Prenatal stress is associated with depression-related electroencephalographic sleep changes in adult male rats: a preliminary report

A framework for testing pathways from prenatal stress-responsive hormones to cardiovascular disease risk

Cardiovascular disease (CVD) is a leading cause of death globally, with the prevalence projected to keep rising. Risk factors for adult CVD emerge at least as early as the prenatal period. Alterations in stress-responsive hormones in the prenatal period are hypothesized to contribute to CVD in adulthood, but little is known about relations between prenatal stress-responsive hormones and early precursors of CVD, such as cardiometabolic risk and health behaviors. The current review presents a theoretical model of the relation between prenatal stress-responsive hormones and adult CVD through cardiometabolic risk markers (e.g., rapid catch-up growth, high BMI/adiposity, high blood pressure, and altered blood glucose, lipids, and metabolic hormones) and health behaviors (e.g., substance use, poor sleep, poor diet and eating behaviors, and low physical activity levels). Emerging evidence in human and non-human animal literatures suggest that altered stress-responsive hormones during gestation predict higher cardiometabolic risk and poorer health behaviors in offspring. This review additionally highlights limitations of the current literature (e.g., lack of racial/ethnic diversity, lack of examination of sex differences), and discusses future directions for this promising area of research.

Brain mechanisms of insomnia: new perspectives on causes and consequences

While insomnia is the second most common mental disorder, progress in our understanding of underlying neurobiological mechanisms has been limited. The present review addresses the definition and prevalence of insomnia and explores its subjective and objective characteristics across the 24-hour day. Subsequently, the review extensively addresses how the vulnerability to develop insomnia is affected by genetic variants, early life stress, major life events, and brain structure and function. Further supported by the clear mental health risks conveyed by insomnia, the integrated findings suggest that the vulnerability to develop insomnia could rather be found in brain circuits regulating emotion and arousal than in circuits involved in circadian and homeostatic sleep regulation. Finally, a testable model is presented. The model proposes that in people with a vulnerability to develop insomnia, the locus coeruleus is more sensitive to-or receives more input from-the salience network and related circuits, even during rapid eye movement sleep, when it should normally be sound asleep. This vulnerability may ignite a downward spiral of insufficient overnight adaptation to distress, resulting in accumulating hyperarousal, which, in turn, impedes restful sleep and moreover increases the risk of other mental health adversity. Sensitized brain circuits are likely to be subjectively experienced as "sleeping with one eye open". The proposed model opens up the possibility for novel intervention studies and animal studies, thus accelerating the ignition of a neuroscience of insomnia, which is direly needed for better treatment.

Role of Chronic Administration of Antidepressant Drugs in the Prenatal Stress-Evoked Inflammatory Response in the Brain of Adult Offspring Rats: Involvement of the NLRP3 Inflammasome-Related Pathway

Evidence indicates that adverse experiences in early life may be a factor for immune disturbances leading to the depression in adulthood. Recently, a pivotal role in the pathogenesis of depression has been assigned to the activation of the brain Nod-like receptor pyrin-containing 3 (NLRP3) inflammasome. We investigated the impact of chronic treatment with antidepressant drugs on the behavioral disturbances and the levels of proinflammatory factors in the hippocampus and frontal cortex of adult male rats after prenatal stress exposure. Next, we explored the involvement of the NLRP3 inflammasome-related pathways in the mechanism of antidepressant action. Our study confirmed that chronic antidepressant treatment attenuated depression-like disturbances and exerted an anxiolytic action. All antidepressants diminished the prenatal stress-induced increase in IL-1β in both brain areas, while IL-18 only in the hippocampus. Moreover, tianeptine administration diminished the increase in CCR2 levels in both brain areas, while in the hippocampus, tianeptine, along with venlafaxine CCL2 and iNOS levels. Next, we observed that in the hippocampus, tianeptine and fluoxetine suppressed upregulation of TLR4. Furthermore, venlafaxine suppressed NFкB p65-subunit phosphorylation, while fluoxetine enhanced the IкB level. Importantly, in the hippocampus, all antidepressants normalized evoked by stress changes in caspase-1 level, while tianeptine and venlafaxine also affect the levels of ASC and NLRP3 subunits. Our results provide new evidence that chronic administration of antidepressants exerts anti-inflammatory effects more pronounced in the hippocampus, through suppression of the NLRP3 inflammasome activation. These effects are accompanied by an improvement in the behavioral dysfunctions evoked by prenatal stress.

