Maternal care and the development of stress responses

Epigenetic Modifications and Neuroplasticity in the Pathogenesis of Depression: A Focus on Early Life Stress

Major depressive disorder (MDD) is a debilitating mental illness, and it is considered to be one of the leading causes of disability globally. The etiology of MDD is multifactorial, involving an interplay between biological, psychological, and social factors. Early life represents a critical period for development. Exposure to adverse childhood experiences is a major contributor to the global burden of disease and disability, doubling the risk of developing MDD later in life. Evidence suggests that stressful events experienced during that timeframe play a major role in the emergence of MDD, leading to epigenetic modifications, which might, in turn, influence brain structure, function, and behavior. Neuroplasticity seems to be a primary pathogenetic mechanism of MDD, and, similarly to epigenetic mechanisms, it is particularly sensitive to stress in the early postnatal period. In this review, we will collect and discuss recent studies supporting the role of epigenetics and neuroplasticity in the pathogenesis of MDD, with a focus on early life stress (ELS). We believe that understanding the epigenetic mechanisms by which ELS affects neuroplasticity offers potential pathways for identifying novel therapeutic targets for MDD, ultimately aiming to improve treatment outcomes for this debilitating disorder.

Postnatal maternal care moderates the effects of prenatal bisphenol exposure on offspring neurodevelopmental, behavioral, and transcriptomic outcomes

Bisphenols (BP), including BPA and "BPA-free" structural analogs, are commonly used plasticizers that are present in many plastics and are known endocrine disrupting chemicals. Prenatal exposure to BPA has been associated with negative neurodevelopmental and behavioral outcomes in children and in rodent models. Prenatal BPA exposure has also been shown to impair postnatal maternal care provisioning, which can also affect offspring neurodevelopment and behavior. However, there is limited knowledge regarding the biological effects of prenatal exposure to bisphenols other than BPA and the interplay between prenatal bisphenol exposure and postnatal maternal care on adult behavior. The purpose of the current study was to determine the interactive impact of prenatal bisphenol exposure and postnatal maternal care on neurodevelopment and behavior in rats. Our findings suggest that the effects of prenatal bisphenol exposure on eye-opening, adult attentional set shifting and anxiety-like behavior in the open field are dependent on maternal care in the first five days of life. Interestingly, maternal care might also attenuate the effects of prenatal bisphenol exposure on eye opening and adult attentional set shifting. Finally, transcriptomic profiles in male and female medial prefrontal cortex and amygdala suggest that the interactive effects of prenatal bisphenol exposure and postnatal maternal care converge on estrogen receptor signaling and are involved in biological processes related to gene expression and protein translation and synthesis. Overall, these findings indicate that postnatal maternal care plays a critical role in the expression of the effects of prenatal bisphenol exposure on neurodevelopment and adult behavior. Understanding the underlying biological mechanisms involved might allow us to identify potential avenues to mitigate the adverse effects of prenatal bisphenol exposure and improve health and well-being in human populations.

The role of SIRT3 in mediating the cognitive deficits and neuroinflammatory changes associated with a developmental animal model of schizophrenia

The neuroinflammatory state may contribute to the pathogenesis of many mental disorders including schizophrenia. Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor for activation of proteins involved in mitochondria quality control, such as Sirtuin3 (SIRT3). Our previous study has found that NAD+ supplement could rescue early life stress (ELS)-induced neuroinflammation and down-regulation of SIRT3 in adult offspring. However, it is unclear whether SIRT3 is the key to the neuroprotective effects of NAD+ supplement in this animal model of schizophrenia. The present study used 24 h maternal separation (MS) as ELS to Wistar rat pups on the postnatal day (PND) 9. Schizophrenia-like behaviors and memory impairments were detected by behavioral tests. Microglial activation, pro-inflammatory cytokine expression, and NAD+/SIRT3 expression were detected in the prefrontal cortex and hippocampus. Meanwhile, NAM (a precursor of NAD+), and the SIRT3 activator Honokiol (HNK), and the SIRT3 inhibitor 3-TYP were used as an intervention in vivo. Our results showed that ELS could induce schizophrenia-like behaviors and M1 microglial activation, NAD+ decline, lower expression of SIRT3, and increased acetylated superoxide dismutase 2 expression at the adult stage. NAD+ supplement or HNK administration could block this process and normalize the behavioral alterations of the MS animals. 3-TYP administration in the control group and the NAM-treated MS rats caused M1 microglial activation and cognitive deficits. Our results demonstrated that SIRT3 mediated the stabilizing effect of NAD+ on normalizing M1 microglial activation and behavioral phenotypes in MS rats.

Large litters have a detrimental impact on litter performance and postpartum maternal behaviour in primiparous sows

BACKGROUND

Our previous study confirmed that large litter size adversely affects prepartum maternal hormones and behaviour, concurrently with heightened oxidative stress in primiparous sows. The purpose of this study was to examine the effect of large litter size on litter performance, postpartum maternal behaviour, salivary cortisol levels, and colostral immunoglobulin levels in sows, as well as investigate their correlations with the levels of oxidative stress parameters.

RESULTS

A total of 24 primiparous sows (Landrace[Formula: see text]Large white) and their offspring were categorised into two groups based on litter size: NORMAL (n = 8) with litter size ranging from 7 to 14 (mean 11.5[Formula: see text]2.7), and LARGE (n=16) with litter size ranging from 15 to 20 (mean 15.9[Formula: see text]1.4). All sows were housed in a group housing system during gestation and transitioned to an adaptable loose housing system (2.4[Formula: see text]2.3 m) during the farrowing and lactation periods. The nursing and carefulness behaviour of the sows was monitored over a 24-h period between 72 and 96 h after parturition. Saliva samples were collected for cortisol assay on 35, 21, and 7 days before parturition (D-35, D-21, and D-7, respectively), as well as on days 1, 7, and 28 after parturition (D1, D7, and D28, respectively). On D1, higher piglet mortality rates were observed among the LARGE group compared to the NORMAL group (p<0.01). The total and successful nursing behaviours of the sows were less frequent in the LARGE group than in the NORMAL group (p<0.05, for both), and the carefulness score of the LARGE group was also lower than that of the NORMAL group (p< 0.01). On D1, cortisol levels in LARGE sows were higher than those in NORMAL sows (p< 0.05), and for other time points (D-21, D-7, D7, and D28), cortisol levels in LARGE sows tended to be higher than those in NORMAL sows (p < 0.10, for all). Successful nursing behaviour displayed negative correlations with levels of salivary cortisol and certain oxidative stress parameters measured on D1.

CONCLUSIONS

These findings suggest that the strategy for alleviating physiological and oxidative stress during the peripartum periods could benefit potential postpartum maternal behaviour and litter performance in the sows with large litters.

Improving behavioral deficits induced by perinatal ethanol and stress exposure in adolescent male rat progeny via maternal melatonin treatment

BACKGROUND AND AIM

Early-life stressful situations and binge drinking have been thus far acknowledged as two burdensome conditions that potentially give rise to negative outcomes and then synergistically affect brain development. In this context, the hippocampus, with the greatest number of glucocorticoid receptors (GCRs) in the brain, is responsible for regulating negative responses to stress. Prolonged glucocorticoid (GC) exposure can accordingly cause oxidative stress (OS), leading to cognitive and emotional dysfunction. Against this background, melatonin, as a powerful antioxidant and hypothalamus-pituitary-adrenal (HPA) axis regulator, was administered in this study to ameliorate cognitive impairments induced by perinatal ethanol and stress exposure in adolescent male rat progeny.

