase-3 in the amygdala was greater following prenatal compared with postnatal treatment, yet in both instances, elevations in cleaved caspase-3 correlated with an increase in pro-apoptotic Bax mRNA expression. Dual-label immunohistochemistry of cleaved caspase-3 and the neuronal marker NeuN confirmed that virtually all cleaved caspase-3-positive cells in the amygdala were neurons, and a subset of these cells (primarily following postnatal treatment) expressed a GABAergic calcium-binding protein phenotype (calbindin or calretinin). Together these results indicate that early developmental GC exposure induces neuronal apoptosis within the amygdala in an age-, sex-, and region-dependent manner.

Prenatal corticosteroid exposure alters early developmental seizures and behavior

In humans, corticosteroids are often administered prenatally to improve lung development in preterm neonates. Studies in exposed children as well as in children, whose mothers experienced significant stress during pregnancy indicate behavioral problems and possible increased occurrence of epileptic spasms. This study investigated whether prenatal corticosteroid exposure alters early postnatal seizure susceptibility and behaviors. On gestational day 15, pregnant rats were injected i.p. with hydrocortisone (2×10mg/kg), betamethasone (2×0.4mg/kg) or vehicle. On postnatal day (P)15, seizures were induced by flurothyl or kainic acid (3.5 or 5.0mg/kg). Horizontal bar holding was determined prior to seizures and again on P17. Performance in the elevated plus maze was assessed on P20-22. Prenatal exposure to betamethasone decreased postnatal susceptibility to flurothyl-induced clonic seizures but not to kainic acid-induced seizures. Prenatal hydrocortisone decreased postnatal weight but did not affect seizure susceptibility. Hydrocortisone alone did not affect performance in behavioral tests except for improving horizontal bar holding on P17. A combination of prenatal hydrocortisone and postnatal seizures resulted in increased anxiety. Prenatal exposure to mineralocorticoid receptor blocker canrenoic acid did not attenuate, but surprisingly amplified the effects of hydrocortisone on body weight and significantly worsened horizontal bar performance. Thus, prenatal exposure to excess corticosteroids alters postnatal seizure susceptibility and behaviors. Specific effects may depend on corticosteroid species.

The timing of prenatal exposure to maternal cortisol and psychosocial stress is associated with human infant cognitive development

The consequences of prenatal maternal stress for development were examined in 125 full-term infants at 3, 6, and 12 months of age. Maternal cortisol and psychological state were evaluated 5 times during pregnancy. Exposure to elevated concentrations of cortisol early in gestation was associated with a slower rate of development over the 1st year and lower mental development scores at 12 months. Elevated levels of maternal cortisol late in gestation, however, were associated with accelerated cognitive development and higher scores at 12 months. Elevated levels of maternal pregnancy-specific anxiety early in pregnancy were independently associated with lower 12-month mental development scores. These data suggest that maternal cortisol and pregnancy-specific anxiety have programming influences on the developing fetus.

Neonatal exposure to fenoterol and betamethasone: effects on the behavioral development in the rat

We investigated longitudinally the behavioral development in the rat following exposure to beta-agonists and glucocorticoids (GC). Neonatal rats received either 1 mg/kg fenoterol (FEN), 0.3 mg/kg betamethasone (BET), or saline (SAL). Weanling and young adult rats were tested in the open field, the elevated-plus maze, and the water maze. FEN-treated as well as BET-treated animals displayed increased anxiety-like behavior. Furthermore, BET-treated adult animals showed a reduced locomotor activity. An enhanced 24-h memory in the water maze in both treatment groups may be facilitated by emotional arousal due to the increased anxiety levels. The possible neurobiological underpinnings are discussed in detail.

Direct and dam-mediated effects of prenatal dexamethasone on emotionality, cognition and HPA axis in adult Wistar rats