Developmental pathways towards mood disorders in adult life: Is there a role for sleep disturbances?

INTRODUCTION

Mood disorders are among the most prevalent and serious mental disorders and rank high among to the leading global burdens of disease. The developmental psychopathology framework can offer a life course perspective on them thus providing a basis for early prevention and intervention. Sleep disturbances, are considered risk factors for mood disorders across childhood, adolescence and adulthood. Assuming that sleep disturbances may play a pivotal role in the pathogenesis of mood disorders from a life course point of view, we reviewed the data on developmental pathways towards mood disorders in adult life in relation to sleep disturbances.

METHOD

From February 2017, a systematic search was conducted in PubMed, PsycINFO and Embase electronic databases for literature on developmental pathways to mood disorders in adult life in relation to sleep disturbances and to 1) pre-natal stress, 2) early brain developmental processes, and 3) temperaments, character and attachment style.

RESULTS

Eleven, 54 and 15 articles were respectively selected.

CONCLUSIONS

Experimental and clinical studies revealed that exposure to prenatal/early life stress results in sleep disturbances such as poor sleep and altered circadian regulation phases and may predict or even precipitate mood disorders in adulthood. Chronic sleep disruption may interfere with neuronal plasticity, connectivity and the developing brain thus contributing to the development of mood disorders. In addition sleep and circadian dysregulations have been shown to be related to those temperaments, character and attachment styles which are considered precursors of mood disorders. Sleep and circadian behaviours may serve as early targets regarding mood disorders.

The reduced level of growth factors in an animal model of depression is accompanied by regulated necrosis in the frontal cortex but not in the hippocampus

In the present study, we asked if the different types of stress alter neuronal plasticity markers distinctively in the frontal cortex (FCx) and in the hippocampus (Hp). To do so, we implemented various stress regimens to analyze changes evoked in these rat brain structures. We utilized several molecular techniques, including western blot, ELISA, quantitative RT-PCR, and various biochemical assays, to examine a range of proteins and subjected rats to behavioral tests to evaluate potential maladaptive alterations. A decrease in the level of growth factors in the FCx was accompanied by changes suggesting damage of this structure in the manner of regulated necrosis, while the Hp appeared to be protected. The observed changes in the brain region-specific alterations in neurotrophin processing may also depend on the period of life, in which an animal experiences stress and the duration of the stressful stimuli. We conclude that chronic stress during pregnancy can result in serious alterations in the functioning of the FCx of the progeny, facilitating the development of depressive behavior later in life. We also suggest that the altered energy metabolism may redirect pro-NGF/p75^NTR/ATF2 signaling in the cortical neurons towards cellular death resembling regulated necrosis, rather than apoptosis.

Sleep patterning changes in a prenatal stress model of depression

Clinical depression is accompanied by changes in sleep patterning, which is controlled in a circadian fashion. It is thus desirable that animal models of depression mirror such diurnally-specific state alterations, along with other behavioral and physiological changes. We previously found several changes in behavior indicative of a depression-like phenotype in offspring of rats subjected to repeated, variable prenatal stress (PNS), including increased locomotor activity during specific periods of the circadian cycle. We, therefore, investigated whether PNS rats also exhibit alterations in sleep/wakefulness behavior around the change from light-to-dark phase. Control and PNS Sprague-Dawley rats were implanted with electrodes for continuous monitoring of electroencephalic activity used to determine behavioral state. The distribution of slow-wave sleep (SWS), rapid eye movement sleep (REMS) and wakefulness was compared for periods before and after lights were turned off, between baseline conditions and after exposure to an acute stressor. Both REMS and SWS amounts were increased in PNS rats relative to control animals in the beginning of the dark phase. REMS changes were due to an increase in REMS bout number, rather than in bout duration. During this circadian time period, we did not find any sex differences in the state changes. These results indicate that PNS affects baseline sleep patterning in both male and female rats around active-phase onset.