METHODS

Wistar rat dams were exposed to ethanol (4 g/kg) and melatonin (10 mg/kg) from gestational day (GD) 6 to postnatal day (PND) 14 and then limited nesting material (LNS) from PND0 to PND14 individually or in combination. Maternal behavior was then investigated in mothers. Afterward, the plasma corticosterone (CORT) concentration, the OS marker, the corticotropin-releasing hormone receptor type 1 (CRHR1) expression, and the GCR and brain-derived neurotrophic factor (BDNF) levels were measured in the male pups. Moreover, behavioral tasks, including the elevated plus maze (EPM), the Morris water maze (MWM), the novel object recognition (NORT), and the object-location memory (OLM) tests were completed and assessed.

RESULTS

The quantity and quality of maternal care significantly decreased in the mothers with dual exposure to ethanol and stress. The plasma CORT concentration in the progeny also dropped in the Ethanol + LNS group, but the risk-taking behavior elevated significantly. The ethanol and stress exposure further revealed a significant fall in the GCR and CRHR1 expression levels, compared with stress alone. The results of learning and memory tasks also indicated a significant reduction in spatial learning and memory among animals exposed to ethanol and stress. The BDNF mRNA levels correspondingly increased in the Ethanol + LNS group, compared with LNS alone. In the presence of ethanol and stress, the superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities correspondingly declined. On the other hand, the malondialdehyde (MDA) levels augmented in the hippocampus of the animals with ethanol and LNS dual exposure, as compared with the control group. Melatonin treatment (MT) thus improved nursing behaviors in dams, prevented OS, enhanced the CRHR1 and GCR expression, and reduced the BDNF levels to the similar ones in the control group. The animals in the Ethanol + LNS + MT group ultimately showed an ameliorated performance at behavioral tasks, including the memory and risk-taking behavior.

CONCLUSION

It was concluded that MT could prevent stress response and memory impairments arising from dual exposure to ethanol and stress by inhibiting OS.

Maternal care behavior and physiology moderate offspring outcomes following gestational exposure to opioids

The opioid epidemic has resulted in a drastic increase in gestational exposure to opioids. Opioid-dependent pregnant women are typically prescribed medications for opioid use disorders ("MOUD"; e.g., buprenorphine [BUP]) to mitigate the harmful effects of abused opioids. However, the consequences of exposure to synthetic opioids, particularly BUP, during gestation on fetal neurodevelopment and long-term outcomes are poorly understood. Further, despite the known adverse effects of opioids on maternal care, many preclinical and clinical studies investigating the effects of gestational opioid exposure on offspring outcomes fail to report on maternal care behaviors. Considering that offspring outcomes are heavily dependent upon the quality of maternal care, it is important to evaluate the effects of gestational opioid exposure in the context of the mother-infant dyad. This review compares offspring outcomes after prenatal opioid exposure and after reduced maternal care and integrates this information to potentially identify common underlying mechanisms. We explore whether adverse outcomes after gestational BUP exposure are due to direct effects of opioids in utero, deficits in maternal care, or a combination of both factors. Finally, suggestions for improving preclinical models of prenatal opioid exposure are provided to promote more translational studies that can help to improve clinical outcomes for opioid-dependent mothers.

Maternal upbringing and selective breeding for voluntary exercise behavior modify patterns of DNA methylation and expression of genes in the mouse brain

Selective breeding has been utilized to study the genetic basis of exercise behavior, but research suggests that epigenetic mechanisms, such as DNA methylation, also contribute to this behavior. In a previous study, we demonstrated that the brains of mice from a genetically selected high runner (HR) line have sex-specific changes in DNA methylation patterns in genes known to be genomically imprinted compared to those from a non-selected control (C) line. Through cross-fostering, we also found that maternal upbringing can modify the DNA methylation patterns of additional genes. Here, we identify an additional set of genes in which DNA methylation patterns and gene expression may be altered by selection for increased wheel-running activity and maternal upbringing. We performed bisulfite sequencing and gene expression assays of 14 genes in the brain and found alterations in DNA methylation and gene expression for Bdnf, Pde4d and Grin2b. Decreases in Bdnf methylation correlated with significant increases in Bdnf gene expression in the hippocampus of HR compared to C mice. Cross-fostering also influenced the DNA methylation patterns for Pde4d in the cortex and Grin2b in the hippocampus, with associated changes in gene expression. We also found that the DNA methylation patterns for Atrx and Oxtr in the cortex and Atrx and Bdnf in the hippocampus were further modified by sex. Together with our previous study, these results suggest that DNA methylation and the resulting change in gene expression may interact with early-life influences to shape adult exercise behavior.

Postnatal maternal care moderates the effects of prenatal bisphenol exposure on offspring neurodevelopmental, behavioral, and transcriptomic outcomes

Bisphenols (BPs), including BPA and "BPA-free" structural analogs, are commonly used plasticizers that are present in many plastics and are known endocrine disrupting chemicals. Prenatal exposure to BPA has been associated with negative neurodevelopmental and behavioral outcomes in children and rodent models. Prenatal BPA exposure has also been shown to impair postnatal maternal care provisioning, which can also affect offspring neurodevelopment and behavior. However, there is limited knowledge regarding the biological effects of prenatal exposure to bisphenols other than BPA and the interplay between prenatal BP exposure and postnatal maternal care on adult behavior. The purpose of the current study was to determine the interactive impact of prenatal BP exposure and postnatal maternal care on neurodevelopment and behavior. Our findings suggest that the effects of prenatal BP exposure on eye-opening, adult attentional set shifting and anxiety-like behavior in the open field are dependent on maternal care in the first five days of life. Interestingly, maternal care might also attenuate the effects of prenatal BP exposure on eye opening and adult attentional set shifting. Finally, transcriptomic profiles in male and female medial prefrontal cortex and amygdala suggest that the interactive effects of prenatal BP exposure and postnatal maternal care converge on estrogen receptor signaling and are involved in biological processes related to gene expression and protein translation and synthesis. Overall, these findings indicate that postnatal maternal care plays a critical role in the expression of the effects of prenatal BP exposure on neurodevelopment and adult behavior. Understanding the underlying biological mechanisms involved might allow us to identify potential avenues to mitigate the adverse effects of prenatal BP exposure and improve health and well-being in human populations.

Enhanced maternal behaviors in a mouse model of congenital blindness

In mammals, mothering is one of the most important prosocial female behavior to promote survival, proper sensorimotor, and emotional development of the offspring. Different intrinsic and extrinsic factors can initiate and maintain these behaviors, such as hormonal, cerebral, and sensory changes. Infant cues also stimulate multisensory systems and orchestrate complex maternal responsiveness. To understand the maternal behavior driven by complex sensory interactions, it is necessary to comprehend the individual sensory systems by taking out other senses. An excellent model for investigating sensory regulation of maternal behavior is a murine model of congenital blindness, the ZRDBA mice, where both an anophthalmic and sighted mice are generated from the same litter. Therefore, this study aims to assess whether visual inputs are essential to driving maternal behaviors in mice. Maternal behaviors were assessed using three behavioral tests, including the pup retrieval test, the home cage maternal behavior test, and the maternal aggression test. Our results show that blind mothers (1) took less time to retrieve their offspring inside the nest, (2) spent more time nursing and licking their offspring in the second- and third-week postpartum, and (3) exhibited faster aggressive behaviors when exposed to an intruder male, compared to the sighted counterparts. This study provides evidence that congenitally blind mothers show more motivation to retrieve the pups, care, and protection towards their pups than sighted ones, likely due to a phenomenon of sensory compensation.

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.

