Dysfunctional nurturing behavior in rat dams with limited access to nesting material: a clinically relevant model for early-life stress

Postpartum scarcity-adversity increases adverse caregiving in the absence of basal corticosterone elevation

Maternal behavior is disturbed by exposure to environmental adversity, including resource scarcity, which can impair maternal care and increase adverse caregiving behaviors like abuse and maltreatment. In rats, exposure to resource scarcity disrupts mother-infant interactions and results in adverse pup-directed maternal behaviors. These changes in maternal behavior are thought to be due to hyperactivity within the hypothalamic-pituitary-adrenal (HPA)-axis, which mediates the stress response. In accordance, upregulation of HPA-axis function is sufficient to drive changes in maternal behavior in rodents. Based on these data, we hypothesized that scarcity-adversity induced changes in maternal behavior would be associated with HPA-axis hyperactivity, as indexed by elevated basal levels of the stress hormone corticosterone (CORT) in rat dams. To test this, we employed a scarcity-adversity paradigm based on creating an impoverished cage environment during postpartum days (PD) 2-9 and examined effects on naturalistic maternal behaviors and basal fecal boli CORT levels (PD 3, PD 5, PD 7) or basal and stress-induced serum CORT levels (PD 9). Surprisingly, rat dams exposed to scarcity-adversity exhibited increases in adverse pup-directed behaviors (e.g., stepping, dragging, shoving) but no elevations in basal or stress-induced CORT levels at any of the time-points assessed. These findings suggest that scarcity-adversity can increase adverse caregiving in a CORT-independent manner. Thus, increases in basal CORT levels are not necessary to induce aberrant maternal behavior in the scarcity-adversity paradigm.

The evolving neurobiology of early-life stress

Because early-life stress is common and constitutes a strong risk factor for cognitive and mental health disorders, it has been the focus of a multitude of studies in humans and experimental models. Yet, we have an incomplete understanding of what is perceived as stressful by the developing brain, what aspects of stress influence brain maturation, what developmental ages are particularly vulnerable to stress, which molecules mediate the effects of stress on brain operations, and how transient stressful experiences can lead to enduring emotional and cognitive dysfunctions. Here, we discuss these themes, highlight the challenges and progress in resolving them, and propose new concepts and avenues for future research.

Female rats exposed to early life scarcity-adversity are resilient to later life changes in maternal behavior

In both humans and rodents, maternal care is disturbed by exposure to environmental adversity, including low resource conditions (i.e., poverty, scarcity). Maternal adversity is associated with compromised quality of mother-infant attachment and increased adverse caregiving patterns such as abuse, maltreatment and/or neglect, which disrupt behavioral development in the female offspring. Importantly, maternal behavior is thought to be an intergenerational behavior, meaning that the quality of maternal care a female experiences during early life is thought to influence the quality of care she will display towards her own offspring when she becomes a mother. Here, we tested this idea by employing a rodent model of postpartum environmental adversity based on creating an impoverished nesting environment during postpartum days (PD) 2-9, which disrupts mother-infant interactions and is thought to upregulate hypothalamic-pituitary-adrenal (HPA)-axis function in the pups. We examined the impact of this form of early life adversity on pup stress hormone (i.e., corticosterone- CORT) levels by collecting trunk blood and later life maternal behavior by conducting maternal behavior observations and maternal motivation tests (e.g., T-Maze, pup retrieval, pup-associated conditioned place preference) in the first filial (F1) generation. We report no impact of early life scarcity-adversity/adverse caregiving on pup CORT levels or later life naturalistic or motivated maternal behaviors. In sum, we show that female rat pups who experienced adverse caregiving during early life showed resilience towards developing negative caregiving patterns, as they did not perpetuate the same aberrant maternal behavior that they received from their mothers.