Prenatal stress can affect foetal neurodevelopment and result in increased risk of depression in adulthood. It promotes increased maternal hypothalamo-pituitary-adrenal gland (HPA) secretion of glucocorticoid (GC), leading to increased foetal and maternal GC receptor activity. Prenatal GC receptor activity is also increased during prenatal treatment with dexamethasone (DEX), which is commonly prescribed as a prophylactic treatment of preterm delivery associated morbid symptoms. Here, we exposed pregnant Wistar rats to 0.1 mg/kg/d DEX during the last week of pregnancy and performed cross-fostering at birth. In the adult offspring we then studied the effects of prenatal DEX exposure per se and the effects of rearing by a dam exposed to prenatal DEX. Offspring were assessed in the following paradigms testing biobehavioural processes that are altered in depression: progressive ratio schedule of reinforcement (anhedonia), Porsolt forced swim test (behavioural despair), US pre-exposure active avoidance (learned helplessness), Morris water maze (spatial memory) and HPA axis activity (altered HPA function). Responsiveness to a physical stressor in terms of HPA activity was increased in male offspring exposed prenatally to DEX. Despite this increased HPA axis reactivity, we observed no alteration of the assessed behaviours in offspring exposed prenatally to DEX. We observed impairment in spatial memory in offspring reared by DEX exposed dams, independently of prenatal treatment. This study does not support the hypothesis that prenatal DEX exposure leads to depression-like symptoms in rats, despite the observed sex-specific programming effect on HPA axis. It does however emphasise the importance of rearing environment on adult cognitive performances.

Glucocorticoids and neuro- and behavioural development

Epidemiological evidence links exposure to stress hormones during fetal or early postnatal development with lifetime prevalence of cardiac, metabolic, auto-immune, neurological and psychiatric disorders. This has led to the concept of 'developmental programming through stress'. Importantly, these effects (specifically, hypertension, hyperglycaemia and neurodevelopmental and behavioural abnormalities) can be reproduced by exposure to high glucocorticoid levels, indicating a crucial role of glucocorticoids in their causation. However, there can be important differences in outcome, depending on the exact time of exposure, as well as duration and receptor selectivity of the glucocorticoid applied. The mechanisms underlying programming by stress are still unclear but it appears that these environmental perturbations exploit epigenetic modifications of DNA and/or histones to induce stable modifications of gene expression. Programming of neuro- and behavioural development by glucocorticoids and stress are important determinants of lifetime health and should be a consideration when choosing treatments in obstetric and neonatal medicine.

Effects of prenatal dexamethasone treatment on physical growth, pituitary-adrenal hormones, and performance of motor, motivational, and cognitive tasks in juvenile and adolescent common marmoset monkeys

Synthetic glucocorticoids such as dexamethasone (DEX) are commonly used to prevent respiratory distress syndrome in preterm infants, but there is emerging evidence of subsequent neurobehavioral abnormalities (e.g. problems with inattention/hyperactivity). In the present study, we exposed pregnant common marmosets (Callithrix jacchus, primates) to daily repeated DEX (5 mg/kg by mouth) during either early (d 42-48) or late (d 90-96) pregnancy (gestation period of 144 days). Relative to control, and with a longitudinal design, we investigated DEX effects in offspring in terms of physical growth, plasma ACTH and cortisol titers, social and maintenance behaviors, skilled motor reaching, motivation for palatable reward, and learning between infancy and adolescence. Early DEX resulted in reduced sociability in infants and increased motivation for palatable reward in adolescents. Late DEX resulted in a mild transient increase in knee-heel length in infants and enhanced reversal learning of stimulus-reward association in adolescents. There was no effect of either early or late DEX on basal plasma ACTH or cortisol titers. Both treatments resulted in impaired skilled motor reaching in juveniles, which attenuated in early DEX but persisted in late DEX across test sessions. The increased palatable-reward motivation and decreased social motivation observed in early DEX subjects provide experimental support for the clinical reports that prenatal glucocorticoid treatment impairs social development and predisposes to metabolic syndrome. These novel primate findings indicate that fetal glucocorticoid overexposure can lead to abnormal development of motor, affective, and cognitive behaviors. Importantly, the outcome is highly dependent upon the timing of glucocorticoid overexposure.

