Vulnerability versus resilience to prenatal stress in male and female rats; implications from gene expression profiles in the hippocampus and frontal cortex

Immune alterations in the intrauterine environment shapes offspring brain development in a sex-specific manner

Exposure to inflammation in utero or in early life is known to increase risk for neuropsychiatric illness. The sources of inflammation can be varied, including acute exposures due to maternal infection or acute stress, or persistent exposures due to chronic stress, obesity, malnutrition, or autoimmune diseases. These exposures may cause subtle alteration in brain development, structure, and function that can become progressively magnified across the lifespan, potentially increasing risk for neuropsychiatric conditions. There is some evidence that males are more susceptible to early life inflammatory challenges compared to females. In this review, we discuss the various sources of in utero or early life inflammation, and the known effects on fetal development. We also discuss these changes with a focus on sex differences in the brain, leveraging neuroimaging, as well as behavioral, cellular, and neurochemical findings. Gaining clarity on how the intrauterine environment affects offspring development is of critical importance for informing preventative and early intervention measures that may buffer against the effects of these early life risk factors.

Parental preconception stress in zebrafish induces long-lasting anxiety in offspring

The growth and function of the vertebrate brain are impacted by environmental stimuli and early life stress. Adults who experience chronic stress during early life are more likely to suffer various neurodevelopmental and health issues. However, our understanding of how these specific environmental signals at different developmental stages affect brain development is poorly understood. In this study, we investigated if stress in parents prior to conception modulates neurodevelopment in offspring. We used a chronic unpredictable stress model adapted to zebrafish, which is an increasingly popular vertebrate model in neuroscience research to investigate the effects of both maternal and paternal preconception stress on offspring behavior. We evaluated the responsiveness of three anxiety-related behavioral paradigms in zebrafish: the novel tank test, thigmotaxis, and shoaling behavior. We found larvae from stressed females exhibited anxiety-like behavior in a thigmotaxis assay. As these larvae matured into adults, they continued to exhibit anxiety-like behavior in a novel tank and shoaling behavioral assay. These studies indicate preconception stress exposure in parents can induce life-long alterations in offspring neurodevelopment. Further, these results expand the hypothesis that chronically elevated glucocorticoid signaling not only in stressed mothers, but also stressed dads can affect neurodevelopment in offspring. We propose that zebrafish may be a useful model to study the transgenerational effects of chronic stress mediated via the maternal and paternal line.

Geniposide improves depression-like behavior in prenatal stress male offspring through restoring HPA axis- and glucocorticoid receptor-associated dysfunction

AIMS

Prenatal stress (PS) has an important impact on the brain development of offspring, which can lead to attention deficits, anxiety and depression in offspring. Geniposide (GE) is a kind of iridoid glycoside extracted from Gardenia jasminoides Ellis. It has various pharmacological effects and has been proved that have antidepressant effects. The aim of this study was to investigate the effect of GE on depression-like behavior in PS-induced male offspring mice and explore the possible molecular mechanisms.

METHODS

We used a prenatal restraint stress model, focusing on male PS-induced offspring mice to study the effects of GE.

KEY FINDINGS

The results showed that GE administration for 4 weeks significantly improved the depression-like behavior in PS offspring mice, which was manifested by markedly increasing the sucrose preference of PS offspring and the activity in the open field test, and reducing the immobility time in the forced swimming test. In addition, GE significantly reduced the levels of hypothalamic-pituitary-adrenal (HPA) axis-related hormones and exceedingly increased the protein expression of MAP2 and GAP43 in PS offspring. Furthermore, GE increased Glucocorticoid receptors (GR) nuclear translocation in the hippocampus of PS offspring, and enhanced the expression of synaptic plasticity-related proteins.

CONCLUSION

The results of this study showed that GE exerts antidepressant effects in male PS offspring mice by regulating the HPA axis, GR function and proteins related to synaptic plasticity.

Perinatal environmental enrichment changes anxiety-like behaviours in mice and produces similar intergenerational benefits in offspring

Environmental enrichment implemented in early life is able to induce long-term changes in gene expression, synaptic function and behavioural responses. In this study, we evaluated the adult behavioural effects of perinatal environment enrichment in male and female mice (PEE), as well as the males and females of PEE male offspring (OPEE). For this purpose, animals were submitted to the following battery of behavioural analyses: elevated plus maze, open field test, light-dark box and novelty suppression feeding test. The frontal cortex and ventral hippocampus of PEE mice were collected for the evaluation of the expression of gamma-aminobutyric acid (GABA)-related genes. The PEE animals showed an increase in exploratory activity, associated with a reduction in anxiety-like behaviours on the elevated plus maze; this effect was mainly observed in males. Additionally, the male OPEE showed a reduction in anxiety-like behaviours on the elevated plus maze, mainly observed in a reduction of risk assessment-related behaviours. The PEE male mice also showed reduced expression of Gabra3 in the ventral hippocampus when compared to the control group. These results demonstrate that perinatal environmental enrichment promotes a reduction in anxiety-like behaviour that can be transferred intergenerationally.

Environmental Enrichment Promotes Transgenerational Programming of Uterine Inflammatory and Stress Markers Comparable to Gestational Chronic Variable Stress

Prenatal maternal stress is linked to adverse pregnancy and infant outcomes, including shortened gestation lengths, low birth weights, cardio-metabolic dysfunction, and cognitive and behavioural problems. Stress disrupts the homeostatic milieu of pregnancy by altering inflammatory and neuroendocrine mediators. These stress-induced phenotypic changes can be passed on to the offspring epigenetically. We investigated the effects of gestational chronic variable stress (CVS) in rats using restraint and social isolation stress in the parental F0 generation and its transgenerational transmission across three generations of female offspring (F1-F3). A subset of F1 rats was housed in an enriched environment (EE) to mitigate the adverse effects of CVS. We found that CVS is transmitted across generations and induces inflammatory changes in the uterus. CVS did not alter any gestational lengths or birth weights. However, inflammatory and endocrine markers changed in the uterine tissues of stressed mothers and their offspring, suggesting that stress is transgenerationally transmitted. The F2 offspring reared in EE had increased birth weights, but their uterine gene expression patterns remained comparable to those of stressed animals. Thus, ancestral CVS induced changes transgenerationally in fetal programming of uterine stress markers over three generations of offspring, and EE housing did not mitigate these effects.

Prolactin and glucocorticoid receptors in the prefrontal cortex are associated with anxiety-like behavior in prenatally stressed adolescent offspring rats

Prenatal stress (PS) causes anxiety in mothers and their offspring and chewing is a commonly observed behavior during maternal stress. Prolactin (PRL) is an anti-anxiety factor that suppresses the hypothalamic-pituitary-adrenal axis. Here, we studied the roles of PRL, corticosterone (CORT), and their receptors in PS-induced anxiety-like behavior in dams and their offspring. We further investigated whether chewing during maternal stress could prevent PS-induced harmful consequences. Pregnant rats were randomly divided into PS, PS + chewing, and control groups. Anxiety-like behaviors of dams and their adolescent offspring were assessed using the open field test and elevated plus maze. Serum levels of PRL and CORT were measured by ELISA. Expression of mRNA and protein of PRLR and glucocorticoid receptor (GR) in the prefrontal cortex (PFC) were evaluated by qRT-PCR and western blotting, respectively. Compared to the control rats, dams and their female offspring, but not male offspring, in the PS group showed increased anxiety-like behaviors. The PS-affected rats had a lower serum PRL level and increased PRLR expression in the PFC. In contrast, these rats had a higher serum CORT level and decreased GR expression in the PFC. Chewing ameliorated anxiety-like behaviors and counteracted stress-induced changes in serum PRL and CORT, as well as the expression of their receptors in the PFC. Conclusion: PS-induced anxiety-like behavior is associated with changes in the serum levels of PRL and CORT and expression of their receptors in the PFC. Moreover, chewing blunts the hormonal and receptor changes and may serve as an effective stress-coping method for preventing PS-induced anxiety-like behavior.