Offspring genetic diversity regulates rearing experiences that predict differential susceptibility to Chd8 haploinsufficiency

Mouse models of human disease focus on determining the direct impact of genetic mutations on phenotypes related to clinical presentations. For example, loss of function mutations in the autism-associated CHD8 gene is highly penetrant for trait and behavioral abnormalities in children, but there is substantial clinical heterogeneity in the occurrence and extent of disruptions between individuals. Using a large genetic reference panel of mice, we recently showed that genetic background strongly regulates variability in trait disruptions caused by Chd8 haploinsufficiency. Here, we hypothesized that genetics could also impact the variability in response to early life experiences, thus contributing to differential susceptibility to neurodevelopmental disorders. To examine how genetic diversity impacts rearing experience, we systematically observed the behavior of genetically diverse offspring raised by genetically identical mothers. The results reveal strain differences in pup and maternal behaviors. Machine learning analysis reveals that early life litter experiences are strong predictors of sex-dependent postweaning social, anxiety-like, and cognitive trait disruptions due to Chd8 haploinsufficiency. The study suggests that offspring phenotypes in mutant models of disease are due to a combination of heritable and early experience factors, demonstrating the utility of incorporating genetic diversity in studies to model the mechanisms that underlie the heterogeneity of disrupted phenotypes in neurodevelopmental disorders.

Early-life stress sensitizes response to future stress: Evidence and mechanisms

Early-life stress sensitizes individuals to additional stressors and increases lifetime risk for mood and anxiety disorders. Research in both human populations and rodent models of early-life stress have sought to determine how different types of stressors contribute to vulnerability, and whether there are developmental sensitive periods for such effects. Although differences in the type and timing of rodent early-life stress paradigms have led to differences in specific behavioral outcomes, this complexity is present among humans as well. Robust rodent research now shows how early-life stress increases sensitivity to future stressors at behavioral, neural circuit, and molecular levels. These recent discoveries are laying the foundation for translation to more effective interventions relevant for those who experienced childhood stress and trauma.

Infant Maltreatment Induces Early Alterations in Adrenal Glands and Stress Response in Juvenile Rat Offspring

Chronic stressors, such as infant maltreatment during early development, can have long-lasting effects on an individual's health and stress-coping abilities across the lifespan. In this study, we applied the scarcity-adversity model (SAM) to Wistar rats from postnatal days (PND) 8 to 12 to evaluate the impact of scarcity condition on adrenal glands morphology and stress response in juvenile offspring (PND 21-35) of both sexes. Our results demonstrate that SAM exposure leads to significant alterations in the adrenal glands of offspring. Notably, the cortex-to-medulla ratio was reduced in SAM pups starting at PND 28. Morphological analysis of the adrenal cortex revealed an increased thickness of the undifferentiated zone, suggesting enhanced cell proliferation, alongside a transient reduction in the thickness of the zona fasciculata, where glucocorticoid-synthesizing cells are located. Additionally, we observed a reduction in the cytoplasmic diameter of zona fasciculata cells, coupled with an increase in the thickness of blood capillaries in this region in SAM offspring of both sexes. An increase in BrdU + cells in the cortex at PND 28 was observed in male SAM pups, but not in females. Endocrine assessments revealed a marked increase in corticosterone levels following stress induced by movement restriction in juvenile SAM offspring of both sexes. In conclusion, our findings underscore the significant impact of early-life stress on adrenal gland morphology and stress responsiveness, with potential long-term consequences for health and stress-coping mechanisms in offspring.

Sex-Specific Outcomes in a Rat Model of Early-Life Stress Due to Adverse Caregiving