The intersection of genome, epigenome and social experience in autism spectrum disorder: Exploring modifiable pathways for intervention

The number of children diagnosed with autism spectrum disorder (ASD) has increased substantially over the past two decades. Current research suggests that both genetic and environmental risk factors are involved in the etiology of ASD. The goal of this paper is to examine how one specific environmental factor, early social experience, may be correlated with DNA methylation (DNAm) changes in genes associated with ASD. We present an innovative model which proposes that polygenic risk and changes in DNAm due to social experience may both contribute to the symptoms of ASD. Previous research on genetic and environmental factors implicated in the etiology of ASD will be reviewed, with an emphasis on the oxytocin receptor gene, which may be epigenetically altered by early social experience, and which plays a crucial role in social and cognitive development. Identifying an environmental risk factor for ASD (e.g., social experience) that could be modified via early intervention and which results in epigenetic (DNAm) changes, could transform our understanding of this condition, facilitate earlier identification of ASD, and guide early intervention efforts.

Neuroendocrine mechanisms in oxaliplatin-induced hyperalgesic priming

ABSTRACT

Stress plays a major role in the symptom burden of oncology patients and can exacerbate cancer chemotherapy-induced peripheral neuropathy (CIPN), a major adverse effect of many classes of chemotherapy. We explored the role of stress in the persistent phase of the pain induced by oxaliplatin. Oxaliplatin induced hyperalgesic priming, a model of the transition to chronic pain, as indicated by prolongation of hyperalgesia produced by prostaglandin E 2 , in male rats, which was markedly attenuated in adrenalectomized rats. A neonatal handling protocol that induces stress resilience in adult rats prevented oxaliplatin-induced hyperalgesic priming. To elucidate the role of the hypothalamic-pituitary-adrenal and sympathoadrenal neuroendocrine stress axes in oxaliplatin CIPN, we used intrathecally administered antisense oligodeoxynucleotides (ODNs) directed against mRNA for receptors mediating the effects of catecholamines and glucocorticoids, and their second messengers, to reduce their expression in nociceptors. Although oxaliplatin-induced hyperalgesic priming was attenuated by intrathecal administration of β 2 -adrenergic and glucocorticoid receptor antisense ODNs, oxaliplatin-induced hyperalgesia was only attenuated by β 2 -adrenergic receptor antisense. Administration of pertussis toxin, a nonselective inhibitor of Gα i/o proteins, attenuated hyperalgesic priming. Antisense ODNs for Gα i 1 and Gα o also attenuated hyperalgesic priming. Furthermore, antisense for protein kinase C epsilon, a second messenger involved in type I hyperalgesic priming, also attenuated oxaliplatin-induced hyperalgesic priming. Inhibitors of second messengers involved in the maintenance of type I (cordycepin) and type II (SSU6656 and U0126) hyperalgesic priming both attenuated hyperalgesic priming. These experiments support a role for neuroendocrine stress axes in hyperalgesic priming, in male rats with oxaliplatin CIPN.

Nicotinamide ameliorates mitochondria-related neuronal apoptosis and cognitive impairment via the NAD+/SIRT3 pathway

Emerging evidence suggests that mitochondria play a central role in mental health disorders including schizophrenia. Here we investigated whether nicotinamide (NAM) normalized cognitive impairment via a mechanism involving the mitochondrial Sirtuin 3 (SIRT3) pathway. The 24 h maternal separation (MS) rat model was used to mimic schizophrenia-associate phenotypes. Schizophrenia-like behaviors and memory impairments were detected using the pre-pulse inhibition test, novel object recognition test, and Barnes maze test, and neuronal apoptosis was characterized using multiple assays. SIRT3 activity was inhibited pharmacologically or by knockdown in HT22 cells, and BV2 microglia and SIRT3-knockdown HT22 cells were co-cultured in vitro. Mitochondrial molecules were measured by western blotting, and mitochondrial damage was measured with reactive oxygen species and mitochondrial membrane potential assays. Proinflammatory cytokines were assayed by ELISA and microglial activation was detected by immunofluorescence. MS animals showed behavioral and cognitive impairment and increased neuronal apoptosis. Supplementation with NAM or administration of honokiol, a SIRT3 activator, reversed all of the changes in behavioral and neuronal phenotypes. Administration of the SIRT3 inhibitor 3-TYP in control and NAM-treated MS rats caused behavioral and neuronal phenotypes similar to MS. In vitro, inhibition of SIRT3 activity with 3-TYP or by knockdown in HT22 cells increased ROS accumulation and caused neuronal apoptosis in a single-culture system. In co-culture systems, SIRT3 knockdown in HT22 cells activated BV2 microglia and increased levels of TNF-α, IL-6, and IL-1β. The administration of NAM blocked these alterations. Taken together, these data suggest that NAM can rescue neuronal apoptosis and microglial over-activation through the nicotinamide adenine dinucleotide (NAD⁺)-SIRT3-SOD2 signaling pathway, furthering our understanding of the pathogenesis of schizophrenia and providing avenues for novel treatments.

Prenatal programming of environmental sensitivity

According to several theories, people differ in their sensitivity to environmental influences with some more susceptible than others to both supportive and adverse contextual conditions. Such differences in environmental sensitivity have a genetic basis but are also shaped by environmental factors. Herein we narratively build on our previous work proposing that prenatal experiences contribute to the development of environmental sensitivity. This hypothesis of prenatal programming of postnatal plasticity has considerable empirical support. After presenting illustrative animal and human evidence consistent with this claim, we discuss a range of biological mechanisms likely involved in the pathway from prenatal stress exposure to postnatal environmental sensitivity. We also consider work suggesting that genetic differences, gender, as well as the timing, duration and intensity of prenatal exposures may moderate the effects of prenatal programming on postnatal environmental susceptibility or sensitivity. Before concluding, we highlight "unknowns in the prenatal programming of environmental sensitivity" and their practical implications. Ultimately, we conclude that prenatal stress does not necessarily predispose individuals to problematical development, but rather increases sensitivity to both adverse and supportive postnatal contexts. Thus, prenatal stress may actually foster positive development if paired with supportive and caring postnatal environments.

Early life exposure to high fructose diet induces metabolic dysregulation associated with sex-specific cognitive impairment in adolescent rats

The incidence of adolescent mental health disorders is on the rise. Epidemiological studies suggest that poor nutrition is a significant contributor to this public health crisis, specifically through exposure to high level of dietary sugar, including fructose, during critical periods of development. Previous studies have shown that elevated fructose exposure during adolescence disrupts mental health. Despite these data, it is currently unknown how fructose exposure, specifically during infancy, may impact adolescent mental health. We developed a rat experimental protocol to investigate the effects of fructose exposure during infancy on behavioral, cognitive and metabolic endpoints in adolescence. We found that exposing rats to high fructose from birth to weaning resulted in higher circulating glucose, insulin and leptin levels in adolescence. High fructose during infancy also increased bodyweight, disrupted metabolic homeostasis in the basolateral amygdala (BLA) as indicated by decreased activity of the cellular energy sensor AMPK, and impaired attention and impulsivity in a male-specific manner. This impaired attention observed in adolescent male rats following neonatal fructose exposure was partially rescued by viral-mediated, in vivo expression of a constitutively active form of AMPK in principal neurons of the BLA. Our results suggest that exposure to high level of fructose during infancy may impact adolescent mental health in a male-specific manner and that manipulation of AMPK activity may mitigate this impact.

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'.

Mother-Young Bonding: Neurobiological Aspects and Maternal Biochemical Signaling in Altricial Domesticated Mammals

Mother-young bonding is a type of early learning where the female and their newborn recognize each other through a series of neurobiological mechanisms and neurotransmitters that establish a behavioral preference for filial individuals. This process is essential to promote their welfare by providing maternal care, particularly in altricial species, animals that require extended parental care due to their limited neurodevelopment at birth. Olfactory, auditory, tactile, and visual stimuli trigger the neural integration of multimodal sensory and conditioned affective associations in mammals. This review aims to discuss the neurobiological aspects of bonding processes in altricial mammals, with a focus on the brain structures and neurotransmitters involved and how these influence the signaling during the first days of the life of newborns.

