Effects of Early-Life Stress on Social and Anxiety-Like Behaviors in Adult Mice: Sex-Specific Effects

Activation of somatostatin neurons in the medial amygdala reverses long-term aggression and social deficits associated to early-life stress in male mice

Early postnatal development is a critical period for the configuration of neural networks that support social and affective-like behaviors. In this sense, children raised in stressful environments are at high risk to develop maladaptive behaviors immediately or later in life, including anti-social and aggressive behaviors. However, the neurobiological bases of such phenomena remain poorly understood. Here we showed that, at long-term, maternal separation with early weaning (MSEW) decreased the density of somatostatin-expressing (SST+) neurons in the basolateral amygdala (BLA) of females and males, while their activity was only reduced in the medial amygdala (MeA) of males. Interestingly, only MSEW males exhibited long-term behavioral effects, including reduced sociability and social novelty preference in the 3-chamber test (3CH), decreased social interest in the resident-intruder test (RI), and increased aggressivity in both the RI and the tube dominance test (TT). To test whether the manipulation of MeASST+ neurons was sufficient to reverse these negative behavioral outcomes, we expressed the chemogenetic excitatory receptor hM3Dq in MSEW adult males. We found that the activation of MeASST+ neurons ameliorated social interest in the RI test and reduced aggression traits in the TT and RI assays. Altogether, our results highlight a role for MeASST+ neurons in the regulation of aggressivity and social interest and point to the loss of activity of these neurons as a plausible etiological mechanism linking early life stress to these maladaptive behaviors in later life.

Unraveling sex differences in maternal and paternal care impacts on social behaviors and neurobiological responses to early-life adversity

Early-life stress (ELS) affects the development of prosocial behaviors and social-cognitive function, often leading to structural brain changes and increased psychosocial disorders. Recent studies suggest that mother- and father-child relationships independently influence social development in a sex-specific manner, but the effects of impaired father-child relationships are often overlooked. This review examines preclinical rodent studies to explore how parental neglect impacts neuroplasticity and social behaviors in offspring. We highlight that disruptions in maternal interactions may affect male pups more in uniparental rodents, while impaired paternal interactions in biparental rodents tend to impact female pups more. Due to limited research, the separate effects of maternal and paternal neglect on brain development and social behaviors in biparental species remain unclear. Addressing these gaps could clarify the sex-specific mechanisms underlying social and neurobiological deficits following parental neglect.

Sex-specific changes in voluntary alcohol consumption and nucleus accumbens synaptic plasticity in C57BL/6J mice exposed to neonatal maternal separation

The long-term influence of early-life stress on brain neurophysiology has been extensively investigated using different animal models. Among these, repeated maternal separation (RMS) in rodents is one of the most commonly adopted. In this study, we elucidated the long-lasting effects of exposure to postnatal RMS in C57BL/6J adult mice on voluntary alcohol consumption and nucleus accumbens (NAc) neurophysiology. Mice were separated from their dam for 360 min daily from postnatal day 2 (PND2) to PND17, and experiments were then performed in adult (PND60) animals. In addition, as recent evidence showed that circulating estrogens may play a protective role against stress effects on brain function, including the organization and activation of neuronal structures, we also evaluated the effect of a single injection of β-estradiol 3-benzoate (EB) at PND2, which is known to disrupt male sex differentiation, in male RMS mice. The RMS exposure was associated with an increased voluntary alcohol consumption and preference in male mice, but not in female mice or male mice treated with a single injection of EB. Patch clamp experiments conducted in NAc medium spiny neurons (MSNs) revealed that excitatory but not inhibitory synaptic transmission and long-term plasticity of glutamatergic synapses were significantly impaired in male but not in female mice exposed to the RMS protocol. This effect was again prevented in RMS male mice treated with EB. Our findings strengthen the idea of a sex-dependent influence of early-life stress on long-lasting modifications in synaptic transmission and plasticity in brain areas involved in goal-directed behavior and alcohol intake.

Early life stress induces decreased expression of CB1R and FAAH and epigenetic changes in the medial prefrontal cortex of male rats

Several studies in both animal models and in humans have provided substantial evidence that early life stress (ELS) induces long-term changes in behavior and brain function, making it a significant risk factor in the aetiology of various mental disorders, including anxiety and depression. In this study, we tested the hypothesis that ELS in male rats (i) leads to increased anxiety and depressive-like symptoms; and (ii) that these behavioral changes are associated with functional alterations in the endocannabinoid system of the medial prefrontal cortex (mPFC). We further assessed whether the predicted changes in the gene expression of two key components of the endocannabinoid system, cannabinoid receptor 1 (CB1R) and the fatty acid amide hydrolase (FAAH), are regulated by epigenetic mechanisms. Behavioral profiling revealed that the proportion of behaviorally affected animals was increased in ELS exposed male rats compared to control animals, specifically showing symptoms of anhedonia and impaired social behavior. On the molecular level we observed a decrease in CB1R and FAAH mRNA expression in the mPFC of adult ELS exposed animals. These gene expression changes were accompanied by reduced global histone 3 acetylation in the mPFC, while no significant changes in DNA methylation and no significant changes of histone-acetylation at the promoter regions of the analyzed genes were detected. Taken together, our data provide evidence that ELS induces a long-term reduction of CB1R and FAAH expression in the mPFC of adult male rats, which may partially contribute to the ELS-induced changes in adult socio-emotional behavior.

The impact of estrous cycle on anxiety-like behaviour during unlearned fear tests in female rats and mice: A systematic review and meta-analysis

Anxiety fluctuates across the human menstrual cycle, with symptoms worsening during phases of declining or low ovarian hormones. Similar findings have been observed across the rodent estrous cycle, however, the magnitude and robustness of these effects have not been meta-analytically quantified. We conducted a systematic review and meta-analysis of estrous cycle effects on anxiety-like behaviour (124 articles; k = 259 effect sizes). In both rats and mice, anxiety-like behaviour was higher during metestrus/diestrus (lower ovarian hormones) than proestrus (higher ovarian hormones) (g = 0.44 in rats, g = 0.43 in mice). There was large heterogeneity in the data, which was partially accounted for by strain, experimental task, and reproductive status. Nonetheless, the effect of estrous cycle on anxiety-like behaviour was highly robust, with the fail-safe N test revealing the effect would remain significant even if 21,388 additional studies yielded null results. These results suggest that estrous cycle should be accounted for in studies of anxiety in females. Doing so will facilitate knowledge about menstrual-cycle regulation of anxiety disorders in humans.

Understanding the role of early life stress and schizophrenia on anxiety and depressive like outcomes: An experimental study

BACKGROUND

Adverse experiences due to early life stress (ELS) or parental psychopathology such as schizophrenia (SZ) have a significant implication on individual susceptibility to psychiatric disorders in the future. However, it is not fully understood how ELS affects social-associated behaviors as well as the developing prefrontal cortex (PFC).

OBJECTIVE

The aim of this study was to investigate the impact of ELS and ketamine induced schizophrenia like symptoms (KSZ) on anhedonia, social behavior and anxiety-like behavior.

METHODS

Male and female Sprague-Dawley rat pups were allocated randomly into eight experimental groups, namely control, gestational stress (GS), GS+KSZ, maternal separation (MS), MS+KSZ pups, KSZ parents, KSZ parents and Pups and KSZ pups only. ELS was induced by subjecting the pups to GS and MS, while schizophrenia like symptoms was induced through subcutaneous administration of ketamine. Behavioral assessment included sucrose preference test (SPT) and elevated plus maze (EPM), followed by dopamine testing and analysis of astrocyte density. Statistical analysis involved ANOVA and post hoc Tukey tests, revealing significant group differences and yielding insights into behavioral and neurodevelopmental impacts.

RESULTS

GS, MS, and KSZ (dams) significantly reduced hedonic response and increased anxiety-like responses (p < 0.05). Notably, the presence of normal parental mental health demonstrated a reversal of the observed decline in Glial Fibrillary Acidic Protein-positive astrocytes (GFAP+ astrocytes) (p < 0.05) and a reduction in anxiety levels, implying its potential protective influence on depressive-like symptoms and PFC astrocyte functionality.

CONCLUSION

The present study provides empirical evidence supporting the hypothesis that exposure to ELS and KSZ on dams have a significant impact on the on development of anxiety and depressive like symptoms in Sprague Dawley rats, while positive parenting has a reversal effect.

