Epigenetic programming of the stress response in male and female rats by prenatal restraint stress

A genome-wide methylation analysis of Chinese Han patients with chronic insomnia disorder

BACKGROUND

As the most common sleep disorder, chronic insomnia disorder (CID) has become a global health burden to the public. However, it remains unclear about the pathogenesis of this disease. Epigenetic changes may provide important insights into the gene-environment interaction in CID. Therefore, this study was conducted to investigate the DNA methylation pattern in CID and reveal the epigenetic mechanism of this disease.

METHODS

In this study, whole blood DNA was extracted from 8 CID patients (the CID group) and 8 healthy controls (the control group), respectively. Besides, genome-wide DNA methylation was detected by Illumina Human Methylation 850 K Beadchip. Moreover, the sleep quality and insomnia severity were evaluated by the Pittsburgh Sleep Quality Index (PSQI) and Insomnia Severity Index (ISI), respectively.

RESULTS

A total of 369 differentially methylated positions (DMPs) and 23 differentially methylated regions (DMRs) were identified between the CID and control groups. LHX6 was identified as the most important differentially methylated gene (DMG). The Gene Ontology (GO) analysis results corroborated that DMPs were significantly enriched in 105 GO terms, including cell signaling, homogenous cell adhesion of plasma membrane adhesion molecules, nervous system development, cell adhesion, and calcium ion binding. In addition, it was demonstrated that DMPs were significantly enriched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, including the hippo signaling pathway, Ras signaling pathway, and vitamin B6 metabolism. The DMR-related GO analysis results revealed the positive regulation of protein kinase activities.

CONCLUSIONS

DNA methylation plays a critical role in the development of CID, and LHX6 is validated to be an important DMG.

Unraveling the molecular basis of cannabidiolic acid methyl Ester's anti-depressive effects in a rat model of treatment-resistant depression

Major depressive disorder (MDD) stands as a significant cause of disability globally. Cannabidiolic Acid-Methyl Ester (CBDA-ME) (EPM-301, HU-580), a derivative of Cannabidiol, demonstrates immediate antidepressant-like effects, yet it has undergone only minimal evaluation in psychopharmacology. Our goal was to investigate the behavioral and potential molecular mechanisms associated with the chronic oral administration of this compound in the Wistar Kyoto (WKY) genetic model of treatment-resistant depression. Male WKY rats were subjected to behavioral assessments before and after receiving chronic (14-day) oral doses of CBDA-ME (0.5 mg/kg), 15 mg/kg of imipramine or vehicle. At the end of the study, plasma corticosterone levels and mRNA expression of various genes in the medial Prefrontal Cortex and Hippocampus were measured. Behavioral outcomes from CBDA-ME treatment indicated an antidepressant-like effect similar to imipramine, as oral ingestion reduced immobility and increased swimming duration in the Forced Swim Test. Neither treatment influenced locomotion in the Open Field Test nor preference in the Saccharin Preference Test. The behavioral impact in WKY rats coincided with reduced corticosterone serum levels, upregulated mRNA expression of Cannabinoid receptor 1, Fatty Acid Amide Hydrolase, and Corticotropin-Releasing Hormone Receptor 1, alongside downregulation of the Serotonin Transporter in the hippocampus. Additionally, there was an upregulation of CB1 mRNA expression and downregulation of Brain-Derived Neurotrophic Factor in the mPFC. These findings contribute to our limited understanding of the antidepressant effects of CBDA-ME and shed light on its potential psychopharmacological mechanisms. This discovery opens up possibilities for utilizing cannabinoids in the treatment of major depressive disorder and related conditions.

The Role of Piromelatine on Peripheral and Hippocampal Insulin Resistance in Rat Offspring Exposed to Chronic Maternal Stress

Prenatal stress (PNS), which alters the hypothalamic-pituitary-adrenal axis function in the offspring, predisposes to insulin resistance (IR) in later life and is associated with numerous disorders, including cognitive and memory impairments. At present, our main goal is to assess the effects of chronic piromelatine (Pir) administration, a melatonin analogue, on PNS-provoked IR in the periphery and the hippocampus in male and female offspring. Pregnant Sprague-Dawley rats were exposed to chronic stress (one short-term stressor on a daily basis and one long-term stressor on a nightly basis) from the first gestation week until birth. Vehicle or Pir 20 mg/kg were administered intraperitoneally for 21 days. Plasma glucose, serum insulin levels, and the homeostasis model assessment of insulin resistance (HOMA-IR) were determined as markers of peripheral IR. For the hippocampal IR assessment, insulin receptors (IRs) and glucose transporter 4 (GLUT4) were examined. Prenatally stressed offspring of both sexes indicated enhanced plasma glucose and serum insulin concentrations, increased HOMA-IR, and decreased hippocampal GLUT4 only in male rats. The PNS-induced changes were corrected by chronic treatment with Pir. The present results suggest that the melatoninergic compound Pir exerts beneficial effects on altered glucose/insulin homeostasis in PNS-exposed offspring.

Prenatal restraint stress affects early neurobehavioral response and oxidative stress in mice pups

Prenatal stress (PS), in both humans and animals, presents a potential risk to the mother and her fetus throughout gestation. PS is always associated with physiological changes that alter embryonic development and predispose the individual to lifelong health problems, including susceptibility to mental illness. This study aims to identify the harmful effects of prenatal restraint stress (PRS), commonly employed to induce stress painlessly and without any lasting debilitation during gestation. This stress is applied to pregnant Swiss albino mice from E7.5 to delivery for three hours daily. Our results show that PS affects dams' weight gain during the gestational period; moreover, the PS dams prefer passive nursing, exhibit a lower percentage of licking and grooming, and impair other maternal behaviors, including nesting and pup retrieval. Concerning the offspring, this stress induces neurobehavioral impairments, including a significant increase in the time of recovery of the young stressed pups in the surface righting reflex, the latency to avoid the cliff in the cliff avoidance test, longer latencies to accomplish the task in negative geotaxis, and a lower score in swimming development. These alterations were accompanied by increased Malondialdehyde activity (MDA) at PND17 and 21 and downregulation of AchE activity in the whole brain of pups on postnatal days 7 and 9. These findings demonstrated that PS causes deleterious neurodevelopmental impairments that can alter various behaviors later in life.

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.

Epigenetic modification impacting brain functions: Effects of physical activity, micronutrients, caffeine, toxins, and addictive substances

Changes in gene expression are involved in many brain functions. Epigenetic processes modulate gene expression by histone modification and DNA methylation or RNA-mediated processes, which is important for brain function. Consequently, epigenetic changes are also a part of brain diseases such as mental illness and addiction. Understanding the role of different factors on the brain epigenome may help us understand the function of the brain. This review discussed the effects of caffeine, lipids, addictive substances, physical activity, and pollutants on the epigenetic changes in the brain and their modulatory effects on brain function.

Associations between prenatal maternal stress, maternal inflammation during pregnancy, and children's internalizing and externalizing symptoms throughout childhood

BACKGROUND

Maternal immune activation is a potential mechanism underlying associations between maternal stress during pregnancy and offspring mental health problems. This study examined associations between prenatal maternal stress, maternal inflammation during pregnancy, and children's internalizing and externalizing symptoms from 3 to 10 years of age, and whether maternal inflammation mediated the associations between prenatal maternal stress and children's internalizing and externalizing symptoms.