Early androgen exposure modulates spatial cognition in congenital adrenal hyperplasia (CAH)

Major questions remain about the exact role of hormones in cognition. Furthermore, the extent to which early perturbation in steroid function affects human brain development continues to be a wide open area of research. Congenital adrenal hyperplasia (CAH), a genetic disorder of steroid dysfunction characterized in part by in utero over-production of testosterone, was used as a natural model for addressing this question. Here, CAH (n=54, mean age=17.53, 31 female) patients were compared to healthy age- and sex-matched individuals (n=55, mean age=19.02, 22 female) on a virtual equivalent of the Morris Water Maze task [Morris, R., 1984. Developments of a water-maze procedure for studying spatial learning in the rat. J. Neurosci. Methods 11, 47-60], an established measure of sex differences in spatial cognition in rodents. Findings revealed that females with CAH with the most severe form of the disease and expected highest level of in utero exposure to androgens were found to perform similarly to both healthy males and CAH males, whereas strong sex differences were apparent in milder forms of the disorder and in controls. Moreover, advanced bone age, an indicator of long-term childhood exposure to testosterone was correlated with improved performance. The results indicate that individuals exposed to both excess androgens prenatally and prolonged exposure during childhood may manifest long-lasting changes in cognitive function. Such finding suggests a pivotal role of hormonal function on brain development in humans, mirroring results from the animal literature.

No long-term effect two years after intrauterine exposure to dexamethasone on dentate gyrus volume, neuronal proliferation and differentiation in common marmoset monkeys

Glucocorticoids are prenatally administered to promote the maturation of the lungs. They, however, can affect neuronal proliferation and differentiation. In newborn marmoset monkeys, intrauterine hyperexposure to dexamethasone (DEX) resulted in a significantly decreased proliferation rate in the hippocampal dentate gyrus without affecting neuronal differentiation. In this study, marmoset monkeys received 5 mg/kg body weight DEX either during early (days 42-48) or late (days 90-96) pregnancy. The volume of the dentate granule cell layer as well as the proliferation and neuronal differentiation in the dentate gyrus of their 2-year-old offspring were investigated. The density of proliferating cells (Ki-67), apoptotic cells (in situ tailing) and cells differentiating to neurons (double cortin, TUC-4 and calretinin) were determined immunohistochemically. Analysis of the dentate granule cell layer volume showed no significant differences between early or late DEX-exposed marmosets and untreated control animals. Similarly, proliferation and neuronal differentiation in DEX-treated animals was not significantly different in comparison with controls. In summary, the decreased proliferation rate observed in newborn marmosets after intrauterine exposure to DEX was no longer detectable in their 2-year-old siblings suggesting no long-lasting effect of prenatal hyperexposure to DEX on neuronal proliferation and differentiation in the dentate gyrus of marmoset monkeys.

The size and distribution of midbrain dopaminergic populations are permanently altered by perinatal glucocorticoid exposure in a sex- region- and time-specific manner

Central dopaminergic (DA) systems appear to be particularly vulnerable to disruption by exposure to stressors in early life, but the underlying mechanisms are poorly understood. As endogenous glucocorticoids (GCs) are implicated in other aspects of neurobiological programming, this study aimed to characterize the effects of perinatal GC exposure on the cytoarchitecture of DA populations in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA). Dexamethasone was administered non-invasively to rat pups via the mothers' drinking water during embryonic days 16-19 or postnatal days 1-7, with a total oral intake circa 0.075 or 0.15 mg/kg/day, respectively; controls received normal drinking water. Analysis of tyrosine hydroxylase-immunoreactive cell counts and regional volumes in adult offspring identified notable sex differences in the shape and volume of the SNc and VTA, as well as the topographical organization and size of the DA populations. Perinatal GC treatments increased the DA population size and altered the shape of the SNc and VTA as well as the organization of the DA neurons by expanding and/or shifting them in a caudal direction. This response was sexually dimorphic and included a feminization or demasculinization of the three-dimensional cytoarchitecture in males, and subtle differences that were dependent on the window of exposure. These findings demonstrate that inappropriate perinatal exposure to GCs have enduring effects on the organization of midbrain DA systems that are critically important for normal brain function throughout life.

Maternal care modulates the relationship between prenatal risk and hippocampal volume in women but not in men

Smaller hippocampal volume is associated with psychiatric disorders. Variations in hippocampal volume are discussed as both a consequence of the neurotoxic effects of stress and as a pre-existing condition leading to increased vulnerability for cognitive and emotional impairments. To investigate whether early experience can account for variability in hippocampal volume in adulthood (vulnerability hypothesis), we assessed the relationship between birth weight and hippocampal volume in 44 subjects. The reported quality of maternal care in early childhood, as evaluated by the Parental Bonding Inventory, was used as index of the quality of the postnatal environment. Hippocampal volume was assessed from magnetic resonance images using a manual segmentation protocol. We show that birth weight significantly predicts hippocampal volume in adulthood only in female subjects reporting low maternal care. The results suggest that the postnatal environment modulates the neurodevelopmental consequences of prenatal risk and that this effect is sex-specific.