Transgenerational Epigenetic Inheritance of Traumatic Experience in Mammals

In recent years, we have seen an increasing amount of evidence pointing to the existence of a non-genetic heredity of the effects of events such as separation from parents, threat to life, or other traumatising experiences such as famine. This heredity is often mediated by epigenetic regulations of gene expression and may be transferred even across several generations. In this review, we focus on studies which involve transgenerational epigenetic inheritance (TEI), with a short detour to intergenerational studies focused on the inheritance of trauma or stressful experiences. The reviewed studies show a plethora of universal changes which stress exposure initiates on multiple levels of organisation ranging from hormonal production and the hypothalamic-pituitary-adrenal (HPA) axis modulation all the way to cognition, behaviour, or propensity to certain psychiatric or metabolic disorders. This review will also provide an overview of relevant methodology and difficulties linked to implementation of epigenetic studies. A better understanding of these processes may help us elucidate the evolutionary pathways which are at work in the course of emergence of the diseases and disorders associated with exposure to trauma, either direct or in a previous generation.

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.

Both age and experience are important for successful problem solving in juvenile fawn-footed mosaic-tailed rats Melomys cervinipes

Problem solving ability is affected by many factors, including physiology, personality, and cognition. However, how age and experience influence problem-solving ability during development is harder to untangle. We tested how age and experience affected problem solving in a native Australian rodent, the fawn-footed mosaic-tailed rat Melomys cervinipes. Juveniles were divided into two groups (different ages at start of testing) and then received a food-baited cardboard matchbox every 10 days for a total of three tests. We compared the problem-solving ability of individuals from both groups, which allowed us to separate the effects of age and experience. Juveniles with more experience solved the task faster than juveniles with less experience. Furthermore, inexperienced older juveniles interacted with the problems more than inexperienced younger juveniles. Previous solving experience may be important for short-term solving success, while age, in the absence of experience, might be associated with increased exploration, leading to increased investigation of novel problems. Previous experience at manipulating objects generally may also be important for problem-solving success, which likely provides an advantage as resources and habitats change seasonally and annually.

Problem solving in fawn-footed mosaic-tailed rats Melomys cervinipes is not significantly influenced by maternal care or genetic effects

Innovative problem solving is thought to be a flexible trait that allows animals to adjust to changing or challenging environmental conditions. However, it is not known how problem solving develops during an animal's early life, or whether it may have a heritable component. We investigated whether maternal genetic and nongenetic effects influenced problem-solving ability in a native Australian rodent, the fawn-footed mosaic-tailed rat Melomys cervinipes. We measured direct (time spent grooming and huddling), indirect (time spent nesting), and total amount of maternal care received across pup development (postnatal Days 1-13). We measured problem solving in juveniles using matchbox tasks, and in mothers and adult offspring using six tasks of varying complexity (matchbox, cylinder, obstruction, pillar, tile, and lever tasks). We found no relationship between any maternal care measures and problem-solving abilities across multiple tests, suggesting limited (if any) maternal nongenetic effects. We also found that, as shown by low heritability estimates, problem solving only had a small heritable component in some tasks, but this was nonsignificant and requires further investigation. These results suggest that problem solving is unlikely to be constrained by maternal effects experienced during early development, and is, instead, more likely to be influenced by other factors (e.g., experience) later in an individual's lifetime.

Nicotinamide reverses deficits in puberty-born neurons and cognitive function after maternal separation

Background

Early life stress (ELS) is associated with the development of schizophrenia later in life. The hippocampus develops significantly during childhood and is extremely reactive to stress. In rodent models, ELS can induce neuroinflammation, hippocampal neuronal loss, and schizophrenia-like behavior. While nicotinamide (NAM) can inhibit microglial inflammation, it is unknown whether NAM treatment during adolescence reduces hippocampal neuronal loss and abnormal behaviors induced by ELS.

Methods

Twenty-four hours of maternal separation (MS) of Wistar rat pups on post-natal day (PND)9 was used as an ELS. On PND35, animals received a single intraperitoneal injection of BrdU to label dividing neurons and were given NAM from PND35 to PND65. Behavioral testing was performed. Western blotting and immunofluorescence staining were used to detect nicotinamide adenine dinucleotide (NAD⁺)/Sirtuin3 (Sirt3)/superoxide dismutase 2 (SOD2) pathway-related proteins.

Results

Compared with controls, only MS animals in the adult stage (PND56–65) but not the adolescent stage (PND31–40) exhibited pre-pulse inhibition deficits and cognitive impairments mimicking schizophrenia symptoms. MS decreased the survival and activity of puberty-born neurons and hippocampal NAD⁺ and Sirt3 expression in adulthood. These observations were related to an increase in acetylated SOD2, microglial activation, and significant increases in pro-inflammatory IL-1β, TNF-α, and IL-6 expression. All the effects of MS at PND9 were reversed by administering NAM in adolescence (PND35–65).

Conclusions

MS may lead to schizophrenia-like phenotypes and persistent hippocampal abnormalities. NAM may be a safe and effective treatment in adolescence to restore normal hippocampal function and prevent or ameliorate schizophrenia-like behavior.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02591-y.

Parental Depression Screening in Pediatric Health Care Settings: A Scoping Review

BACKGROUND AND OBJECTIVES

Parental depression affects as many as 1 in 5 US families. Pediatric professionals can play an important role in detecting parental depression, yet most studies on parental depression screening focus only on the postpartum period. The authors performed this scoping review to understand the existing literature on parental depression screening outside the postpartum period (child >12 months old) and to identify knowledge gaps.

METHODS

Sources for this research include PubMed, CINAHL, SCOPUS, Web of Science, and APA Psych Info. We included English language papers concerning screening for maternal and/or paternal depression or mood disorders outside of the postpartum period by pediatric clinicians or in a pediatric health care setting. Extracted variables included publication year, title, author(s), country, geographic setting, clinical setting, child age range (in years), parental focus, sample size, study type, approach, screening instrument(s), and findings.

RESULTS

Forty-one papers were included. The proportion of positive parental depression screens was consistently high across the included studies. Relatively few structured screening programs outside of the postpartum period were identified, especially for fathers. The included studies suggest that screening can be accomplished in pediatric settings, but appropriate referral and follow-up of positive screens poses a major challenge. This review was limited to English language papers concerning parental depression outside of the postpartum period.

CONCLUSIONS

These findings suggest that screening for parental depressive symptoms outside the postpartum period could identify families in need of support. Research is required to identify best practices for referral and follow-up of parents who screen positive.

Behavioral Phenotype in Heterozygous DAT Rats: Transgenerational Transmission of Maternal Impact and the Role of Genetic Asset

Dopamine transporter (DAT) is involved in dopamine (DA) reuptake in presynaptic terminals. Deletion of DAT results in a hyperdopaminergic KO-rat phenotype. To conduct our studies in heterozygous DAT rats, several pedigree lines were created, with known derivation of the allele (i.e., maternal or paternal). Our purpose was to elucidate the role of parental origin rather than maternal care, assessing if maternal maltreatments generated sequelae in female offspring. In the first experiment, female rats and their pups were observed during postnatal lactation. Control dams were WT and heterozygous ones were MAT (but K-MAT, with previous experience of early maltreatment by their KO adoptive dams). WT dams were highly attracted to their offspring (predictably, they spent a lot of time licking their pups); in contrast, K-MAT dams showed strangely comparable levels of caring for their pups and exploring the environment. Subsequently, peculiar features of the circadian cycle were found in adolescent rats with different epigenotypes (WT, MUX = offspring of MAT father, MIK = offspring of K-MAT dam). The MIK epigenotype produced locomotor hyperactivity also during resting hours, well above typical values. The MUX epigenotype, on the other hand, was less active and presented a depression-like profile. This study is unique: maltreatment was generated in a spontaneous way from a DAT-KO mother to offspring. We highlight how future studies will address separate contributions by genotype and upbringing. In conclusion, paternal-allele asset generates sequelae diametrically opposed to the inheritance of early maternal trauma.