Epigenetic Mechanism of Early Life Stress-Induced Depression: Focus on the Neurotransmitter Systems

Depression has an alarmingly high prevalence worldwide. A growing body of evidence indicates that environmental factors significantly affect the neural development and function of the central nervous system and then induce psychiatric disorders. Early life stress (ELS) affects brain development and has been identified as a major cause of depression. It could promote susceptibility to stress in adulthood. Recent studies have found that ELS induces epigenetic changes that subsequently affect transcriptional rates of differentially expressed genes. The epigenetic modifications involved in ELS include histone modifications, DNA methylation, and non-coding RNA. Understanding of these genetic modifications may identify mechanisms that may lead to new interventions for the treatment of depression. Many reports indicate that different types of ELS induce epigenetic modifications of genes involved in the neurotransmitter systems, such as the dopaminergic system, the serotonergic system, the gamma-aminobutyric acid (GABA)-ergic system, and the glutamatergic system, which further regulate gene expression and ultimately induce depression-like behaviors. In this article, we review the effects of epigenetic modifications on the neurotransmitter systems in depression-like outcomes produced by different types of ELS in recent years, aiming to provide new therapeutic targets for patients who suffer from depression.

Baseline Depression-Like Behaviors in Wild-Type Adolescent Mice Are Strain and Age but Not Sex Dependent

Depression is a major neuropsychiatric disorder, decreasing the ability of hundreds of millions of individuals worldwide to function in social, academic, and employment settings. Beyond the alarming public health problem, depression leads to morbidity across the entire age including adolescence and adulthood. Modeling depression in rodents has been used to understand the pathophysiological mechanisms behind this disorder and create new therapeutics. Although women are two times more likely to be diagnosed with depression compared to men, behavioral experiments on rodent models of depression are mainly performed in males based on the assumption that the estrous cycles in females may affect the behavioral outcome and cause an increase in the intrinsic variability compared to males. Still, the inclusion of female rodents in the behavioral analysis is mandatory to establish the origin of sex bias in depression. Here, we investigated the baseline depression-like behaviors in male and female mice of three adolescent wild-type inbred strains, C57BL/6N, DBA/2, and FVB/N, that are typically used as background strains for mouse models of neuropsychiatric disorders. Our experiments, performed at two different developmental stages during adolescence (P22-P26 and P32-P36), revealed strain but no sex differences in a set of depression-related tests, including tail suspension, sucrose preference and forced swim tests. Additionally, the 10-day interval during this sensitive period uncovered a strong impact on the behavioral outcome of C57BL/6N and FVB/N mice, highlighting a significant effect of maturation on behavioral patterns. Since anxiety-related behavioral tests are often performed together with depression tests in mouse models of neuropsychiatric disorders, we extended our study and included hyponeophagia as an anxiety test. Consistent with a previous study revealing sex differences in other anxiety tests in adolescent mice, male and females mice behaved differently in the hyponeophagia test at P27. Our study gives insight into the behavioral experiments assessing depression and stresses the importance of considering strain, age and sex when evaluating neuropsychiatric-like traits in rodent models.

Prenatal stress and increased susceptibility to anxiety-like behaviors: role of neuroinflammation and balance between GABAergic and glutamatergic transmission

Neuroplasticity during the prenatal period allows neurons to regenerate anatomically and functionally for re-programming the brain development. During this critical period of fetal programming, the fetus phenotype can change in accordance with environmental stimuli such as stress exposure. Prenatal stress (PS) can exert important effects on brain development and result in permanent alterations with long-lasting consequences on the physiology and behavior of the offspring later in life. Neuroinflammation, as well as GABAergic and glutamatergic dysfunctions, has been implicated as potential mediators of behavioral consequences of PS. Hyperexcitation, due to enhanced excitatory transmission or reduced inhibitory transmission, can promote anxiety. Alterations of the GABAergic and/or glutamatergic signaling during fetal development lead to a severe excitatory/inhibitory imbalance in neuronal circuits, a condition that may account for PS-precipitated anxiety-like behaviors. This review summarizes experimental evidence linking PS to an elevated risk to anxiety-like behaviors and interprets the role of the neuroinflammation and alterations of the brain GABAergic and glutamatergic transmission in this phenomenon. We hypothesize this is an imbalance in GABAergic and glutamatergic circuits (as a direct or indirect consequence of neuroinflammation), which at least partially contributes to PS-precipitated anxiety-like behaviors and primes the brain to be vulnerable to anxiety disorders. Therefore, pharmacological interventions with anti-inflammatory activities and with regulatory effects on the excitatory/inhibitory balance can be attributed to the novel therapeutic target for anxiety disorders.

Perinatal fluoxetine dose-dependently affects prenatal stress-induced neurobehavioural abnormalities, HPA-axis functioning and underlying brain alterations in rat dams and their offspring

Both untreated and SSRI antidepressant treated maternal depression during the perinatal period can pose both short-and long-term health risks to the offspring. Therefore, it is essential to have an effective SSRI treatment consisting of the lowest effective dose beneficial to the mother, without causing adverse effects on offspring development. The effects of prenatal stress on neurobehavioral outcomes were studied in the pregnant and lactating rat dam, and her offspring. Furthermore, stressed dams were treated with different doses of fluoxetine (FLX; 5, 10and 25 mg/kg) during pregnancy and the postpartum period. We found that prenatal stress-induced anxiety-and depressive-like behaviour and increased HPA-axis function in pregnant and postpartum dams, and in offspring. Maternal stress impaired object recognition but did not affect spatial memory in offspring. Prenatal stress decreased whole-brain serotonin and brain-derived-neurotrophic-factor, and increased interleukin-17 and malondialdehyde, but did not affect oxytocin and interleukin-6 in the brains of offspring. Maternal treatment with 5 mg/kg FLX during the perinatal period did not rescue any stress-induced anxiety/depressive-like behaviour in the pregnant and postpartum dam and had only a few rescuing effects in offspring. Maternal FLX treatment with 10 mg/kg did rescue most stress-induced anxiety-and depressive-like behaviour or HPA-axis-function in dams and offspring. The highest dose tested, 25 mg/kg FLX, had the rescuing properties in dams while having the same, or an even greater, detrimental effect as prenatal stress on offspring behaviour and molecular alterations in the brain. Our results show prenatal stress rescuing properties for FLX treatment in the pregnant and postpartum dam, with dose-dependent effects on the offspring.

Environmental enrichment improves lifelong persistent behavioral and epigenetic changes induced by early-life stress

This study aimed to evaluate the effects of environmental enrichment (EE) in Wistar rats subjected to maternal deprivation (MD). MD was performed in the first post-natal days (PND) ten for 3 h/day. The groups were: control; deprived without EE; and deprived with EE. The EE was applied for 3 h/day. Forced swimming test (FST) and open field test were performed, and histone deacetylase (HDAC) and DNA methyltransferase (DNMT) activities in the prefrontal cortex (PFC) and hippocampus were evaluated on 31, 41, and 61 PND. MD altered spontaneous locomotor activity and immobility time in FST, but the effects were sex- and developmental period dependent. In deprived females at PND 31, 41, and 61, HDAC and DNMT increased in the PFC and hippocampus. In females exposed to EE for 20 days, there was a decrease of HDAC in the hippocampus and DNMT in the PFC and hippocampus. Exposure of females to EE for 40 days can reverse HDAC and DNMT increase in all brain areas. In deprived males at PND 31, 41, and 61, HDAC and DNMT increased in the hippocampus, and in the group exposed to EE for 40 days, there was a decrease in hippocampal activity. In PFC of male deprived rats at PND 61 and EE for 40 days, there was a reduction of HDAC and DNMT. MD induced lifelong persistent behavioral and epigenetic changes, and such effects were more evident in female than male rats. EE can be considered an essential non-pharmacological strategy to treat long-term trauma-induced early life changes.