METHODS

This study comprised 4,902 mother-child dyads in the Generation R study. Prenatal maternal stress was assessed using self-reported data collected during pregnancy and analyzed as a latent variable consisting of four stress domains. Maternal inflammation during pregnancy was assessed using serum concentrations of C-reactive protein (CRP) measured at a median of 13.5 weeks' gestation. Child internalizing and externalizing symptoms were assessed using the Child Behavior Checklist (CBCL) by maternal report at ages 3 years, 5 years, and 10 years; paternal-reported CBCL data were also available at 3 years and 10 years.

RESULTS

Prenatal maternal stress was associated with maternal-reported internalizing and externalizing symptoms of the child at 3, 5, and 10 years of age, and with paternal-reported internalizing and externalizing symptoms at 3 and 10 years. Prenatal maternal stress was associated with maternal CRP concentrations prior to, but not after, covariate adjustment. Maternal CRP concentrations during pregnancy were associated with paternal-reported internalizing symptoms of offspring at 10 years of age prior to, but not after, covariate adjustment. There was no evidence that CRP concentrations mediated the associations between prenatal maternal stress and children's internalizing or externalizing symptoms.

CONCLUSIONS

Maternal stress during pregnancy is associated with higher levels of internalizing and externalizing symptoms in children, but this association is not because of differences in maternal immune activation linked to maternal stress. Replication of these findings in other cohorts is required; examination of other biomarkers or variation in immune activity during pregnancy would also benefit from further exploration.

The effects of forced exercise and zinc supplementation during pregnancy on prenatally stress-induced behavioral and neurobiological consequences in adolescent female rat offspring

Prenatal manipulations can lead to neurobehavioral changes in the offspring. In this study, individual and combined effects of forced exercise and zinc supplementation during pregnancy on prenatally restraint stress (PRS)-induced behavioral impairments, neuro-inflammatory responses, and oxidative stress have been investigated in adolescent female rat offspring. Pregnant rats were divided into five groups: control; restraint stress (RS); RS + exercise stress (RS + ES), RS + zinc supplementation (RS + Zn); and RS + ES + Zn. All the pregnant rats (except control) were exposed to RS from gestational days 15 to 19. Pregnant rats in ES groups were subjected to forced treadmill exercise (30 min/daily), and in Zn groups to zinc sulfate (30 mg/kg/orally), throughout the pregnancy. At postnatal days 25-27, anxiety-like and stress-coping behaviors were recorded, and the gene expressions of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) and the concentration of total antioxidant capacity were measured in the prefrontal cortex. PRS significantly enhanced anxiety, generated passive coping behaviors, increased IL-1β and TNF-α expression, and decreased the antioxidant capacity. ES potentiated while zinc reversed PRS-induced behavioral impairments. Prenatal zinc also restored the anti-inflammatory and antioxidant capacity but had no effect on additive responses imposed by the combination of RS and ES. Suppression of PRS-induced behavioral and neurobiological impairments by zinc suggests the probable clinical importance of zinc on PRS-induced changes on child temperament.

Targeted Therapy for Orofacial Pain: A Novel Perspective for Precision Medicine

Orofacial pain (OFP) is a dental specialty that includes the diagnosis, management and treatment of disorders of the jaw, mouth, face, head and neck. Evidence-based understanding is critical in effectively treating OFPs as the pathophysiology of these conditions is multifactorial. Since OFP impacts the quality of life of the affected individuals, treating patients successfully is of the utmost significance. Despite the therapeutic choices available, treating OFP is still quite challenging, owing to inter-patient variations. The emerging trends in precision medicine could probably lead us to a paradigm shift in effectively managing the untreatable long-standing pain conditions. Precision medicine is designed based on the patient's genetic profile to meet their needs. Several significant relationships have been discovered based on the genetics and genomics of pain in the past, and some of the notable targets are discussed in this review. The scope of this review is to discuss preclinical and clinical trials that include approaches used in targeted therapy for orofacial pain. Future developments in pain medicine should benefit from current trends in research into novel therapeutic approaches.

Transcriptomic profiling of the developing brain revealed cell-type and brain-region specificity in a mouse model of prenatal stress

BACKGROUND

Prenatal stress (PS) is considered as a risk factor for many mental disorders. PS-induced transcriptomic alterations may contribute to the functional dysregulation during brain development. Here, we used RNA-seq to explore changes of gene expression in the mouse fetal brain after prenatal exposure to chronic unpredictable mild stress (CUMS).

RESULTS

We compared the stressed brains to the controls and identified groups of significantly differentially expressed genes (DEGs). GO analysis on up-regulated DEGs revealed enrichment for the cell cycle pathways, while down-regulated DEGs were mostly enriched in the neuronal pathways related to synaptic transmission. We further performed cell-type enrichment analysis using published scRNA-seq data from the fetal mouse brain and revealed cell-type-specificity for up- and down-regulated DEGs, respectively. The up-regulated DEGs were highly enriched in the radial glia, while down-regulated DEGs were enriched in different types of neurons. Cell deconvolution analysis further showed altered cell fractions in the stressed brain, indicating accumulation of neuroblast and impaired neurogenesis. Moreover, we also observed distinct brain-region expression pattern when mapping DEGs onto the developing Allen brain atlas. The up-regulated DEGs were primarily enriched in the dorsal forebrain regions including the cortical plate and hippocampal formation. Surprisingly, down-regulated DEGs were found excluded from the cortical region, but highly expressed on various regions in the ventral forebrain, midbrain and hindbrain.

CONCLUSION

Taken together, we provided an unbiased data source for transcriptomic alterations of the whole fetal brain after chronic PS, and reported differential cell-type and brain-region vulnerability of the developing brain in response to environmental insults during the pregnancy.

Latent Trajectories and Risk Factors of Prenatal Stress, Anxiety, and Depression in Southwestern China-A Longitudinal Study

(1) Background: Few studies have explored the heterogeneity of trajectories of stress, anxiety, and depressive symptoms during pregnancy. This study aimed to explore the trajectory groups of stress, anxiety, and depressive symptoms in women during pregnancy and the risk factors associated with those groups. (2) Methods: Data came from pregnant women recruited from January to September 2018 in four hospitals in Chongqing Province, China. A structured questionnaire was given to pregnant women, which collected basic information, including personal, family, and social information. The growth mixture model was applied to identify potential trajectory groups, and multinomial logistic regression was applied to analyze factors of trajectory groups. (3) Results: We identified three stress trajectory groups, three anxiety trajectory groups, and four depression trajectory groups. Less developed regions, inadequate family care, and inadequate social support were associated with a high risk of stress; residence, use of potentially teratogenic drugs, owning pets, family care, and social support were strongly associated with the anxiety trajectory group; family care and social support were the most critical factors for the depression trajectory group. (4) Conclusions: The trajectories of prenatal stress, anxiety, and depressive symptoms are dynamic and heterogeneous. This study may provide some critical insights into the characteristics of women in the high-risk trajectory groups for early intervention to mitigate worsening symptoms.