Stress during development: Impact on neuroplasticity and relevance to psychopathology

Development represents a critical moment for shaping adult behavior and may set the stage to disease vulnerability later in life. There is now compelling evidence that stressful experiences during gestation or early in life can lead to enhanced susceptibility for mental illness. In this paper we review the data from experimental studies aimed at investigating behavioral, hormonal, functional and molecular consequences of exposure to stressful events during prenatal or early postnatal life that might contribute to later psychopathology. The use of the newest methodology in the field and the intensive efforts produced by researchers have opened the possibility to reveal the complex, finely tuned and previously unappreciated sets of molecular interactions between different factors that are critical for neurodevelopment thus leading to important discoveries regarding perinatal life. The major focus of our work has been to revise and discuss data from animal studies supporting the role of neuronal plasticity in the long-term effects produced by developmental adversities on brain function as well as the possible implications for disease vulnerability. We believe these studies might prove useful for the identification of novel targets for more effective pharmacological treatments of mental illnesses.

Maternal glucocorticoid deficit affects hypothalamic-pituitary-adrenal function and behavior of rat offspring

Detrimental consequences of prenatal stress include increased hypothalamic-pituitary-adrenal (HPA) function, anxiety and depression-like behavior in adult offspring. To identify the role of maternal corticosterone milieu in the fetal programming of adult function, we measured these same behavioral and hormonal endpoints after maternal adrenalectomy (ADX) and replacement with normal or moderately high levels of corticosterone (CORT). Adult male and female offspring exhibited differing HPA responses to maternal ADX. In female offspring of ADX mothers, exaggerated plasma ACTH stress responses were reversed by the higher, but not the lower, dose of maternal CORT. In contrast, male offspring of both ADX and ADX dams with higher CORT replacement showed exaggerated ACTH stress responses. Hypothalamic glucocorticoid receptor (GR) expression was decreased in these latter groups, while hippocampal GR increased only in the ADX offspring. Activity of young offspring of ADX dams replaced with the higher dose of CORT decreased in the open field test of exploration/anxiety, while immobility behavior of adult offspring in the forced swim test of depression increased following maternal ADX or higher levels of CORT replacement. Interestingly, for some measures, none or moderately high CORT replacement resulted in similar deficits in this study. These findings are in accord with consequences of prenatal stress or prenatal dexamethasone exposure, suggesting that a common mechanism may underlie the effects of too low or too high maternal glucocorticoids on adult HPA function and behavior.

Prenatal glucocorticoid exposure affects learning and vulnerability of cholinergic neurons

Prenatal treatment with synthetic glucocorticoids is commonly used as a treatment for women at risk of preterm delivery. However, little is known about the life-long consequences of these treatments on the fetus. In the present study, we evaluated cognitive function as well as susceptibility of cholinergic neurons to (192)IgG-saporin immunolesion in adult rats after prenatal glucocorticoid treatment. Morris water maze results revealed a significant difference in learning and memory function in adult rats that were prenatally exposed to dexamethasone, and further cognitive deficits after (192)IgG-saporin exposure. Choline acetyl transferase activity was decreased in the cortex of dexamethasone-treated rats compared with controls. In addition, rats prenatally exposed to either dexa, or betamethasone revealed a dramatic decrease in choline acetyl transferase activity compared to control rats after (192)IgG-saporin lesion. We report behavioral and biochemical evidence for altered cognitive function and increased susceptibility of cholinergic neurons to (192)IgG-saporin in adult rats after prenatal glucocorticoid treatment. Taken together, these results suggest that prenatal treatment with dexamethasone could affect cognitive functions and render cholinergic neurons more vulnerable to challenges later in life.