Ventral tegmental area glutamate neurons mediate nonassociative consequences of stress

Exposure to trauma is a risk factor for the development of a number of mood disorders, and may enhance vulnerability to future adverse life events. Recent data demonstrate that ventral tegmental area (VTA) neurons expressing the vesicular glutamate transporter 2 (VGluT2) signal and causally contribute to behaviors that involve aversive or threatening stimuli. However, it is unknown whether VTA VGluT2 neurons regulate transsituational outcomes of stress and whether these neurons are sensitive to stressor controllability. This work adapted an operant mouse paradigm to examine the impact of stressor controllability on VTA VGluT2 neuron function as well as the role of VTA VGluT2 neurons in mediating transsituational stressor outcomes. Uncontrollable (inescapable) stress, but not physically identical controllable (escapable) stress, produced social avoidance and exaggerated fear in male mice. Uncontrollable stress in females led to exploratory avoidance of a novel brightly lit environment. Both controllable and uncontrollable stressors increased VTA VGluT2 neuronal activity, and chemogenetic silencing of VTA VGluT2 neurons prevented the behavioral sequelae of uncontrollable stress in male and female mice. Further, we show that stress activates multiple genetically-distinct subtypes of VTA VGluT2 neurons, especially those that are VGluT2+VGaT+, as well as lateral habenula neurons receiving synaptic input from VTA VGluT2 neurons. Our results provide causal evidence that mice can be used for identifying stressor controllability circuitry and that VTA VGluT2 neurons contribute to transsituational stressor outcomes, such as social avoidance, exaggerated fear, or anxiety-like behavior that are observed within trauma-related disorders.

Early life adversity reduces affiliative behavior with a stressed cagemate and leads to sex-specific alterations in corticosterone responses in adult mice

Experiencing early life adversity (ELA) alters stress physiology and increases the risk for developing psychiatric disorders. The social environment can influence dynamics of stress responding and buffer and/or transfer stress across individuals. Yet, the impact of ELA on sensitivity to the stress of others and social behavior following stress is unknown. Here, to test the impact of ELA on social and physiological responses to stress, circulating blood corticosterone (CORT) and social behaviors were assessed in adult male and female mice reared under limited bedding and nesting (LBN) or control conditions. To induce stress, one cagemate of a pair-housed cage underwent a footshock paradigm and was then returned to their unshocked partner. CORT was measured in both groups of mice 20 or 90 min after stress exposure, and social behaviors were recorded and analyzed. ELA rearing influenced the CORT response to stress in a sex-specific manner. In males, both control and ELA-reared mice exhibited similar stress transfer to unshocked cagemates and similar CORT dynamics. In contrast, ELA females showed a heightened stress transfer to unshocked cagemates, and sustained elevation of CORT relative to controls, indicating enhanced stress contagion and a failure to terminate the stress response. Behaviorally, ELA females displayed decreased allogrooming and increased investigative behaviors, while ELA males showed reduced huddling. Together, these findings demonstrate that ELA influenced HPA axis dynamics, social stress contagion and social behavior. Further research is needed to unravel the underlying mechanisms and long-term consequences of ELA on stress systems and their impact on behavioral outcomes.

Dietary Marine Hydrolysate Improves Memory Performance and Social Behavior through Gut Microbiota Remodeling during Aging

Aging is characterized by a decline in social behavior and cognitive functions leading to a decrease in life quality. In a previous study, we show that a fish hydrolysate supplementation prevents age-related decline in spatial short-term memory and long-term memory and anxiety-like behavior and improves the stress response in aged mice. The aim of this study was to determine the effects of a fish hydrolysate enriched with EPA/DHA or not on the cognitive ability and social interaction during aging and the biological mechanisms involved. We showed for the first time that a fish hydrolysate enriched with EPA/DHA or not improved memory performance and preference for social novelty that were diminished by aging. These changes were associated with the modulation of the gut microbiota, normalization of corticosterone, and modulation of the expression of genes involved in the mitochondrial respiratory chain, circadian clock, neuroprotection, and antioxidant activity. Thus, these changes may contribute to the observed improvements in social behavior and memory and reinforced the innovative character of fish hydrolysate in the prevention of age-related impairments.

Early life adversity has sex-dependent effects on survival across the lifespan in rhesus macaques

Exposure to adversity during early life is linked to lasting detrimental effects on evolutionary fitness across many taxa. However, due to the challenges of collecting longitudinal data, especially in species where one sex disperses, direct evidence from long-lived species remains relatively scarce. Here we test the effects of early life adversity on male and female longevity in a free-ranging population of rhesus macaques (Macaca mulatta) at Cayo Santiago, Puerto Rico. We leveraged six decades of data to quantify the relative importance of ten forms of early life adversity for 6,599 macaques (3,230 male, 3,369 female), with a smaller sample size (N=299) for one form of adversity (maternal social isolation) which required high-resolution behavioral data. We found that individuals who experienced more early life adversity died earlier than those who experienced less adversity. Mortality risk was highest during early life, defined as birth to four years old, suggesting acute survival effects of adversity, but heightened mortality risk was also present in macaques who survived to adulthood. Females and males were affected differently by some forms of adversity, and these differences might be driven by varying energetic demands, female philopatry, and male dispersal. By leveraging data on thousands of macaques collected over decades, our results show that the fitness consequences of early life adversity are not uniform across individuals but vary as a function of the type of adversity, timing, and social context, and thus contribute to our limited but growing understanding of the evolution of early life sensitivities in long-lived species.

Effect of apparatus characteristics on anxiety-like behavior in young adult and old mice of both sexes assessed by the elevated plus maze assay

Incidence of anxiety-like disorders in humans has been shown to decrease with aging; however, it is still under debate whether there are similarities in mice, which would support the use of mouse models in understanding the neuronal network changes that regulate anxiety-like behavior in aging. One of the most common tests used to assess anxiety-like behavior in laboratory animals is the elevated plus maze (EPM). Although several variables, such as room brightness and width of the maze arms, have been shown to influence the spontaneous animal behavior during the EPM test, none of these variables have ever been evaluated in aging to understand their possible differential effect on younger and older mice. We therefore decided to investigate the effect of apparatus construction on young adult and old mice of both sexes on EPM test performance. Our results show that distance traveled during the test is the variable that is most affected by apparatus characteristics independent of age and sex. We also found that apparatus construction was key in demonstrating that old mice spent more time and had relatively more entries in the open arms as compared to young mice, suggesting a decrease in anxiety-like behavior with age. Taken together, our data demonstrate that EPM apparatus characteristics dramatically affect test outcome with a wider arm apparatus being more effective in revealing age-dependent changes in anxiety-like behavior, thus, suggesting the use of a wider arm EPM when conducting aging studies in mice.

Impacts of maternal separation stress on ethanol-related responses, anxiety- and depressive-like behaviors in adolescent mice

The present work evaluated the consequences of chronic maternal separation (MS), an animal model of early-life stress, on ethanol intake and striatal Fos expression induced by ethanol consumption. Furthermore, we analyzed MS impacts on anxiety- and depressive-like behaviors and on locomotor and plasma corticosterone responses to intraperitoneal treatment with ethanol in adolescent mice. For that, male and female C57BL/6J mice were exposed or not to MS stress, for 3 h per day, from postnatal day (PND) 1 to 14, and submitted to behavioral tests from PND 28. In Experiment 1, MS and control groups of mice were submitted to an involuntary ethanol intake protocol, and striatal Fos expression following ethanol exposure was analyzed. In Experiment 2, mice behavior was assessed in elevated plus-maze, sucrose splash, saccharin preference, and open field tests. Locomotor and plasma corticosterone responses induced by a systemic dose of ethanol (1.75 g/kg) were also evaluated. Our results demonstrated that MS increased ethanol intake only in an acute manner and did not impact ethanol-induced Fos expression in the dorsal striatum and nucleus accumbens (NAc) core and shell subregions. MS did not change the parameters analyzed during elevated plus-maze, sucrose splash, preference for saccharin, and open field tests. MS did not affect locomotor activity following ethanol injection nor plasma corticosterone response to the drug. Thus, our data showed that MS transiently increased ethanol intake. However, early-life stress did not impact Fos, locomotor, or plasma corticosterone responses to the drug. In addition, MS did not affect anxiety- and depressive-like behaviors in adolescent mice.

