Differential adaptive responses to chronic stress of maternally stressed male mice offspring

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

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

Gestational administration of vitamin D improves maternal care and prevents anxiety-like behavior in male and female Wistar rats prenatally exposed to dexamethasone

Prenatal overexposure to glucocorticoids (GC) can lead to behavioral changes in adulthood. We aimed to explore the effects of gestational administration of vitamin D on the behavioral responses of dams and their offspring prenatally exposed to dexamethasone (DEX). Vitamin D (500UI) was given daily during the whole pregnancy (VD group). Half of the groups that received vitamin D were treated with DEX (0.1 mg/kg, VD + DEX group) daily between the 14th and 19th days of pregnancy. The corresponding control groups of progenitors were assigned (CTL and DEX groups, respectively). Maternal care and the dam's behaviors were evaluated during lactation. The offspring had developmental and behavioral parameters evaluated during lactation and at 3, 6, and 12 months of age. Gestational administration of vitamin D increased maternal care and had an anxiolytic-like effect on the dams, but the latter was blocked in DEX-treated dams. Prenatal DEX partially impaired neural development and caused an anxiety-like phenotype in the male and female offspring at 6 months, which was prevented by gestational administration of vitamin D. As well, gestational vitamin D improved memory just in the male offspring, but this response was suppressed by prenatal DEX. We concluded that gestational vitamin D could prevent anxiety-like behavior in adult male and female rats prenatally exposed to DEX, which might be, in part, a result of the maternal care improvement.

Perinatal Stress and Methamphetamine Exposure Decreases Anxiety-Like Behavior in Adult Male Rats

Methamphetamine (MA) is an illicit synthetic psychostimulant drug, and its abuse is growing worldwide. MA has been reported as the primary drug of choice, by drug-abusing women, during pregnancy. Since MA easily crosses the placental barrier, the fetus is exposed to MA in a similar fashion to the mother. This study aimed to evaluate the effect of long-term perinatal stressors and drug exposure on anxiety-like behavior in adult male rats using the open field test (OF) and elevated plus maze (EPM). Dams were divided into three groups according to drug treatment during pregnancy: controls (C), saline-SA [subcutaneous (s.c.), 1 ml/kg], and MA (s.c., 5 mg/kg). Litters were divided into four groups according to postnatal stressors: non-stressed controls (N), maternal separation (S), maternal cold water stress (W), and maternal separation plus maternal cold water stress (SW). Forty-five minutes before testing (in both OF and EPM), one-half of adult male rats received an (s.c.) injection of MA and the other half received an SA injection. Prenatal MA/stress exposure did not affect anxiety-like behavior in adult male rats in both tests. In the OF, an acute MA dose in adulthood increased the time spent in the central disk area, decreased time spent in the corners, and decreased time spent immobile and grooming. Also, postnatal stress increased time spent in the central disk area, decreased time spent in corners, and increased mobility compared to controls. All groups of rats exposed to postnatal stressors spent significantly less time in the closed arms of the EPM compared to controls. Overall, our results indicate that early postnatal stress and a single acute MA administration in adulthood decreases the parameters of anxiety-like behavior in adult male rats regardless of prenatal MA exposure. Moreover, postnatal stress via maternal separation impacts the effect of acute MA administration in adulthood. Long-term postnatal stress may thus result in improved adaptation to subsequent stressful experiences later in life.

Pre-reproductive stress in adolescent female rats alters oocyte microRNA expression and offspring phenotypes: pharmacological interventions and putative mechanisms

Pre-reproductive stress (PRS) to adolescent female rats alters anxiogenic behavior in first (F1)- and second-generation (F2) offspring and increases mRNA expression of corticotropin-releasing factor receptor type 1 (Crhr1) in oocytes and in neonate offspring brain. Here, we ask whether the expression of Crhr1 and Crhr1-targeting microRNA is altered in brain, blood, and oocytes of exposed females and in the brain of their neonate and adult F1 and F2 offspring. In addition, we inquire whether maternal post-stress drug treatment reverses PRS-induced abnormalities in offspring. We find that PRS induces a selective increase in Crhr1-targeting mir-34a and mir-34c in blood and oocytes, while non-Crhr1 microRNA molecules remain unaltered. PRS induces similar microRNA changes in prefrontal cortex of F1 and F2 neonates. In adult animals, cortical Crhr1, but not mir-34, expression is affected by both maternal and direct stress exposure. Post-PRS fluoxetine (FLX) treatment increases pup mortality, and both FLX and the Crhr1 antagonist NBI 27914 reverse some of the effects of PRS and also have independent effects on F1 behavior and gene expression. PRS also alters behavior as well as gene and miRNA expression patterns in paternally derived F2 offspring, producing effects that are different from those previously found in maternally derived F2 offspring. These findings extend current knowledge on inter- and trans-generational transfer of stress effects, point to microRNA changes in stress-exposed oocytes as a potential mechanism, and highlight the consequences of post-stress pharmacological interventions in adolescence.

Early-life exposure to artificial light at night elevates physiological stress in free-living songbirds☆

Artificial light at night (ALAN) can disrupt adaptive patterns of physiology and behavior that promote high fitness, resulting in physiological stress and elevation of steroid glucocorticoids (corticosterone, CORT in birds). Elevated CORT may have particularly profound effects early in life, with the potential for enduring effects that persist into adulthood. Research on the consequences of early-life exposure to ALAN remains limited, especially outside of the laboratory, and whether light exposure affects CORT concentrations in wild nestling birds particularly remains to be elucidated. We used an experimental setup to test the hypothesis that ALAN elevates CORT concentrations in developing free-living birds, by exposing nestling great tits (Parus major) to ALAN inside nest boxes. We measured CORT in feathers grown over the timeframe of the experiment (7 nights), such that CORT concentrations represent an integrative metric of hormone release over the period of nocturnal light exposure, and of development. We also assessed the relationships between feather CORT concentrations, body condition, nestling size rank and fledging success. In addition, we evaluated the relationship between feather CORT concentrations and telomere length. Nestlings exposed to ALAN had higher feather CORT concentrations than control nestlings, and nestlings in poorer body condition and smaller brood members also had higher CORT. On the other hand, telomere length, fledging success, and recruitment rate were not significantly associated with light exposure or feather CORT concentrations. Results indicate that exposure to ALAN elevates CORT concentrations in nestlings, which may reflect physiological stress. In addition, the organizational effects of CORT are known to be substantial. Thus, despite the lack of an effect on telomere length and survivorship, elevated CORT concentrations in nestlings exposed to ALAN may have subsequent impacts on later-life fitness and stress sensitivity.