Maternal Separation Induces Sex-Specific Differences in Sensitivity to Traumatic Stress

Post-traumatic stress disorder (PTSD) is a debilitating psychiatric disorder with a high economic burden. Two risk factors for increasing the chances of developing PTSD are sex (being female) and early life stress. These risk factors suggest that early life stress-induced changes and sex differences in emotional circuits and neuroendocrinological systems lead to susceptibility to traumatic stress. Exploring mechanisms via which stress leads to specific effects can be accomplished in animal models, but reliable animal models that allow for an examination of how early life stress interacts with sex to increase susceptibility to traumatic stress is lacking. To address this, we examined the effects of early life stress [using the maternal separation (MS) model] and late adolescence/early adult traumatic stress [using the single prolonged stress (SPS) model] on startle reactivity, anxiety-like behavior in the open field (OF), and basal corticosterone levels in male and female rats. Female rats exposed to MS and SPS (MS/SPS) showed enhanced startle reactivity relative to MS/control female rats. Enhanced startle reactivity was not observed in MS/SPS male rats. Instead, non-maternally separated male rats that were exposed to SPS showed enhanced startle reactivity relative to controls. Female rats had enhanced locomotor activity in the OF and higher basal corticosterone levels in comparison to males, but measures in the OF and basal corticosterone were not affected by MS or SPS. Overall the results suggest that the combined MS and SPS models can be used to explore how changes in maternal care during infancy lead to sex differences in sensitivity to the effects of traumatic stress as adolescents and adults.

Stress and Loss of Ovarian Function: Novel Insights into the Origins of Sex-Based Differences in the Manifestations of Respiratory Control Disorders During Sleep

The respiratory system of women and men develops and functions in distinct neuroendocrine milieus. Despite differences in anatomy and neural control, homeostasis of arterial blood gases is ensured in healthy individuals regardless of sex. This convergence in function differs from the sex-based differences observed in many respiratory diseases. Sleep-disordered breathing (SDB) results mainly from episodes of upper airway closure. This complex and multifactorial respiratory disorder shows significant sexual dimorphism in its clinical manifestations and comorbidities. Guided by recent progress from basic research, this review discusses the hypothesis that stress is necessary to reveal the sexual dimorphism of SDB.

Poly (I:C)-induced maternal immune activation modifies ventral hippocampal regulation of stress reactivity: prevention by environmental enrichment

Environmental enrichment (EE) has been successfully implemented in human rehabilitation settings. However, the mechanisms underlying its success are not understood. Incorporating components of EE protocols into our animal models allows for the exploration of these mechanisms and their role in mitigation. Using a mouse model of maternal immune activation (MIA), the present study explored disruptions in social behavior and associated hypothalamic pituitary adrenal (HPA) axis functioning, and whether a supportive environment could prevent these effects. We show that prenatal immune activation of toll-like receptor 3, by the viral mimetic polyinosinic-polycytidylic acid (poly(I:C)), led to disrupted maternal care in that dams built poorer quality nests, an effect corrected by EE housing. Standard housed male and female MIA mice engaged in higher rates of repetitive rearing and had lower levels of social interaction, alongside sex-specific expression of several ventral hippocampal neural stress markers. Moreover, MIA males had delayed recovery of plasma corticosterone in response to a novel social encounter. Enrichment housing, likely mediated by improved maternal care, protected against these MIA-induced effects. We also evaluated c-Fos immunoreactivity associated with the novel social experience and found MIA to decrease neural activation in the dentate gyrus. Activation in the hypothalamus was blunted in EE housed animals, suggesting that the putative circuits modulating social behaviors may be different between standard and complex housing environments. These data demonstrate that augmentation of the environment supports parental care and offspring safety/security, which can offset effects of early health adversity by buffering HPA axis dysregulation. Our findings provide further evidence for the viability of EE interventions in maternal and pediatric settings.

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.

Enriched environment and social isolation differentially modulate addiction-related behaviors in male offspring of morphine-addicted dams: The possible role of μ-opioid receptors and ΔFosB in the brain reward pathway

Prenatal opioids exposure negatively affects the neurobehavioral abilities of children born from dependence dams. Adolescent housing conditions can buffer the detrimental impacts of early life experiences or contradictory can worsen individual psychosocial functions. The present study investigated the effects of maternal morphine dependence and different rearing conditions on behaviors and protein expression in brain reward circuits of male pups. Female Wistar rats a week before conception, during pregnancy and lactation were injected twice daily with escalating doses of morphine or saline. On a postnatal day 21, male pups were weaned and subjected to three different environments for two months: standard (STD), isolated (ISO), or enriched environment (EE). The anxiety and drug-related reward were measured using elevated plus maze, open field test, and conditioned place preference. Western blotting was used to determine the protein level of ΔFosB and μ-opioid receptor proteins in the striatum and the midbrain of male offspring, respectively. Results showed that maternal morphine administration dramatically increased anxiety-like and morphine place preference behaviors in offspring. Also, ISO condition aggravated these behavioral outcomes. While, rearing in EE could attenuate anxiety and morphine conditioning in pups. At molecular levels, maternal morphine exposure and social isolation markedly increased both of ΔFosB and μ-opioid receptor proteins expression. However, rearing in the EE declined ΔFosB protein expression. Together, these findings help to elucidate long lasting impacts of early life morphine exposure and rearing environment on the behavioral and molecular profile of addicted individuals.

Recalled Parental Bonding Interacts with Oxytocin Receptor Gene Polymorphism in Modulating Anxiety and Avoidance in Adult Relationships

Early interactions with significant individuals affect social experience throughout the course of a lifetime, as a repeated and prolonged perception of different levels of care, independence, or control influences the modulation of emotional regulatory processes. As many factors play a role in shaping the expectations and features of social interaction, in this study, we considered the influence of parental bonding and genetic allelic variation of oxytocin receptor gene polymorphism (rs53576) over levels of experienced anxiety and avoidance in 313 young adults belonging to two different cultural contexts, namely Italy and Singapore. Results highlighted a major effect of maternal characteristics, care, and overprotection, with differences between the two cultural groups. Additionally, the interaction between rs53576 and maternal overprotection suggested different environmental susceptibility in the Italian sample and the Singaporean one. Implications for clinical work and future steps are described in the Conclusion.

Sex-dependent and ontogenetic effects of low dose ethanol on social behavioral deficits induced by mouse maternal separation

Early life stress can induce lifelong emotional and social behavioral deficits that may in some cases be alleviated by drugs or alcohol. A model for early life stress, rodent maternal separation, recapitulates these behavioral sequelae, which are not limited to potentiated anxiety-like behavior, attenuated social motivation, and altered reward-seeking. Here we employed mouse maternal separation with early weaning (MSEW), consisting of pup-dam separation lasting 4-8 hours on postnatal days (PD) 2-16, with early weaning on PD 17. Prior MSEW studies have limited subjects by age or sex, so we more comprehensively investigated MSEW effects in both sexes, during adolescence and adulthood. We found universal effects of MSEW to include lifelong enhancement of anxiety-like and despair behavior, as well as deficits in social motivation. We also observed some sex-dependent effects of MSEW, namely that female MSEW mice exhibited social habituation to a greater degree than their male counterparts. Low dose ethanol administration had no major effects on the social behavior of non-stressed mice. But interestingly, MSEW-induced social habituation was counteracted by low dose ethanol in adolescent female mice, and potentiated in adolescent male mice. These effects were absent in adult animals, suggesting that ethanol may exert differential effects on the developing brain in such a manner to produce age-, sex-, and stress-dependent effects upon social behavior. Together, results indicate that MSEW reliably produces long-lasting impairments in emotional and social behaviors in both sexes and across the lifespan, but may exert more salient social behavioral effects on female animals.