Molecular and long-term behavioral consequences of neonatal opioid exposure and withdrawal in mice

Introduction

Infants exposed to opioids in utero are at high risk of exhibiting Neonatal Opioid Withdrawal Syndrome (NOWS), a combination of somatic withdrawal symptoms including high pitched crying, sleeplessness, irritability, gastrointestinal distress, and in the worst cases, seizures. The heterogeneity of in utero opioid exposure, particularly exposure to polypharmacy, makes it difficult to investigate the underlying molecular mechanisms that could inform early diagnosis and treatment of NOWS, and challenging to investigate consequences later in life.

Methods

To address these issues, we developed a mouse model of NOWS that includes gestational and post-natal morphine exposure that encompasses the developmental equivalent of all three human trimesters and assessed both behavior and transcriptome alterations.

Results

Opioid exposure throughout all three human equivalent trimesters delayed developmental milestones and produced acute withdrawal phenotypes in mice reminiscent of those observed in infants. We also uncovered different patterns of gene expression depending on the duration and timing of opioid exposure (3-trimesters, in utero only, or the last trimester equivalent only). Opioid exposure and subsequent withdrawal affected social behavior and sleep in adulthood in a sex-dependent manner but did not affect adult behaviors related to anxiety, depression, or opioid response.

Discussion

Despite marked withdrawal and delays in development, long-term deficits in behaviors typically associated with substance use disorders were modest. Remarkably, transcriptomic analysis revealed an enrichment for genes with altered expression in published datasets for Autism Spectrum Disorders, which correlate well with the deficits in social affiliation seen in our model. The number of differentially expressed genes between the NOWS and saline groups varied markedly based on exposure protocol and sex, but common pathways included synapse development, the GABAergic and myelin systems, and mitochondrial function.

Age, β-endorphin, and sex dependent effects of maternal separation on locomotor activity, anxiety-like behavior, and alcohol reward

Introduction

Childhood adversity is pervasive and linked to numerous disadvantages in adulthood, including physical health problems, mental illness, and substance use disorders. Initial sensitivity to the rewarding effects of alcohol predicts the risk of developing an alcohol use disorder, and may be linked to developmental stress. The opioid peptide β-endorphin (β-E) regulates the stress response and is also implicated in the risk for excessive alcohol consumption.

Methods

We explored the influence of β-E in an animal model of early life adversity using controlled maternal separation by evaluating changes in locomotor activity, anxiety-like behavior, and the initial rewarding effects of alcohol in a single exposure conditioned place preference paradigm in control C57BL/6J and β-E deficient β-E +/+ 0.129S2-Pomc tm1Low/J; β-E −/− mice. Maternal separation (MS) occurred for 3 h each day from post-natal days (PND) 5–18 in approximately half the subjects.

Results

Maternal interactions increased following the separation protocol equally in both genotypes. MS and control subjects were tested as adolescents (PND 26–32) or adults (PND 58–72); the effects of MS were generally more pronounced in older subjects. Adults were more active than adolescents in the open field, and MS decreased activity in adolescent mice but increased it in adults. The increase in adult activity as a result of early life stress depended on both β-E and sex. β-E also influenced the effect of maternal separation on anxiety-like behavior in the Elevated Plus Maze. MS promoted rewarding effects of alcohol in male β-E deficient mice of either age, but had no effect in other groups.

Discussion

Taken together, these results suggest that the effects of MS develop over time and are β-E and sex dependent and may aid understanding of how individual differences influence the impact of adverse childhood experiences.

Early life adversity impaired dorsal striatal synaptic transmission and behavioral adaptability to appropriate action selection in a sex-dependent manner

Early life adversity (ELA) is a major health burden in the United States, with 62% of adults reporting at least one adverse childhood experience. These experiences during critical stages of brain development can perturb the development of neural circuits that mediate sensory cue processing and behavioral regulation. Recent studies have reported that ELA impaired the maturation of dendritic spines on neurons in the dorsolateral striatum (DLS) but not in the dorsomedial striatum (DMS). The DMS and DLS are part of two distinct corticostriatal circuits that have been extensively implicated in behavioral flexibility by regulating and integrating action selection with the reward value of those actions. To date, no studies have investigated the multifaceted effects of ELA on aspects of behavioral flexibility that require alternating between different action selection strategies or higher-order cognitive processes, and the underlying synaptic transmission in corticostriatal circuitries. To address this, we employed whole-cell patch-clamp electrophysiology to assess the effects of ELA on synaptic transmission in the DMS and DLS. We also investigated the effects of ELA on the ability to update action control in response to outcome devaluation in an instrumental learning paradigm and reversal of action-outcome contingency in a water T-maze paradigm. At the circuit level, ELA decreased corticostriatal glutamate transmission in male but not in female mice. Interestingly, in DMS, glutamate transmission is decreased in male ELA mice, but increased in female ELA mice. ELA impaired the ability to update action control in response to reward devaluation in a context that promotes goal-directedness in male mice and induced deficits in reversal learning. Overall, our findings demonstrate the sex- and region-dependent effects of ELA on behavioral flexibility and underlying corticostriatal glutamate transmission. By establishing a link between ELA and circuit mechanisms underlying behavioral flexibility, our findings will begin to identify novel molecular mechanisms that can represent strategies for treating behavioral inflexibility in individuals who experienced early life traumatic incidents.

Oxytocin treatments or activation of the paraventricular nucleus-the shell of nucleus accumbens pathway reduce adverse effects of chronic social defeat stress on emotional and social behaviors in Mandarin voles

Chronic social stress can cause psychological disease. Although oxytocin (OT) has been showed to modulate effects of chronic social defeat stress (CSDS) on emotional and social behaviors, however, how OT circuits mediate effects of CSDS on emotional and social abnormalities remains unclear. Here, we found that repeated intraperitoneal OT administration in the process of CSDS buffered adverse effects of CSDS on emotional and social behaviors in mandarin voles (Microtus mandarinus) of both sexes except no effect on depression-like behavior of males. Repeated OT treatments during CSDS prevented decrease of oxytocin receptors in nucleus accumbens (NAc) in females, but produced no effects on males. Furthermore, using designer receptors exclusively activated by designer drugs (DREADDs)-based chemogenetic tools, we determined that the activation of the paraventricular nucleus (PVN)-the shell of NAc (NAcs) projections before social defeat during CSDS process significantly prevented the increase of the anxiety-like behaviors and social avoidance induced by CSDS in both sexes, and reversed the depressive-like behaviors induced by CSDS only in females. Besides, optogenetic activation of PVN-NAcs projections after CSDS reduced anxiety-like behaviors and increased levels of sociality. Collectively, we suggest that PVN-NAcs projections modulate emotional and social behaviors during or after the process of CSDS sex-specifically, although AAV viruses did not specifically infect OT neurons. These findings offer potential targets for preventing or treating emotional and social disorders induced by chronic stress.

Lasting impact of postnatal maternal separation on the developing BNST: Lifelong socioemotional consequences

Nearly one percent of children in the US experience childhood neglect or abuse, which can incite lifelong emotional and behavioral disorders. Many studies investigating the neural underpinnings of maleffects inflicted by early life stress have largely focused on dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. Newer veins of evidence suggest that exposure to early life stressors can interrupt neural development in extrahypothalamic areas as well, including the bed nucleus of the stria terminalis (BNST). One widely used approach in this area is rodent maternal separation (MS), which typically consists of separating pups from the dam for extended periods of time, over several days during the first weeks of postnatal life - a time when pups are highly dependent on maternal care for survival. MS has been shown to incite myriad lasting effects not limited to increased anxiety-like behavior, hyper-responsiveness to stressors, and social behavior deficits. The behavioral effects of MS are widespread and thus unlikely to be limited to hypothalamic mechanisms. Recent work has highlighted the BNST as a critical arbiter of some of the consequences of MS, especially socioemotional behavioral deficits. The BNST is a well-documented modulator of anxiety, reward, and social behavior by way of its connections with hypothalamic and extra-hypothalamic systems. Moreover, during the postnatal period when MS is typically administered, the BNST undergoes critical neural developmental events. This review highlights evidence that MS interferes with neural development to permanently alter BNST circuitry, which may account for a variety of behavioral deficits seen following early life stress. This article is part of the Special Issue on 'Fear, Anxiety and PTSD'.