Chronic Piromelatine Treatment Alleviates Anxiety, Depressive Responses and Abnormal Hypothalamic-Pituitary-Adrenal Axis Activity in Prenatally Stressed Male and Female Rats

The prenatal stress (PNS) model in rodents can induce different abnormal responses that replicate the pathophysiology of depression. We applied this model to evaluate the efficacy of piromelatine (Pir), a novel melatonin analog developed for the treatment of insomnia, in male and female offspring. Adult PNS rats from both sexes showed comparable disturbance associated with high levels of anxiety and depressive responses. Both males and females with PNS demonstrated impaired feedback inhibition of the hypothalamic-pituitary-adrenal (HPA) axis compared to the intact offspring and increased glucocorticoid receptors in the hippocampus. However, opposite to female offspring, the male PNS rats showed an increased expression of mineralocorticoid receptors in the hippocampus. Piromelatine (20 mg/kg, i.p., for 21 days injected from postnatal day 60) attenuated the high anxiety level tested in the open field, elevated plus-maze and light-dark test, and depressive-like behavior in the sucrose preference and the forced swimming tests in a sex-specific manner. The drug reversed to control level stress-induced increase of plasma corticosterone 120 min later in both sexes. Piromelatine also corrected to control level the PNS-induced alterations of corticosteroid receptors only in male offspring. Our findings suggest that the piromelatine treatment exerts beneficial effects on impaired behavioral responses and dysregulated HPA axis in both sexes, while it corrects the PNS-induced changes in the hippocampal corticosteroid receptors only in male offspring.

BDNF Overexpression in the Ventral Hippocampus Promotes Antidepressant- and Anxiolytic-Like Activity in Serotonin Transporter Knockout Rats

BDNF plays a pivotal role in neuroplasticity events, vulnerability and resilience to stress-related disorders, being decreased in depressive patients and increased after antidepressant treatment. BDNF was found to be reduced in patients carrying the human polymorphism in the serotonin transporter promoter region (5-HTTLPR). The serotonin knockout rat (SERT^-/-) is one of the animal models used to investigate the underlying molecular mechanisms of depression in humans. They present decreased BDNF levels, and anxiety- and depression-like behavior. To investigate whether upregulating BDNF would ameliorate the phenotype of SERT^-/- rats, we overexpressed BDNF locally into the ventral hippocampus and submitted the animals to behavioral testing. The results showed that BDNF overexpression in the vHIP of SERT^-/- rats promoted higher sucrose preference and sucrose intake; on the first day of the sucrose consumption test it decreased immobility time in the forced swim test and increased the time spent in the center of a novel environment. Furthermore, BDNF overexpression altered social behavior in SERT^-/- rats, which presented increased passive contact with test partner and decreased solitary behavior. Finally, it promoted decrease in plasma corticosterone levels 60 min after restraint stress. In conclusion, modulation of BDNF IV levels in the vHIP of SERT^-/- rats led to a positive behavioral outcome placing BDNF upregulation in the vHIP as a potential target to new therapeutic approaches to improve depressive symptoms.

The Potential of Hydrogen for Improving Mental Disorders

In 2007, Ohsawa and colleagues reported that molecular hydrogen (H₂) gas significantly reduced the infarct volume size in a rat model of cerebral infarction, which was, at least, partially due to scavenging hydroxyl radicals. Since then, multiple studies have shown that H₂ has not only anti-oxidative but also anti-inflammatory and anti-apoptotic properties, which has ignited interest in the clinical use of H₂ in diverse diseases. A growing body of studies has indicated that H₂ affects both mental and physical conditions. Mental disorders are characterized by disordered mood, thoughts, and behaviors that affect the ability to function in daily life. However, there is no sure way to prevent mental disorders. Although antidepressant and antianxiety drugs relieve symptoms of depression and anxiety, they have efficacy limitations and are accompanied by a wide range of side effects. While mental disorders are generally thought to be caused by a variety of genetic and/or environmental factors, recent progress has shown that these disorders are strongly associated with increased oxidative and inflammatory stress. Thus, H₂ has received much attention as a novel therapy for the prevention and treatment of mental disorders. This review summarizes the recent progress in the use of H₂ for the treatment of mental disorders and other related diseases. We also discuss the potential mechanisms of the biomedical effects of H₂ and conclude that H₂ could offer relief to people suffering from mental disorders.

CNS genomic profiling in the mouse chronic social stress model implicates a novel category of candidate genes integrating affective pathogenesis

Despite high prevalence, medical impact and societal burden, anxiety, depression and other affective disorders remain poorly understood and treated. Clinical complexity and polygenic nature complicate their analyses, often revealing genetic overlap and cross-disorder heritability. However, the interplay or overlaps between disordered phenotypes can also be based on shared molecular pathways and 'crosstalk' mechanisms, which themselves may be genetically determined. We have earlier predicted (Kalueff et al., 2014) a new class of 'interlinking' brain genes that do not affect the disordered phenotypes per se, but can instead specifically determine their interrelatedness. To test this hypothesis experimentally, here we applied a well-established rodent chronic social defeat stress model, known to progress in C57BL/6J mice from the Anxiety-like stage on Day 10 to Depression-like stage on Day 20. The present study analyzed mouse whole-genome expression in the prefrontal cortex and hippocampus during the Day 10, the Transitional (Day 15) and Day 20 stages in this model. Our main question here was whether a putative the Transitional stage (Day 15) would reveal distinct characteristic genomic responses from Days 10 and 20 of the model, thus reflecting unique molecular events underlining the transformation or switch from anxiety to depression pathogenesis. Overall, while in the Day 10 (Anxiety) group both brain regions showed major genomic alterations in various neurotransmitter signaling pathways, the Day 15 (Transitional) group revealed uniquely downregulated astrocyte-related genes, and the Day 20 (Depression) group demonstrated multiple downregulated genes of cell adhesion, inflammation and ion transport pathways. Together, these results reveal a complex temporal dynamics of mouse affective phenotypes as they develop. Our genomic profiling findings provide first experimental support to the idea that novel brain genes (activated here only during the Transitional stage) may uniquely integrate anxiety and depression pathogenesis and, hence, determine the progression from one pathological state to another. This concept can potentially be extended to other brain conditions as well. This preclinical study also further implicates cilial and astrocytal mechanisms in the pathogenesis of affective disorders.

Early Biomarkers and Intervention Programs for the Infant Exposed to Prenatal Stress

Functional development of affective and reward circuits, cognition and response inhibition later in life exhibits vulnerability periods during gestation and early childhood. Extensive evidence supports the model that exposure to stressors in the gestational period and early postnatal life increases an individual's susceptibility to future impairments of functional development. Recent versions of this model integrate epigenetic mechanisms of the developmental response. Their understanding will guide the future treatment of the associated neuropsychiatric disorders. A combination of non-invasively obtainable physiological signals and epigenetic biomarkers related to the principal systems of the stress response, the Hypothalamic-Pituitary axis (HPA) and the Autonomic Nervous System (ANS), are emerging as the key predictors of neurodevelopmental outcomes. Such electrophysiological and epigenetic biomarkers can prove to timely identify children benefiting most from early intervention programs. Such programs should ameliorate future disorders in otherwise healthy children. The recently developed Early Family-Centered Intervention Programs aim to influence the care and stimuli provided daily by the family and improving parent/child attachment, a key element for healthy socio-emotional adult life. Although frequently underestimated, such biomarker-guided early intervention strategy represents a crucial first step in the prevention of future neuropsychiatric problems and in reducing their personal and societal impact.

Gender-specific effect of pregnancy-related anxiety on preschooler's emotional and behavioral development: A population-based cohort study

BACKGROUND

Pregnancy-related anxiety plays a major role in shaping offspring's neural development. However, its gender-specific effect on children's emotional and behavioral development is controversial and the knowledge of critical period is limited. This study aims to examine gender-specific effect of pregnancy-related anxiety on preschooler's emotional and behavioral development.

METHODS

This study was based on the China-Anhui Birth Cohort Study (C-ABCS). A total of 3443 mother-child pairs were included in final data analysis. Pregnancy-related anxiety was assessed by Pregnancy-Related Anxiety Questionnaire respectively in the 1^st and 3^rd trimester of pregnancy. Strengths and Difficulties Questionnaires (SDQ) were completed by parents to assess preschool emotional and behavioral development in boys and girls. Logistic regression models were used to examine the association between pregnancy-related anxiety and preschoolers' emotional and behavioral problems.