Predator odor exposure increases social contact in adolescents and parental behavior in adulthood in Brandt's voles

Research suggests that predation risk during adolescence can program adult stress response and emotional behavior; however, little is known about the short-term and lasting residual effects of this experience on social behavior. We explored this concept in social Brandt's voles (Lasiopodomys brandtii). Adolescent male and female voles were exposed to distilled water, rabbit urine (as a non-predator stimulus), and cat urine for 60 min daily from postnatal day (PND) 28-49. Social play tests were conducted immediately following exposure on PND 28, 35, 42, and 49. In the social play test, repeated cat odor (CO) exposure enhanced the contact behavior of voles with their cagemate. Adolescent exposure to CO did not affect behavioral responses toward unrelated pups in the alloparental behavior test or same-sex individuals in the social interaction test. However, exposure to CO significantly enhanced the licking/grooming behavior of voles towards their own pups in the home cage parental behavior test. Repeated CO exposure significantly inhibited weight gain in male voles during adolescence. This effect was transmitted to the next generation, with lower weight gain in offspring before weaning. Following repeated CO exposure, males tended to have more female offspring whereas females produced more offspring, suggesting an adaptive strategy to increase inclusive fitness under predatory risk. These findings demonstrate that adolescent exposure to predatory risk augments adolescent social contact and adult parental behavior and suggest a role for improved inclusive fitness in mediating long-term outcomes.

Inhibition of Fatty Acid Amide Hydrolase (FAAH) During Adolescence and Exposure to Early Life Stress may Exacerbate Depression-like Behaviors in Male and Female Rats

Early-life stress (ELS) is associated with later onset of depression. Early cannabis use may be a risk factor that interacts with environmental factors to increase the risk of psychopathologies. We aimed to examine the long-term effects of ELS on depression- and anxiety-like behavior, and examine whether chronic fatty acid amide hydrolase (FAAH) inhibition during mid-adolescence could ameliorate or exacerbate ELS effects on behavior. Male and female rats were exposed to ELS during post-natal days (P) 7-14, injected with the FAAH inhibitor URB597 (0.4 mg/kg, i.p.) or vehicle for 2 weeks during mid-adolescence (P30-45) or late-adolescence (P45-60). Rats were tested in adulthood for behavior and alterations in CB1 receptors (CB1r) and glucocorticoid receptors (GRs) in the brains' stress circuit. ELS produced decreased social preference, impaired social recognition, increased learned helplessness and anxiety-like behavior. Administering URB597 during mid-adolescence did not prevent the deleterious long-term effects of ELS on behavior in males and females. When URB597 was administered during late-adolescence, it ameliorated ELS-induced depression- and anxiety-like behavior. Moreover, in males, ELS and URB597 decreased CB1r levels in the prefrontal cortex (PFC) and CA1 and GRs in the PFC and basolateral amygdala (BLA). In females, ELS and URB decreased CB1r in the BLA and GRs in the CA1 and BLA. The findings suggest that mid-adolescence, as opposed to late-adolescence, may not be a potential developmental period for chronic treatment with FAAH inhibitors and that sex-dependent alterations in CB1r and GRs expression in the BLA-PFC-CA1 circuit may contribute to the depressive behavioral phenotype.

Prenatal hypoxia predisposes vascular functional and structural changes associated with oxidative stress damage and depressive behavior in adult offspring male rats

Intrauterine hypoxia-ischemia (HI) provides a strong stimulus for a developmental origin of both the central nervous system and cardiovascular diseases. This study aimed to investigate vascular functional and structural changes, oxidative stress damage, and behavioral alterations in adult male offspring submitted to HI during pregnancy. The pregnant Wistar rats had a uterine artery clamped for 45 min on the 18th gestational day, submitting the offspring to hypoxic-ischemic conditions. The Sham group passed to the same surgical procedure as the HI rats, without occlusion of the maternal uterine artery, and the controls consisted of non-manipulated healthy animals. After weaning, the male pups were divided into three groups: control, sham, and HI, according to the maternal procedure. At postnatal day 90 (P90), the adult male offspring performed the open field and forced swim tests. In P119, the rats had their blood pressure checked and were euthanized. Prenatal HI induced a depressive behavior in adult male offspring associated with a reduced vasodilator response to acetylcholine in perfused mesenteric arterial bed, and reduced superoxide dismutase and glutathione peroxidase activities in the aorta compared to control and sham groups. Prenatal HI also increased the vasoconstrictor response to norepinephrine, the media thickness, collagen deposition, and the oxidative damage in the aorta from adult male offspring compared to control and sham groups. Our results suggest an association among prenatal HI and adult vascular structural and functional changes, oxidative stress damage, and depressive behavior.

The effects of maternal separation stress experienced by parents on male reproductive potential in the next generation

There is little information available about the effects of early-life parental stress on the reproductive potential of the next generation. The aim of this study is to examine the reproductive potential of male mice whose parents experienced maternal separation stress. In the present study, male first-generation offspring from parents were undergone of maternal separation (MS) were examined. Sperm characteristics, histological changes in testis, reactive oxygen species (ROS) production, expression of apoptotic and inflammatory genes and proteins were assessed. Findings showed that MS experienced by parents significantly decreased the morphology and viability of spermatozoa. Furthermore, significant changes in testicular tissue histology were observed. Increased production of ROS, decreased glutathione peroxidase (GPX) and adenosine triphosphate (ATP) concentrations, and affected the expression of genes and cytokines involved in inflammation. Finally, the mean percentage of caspase-1 and NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) positive cells was significantly higher in first-generation group. MS experienced by parents may negatively affect the reproduction of first generation offspring.

The effect of premature maternal separation on distress vocalizations and activity in kittens (Felis catus) during a brief nest separation

It is unknown how premature maternal separation affects the responses of kittens to potentially stressful events. In the United States, thousands of kittens are orphaned each year due to death of the queen, neglect, or accidental separation by humans. Neonatal mammals emit distress calls and increase locomotion when socially isolated, suggesting that being separated from the nest is a stressful event. Increased vocalization and activity of isolated neonates may aid maternal retrieval or relocation of the nest. In the current study, we assessed the effects of early maternal separation on later vocalizations and activity of 49 kittens (28 orphaned, 21 mother-reared; 23 female, 26 male) from 11 litters (5 mothered, 6 orphaned) during an open field test when the kittens were one and three weeks of age. We conducted a total of 79 trials. Each kitten was placed individually in a 1-meter diameter pen away from the rest of the litter and/or mother for two minutes. The number of calls emitted and total activity (in seconds) were recorded for each kitten on every trial. We assessed the effects of age, sex, orphan status, and interactions between orphan status with sex and age on activity and vocalizations. Orphaned kittens were more active than mother-reared kittens at both times (t(46) = 4.62, p < 0.001), with an interaction between age and orphan status (t(28) = -2.84, p = 0.008). Orphaned kittens emitted more vocalizations at both times (Z = 2.38, p = 0.018), with an interaction between age and orphan status (Z = -3.18, p = 0.001). Orphaned kittens showed increased activity and vocalizations in response to a brief nest separation compared to mother-reared kittens. This effect was still present after over two weeks of maternal separation, suggesting that maternal separation may lead to long-term changes in stress responses. Future research should explore if such effects of maternal separation are present in older kittens or adult cats.