A comparison of stress reactivity between BTBR and C57BL/6J mice: an impact of early-life stress

Early-life stress (ELS) is associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation and can increase the risk of psychiatric disorders later in life. The aim of this study was to investigate the influence of ELS on baseline HPA axis functioning and on the response to additional stress in adolescent male mice of strains C57BL/6J and BTBR. As a model of ELS, prolonged separation of pups from their mothers (for 3 h once a day: maternal separation [MS]) was implemented. To evaluate HPA axis activity, we assessed serum corticosterone levels and mRNA expression of corticotropin-releasing hormone (Crh) in the hypothalamus, of steroidogenesis genes in adrenal glands, and of an immediate early gene (c-Fos) in both tissues at baseline and immediately after 1 h of restraint stress. HPA axis activity at baseline did not depend on the history of ELS in mice of both strains. After the exposure to the acute restraint stress, C57BL/6J-MS mice showed less pronounced upregulation of Crh and of corticosterone concentration as compared to the control, indicating a decrease in stress reactivity. By contrast, BTBR-MS mice showed stronger upregulation of c-Fos in the hypothalamus and adrenal glands as compared to controls, thus pointing to greater activation of these organs in response to the acute restraint stress. In addition, we noted that BTBR mice are more stress reactive (than C57BL/6J mice) because they exhibited greater upregulation of corticosterone, c-Fos, and Cyp11a1 in response to the acute restraint stress. Taken together, these results indicate strain-specific and situation-dependent effects of ELS on HPA axis functioning and on c-Fos expression.

Preadolescent exposure to a sexually mature, unrelated male rat reduces postadolescent social recognition memory and CA2 c-Fos labeling

Introduction

Social memory involves social recognition: the ability to discriminate between two or more conspecifics when one has been previously encountered. The CA2 region of the hippocampus has been implicated in social memory, as lesions and dysfunction to this area lead to social memory impairments. A variety of psychogenic manipulations during postnatal sensitive developmental periods are associated with social memory impairments later in life.

Methods

In this study, we exposed preadolescent rats to a sexually, mature unrelated male and examined whether this was associated with changes in postadolescent social memory and c-Fos labeling in the CA2 region. Male and female Long-Evans rats were exposed to a male, adult rat on postnatal days 19-21 (P19-21). Social memory was measured during the postadolescent period and defined as increased interactions towards a novel age-matched rat in contrast to a previously-encountered age-matched rat. After the test, rats were euthanized and brain tissue was then collected to quantify c-Fos labeling within the CA2 region.

Results

Compared to home cage controls and controls not exposed to the adult male, male and female rats exposed to the unrelated adult during preadolescence were unable to discriminate between a novel and previously encountered conspecific during the postadolescent test showing social memory deficits. The groups that showed social recognition deficits also had significantly fewer c-Fos-positive cells within the CA2 region compared to the control groups.

Discussion

These findings indicate that threatening psychogenic encounters during preadolescence can have detrimental long-term effects on social memory potentially via disrupted activity in the CA2 hippocampal region.

Sex-dependent changes of hippocampal synaptic plasticity and cognitive performance in C57BL/6J mice exposed to neonatal repeated maternal separation

The repeated maternal separation (RMS) is a useful experimental model useful in rodents to study the long-term influence of early-life stress on brain neurophysiology. We here investigated the influence of RMS exposure on hippocampal inhibitory and excitatory synaptic transmission, long-term synaptic plasticity and the related potential alterations in learning and memory performance in adult male and female C57Bl/6J mice. Mice were separated daily from their dam for 360 min, from postnatal day 2 (PND2) to PND17, and experiments were performed at PND 60. Patch-clamp recordings in hippocampal CA1 pyramidal neurons revealed a significant enhancement of GABAergic miniature IPSC (mIPSC) frequency, and a decrease in the amplitude of glutamatergic mEPSCs in male mice exposed to RMS. Only a slight but significant reduction in the amplitude of GABAergic mIPSCs was observed in females exposed to RMS compared to the relative controls. A marked increase in long-term depression (LTD) at CA3-CA1 glutamatergic synapses and in the response to the CB1r agonist win55,212 were detected in RMS male, but not female mice. An impaired spatial memory and a reduced preference for novelty was observed in males exposed to RMS but not in females. A single injection of β-ethynyl estradiol at PND2, prevented the changes observed in RMS male mice, suggesting that estrogens may play a protective role early in life against the exposure to stressful conditions. Our findings strengthen the idea of a sex-dependent influence of RMS on long-lasting modifications in synaptic transmission, effects that may be relevant for cognitive performance.

Limited bedding nesting paradigm alters maternal behavior and pup's early developmental milestones but did not induce anxiety- or depressive-like behavior in two different inbred mice

Animal models are crucial to understanding the mechanisms underlying the deleterious consequences of early-life stress. Here, we aimed to examine the effect of the limited bedding nesting (LBN) paradigm on early life development milestones and anxiety- and/or depression-like behavior in adolescent and adult mice from two inbred mice of both sexes. C57BL/6NCrl and BALB/c litters were exposed to the LBN paradigm postnatal day (PND) 2-9. Maternal behavior recording occurred on PND 3-9, and pups were weighed daily and examined to verify the eye-opening on PND 10-22. The male and female offspring underwent evaluation in the open field test, elevated plus-maze, and the forced swimming test during adolescence (PND 45-49) and adulthood (PND 75-79). We found that LBN impaired the maternal behavior patterns of both strain dams, mainly on C57BL/6NCrl strain. Also, LBN delayed the pup's eye-opening time and reduced body weight gain, impacting C57BL/6NCrl pups more. We also found that LBN decreased anxiety-related indices in adolescent and adult male but not female mice of both strains. Furthermore, LBN decreased depression-related indices only adolescent female and male BALB/c and female but not male C57BL/6NCrl mice. These findings reinforce the evidence that the LBN paradigm impairs the maternal behavior pattern and pup's early developmental milestones but does not induce anxiety- or depressive-like behavior outcomes during later life.

Sex differences in addiction-relevant behavioral outcomes in rodents following early life stress

In humans, exposure to early life stress (ELS) is an established risk factor for the development of substance use disorders (SUDs) during later life. Similarly, rodents exposed to ELS involving disrupted mother-infant interactions, such as maternal separation (MS) or adverse caregiving due to scarcity-adversity induced by limited bedding and nesting (LBN) conditions, also exhibit long-term alterations in alcohol and drug consumption. In both humans and rodents, there is a range of addiction-related behaviors that are associated with drug use and even predictive of subsequent SUDs. In rodents, these include increased anxiety-like behavior, impulsivity, and novelty-seeking, altered alcohol and drug intake patterns, as well as disrupted reward-related processes involving consummatory and social behaviors. Importantly, the expression of these behaviors often varies throughout the lifespan. Moreover, preclinical studies suggest that sex differences play a role in how exposure to ELS impacts reward and addiction-related phenotypes as well as underlying brain reward circuitry. Here, addiction-relevant behavioral outcomes and mesolimbic dopamine (DA) dysfunction resulting from ELS in the form of MS and LBN are discussed with a focus on age- and sex-dependent effects. Overall, these findings suggest that ELS may increase susceptibility for later life drug use and SUDs by interfering with the normal maturation of reward-related brain and behavioral function.

Enduring effects of early-life adversity on reward processes: A systematic review and meta-analysis of animal studies

Two-thirds of individuals experience adversity during childhood such as neglect, abuse or highly-stressful events. Early-life adversity (ELA) increases the life-long risk of developing mood and substance use disorders. Reward-related deficits has emerged as a key endophenotype of such psychiatric disorders. Animal models are invaluable for studying how ELA leads to reward deficits. However, the existing literature is heterogenous with difficult to reconcile findings. To create an overview, we conducted a systematic review containing multiple meta-analyses regarding the effects of ELA on reward processes overall and on specific aspects of reward processing in animal models. A comprehensive search identified 120 studies. Most studies omitted key details resulting in unclear risk of bias. Overall meta-analysis showed that ELA significantly reduced reward behaviors (SMD: -0.42 [-0.60; -0.24]). The magnitude of ELA effects significantly increased with longer exposure. When reward domains were analyzed separately, ELA only significantly dampened reward responsiveness (SMD: -0.525[-0.786; -0.264]) and social reward processing (SMD: -0.374 [-0.663; -0.084]), suggesting that ELA might lead to deficits in specific reward domains.