Maternal adrenal hormone secretion mediates behavioural alterations induced by prenatal stress in male and female rats

Prenatal stress in rats has been shown to impair the regulation of the hypothalamic pituitary adrenal (HPA) axis and predispose to anxiogenic and depressive-like behaviour. In a previous study, abolition of excess corticosterone (COR) release during stress by maternal adrenalectomy prevented the dysregulation of the HPA axis. In the present study, we determined whether excess maternal COR is also responsible for the alterations in offspring behaviour. Pregnant Wistar rats were adrenalectomized or sham-operated on day 11 of gestation and subjected once daily to mild restraint for 30 min on days 14-21 of gestation. An undisturbed group of pregnant females served as controls. All experiments were performed in male and female offspring. Pup weight and anogenital distance of males were measured after birth; anxiogenic behaviour was assessed in the elevated plus maze (EPM) at the age of 5 weeks and spatial memory in the Morris water maze in littermates at 3-4 months. Prenatally stressed (PS) males did not show a reduction in anogenital distance, and their increase in anxiogenic behaviour in the EPM was less than that in PS females. On the other hand, impairment of spatial learning was only seen in PS males. Both the anxiogenic behaviour of PS males and females and the learning deficit in males were completely abolished by adrenalectomy. These data show that excess stress-induced COR can alter the programming of the foetal brain and predispose it to alterations in behaviour that are gender specific.

Antenatal steroid therapy: have we undervalued the risks?

Antenatal corticosteroid therapy to enhance fetal lung maturation in pregnancies at risk for preterm delivery is used commonly, based on the assumption that its established benefits outweigh associated risks. Corticosteroid treatment does confer some risks, particularly with respect to restricted brain growth and disordered neuronal development. These alterations have the potential for long-term effects on health. They deserve further study, and should not be undervalued. Corticosteroid therapy should be applied selectively in those situations in which the risk of preterm birth is very high and the likelihood of severe respiratory distress syndrome substantial.

Prenatal dexamethasone exposure, postnatal development, and adulthood prepulse inhibition and latent inhibition in Wistar rats

Prenatal stress is an important risk factor in schizophrenia, and the aetiological factors mediating this relationship are central to the neurodevelopmental hypothesis of schizophrenia. The glucocorticoid receptor (GR) agonist dexamethasone (DEX) is commonly prescribed for prenatal conditions, and results in GR activation, which is part of the stress response. To investigate animal evidence for whether prenatal DEX leads to development of schizophrenia-like phenotypes, Wistar rats were prenatally exposed to DEX (0.1mg/kg/day) between the gestational days 15 and 21, and tested in two paradigms known to be disrupted in schizophrenia patients: prepulse inhibition (PPI) and latent inhibition (LI). A cross-fostering design was used to allow dissociation of any direct prenatal effects on offspring from effects dependent on DEX exposure of the rearing dam. Pup birth weight was reduced by prenatal DEX treatment. DEX-treated dams demonstrated increased pup-directed behaviour. There were additive effects of prenatal DEX treatment and DEX treatment of rearing dam in terms of reduced body weight in adulthood. In one of two replications, PPI was increased by prenatal DEX in males only and specific to the highest prepulse intensity. There was no evidence that LI was disrupted by prenatal DEX treatment. This study does not provide support for the hypothesis that prenatal DEX exposure leads to schizophrenia-like deficits in PPI or LI, suggesting that GR prenatal programming is not a mechanism of direct relevance to the neurodevelopmental hypothesis of schizophrenia.

Prenatal exposure to dexamethasone alters hippocampal drive on hypothalamic-pituitary-adrenal axis activity in adult male rats

Glucocorticoids are essential for normal hypothalamic-pituitary-adrenal (HPA) axis activity; however, recent studies warn that exposure to excess endogenous or synthetic glucocorticoid during a specific period of prenatal development adversely affects HPA axis stability. We administered dexamethasone (DEX) to pregnant rats during the last week of gestation and investigated subsequent HPA axis regulation in adult male offspring in unrestrained and restraint-stressed conditions. With the use of real-time PCR and RIA, we examined the expression of regulatory genes in the hippocampus, hypothalamus, and pituitary, including corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), glucocorticoid receptors (GR), mineralcorticoid receptors (MR), and 11-β-hydroxysteroid dehydrogenase-1 (11β-HSD-1), as well as the main HPA axis hormones, adrenal corticotropic hormone (ACTH) and corticosterone (CORT). Our results demonstrate that the DEX-exposed group exhibited an overall change in the pattern of gene expression and hormone levels in the unrestrained animals. These changes included an upregulation of CRH in the hypothalamus, a downregulation of MR with a concomitant upregulation of 11β-HSD-1 in the hippocampus, and an increase in circulating levels of both ACTH and CORT relative to unrestrained control animals. Interestingly, both DEX-exposed and control rats exhibited an increase in pituitary GR mRNA levels following a 1-h recovery from restraint stress; however, the increased expression in DEX-exposed rats was significantly less and was associated with a slower return to baseline CORT compared with controls. In addition, circulating levels of ACTH and CORT as well as hypothalamic CRH and hippocampal 11β-HSD-1 expression levels were significantly higher in the DEX-exposed group compared with controls following restraint stress. Taken together, these data demonstrate that late-gestation DEX exposure in rats is associated with persistent changes in both the modulation of HPA axis activity and the HPA axis-mediated response to stress.