The role of mGlu receptors in susceptibility to stress-induced anhedonia, fear, and anxiety-like behavior

Stress and trauma exposure contribute to the development of psychiatric disorders such as post-traumatic stress disorder (PTSD) and major depressive disorder (MDD) in a subset of people. A large body of preclinical work has found that the metabotropic glutamate (mGlu) family of G protein-coupled receptors regulate several behaviors that are part of the symptom clusters for both PTSD and MDD, including anhedonia, anxiety, and fear. Here, we review this literature, beginning with a summary of the wide variety of preclinical models used to assess these behaviors. We then summarize the involvement of Group I and II mGlu receptors in these behaviors. Bringing together this extensive literature reveals that mGlu5 signaling plays distinct roles in anhedonia, fear, and anxiety-like behavior. mGlu5 promotes susceptibility to stress-induced anhedonia and resilience to stress-induced anxiety-like behavior, while serving a fundamental role in the learning underlying fear conditioning. The medial prefrontal cortex, basolateral amygdala, nucleus accumbens, and ventral hippocampus are key regions where mGlu5, mGlu2, and mGlu3 regulate these behaviors. There is strong support that stress-induced anhedonia arises from decreased glutamate release and post-synaptic mGlu5 signaling. Conversely, decreasing mGlu5 signaling increases resilience to stress-induced anxiety-like behavior. Consistent with opposing roles for mGlu5 and mGlu2/3 in anhedonia, evidence suggests that increased glutamate transmission may be therapeutic for the extinction of fear learning. Thus, a large body of literature supports the targeting of pre- and post-synaptic glutamate signaling to ameliorate post-stress anhedonia, fear, and anxiety-like behavior.

Changes in Stereotypies: Effects over Time and over Generations

Simple Summary

Herein, we propose that there should be discussion about the function and effects of stereotypies in relation to the time during which they are shown. In the first stages, stereotypies may help animals deal with challenges. However, behavior can potentially alter the brain, impairing its function due the absence of a diverse repertory, and change brain connections, neurophysiology and later neuroanatomy. The neuroanatomical changes in individuals showing stereotypies could be an effect rather than a cause of the stereotypy. As a consequence, studies showing different outcomes for animal welfare from stereotypy expression could be due to variation in a timeline of expression. Stereotypies are widely used as an animal welfare indicator, and their expression can tell us about psychological states. However, there are questions about the longer-term consequences if animals express stereotypies: do the stereotypies help in coping? During the prenatal period, stereotypic behavior expressed by the mother can change the phenotype of the offspring, especially regarding emotionality, one mechanism acting via methylation in the limbic system in the brain. Are individuals that show stereotypies for shorter or longer periods all better adjusted, and hence have better welfare, or is the later welfare of some worse than that of individuals that do not show the behavior?

Abstract

Stereotypies comprise a wide range of repeated and apparently functionless behaviors that develop in individuals whose neural condition or environment results in poor welfare. While stereotypies are an indicator of poor welfare at the time of occurrence, they may have various consequences. Environmental enrichment modifies causal factors and reduces the occurrence of stereotypies, providing evidence that stereotypies are an indicator of poor welfare. However, stereotypy occurrence and consequences change over time. Furthermore, there are complex direct and epigenetic effects when mother mammals that are kept in negative conditions do or do not show stereotypies. It is proposed that, when trying to deal with challenging situations, stereotypies might initially help animals to cope. After further time in the conditions, the performance of the stereotypy may impair brain function and change brain connections, neurophysiology and eventually neuroanatomy. It is possible that reported neuroanatomical changes are an effect of the stereotypy rather than a cause.

Hippocampal AMPA receptors mediate the impairment of spatial learning and memory in prenatally stressed offspring rats

Numerous studies have shown that prenatal stress (PS) induces learning and memory deficits in offspring, yet the specific mechanisms and effective interventions remain limited. Chewing has been known as one of the active coping strategies to suppress stress, but its effects during PS on learning and memory are unknown. The purpose of this study was to investigate the role of hippocampal AMPA receptors in the adverse effects of PS on spatial learning and memory, and whether chewing during PS could prevent these effects in prenatally stressed adult offspring rats. Prenatal restraint stress with or without chewing to dams during the day 11-20 of pregnancy was used to analyze the impact of different treatments for offspring. The spatial learning and memory were tested by the Morris water maze. The mRNA and protein expression of AMPA receptors in the hippocampus were measured by qRT-PCR and Western blot, respectively. The methylation of AMPA receptors was detected by bisulfite sequencing PCR. Our results revealed that PS impaired spatial learning acquisition and memory retrieval in adult offspring rats, but chewing could relieve this effect. Hippocampal GluA1-4 expression was significantly reduced in prenatally stressed offspring, while there were no changes in the methylation level of GluA2 and GluA4 promoters. Moreover, chewing increased PS-induced suppression of AMPA receptors in the hippocampus. In short, hippocampal AMPA receptors mediate the impairment of spatial learning and memory in prenatally stressed offspring, whereas chewing during PS could ameliorate PS-induced memory deficits.

The Transition to Parenthood in Obstetrics: Enhancing Prenatal Care for Two Generation Impact

Obstetrics, the specialty overseeing infant and parent health before birth, could be expanded to address the inter-related areas of parents' prenatal impact on children's brain development and their own psychosocial needs during a time of immense change and neuroplasticity. Obstetrics is primed for the shift that is happening in pediatrics, which is moving from its traditional focus on physical health to a coordinated, whole child, two or multi-generation approach. Pediatric care now includes developmental screening, parenting education, parent coaching, access to developmental specialists, brain-building caregiving skills, linkages to community resources, and tiered interventions with psychologists. Drawing on decades of Developmental Origins of Health and Disease research highlighting the prenatal beginnings of future health and new studies on the transition to parenthood describing adult development from pregnancy to early postpartum, we propose that, similar to pediatrics, the integration of education and intervention strategies into the prenatal care ecosystem should be tested for its potential to improve child cognitive and social-emotional development and parental mental health. Pediatric care programs can serve as models of change for the systematic development, testing and, incorporation of new content into prenatal care as universal, first-tier treatment as well as evidenced-based, triaged interventions according to level of need. To promote optimal beginnings for the whole family, we propose an augmented prenatal care ecosystem that aligns with, and could build on, current major efforts to enhance perinatal care individualization through consideration of medical, social, and structural determinants of health.

Prenatal psychological or metabolic stress increases the risk for psychiatric disorders: the "funnel effect" model

Adverse stressful experiences in utero can redirect fetal brain development, ultimately leading to increased risk for psychiatric disorders. Obesity during pregnancy can have similar effects as maternal stress, affecting mental health in the offspring. In order to explain how similar outcomes may originate from different prenatal conditions, we propose a "funnel effect" model whereby maternal psychological or metabolic stress triggers the same evolutionarily conserved response pathways, increasing vulnerability for psychopathology. In this context, the placenta, which is the main mother-fetus interface, appears to facilitate such convergence, re-directing "stress" signals to the fetus. Characterizing converging pathways activated by different adverse environmental conditions is fundamental to assess the emergence of risk signatures of major psychiatric disorders, which might enable preventive measures in risk populations, and open up new diagnostics, and potentially therapeutic approaches for disease prevention and health promotion already during pregnancy.

Chronic corticosterone disrupts the circadian rhythm of CRH expression and m6A RNA methylation in the chicken hypothalamus

BACKGROUND

Corticotropin-releasing hormone (CRH), the major secretagogue of the hypothalamic-pituitary-adrenal (HPA) axis, is intricately intertwined with the clock genes to regulate the circadian rhythm of various body functions. N6-methyladenosine (m⁶A) RNA methylation is involved in the regulation of circadian rhythm, yet it remains unknown whether CRH expression and m⁶A modification oscillate with the clock genes in chicken hypothalamus and how the circadian rhythms change under chronic stress.