Sex-specific behavioral outcomes of early-life adversity and emerging microglia-dependent mechanisms

Early-life adversity (ELA) is known to alter brain circuit maturation as well as increase vulnerability to cognitive and emotional disorders. However, the importance of examining sex as a biological variable when researching the effects of ELA has not been considered until recently. This perspective discusses the sex-specific behavioral outcomes of ELA in both humans and animal models, then proposes microglia-mediated mechanisms as a potential underlying cause. Recent work in rodent models suggests that ELA provokes cognitive deficits, anhedonia, and alcohol abuse primarily in males, whereas females exhibit greater risk-taking and opioid addiction-related behaviors. In addition, emerging evidence identifies microglia as a key target of ELA. For example, we have recently shown that ELA inhibits microglial synapse engulfment and process dynamics in male mice, leading to an increase in excitatory synapse number onto corticotrophin-releasing hormone (CRH)-expressing neurons in the paraventricular nucleus of the hypothalamus (PVN) and aberrant stress responses later in life. However, ELA-induced synaptic rewiring of neural circuits differs in females during development, resulting in divergent behavioral outcomes. Thus, examining the role of microglia in the sex-specific mechanisms underlying ELA-induced neuropsychiatric disorders is an important topic for future research.

Sex-dependence and comorbidities of the early-life adversity induced mental and metabolic disease risks: Where are we at?

Early-life adversity (ELA) is a major risk factor for developing later-life mental and metabolic disorders. However, if and to what extent ELA contributes to the comorbidity and sex-dependent prevalence/presentation of these disorders remains unclear. We here comprehensively review and integrate human and rodent ELA (pre- and postnatal) studies examining mental or metabolic health in both sexes and discuss the role of the placenta and maternal milk, key in transferring maternal effects to the offspring. We conclude that ELA impacts mental and metabolic health with sex-specific presentations that depend on timing of exposure, and that human and rodent studies largely converge in their findings. ELA is more often reported to impact cognitive and externalizing domains in males, internalizing behaviors in both sexes and concerning the metabolic dimension, adiposity in females and insulin sensitivity in males. Thus, ELA seems to be involved in the origin of the comorbidity and sex-specific prevalence/presentation of some of the most common disorders in our society. Therefore, ELA-induced disease states deserve specific preventive and intervention strategies.

Neonatal immune challenge influences the microbiota and behaviour in a sexually dimorphic manner

There is comorbidity between anxiety disorders and gastrointestinal disorders, with both linked to adverse early life events. The microbiome gut-brain-axis, a bidirectional communication system, is plastic throughout the neonatal period and is a possible mediator of this relationship. Here, we used a well-established neonatal rodent immune activation model to investigate the long-term effect of neonatal lipopolysaccharide (LPS) exposure on adult behaviour and the relationship to microbiome composition. Wistar rats were injected with LPS (0.05 mg/kg) or saline (equivolume) on postnatal days 3 and 5. In adulthood, behavioural tests were performed to assess anxiety-like behaviour, and microbiota sequencing was performed on stool samples. There were distinctly different behavioural phenotypes for LPS-exposed males and females. LPS-exposed males displayed typical anxiety-like behaviours with significantly decreased social interaction (F_(1,22) = 7.576, p = 0.009) and increased defecation relative to saline controls (F_(1,23) = 8.623, p = 0.005). LPS-exposed females displayed a different behavioural phenotype with significantly increased social interaction (F_(1,22) = 6.094, p = 0.018), and exploration (F_(1,24) = 6.359, p = 0.015), compared to saline controls. With respect to microbiota profiling data, Bacteroidota was significantly increased for LPS-exposed females (F_(1,14) = 4.931p = 0.035) and Proteobacteria was decreased for LPS-exposed rats of both sexes versus controls (F_(1,30) = 4.923p = 0.035). Furthermore, alterations in predicted functional pathways for neurotransmitters in faeces were observed with a decrease in the relative abundance of D-glutamine and D-glutamate metabolism in LPS exposed females compared to control females (p < 0.05). This suggests that neonatal immune activation alters both later life behaviour and adult gut microbiota in sex-specific ways. These findings highlight the importance of sex in determining the impact of neonatal immune activation on social behaviour and the gut microbiota.

The anxiogenic effects of adolescent psychological stress in male and female mice

Adolescence is a period of transition during which there is extensive development of the brain and the hypothalamic-pituitary-adrenal axis. However, the term adolescence is broad and covers a number of important developmental periods ranging from pre-pubescence to sexual maturity. Using a predator stress model, we investigated the effects of chronic psychological stress on anxiety-like, depression-like, and social behaviours in male and female mice during early adolescence, when mice are pre-pubertal, and late adolescence, when mice are sexually mature. All stressed mice showed hyperactivity and increased anxiety-like behaviours. The anxiogenic effects were generally more pronounced in mice exposed to late, rather than early adolescent stress, but were clearly evident when stress was experienced at either timepoint. Risk assessment behaviours were also affected by the stress treatments, but the direction of these changes were sometimes sex- and age-specific. Surprisingly, mice stressed during adolescence showed no depressive-like behaviours as adults. This study provides evidence that adolescent psychological stress has pronounced long-term anxiogenic effects but that the precise behavioural phenotype differs based on sex and the sub-stage of adolescence during which the individual is exposed.

Neurobiological Links between Stress, Brain Injury, and Disease

Stress, which refers to a combination of physiological, neuroendocrine, behavioral, and emotional responses to novel or threatening stimuli, is essentially a defensive adaptation under physiological conditions. However, strong and long-lasting stress can lead to psychological and pathological damage. Growing evidence suggests that patients suffering from mild and moderate brain injuries and diseases often show severe neurological dysfunction and experience severe and persistent stressful events or environmental stimuli, whether in the acute, subacute, or recovery stage. Previous studies have shown that stress has a remarkable influence on key brain regions and brain diseases. The mechanisms through which stress affects the brain are diverse, including activation of endoplasmic reticulum stress (ERS), apoptosis, oxidative stress, and excitatory/inhibitory neuron imbalance, and may lead to behavioral and cognitive deficits. The impact of stress on brain diseases is complex and involves impediment of recovery, aggravation of cognitive impairment, and neurodegeneration. This review summarizes various stress models and their applications and then discusses the effects and mechanisms of stress on key brain regions—including the hippocampus, hypothalamus, amygdala, and prefrontal cortex—and in brain injuries and diseases—including Alzheimer’s disease, stroke, traumatic brain injury, and epilepsy. Lastly, this review highlights psychological interventions and potential therapeutic targets for patients with brain injuries and diseases who experience severe and persistent stressful events.

Imbalance in Sirt1 Alternative Splicing in Response to Chronic Stress during the Adolescence Period in Female Mice

Stressful unpredictable life events have been implicated in numerous diseases. It is now becoming clear that some life periods are more vulnerable than others. As adolescence is a sensitive period in brain development, the long-term effects of stress during this period could be significant. We investigated the long-term effects of exposure to unpredictable chronic mild stress in adolescent mice on alternative splicing of Sirtuin 1. One-month-old mice were exposed to 4 weeks of UCMS and examined for anxiety and cognition at the age of 2, 4 and 6 months. We found a rise in anxious behavior immediately after the exposure to stress. Notably, there was a long-term impairment of performance in cognitive tasks and an imbalance in Sirtuin 1 and TrkB receptor alternative splicing in the stress-exposed mice compared with controls. To conclude, our results show that exposure to unpredictable chronic mild stress during adolescence affects cognition in adulthood. Understanding pathways affiliated with stress may help minimize the long-term emotional effects of an unpredictable, stressful event.