The Stress Acceleration Hypothesis of Nightmares

Adverse childhood experiences can deleteriously affect future physical and mental health, increasing risk for many illnesses, including psychiatric problems, sleep disorders, and, according to the present hypothesis, idiopathic nightmares. Much like post-traumatic nightmares, which are triggered by trauma and lead to recurrent emotional dreaming about the trauma, idiopathic nightmares are hypothesized to originate in early adverse experiences that lead in later life to the expression of early memories and emotions in dream content. Accordingly, the objectives of this paper are to (1) review existing literature on sleep, dreaming and nightmares in relation to early adverse experiences, drawing upon both empirical studies of dreaming and nightmares and books and chapters by recognized nightmare experts and (2) propose a new approach to explaining nightmares that is based upon the Stress Acceleration Hypothesis of mental illness. The latter stipulates that susceptibility to mental illness is increased by adversity occurring during a developmentally sensitive window for emotional maturation—the infantile amnesia period—that ends around age 3½. Early adversity accelerates the neural and behavioral maturation of emotional systems governing the expression, learning, and extinction of fear memories and may afford short-term adaptive value. But it also engenders long-term dysfunctional consequences including an increased risk for nightmares. Two mechanisms are proposed: (1) disruption of infantile amnesia allows normally forgotten early childhood memories to influence later emotions, cognitions and behavior, including the common expression of threats in nightmares; (2) alterations of normal emotion regulation processes of both waking and sleep lead to increased fear sensitivity and less effective fear extinction. These changes influence an affect network previously hypothesized to regulate fear extinction during REM sleep, disruption of which leads to nightmares. This network consists of a fear circuit that includes amygdala, hippocampus, and medial prefrontal cortex and whose substantial overlap with the stress acceleration findings allows the latter to be incorporated into a wider, more developmentally coherent framework.

The Beneficial Impact of Antidepressant Drugs on Prenatal Stress-Evoked Malfunction of the Insulin-Like Growth Factor-1 (IGF-1) Protein Family in the Olfactory Bulbs of Adult Rats

Insulin-like growth factor-1 (IGF-1) promotes the growth, differentiation, and survival of both neurons and glial cells, and it is believed to exert antidepressant-like activity. Thus, disturbances in the IGF-1 system could be responsible for the course of depression. To date, there have been no papers showing the impact of chronic antidepressant treatment on the IGF-1 network in the olfactory bulb (OB) in an animal model of depression. Prenatal stress was used as model of depression. Twenty-four 3-month-old male offspring of control and stressed mothers were subjected to behavioral testing (forced swim test). The mRNA expression of IGF-1 and IGF-1 receptor (IGF-1R) and the protein level of IGF-1 and its phosphorylation, as well as the concentrations of IGF-binding proteins (IGFBP-2, -4, -3, and -6), were measured in OBs before and after chronic imipramine, fluoxetine, or tianeptine administration. Adult rats exposed prenatally to stressful stimuli displayed not only depression-like behavior but also decreased IGF-1 expression, dysregulation in the IGFBP network, and diminished mRNA expression, as well as IGF-1R phosphorylation, in the OB. The administration of antidepressants normalized most of the changes in the IGF-1 system of the OB evoked by prenatal stress. These results suggested a beneficial effect of chronic antidepressant drug treatment in the alleviation of IGF-1 family malfunction in OBs in an animal model of depression.