Programming effects of maternal stress on the circadian system of adult offspring

Maternal stress has long-lasting influences on the brain functions of offspring, and several brain regions have been proposed to mediate such programming. Although perinatal programming of crosstalk between the circadian and stress systems has been proposed, the functional consequences of prenatal stress on the circadian system and the underlying mechanisms remain largely unknown. Therefore, we investigated whether exposing pregnant mice to chronic restraint stress had prolonged effects on the suprachiasmatic nucleus (SCN), which bears the central pacemaker for mammalian circadian rhythms, of offspring. SCN explants from maternally stressed mice exhibited altered cyclic expression patterns of a luciferase reporter under control of the mouse Per1 promoter (mPer1::LUC), which manifested as a decreased amplitude and impaired stability of the rhythm. Bioluminescence imaging at the single-cell level subsequently revealed that impaired synchrony among individual cells was responsible for the impaired rhythmicity. These intrinsic defects appeared to persist during adulthood. Adult male offspring from stressed mothers showed advanced-phase behavioral rhythms with impaired stability as well as altered clock gene expression in the SCN. In addition to affecting the central rhythm, maternal stress also had prolonged influences on the circadian characteristics of the adrenal gland and liver, as determined by circulating corticosterone levels and hepatic glycogen content, and on canonical clock gene mRNA expression in those tissues. Taken together, our findings suggest that the SCN is a key target of the programming effects of maternal stress. The widespread effects of circadian disruptions caused by a misprogrammed clock may have further impacts on metabolic and mental health in later life.

When pregnant mothers are stressed, the fetus’s circadian rhythms are reprogrammed, increasing the risk of health complications later in life. Stress during pregnancy was known to negatively affect the fetus, but how it affected circadian rhythms (day/night patterns of alertness) was poorly understood. Kyungjin Kim (Daegu Gyeongbuk Institute of Science and Technology) and Sooyoung Chung (Ewha Womans University, Seoul), both in South Korea, and co-workers stressed pregnant mice by confining them in small tubes, then measured the effects on their offspring. Pups of stressed mothers showed disturbed circadian rhythms, and the effects persisted into adulthood. Further analysis showed that the rhythms were disrupted because individual cells in the key brain region regulating circadian rhythms were poorly synchronized. These results suggest potential treatments to counteract the negative effects of prenatal stress on circadian rhythms.

Different effects of chronic social defeat on social behavior and the brain CRF system in adult male C57 mice with different susceptibilities

Chronic social defeat stress (CSDS) has been found to produce different impacts on anxiety-like behaviors, spatial cognitive function and memory in rodents with different susceptibilities. However, the impacts of chronic social defeat on social behaviors in adult male mice with different susceptibilities to social defeat and the underlying mechanisms in the brain remain unclear. In the present study, we found that ten days of social defeat reduced the tendency of susceptible adult male C57 mice to approach an unfamiliar individual and increased their avoidance of an unfamiliar CD-1 mouse but had no effects on resilient individuals. In addition, CSDS enhanced anxiety-like behavior in susceptible animals, but produced no effects in the resilient group. Meanwhile, CSDS increased the number of corticotropin-releasing factor (CRF)-positive neurons in the paraventricular nucleus of the hypothalamus and CRF-R2-positive neurons in the accumbens nucleus shell in both resilient and susceptible animals. CSDS increased the number of CRF-R1-positive neurons and CRF-R1 mRNA expression in the prelimbic cortex (PrL) and the number of CRF-R2-positive neurons in the basolateral amygdala, but reduced the number of CRF-R2-positive neurons and mRNA expression in the PrL in susceptible animals. Therefore, the different effects of CSDS on sociability and anxiety-like behavior in mice with different susceptibilities may be associated with region- and type-specific alterations in CRF receptor levels. These findings help us understand the underlying mechanism by which social stress affects emotion and social behavior and provides an important basis for the treatment of disorders of social and emotional behavior caused by social stress.

Modulation of the Hypothalamic-Pituitary-Adrenal Axis by Early Life Stress Exposure

Exposure to stress during critical periods in development can have severe long-term consequences, increasing overall risk on psychopathology. One of the key stress response systems mediating these long-term effects of stress is the hypothalamic-pituitary-adrenal (HPA) axis; a cascade of central and peripheral events resulting in the release of corticosteroids from the adrenal glands. Activation of the HPA-axis affects brain functioning to ensure a proper behavioral response to the stressor, but stress-induced (mal)adaptation of the HPA-axis' functional maturation may provide a mechanistic basis for the altered stress susceptibility later in life. Development of the HPA-axis and the brain regions involved in its regulation starts prenatally and continues after birth, and is protected by several mechanisms preventing corticosteroid over-exposure to the maturing brain. Nevertheless, early life stress (ELS) exposure has been reported to have numerous consequences on HPA-axis function in adulthood, affecting both its basal and stress-induced activity. According to the match/mismatch theory, encountering ELS prepares an organism for similar ("matching") adversities during adulthood, while a mismatching environment results in an increased susceptibility to psychopathology, indicating that ELS can exert either beneficial or disadvantageous effects depending on the environmental context. Here, we review studies investigating the mechanistic underpinnings of the ELS-induced alterations in the structural and functional development of the HPA-axis and its key external regulators (amygdala, hippocampus, and prefrontal cortex). The effects of ELS appear highly dependent on the developmental time window affected, the sex of the offspring, and the developmental stage at which effects are assessed. Albeit by distinct mechanisms, ELS induced by prenatal stressors, maternal separation, or the limited nesting model inducing fragmented maternal care, typically results in HPA-axis hyper-reactivity in adulthood, as also found in major depression. This hyper-activity is related to increased corticotrophin-releasing hormone signaling and impaired glucocorticoid receptor-mediated negative feedback. In contrast, initial evidence for HPA-axis hypo-reactivity is observed for early social deprivation, potentially reflecting the abnormal HPA-axis function as observed in post-traumatic stress disorder, and future studies should investigate its neural/neuroendocrine foundation in further detail. Interestingly, experiencing additional (chronic) stress in adulthood seems to normalize these alterations in HPA-axis function, supporting the match/mismatch theory.

Cooperative roles of the suprachiasmatic nucleus central clock and the adrenal clock in controlling circadian glucocorticoid rhythm

The mammalian circadian timing system consists of the central clock in the hypothalamic suprachiasmatic nucleus (SCN) and subsidiary peripheral clocks in other tissues. Glucocorticoids (GCs) are adrenal steroid hormones with widespread physiological effects that undergo daily oscillations. We previously demonstrated that the adrenal peripheral clock plays a pivotal role in circadian GC rhythm by driving cyclic GC biosynthesis. Here, we show that the daily rhythm in circulating GC levels is controlled by bimodal actions of central and adrenal clockwork. When mice were subjected to daytime restricted feeding to uncouple central and peripheral rhythms, adrenal GC contents and steroidogenic acute regulatory protein expression peaked around zeitgeber time 00 (ZT00), consistent with shifted adrenal clock gene expression. However, restricted feeding produced two distinct peaks in plasma GC levels: one related to adrenal GC content and the other around ZT12, which required an intact SCN. Light pulse-evoked activation of the SCN increased circulating GC levels in both wild-type and adrenal clock-disrupted mutant mice without marked induction of GC biosynthesis. In conclusion, we demonstrate that adrenal clock-dependent steroidogenesis and a SCN-driven central mechanism regulating GC release cooperate to produce daily circulatory GC rhythm.