Effects of early life stress during stress hyporesponsive period (SHRP) on anxiety and curiosity in adolescent rats

Repeated exposure to adverse experiences in early life, termed Early Life Stress (ELS), can increase anxiety disorders later in life. Anxiety is directly associated with curiosity, a form of intrinsic drive state associated with increased novelty-seeking behaviour and risk taking for challenging opportunities and could probably modulate learning and memory. In humans, elevated curiosity during adolescence tends to elicit increased exploration, novelty seeking, high risk-taking behaviour and heightened emotionality. Such behaviours are beneficial in maintaining social skills and cognitive functions later in life. We investigated whether ELS-induced anxiety impacts curiosity-like behaviour at adolescence in an animal model. ELS was induced by subjecting Sprague Dawley rat pups to maternal separation and isolation (MS) stress during the stress hyporesponsive period (SHRP) from post-natal days (PND) 4-PND 14. This rat model was tested for anxiety, spontaneous exploratory behaviour and curiosity-like behaviour in a custom-designed arena during adolescence (PND 30-45). ELS-induced changes in the stress were confirmed by corticosterone, while, basal dopamine level was estimated to understand the neurochemical basis of MS stress-induced changes in curiosity. We observed an increase in the levels of anxiety and intrinsic drive state such as curiosity-like behaviour, which was associated with elevated plasma corticosterone and dopamine in MS animals during adolescence suggesting the impact of ELS during SHRP on adolescent behaviour.

The stressed synapse 2.0: pathophysiological mechanisms in stress-related neuropsychiatric disorders

Stress is a primary risk factor for several neuropsychiatric disorders. Evidence from preclinical models and clinical studies of depression have revealed an array of structural and functional maladaptive changes, whereby adverse environmental factors shape the brain. These changes, observed from the molecular and transcriptional levels through to large-scale brain networks, to the behaviours reveal a complex matrix of interrelated pathophysiological processes that differ between sexes, providing insight into the potential underpinnings of the sex bias of neuropsychiatric disorders. Although many preclinical studies use chronic stress protocols, long-term changes are also induced by acute exposure to traumatic stress, opening a path to identify determinants of resilient versus susceptible responses to both acute and chronic stress. Epigenetic regulation of gene expression has emerged as a key player underlying the persistent impact of stress on the brain. Indeed, histone modification, DNA methylation and microRNAs are closely involved in many aspects of the stress response and reveal the glutamate system as a key player. The success of ketamine has stimulated a whole line of research and development on drugs directly or indirectly targeting glutamate function. However, the challenge of translating the emerging understanding of stress pathophysiology into effective clinical treatments remains a major challenge.

Sex Differences in Affective Dysfunction and Alterations in Parvalbumin in Rodent Models of Early Life Adversity

The early life environment markedly influences brain and behavioral development, with adverse experiences associated with increased risk of anxiety and depressive phenotypes, particularly in females. Indeed, early life adversity (ELA) in humans (i.e., caregiver deprivation, maltreatment) and rodents (i.e., maternal separation, resource scarcity) is associated with sex-specific emergence of anxious and depressive behaviors. Although these disorders show clear sex differences in humans, little attention has been paid toward evaluating sex as a biological variable in models of affective dysfunction; however, recent rodent work suggests sex-specific effects. Two widely used rodent models of ELA approximate caregiver deprivation (i.e., maternal separation) and resource scarcity (i.e., limited bedding). While these approaches model aspects of ELA experienced in humans, they span different portions of the pre-weaning developmental period and may therefore differentially contribute to underlying mechanistic risk. This is borne out in the literature, where evidence suggests differences in trajectories of behavior depending on the type of ELA and/or sex; however, the neural underpinning of these differences is not well understood. Because anxiety and depression are thought to involve dysregulation in the balance of excitatory and inhibitory signaling in ELA-vulnerable brain regions (e.g., prefrontal cortex, amygdala, hippocampus), outcomes are likely driven by alterations in local and/or circuit-specific inhibitory activity. The most abundant GABAergic subtypes in the brain, accounting for approximately 40% of inhibitory neurons, contain the calcium-binding protein Parvalbumin (PV). As PV-expressing neurons have perisomatic and proximal dendritic targets on pyramidal neurons, they are well-positioned to regulate excitatory/inhibitory balance. Recent evidence suggests that PV outcomes following ELA are sex, age, and region-specific and may be influenced by the type and timing of ELA. Here, we suggest the possibility of a combined role of PV and sex hormones driving differences in behavioral outcomes associated with affective dysfunction following ELA. This review evaluates the literature across models of ELA to characterize neural (PV) and behavioral (anxiety- and depressive-like) outcomes as a function of sex and age. Additionally, we detail a putative mechanistic role of PV on ELA-related outcomes and discuss evidence suggesting hormone influences on PV expression/function which may help to explain sex differences in ELA outcomes.

Environmental Enrichment Ameliorates Anxiety-Like Behavior in Rats without Altering Plasma Corticosterone Level

BACKGROUND: Anxiety disorder is one of the most common psychiatric problems. Prolonged stress gives rise to anxiety-like behavior in animals. Environmental interventions influence the outcome of anxiety treatment. Environmental enrichment (EE) can modulate brain’s structure and function. AIM: The objective of the study was to evaluate EE effects on anxiety-like behavior and corticosterone (CORT) level after unpredictable chronic mild stress (UCMS). METHODS: A total of 28 rats were assigned into four groups randomly: Control, UCMS, UCMS+EE, and UCMS+fluoxetine. UCMS, EE, and fluoxetine were given for 21 days. Anxiety behavior was measured on day 22nd using Elevated Plus Maze. Behavioral measurement was based on the total time spent and total entries onto open and closed arms. CORT was measured using ELISA. RESULTS: UCMS increased anxiety-like behavior as seen from reduced number of entries and time spent in open arms as well as increased number of entries and time spent in in closed arms in UCMS group than control. Rats in EE group spent more time and made more entries in the open arms than UCMS group (both p = 0.002). Anxiolytic effect of EE was stronger than fluoxetine. Plasma CORT level among groups did not differ significantly (p = 0.351). CONCLUSION: EE can ameliorate stress-induced anxiety-like behavior without affecting CORT level.

Understanding how stress responses and stress-related behaviors have evolved in zebrafish and mammals

Stress response is essential for the organism to quickly restore physiological homeostasis disturbed by various environmental insults. In addition to well-established physiological cascades, stress also evokes various brain and behavioral responses. Aquatic animal models, including the zebrafish (Danio rerio), have been extensively used to probe pathobiological mechanisms of stress and stress-related brain disorders. Here, we critically discuss the use of zebrafish models for studying mechanisms of stress and modeling its disorders experimentally, with a particular cross-taxon focus on the potential evolution of stress responses from zebrafish to rodents and humans, as well as its translational implications.

Traumatic Injury to the Developing Brain: Emerging Relationship to Early Life Stress

Despite the high incidence of brain injuries in children, we have yet to fully understand the unique vulnerability of a young brain to an injury and key determinants of long-term recovery. Here we consider how early life stress may influence recovery after an early age brain injury. Studies of early life stress alone reveal persistent structural and functional impairments at adulthood. We consider the interacting pathologies imposed by early life stress and subsequent brain injuries during early brain development as well as at adulthood. This review outlines how early life stress primes the immune cells of the brain and periphery to elicit a heightened response to injury. While the focus of this review is on early age traumatic brain injuries, there is also a consideration of preclinical models of neonatal hypoxia and stroke, as each further speaks to the vulnerability of the brain and reinforces those characteristics that are common across each of these injuries. Lastly, we identify a common mechanistic trend; namely, early life stress worsens outcomes independent of its temporal proximity to a brain injury.

Prolonged Maternal Separation Induces the Depression-Like Behavior Susceptibility to Chronic Unpredictable Mild Stress Exposure in Mice

Early life stress is an important determinant for developing depression later in life. It is reported that maternal separation (MS) could trigger stress sensitivity in adulthood when exposed to stress again. However, it could also result in resilience to stress-induced depression. The conclusions are contradictory. To address this issue, C57BL/6N newborn pups were exposed to either daily short MS (MS for 15 min per day; MS15) or prolonged MS (MS for 180 min per day; MS180) from the first day postpartum (PD1) to PD21. Adult mice were then subjected to chronic unpredictable mild stress (CUMS) exposure from PD64 to PD105. The behavior tests such as the forced swimming test (FST), tail suspension test (TST), and open-field test were performed once a week during this time. Besides, the hippocampal neurosteroids, serum stress hormones, and hippocampal monoamine neurotransmitters were measured at PD106. We found that mice in the MS180 group displayed the reduced struggling time and the increased latency to immobility in both FST and TST. However, there was no significant difference in the MS15 group. The levels of hippocampal neurosteroids (progesterone and allopregnanolone) were decreased, and the serum levels of corticosterone, corticotropin-releasing hormone, and adrenocorticotropic hormone were overexpressed in the MS180 group. Besides, the expressions of monoamine neurotransmitters such as 5-hydroxytryptamine and 5-hydroxy indole acetic acid significantly decreased in the MS180 group, but not in the MS15 group. All findings revealed that prolonged MS, rather than short MS, could increase the susceptibility to depression-like behavior when reexposed to stress in adulthood. However, future studies are warranted to identify the underlying neuromolecular mechanism of the MS experience on the susceptibility to adult stress reexposure.