Stress-induced alterations in 5-HT1A receptor transcriptional modulators NUDR and Freud-1

The effect of stress on the mRNA and protein level of the 5-HT1A receptor and two of its key transcriptional modulators, NUDR and Freud-1, was examined in the prefrontal cortex (PFC) and hippocampus (Hp) using rodent models: olfactory bulbectomy (OB) and prenatal stress (PS) in male and female rats; chronic mild stress in male rats (CMS) and pregnancy stress. In PFC, CMS induced the most widespread changes, with significant reduction in both mRNA and protein levels of NUDR, 5-HT1A receptor and in Freud-1 mRNA; while in Hp 5-HT1A receptor and Freud-1 protein levels were also decreased. In male, but not female OB rats PFC Freud-1 and 5-HT1A receptor protein levels were reduced, while in Hp 5-HT1A receptor, Freud-1 and NUDR mRNA's but not protein were reduced. In PS rats PFC 5-HT1A receptor protein was reduced more in females than males; while in Hp Freud-1 protein was increased in females. In pregnancy stress, PFC NUDR, Freud-1 and 5-HT1A protein receptor levels were reduced, and in HP 5-HT1A receptor protein levels were also reduced; in HP only NUDR and Freud-1 mRNA levels were reduced. Overall, CMS and stress during pregnancy produced the most salient changes in 5-HT1A receptor and transcription factor expression, suggesting a primary role for altered transcription factor expression in chronic regulation of 5-HT1A receptor expression. By contrast, OB (in males) and PS (in females) produced gender-specific reductions in PFC 5-HT1A receptor protein levels, suggesting a role for post-transcriptional regulation. These and previous data suggest that chronic stress might be a key regulator of NUDR/Freud-1 gene expression.

Prenatal stress affects insulin-like growth factor-1 (IGF-1) level and IGF-1 receptor phosphorylation in the brain of adult rats

It has been shown that stressful events occurring in early life have a powerful influence on the development of the central nervous system. Insulin-like growth factor-1 (IGF-1) promotes the growth, differentiation and survival of both neurons and glial cells and is thought to exert antidepressant-like activity. Thus, it is possible that disturbances in the function of the IGF-1 system may be responsible for disturbances observed over the course of depression. Prenatal stress was used as a valid model of depression. Adult male offspring of control and stressed rat dams were subjected to behavioural testing (forced swim test). The level of IGF-1 in the blood and the expression of IGF-1, IGF-1R, and IRS-1/2 in the hippocampus and frontal cortex using RT-PCR, ELISA and western blotting were measured. In addition the effect of intracerebroventricularly administered IGF-1 and/or the IGF-1R receptor antagonist JB1 in the forced swim test was studied. Prenatally stressed rats showed depressive like behaviour, including increased immobility time as well as decreased mobility and climbing. Intracerebroventricular administration of IGF-1 reversed these effects in stressed animals, whereas concomitant administration of the IGF-1R antagonist JB1 completely blocked the effects. Biochemical analysis of homogenates from the hippocampus and frontal cortex revealed decreases in IGF-1 level and IGF-1R phosphorylation along with disturbances in IRS-1 phosphorylation. These findings reveal that prenatal stress alters IGF-1 signalling, which may contribute to the behavioural changes observed in depression.

Prenatal stress leads to changes in IGF-1 binding proteins network in the hippocampus and frontal cortex of adult male rat

Depression is a mental disorder of still unknown origin. Currently, much attention is paid to the potential influence of disturbances in the functioning of neurotrophic factors on the onset of this disease. Insulin-like growth factor 1 (IGF-1) is one of the most important growth agents affecting processes that are crucial for brain development. To date, there are no data showing the impact of prenatal stress on the family of six IGF binding proteins (IGFBP 1-6) that regulate IGF-1 bioactivity. The goal of this study was to investigate whether the decreased expression of IGF-1 in the frontal cortex (FCx) and hippocampus (Hp) of adult male rats following a prenatal stress procedure is related to changes in the IGFBP family. Our results show that rats exposed prenatally to stressful stimuli displayed depression-like behavior based on sucrose preference and elevated plus maze tests. In both cases, in the adult rat brain structures that were examined after the prenatal stress procedure, the IGF-1 protein level was reduced. Moreover, we observed changes of varying degrees in the levels of IGFBPs in stressed animals. A decrease in IGFBP-2 and IGFBP-3 accompanied by an increase in the IGFBP-4 concentration in the Hp and the FCx was detected. There were no differences in IGFBP-1 and IGFBP-6 brain levels between the stressed and control animals, whereas IGFBP-5 concentration was decreased in the Hp of prenatally stressed animals. This study demonstrated that stress during pregnancy may lead not only to behavioral disturbances but also to a decrease in IGF-1 level and the dysregulation of the IGF-1 binding protein network in adult rat offspring.