Induction of a hyperanxious state by antenatal dexamethasone: a case for less detrimental natural corticosteroids

BACKGROUND

Synthetic glucocorticoids are commonly prescribed during pregnancy, despite a lack of systematic investigations of their potential impact on the developing brain and neurological and behavioral performance.

METHODS

Neuroendocrine parameters and behavior in the adult offspring of pregnant Wistar rats treated antenatally with either dexamethasone (DEX) or corticosterone (CORT) were monitored; DEX (.1 mg/kg and 1 mg/kg) and CORT (25 mg/kg) were given to pregnant rat dams on gestation days 18 and 19.

RESULTS

Despite normal basal levels of corticosterone, the adult offspring of mothers given DEX or CORT displayed abnormal responses in the dexamethasone-suppression test. Neither treatment influenced spatial memory performance, but both DEX and CORT facilitated development of depression-like behavior following chronic stress. The latter finding demonstrates that high-dose antenatal corticotherapy can impair the organism's resilience to stress in adulthood. Interestingly, comparison of the progeny of CORT-treated and DEX-treated mothers revealed that the latter were more anxious.

CONCLUSIONS

Since DEX and CORT differ in their affinity for glucocorticoid and mineralocorticoid receptors and corticosteroid-binding globulin, our findings emphasize the need to consider the pharmacologic properties of antenatal corticotherapies and demonstrate the potential long-term benefits of ligands that can bind to both receptors.

Mathematical modeling of the hypothalamic-pituitary-adrenal system activity

Mathematical modeling has proven to be valuable in understanding of the complex biological systems dynamics. In the present report we have developed an initial model of the hypothalamic-pituitary-adrenal system self-regulatory activity. A four-dimensional non-linear differential equation model of the hormone secretion was formulated and used to analyze plasma cortisol levels in humans. The aim of this work was to explore in greater detail the role of this system in normal, homeostatic, conditions, since it is the first and unavoidable step in further understanding of the role of this complex neuroendocrine system in pathophysiological conditions. Neither the underlying mechanisms nor the physiological significance of this system are fully understood yet.

A single course of antenatal betamethasone reduces neurotrophic factor S100B concentration in the hippocampus and serum in the neonatal rat

The effects of a single course of antenatal betamethasone on S100B protein concentration were investigated in Fisher 344 rats. On day 20 of gestation, pregnant rats were injected twice 8 h apart with either (1) 170 microg kg(-1) body weight betamethasone ("clinically-equivalent dose", equivalent to 12 mg twice, 24 h apart in humans), (2) half of this dose (equivalent to 6 mg) or (3) vehicle. We report reference values for S100B protein in the serum and different brain regions in both genders at 1, 2, and 21 days after birth. Interestingly, S100B concentration showed a time-dependent and brain region-specific pattern of expression. At P1, S100B was higher in the serum of males compared to females. In addition, we show that both doses of betamethasone decreased S100B concentration in the serum of males at P1, whereas in the hippocampus, it was reduced by the clinically-equivalent dose only. This suggests that lowering the dose of antenatal betamethasone may be less detrimental for brain maturation and therefore we reiterate the need for clinical trials with a low dose regimen.

Behavioral deficits associated with fetal alcohol exposure are reversed by prenatal thyroid hormone treatment: a role for maternal thyroid hormone deficiency in FAE