RESULTS

The overall prevalence of pregnancy-related anxiety was 31.6%. Compared with those whose mothers without pregnancy-related anxiety in either 1^st or 3^rd trimester, preschool boys born of mothers with pregnancy-related anxiety in the 1^st trimester and in the 3^rd trimester had an increased risk of conduct problems. Pregnancy-related anxiety in the 1^st, 3^rd trimester and in both trimesters all related with preschool boys' hyperactivity and total difficult problems. Pregnancy-related anxiety in the 1^st trimester and in both 1^st and 3^rd trimester increased the risk of preschool girls' emotional problems and total difficult problems.

CONCLUSION

Pregnancy-related anxiety may relate with preschool boys' externalizing problems in early and late of pregnancy and increase the risk of internalizing problems in girls in early pregnancy.

LIMITATIONS

There was no data on pregnancy-related anxiety in the second trimester.

RNASeq analysis reveals upregulation of complement C3 in the offspring gut following prenatal stress in mice

Dysregulated activation of inflammatory signaling by the immature neonatal immune system could lead to the development of many pediatric diseases including necrotizing enterocolitis (NEC). While the mechanism(s) of pathogenesis is unknown, NEC is believed to have multifactorial causes. Microbial dysbiosis and intestinal immaturity have been implicated as potential triggers for this disease. We hypothesized that psychological stress during pregnancy negatively impacts the development of intestinal tissues in offspring and contributes to development of NEC. Consistent with this hypothesis, we previously observed shorter villi and a decrease in total surface area in the small intestine of pups derived from mice that were chronically stressed during gestation. In this study, we performed RNASeq analysis to determine the gene expression changes in the offspring gut following prenatal stress in pregnant mice and identified several differentially expressed genes (DEGs) and biological pathways. Notably, C3 was upregulated in the small intestine and contributed to a higher tissue injury score in a mesenteric ischemia model compared to unstressed controls. We discuss the potential implications of these stress-induced genes expression changes and their contribution to development of intestinal inflammation.

Sexual Dimorphism of Size Ontogeny and Life History

Background: Ecological and physiological factors and social and economic constraints affect sex-specific body size. Here, we used the male/female (M/F) height ratio as an indicator of the combined effect of genetic and sex characteristics. We hypothesized that (1) sexual dimorphism in body size will be established during infancy and adolescence when growth velocity is maximal, (2) living standards and health are important factors which can affect sexual dimorphism in body size, (3) variations in sexual dimorphism in body size are due to the differential response of boys and girls to environmental cues, and (4) sexual dimorphism in body size will be more pronounced in those populations whose average height and weight are the greatest. Methods: To study the ontogeny of sexual dimorphism from birth until the age of 18 years, we used the 2000 CDC growth data. Data on height by country, life expectancy, and gross domestic product (GDP) per capita based on purchasing power parity were extracted from the national accounts data of NCD Risk Factor Collaboration, the World Bank, Eurostat: Demographic Statistics, Secretariat of the Pacific Community: Statistics and Demography Program, and the US Census Bureau. Results: We found that sexual dimorphism in body size starts at age 1 month, peaks at age 3 months, and diminishes by age 24 months. During childhood, there is no sexual difference in body size, and it is gradually established when the boys enter puberty. The M/F height ratio correlates positively with the average male and female height and weight by country. Conclusion: Sexual dimorphism in body size occurs when (a) the growth velocity is maximal during infancy and adolescence, (b) living standards are high, and health correlate positively with male/female height ratio. Anthropological studies and our results emphasize mostly the female resiliency hypothesis: shorter male heights in times of environmental stress lead to smaller sexual dimorphism in body size.

Interleukin-18 levels in the hippocampus and behavior of adult rat offspring exposed to prenatal restraint stress during early and late pregnancy

Exposure to maternal stress during prenatal life is associated with an increased risk of neuropsychiatric disorders, such as depression and anxiety, in offspring. It has also been increasingly observed that prenatal stress alters the phenotype of offspring via immunological mechanisms and that immunological dysfunction, such as elevated interleukin-18 levels, has been reported in cultures of microglia. Prenatal restraint stress (PRS) in rats permits direct experimental investigation of the link between prenatal stress and adverse outcomes. However, the majority of studies have focused on the consequences of PRS delivered in the second half of pregnancy, while the effects of early prenatal stress have rarely been examined. Therefore, pregnant rats were subjected to PRS during early/middle and late gestation (days 8-14 and 15-21, respectively). PRS comprised restraint in a round plastic transparent cylinder under bright light (6500 lx) three times per day for 45 minutes. Differences in interleukin-18 expression in the hippocampus and in behavior were compared between offspring rats and control rats on postnatal day 75. We found that adult male offspring exposed to PRS during their late prenatal periods had higher levels of anxiety-related behavior and depression than control rats, and both male and female offspring exhibited higher levels of depression-related behavior, impaired recognition memory and diminished exploration of novel objects. Moreover, an elevated level of interleukin-18 was observed in the dorsal and ventral hippocampus of male and female early- and late-PRS offspring rats. The results indicate that PRS can cause anxiety and depression-related behaviors in adult offspring and affect the expression of interleukin-18 in the hippocampus. Thus, behavior and the molecular biology of the brain are affected by the timing of PRS exposure and the sex of the offspring. All experiments were approved by the Animal Experimentation Ethics Committee at Kunming Medical University, China (approval No. KMMU2019074) in January 2019.

Transgenerational deep sequencing revealed hypermethylation of hippocampal mGluR1 gene with altered mRNA expression of mGluR5 and mGluR3 associated with behavioral changes in Sprague Dawley rats with history of prolonged febrile seizure

The impact of febrile seizure has been shown to transcend immediate generation with the alteration of glutamatergic pathway being implicated. However, transgenerational effects of this neurological disorder particularly prolonged febrile seizure (PFS) on neurobehavioral study and methylation profile is unknown. We therefore hypothesized that transgenerational impact of prolonged febrile seizure is dependent on methylation of hippocampal mGluR1 gene. Prolonged febrile seizure was induced on post-natal day (PND) 14, by injecting lipopolysaccharide (LPS; 217μg/kg ip) and kainic acid (KA; 1.83 mg/kg ip). Sucrose preference test (SPT) and Forced swim test (FST) were carried out in the first generation (F0) of animals at PND37 and PND60. The F0 rats were decapitated at PND 14, 37 and 60 which corresponded to childhood, adolescent and adulthood respectively and their hippocampal tissue collected. The second generation (F1) rats were obtained by mating F0 generation at PND 60 across different groups, F1 rats were subjected to SPT and FST test on PND 37 only. Decapitation of F1rats and collection of hippocampal tissues were done on PND 14 and 37. Assessment of mGluR5 and mGluR3 mRNA was done with PCR while mGluR1 methylation profile was assessed with the Quantitative MassARRAY analysis. Results showed that PFS significantly leads to decreased sucrose consumption in the SPT and increased immobility time in the FST in both generations of rats. It also leads to significant decrease in mGluR5 mRNA expression with a resultant increased expression of mGluR3 mRNA expression and hypermethylation of mGluR1 gene across both generations of rats. This study suggested that PFS led to behavioral changes which could be transmitted on to the next generation in rats.

Multiple prenatal stresses increase sexual dimorphism in adult offspring behavior

INTRODUCTION

Maternal gestational stress and immune activation have independently been associated with affective and neurodevelopmental disorders across the lifespan. We investigated whether rats exposed to prenatal maternal stressors (PNMS) consisting of psychological stress, interleukin (IL)-1β or both (two-hit stress) during critical developmental windows displayed a behavioral phenotype representative of these conditions.

METHODS

Long-Evans dams were exposed to psychological stressors consisting of restraint stress and forced swimming from gestational day (GD)12 to 18 or to no stress (controls). From GD17 until day of delivery, these same animals were injected with saline or IL-1β as a second hit and immune stressor (5 μg/day, intraperitoneally). The behavior of F1 offspring adults was tested on the open field test, elevated plus maze and affective exploration task on postnatal days (P)90, 100 and 110 respectively.