Sleep and protein synthesis-dependent synaptic plasticity: impacts of sleep loss and stress

Sleep has been ascribed a critical role in cognitive functioning. Several lines of evidence implicate sleep in the consolidation of synaptic plasticity and long-term memory. Stress disrupts sleep while impairing synaptic plasticity and cognitive performance. Here, we discuss evidence linking sleep to mechanisms of protein synthesis-dependent synaptic plasticity and synaptic scaling. We then consider how disruption of sleep by acute and chronic stress may impair these mechanisms and degrade sleep function.

Elevated brain glucose and glycogen concentrations in an animal model of depression

INTRODUCTION

Recent data indicate that there is a link between depression and diabetes and that excess glucocorticoids may play an underlying role in the pathogenesis of both of these diseases. The aim of the present study was to determine whether there are any alterations in glucose, glycogen, glucose transporters, insulin, insulin receptors or corticosterone concentrations in the hippocampus and frontal cortex in a prenatal stress rat model of depression.

METHODS

Male rats whose mothers had been subjected to stress and control animals were subjected to the Porsolt test to verify the experimental model. Next, some of the rats were subjected to acute stress and/or were administered glucose. Glucose, glycogen, corticosterone, insulin, insulin receptor, phospho-insulin receptor and glucose transporter (GLUT1, GLUT3 and GLUT4) concentrations were assayed.

RESULTS

Prenatally stressed rats exhibited glucose and glycogen concentrations in both investigated brain structures that exceeded those of the control animals. Prenatal stress also increased the levels of glucose transporters - GLUT1 in both tissues and GLUT4 in the frontal cortex. The changes in the prenatally stressed rats were more prominent in the animals that were subjected to stress or glucose loading in adulthood.

CONCLUSION

The increase in carbohydrate brain concentrations evoked by prenatal stress may result from changes in the amounts of glucose transporters, especially GLUT1. Moreover, the obtained results support the hypothesis that stress during the perinatal period permanently increases the sensitivity of brain tissue to factors that act in adulthood. © 2014 S. Karger AG, Basel.

REM sleep dysregulation in depression: state of the art

Disturbances of sleep are typical for most depressed patients and belong to the core symptoms of the disorder. Since the 1960s polysomnographic sleep research has demonstrated that besides disturbances of sleep continuity, depression is associated with altered sleep architecture, i.e., a decrease in slow wave sleep (SWS) production and disturbed rapid eye movement (REM) sleep regulation. Shortened REM latency (i.e., the interval between sleep onset and the occurrence of the first REM period), increased REM sleep duration and increased REM density (i.e., the frequency of rapid eye movements per REM period) have been considered as biological markers of depression which might predict relapse and recurrence. High risk studies including healthy relatives of patients with depression demonstrate that REM sleep alterations may precede the clinical expression of depression and may thus be useful in identifying subjects at high risk for the illness. Several models have been developed to explain REM sleep abnormalities in depression, like the cholinergic-aminergic imbalance model or chronobiologically inspired theories, which are reviewed in this overview. Moreover, REM sleep alterations have been recently considered not only as biological "scars" but as true endophenotypes of depression. This review discusses the genetic, neurochemical and neurobiological factors that have been implicated to play a role in the complex relationships between REM sleep and depression. We hypothesize on the one hand that REM sleep dysregulation in depression may be linked to a genetic predisposition/vulnerability to develop the illness; on the other hand it is conceivable that REM sleep disinhibition in itself is a part of a maladaptive stress reaction with increased allostatic load. We also discuss whether the REM sleep changes in depression may contribute themselves to the development of central symptoms of depression such as cognitive distortions including negative self-esteem and the overnight consolidation of negatively toned emotional memories.