Animal Models of Maternal Immune Activation in Depression Research

Abstract: Background

Depression and schizophrenia are debilitating mental illnesses with significant socio-economic impact. The high degree of comorbidity between the two disorders, and shared symptoms and risk factors, suggest partly common pathogenic mechanisms. Supported by human and animal studies, maternal immune activation (MIA) has been intimately associated with the development of schizophrenia. However, the link between MIA and depression has remained less clear, in part due to the lack of appropriate animal models.

Objective

Here we aim to summarize findings obtained from studies using MIA animal models and discuss their relevance for preclinical depression research.

Methods

Results on molecular, cellular and behavioral phenotypes in MIA animal models were collected by literature search (PubMed) and evaluated for their significance for depression.

Results

Several reports on offspring depression-related behavioral alterations indicate an involvement of MIA in the development of depression later in life. Depression-related behavioral phenotypes were frequently paralleled by neurogenic and neurotrophic deficits and modulated by several genetic and environmental factors.

Conclusion

Literature evidence analyzed in this review supports a relevance of MIA as animal model for a specific early life adversity, which may prime an individual for the development of distinct psychopathologies later life. MIA animal models may present a unique tool for the identification of additional exogenous and endogenous factors, which are required for the manifestation of a specific neuropsychiatric disorder, such as depression, later in life. Hereby, novel insights into the molecular mechanisms involved in the pathophysiology of depression may be obtained, supporting the identification of alternative therapeutic strategies.

Prenatal stress changes courtship vocalizations and bone mineral density in mice

Stress during the prenatal period has various effects on social and sexual behavior in both human and animal offspring. The present study examines the effects of chronic restraint stress in the second vs third trimester in pregnancy and glucocorticoid receptor (GR) heterozygous mutation on C57BL/6N male offspring's vocal courtship behavior in adulthood by applying a novel analyzing method. Finally, corticosterone and testosterone levels as well as bone mineral density were measured. Prenatal stress in the third, but not in the second trimester caused a significant qualitative change in males' courtship vocalizations, independent of their GR genotype. Bone mineral density was decreased also by prenatal stress exclusively in the third trimester in GR mutant and wildtype mice and - in contrast to corticosterone and testosterone - highly correlated with courtship vocalizations. In Gr^+/- males corticosterone serum levels were significantly increased in animals that had experienced prenatal stress in the third trimester. Testosterone serum levels were overall increased in Gr^+/- males in comparison to wildtypes as a tendency - whereas prenatal stress had no influence. Prenatal stress alters adult males' courtship vocalizations exclusively when applied in the third trimester, with closely related changes in bone mineral density. Bone mineral density seems to reflect best the complex neuroendocrine mechanisms underlying the production of courtship vocalizations. Besides, we demonstrated for the first time elevated basal corticosterone levels in Gr^+/- males after prenatal stress which suggests that the Gr^+/- mouse model of depression might also serve as a model of prenatal stress in male offspring.

Long-term consequences of prenatal stress and neurotoxicants exposure on neurodevelopment

There is a large consensus that the prenatal environment determines the susceptibility to pathological conditions later in life. The hypothesis most widely accepted is that exposure to insults inducing adverse conditions in-utero may have negative effects on the development of target organs, disrupting homeostasis and increasing the risk of diseases at adulthood. Several models have been proposed to investigate the fetal origins of adult diseases, but although these approaches hold true for almost all diseases, particular attention has been focused on disorders related to the central nervous system, since the brain is particularly sensitive to alterations of the microenvironment during early development. Neurobiological disorders can be broadly divided into developmental, neurodegenerative and neuropsychiatric disorders. Even though most of these diseases share genetic risk factors, the onset of the disorders cannot be explained solely by inheritance. Therefore, current understanding presumes that the interactions of environmental input, may lead to different disorders. Among the insults that can play a direct or indirect role in the development of neurobiological disorders are stress, infections, drug abuse, and environmental contaminants. Our laboratories have been involved in the study of the neurobiological impact of gestational stress on the offspring (Dr. Antonelli's lab) and on the effect of gestational exposure to toxicants, mainly methyl mercury (MeHg) and perfluorinated compounds (PFCs) (Dr. Ceccatelli's lab). In this focused review, we will review the specialized literature but we will concentrate mostly on our own work on the long term neurodevelopmental consequences of gestational exposure to stress and neurotoxicants.

The role of inositol 1,4,5-trisphosphate 3-kinase A in regulating emotional behavior and amygdala function

Inositol 1,4,5-trisphosphate 3-kinase A (IP₃K-A) is a molecule enriched in the brain and neurons that regulates intracellular calcium levels via signaling through the inositol trisphosphate receptor. In the present study, we found that IP₃K-A expression is highly enriched in the central nucleus of the amygdala (CeA), which plays a pivotal role in the processing and expression of emotional phenotypes in mammals. Genetic abrogation of IP₃K-A altered amygdala gene expression, particularly in genes involved in key intracellular signaling pathways and genes mediating fear- and anxiety-related behaviors. In agreement with the changes in amygdala gene expression profiles, IP₃K-A knockout (KO) mice displayed more robust responses to aversive stimuli and spent less time in the open arms of the elevated plus maze, indicating high levels of innate fear and anxiety. In addition to behavioral phenotypes, decreased excitatory and inhibitory postsynaptic current and reduced c-Fos immunoreactivity in the CeA of IP₃K-A KO mice suggest that IP₃K-A has a profound influence on the basal activities of fear- and anxiety-mediating amygdala circuitry. In conclusion, our findings collectively demonstrate that IP₃K-A plays an important role in regulating affective states by modulating metabotropic receptor signaling pathways and neural activity in the amygdala.

Lasting Differential Effects on Plasticity Induced by Prenatal Stress in Dorsal and Ventral Hippocampus

Early life adversaries have a profound impact on the developing brain structure and functions that persist long after the original traumatic experience has vanished. One of the extensively studied brain structures in relation to early life stress has been the hippocampus because of its unique association with cognitive processes of the brain. While the entire hippocampus shares the same intrinsic organization, it assumes different functions in its dorsal and ventral sectors (DH and VH, resp.), based on different connectivity with other brain structures. In the present review, we summarize the differences between DH and VH and discuss functional and structural effects of prenatal stress in the two sectors, with the realization that much is yet to be explored in understanding the opposite reactivity of the DH and VH to stressful stimulation.