RESULTS

The effects of PNMS differed depending on the specific testing environment and potentially the age at assessment, especially in female offspring. Both locomotion and anxiety-like behavioral measures were susceptible to PNMS effects. In females, psychological stress increased anxiety-like behavior, whereas IL-1β had an opposite effect, inducing exploration and risk-taking behavior on the open field test and the elevated plus maze. When present, interactions between both stressors limited the anxiogenic effect of psychological stress on its own. In contrast, prenatal psychological stress increased anxiety-like behavior in adult males overall. A similar anxiogenic effect of IL-1β was only found on the open field test while the Stress*IL-1β interaction appeared to limit the effect of either alone. Contrarily, the PNMS effects on anxiety-like behavior on the affective exploration task were highly similar between both sexes. Analysis of males and females together revealed an additive effect of Stress and IL-1β on the number of exits from the refuge, a measure of risk assessment and thus correlated with anxiety.

CONCLUSION

PNMS affected offspring adult behavior in a sex-dependent manner. Effects on females were more variable, whereas psychological stress mostly induced anxiety-like behavior in males. These data highlight the sexual dimorphism in vulnerability to prenatal stressors. Maternal or stress-induced programming of the stress response and neuroinflammation may play an important role in mediating stress effects on offspring adult behavior.

Hippocampal transcriptome reveals novel targets of FASD pathogenesis

INTRODUCTION

Prenatal alcohol exposure can contribute to fetal alcohol spectrum disorders (FASD), characterized by a myriad of developmental impairments affecting behavior and cognition. Studies show that many of these functional impairments are associated with the hippocampus, a structure exhibiting exquisite vulnerability to developmental alcohol exposure and critically implicated in learning and memory; however, mechanisms underlying alcohol-induced hippocampal deficits remain poorly understood. By utilizing a high-throughput RNA-sequencing (RNA-seq) approach to address the neurobiological and molecular basis of prenatal alcohol-induced hippocampal functional deficits, we hypothesized that chronic binge prenatal alcohol exposure alters gene expression and global molecular pathways in the fetal hippocampus.

METHODS

Timed-pregnant Sprague-Dawley rats were randomly assigned to a pair-fed control (PF) or binge alcohol (ALC) treatment group on gestational day (GD) 4. ALC dams acclimatized from GDs 5-10 with a daily treatment of 4.5 g/kg alcohol and subsequently received 6 g/kg on GDs 11-20. PF dams received a once daily maltose dextrin gavage on GDs 5-20, isocalorically matching ALC counterparts. On GD 21, bilateral hippocampi were dissected, flash frozen, and stored at -80° C. Total RNA was then isolated from homogenized tissues. Samples were normalized to ~4nM and pooled equally. Sequencing was performed by Illumina NextSeq 500 on a 75 cycle, single-end sequencing run.

RESULTS

RNA-seq identified 13,388 genes, of these, 76 genes showed a significant difference (p < 0.05, log2 fold change ≥2) in expression between the PF and ALC groups. Forty-nine genes showed sex-dependent dysregulation; IPA analysis showed among female offspring, dysregulated pathways included proline and citrulline biosynthesis, whereas in males, xenobiotic metabolism signaling and alaninine biosynthesis etc. were altered.

CONCLUSION

We conclude that chronic binge alcohol exposure during pregnancy dysregulates fetal hippocampal gene expression in a sex-specific manner. Identification of subtle, transcriptome-level dysregulation in hippocampal molecular pathways offers potential mechanistic insights underlying FASD pathogenesis.

Sex specific effects of pre-pubertal stress on hippocampal neurogenesis and behaviour

Experience of traumatic events in childhood is linked to an elevated risk of developing psychiatric disorders in adulthood. The neurobiological mechanisms underlying this phenomenon are not fully understood. The limbic system, particularly the hippocampus, is significantly impacted by childhood trauma. In particular, it has been hypothesised that childhood stress may impact adult hippocampal neurogenesis (AHN) and related behaviours, conferring increased risk for later mental illness. Stress in utero can lead to impaired hippocampal synaptic plasticity, and stress in the first 2-3 weeks of life reduces AHN in animal models. Less is known about the effects of stress in the post-weaning, pre-pubertal phase, a developmental time-point more akin to human childhood. Therefore, we investigated persistent effects of pre-pubertal stress (PPS) on functional and molecular aspects of the hippocampus. AHN was altered following PPS in male rats only. Specifically males showed reduced production of new neurons following PPS, but increased survival in the ventral dentate gyrus. In adult males, but not females, pattern separation and trace fear conditioning, behaviours that rely heavily on AHN, were also impaired after PPS. PPS also increased the expression of parvalbumin-positive GABAergic interneurons in the ventral dentate gyrus and increased glutamic acid decarboxylase 67 expression in the ventral hilus, in males only. Our results demonstrate the lasting effects of PPS on the hippocampus in a sex- and time-dependent manner, provide a potential mechanistic link between PPS and later behavioural impairments, and highlight sex differences in vulnerability to neuropsychiatric conditions after early-life stress.

A rat model to study maternal depression during pregnancy and postpartum periods, its comorbidity with cardiovascular diseases and neurodevelopmental impact in the offspring

This study aimed to develop an animal model of human depression during pregnancy and lactation to examine the effect of maternal, perinatal depression on offspring development. Maternal depression during pregnancy affects up to 20% of women and is a risk factor for both the developmental and long-term health issues. It is often comorbid with the cardiovascular disease (CVD) that affects the uteroplacental circulation and impacts offspring development. More than half of the expecting mothers with depression use antidepressants that cross the placenta and may interfere with the neurodevelopmental programming. Thus, depressed pregnant mothers face a difficult choice whether "to use or not to use" antidepressant therapy, since both untreated depression and antenatal antidepressant exposure present increased risks of neurodevelopmental pathologies. The ongoing clinical debate presents inconclusive data, while the existing animal models of maternal depression do not include early gestational periods, and, do not monitor depressive-like behavior nor address the cardiovascular abnormalities. The presented model includes pregestational depressive behavior extending into pregnancy and lactation, periods that have not been previously examined. Rat dams exposed to pre-gestational chronic mild stress (CMS) developed a sustained decrease in self-grooming behavior, correlated with hormonal, behavioral, and cardiac changes persisting through the postpartum period. Preliminary data indicate neurodevelopmental delays, behavioral and cardiac abnormalities, and altered levels of both the brain and the heart markers in the offspring of stressed dams. Furthermore, the preliminary data predict that maternal pregnancy during the perinatal period is likely to impact the neurodevelopmental process in a sex-dependent manner. Thus the presented here model (PG-LAC CMS) fulfills both the face and the construct validity criteria for maternal stress-induced depression during pregnancy and postpartum that may facilitate further studies of the relative risks of untreated vs. antidepressant-treated maternal depression during pregnancy to the mother and her offspring.

Different Behavioral Experiences Produce Distinctive Parallel Changes in, and Correlate With, Frontal Cortex and Hippocampal Global Post-translational Histone Levels

While it is clear that behavioral experience modulates epigenetic profiles, it is less evident how the nature of that experience influences outcomes and whether epigenetic/genetic "biomarkers" could be extracted to classify different types of behavioral experience. To begin to address this question, male and female mice were subjected to either a Fixed Interval (FI) schedule of food reward, or a single episode of forced swim followed by restraint stress, or no explicit behavioral experience after which global expression levels of two activating (H3K9ac and H3K4me3) and two repressive (H3K9me2 and H3k27me3) post-translational histone modifications (PTHMs), were measured in hippocampus (HIPP) and frontal cortex (FC). The specific nature of the behavioral experience differentiated profiles of PTHMs in a sex- and brain region-dependent manner, with all 4 PTHMs changing in parallel in response to different behavioral experiences. These different behavioral experiences also modified the pattern of correlations of PTHMs both within and across FC and HIPP. Unexpectedly, highly robust correlations were found between global PTHM levels and behavioral performances, suggesting that global PTHMs may provide a higher-order pattern recognition function. Further efforts are needed to determine the generality of such findings and what characteristics of behavioral experience are critical for modulating PTHM responses.