Sensitive phases in the development of rodent social behavior

Here, we summarize recent advances on how environmental influences during sensitive phases alter the social behavioral phenotype of rodents later in life. Current studies support the view that the prenatal, early postnatal and adolescent periods of life can be regarded as sensitive phases. Environmental cues acting on the organism during these phases have a wide variety of effects on adult social behavior. One pattern that emerges across species and sensitive phases is that adversity tends to reduce social interactions and particularly affiliative social behavior. Concerning underlying mechanisms, various hormones can be involved; however, glucocorticoids frequently serve as the signal instigating plasticity. There is also increasing appreciation of non-endocrine mechanisms, specifically epigenetics and the microbiome. Concerning function, some evidence exists that sensitive phase outcomes adjust the individual's social phenotype to the nature of the social environment to be present during adulthood and breeding, though additional empirical support is still needed.

Catechol-O-methyltransferase Val158Met Genotype and Early-Life Family Adversity Interactively Affect Attention-Deficit Hyperactivity Symptoms Across Childhood

Attention-deficit hyperactivity disorder (ADHD) is among the most commonly diagnosed psychiatric disorders of childhood. The dopaminergic system has been shown to have substantial effects on its etiology, with both functional Catechol-O-methyltransferase (COMT) Val158Met genotype and early-life environmental adversity involved in the risk of inattention and hyperactivity/impulsivity symptoms. In this prospective longitudinal study, we examined for the first time the impact of proximal and distal early-life family adversity and COMT Val158Met polymorphism gene - both the direct and the interactive effects, on children's ADHD symptoms across childhood. Data came from the Family Life Project, a prospective longitudinal study of 1,292 children and families in high poverty from birth to 11 years. In infancy, data regarding socioeconomic (SES)-risk-factors, observed-caregiving behaviors, and DNA genotyping were collected. In early and middle childhood teachers rated the occurrence and severity of the child's ADHD symptoms. Multilevel growth curve models revealed independent effects of COMT, early-life SES-risk and negative caregiving on ADHD symptoms in early and middle childhood. Significant gene-environment interactions were found, indicating that overall, carriers of at least one COMT158Met allele were more sensitive to early-life adversity, showing higher inattention and hyperactivity/impulsivity symptoms severity in childhood when exposed to high SES-risk factors in infancy, compared to Val-Val carriers. Findings provide new insights into the complex etiology of ADHD and underline the need for further investigation of the neuronal mechanisms underlying gene-environment interactions. Findings might have implications for prevention and intervention strategies with a focus on early-life family relationships in genetically at-risk children.

Chemogenetic manipulation of the bed nucleus of the stria terminalis counteracts social behavioral deficits induced by early life stress in C57BL/6J mice

Trauma during critical periods of development can induce long-lasting adverse effects. To study neural aberrations resulting from early life stress (ELS), many studies utilize rodent maternal separation, whereby pups are intermittently deprived of maternal care necessary for proper development. This can produce adulthood behavioral deficits related to anxiety, reward, and social behavior. The bed nucleus of the stria terminalis (BNST) encodes aspects of anxiety-like and social behaviors, and also undergoes developmental maturation during the early postnatal period, rendering it vulnerable to effects of ELS. Mice underwent maternal separation (separation 4 hr/day during postnatal day (PD)2-5 and 8 hr/day on PD6-16) with early weaning on PD17, which induced behavioral deficits in adulthood performance on two-part social interaction task designed to test social motivation (choice between a same-sex novel conspecific or an empty cup) and social novelty preference (choice between the original-novel conspecific vs. a new-novel conspecific). We used chemogenetics to non-selectively silence or activate neurons in the BNST to examine its role in social motivation and social novelty preference, in mice with or without the history of ELS. Manipulation of BNST produced differing social behavior effects in non-stressed versus ELS mice; social motivation was decreased in non-stressed mice following BNST activation, but unchanged following BNST silencing, while ELS mice showed no change in social behavior after BNST activation, but exhibited enhancement of social motivation-for which they were deficient prior-following BNST silencing. Findings emphasize the BNST as a potential therapeutic target for social anxiety disorders instigated by childhood trauma.

Oxytocin receptor gene and parental bonding modulate prefrontal responses to cries: a NIRS Study

The ability to interpret and regulate emotions relies on experiences of emotional socialization, obtained firstly through the interaction with the parents, and on genetic features that affect how individuals take on social situations. Evidence from the genetic field states that specific allelic variations of the oxytocin receptor gene polymorphisms regulate physiological modulation of human behavior, especially concerning responses to social cues and affiliative behaviors. Starting from this gene-by-environment interaction frame, we assessed 102 young adults for OXTr rs53576 and rs2254298, recalled parental bonding (using the Parental Bonding Instrument), and recorded participants' neural responses to social stressors using Near InfraRed Spectroscopy (NIRS). The results highlight that higher genetic susceptibility (G/G homozygous) to familiar context and positive early life interactions modulate more optimal neural responses to general social cues, in terms of promptness to action. With regards to the dimensions of parental bonding, we found lateralized effects, with greater activation in the right prefrontal cortex for Care subscales, and on the left side of the prefrontal cortex for Overprotection. Results provide evidence to understand the neurological mechanisms behind the negative impact of poor parenting practices on the child.

Repeated predator odor exposure alters maternal behavior of postpartum Brandt's voles and offspring's locomotor activity

Recent evidence indicates that predation risk plays a special role in the rodent behavior of dams and offspring, but little is known about the effect of maternal exposure to the predator cues in the absence of pups. Here, we assessed the effects of repeated predator odor exposure on various maternal responses in postpartum Brandt's voles (Lasiopodomys brandtii). We also examined offspring's behavioral response to a novel environment. Only mother voles were exposed to distilled water, rabbit urine and cat urine for 60 min daily from postpartum day (PP) 1-18. Maternal behavior was immediately tested after these exposures on PP1, 3, 6, 9 and 18. Repeated cat odor (CO) and rabbit odor (RO) exposure disrupted hovering over pups in a time-dependent fashion. Repeated CO exposure also time-dependently disrupted pup retrieval, whereas RO exposure induced long-term reduction in pup licking. Juvenile offspring of CO-exposed mothers showed increased locomotor activity and decreased rearing in the open field at postnatal day 30. These findings demonstrated that maternal exposure to predator or non-predator odors had a disruptive effect on the maternal behavior of Brandt's voles when only the mother was exposed to these odors, and that the adversity experience with predation risk significantly impacted the behavioral development of offspring. Future work should explore possible behavioral mechanisms, such as the effect of predation risk, on the dams' emotional processing or pup preference.

Making headway towards understanding how epigenetic mechanisms contribute to early-life effects

It has become clear that in addition to the DNA sequence there is another layer of information, termed epigenetic modifications, that can influence phenotypes and traits. In particular, environmental epigenomics, which addresses the effect of the environment on the epigenome and human health, is becoming an area of great interest for many researchers working in different scientific fields. In this review, we will consider the current evidence that early-life environmental signals can have long-term effects on the epigenome. We will further evaluate how recent technological advances may enable us to unravel the molecular mechanisms underlying these phenomena, which will be crucial for understanding heritability in health and disease. This article is part of the theme issue 'Developing differences: early-life effects and evolutionary medicine'.