The effect of antidepressant drugs on the HPA axis activity, glucocorticoid receptor level and FKBP51 concentration in prenatally stressed rats

Dysregulation of hypothalamic-pituitary-adrenal (HPA) axis activity is thought to be an important factor in pathogenesis of depression. In animals, stress or glucocorticoids given in prenatal period lead to long-lasting behavioral and neuroendocrine changes similar to those observed in depressed patients. However, molecular basis for HPA disturbances in animals exposed to prenatal stress - a model of depression - have been only partially recognized. Therefore, in the present study we investigated the effect of prenatal stress on behavioral changes, blood corticosterone level, concentrations of glucocorticoid receptor (GR) and its cochaperone, FKBP51, in the hippocampus and frontal cortex in adult rats. It has been found that prenatally stressed rats display high level of immobility in the Porsolt test and anxiety-like behavior. The HPA axis hyperactivity in theses animals was evidenced by corticosterone hypersecretion at the end of the light phase and 1h following acute stress. Western blot study revealed that GR level was significantly elevated in the hippocampus but not in the frontal cortex of prenatally stressed rats, whereas concentration of FKBP51 was decreased only in the former brain structure. Chronic treatment with imipramine, fluoxetine, mirtazapine and tianeptine have diminished both behavioral and biochemical alterations observed in this animal model of depression. These data indicate that the increase in hippocampal GR level and low concentration of FKBP51 in the frontal cortex may be responsible for enhanced glucocorticoid action in depression.

Prenatal stress in rats predicts immobility behavior in the forced swim test

Prenatally-stressed (PS) rats are characterized by a general impairment of the hypothalamo-pituitary-adrenal (HPA) axis and sleep disturbances indicating that this model has face validity with some clinical features observed in a subpopulation of depressed patients. The prolonged corticosterone secretion shown by PS rats in response to stress was positively correlated with an increased immobility behavior in the forced swim test. To investigate the predictive validity of this model, a separate group of animals was chronically treated with the antidepressant tianeptine (10 mg/kg i.p. for 21 days). Such chronic treatment reduced in PS rats immobility time in the forced swim test. These findings suggest that the PS rat is an interesting animal model for the evaluation of antidepressant treatment.

Effects of early handling on basal and stress-induced sleep parameters in rats

Exposure of humans and animals to stressful events early in life leads to significant and often permanent behavioural, neuroendocrine and central alterations. Early handling consists of removing the litter from the nest for 15 min/day, from post-natal days 2 to 14 and results in lowered ACTH and corticosterone stress response and reduced anxiety-like and fear behaviours. Stress-induced sleep alterations usually consists of increased sleep time, known as sleep rebound. In the present study, basal and stress-induced sleep pattern of control non-manipulated (CTL) and early handled (EH) adult male rats was investigated. Sleep was evaluated by 21-h polysomnographic recordings (from 10:00 to 07:00 h of the next day) before and after a 1-h session of restraint stress. The results showed that in the first 3 h following stress, both CTL and EH animals exhibited an impairment of sleep, with a reduction of sleep efficiency, duration of slow wave sleep and of paradoxical sleep. On the contrary, time awake and awakening bouts were augmented in this period. Sleep rebound was observed mainly in the dark period of the light-dark cycle. Stress-induced sleep changes were similar between CTL and EH animals for most sleep parameters. However, EH animals exhibited more bouts of paradoxical sleep on the night following stress exposure and longer bouts of paradoxical sleep in the light period that followed restraint stress. These data indicate that stress-induced alterations of sleep in early handled animals are similar to that observed in control animals, except for some parameters related to paradoxical sleep.