Children prenatally exposed to alcohol typically exhibit behavioral abnormalities, including hyperactivity, learning deficits, and an increased prevalence of depression. Similar impairments are found in children of hypothyroid mothers, and we have shown that alcohol-consuming rat dams have suppressed hypothalamic-pituitary-thyroid (HPT) function. Therefore, we hypothesized that suppressed maternal thyroid hormonal milieu may contribute to the deleterious consequences of prenatal alcohol exposure. We aimed first to confirm and then to reverse the behavioral deficits in the fetal alcohol exposed (FAE) rat offspring by administration of thyroxine (T4) to the alcohol-consuming dams. Adult offspring prenatally exposed to ethanol (FAE; 35% ethanol-derived calories), pair-fed (PF) or control (C) diets were tested in the Morris water maze (MWM), the forced swim test (FST), and the open field test (OFT) to assess spatial learning, depressive behavior, and exploratory behavior/anxiety, respectively. Adult FAE offspring took longer to locate a hidden platform in the MWM and showed increased depressive behavior in the FST both of which were reversed by administration of T4 to the alcohol-consuming mother. We found sex and brain region-specific alterations in expression of genes involved in these behaviors in FAE adult offspring. Specifically, decreased hippocampal GAP-43 mRNA levels in adult FAE females and decreased glucocorticoid receptor (GR) expression in the amygdala of male and female FAE offspring were observed. The decreased mRNA levels of GAP-43 and GR were normalized by T4 treatment to the alcohol-consuming mother. Our results suggest that the suppressed HPT function of the alcohol-consuming mother contributes to the behavioral and cognitive dysfunctions observed in the offspring.

RETRACTED: Maternal adversity, glucocorticoids and programming of neuroendocrine function and behaviour

The fetus may be exposed to increased endogenous glucocorticoid or synthetic glucocorticoid in late gestation. Approximately 7% of pregnant women in Europe and North America are treated with synthetic glucocorticoid to promote lung maturation in fetuses at risk of preterm delivery. Very little is known about the mechanisms by which synthetic glucocorticoid or prenatal stress influence neurodevelopment in the human, or whether specific time windows of increased sensitivity exist. Glucocorticoids are essential for many aspects of normal brain development, but exposure of the fetal brain to excess glucocorticoid can have life-long effects on neuroendocrine function and behaviour. Both endogenous glucocorticoid and synthetic glucocorticoid exposure have a number of rapid effects in the fetal brain, including modification of neurotransmitter systems and transcriptional machinery. Such fetal exposure permanently alters hypothalamo-pituitary-adrenal (HPA) function in prepubertal, postpubertal and aging offspring, in a sex-dependent manner. Prenatal glucocorticoid manipulation also leads to modification of behaviour, brain and organ morphology, as well as altered regulation of other endocrine systems. Permanent changes in endocrine function will impact on health, since elevated cumulative exposure to endogenous glucocorticoid is linked to the premature onset of pathologies associated with aging.

Effect of neonatal dexamethasone exposure on growth and neurological development in the adult rat

Until recently, the synthetic glucocorticoid dexamethasone was commonly used to lessen the morbidity of chronic lung disease in premature infants. This practice diminished as dexamethasone use was linked to an increased incidence of cerebral palsy and short-term neurodevelopmental delay. Of more concern is the fact that we know little regarding dexamethasone effects on long-term neurodevelopment. To study the effects of neonatal dexamethasone exposure on long-term neurodevelopment, we have developed a rat model where newborn pups are exposed to tapering doses of dexamethasone at time points corresponding to the neurodevelopmental age when human infants are traditionally exposed to this drug in the neonatal intensive care unit. Using a within-litter design, pups were assigned to one of three groups on postnatal day 2 (P2): handled controls, saline-injected controls, and animals receiving intramuscular dexamethasone between P3 and P6. Somatic growth was decreased in dexamethasone-treated animals. Dexamethasone-treated animals demonstrated slight delays in indexes of neurodevelopment and physical maturation at P7 and P14, but not P20. In adolescence (P45), there was no difference between groups in an open field test. However, as adult dexamethasone-treated animals were less active in the open field and spent more time in closed arms of the elevated plus maze. The serum corticosterone response to crowding stress in dexamethasone-treated animals was no different from controls, but they demonstrate a delay in return of corticosterone levels to baseline. These differences in behavior and hormonal stress responsiveness suggest that neonatal dexamethasone exposure may permanently alter function of the neuroendocrine stress axis.