The synergistic effect of density stress during the maternal period and adulthood on immune traits of root vole (Microtus oeconomus) individuals-a field experiment

The literature reveals that stress in early life or adulthood can influence immune function. As most studies on this are from the laboratory, there is a need for replicated studies in wild animals. This study aims to examine the effects of density stress during the maternal period and adulthood on immune traits of root vole (Microtus oeconomus) individuals. Four replicated high- and low-density parental populations were established, from which we obtained offspring and assigned each into four enclosures, two for each of the two density treatments used in establishing parental populations. The F1 offspring fecal corticosterone metabolite response to acute immobilization stress, anti-keyhole limpet hemocyanin immunoglobulin G (anti-KLH IgG) level, phytohemagglutinin (PHA)-delayed hypersensitivity and hematology at the end of the first breeding season, and prevalence and intensity of coccidial infection throughout the two breeding seasons, were tested. Density-induced maternally stressed offspring had delayed responses to acute immobilization stress. Density-stressed offspring as adults had reduced anti-KLH IgG levels and PHA responses, and the effects further deteriorated in maternally stressed offspring, leading to higher coccidial infection in the first breeding season than in the second. No correlations were found between immune traits or coccidial infection and survival over winter. These findings indicated that the combined density stresses during the maternal period and adulthood exhibited negative synergistic effects on immune traits. The synergistic effects lead to higher coccidial infection; however, this consequently reduced the risk of subsequent infection. The increased coccidial infection mediated by the synergistic effects may have an adaptive value in the context of the environment.

Lifetime development of behavioural phenotype in the house mouse (Mus musculus)

With each trajectory taken during the ontogeny of an individual, the number of optional behavioural phenotypes that can be expressed across its life span is reduced. The initial range of phenotypic plasticity is largely determined by the genetic material/composition of the gametes whereas interacting with the given environment shapes individuals to adapt to/cope with specific demands. In mammalian species, the phenotype is shaped as the foetus grows, depending on the environment in the uterus, which in turn depends on the outer environment the mother experiences during pregnancy. After birth, a complex interaction between innate constitution and environmental conditions shapes individual lifetime trajectories, bringing about a wide range of diversity among individual subjects.

In laboratory mice inbreeding has been systematically induced in order to reduce the genetic variability between experimental subjects. In addition, within most laboratories conducting behavioural phenotyping with mice, breeding and housing conditions are highly standardised. Despite such standardisation efforts a considerable amount of variability persists in the behaviour of mice. There is good evidence that phenotypic variation is not merely random but might involve individual specific behavioural patterns consistent over time. In order to understand the mechanisms and the possible adaptive value of the maintenance of individuality we review the emergence of behavioural phenotypes over the course of the life of (laboratory) mice. We present a literature review summarizing developmental stages of behavioural development of mice along with three illustrative case studies. We conclude that the accumulation of environmental differences and experiences lead to a “mouse individuality” that becomes increasingly stable over the lifetime.

Long-Term Effects of Prenatal Hypoxia on Schizophrenia-Like Phenotype in Heterozygous Reeler Mice

Prenatal hypoxia (PHX) is a well-known environmental factor implicated in the pathophysiology of schizophrenia. However, the long-term effects of PHX on schizophrenia-related neuroplasticity are poorly understood. Using behavioral tasks, MRI imaging, and biochemical studies, we examined the long-term effects of PHX in heterozygous reeler mice (HRM; mice deficient for reelin, a candidate gene for schizophrenia). PHX at E17 failed to induce any significant deficits in prepulse inhibition, spatial memory, anxiety-like behavior, or blood flow in wild type (WT) and HRM at 6 months of age. However, PHX induced a significant increase in frontal cortex volume in WT whereas the higher frontal cortical volume found in HRM was significantly reduced by PHX. A significant decrease in reelin levels was observed in frontal cortex of WT and HRM and hippocampus of HRM following PHX. In addition, PHX induced significant reductions in hypoxia inducible factor-1α (HIF-1α) levels in frontal cortex and hippocampus of HRM. Although no significant effect of PHX was observed in vascular endothelial growth factor (VEGF) protein levels in frontal cortex and hippocampus of WT and HRM, serum VEGF levels were found higher in HRM following PHX. Moreover, glucocorticoid receptor (GR) protein levels were significantly lower in frontal cortex of WT and HRM and hippocampus of HRM following PHX. We found a significant reduction in serum corticosterone levels of PHX-treated WT mice. These findings suggest that future experiments addressing gene-environment interaction in schizophrenia should consider age-dependent effects of the environmental factor, in addition to the specificity of the gene of interest.

Pre and post-natal antigen exposure can program the stress axis of adult zebra finches: evidence for environment matching

Both maternal exposure to stressors and exposure of offspring to stressors during early life can have lifelong effects on the physiology and behavior of offspring. Stress exposure can permanently shape an individual's phenotype by influencing the development of the hypothalamic-pituitary-adrenal (HPA) axis, which is responsible for the production and regulation of glucocorticoids such as corticosterone (CORT). In this study we used captive zebra finches (Taeniopygia guttata) to examine the effects of matching and mismatching maternal and early post-natal exposure to one of two types of antigens or a control on HPA axis reactivity in adult offspring. Prior to breeding, adult females were injected with lipopolysaccharide (LPS), keyhole limpet hemocyanin (KLH) or a control. Offspring of females in each of the three treatments were themselves exposed to LPS, KLH or a control injection at 5 and 28days post-hatch. When offspring were at least 18months of age, standardized capture and restraint stress tests were conducted to determine the impact of the treatments on adult stress responsiveness. We found significant interaction effects between maternal and offspring treatments on stress-induced CORT levels, and evidence in support of the environment matching hypothesis for KLH-treated birds, not LPS-treated birds. KLH-treated offspring of KLH-treated mothers exhibited reduced stress-induced CORT levels, whereas LPS-treated or control offspring of KLH-treated mothers exhibited elevated stress-induced CORT levels. Although the treatment effects on baseline CORT were non-significant, the overall pattern was similar to the effects observed on stress-induced CORT levels. Our results highlight the complex nature of HPA axis programming, and to our knowledge, provide the first evidence that a match or mismatch between pre and post-natal antigen exposure can have life-long consequences for HPA axis function.

Modifications of glucocorticoid receptors mRNA expression in the hypothalamic-pituitary-adrenal axis in response to early-life stress in female Japanese quail

Stress exposure during early-life development can programme individual brain and physiology. The hypothalamic-pituitary-adrenal (HPA) axis is one of the primary targets of this programming, which is generally associated with a hyperactive HPA axis, indicative of a reduced negative-feedback. This reduced feedback efficiency usually results from a reduced level of the glucocorticoid receptor (GR) and/or the mineralocorticoid receptor (MR) within the HPA axis. However, a few studies have shown that early-life stress exposure results in an attenuated physiological stress response, suggesting an enhance feedback efficiency. In the present study, we aimed to determine whether early-life stress had long-term consequences on GR and MR levels in quail and whether the effects on the physiological response to acute stress observed in prenatally stressed individuals were underpinned by changes in GR and/or MR levels in one or more HPA axis components. We determined GR and MR mRNA expression in the hippocampus, hypothalamus and pituitary gland in quail exposed to elevated corticosterone during prenatal development, postnatal development, or both, and in control individuals exposed to none of the stressors. We showed that prenatal stress increased the GR:MR ratio in the hippocampus, GR and MR expression in the hypothalamus and GR expression in the pituitary gland. Postnatal stress resulted in a reduced MR expression in the hippocampus. Both early-life treatments permanently affected the expression of both receptor types in HPA axis regions. The effects of prenatal stress are in accordance with a more efficient negative-feedback within the HPA axis and thus can explain the attenuated stress response observed in these birds. Therefore, these changes in receptor density or number as a consequence of early-life stress exposure might be the mechanism that allows an adaptive response to later-life stressful conditions.