RESULTS

Chronic exposure to corticosterone (CORT) eliminated the diurnal patterns of plasma CORT and melatonin levels in the chicken. The circadian rhythms of clock genes in hippocampus, hypothalamus and pituitary are all disturbed to different extent in CORT-treated chickens. The most striking changes occur in hypothalamus in which the diurnal fluctuation of CRH mRNA is flattened, together with mRNA of other feeding-related neuropeptides. Interestingly, hypothalamic m⁶A level oscillates in an opposite pattern to CRH mRNA, with lowest m⁶A level after midnight (ZT18) corresponding to the peak of CRH mRNA before dawn (ZT22). CORT diminished the circadian rhythm of m⁶A methylation with significantly increased level at night. Further site-specific m⁶A analysis on 3'UTR of CRH mRNA indicates that higher m⁶A on 3'UTR of CRH mRNA coincides with lower CRH mRNA at night (ZT18 and ZT22).

CONCLUSIONS

Our results indicate that chronic stress disrupts the circadian rhythms of CRH expression in hypothalamus, leading to dysfunction of HPA axis in the chicken. RNA m⁶A modification is involved in the regulation of circadian rhythms in chicken hypothalamus under both basal and chronic stress conditions.

Severe Gestational Low-Protein Intake Impacts Hippocampal Cellularity, Tau, and Amyloid-β Levels, and Memory Performance in Male Adult Offspring: An Alzheimer-Simile Disease Model?

BACKGROUND

Maternal undernutrition has been associated with psychiatric and neurological disorders characterized by learning and memory impairment.

OBJECTIVE

Considering the lack of evidence, we aimed to analyze the effects of gestational protein restriction on learning and memory function associated with hippocampal cell numbers and neurodegenerative protein content later in life.

METHODS

Experiments were conducted in gestational low- (LP, 6% casein) or regular-protein (NP, 17% casein) diet intake offspring. Behavioral tests, isolated hippocampal isotropic fractionator cell studies, immunoblotting, and survival lifetime were observed.

RESULTS

The birthweight of LP males is significantly reduced relative to NP male progeny, and hippocampal mass increased in 88-week-old LP compared to age-matched NP offspring. The results showed an increased proximity measure in 87-week-old LP compared to NP offspring. Also, LP rats exhibited anxiety-like behaviors compared to NP rats at 48 and 86-wk of life. The estimated neuron number was unaltered in LP rats; however, non-neuron cell numbers increased compared to NP progeny. Here, we showed unprecedented hippocampal deposition of brain-derived neurotrophic factor, amyloid-β peptide (Aβ), and tau protein in 88-week-old LP relative to age-matched NP offspring.

CONCLUSION

To date, no predicted studies showed changes in hippocampal morphological structure in maternal protein-restricted elderly offspring. The current data suggest that gestational protein restriction may accelerate hippocampal function loss, impacting learning/memory performance, and supposedly developing diseases similar to Alzheimer's disease (AD) in elderly offspring. Thus, we propose that maternal protein restriction could be an elegant and novel method for constructing an AD-like model in adult male offspring.

Impacts of a perinatal exposure to manganese coupled with maternal stress in rats: Maternal somatic measures and the postnatal growth and development of rat offspring

Psychological stress experienced by the mother during pregnancy has been associated with emotional and cognitive disorders in children such as depression and anxiety. Socioeconomically disadvantaged populations are vulnerable to adverse life experiences and can also be disproportionally exposed to environmental contaminants. To better understand the neurodevelopmental impacts of an environmental toxicant coupled with elevated psychological stress, we exposed pregnant rats to a series of perinatal stressors. Manganese (Mn), a neurotoxicant at excessive concentrations was delivered through drinking water (0, 2, or 4 mg/mL) from gestational day (GD) 7 to postnatal day (PND) 22. A variable stress paradigm was applied to half of the animals from GD13 to PND9. Measurements of somatic development and behavior were examined in the offspring at different developmental stages. No evidence of overt maternal toxicity was observed although the 4 mg/mL Mn-exposed dams gained less body weight during gestation compared to the other dams. Stress also reduced gestational maternal weight gain. Daily fluid consumption normalized for body weight was decreased in the Mn-exposed dams in a dose-dependent manner but was not altered by the stress paradigm. Maternal stress and/or Mn exposure did not affect litter size or viability, but pup weight was significantly reduced in the 4 mg/mL Mn-exposed groups on PNDs 9 through 34 when compared to the other offspring groups. The efficacy of the manipulations to increase maternal stress levels was determined using serum corticosterone as a biomarker. The baseline concentration was established prior to treatment (GD7) and levels were low and similar in all treatment groups. Corticosterone levels were elevated in the perinatal-stress groups compared to the no-stress groups, regardless of Mn exposure, on subsequent time points (GD16, PND9), but were only significantly different on GD16. An analysis of tissue concentrations revealed Mn was elevated similarly in the brain and blood of offspring at PND2 and at PND22 in a significant dose-dependent pattern. Dams also showed a dose-dependent increase in Mn concentrations in the brain and blood; the addition of stress increased the Mn concentrations in the maternal blood but not the brain. Perinatal stress did not alter the effects of Mn on the maternal or offspring somatic endpoints described here.

Cerebral Erythropoietin Prevents Sex-Dependent Disruption of Respiratory Control Induced by Early Life Stress

Injuries that occur early in life are often at the root of adult illness. Neonatal maternal separation (NMS) is a form of early life stress that has persistent and sex-specific effects on the development of neural networks, including those that regulate breathing. The release of stress hormones during a critical period of development contributes to the deleterious consequences of NMS, but the role of increased corticosterone (CORT) in NMS-induced respiratory disturbance is unknown. Because erythropoietin (EPO) is a potent neuroprotectant that prevents conditions associated with hyperactivation of the stress neuroaxis in a sex-specific manner, we hypothesized that EPO reduces the sex-specific alteration of respiratory regulation induced by NMS in adult mice. Animals were either raised under standard conditions (controls) or exposed to NMS 3 h/day from postnatal days 3–12. We tested the efficacy of EPO in preventing the effects of NMS by comparing wild-type mice with transgenic mice that overexpress EPO only in the brain (Tg21). In 7-days-old pups, NMS augmented CORT levels ~2.5-fold by comparison with controls but only in males; this response was reduced in Tg21 mice. Respiratory function was assessed using whole-body plethysmography. Apneas were detected during sleep; the responsiveness to stimuli was measured by exposing mice to hypoxia (10% O₂; 15 min) and hypercapnia (5% CO₂; 10 min). In wild-type, NMS increased the number of apneas and the hypercapnic ventilatory response (HcVR) only in males; with no effect on Tg21. In wild-type males, the incidence of apneas was positively correlated with HcVR and inversely related to the tachypneic response to hypoxia. We conclude that neural EPO reduces early life stress-induced respiratory disturbances observed in males.