Prenatal stress and long-term consequences: implications of glucocorticoid hormones

We have shown that prenatal restraint stress (PNRS) induces higher levels of anxiety, greater vulnerability to drugs, a phase advance in the circadian rhythm of locomotor activity and an increase in the paradoxical sleep in adult rats. These behavioral effects result from permanent modifications to the functioning of the brain, particularly in the feedback mechanisms of the hypothalamic-pituitary-adrenal (HPA) axis: the secretion of corticosterone is prolonged after stress and the number of the central glucocorticoid receptors is reduced. These abnormalities are associated with modifications in the synthesis and/or release of certain neurotransmitters. Dysfunction of the HPA axis is due, in part, to stress-induced maternal increase of glucocorticoids, which influences fetal brain development. Some biological abnormalities in depression can be related to those found in PNRS rats reinforcing the idea of the usefulness of PNRS rats as an appropriate animal model to study new pharmacological approaches.

Alterations induced by gestational stress in brain morphology and behaviour of the offspring

Retrospective studies in humans suggest that chronic maternal stress during pregnancy, associated with raised plasma levels of CRH, ACTH and cortisol may increase the likelihood of preterm birth, developmental delays and behavioural abnormalities in the children. In adulthood, it may contribute to the significant association between the incidence of schizophrenia, increased left or mixed handedness, reduction in cerebral asymmetry and anomalies in brain morphology. Our studies and others have shown that prenatal stress in rats can mimic these developmental and behavioural alterations. These rats show a reduced propensity for social interaction, increased anxiety in intimidating or novel situations and a reduction in cerebral asymmetry and dopamine turnover, consistent with those in schizophrenic humans. Prenatally-stressed (PS) rats also show behaviour consistent with depression, including a phase-shift in their circadian rhythm for corticosterone, sleep abnormalities, a hedonic deficit and greater acquisition of learned helplessness under appropriate conditions. These behavioural abnormalities are associated with impaired regulation of the hypothalamic-pituitary-adrenal axis response to stress and increased CRH activity. PS males may show demasculinisation and feminisation of their sexual behaviour. The developmental and behavioural abnormalities in PS offspring could occur through sensitisation of the foetal brain by maternal stress hormones to the action of glucocorticoid and CRH and to neurotransmitters affected by them. This may have long-lasting consequences and could explain the precipitation of depressive symptoms or schizophrenia by psychosocial stress in later life. The character of the behavioural abnormalities probably depends on the timing of the maternal stress in relation to development of the particular neuronal systems.

The impact of corticosteroids on the developing animal

Infants are subjected to both endogenous and exogenous corticosteroids in the pre- and postnatal periods. Stress to the mother before birth, or to the child postpartum, can give rise to high, chronic endogenous corticosteroid levels caused by activation of the hypothalamic-pituitary-adrenal (HPA) axis. Physician-administered exogenous corticosteroids are also used in the management of a wide spectrum of pre- and postnatal conditions. The long-term effects of corticosteroids in developing humans are not well known. Studies in animals, however, indicate that both natural stress and exogenous corticosteroids can have long-lasting and deleterious effects on the body, brain, behavior, and hypothalamic-pituitary-adrenal axis of developing infants. These data suggest that exogenous corticosteroids should be administered with caution, after careful benefit/risk analyses, and that, as far as possible, the developing brain should be protected against the effects of pre- and postnatal stress.

Effects of maternal stress on development and behaviour in rat offspring

Retrospective studies suggest that gestational stress in humans can delay the attainment of developmental milestones, increase the incidence of allergic reactions and respiratory infections and cause behavioural abnormalities in the children. Our studies and others have shown that prenatal stress in rats can mimic several of these developmental and behavioural alterations. These include a suppression of immune function, but also enhanced sensitivity to allergens. Prenatally-stressed rats, like children, show a reduced propensity for social interaction and increased anxiety in intimidating or novel situations. They have physiological and behavioural alterations consistent with depressive symptoms, including a phase-shift in their circadian rhythm for corticosterone, sleep abnormalities, and greater acquisition of learned helplessness under appropriate conditions. Prenatally-stressed male rats also show demasculinisation and feminisation of their sexual behaviour. The developmental and behavioural abnormalities in prenatally-stressed offspring may be mediated by alterations in the activity of endogenous opioids or neurosteroids, since several of them can be corrected by maternal administration of an opioid antagonist or by drugs like diazepam and allopregnanolone that modulate GABA transmission.