Early parental care is critical for the development of cortico-limbic circuits regulating stress responses and emotional well-being. Conversely, infant maltreatment can increase susceptibility to mood disorders-such as anxiety and depression-and impair stress-coping abilities. Here, we employed the Scarcity-Adversity Model (SAM) in rats, limiting nesting resources from postnatal days 8-12, to examine its effects on maternal and adult offspring behavior. SAM-exposed mothers exhibited fragmented care and increased violence towards pups. By postpartum day (PPD) 13, maternal fecal corticosterone metabolites (FCM) were elevated, indicating heightened stress. At weaning, SAM dams also showed increased anxiety-like behavior in the Elevated Plus Maze (EPM), suggesting significant emotional alterations. In adulthood, SAM-exposed offspring underwent anxiogenic tests. Both male and female SAM offspring showed increased latency to enter open arms and reduced risk-assessment in the EPM, though females displayed anxiolytic-like behavior in the Light-Dark Box. Male SAM rats had reduced locomotion in the Open Field, earlier onset and increased immobility in the Forced Swim, and increased latency to groom in the Sucrose Splash. When exposed to acute stress, male SAM rats had lower FCM levels, consistent with their passive stress reactivity. These findings confirm SAM induces long-lasting, sex-specific changes in risk-taking, novelty responsiveness, and stress reactions, underscoring the importance of early nurturing in promoting well-being and reducing psychopathological risk.

Peripartum buprenorphine and oxycodone exposure impair maternal behavior and increase neuroinflammation in new mother rats

7 % of pregnant people use opioids. Opioid use during pregnancy can negatively impact maternal and offspring health. Medications for opioid use disorder (MOUD), commonly buprenorphine, are the recommended treatment for opioid use disorder during pregnancy to prevent cycles of withdrawal and relapse. In addition to effects on opioid receptors, opioids have strong binding affinity to toll-like receptor (TLR) 4, an immune cell receptor, and thereby impact neuroinflammatory signaling. We have previously shown that neuroimmune alterations are important for the display of maternal behavior. Here, we used a rodent model to assess the impact of chronic peripartum opioid exposure or MOUD on maternal caregiving and neuroinflammation in the postpartum brain. Female rats were exposed to vehicle (VEH), buprenorphine (BUP) to model MOUD, or oxycodone (OXY), to model peripartum drug use, before, during, and after pregnancy. Opioid exposure reduced gestation length and maternal weight gain. Postpartum maternal caretaking behaviors, including pup retrieval, huddling and nursing, and pup-directed sniffing and licking, were reduced in opioid-exposed mothers. Following behavioral testing, tissue was collected from brain regions important for maternal caretaking, including the prefrontal cortex (PFC), nucleus accumbens (NAc), preoptic area (POA), amygdala (AMY), and periaqueductal grey (PAG). Immunofluorescent labeling showed that BUP increased astrocyte labeling, while OXY increased microglia labeling in the PAG, but not other regions. Gene expression analysis also showed regional and treatment differences in immune transcripts. BUP and OXY increased TLR4 in the PFC. BUP increased TNF in the NAc but decreased IL1β in the POA. OXY increased CD68 in the POA, and IL1β, TNF, and TLR4 in the PAG. Together, these results provide novel evidence of peripartum neuroimmune alterations following chronic opioid exposure that could be mediating maternal care deficits. This work provides a foundation to explore the extent to which modulation of neuroimmune activation may be a potential intervention for caregiving deficits in mothers exposed to opioids during pregnancy.

Early-life enrichment in American mink (Neogale vison): Enrichment of the perinatal environment improves maternal nest building and reduces stereotypic behaviour

Pens for farmed mink (Neogale vison) commonly include separate nesting areas to provide privacy and warmth in the perinatal period. However, standard bedding materials may not be sufficient to allow intrinsically motivated nest-building behaviours in dams. Further, these materials may not produce optimal nest structures for the rearing of kits. In the present study, we provided extra, relatively high-quality nest-building materials and a chewable sisal rope enrichment for mink dams in the perinatal period (a group enriched at whelping; EW). The effects of these enrichments on various measures of welfare and maternal behaviour were compared to those of mink dams in standard housing (SH) and mink dams whose kits were enriched later in development (EK). EW dams performed less stereotypic behaviour and built higher quality nests than dams of other housing conditions, although dams' basal faecal cortisol metabolite levels (FCM) were not affected. The stress responsiveness of these dams' offspring was later assessed by sampling FCM before and after a handling event, however, this event did not appear to induce a measurable stress response and thus no conclusions could be drawn regarding effects of perinatal enrichment on HPA-axis development. Overall, provision of higher quality nest-building materials and a chewable rope enrichment benefited dam stereotypic behaviour and nest building in the perinatal period. We present suggestions for future studies to further investigate whether perinatal enrichment can impact maternal care and offspring HPA-axis development in mink.