Interleukin 1 beta enhances conditioned fear memory in rats: possible involvement of glucocorticoids

Central administration of 15 ng interleukin (IL)-1beta in the rat significantly enhanced conditioned fear memory assessed by a passive avoidance task, when retested at 24 and 48 h post-training. Pain threshold was unaffected by 15 ng IL-1beta administration. IL-1beta treatment also increased serum corticosterone. This increase in serum corticosterone was further enhanced in rats given both IL-1beta and footshock. Furthermore, the glucocorticoid receptor antagonist mifepristone blocked IL-1beta-induced elevation in corticosterone and also attenuated the enhanced conditioned fear memory. Central administration of IL-1beta significantly increased prostaglandin E2 and decreased the anti-inflammatory cytokine IL-10 release from whole blood cultures; therefore this treatment appears to be effective in inducing an inflammatory response in both the periphery and the brain. The present study confirms that IL-1beta can enhance conditioned fear memory, an effect which is correlated with changes in glucocorticoid function. This facilitation of defensive behaviour could reflect adaptive responses which may enhance survival during sickness.

A single course of prenatal betamethasone in the rat alters postnatal brain cell proliferation but not apoptosis

The aim of this study was to determine the effects of a clinically relevant single course of prenatal betamethasone in the rat on growth parameters with particular reference to brain cell proliferation and apoptosis. We report that administration of 170 microg kg-1 betamethasone twice within 4 h to E20 pregnant rats conveys moderate somatic growth retardation. Further, using a measure of brain cell proliferation independent of blood-brain barrier (BBB) permeability, we demonstrate for the first time that betamethasone is chronically anti-proliferative to brain cells without inducing caspase-3-mediated apoptosis. More importantly we show that there is a significant and sexually divergent rebound of neural proliferation which occurs earlier in males than in females and continues until at least 21 days of postnatal life. BBB permeability to [3H]thymidine was significantly increased by steroid treatment re-iterating the fact that tracer studies not correcting for BBB permeability, such as bromodeoxyuridine (BrdU), may be questionable in this type of study. Further, prenatal steroid treatment did not alter postnatal corticosterone levels. In summary we show that prenatal betamethasone conveys significant and long-lasting side effects and that its human clinical application in preterm labour needs more careful consideration as compared to the relative ease with which it is prescribed today.

A delayed increase in hippocampal proliferation following global asphyxia in the neonatal rat

Adult neurogenesis has been shown to be upregulated following a wide variety of brain injury paradigms. During the first weeks of postnatal life there is around 50 fold more neurogenesis occurring than in the adult CNS, yet little is known regarding the effect of neonatal brain injury on this developmental proliferation. We have investigated the effect of a global perinatal birth asphyxia on postnatal proliferation at 2, 5, 8, 11, 15, 21 and 28 days after birth (injury) using a 3H-thymidine tracer study. We found a specific upregulation of proliferation at 5 days after the injury within the injured hippocampus only, with an associated increase in hippocampal mass and without any changes in GFAP content at any timepoint. Perinatal asphyxia did not alter proliferation within the cerebellum, sub ventricular zone, olfactory bulb, cervical or thoracic spinal cord. Similarly, no changes in corticosterone levels were induced by the injury. Since there were no changes in GFAP content we hypothesize that this increased proliferation is likely neurogenetic, similar to what is seen in the adult brain following injury. Further we show that the dramatic increase in corticosterone at the end of the stress hyporesponsive period is not responsible for the equally dramatic decrease in postnatal proliferation within the CNS.

Effects of tapering neonatal dexamethasone on rat growth, neurodevelopment, and stress response

Dexamethasone is commonly used to lessen the morbidity of chronic lung disease in premature infants, but little is known regarding neurological consequences of its prolonged use. To study neurological effects of dexamethasone, we have developed a rat model in which newborn pups are exposed to tapering doses of dexamethasone at a time corresponding neurodevelopmentally to human exposure in the neonatal intensive care unit. On postnatal day (PD) 2, litters were divided into three groups: 1) handled controls, 2) saline-injected animals, and 3) animals injected with tapering doses of intramuscular dexamethasone between PD 3 and 6. Somatic growth and brain weight were decreased in dexamethasone-treated animals. Dexamethasone-treated animals demonstrated delays in gross neurological development on PD 7 and 14 but not PD 20. In late adolescence (PD 33), dexamethasone-treated animals were less active in light and dark environments, while demonstrating a blunted serum corticosterone response to a novel stress. The dissociation between behavioral and hormonal stress responsiveness suggests that neonatal dexamethasone exposure permanently alters central nervous system function, particularly within the neuroendocrine stress axis. This may lead to increased risk for learning impairment and maladaptive responses to the environment.