Age- and sex-specific effects of stress on parvalbumin interneurons in preclinical models: Relevance to sex differences in clinical neuropsychiatric and neurodevelopmental disorders

Stress is a major risk factor for neurodevelopmental and neuropsychiatric disorders, with the capacity to impact susceptibility to disease as well as long-term neurobiological and behavioral outcomes. Parvalbumin (PV) interneurons, the most prominent subtype of GABAergic interneurons in the cortex, are uniquely responsive to stress due to their protracted development throughout the highly plastic neonatal period and into puberty and adolescence. Additionally, PV + interneurons appear to respond to stress in a sex-specific manner. This review aims to discuss existing preclinical studies that support our overall hypothesis that the sex-and age-specific impacts of stress on PV + interneurons contribute to differences in individual vulnerability to stress across the lifespan, particularly in regard to sex differences in the diagnostic rate of neurodevelopmental and neuropsychiatric diseases in clinical populations. We also emphasize the importance of studying sex as a biological variable to fully understand the mechanistic and behavioral differences between males and females in models of neuropsychiatric disease.

Comparison of survival rates in four inbred mouse strains under different housing conditions: effects of environmental enrichment

Housing conditions can affect the well-being of laboratory animals and thereby affect the outcomes of experiments. The appropriate environment is essential for the expression of natural behavior in animals. Here, we compared survival rates in four inbred mouse strains maintained under three different environmental conditions. Three mouse strains (C57BL/6J, C3H/HeN, and DBA/2J) housed under environmental enrichment (EE) conditions showed improved survival; however, EE did not alter the survival rate of the fourth strain, BALB/c. None of the strains showed significant differences in body weights or plasma corticosterone levels in the three environmental conditions. For BALB/c mice, the rates of debility were higher in the EE group. Interestingly, for C57BL/6J and C3H/HeN mice, the incidence of animals with alopecia was significantly lower in the EE groups than in the control group. It is possible that the enriched environment provided greater opportunities for sheltering in a secure location in which to avoid interactions with other mice. The cloth mat flooring used for the EE group was bitten and chewed by the mice. Our findings suggest that depending on the mouse strains different responses to EE are caused with regard to health and survival rates. The results of this study provide basic data for further studies on EE.

Circadian Rhythms in Mood Disorders

Altered behavioral rhythms are a fundamental diagnostic feature of mood disorders. Patients report worse subjective sleep and objective measures confirm this, implicating a role for circadian rhythm disruptions in mood disorder pathophysiology. Molecular clock gene mutations are associated with increased risk of mood disorder diagnosis and/or severity of symptoms, and mouse models of clock gene mutations have abnormal mood-related behaviors. The mechanism by which circadian rhythms contribute to mood disorders remains unknown, however, circadian rhythms regulate and are regulated by various biological systems that are abnormal in mood disorders and this interaction is theorized to be a key component of mood disorder pathophysiology. A growing body of evidence has begun defining how the interaction of circadian and neurotransmitter systems influences mood and behavior, including the role of current antidepressants and mood stabilizers. Additionally, the hypothalamus-pituitary-adrenal (HPA) axis interacts with both circadian and monoaminergic systems and may facilitate the contribution of environmental stressors to mood disorder pathophysiology. The central role of circadian rhythms in mood disorders has led to the development of chronotherapeutics, which are treatments designed specifically to target circadian rhythm regulators, such as sleep, light, and melatonin, to produce an antidepressant response.

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.

A Behavioral Index for Assessing Bison Stress Level during Handling and Demographic Predictors of Stress Response

There are an estimated half-a-million Plains Bison (Bison bison) present in North America in commercial and conservation herds. Most bison are rounded up and "worked" annually for parasite control, veterinarian attention, and processing, making it important to understand the impacts of these operations. Research indicates bison generally experience higher levels of stress than cattle during similar handling processes. However, most methods for assessing stress-level during working are invasive, increase handling time, and paradoxically increase stress levels. We designed a behavioral index to assess bison stress level during handling and used it to evaluate various predictors of stress response in a semi-wild bison herd. We examined how sex, age, herd of origin, previous experience, calf rearing, and body condition influenced bison stress response during working operations from 2015 to 2017. Our results indicate that stress level decreased with age and previous experience being worked through a particular facility. Additionally, herd of origin influenced stress level, indicating that stress response may have a genetic or epigenetic component. Our study provides an easily applicable tool for monitoring bison stress levels.

Altering the development of the dopaminergic system through social play in rats: Implications for anxiety, depression, hyperactivity, and compulsivity

Dopamine is essential to many functions like reward, motivation, and attention; when its neural pathways do not function properly, various disorders (e.g., anxiety, depression, hyperactivity, compulsions) can arise. Truncated-DAT rats display persistent stereotypies and aggressiveness; hence they are a new valuable animal model to study the pathogenesis of these disorders. The focus of research is often on the individual epigenetic determinants and much less on the impact of social experiences. Here, we investigate the developmental impact of the social environment on adolescent wild type (WT) rats. We divided subjects at weaning into three groups: living with another adolescent (WT Peer), with a WT adult, or with a truncated-DAT one, and we observed homecage social behavior of these pairs (play, jump, victory, and "bullying") during whole adolescence. When adult, we observed the same subjects in plus maze, forced swim, and social preference tests to measure levels of anxiety, depression, and quality of social interactions. Compared to the other groups, WT rats that had spent their adolescence with a truncated-DAT adult as companion show more anxious, depressive, hyperactive, impulsive, and compulsive behaviours. Results confirm that social interactions and healthy play (i.e., when play has behavioural, social, and psychomotor rewards that support the cognitive, emotional and physical development of the individual) are essential to neurobehavioral maturation. Conversely, anomalous interactions like poor play and "bullying" in developing rats may impact onto their dopaminergic system. Consequently, an impoverished social play could be one of the factors contributing to the appearance of putative indexes of attention deficit hyperactivity disorder (ADHD) and\or obsessive-compulsive disorder (OCD).

Intergenerational trauma transmission is associated with brain metabotranscriptome remodeling and mitochondrial dysfunction

Intergenerational trauma increases lifetime susceptibility to depression and other psychiatric disorders. Whether intergenerational trauma transmission is a consequence of in-utero neurodevelopmental disruptions versus early-life mother–infant interaction is unknown. Here, we demonstrate that trauma exposure during pregnancy induces in mouse offspring social deficits and depressive-like behavior. Normal pups raised by traumatized mothers exhibited similar behavioral deficits to those induced in pups raised by their biological traumatized mothers. Good caregiving by normal mothers did not reverse prenatal trauma-induced behaviors, indicating a two-hit stress mechanism comprising both in-utero abnormalities and early-life poor parenting. The behavioral deficits were associated with profound changes in the brain metabotranscriptome. Striking increases in the mitochondrial hypoxia marker and epigenetic modifier 2-hydroxyglutaric acid in the brains of neonates and adults exposed prenatally to trauma indicated mitochondrial dysfunction and epigenetic mechanisms. Bioinformatic analyses revealed stress- and hypoxia-response metabolic pathways in the neonates, which produced long-lasting alterations in mitochondrial energy metabolism and epigenetic processes (DNA and chromatin modifications). Most strikingly, early pharmacological interventions with acetyl-L-carnitine (ALCAR) supplementation produced long-lasting protection against intergenerational trauma-induced depression.

Sammy Alhassen, Siwei Chen, et al. use mouse models to examine the effects of prenatal and postnatal stress on metabolomic and transcriptomic pathways in the brain. Their results suggest that altered mitochondrial metabolism may underlie trauma-induced behavioral deficits, and that correcting metabolism with ALCAR supplementation may protect against intergenerational transmission of traumatic stress.

Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction

As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O₂ sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.

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.

Moderation of the transgenerational transference of antenatal stress-induced anxiety

Maternal stress has debilitating implications for both mother and child, including increased risk for anxiety. The current COVID-19 pandemic escalates these phenomena, thus, urging the need to further explore and validate feasible therapeutic options. Unlike the protracted nature of clinical studies, animal models could offer swift evidence. Prominent candidates for treatment are selective serotonin reuptake inhibitors (SSRIs) to the mother, that putatively accommodate maternal functioning, and, thereby, also protect the child. However, SSRIs might have deleterious effects. It is important to assess whether SSRIs and other pharmacotherapies can moderate the transference of anxiety by soothing maternal anxiety and to examine the extent of offspring's exposure to the drugs via lactation. To our knowledge, the possibility that antenatal stress exacerbates lactation-driven exposure to SSRIs has not been tested yet. Thirty ICR-outbred female mice were exposed to stress during gestation and subsequently administered with either the SSRI, escitalopram, or the novel herbal candidate, shan-zha, during lactation. Upon weaning, both dams' and pups' anxiety-like behavior and serum escitalopram levels were assessed. The major findings of the current study show that both agents moderated the antenatal stress-induced transgenerational transference of anxiety by ameliorating dams' anxiety. Interestingly though, pups' exposure to escitalopram via lactation was exacerbated by antenatal stress. The latter finding provides a significant insight into the mechanism of lactation-driven exposure to xenobiotics and calls for a further consideration vis-à-vis the administration of other drugs during breastfeeding.

Sexual Dimorphism in Glucocorticoid Stress Response

Chronic stress is encountered in our everyday life and is thought to contribute to a number of diseases. Many of these stress-related disorders display a sex bias. Because glucocorticoid hormones are the main biological mediator of chronic stress, researchers have been interested in understanding the sexual dimorphism in glucocorticoid stress response to better explain the sex bias in stress-related diseases. Although not yet demonstrated for glucocorticoid regulation, sex chromosomes do influence sex-specific biology as soon as conception. Then a transient rise in testosterone start to shape the male brain during the prenatal period differently to the female brain. These organizational effects are completed just before puberty. The cerebral regions implicated in glucocorticoid regulation at rest and after stress are thereby impacted in a sex-specific manner. After puberty, the high levels of all gonadal hormones will interact with glucocorticoid hormones in specific crosstalk through their respective nuclear receptors. In addition, stress occurring early in life, in particular during the prenatal period and in adolescence will prime in the long-term glucocorticoid stress response through epigenetic mechanisms, again in a sex-specific manner. Altogether, various molecular mechanisms explain sex-specific glucocorticoid stress responses that do not exclude important gender effects in humans.

Review of psychological stress on oocyte and early embryonic development in female mice

Psychological stress can cause adverse health effects in animals and humans. Accumulating evidence suggests that psychological stress in female mice is associated with ovarian developmental abnormalities accompanied by follicle and oocyte defects. Oocyte and early embryonic development are impaired in mice facing psychological stress, likely resulting from hormone signalling disorders, reactive oxygen species (ROS) accumulation and alterations in epigenetic modifications, which are primarily mediated by the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-ovarian (HPO) axes. The present evidence suggests that psychological stress is increasingly becoming the most common causative factor for female subfertility. Here, we review recent progress on the impact of psychological stress on female reproduction, particularly for oocyte and early embryonic development in female mice. This review highlights the connection between psychological stress and reproductive health and provides novel insight on human subfertility.

Epigenetic landscape of stress surfeit disorders: Key role for DNA methylation dynamics

Chronic exposure to stress throughout lifespan alters brain structure and function, inducing a maladaptive response to environmental stimuli, that can contribute to the development of a pathological phenotype. Studies have shown that hypothalamic-pituitary-adrenal (HPA) axis dysfunction is associated with various neuropsychiatric disorders, including major depressive, alcohol use and post-traumatic stress disorders. Downstream actors of the HPA axis, glucocorticoids are critical mediators of the stress response and exert their function through specific receptors, i.e., the glucocorticoid receptor (GR), highly expressed in stress/reward-integrative pathways. GRs are ligand-activated transcription factors that recruit epigenetic actors to regulate gene expression via DNA methylation, altering chromatin structure and thus shaping the response to stress. The dynamic interplay between stress response and epigenetic modifiers suggest DNA methylation plays a key role in the development of stress surfeit disorders.

Prenatal stress induced chromatin remodeling and risk of psychopathology in adulthood

New insights into the pathophysiology of psychiatric disorders suggest the existence of a complex interplay between genetics and environment. This notion is supported by evidence suggesting that exposure to stress during pregnancy exerts profound effects on the neurodevelopment and behavior of the offspring and predisposes them to psychiatric disorders later in life. Accumulated evidence suggests that vulnerability to psychiatric disorders may result from permanent negative effects of long-term changes in synaptic plasticity due to altered epigenetic mechanisms (histone modifications and DNA methylation) that lead to condensed chromatin architecture, thereby decreasing the expression of candidate genes during early brain development. In this chapter, we have summarized the literature of clinical studies on psychiatric disorders induced by maternal stress during pregnancy. We also discussed the epigenetic alterations of gene regulations induced by prenatal stress. Because the clinical manifestations of psychiatric disorders are complex, it is obvious that the biological progression of these diseases cannot be studied only in postmortem brains of patients and the use of animal models is required. Therefore, in this chapter, we have introduced a well-established mouse model of prenatal stress (PRS) generated in restrained pregnant dams. The behavioral phenotypes of the offspring (PRS mice) born to the stressed dam and underlying epigenetic changes in key molecules related to synaptic activity were described and highlighted. PRS mice may serve as a useful model for investigating the pathogenesis of psychiatric disorders and may be a useful tool for screening for the potential compounds that may normalize aberrant epigenetic mechanisms induced by prenatal stress.

Maternal separation induces retinal and peripheral blood mononuclear cell alterations across the lifespan of female rats

Early life stress alters the function and feedback regulation of the hypothalamic-pituitaryadrenal (HPA) axis, and can contribute to neuroinflammation and neurodegeneration by modifying peripheral blood mononuclear cell (PBMC) activity. The retina, as part of the nervous system, is sensitive to immune changes induced by stress. However, the consequences of stress experienced at an early age on retinal development have not yet been elucidated. Here we aimed to evaluate the impact of maternal separation (MatSep) across three stages of the lifespan (adolescent, adult, and aged) on the retina, as well as on progression through the cell cycle and mitochondrial activity in PBMCs from female Wistar rats. Newborn pups were separated from their mother from postnatal day (PND) 2 until PND 14 for 3 h/day. Retinal analysis from the MatSep groups showed architectural alterations such as a diminished thickness of retinal layers, as well as increased expression of proinflammatory markers DJ-1, Iba-1, and CD45 and the gliotic marker GFAP. Additionally, MatSep disrupted the cell cycle and caused long-term increases in mitochondrial activity in PBMCs from adolescent and adult rats. Changes in the cell cycle profile of the PBMCs from aged MatSep rats were undetected. However, these PBMCs exhibited increased sensitivity to H₂O₂-induced oxidative stress in vitro. Therefore, these results suggest that early life stress can have long-term effects on retinal structure and function, possibly elicited by neonatal immune preconditioning.