The effects of sertraline administration from adolescence to adulthood on physiological and emotional development in prenatally stressed rats of both sexes

Sertraline (SERT) is a clinically effective Selective Serotonin Reuptake Inhibitor (SSRI) known to increase and stabilize serotonin levels. This neurotransmitter plays an important role in adolescent brain development in both rodents and humans, and its dysregulation has been correlated with deficits in behavior and emotional regulation. Since prenatal stress may disturb serotoninergic homeostasis, the aim of this study was to examine the long-lasting effects of exposure to SERT throughout adolescence on behavioral and physiological developmental parameters in prenatally stressed Wistar rats. SERT was administered (5 mg/kg/day p.o.) from the age of 1-3 months to half of the progeny, of both sexes, of gestating dams stressed by use of a restraint (PS) or not stressed. Our data reveal that long-term SERT treatment slightly reduced weight gain in both sexes, but reversed the developmental disturbed "catch-up" growth found in PS females. Neither prenatal stress nor SERT treatment induced remarkable alterations in behavior and had no effects on mean startle reflex values. However, a sex-dependent effects of PS was found: in males the PS paradigm slightly increased anxiety-like behavior in the open field, while in females, it impaired startle habituation. In both cases, SERT treatment reversed the phenomena. Additionally, the PS animals exhibited a disturbed leukocyte profile in both sexes, which was reversed by SERT. The present findings are evidence that continuous SERT administration from adolescence through adulthood is safe in rodents and lessens the impact of prenatal stress in rats.

Impact of circadian nuclear receptor REV-ERBα on midbrain dopamine production and mood regulation

The circadian nature of mood and its dysfunction in affective disorders is well recognized, but the underlying molecular mechanisms are still unclear. Here, we show that the circadian nuclear receptor REV-ERBα, which is associated with bipolar disorder, impacts midbrain dopamine production and mood-related behavior in mice. Genetic deletion of the Rev-erbα gene or pharmacological inhibition of REV-ERBα activity in the ventral midbrain induced mania-like behavior in association with a central hyperdopaminergic state. Also, REV-ERBα repressed tyrosine hydroxylase (TH) gene transcription via competition with nuclear receptor-related 1 protein (NURR1), another nuclear receptor crucial for dopaminergic neuronal function, thereby driving circadian TH expression through a target-dependent antagonistic mechanism. In conclusion, we identified a molecular connection between the circadian timing system and mood regulation, suggesting that REV-ERBα could be targeting in the treatment of circadian rhythm-related affective disorders.

Prenatal stress induces up-regulation of glucocorticoid receptors on lymphoid cells modifying the T-cell response after acute stress exposure in the adult life

It has been demonstrated that a short-duration stress (acute stress) may result in immunopreparatory or immunoenhancing physiological conditions. The aim of the present study was to investigate whether exposure to prenatal restraint stress (PRS) influences the impact of acute stress on the T-cell response in the adult life. We found that female mice exposed to PRS (PS mice) did not exhibit changes in the T-cell-dependent IgG antibody production with respect to prenatally non-stressed mice (no-PS mice). However, no-PS mice exposed to acute stress showed an increase of antibody production after antigen stimulation. In contrast, PS mice exhibited a decreased response after an acute situation. Spleen catecholamines and plasma corticosterone levels were increased in acute stress in both PS and no-PS mice. Nevertheless, lymphocyte response to hormones was altered in PS mice. Particularly, inhibitory effect of corticosterone was higher on lymphocytes from PS mice. In addition, an increase in protein levels and mRNA expression of glucocorticoid receptor was found in lymphoid cells from PS mice. These results show that prenatal stress alters the immune intrinsic regulatory mechanism that in turn induces an increased vulnerability to any stressful situation able to modify immune homeostasis.

Mismatch or Cumulative Stress

In the study reported here, the main question we investigated was whether attention style could be a conditional adaptation. We organized participants of the TRacking Adolescents’ Individual Lives Survey (TRAILS; N = 2,230) into shifters, sustainers, and two comparison groups, depending on their performance on a shifting- and a sustained-attention task at age 11 years. Compared with sustainers, shifters reported more pre- and perinatal risk factors and more childhood stress, and they adopted a faster life-history strategy. These differences were not found between the comparison groups, who performed well or poorly on both tasks, which suggests that specialization for either sustained or shifting attention is the key to conditional adaptation. In a subsample ( n = 860), we found that stress did not increase depression risk in shifters, whereas a mismatch between early and recent stress predicted depression in sustainers. Cumulative stress predicted depression in the comparison group. These results suggest that shifters retain high levels of plasticity throughout life, whereas sustainers’ adapted their phenotype early in life to the expected mature environment.

Prenatal exposure to zinc oxide particles alters monoaminergic neurotransmitter levels in the brain of mouse offspring

Zinc oxide (ZnO) nano-sized particles (NPs) are beneficial materials used for sunscreens and cosmetics. Although ZnO NPs are widely used for cosmetics, the health effects of exposure during pregnancy on offspring are largely unknown. Here we investigated the effects of prenatal exposure to ZnO NPs on the monoaminergic system of the mouse brain. Subcutaneous administration of ZnO NPs to the pregnant ICR mice (total 500 μg/mouse) were carried out and then measured the levels of dopamine (DA), serotonin (5-HT), and noradrenalin, and their metabolites in 9 regions of the brain of offspring (6-week-old) using high performance liquid chromatography (HPLC). HPLC analysis demonstrated that DA levels were increased in hippocampus in the ZnO NP exposure group. In the levels of DA metabolites, homovanillic acid was increased in the prefrontal cortex and hippocampus, and 3, 4-dihydroxyphenylacetic acid was increased in the prefrontal cortex by prenatal ZnO NP exposure. Furthermore, DA turnover levels were increased in the prefrontal cortex, neostriatum, nucleus accumbens, and amygdala in the ZnO NP exposure group. We also found changes of the levels of serotonin in the hypothalamus, and of the levels of 5-HIAA (5-HT metabolite) in the prefrontal cortex and hippocampus in the ZnO NP-exposed group. The levels of 5-HT turnover were increased in each of the regions except for the cerebellum by prenatal ZnO NP exposure. The present study indicated that prenatal exposure to ZnO NPs might disrupt the monoaminergic system, and suggested the possibility of detrimental effects on the mental health of offspring.