Methods for Modeling Early Life Stress in Rodents

Animal models of early life stress/adversity (ELS) have provided a foundation from which our understanding of the psychoneuroimmunology of childhood trauma has expanded over recent decades. Rodent models are a cornerstone of the ELS literature with many studies utilizing paradigms based on early life separation/deprivation protocols and manipulating the cage environment. However, no animal model is perfect. In particular, the lack of standardization across ELS models has led to inconsistent results and raised questions regarding the translational value of common preclinical models. In this chapter, we present an overview of the history of ELS rodent models and discuss considerations relevant to the ongoing efforts to both improve existing models and generate novel paradigms to meet the evolving needs of molecular- and mechanism-based ELS research.

Mothering matters: Towards a better understanding of disrupted infant-caregiver relationships in both mother and offspring

The mother-infant bond is among the strongest social relationships formed in humans and nonhuman mammals. As such, disrupted infant-caregiver relationships have the capacity to result in potent adverse effects not only in the offspring, but also in the mother. Here, I provide a brief overview of my prior work showing adversity-induced alterations in offspring and maternal behavioral and brain function. I also share my vision for future directions for developmental and maternal neurobiology research in the context of stress and/or adversity exposure.

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.

Stress and parental behaviors

In nearly all mammalian species, newborn pups are weak and vulnerable, relying heavily on care and protection from parents for survival. Thus, developmentally hardwired neural circuits are in place to ensure the timely expression of parental behaviors. Furthermore, several neurochemical systems, including estrogen, oxytocin, and dopamine, facilitate the emergence and expression of parental behaviors. However, stress can adversely affect these systems, impairing parental behaviors. In this review, we will summarize our current knowledge regarding the impact of stress on pup-directed behavior circuits that lead to infant neglect, abuse, and, in extreme cases, killing. We will discuss various stressors that influence parental behaviors at different life stages and how stress induces changes in the neurochemical systems that support parental care, ultimately leading to its poor performance.

FAAH Inhibition Reverses Depressive-like Behavior and Sex-Specific Neuroinflammatory Alterations Induced by Early Life Stress

Early life stress (ELS) increases predisposition to major depressive disorder (MDD), with neuroinflammation playing a crucial role. This study investigated the long-term effects of the fatty acid amide hydrolase (FAAH) inhibitor URB597 on ELS-induced depressive-like behavior and messenger RNA (mRNA) of pro-inflammatory cytokines in the medial prefrontal cortex (mPFC) and CA1 regions. We also assessed whether these gene expression alterations were present at the onset of URB597 treatment during late adolescence. ELS induced a depressive-like phenotype in adult male and female rats, which was reversed by URB597. In the mPFC, ELS downregulated nuclear factor kappa B1 (nfκb1) in both sexes, while URB597 normalized this expression exclusively in males. In females, ELS downregulated interleukin (il) 6 and tumor necrosis factor alpha (tnfα) but upregulated il1β and corticotropin-releasing factor (crf); URB597 normalized il6, il1β, and crf. In the CA1, ELS downregulated il1β and tnfα in males and upregulated il1β expression in females, which was reversed by URB597. Some of these effects began in late adolescence, including mPFC-nfκb1 expression in both sexes, mPFC-il6 and mPFC-il1β in females, CA1-il1β and CA1-tnfα in males, and CA1-il1β in females. These findings highlight URB597 as a therapeutic approach for reversing ELS-induced depressive-like behavior by associating with changes in the gene expression of neuroinflammatory cytokines, with notable sex differences.