Unpredictable chronic prenatal stress and manifestation of generalized anxiety and panic in rat's offspring

Often the manifestation of anxiety cannot be explained by known environmental or hereditary factors. With this perspective, it has been reported that prenatal stress may lead to emotional disturbances in the offspring. However, studies relating prenatal stress to anxiety are controversial and generally the stressors used do not mimicks the reality experienced by mothers. Thus, this investigation evaluated the effects of an unpredictable chronic stress scheme applied in one of the three gestational weeks of rats on the manifestation of generalized anxiety and panic disorder in the progeny (males), analyzing, respectively, the avoidances and escapes in the elevated T-maze, at the 1st, 3rd or 6th month of progeny life. Control offspring showed increased generalized anxiety disorder and reduced panic at 6 months. The effects of prenatal stress depended on the gestational week where it occurred and on the progeny age: during the 1st gestational week the generalized anxiety decreased in 6 month old rats. Animals in the 3rd month, prenatally stressed during the last gestational week, showed anxiogenesis and panicogenesis, but effects reverted at the 6th month, when they presented anxiolysis and no changes related to panic. Together the results show that not only the gestational period in which the aversive experience occurred was important, but the age of the evaluated progeny, since the type and the intensity of behaviors related to anxiety may vary with the developmental stage. For the model of stress used in the present study, the effects of prenatal stress were more prominent when the exposure occurred during the 3rd gestational week in rats.

Mild Prenatal Stress Causes Emotional and Brain Structural Modifications in Rats of Both Sexes

Stress or high levels of glucocorticoids (GCs) during developmental periods is known to induce persistent effects in the neuroendocrine circuits that control stress response, which may underlie individuals’ increased risk for developing neuropsychiatric conditions later in life, such as anxiety or depression. We developed a rat model (Wistar han) of mild exposure to unpredictable prenatal stress (PS), which consists in a 4-h stressor administered three times per week on a random basis; stressors include strobe lights, noise and restrain. Pregnant dams subjected to this protocol present disrupted circadian corticosterone secretion and increased corticosterone secretion upon acute stress exposure. Regarding progeny, both young adult (2 months old) male and female rats present increased levels of circulating corticosterone and hyperactivity of the hypothalamus-pituitary-adrenal axis to acute stress exposure. Both sexes present anxious- and depressive-like behaviors, shown by the decreased time spent in the open arms of the elevated plus maze (EPM) and in the light side of the light-dark box (LDB), and by increased immobility time in the forced swim test, respectively. Interestingly, these results were accompanied by structural modifications of the bed nucleus of stria terminalis (BNST) and hippocampus, as well as decreased norepinephrine and dopamine levels in the BNST, and serotonin levels in the hippocampus. In summary, we characterize a new model of mild PS, and show that stressful events during pregnancy can lead to long-lasting structural and neurochemical effects in the offspring, which affect behavior in adulthood.

Cerebral oxidative metabolism mapping in four genetic mouse models of anxiety and mood disorders

The psychopathology of depression is highly complex and the outcome of studies on animal models is divergent. In order to find brain regions that could be metabolically distinctively active across a variety of mouse depression models and to compare the interconnectivity of brain regions of wild-type and such genetically modified mice, histochemical mapping of oxidative metabolism was performed by the measurement of cytochrome oxidase activity. We included mice with the heterozygous knockout of the vesicular glutamate transporter (VGLUT₁^-/+), full knockout of the cannabinoid 1 receptor (CB1^-/-), an anti-sense knockdown of the glucocorticoid receptor (GRi) and overexpression of the human 5-hydroxytryptamine transporter (h5-HTT). Altogether 76 mouse brains were studied to measure oxidative metabolism in one hundred brain regions, and the obtained dataset was submitted to a variety of machine learning algorithms and multidimensional scaling. Overall, the top brain regions having the largest contribution to classification into depression model were the lateroanterior hypothalamic nucleus, the anterior part of the basomedial amygdaloid nucleus, claustrum, the suprachiasmatic nucleus, the ventromedial hypothalamic nucleus, and the anterior hypothalamic area. In terms of the patterns of inter-regional relationship between wild-type and genetically modified mice there was little overall difference, while the most deviating brain regions were cortical amygdala and ventrolateral and ventral posteromedial thalamic nuclei. The GRi mice that most clearly differed from their controls exhibited deviation of connectivity for a number of brain regions, such as ventrolateral thalamic nucleus, the intermediate part of the lateral septal nucleus, the anteriodorsal part of the medial amygdaloid nucleus, the medial division of the central amygdaloid nucleus, ventral pallidum, nucleus of the vertical limb of the diagonal band, anteroventral parts of the thalamic nucleus and parts of the bed nucleus of the stria terminalis. Conclusively, the GRi mouse model was characterized by changes in the functional connectivity of the extended amygdala and stress response circuits.

Effects of Tianeptine on Adult Rats Following Prenatal Stress

Objective

Exposing a pregnant female to stress during the critical period of embryonic fetal brain development increases the risk of psychiatric disorders in the offspring. The objective of this study was to investigate the effect of antidepressant tianeptine on prenatally stressed (PNS) rats.

Methods

In this study, a repeated variable stress paradigm was applied to pregnant rats during the last week of gestation. To investigate the effects of antidepressant tianeptine on PNS rats, behavioral and protein expression analyses were performed. Forced swim test, open field test, and social interaction test were performed to determine changes in PNS rats compared to non-stressed offspring. Haloperidol was used as a positive control as an antipsychotic drug based on previous studies.

Results

Behavioral changes were restored after treatment with tianeptine or haloperidol. Western blot and immunohistochemical analyses of the prefrontal cortex revealed downregulation of several neurodevelopmental proteins in PNS rats. After treatment with tianeptine or haloperidol, their expression levels were increased.

Conclusion

Downregulation of several proteins in PNS rats might have caused subsequent behavioral changes in PNS rats. After tianeptine or haloperidol treatment, behavioral changes in PNS rats were restored. Therefore, tianeptine might decrease incidence of prenatal stress related-psychiatric disorders such as depression and schizophrenia.

The Impact and Mechanism of Methylated Metabotropic Glutamate Receptors 1 and 5 in the Hippocampus on Depression-Like Behavior in Prenatal Stress Offspring Rats

An increasing number of epidemiological investigations and animal models research suggest that prenatal stress (PS) could cause depression-like behavior in the offspring, which is sex specific. However, the underlying mechanisms remain to be elucidated. This study is to investigate the promoter methylation of metabotropic glutamate receptor 1 (mGluR1) and metabotropic Glutamate Receptor 5 (mGluR5) gene modification on PS induced depression-like behavior in offspring rats (OR). PS models were established, with or without 5-aza-2′-deoxycytidine (5-azaD, decitabine) treatment. Animal behavior was assessed by the sucrose preference test (SPT), forced swimming test (FST), and open field test (OFT). The mRNA and protein expression levels of mGluR1 and mGluR5 in the hippocampus of offspring were detected with quantitative real-time PCR and Western blot analysis, respectively. The promoter methylation in the hippocampus of mGluR1 and mGluR5 OR were also analyzed. SPT showed significantly reduced sucrose preference in PS induced OR. FST showed significantly prolonged immobility time in PS induced OR. OFT showed significantly reduced central residence time in PS induced OR and no significantly influence in rearing as well as in frequency of micturition. Moreover, the mRNA, protein expression levels, and gene promoter methylation level of mGluR1 and mGluR5 in the hippocampus were significantly increased in the PS induced male OR, while no significantly influence in the PS induced female OR. Furthermore, the PS induced effects in male OR could be reversed by the microinjection of 5-azaD. In conclusion, our results showed that the promoter methylation of mGluR1 and mGluR5 gene modification is only involved in PS induced depression-like behavior in male OR in a sex-specific manner. These findings might contribute to the understanding of the disease pathogenesis and clinical treatment in future.