Sex-specific behavioral and structural alterations caused by early-life stress in C57BL/6 and BTBR mice

Lately, the development of various mental illnesses, such as depression, personality disorders, and autism spectrum disorders, is often associated with traumatic events in childhood. Nonetheless, the mechanism giving rise to this predisposition is still unknown. Because the development of a disease often depends on a combination of a genetic background and environment, we decided to evaluate the effect of early-life stress on BTBR mice, which have behavioral, neuroanatomical, and physiological features of autism spectrum disorders. As early-life stress, we used prolonged separation of pups from their mothers in the first 2 weeks of life (3 h once a day). We assessed effects of the early-life stress on juvenile (postnatal day 23) and adolescent (postnatal days 37-38) male and female mice of strains C57BL/6 (B6) and BTBR. We found that in both strains, the early-life stress did not lead to changes in the level of social behavior, which is an important characteristic of autism-related behavior. Nonetheless, the early-life stress resulted in increased locomotor activity in juvenile BTBR mice. In adolescent mice, the stress early in life caused a low level of anxiety in B6 males and BTBR females and increased exploratory activity in adolescent BTBR males and females. In addition, adolescent B6 male and female mice with a history of the early-life stress tended to have a thinner motor cortex as assessed by magnetic resonance imaging. As compared to B6 mice, BTBR mice showed reduced levels of social behavior and exploratory activity but their level of locomotor activity was higher. BTBR mice had smaller whole-brain, cortical, and dorsal hippocampal volumes; decreased motor cortex thickness; and increased ventral-hippocampus volume as compared to B6 mice, and these parameters correlated with the level of exploratory behavior of BTBR mice. Overall, the effects of early postnatal stress are sex- and strain-dependent.

Combination of MAP6 deficit, maternal separation and MK801 in female mice: A 3-hit animal model of neurodevelopmental disorder with cognitive deficits

Schizophrenia is a major psychiatric disease still lacking efficient treatment, particularly for cognitive deficits. To go further in research of new treatments that would encompass all the symptoms associated with this pathology, preclinical animal models need to be improved. To date, the aetiology of schizophrenia is unknown, but there is increasing evidence to highlight its multifactorial nature. We built a new neurodevelopmental mouse model gathering a triple factor combination (3-M): a genetic factor (partial deletion of MAP6 gene), an early stress (maternal separation) and a late pharmacological factor (MK801 administration, 0.05 mg/kg, i.p., daily for 5 days). The effects of each factor and of their combination were investigated on several behaviours including cognitive functions. While each individual factor induced slight deficits in one or another behavioural test, 3-M conditioning induces a wider phenotype with hyperlocomotion and cognitive deficits (working memory and social recognition). This study confirms the hypothesis that genetic, environmental and pharmacological factors, even if not deleterious by themselves, could act synergistically to induce a deleterious behavioural phenotype. It moreover encourages the use of such combined models to improve translational research on neurodevelopmental disorders.

The impact of chronic unpredictable early-life stress (CUELS) on boldness and stress-reactivity: Differential effects of stress duration and context of testing

Early-life stress (ELS) has been shown to result in a diverse array of long-lasting impacts; for example, increasing vulnerability to disease or building 'resilience' in adulthood. Previously, zebrafish (Danio rerio) have been used to understand the mechanisms by which ELS induces different behavioral phenotypes in adults, with alterations in both learning and anxiety observed in exposed individuals. Here, we subjected zebrafish larvae to chronic unpredictable early-life stress (CUELS) for 7 or 14 days, to investigate the impact on boldness towards a new environment and novel object, and stress-reactivity. We observed that 7 days of CUELS resulted in increased time spent in the top of a novel tank (indicating boldness) but did not alter approach to a novel object. Although CUELS did not affect stress-reactivity in terms of cortisol levels, decreased anxiety-like response to conspecific alarm substance (CAS) was observed in both ELS groups (7 and 14 days of CUELS). Therefore, for the first time, we observe a potential negative effect of CUELS by dampening the behavioral stress response following exposure to CAS. Overall, these data support the use of zebrafish as a translational model to study the broad range of ELS-induced permanent changes in behavior. It could also be used to investigate the mechanisms underlying both the positive and the negative effects of early-life adversity.

Altered hypothalamic DNA methylation and stress-induced hyperactivity following early life stress

Exposure to early life stress (ELS) during childhood or prenatally increases the risk of future psychiatric disorders. The effect of stress exposure during the neonatal period is less well understood. In preterm infants, exposure to invasive procedures is associated with altered brain development and future stress responses suggesting that the neonatal period could be a key time for the programming of mental health. Previous studies suggest that ELS affects the hypothalamic epigenome, making it a good candidate to mediate these effects. In this study, we used a mouse model of early life stress (modified maternal separation; MMS). We hypothesised MMS would affect the hypothalamic transcriptome and DNA methylome, and impact on adult behaviour. MMS involved repeated stimulation of pups for 1.5 h/day, whilst separated from their mother, from postnatal day (P) 4-6. 3'mRNA sequencing and DNA methylation immunoprecipitation (meDIP) sequencing were performed on hypothalamic tissue at P6. Behaviour was assessed with the elevated plus, open field mazes and in-cage monitoring at 3-4 months of age. MMS was only associated with subtle changes in gene expression, but there were widespread alterations in DNA methylation. Notably, differentially methylated regions were enriched for synapse-associated loci. MMS resulted in hyperactivity in the elevated plus and open field mazes, but in-cage monitoring revealed that this was not representative of habitual hyperactivity. ELS has marked effects on DNA methylation in the hypothalamus in early life and results in stress-specific hyperactivity in young adulthood. These results have implications for the understanding of ELS-mediated effects on brain development.

Does neonatal manipulation on continuous or alternate days change maternal behavior?

Maternal separation and neonatal manipulation of pups produce changes in maternal behavior after the dam-pup reunion. Here, we examined whether continuous versus alternating days of neonatal manipulation during the first 8 postnatal days produces differential changes in maternal and non-maternal behaviors in rats. We found that both maternal separation protocols increased anogenital licking after dam-pup reunion, reflecting increased maternal care of pups.

Unilateral brain injury to pregnant rats induces asymmetric neurological deficits in the offspring

Effects of environmental factors may be transmitted to the following generation, and cause neuropsychiatric disorders including depression, anxiety, and posttraumatic stress disorder in the offspring. Enhanced synaptic plasticity induced by environmental enrichment may be also transmitted. We here test the hypothesis that the effects of brain injury in pregnant animals may produce neurological deficits in the offspring. Unilateral brain injury (UBI) by ablation of the hindlimb sensorimotor cortex in pregnant rats resulted in the development of hindlimb postural asymmetry (HL-PA), and impairment of balance and coordination in beam walking test in the offspring. The offspring of rats with the left UBI exhibited HL-PA before and after spinal cord transection with the contralesional (i.e., right) hindlimb flexion. The right UBI caused the offspring to develop HL-PA that however was cryptic and not-lateralized; it was evident only after spinalization, and was characterized by similar occurrence of the ipsi- and contralesional hindlimb flexion. The HL-PA persisted after spinalization suggesting that the asymmetry was encoded in lumbar spinal neurocircuits that control hindlimb muscles. Balance and coordination were affected by the right UBI but not the left UBI. Thus, the effects of a unilateral brain lesion in pregnant animals may be intergenerationally transmitted, and this process may depend on the side of brain injury. The results suggest the existence of left-right side-specific mechanisms that mediate transmission of the lateralized effects of brain trauma from mother to fetus.