Developmental programming: cumulative effects of increased pre-hatching corticosterone levels and post-hatching unpredictable food availability on physiology and behaviour in adulthood

Prolonged exposure to stress during development can have long-term detrimental effects on health and wellbeing. However, the environmental matching hypothesis proposes that developmental stress programs physiology and behaviour in an adaptive way that can enhance fitness if early environments match those experienced later in life. Most research has focused on the harmful effects that stress during a single period in early life may exert in adulthood. In this study, we tested the potential additive and beneficial effects that stress experienced during both pre- and post-hatching development may have on adult physiology and behaviour. Japanese quail experienced different stress-related treatments across two developmental life stages: pre-hatching corticosterone (CORT) injection, post-hatching unpredictable food availability, both pre- and post-hatching treatments, or control. In adulthood, we determined quails' acute stress response, neophobia and novel environment exploration. The pre-hatching CORT treatment resulted in attenuated physiological responses to an acute stressor, increased activity levels and exploration in a novel environment. Post-hatching unpredictable food availability decreased adults' latency to feed. Furthermore, there were cumulative effects of these treatments across the two developmental stages: quail subjected to both pre- and post-hatching treatments were the most explorative and risk-taking of all treatment groups. Such responses to novel environments could enhance survival in unpredictable environments in later life. Our data also suggest that these behavioural responses may have been mediated by long-term physiological programming of the adrenocortical stress response, creating phenotypes that could exhibit fitness-enhancing behaviours in a changing environment.

Upregulation of PVN CRHR1 by gestational intermittent hypoxia selectively triggers a male-specific anxiogenic effect in rat offspring

We previously reported that gestational intermittent hypoxia (GIH) causes anxiety-like behavior in neonatal rats. Here, we showed that the anxiogenic effect was correlated with upregulation of corticotropin-releasing hormone receptor 1 (CRHR1) in the hypothalamic paraventricular nuclei (PVN) by GIH, and was selective to male offspring. The anxiety-like behavior was assessed by both the open field (OF) and elevated plus maze (EPM) tests. We demonstrated that GIH triggered anxiety-like behavior in male offspring, but not in female offspring or in the postpartum dams. Microinjection of antalarmin, a CRHR1-selective antagonist, into the PVN of the male offspring significantly increased the distance traveled and time spent in the central portion of the OF, and the time spent in the open arms in the EPM compared with controls. However, microinjection of the CRHR2 agonist, urocortin III, into the PVN did not affect anxiogenic behavior in the male offspring. These findings clearly demonstrate a gender-selective effect of GIH to increase anxiety-like behavior and this anxiogenic effect might be linked to embryogenically-driven upregulation of PVN CRHR1.

Mismatch or cumulative stress: toward an integrated hypothesis of programming effects

This paper integrates the cumulative stress hypothesis with the mismatch hypothesis, taking into account individual differences in sensitivity to programming. According to the cumulative stress hypothesis, individuals are more likely to suffer from disease as adversity accumulates. According to the mismatch hypothesis, individuals are more likely to suffer from disease if a mismatch occurs between the early programming environment and the later adult environment. These seemingly contradicting hypotheses are integrated into a new model proposing that the cumulative stress hypothesis applies to individuals who were not or only to a small extent programmed by their early environment, while the mismatch hypothesis applies to individuals who experienced strong programming effects. Evidence for the main effects of adversity as well as evidence for the interaction between adversity in early and later life is presented from human observational studies and animal models. Next, convincing evidence for individual differences in sensitivity to programming is presented. We extensively discuss how our integrated model can be tested empirically in animal models and human studies, inviting researchers to test this model. Furthermore, this integrated model should tempt clinicians and other intervenors to interpret symptoms as possible adaptations from an evolutionary biology perspective.

Sex differences in prenatally programmed anxiety behaviour in rats: differential corticotropin-releasing hormone receptor mRNA expression in the amygdaloid complex

We recently reported that male, but not female, offspring born to mothers exposed to social stress during late gestation show heightened anxiety-type behaviour in adulthood. The amygdala organises anxious behaviour, which involves actions of corticotropin-releasing hormone (CRH). CRH gene expression and/or its release are increased in the amygdala in prenatally stressed (PNS) rats. CRH type 1 receptor (CRH-R1) mediates actions of CRH and urocortin I to promote anxiety-like behaviour, whereas the CRH type 2 receptor (CRH-R2) may mediate anxiolytic actions, through actions of urocortins 2 and 3. Here, using quantitative in situ hybridisation, we investigated whether altered CRH receptor mRNA expression in the amygdaloid nuclei may explain the sex differences in anxiety behaviour in adult male and female PNS rats. CRH-R1 mRNA expression was significantly greater in the central amygdala and basolateral amygdala (BLA) in male PNS rats compared with controls, with no change in the basomedial amygdala (BMA) or medial amygdala (MeA). In PNS females, CRH-R1 mRNA expression was greater than controls only in the MeA. Conversely, CRH-R2 mRNA expression was significantly lower in the BMA of male PNS rats compared with controls, but greater in female PNS rats, with no change in the BLA or MeA in either sex. The ratio of CRH-R1:CRH-R2 mRNA in the amygdaloid nuclei was generally increased in PNS males, but not in the PNS females. In conclusion, sex differences in anxiety-type behaviour in PNS rats may be explained by differential mRNA expression for CRH-R1 (pro-anxiogenic) and CRH-R2 (pro-anxiolytic) in the amygdaloid complex.

Living in a dangerous world decreases maternal care: a study in serotonin transporter knockout mice

Adverse early experiences can profoundly influence the adult behavioral profile. When pregnant and lactating mice are confronted with soiled bedding of unfamiliar males (UMB), these stimuli signal the danger of infanticide and thus simulate a "dangerous world". In a previous study, offspring of UMB treated mothers were shown to display increased anxiety-like behavior and reduced exploratory locomotion as adults, compared to mice treated with neutral bedding (NB, "safe environment"). The aim of this study was to elucidate the mechanisms conveying these effects of living in a "dangerous world" to offspring behavior. We hypothesized the mother to be the major link and focused on the influence of UMB on maternal stress hormones and behavior. Thus, we investigated fecal corticosterone metabolites (CM) and maternal care of pregnant and lactating mice either treated with NB or UMB. The offspring were subsequently tested for their anxiety-like and exploratory behavior. Mothers treated with UMB showed a significantly higher increase of fecal CM following the initial treatment, than NB treated mothers, indicating that the odor cues of potentially infanticidal males represented an ethologically relevant stimulus. Whereas the hormonal stress response habituated, living in a "dangerous world" led to a distinct and consistent reduction of maternal care behavior, particularly concerning the duration of licking and grooming the pups. Surprisingly, we could not confirm our former findings of altered phenotypes in the offspring of UMB treated mothers. In summary, we hypothesize that the frequently described effects of early life adversity on the offspring's behavioral profile are mediated primarily by maternal care in altricial rodents.