H3K9 Acetylation of Tph2 Involved in Depression-like Behavior in Male, but not Female, Juvenile Offspring Rat Induced by Prenatal Stress

Increasing evidence has shown that prenatal stress (PS) could cause depression-like behavior in the offspring, which is sex-specific. However, the underlying mechanisms remain to be elucidated. This study is to investigate the involvement of tryptophan hydroxylase 2 (Tph2) H3K9 acetylation (H3K9ac) modification on PS-induced depression-like behavior in juvenile offspring rats (JOR). PS models were established, with or without trichostatin A (TSA) treatment. Animal behavior was assessed by the sucrose preference test (SPT) and forced swimming test (FST). The mRNA and protein expression levels of TPH2 in the dorsal raphenucleus (DRN), hippocampus, and prefrontal cortex were detected with quantitative real-time PCR and Western blot analysis, respectively. The Tph2 H3K9ac levels in the hippocampus were also analyzed. SPT and FST showed significantly reduced sucrose preference and significantly prolonged immobility in PS-induced male juvenile offspring rats (MJOR). Moreover, the mRNA and protein expression levels of TPH2 in the DRN and hippocampus were significantly declined, while the hippocampal Tph2 H3K9ac levels were significantly declined in the PS-induced MJOR. Furthermore, the PS-induced effects in MJOR could be reversed by the microinjection of TSA. However, no significant effects were observed for the female juvenile offspring rats (FJORs). In conclusion, our results showed that the Tph2 H3K9ac modification is only involved in PS-induced depression-like behavior in MJOR, in a sex-specific manner. These findings might contribute to the understanding of the disease pathogenesis and clinical treatment in future.

Neurobiological Mechanisms of Stress Resilience and Implications for the Aged Population

BACKGROUND

Stress is a common reaction to an environmental adversity, but a dysregulation of the stress response can lead to psychiatric illnesses such as major depressive disorder (MDD), post-traumatic stress disorder (PTSD), and anxiety disorders. Yet, not all individuals exposed to stress will develop psychiatric disorders; those with enhanced stress resilience mechanisms have the ability to adapt successfully to stress without developing persistent psychopathology. Notably, the potential to enhance stress resilience in at-risk populations may prevent the onset of stress-induced psychiatric disorders. This novel idea has prompted a number of studies probing the mechanisms of stress resilience and how it can be manipulated.

METHODS

Here, we review the neurobiological factors underlying stress resilience, with particular focus on the serotoninergic (5-HT), glutamatergic, and γ-Aminobutyric acid (GABA) systems, as well as the hypothalamic-pituitary axis (HPA) in rodents and in humans. Finally, we discuss stress resiliency in the context of aging, as the likelihood of mood disorders increases in older adults.

RESULTS

Interestingly, increased resiliency has been shown to slow aging and improved overall health and quality of life. Research in the neurobiology of stress resilience, particularly throughout the aging process, is a nascent, yet, burgeoning field.

CONCLUSION

Overall, we consider the possible methods that may be used to induce resilient phenotypes, prophylactically in at-risk populations, such as in military personnel or in older MDD patients. Research in the mechanisms of stress resilience may not only elucidate novel targets for antidepressant treatments, but also provide novel insight about how to prevent these debilitating disorders from developing.

Sex differences, gender and addiction

This review discusses alcohol and other forms of drug addiction as both a sociocultural and biological phenomenon. Sex differences and gender are not solely determined by biology, nor are they entirely sociocultural. The interactions among biological, environmental, sociocultural, and developmental influences result in phenotypes that may be more masculine or more feminine. These gender-related sex differences in the brain can influence the responses to drugs of abuse, progressive changes in the brain after exposure to drugs of abuse and whether addiction results from drug-taking experiences. In addition, the basic laboratory evidence for sex differences is discussed within the context of four types of sex/gender differences. © 2016 Wiley Periodicals, Inc.

Impact of social separation during pregnancy on the manifestation of defensive behaviors related to generalized anxiety and panic throughout offspring development

The multiple insecurities, anatomical, physiological and psychological changes arising from the gestational period can generate an overload of stress in the mother and cause disturbances in the offspring, affecting it throughout its development. The existing analysis linking prenatal stress and offspring’s anxiety have divergent results, being limited as to gestational week, type of stressor and age of progeny’s assessment. Social separation has been described as a stressor that causes increase in anxiety. Thus, the present study evaluated the effects of social separation applied in one of the three gestational weeks of rat dams on the manifestation of the defensive behaviors related to generalized anxiety disorder and panic in the Elevated T Maze of the male progeny in three stages of development (1, 3 or 6 months of life). It was found, in the offspring of grouped (control) dams, increased behaviors associated with generalized anxiety disorder and a reduction of panic-like behaviors throughout development. For animals whose dams were socially separated during pregnancy, the most critical period of exposure was the 2^nd gestational week, which affected the acquisition of aversive memory, demonstrated by the impairment on learning of avoidances of the offspring in all ages evaluated. Stressor exposure in this week also increased the avoidances, related to generalized anxiety of progeny in the 1^st month and decreased escapes, related to panic in the 3^rd month of life and, at the age of 6 months old, an inverse situation, with the reduction of the defensive behaviors associated to generalized anxiety disorder. The results show that, when assessing effects of prenatal stress on the manifestation of anxiety, not only the period of exposure is important, but also the age of offspring assessed.

Newborn genome-wide DNA methylation in association with pregnancy anxiety reveals a potential role for GABBR1

BACKGROUND

There is increasing evidence for the role of prenatal stress in shaping offspring DNA methylation and disease susceptibility. In the current study, we aimed to identify genes and pathways associated with pregnancy anxiety using a genome-wide DNA methylation approach.

METHODS

We selected 22 versus 23 newborns from our Prenatal Early Life Stress (PELS) cohort, exposed to the lowest or highest degree of maternal pregnancy anxiety, respectively. Cord blood genome-wide DNA methylation was assayed using the HumanMethylation450 BeadChip (HM450, n = 45) and candidate gene methylation using EpiTYPER (n = 80). Cortisol levels were measured at 2, 4, and 12 months of age to test infant stress system (re)activity.

RESULTS

Data showed ten differentially methylated regions (DMR) when comparing newborns exposed to low versus high pregnancy anxiety scores. We validated a top DMR in the GABA-B receptor subunit 1 gene (GABBR1) revealing the association with pregnancy anxiety particularly in male newborns (most significant CpG Pearson R = 0.517, p = 0.002; average methylation Pearson R = 0.332, p = 0.039). Cord blood GABBR1 methylation was associated with infant cortisol levels in response to a routine vaccination at 4 months old.

CONCLUSIONS

In conclusion, our results show that pregnancy anxiety is associated with differential DNA methylation patterns in newborns and that our candidate gene GABBR1 is associated with infant hypothalamic-pituitary-adrenal axis response to a stressor. Our findings reveal a potential role for GABBR1 methylation in association with stress and provide grounds for further research.

Developmental Lead and/or Prenatal Stress Exposures Followed by Different Types of Behavioral Experience Result in the Divergence of Brain Epigenetic Profiles in a Sex, Brain Region, and Time-Dependent Manner: Implications for Neurotoxicology

Over a lifetime, early developmental exposures to neurocognitive risk factors, such as lead (Pb) exposures and prenatal stress (PS), will be followed by multiple varied behavioral experiences. Pb, PS and behavioral experience can each influence brain epigenetic profiles. Our recent studies show a greater level of complexity, however, as all three factors interact within each sex to generate differential adult variation in global post-translational histone modifications (PTHMs), which may result in fundamentally different consequences for life-long learning and behavioral function. We have reported that PTHM profiles differ by sex, brain region and time point of measurement following developmental exposures to Pb±PS, resulting in different profiles for each unique combination of these parameters. Imposing differing behavioral experience following developmental Pb±PS results in additional divergence of PTHM profiles, again in a sex, brain region and time-dependent manner, further increasing complexity. Such findings underscore the need to link highly localized and variable epigenetic changes along single genes to the highly-integrated brain functional connectome that is ultimately responsible for governing behavioral function. Here we advance the idea that increased understanding may be achieved through iterative reductionist and holistic approaches. Implications for experimental design of animal studies of developmental exposures to neurotoxicants include the necessity of a 'no behavioral experience' group, given that epigenetic changes in response to behavioral testing can confound effects of the neurotoxicant itself. They also suggest the potential utility of the inclusion of salient behavioral experiences as a potential effect modifier in epidemiological studies.