Developmental functions of microglia: Impact of psychosocial and physiological early life stress

Microglia play numerous important roles in brain development. From early embryonic stages through adolescence, these immune cells influence neuronal genesis and maturation, guide connectivity, and shape brain circuits. They also interact with other glial cells and structures, influencing the brain's supportive microenvironment. While this central role makes microglia essential, it means that early life perturbations to microglia can have widespread effects on brain development, potentially resulting in long-lasting behavioral impairments. Here, we will focus on the effects of early life psychosocial versus physiological stressors in rodent models. Psychosocial stress refers to perceived threats that lead to stress axes activation, including prenatal stress, or chronic postnatal stress, including maternal separation and resource scarcity. Physiological stress refers to physical threats, including maternal immune activation, postnatal infection, and traumatic brain injury. Differing sources of early life stress have varied impacts on microglia, and these effects are moderated by factors such as developmental age, brain region, and sex. Overall, these stressors appear to either 1) upregulate basal microglia numbers and activity throughout the lifespan, while possibly blunting their responsivity to subsequent stressors, or 2) shift the developmental curve of microglia, resulting in differential timing and function, impacting the critical periods they govern. Either could contribute to behavioral dysfunctions that occur after the resolution of early life stress. Exploring how different stressors impact microglia, as well as how multiple stressors interact to alter microglia's developmental functions, could deepen our understanding of how early life stress changes the brain's developmental trajectory. This article is part of the Special Issue on "Microglia".

Enduring memory consequences of early-life stress / adversity: Structural, synaptic, molecular and epigenetic mechanisms

Adverse early life experiences are strongly associated with reduced cognitive function throughout life. The link is strong in many human studies, but these do not enable assigning causality, and the limited access to the live human brain can impede establishing the mechanisms by which early-life adversity (ELA) may induce cognitive problems. In experimental models, artificially imposed chronic ELA/stress results in deficits in hippocampus dependent memory as well as increased vulnerability to the deleterious effects of adult stress on memory. This causal relation of ELA and life-long memory impairments provides a framework to probe the mechanisms by which ELA may lead to human cognitive problems. Here we focus on the consequences of a one-week exposure to adversity during early postnatal life in the rodent, the spectrum of the ensuing memory deficits, and the mechanisms responsible. We highlight molecular, cellular and circuit mechanisms using convergent trans-disciplinary approaches aiming to enable translation of the discoveries in experimental models to the clinic.

Effects of Early Life Scarcity-Adversity on Maturational Milestones in Male and Female Rats

Although many studies have shown a long-term negative impact of early life adversity (ELA) in rodents, literature regarding its effects on maturational milestones in rats is scarce. Available evidence suggests that ELA interferes with normal growth and development in rodents and that effects may be sex-dependent even at an early age. In accordance, we hypothesized that early life scarcity-adversity would impair physical and reflex development in male and female rats. To test this, we used an early life resource scarcity paradigm based on reducing home cage bedding during postnatal days (PND) 2-9 and assessed physical landmarks by measuring weight gain, incisor presence, fur development, and eye opening. We also evaluated the impact of early life scarcity-adversity on developmental reflexes by measuring surface righting and grasp reflexes, negative geotaxis, cliff avoidance, bar holding, and auditory startle. Early life scarcity-adversity resulted in earlier complete lower incisor presence in males (PND 6), impaired surface righting (PND 6) and grasp reflexes (PND 8) in both sexes, and impaired cliff avoidance responses in females (PND 12). These results extend previous research examining the effects of ELA on developing male and female rodents by showing that it negatively impacts a subset of physical landmarks and developmental reflexes in a sex-dependent manner.

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.

Altered Patterns of Maternal Behavior Transitions in Rats Exposed to Limited Bedding and Nesting Material Paradigm

INTRODUCTION

Maternal care plays a fundamental role in early life, and the alteration of its patterns can negatively affect the developmental course of the offspring in a myriad of domains in both rats and humans. The limited bedding and nesting (LBN) protocol is an extensively used paradigm in rodents to address the impact of altered maternal behavior patterns on infants' neurodevelopment. Here, we explore the altered patterns of maternal care in rats in LBN conditions by describing sequences of transition between maternal behavior components using network analysis. Using this technique, we capture how often maternal behavior transitions take place during the LBN period and which behaviors play central roles in those transitions over time.