Impairment of fear memory consolidation in maternally stressed male mouse offspring: evidence for nongenomic glucocorticoid action on the amygdala

The environment in early life elicits profound effects on fetal brain development that can extend into adulthood. However, the long-lasting impact of maternal stress on emotional learning remains largely unknown. Here, we focus on amygdala-related learning processes in maternally stressed mice. In these mice, fear memory consolidation and certain related signaling cascades were significantly impaired, though innate fear, fear memory acquisition, and synaptic NMDA receptor expression in the amygdala were unaltered. In accordance with these findings, maintenance of long-term potentiation (LTP) at amygdala synapses, but not its induction, was significantly impaired in the maternally stressed animals. Interestingly, amygdala glucocorticoid receptor expression was reduced in the maternally stressed mice, and administration of glucocorticoids (GCs) immediately after fear conditioning and LTP induction restored memory consolidation and LTP maintenance, respectively, suggesting that a weakening of GC signaling was responsible for the observed impairment. Furthermore, microinfusion of a membrane-impermeable form of GC (BSA-conjugated GC) into the amygdala mimicked the restorative effects of GC, indicating that a nongenomic activity of GC mediates the restorative effect. Together, these findings suggest that prenatal stress induces long-term dysregulation of nongenomic GC action in the amygdala of adult offspring, resulting in the impairment of fear memory consolidation. Since modulation of amygdala activity is known to alter the consolidation of emotionally influenced memories allocated in other brain regions, the nongenomic action of GC on the amygdala shown herein may also participate in the amygdala-dependent modulation of memory consolidation.

The clinical implications of mouse models of enhanced anxiety

Mice are increasingly overtaking the rat model organism in important aspects of anxiety research, including drug development. However, translating the results obtained in mouse studies into information that can be applied in clinics remains challenging. One reason may be that most of the studies so far have used animals displaying 'normal' anxiety rather than 'psychopathological' animal models with abnormal (elevated) anxiety, which more closely reflect core features and sensitivities to therapeutic interventions of human anxiety disorders, and which would, thus, narrow the translational gap. Here, we discuss manipulations aimed at persistently enhancing anxiety-related behavior in the laboratory mouse using phenotypic selection, genetic techniques and/or environmental manipulations. It is hoped that such models with enhanced construct validity will provide improved ways of studying the neurobiology and treatment of pathological anxiety. Examples of findings from mouse models of enhanced anxiety-related behavior will be discussed, as well as their relation to findings in anxiety disorder patients regarding neuroanatomy, neurobiology, genetic involvement and epigenetic modifications. Finally, we highlight novel targets for potential anxiolytic pharmacotherapeutics that have been established with the help of research involving mice. Since the use of psychopathological mouse models is only just beginning to increase, it is still unclear as to the extent to which such approaches will enhance the success rate of drug development in translating identified therapeutic targets into clinical trials and, thus, helping to introduce the next anxiolytic class of drugs.

Mild prenatal stress-modulated behavior and neuronal spine density without affecting amphetamine sensitization

The present study investigated the effect of prenatal stress (PS) on juvenile behavior and adult amphetamine (AMPH) sensitization, as well as the effect of the interaction between experience (i.e. PS) and drug (i.e. AMPH) on cortical thickness and neuronal morphology in corticolimbic regions in rats. Juvenile male and female rats, exposed to gestational stress, were tested in behavioral tasks that included open field locomotion, elevated plus maze, novel object recognition, and play fighting behavior. The development and persistence of drug-induced behavioral sensitization in adults were tested by chronic AMPH administration and challenge, respectively. Spine density in corticolimbic regions was examined for structural plasticity. The findings showed that PS produced anxiety-like behavior in males. Furthermore, PS in males resulted in female-like play and enhanced partial rotation defense, whereas in females PS increased the probability of evasion in response to an attack. AMPH administration resulted in gradual increase in behavioral sensitization that persisted at least for 2 weeks; however, PS did not influence AMPH-induced behavioral sensitization in either male or female rats. Moreover, PS increased the spine density in the nucleus accumbens (NAc) and decreased it in the medial prefrontal cortex (mPFC) without any alteration in the orbital frontal cortex (OFC). Similarly, AMPH administration increased spine density in the NAc and mPFC, whereas a decrease was observed in the OFC. However, PS prevented the drug-induced alterations in the spine density observed in controls. In sum, PS modulated juvenile behavior and altered brain morphology without influencing AMPH-induced behavioral sensitization substantially.

The effects of breeding protocol in C57BL/6J mice on adult offspring behaviour

Animal experiments have demonstrated that a wide range of prenatal exposures can impact on the behaviour of the offspring. However, there is a lack of evidence as to whether the duration of sire exposure could affect such outcomes. We compared two widely used methods for breeding offspring for behavioural studies. The first involved housing male and female C57Bl/6J mice together for a period of time (usually 10–12 days) and checking for pregnancy by the presence of a distended abdomen (Pair-housed; PH). The second involved daily introduction of female breeders to the male homecage followed by daily checks for pregnancy by the presence of vaginal plugs (Time-mated; TM). Male and female offspring were tested at 10 weeks of age on a behavioural test battery including the elevated plus-maze, hole board, light/dark emergence, forced swim test, novelty-suppressed feeding, active avoidance and extinction, tests for nociception and for prepulse inhibition (PPI) of the acoustic startle response. We found that length of sire exposure (LSE) had no significant effects on offspring behaviour, suggesting that the two breeding protocols do not differentially affect the behavioural outcomes of interest. The absence of LSE effects on the selected variables examined does not detract from the relevance of this study. Information regarding the potential influences of breeding protocol is not only absent from the literature, but also likely to be of particular interest to researchers studying the influence of prenatal manipulations on adult behaviour.

Prenatal stress: role in psychotic and depressive diseases

RATIONALE

The birth of neurons, their migration to appropriate positions in the brain, and their establishment of the proper synaptic contacts happen predominately during the prenatal period. Environmental stressors during gestation can exert a major impact on brain development and thereby contribute to the pathogenesis of neuropsychiatric illnesses, such as depression and psychotic disorders including schizophrenia.

OBJECTIVE

The objectives here are to present recent preclinical studies of the impact of prenatal exposure to gestational stressors on the developing fetal brain and discuss their relevance to the neurobiological basis of mental illness. The focus is on maternal immune activation, psychological stresses, and malnutrition, due to the abundant clinical literature supporting their role in the etiology of neuropsychiatric illnesses.

RESULTS

Prenatal maternal immune activation, viral infection, unpredictable psychological stress, and malnutrition all appear to foster the development of behavioral abnormalities in exposed offspring that may be relevant to the symptom domains of schizophrenia and psychosis, including sensorimotor gating, information processing, cognition, social function, and subcortical hyperdopaminergia. Depression-related phenotypes, such as learned helplessness or anxiety, are also observed in some model systems. These changes appear to be mediated by the presence of proinflammatory cytokines and/or corticosteroids in the fetal compartment that alter the development the neuroanatomical substrates involved in these behaviors.

CONCLUSION

Prenatal exposure to environmental stressors alters the trajectory of brain development and can be used to generate animal preparations that may be informative in understanding the pathophysiological processes involved in several human neuropsychiatric disorders.