Molecular hydrogen increases resilience to stress in mice

The inability to successfully adapt to stress produces pathological changes that can lead to depression. Molecular hydrogen has anti-oxidative and anti-inflammatory activities and neuroprotective effects. However, the potential role of molecular hydrogen in stress-related disorders is still poorly understood. The present study aims to investigate the effects of hydrogen gas on resilience to stress in mice. The results showed that repeated inhalation of hydrogen-oxygen mixed gas [67%:33% (V/V)] significantly decreased both the acute and chronic stress-induced depressive- and anxiety-like behaviors of mice, assessed by tail suspension test (TST), forced swimming test (FST), novelty suppressed feeding (NSF) test, and open field test (OFT). ELISA analyses showed that inhalation of hydrogen-oxygen mixed gas blocked CMS-induced increase in the serum levels of corticosterone, adrenocorticotropic hormone, interleukin-6, and tumor necrosis factor-α in mice exposed to chronic mild stress. Finally, inhalation of hydrogen gas in adolescence significantly increased the resilience to acute stress in early adulthood, which illustrates the long-lasting effects of hydrogen on stress resilience in mice. This was likely mediated by inhibiting the hypothalamic-pituitary-adrenal axis and inflammatory responses to stress. These results warrant further exploration for developing molecular hydrogen as a novel strategy to prevent the occurrence of stress-related disorders.

The novel cannabinoid receptor GPR55 mediates anxiolytic-like effects in the medial orbital cortex of mice with acute stress

The G protein-coupled receptor 55 (GPR55) is a novel cannabinoid receptor, whose exact role in anxiety remains unknown. The present study was conducted to explore the possible mechanisms by which GPR55 regulates anxiety and to evaluate the effectiveness of O-1602 in the treatment of anxiety-like symptoms. Mice were exposed to two types of acute stressors: restraint and forced swimming. Anxiety behavior was evaluated using the elevated plus maze and the open field test. We found that O-1602 alleviated anxiety-like behavior in acutely stressed mice. We used lentiviral shRNA to selective ly knockdown GPR55 in the medial orbital cortex and found that knockdown of GPR55 abolished the anxiolytic effect of O-1602. We also used Y-27632, a specific inhibitor of ROCK, and U73122, an inhibitor of PLC, and found that both inhibitors attenuated the effectiveness of O-1602. Western blot analysis revealed that O-1602 downregulated the expression of GluA1 and GluN2A in mice. Taken together, these results suggest that GPR55 plays an important role in anxiety and O-1602 may have therapeutic potential in treating anxiety-like symptoms.

Intergenerational Transmission of Paternal Epigenetic Marks: Mechanisms Influencing Susceptibility to Post-Concussion Symptomology in a Rodent Model

Epigenetic transmission of phenotypic variance has been linked to paternal experiences prior to conception and during perinatal development. Previous reports indicate that paternal experiences increase phenotypic heterogeneity and may contribute to offspring susceptibility to post-concussive symptomology. This study sought to determine if epigenetic tags, specifically DNA methylation of promoter regions, are transmitted from rodent fathers to their sons. Using MethyLight, promoter methylation of specific genes involved in recovery from concussion and brain plasticity were analyzed in sperm and brain tissue. Promoter methylation in sperm differed based on paternal experience. Differences in methylation were often identified in both the sperm and brain tissue obtained from their sons, demonstrating transmission of epigenetic tags. For certain genes, methylation in the sperm was altered following a concussion suggesting that a history of brain injury may influence paternal transmission of traits. As telomere length is paternally inherited and linked to neurological health, this study examined paternally derived differences in telomere length, in both sperm and brain. Telomere length was consistent between fathers and their sons, and between brain and sperm, with the exception of the older fathers. Older fathers exhibited increased sperm telomere length, which was not evident in sperm or brain of their sons.

Lack of Social Support Raises Stress Vulnerability in Rats with a History of Ancestral Stress

Stress is a primary risk factor for psychiatric disorders. However, it is not fully understood why some stressed individuals are more vulnerable to psychiatric disorders than others. Here, we investigated whether multigenerational ancestral stress produces phenotypes that are sensitive to depression-like symptoms in rats. We also examined whether social isolation reveals potentially latent sensitivity to depression-like behaviours. F4 female rats born to a lineage of stressed mothers (F0-F3) received stress in adulthood while housed in pairs or alone. Social isolation during stress induced cognitive and psychomotor retardation only in rats exposed to ancestral stress. Social isolation also hampered the resilience of the hypothalamic-pituitary-adrenal axis to chronic stress and reduced hippocampal volume and brain-derived neurotrophic factor (BDNF) expression. Thus, synergy between social isolation and stress may unmask a latent history of ancestral stress, and raises vulnerability to mental health conditions. The findings support the notion that social support critically promotes stress coping and resilience.

Sex- and brain region- specific effects of prenatal stress and lead exposure on permissive and repressive post-translational histone modifications from embryonic development through adulthood

Developmental exposure to prenatal stress (PS) and lead (Pb) can affect brain development and adversely influence behavior and cognition. Epigenetic-based gene regulation is crucial for normal brain development and mis-regulation, in any form, can result in neurodevelopmental disorders. Post-translational histone modifications (PTHMs) are an integral and dynamic component of the epigenetic machinery involved in gene regulation. Exposures to Pb and/or PS may alter PTHM profiles, promoting lifelong alterations in brain function observed following Pb±PS exposure. Here we examined the effects of Pb±PS on global levels of activating marks H3K9Ac and H3K4Me3 and repressive marks H3K9Me2 and H3K27Me3 at different developmental stages: E18, PND0, PND6 and PND60. Dams were exposed to 0 or 100ppm Pb beginning 2 months prior to breeding followed by no PS (NS) or PS resulting in 4 offspring treatment groups per sex: 0-NS (control), 0-PS, 100-NS and 100-PS. Global levels of PTHMs varied from E18 through adulthood even in control mice, and were influenced by sex and brain-region. The developmental trajectory of these PTHM levels was further modified by Pb±PS in a sex-, brain region- and age-dependent manner. Females showed a preferential response to Pb alone in frontal cortex (FC) and differentially to PS alone and combined Pb+PS in hippocampus (HIPP). In males, PS-induced increases in PTHM levels in FC, whereas PS produced reductions in HIPP. Pb±PS-based changes in PTHM levels continued to be observed in adulthood (PND60), demonstrating the lasting effect of these early life environmental events on these histone marks. These results indicate that epigenetic consequences of Pb±PS and their contribution to mechanisms of toxicity are sex dependent. Additional studies will assist in understanding the functional significance of these changes in PTHM levels on expression of individual genes, functional pathways, and ultimately, their behavioral consequences.

Newborn sex-specific transcriptome signatures and gestational exposure to fine particles: findings from the ENVIRONAGE birth cohort

BACKGROUND

Air pollution exposure during pregnancy has been associated with adverse birth outcomes and health problems later in life. We investigated sex-specific transcriptomic responses to gestational long- and short-term exposure to particulate matter with a diameter < 2.5 μm (PM_2.5) in order to elucidate potential underlying mechanisms of action.

METHODS

Whole genome gene expression was investigated in cord blood of 142 mother-newborn pairs that were enrolled in the ENVIRONAGE birth cohort. Daily PM_2.5 exposure levels were calculated for each mother's home address using a spatial-temporal interpolation model in combination with a dispersion model to estimate both long- (annual average before delivery) and short- (last month of pregnancy) term exposure. We explored the association between gene expression levels and PM_2.5 exposure, and identified modulated pathways by overrepresentation analysis and gene set enrichment analysis.

RESULTS

Some processes were altered in both sexes for long- (e.g. DNA damage) or short-term exposure (e.g. olfactory signaling). For long-term exposure in boys neurodevelopment and RhoA pathways were modulated, while in girls defensin expression was down-regulated. For short-term exposure we identified pathways related to synaptic transmission and mitochondrial function (boys) and immune response (girls).

CONCLUSIONS

This is the first whole genome gene expression study in cord blood to identify sex-specific pathways altered by PM_2.5. The identified transcriptome pathways could provide new molecular insights as to the interaction pattern of early life PM_2.5 exposure with the biological development of the fetus.