Effects of Dark Brooder Rearing and Age on Hypothalamic Vasotocin and Feather Corticosterone Levels in Laying Hens

Chickens cannot independently thermoregulate at hatch and lack opportunity to behaviorally thermoregulate with a hen in the egg layer industry, thus barns are heated to thermoneutral temperatures. Dark brooders are low-energy-consuming hot plates, which may be environmentally advantageous while providing welfare-enhancing aspects of maternal care (i.e., shelter and separation of active and inactive individuals). Dark brooder use has been demonstrated to decrease injurious pecking and mortality well into the production period of layers. To further understand hen development around lay onset and effects of dark brooders on the brain and HPA-axis, we examined effects of rearing with dark brooders on expression of vasotocin (AVT) in the hypothalamus and corticosterone (CORT) in the feathers of in total 48 layer Isa Warren hens at 16 w and 28 w of age (n = 12 per age and treatment). An age-dependent decreased number of AVT-positive neurons was seen in the medial preoptic area, medial preoptic nucleus, paraventricular nucleus, rostral part (prepeduncular hypothalamus), and lateral preoptic area. Trends to effects of brooder rearing were found in both anteromedial preoptic nucleus and supraoptic nucleus, with dark brooder reared animals showing higher mean counts of AVT-positive neurons in both areas. No interactions between brooder raising and age were observed in AVT-positive neuron count. CORT levels were higher in primary wing feathers from 28 week old hens than in those from 16 week hens. No main effects of rearing with dark brooders or interactions between age and treatment were found on CORT levels. The age-dependent effects seen in the hypothalamus and CORT aids in further understanding of the development of chickens around puberty. The use of brooders tended to increase AVT expression in the anteromedial preoptic nucleus and supraoptic nucleus, an indication that dark brooder rearing may affect physiological responses regulated by these areas. The lack of effect of dark brooders on CORT in feathers is at the least an indication that the use of dark brooders is not stressful; in combination with the benefits of dark brooders on injurious pecking, fearfulness and early mortality, this pleads for the use of dark brooders in on-farm situations.

Improving mental health and physiological stress responses in mothers following traumatic childbirth and in their infants: study protocol for the Swiss TrAumatic biRth Trial (START)

INTRODUCTION

Emergency caesarean section (ECS) qualifies as a psychological trauma, which may result in postnatal post-traumatic stress disorder (PTSD). Maternal PTSD may not only have a significant negative impact on mother-infant interactions, but also on long-term infant development. The partner's mental health may also affect infant development. Evidence-based early interventions to prevent the development of postpartum PTSD in mothers are lacking. Immediately after a traumatic event, memory formation is vulnerable to interference. There is accumulating evidence that a brief behavioural intervention including a visuospatial task may result in a reduction in intrusive memories of the trauma.

METHODS AND ANALYSIS

This study protocol describes a double-blind multicentre randomised controlled phase III trial testing an early brief maternal intervention including the computer game 'Tetris' on intrusive memories of the ECS trauma (≤1 week) and PTSD symptoms (6 weeks, primary outcome) of 144 women following an ECS. The intervention group will carry out a brief behavioural procedure including playing Tetris. The attention-placebo control group will complete a brief written activity log. Both simple cognitive tasks will be completed within the first 6 hours following traumatic childbirth. The intervention is delivered by midwives/nurses in the maternity unit.The primary outcome will be differences in the presence and severity of maternal PTSD symptoms between the intervention and the attention-placebo control group at 6 weeks post partum. Secondary outcomes will be physiological stress and psychological vulnerability, mother-infant interaction and infant developmental outcomes. Other outcomes will be psychological vulnerability and physiological regulation of the partner and their bonding with the infant, as well as the number of intrusive memories of the event.

ETHICS AND DISSEMINATION

Ethical approval was granted by the Human Research Ethics Committee of the Canton de Vaud (study number 2017-02142). Dissemination of results will occur via national and international conferences, in peer-reviewed journals, public conferences and social media.

TRIAL REGISTRATION NUMBER

NCT03576586.

Age-dependent differences on neurochemistry and behavior in rats raised with low and high levels of maternal care

In laboratory rats, naturally-occurring variations in maternal care have been used to study the neurobehavioral consequences of maternal nursing and to model the early-life adversity associated with many psychiatric disorders. This study aimed to determine the role of maternal care on behavior and monoamine concentrations at the prepubertal and young adulthood ages. We observed the licking/grooming (LG) behavior of Sprague-Dawley (SD) dams and assigned the litter to either low (LLG) or high (HLG) LG groups. Behavioral testing in the male offspring consisted of the open-field test, the elevated plus-maze, and the forced swimming test. Afterward, neurotransmitters contents were measured in the prefrontal cortex, the nucleus accumbens, the amygdala, and the hippocampus. We found that at the prepubertal stage, the effects of maternal care were only noticeable in the elevated plus-maze and the serotonin concentration in the nucleus accumbens. At adulthood, body weight and monoamines contents increased substantially in LLG rats. Specifically, they showed higher serotonin contents with a reduced turnover in almost all brain regions, followed by higher contents of norepinephrine and dopamine, especially in the nucleus accumbens. Changes in monoamines concentrations seem to be independent of the behavioral phenotype shaped by variations in maternal care, as behavioral effects were somewhat weak in both experiments. If higher monoamines contents in LLG rats represent an adaptive mechanism to deal with further adverse events, the behavioral paradigms used here were insufficiently challenging to bring out noticeable differences, at least in SD rats.

Epigenetic dynamics in infancy and the impact of maternal engagement

The contribution of nature versus nurture to the development of human behavior has been debated for centuries. Here, we offer a piece to this complex puzzle by identifying the human endogenous oxytocin system-known for its critical role in mammalian sociality-as a system sensitive to its early environment and subject to epigenetic change. Recent animal work suggests that early parental care is associated with changes in DNA methylation of conserved regulatory sites within the oxytocin receptor gene (OXTRm). Through dyadic modeling of behavior and OXTRm status across the first year and a half of life, we translated these findings to 101 human mother-infant dyads. We show that OXTRm is dynamic in infancy and its change is predicted by maternal engagement and reflective of behavioral temperament. We provide evidence for an early window of environmental epigenetic regulation of the oxytocin system, facilitating the emergence of individual differences in human behavior.

From maternal tending to adolescent befriending: The adolescent transition of social support

Attachment theory holds that parental relationships have lifelong effects on offspring social lives. The tend-and-befriend hypothesis posits that female friendships among humans evolved as part of a primate-wide coping mechanism to mediate stress by relying on social support. Here we bridge developmental and evolutionary frameworks to examine adolescent girls' perception of their reliance on female friendship for social support, how perceptions of parental relationships affect peer relationships, and the extent to which parent and peer relationships buffer depressive symptoms. We predict perceived maternal relationship quality will be positively associated with close female friendships, and maternal relationships, paternal relationships, and female friendship will buffer depressive symptoms. Participants were adolescent girls from a summer science camp (N = 95). Participants filled out demographic information, social network surveys, the Parent-Adolescent Communication Scale, and the Center for Epidemiology Depression Scale. Data was analyzed with Pearson's correlations, t tests, and path analysis. Adolescent girls with few female friends, compared with girls who had more than two very close female friends, experienced more depressive symptoms (t = 3.382, p = .001, D = 0.784). Adolescent girls with few female friends experienced more depressive symptoms compared to girls with two or more very close female friends (t = 3.382, p = .001, D = 0.784). Stronger maternal and paternal relationships were associated with having more female friends (maternal: t = -3.213, p = .003, D = 0.837; paternal: t = -2.432; p = .017). In the path analysis model, only maternal relationship quality significantly predicted female friendship category (β = .33, CR = 2.770, p < .006). Furthermore, participants with two or more very close female friends and higher paternal relationship quality had significantly fewer depressive symptoms (friends; β = -.19, CR = -2.112, p = .035; paternal: β = -.33, CR = -3.220, p < .001), and older participants had more depressive symptoms (β = .17, CR = -1.931, p = .036). These results provide additional support for the tend-and-befriend hypothesis, suggesting that maternal tending sets the stage for close female friendships.