Serotonin-related rodent models of early-life exposure relevant for neurodevelopmental vulnerability to psychiatric disorders

Mental disorders including depression and anxiety are continuously rising their prevalence across the globe. Early-life experience of individuals emerges as a main risk factor contributing to the developmental vulnerability to psychiatric disorders. That is, perturbing environmental conditions during neurodevelopmental stages can have detrimental effects on adult mood and emotional responses. However, the possible maladaptive neural mechanisms contributing to such psychopathological phenomenon still remain poorly understood. In this review, we explore preclinical rodent models of developmental vulnerability to psychiatric disorders, focusing on the impact of early-life environmental perturbations on behavioral aspects relevant to stress-related and psychiatric disorders. We limit our analysis to well-established models in which alterations in the serotonin (5-HT) system appear to have a crucial role in the pathophysiological mechanisms. We analyze long-term behavioral outcomes produced by early-life exposures to stress and psychotropic drugs such as the selective 5-HT reuptake inhibitor (SSRI) antidepressants or the anticonvulsant valproic acid (VPA). We perform a comparative analysis, identifying differences and commonalities in the behavioral effects produced in these models. Furthermore, this review discusses recent advances on neurodevelopmental substrates engaged in these behavioral effects, emphasizing the possible existence of maladaptive mechanisms that could be shared by the different models.

Trajectories of Mother-Infant Communication: An Experiential Measure of the Impacts of Early Life Adversity

Caretaking stability in the early life environment supports neurobehavioral development, while instability and neglect constitute adverse environments that can alter maturational processes. Research in humans suggests that different types of early life adversity (ELA) can have differential effects on caretaker relationships and later cognitive and social development; however, identifying mechanistic underpinnings will require animal models with translational validity. Two common rodent models, maternal separation (MS) and limited bedding (LB), influence the mother-infant relationship during a critical window of development. We hypothesized that these paradigms may affect the development of communication strategies on the part of the pup. Ultrasonic vocalizations (USVs) are a care-eliciting mechanism and ethologically relevant response to stressors in the rat pup. USV emission rates and acoustic parameters change throughout early development, presenting the opportunity to define developmental milestones in USVs that would reflect neurobehavioral aberrations if disrupted. This study investigated the effects of MS or LB on the dam-pup relationship by quantifying pup USVs, maternal behavior, and the relationship between the two. First, we used a generalized additive model approach to establish typical developmental trajectories of USV acoustic properties and determine windows of change in MS or LB rearing. Additionally, we quantified maternal behaviors and the predictability of maternal care sequences using an entropy rate calculation. MS and LB each shifted the developmental trajectories of USV acoustic parameters and call types in a sex-specific manner. MS more often impacted male USVs, while LB impacted female USVs. MS dams spent more time passive nursing, and LB dams spent more time on the nest. The predictability of maternal care was associated with the rate of USV emissions exclusively in females. Taken together, findings demonstrate sex- and model-specific effects of rearing environments on a novel developmental trajectory involving the mother-infant relationship, facilitating the translation of animal ELA paradigms to assess later-life consequences.

The effects of maternal separation on behaviours under social-housing environments in adult male C57BL/6 mice

Adverse experience in early life can affect the formation of neuronal circuits during postnatal development and exert long-lasting influences on neural functions that can lead to the development of a variety of psychiatric disorders including depression, anxiety disorders, and post-traumatic stress disorder. Many studies have demonstrated that daily repeated maternal separation, an animal model of early-life stress, can induce impairments in emotional behaviours and cognitive function during adolescence and adulthood. However, the behavioural phenotypes of maternally separated mice under long-term group-housing conditions are largely unknown. In this study, we applied our newly developed assay system to investigate the effects of maternal separation on behaviours under group-housing conditions during four days of continuous observations. Using our system, we found that repeated maternal separation resulted in inappropriate social distance from cagemates, altered approach preferences to others, and induced a lower rank in the time spent on the running wheel under group-housing conditions in adult male mice. Focussing on these behavioural abnormalities that appear in an environment with a social context will be important insights to understand the pathogenesis of psychiatric disorders.

Long-term Effects of Maternal Separation on Anxiety-Like Behavior and Neuroendocrine Parameters in Adult Balb/c Mice

Introduction: Disruption of maternal care using maternal separation (MS) models has provided significant evidence of the deleterious long-term effects of early life stress. Several preclinical studies investigating MS showed multiple behavioral and biomolecular alterations. However, there is still conflicting results from MS studies, which represents a challenge for reliability and replicability of those findings. Objective: To address that, this study was conducted to investigate whether MS would affect anxiety-like behaviors using a battery of classical tasks, as well as central and peripheral stress-related biomarkers. Methods: Male Balb/c mice were exposed to MS from postnatal day (PND) 2 to 14 for 180-min per day. Two independent cohorts were performed to evaluate both baseline and anxiety-like behavior responses to MS at PND60. We performed composite scores to evaluate MS effects on anxiety and risk assessment phenotypes. Also, we assessed mRNA gene expression in the medial pre-frontal cortex (mPFC) of glucocorticoid and mineralocorticoid receptors (GR and MR) using real-time PCR and peripheral corticosterone levels (CORT) to investigate possible neurobiological correlates to anxiety behaviors. Results: We found increased anxiety-like behavior and decreased risk assessment and exploratory behaviors in MS mice. The animals exposed to MS also presented a decrease in MR mRNA expression and higher levels of CORT compared to controls. Conclusions: Our findings reinforce the body of evidence suggesting that long-term MS induces effects on anxiety and risk assessment phenotypes following the exposure to a standardized MS protocol. Moreover, MS affected the expression of MR mRNA and induced significant changes on CORT response. This data highlights that the reprograming MS effects on HPA axis could be mediate by MR gene expression in mPFC and chronic overactivity of peripheral CORT levels.

The impact of handling technique and handling frequency on laboratory mouse welfare is sex-specific

Handling is a well-known source of stress to laboratory animals and can affect variability of results and even compromise animal welfare. The conventional tail handling in mice has been shown to induce aversion and anxiety-like behaviour. Recent findings demonstrate that the use of alternative handling techniques, e.g. tunnel handling, can mitigate negative handling-induced effects. Here, we show that technique and frequency of handling influence affective behaviour and stress hormone release of subjects in a sex-dependent manner. While frequent tail handling led to a reduction of wellbeing-associated burrowing and increased despair-like behaviour in male mice, females seemed unaffected. Instead, they displayed a stress response to a low handling frequency, which was not detectable in males. This could suggest that in terms of refinement, the impact in handling could differ between the sexes. Independently from this observation, both sexes preferred to interact with the tunnel. Mice generally explored the tunnel more often than the tail-handling hands of the experimenter and showed more positively rated approaches, e.g. touching or climbing, and at the same time, less defensive burrowing, indicating a strong preference for the tunnel.

[Training simulation during the announcement of fetal malformation discovered on screening ultrasound: Results of a pilot study]

OBJECTIVES

Breaking bad news (BBN) to a pregnant woman with fetal abnormalities (FA) on ultrasound (US) examination is a challenge. Announcement technique influences patient reaction. Physicians receive little training in BBN. The simulation and using a BBN protocol as the English SPIKES protocol which guides the announcement consultation according to 6 steps (Setting Up, Perception, Invitation, Knowledge, Emotions and Empathy, Strategy and Summary) can be used for this teaching. The objective was to assess feasibility simulation scenarii of BBN for FA discovered during US and to evaluate the usefulness of SPIKES protocol in this situation.

METHODS

Two scenarios have been created combining US simulator (US Mentor, Symbionix®) with simulated patient (SP). Scenarii objectives were to diagnose FA and break it to SP. Checklist derived from SPIKES was fulfilled by two investigators thanks to video recording, the SP and every participant (residents, physicians, fetal medicine specialists [FMS]). Participants filled out survey about the usefulness of this exercise too.

RESULTS

Nine physicians (3 residents, 4 physicians, 2 FMS) produced 18 scenarii. Seventy-eight percent of physicians thought simulation was like real situation of BBN during US examination. Majority of participant (88%) found that this simulation training could help them to increase their ability to BBN and that it can be used to teach residents (89%) or physicians (100%). FMS had better SPIKES checklist than physicians (P<0,05).

CONCLUSION

Simulation scenario of BBN for FA discovered during US is feasible by combining US simulator and SP. SPIKES protocol can be useful but a validated checklist should be created.