Psychosocial Stress and Adversity: Effects from the Perinatal Period to Adulthood

Early exposure to stress and adversity can have both immediate and lasting effects on physical and psychological health. Critical periods have been identified in infancy, during which the presence or absence of experiences can alter developmental trajectories. There are multiple explanations for how exposure to psychosocial stress, before conception or early in life, has an impact on later increased risk for developmental delays, mental health, and chronic metabolic diseases. Through both epidemiologic and animal models, the mechanisms by which experiences are transmitted across generations are being identified. Because psychosocial stress has multiple components that can act as stress mediators, a comprehensive understanding of the complex interactions between multiple adverse or beneficial experiences and their ultimate effects on health is essential to best identify interventions that will improve health and outcomes. This review outlines what is known about the biology, transfer, and effects of psychosocial stress and early life adversity from the perinatal period to adulthood. This information can be used to identify potential areas in which clinicians in neonatal medicine could intervene to improve outcomes.

Epigenetic Modifications of GABAergic Interneurons Contribute to Deficits in Adult Hippocampus Neurogenesis and Depression-Like Behavior in Prenatally Stressed Mice

BACKGROUND

Prenatal stress (PRS) is considered a risk factor for depressive disorder. Adult hippocampal neurogenesis is believed to play a role in the regulation of affective behaviors. GABAergic interneuron is a key modulator in adult hippocampal neurogenesis. Growing evidence indicates that PRS has adverse effects on adult hippocampal neurogenesis and DNA epigenetic modifications of the GABAergic system. The aim of this study was to investigate whether epigenetic GABAergic dysfunction participates in the negative impact of PRS on adult hippocampal neurogenesis and related emotional behaviors.

METHODS

Behavioral tests were used to explore PRS-induced depression-like behaviors of adult female mice. Immunohistochemistry staining, real-time reverse transcription-polymerase chain reaction, western blot, and chromatin immunoprecipitation were employed to detect adult neurogenesis and epigenetic changes of the GABAergic system in the hippocampus of PRS mice.

RESULTS

PRS mice developed a depression phenotype accompanied by the inhibited maturation of hippocampal newborn neurons. Compared with control mice, PRS mice showed decreased expression of glutamic acid decarboxylase 67 at the mRNA and protein levels. GABAA receptor agonist phenobarbital could rectify the decrease of 5-bromo-2-deoxyuridine/neuronal nuclei double-positive (BrdU+/NeuN+) cells in PRS mice. PRS mice also showed increased expression of DNA methyltransferase 1 and increased binding of DNA methyltransferase 1 to glutamic acid decarboxylase 67 promoter region. The treatment with DNA methyltransferase 1 inhibitor 5-aza-deoxycytidine restored the decrease of BrdU+/NeuN+ cells and depression-like behaviors in PRS mice via improving GABAergic system.

CONCLUSIONS

The present results indicate that epigenetic changes of the GABAergic system are responsible for adult hippocampus neurogenesis and depression-like behaviors in PRS mice.

Stereotypic Behavior in Sows Is Related to Emotionality Changes in the Offspring

Some effects of expressing stereotypic behavior have not yet been elucidated. During gestation, the environment has the potential to interfere with offspring development and to have prenatal or longer-term consequences. We tested the hypothesis that the occurrence of stereotypic behavior during gestation could affect the phenotype of the offspring. Twenty-eight pregnant sows were studied by comparing two groups differing in the amount of stereotypy shown. We analyzed emotionality in the offspring from sows showing high or low stereotypy frequency using the open field and novel object tests. In the open field test, piglets from sows with a high rate of stereotypies walked more in central sectors (p < 0.0001) and lateral sectors (p = 0.04) than piglets from sows with a low rate of stereotypies. In the novel object test, the offspring from low stereotypy sows vocalized more (p = 0.008). We demonstrate for the first time that the stereotypic behavior by the mother during gestation changes the phenotype of the offspring, in particular, their emotionality.

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.

Ancestral stress programs sex-specific biological aging trajectories and non-communicable disease risk

The incidence of non-communicable diseases (NCDs) is rising globally but their causes are generally not understood. Here we show that cumulative ancestral stress leads to premature aging and raises NCD risk in a rat population. This longitudinal study revealed that cumulative multigenerational prenatal stress (MPS) across four generations (F0-F3) raises age- and sex-dependent adverse health outcomes in F4 offspring. MPS accelerated biological aging processes and exacerbated sex-specific incidences of respiratory and kidney diseases, inflammatory processes and tumors. Unbiased deep sequencing of frontal cortex revealed that MPS altered expression of microRNAs and their target genes involved in synaptic plasticity, stress regulation, immune function and longevity. Multi-layer top-down deep learning metabolite enrichment analysis of urine markers revealed altered metabolic homeodynamics in MPS males. Thus, peripheral metabolic signatures may provide sensitive biomarkers of stress vulnerability and disease risk. Programming by MPS appears to be a significant determinant of lifetime mental health trajectories, physical wellbeing and vulnerability to NCDs through altered epigenetic regulation.

Hypothalamic-pituitary-adrenal axis and stress

Stress is associated with the onset of several stress-related mental disorders that occur more frequently in women than in men, such as major depression or posttraumatic stress disorder (PTSD). The hypothalamic-pituitary-adrenal (HPA) axis is the major component of the neuroendocrine network responding to internal and external challenges. The proper functioning of the HPA axis is critical for the maintenance of mental and physical health, as dysregulations of the HPA axis have been linked to several mental and physical disorders. Numerous studies have observed distinct sex differences in the regulation of the HPA axis in response to stress, and it is supposed that these differences may partially explain the female predominance in stress-related mental disorders. Preclinical models have clearly shown that the HPA axis in females is activated more rapidly and produces a larger output of stress hormones than in males. However, studies with humans often produced inconsistent findings, which might be traced back to the variation of investigated stressors, the use of contraceptives in some of the studies, and different menstrual cycle stages of the female subjects. This article discusses rodent and human literature of sex differences in the function of the HPA axis.

Prenatal immobilization stress and postnatal maternal separation cause differential neuroendocrine responses to fasting stress in adult male rats

Prenatal immobilization stress (PNS) and postnatal maternal separation (MS180) are two widely used rodent models of early-life stress (ELS) that affect the hypothalamus-pituitary-adrenal (HPA) axis, cause behavioral alterations, and affect glucose tolerance in adults. We compared anxiety-like behavior, coping strategies, and HPA axis activity in PNS and MS180 adult (4-month-old) male rats and assessed their glucose tolerance and HPA axis response after mild fasting stress. Both PNS and MS180 induced a passive coping strategy in the forced swimming test, without affecting anxiety-like behavior in the elevated plus-maze. Moreover, both PNS and MS180 increased the hypothalamic corticotropin-releasing hormone expression; however, only MS180 increased the circulating corticosterone levels. Both early life stressors increased fasting glucose levels and this effect was significantly higher in PNS rats. MS180 rats showed impaired glucose tolerance 120 min after intravenous glucose administration, whereas PNS rats displayed an efficient homeostatic response. Moreover, MS180 rats showed higher circulating corticosteroid levels in response to fasting stress (overnight fasting, 12 hr), which were restored after glucose administration. In conclusion, early exposure to postnatal MS180, unlike PNS, increases the HPA axis response to moderate fasting stress, indicating a differential perception of fasting as a stressor in these two ELS models.