Maternal stress retards fetal development in mice with transcriptome-wide impact on gene expression profiles of the limb

The environment of a pregnant mother has a life-long impact on later life of offspring. Maternal stress is known to cause low birth weight and programs several physiological dysfunctions in offspring. However, the direct effects of maternal stress on the developing fetus remain largely unknown. The present study focused on the effect of chronic maternal stress on the developmental program and its molecular mechanisms. Pregnant mice were given 6-hour immobilization stress every day from 8.5 days post coitum. Fetal body weight was significantly decreased by maternal stress throughout development. Importantly, developmental events were retarded in the stressed fetuses. Around embryonic day 13.5 (E13.5), the developmental increment of somite numbers was delayed, although this difference recovered by E15.5. Limb bud formation and regression of interdigital webbing were also retarded by approximately 0.5 days. Subsequently, transcriptomes of developing limbs were analyzed by cDNA microarrays. Approximately, one-tenth of detected transcripts were significantly influenced by maternal stress. Q-PCR AQ analyses further demonstrated that the expression of a subset of limb development-associated genes, including Igf1, Aldh1a2, and Acta1, was changed in the stressed fetus. In conclusion, our findings suggest that maternal stress can retard limb and somite development in mice, with profound impacts on the developmental genetic program of limb.

Prenatal stress induces anxiety-like behavior together with the disruption of central serotonin neurons in mice

Most pregnant women are at risk of showing some emotional abnormality, since some biological functions such as hormonal systems may dramatically change in pregnancy. Some of them may be exposed to strong stress as hesitation of positive drug therapies because of worries regarding adverse effects on the embryo. A growing body of evidence suggests that prenatal stress increases the vulnerability to neuropsychiatric disorders, including depression and anxiety. However, the mechanisms involved are still unknown. To clarify the influence of exposure to prenatal stress on emotional development, we examined behavioral responses in offspring exposed to weak- or strong-prenatal restraint stress. We found that offspring that had been exposed to strong stress displayed anxiety-like behavior as determined by the elevated plus-maze test. It has been widely accepted that central serotonin (5-hydroxytryptamine; 5-HT) neurons play a critical role in emotional behaviors. Immunohistochemical studies showed that exposure to strong-prenatal restraint stress increased the expression of 5-HT-positive cells in the dorsal raphe nuclei in mice. Moreover, under these conditions, tryptophan hydroxylase-like immunoreactivities were also dramatically increased. In contrast, these behavioral and neurochemical abnormalities were not observed in offspring that had been exposed to weak-prenatal restraint stress. These findings indicate that exposure to excessive prenatal stress induces anxiety-like behavior together with disruption of the development of 5-HT neurons in mice.

The weight gain response to stress during adulthood is conditioned by both sex and prenatal stress exposure

Food intake and weight gain are known to be affected by stress. However, the type and duration of the stress may have variable effects, with males and females responding differently. We report the short-term and long-term effects of prenatal and adult immobilization stress, as well as the combination of these two stresses, on weight gain and food intake in male and female rats and the role of post-pubertal gonadal hormones in this process. No long-term effect of prenatal stress on food intake or weight gain was found in either sex. However, during the period of adult stress [at postnatal day (P) 90; 10 days duration] stressed male rats gained significantly less weight than controls and previous exposure to prenatal stress attenuated this effect (control: 31.2+/-2.1g; prenatal stress: 24.6+/-3.8g; adult stress: 8.1+/-3.4g; prenatal and adult stress: 18.2+/-3.3g; p<0.0001). There was no change in food intake in response to either prenatal or adult stress. Adult stress increased circulating corticosterone levels during the initial part of the stress period, in both male and female rats with this rise being greater in male rats. No effect on corticosterone levels was observed on the last day of stress in either sex. No effect on weight gain or food intake was observed in female rats. Following adult stress, male rats increased their weight gain, with no change in food intake, such that 1 month later they reached control levels. At the time of sacrifice (P180), there were no differences in weight or circulating metabolic hormone levels between any of the male groups. Although castration alone modulated body weight in both male and female rats, it did not affect their weight gain response to adult stress. These results indicate that the weight gain response to adult stress is sexually dimorphic and that this is not dependent on post-pubertal gonadal steroids. Furthermore, the outcome of this response closely depends on the time at which the change in weight is analyzed, which could help to explain different results reported in the literature. Indeed, weight and metabolic hormone levels were normalized by the end of the study.

Oleoyl-estrone increases adrenal corticosteroid synthesis gene expression in overweight male rats

Oleoyl-estrone (OE) induces a marked loss of body fat in rats by maintaining energy expenditure, body protein and blood glucose despite decreasing food intake. OE increases glucocorticoids, but they arrest OE lipid-mobilization. We studied here whether OE induces a direct effect on adrenal glands function as part of this feedback regulation. Dietary overweight male rats were given oral 10nmol/g OE gavages for ten days. A group (PF) of pair-fed to OE rats, and controls received vehicle-only gavages. OE rats lost slightly more body than PF, but had larger adrenal glands. Tissue corticosterone levels, and gene expressions for glucocorticoid-synthesizing enzymes were increased in OE versus controls and PF; thus, we assumed that adrenal growth affected essentially its cortex since OE also lowered the expression of the medullar catecholamine synthesis enzyme genes. Serum corticosterone was higher in PF than in OE and controls, but liver expression of corticosteroid-disposing steroid 5alpha-reductase was 3x larger in OE than PF and controls. Circulating glucocorticoids changed little under OE, in spite of higher adrenal gland and liver content, hinting at modulation of glucocorticoid turnover as instrumental in their purported increased activity. In conclusion, we have observed that OE considerable enhanced the expression of the genes controlling the synthesis of glucocorticoids from cholesterol in the rat and increasing the adrenal glands' corticosterone, size and cellularity, but also the liver disposal of corticosteroids, suggesting that OE increases corticosterone synthesis and degradation (i.e. serum turnover), a process not driven by limited energy availability but directly related to the administration of OE.

Disruptions of the mother-infant relationship and stress-related behaviours: altered corticosterone secretion does not explain everything

The hypothalamic-pituitary-adrenal (HPA) axis is the main neuroendocrine system of response to stress, and an imbalance of this system's activity is believed to be at the core of numerous psychiatric pathologies. During the neonatal period, the glucocorticoid response to stress is maintained at low levels by specific maternal behaviours, which is essential for proper brain development. Effective evaluation of the impact of increased secretion of corticosterone during an essentially anabolic developmental period on adulthood behaviour involved separation of the neonate from its mother for periods ranging from 3 to 24h. It has been shown that disinhibition of the stress response is achieved by such procedures. The pioneering studies by Seymour Levine set the stage for a prolific and promising field of study that may help neuroscientists unveil the neurobiological underpinnings of stress-related disorders. Based on a series of studies, we propose that maternal separation and maternal deprivation change stress-related behaviours, but that corticosterone seem to be only partially involved in these changes in adulthood. It appears that extra-hypothalamic corticotrophin-releasing factor and neurotransmitter systems may be the primary mediators of these behavioural outcomes.