Sham-Chewing in Sows Is Associated With Decreased Fear Responses in Their Offspring

We hypothesized that sham-chewing expressed by the dam during gestation affects fetus programming. The goal of this study was to assess the effects of maternal sham-chewing on offspring welfare indicators, such as behavior and physiology. Sows that exhibited consistent sham-chewing on at least two of 6 days of observation (N = 7) were compared with sows that had never performed sham-chewing (non-sham-chewing sows; N = 4) during these 6 days. Salivary samples from sows and piglets were collected and cortisol concentrations were analyzed to assess the hypothalamic pituitary adrenal (HPA) axis activity as cortisol is a physiological indicator of welfare. Moreover, placental tissue was collected, right after farrowing, to assess cortisol and cortisone concentration. Piglet behavior and fear tests were performed after weaning (one couple per sow). In the fear tests, data was collected in an open field test to determine the states of fear indicators. Non-sham-chewing sows had lower concentrations of cortisol on days 91 and 92 of gestation in the morning. In addition to this, placental cortisol was higher among sham-chewing sows than non-sham-chewing sows. In the open field test, piglets born from non-sham-chewing sows demonstrated more latency to move in the arena and less activity, indicating more fear. Based on our data, we concluded that the expression of maternal sham-chewing is related to less fear in their offspring. Although stereotypies have been studied, attention has not been devoted to the effects of the prenatal period in considering a fetal reprogramming approach.

Correlates of maternal glucocorticoid levels in a socially flexible rodent

While it is generally accepted that social isolation has detrimental effects on social species, little is known about the importance of social interactions in less social species-particularly for wild reproductive females. We studied socially-flexible yellow-bellied marmots (Marmota flaviventer) and asked whether features of the social environment are associated with maternal fecal glucocorticoid metabolite (FGM) concentrations. Since changes in maternal baseline glucocorticoids may have positive or negative consequences for offspring fitness, we were also interested in estimating their relationship with measures of reproductive success. We fitted generalized linear mixed effects models to a dataset including maternal FGM measurements, social network metrics, maternal/alloparental care, and pup FGM and survival. Agonistic interactions were positively associated with maternal FGM levels, while mothers that engaged in relatively more affiliative interactions had reduced FGM levels when living in environments with low predator pressure. Pups associated with mothers exhibiting high FGM levels had low annual survival rates, received less maternal/alloparental care and had higher FGM levels. Interestingly, offspring from mothers with high FGM levels were more likely to survive the summer when born in small litters. In sum, social interactions likely influence and are influenced by glucocorticoid levels of facultatively social females. Potential benefits of social bonds may be context-specific, and agonistic interactions may be tightly correlated with fitness. Female marmots exhibiting high FGM levels had overall low reproductive success, which is predicted by the cort-fitness hypothesis. However, under adverse conditions, offspring summer survival can be maximized if pups are born in small litters.

Female pups receive more maltreatment from stressed dams

The effects of exposure to developmental stress often diverge for males and females. Using the scarcity-adversity model of low nesting resources outside the home cage, our lab has discovered sex differences in both behavioral and epigenetic consequences of repeated exposure to caregiver maltreatment. For the measures we have performed to date, we have found more consequences for females. The reasons underlying this sex disparity are unknown. In the current experiment, we aimed to discern the quality of maternal care received by male and female pups in our model. As we have previously found more behavioral and epigenetic consequences in females, we hypothesized that females receive more adverse care compared to their male littermates. Our hypothesis was supported; in our maltreatment condition, we found that female pups received more adverse care than males. This sex difference in adverse care was not present in our two control conditions (cross-foster and normal maternal care). These data lend support to the notion that one reason females in our model incur more behavioral and epigenetic consequences is a result of greater mistreatment by the dam.

Glucocorticoid-induced leucine zipper "quantifies" stressors and increases male susceptibility to PTSD

Post-traumatic stress disorder (PTSD) selectively develops in some individuals exposed to a traumatic event. Genetic and epigenetic changes in glucocorticoid pathway sensitivity may be essential for understanding individual susceptibility to PTSD. This study focuses on PTSD markers in the glucocorticoid pathway, spotlighting glucocorticoid-induced leucine zipper (GILZ), a transcription factor encoded by the gene Tsc22d3 on the X chromosome. We propose that GILZ uniquely "quantifies" exposure to stressors experienced from late gestation to adulthood and that low levels of GILZ predispose individuals to PTSD in males only. GILZ mRNA and methylation were measured in 396 male and female human blood samples from the Grady Trauma Project cohort (exposed to multiple traumatic events). In mice, changes in glucocorticoid pathway genes were assessed following exposure to stressors at distinct time points: (i) CRF-induced prenatal stress (_CRF-inducedPNS) with, or without, additional exposure to (ii) PTSD induction protocol in adulthood, which induces PTSD-like behaviors in a subset of mice. In humans, the number of traumatic events correlated negatively with GILZ mRNA levels and positively with % methylation of GILZ in males only. In male mice, we observed a threefold increase in the number of offspring exhibiting PTSD-like behaviors in those exposed to both _CRF-inducedPNS and PTSD induction. This susceptibility was associated with reduced GILZ mRNA levels and epigenetic changes, not found in females. Furthermore, virus-mediated shRNA knockdown of amygdalar GILZ increased susceptibility to PTSD. Mouse and human data confirm that dramatic alterations in GILZ occur in those exposed to a stressor in early life, adulthood or both. Therefore, GILZ levels may help identify at-risk populations for PTSD prior to additional traumatic exposures.

Fetal and Infant Outcomes in the Offspring of Parents With Perinatal Mental Disorders: Earliest Influences

Mental illness is highly prevalent and runs in families. Mental disorders are considered to enhance the risk for the development of psychopathology in the offspring. This heightened risk is related to the separate and joint effects of inherited genetic vulnerabilities for psychopathology and environmental influences. The early years of life are suggested to be a key developmental phase in the intergenerational psychopathology transmission. Available evidence supports the idea that early exposure to parental psychopathology, during the pregnancy and first postpartum year, may be related to child psychological functioning beyond the postpartum period, up to adulthood years. This not only highlights the importance of intervening early to break the chain of intergenerational transmission of psychopathology but also raises the question of whether early interventions targeting parental mental disorders in this period may alleviate these prolonged adverse effects in the infant offspring. The current article focuses on the specific risk of psychopathology conveyed from mentally ill parents to the offspring during the pregnancy and first postpartum year. We first present a summary of the available evidence on the associations of parental perinatal mental illness with infant psychological outcomes at the behavioral, biological, and neurophysiological levels. Next, we address the effects of early interventions and discuss whether these may mitigate the early intergenerational transmission of risk for psychopathology. The summarized evidence supports the idea that psychopathology-related changes in parents' behavior and physiology in the perinatal period are related to behavioral, biological, and neurophysiological correlates of infant psychological functioning in this period. These alterations may constitute risk for later development of child and/or adult forms of psychopathology and thus for intergenerational transmission. Targeting psychopathology or mother-infant interactions in isolation in the postnatal period may not be sufficient to improve outcomes, whereas interventions targeting both maternal psychopathology and mother-infant interactions seem promising in alleviating the risk of early transmission.