MATERIALS AND METHODS

Female rats and their pups were placed in standard and LBN housing conditions from Postpartum Days 2 to 9, during which maternal behavior was observed during the light and dark phases. We used inferential statistical analysis to compare the maternal behavior profiles of control and LBN dams, and network analysis was used to capture the altered sequence of maternal behavior transitions during the period of LBN.

RESULTS

Compared to control dams, LBN dams significantly increased their high crouch nursing posture during light/dark phases (p = 0.018), and the number of behavioral transitions increased only during the dark phase (p = 0.0004). Network analysis revealed specific altered patterns of behavioral transitions in LBN dams, characterized by the predominance of switches between active nursing postures during the first five days of the LBN protocol.

CONCLUSION

Nursing behavior was the most disrupted component of maternal behavior under the LBN protocol, mainly during the dark phase. Network analysis can complement and extend traditional methods to gain a more thorough understanding of maternal care strategies and behavioral patterns in LBN conditions and potential consequences for the offspring.

Neonatal limited bedding and nesting experience may lead to a sex-dependent increase in panic-like defensive behaviours in adult mice

In humans, adverse physical and/or psychological traumas in childhood may predispose to developing psychiatric disorders in adulthood, including panic disorder. To model early life adversity in mice, we subjected male and female C57BL/6 J mice to a limited bedding and nesting (LBN) protocol between postnatal days 2-9 and investigated its effect on responsiveness to panicogenic challenges in adulthood. Panic-like escape behaviour was assessed during exposure to a high concentration of CO2 (20%) or in the beetle mania task (BMT), used to model respiratory and non-respiratory-related types of panic respectively. Neonatal exposure to LBN increased panic-like jumping during the CO2 challenge in male but not female mice. In an initial pharmacological validation of the BMT as a panic-inducing paradigm, undirected jumping and horizontal escape behaviours were reduced significantly by the panicolytic alprazolam (0.05 and 0.1mg.kg-1 i.p.) whilst tolerance to the close proximity of the aversive robo-beetle increased. The anxiolytic diazepam (1 mg.kg-1 i.p.) reduced only the number of horizontal escape attempts. In both sexes, previous experience of LBN significantly enhanced the number of horizontal escape episodes, indicating a pro-panic phenotype. Directed escape to access a safe ledge on the wall of the test arena, which was seen only in males, was also reduced significantly following LBN. These findings indicate that early life adversity produced by fragmented and unpredictable maternal care promotes a sex-specific increase in susceptibility to panic-like behaviour in adulthood. Whilst non-respiratory-related panic-like behaviour was enhanced in both sexes, females were resilient to respiratory-related challenges.

Prenatal broad-spectrum cannabidiol administration prevents an autism-like phenotype in male offspring from a maternal stress/terbutaline rat model

Recently, the diagnosis of autism spectrum disorder (ASD) has increased from 1 in 150 to every 1 in 36 children in the United States, warranting a need for novel prevention and therapeutic strategies. Broad-spectrum cannabidiol oil, free from delta-9-tetrahydrocannabinol, the psychoactive component of cannabis, may be one such therapeutic. It has a high safety profile and is frequently used as a complementary and integrative intervention by persons experiencing symptoms of anxiety, stress, and inflammation. Using a neurodevelopmental rat model of ASD (based on neuroinflammation induced by stress and terbutaline exposure during pre- and postnatal development), we sought to prevent the development of ASD-like behaviors in male offspring by administering broad-spectrum cannabidiol oil to dams throughout pregnancy (10 mg/kg, i.p., daily, embryonic days 3-16). To assess an ASD-like phenotype in the offspring, we used three behavioral measures relevant to three core ASD symptoms: 1) social communication (time spent vocalizing when alone); 2) repetitive behavior (marbles buried during a marble burying test); and 3) social interaction (time spent interacting with a novel conspecific during the three-chamber social interaction test). Broad-spectrum cannabidiol oil given during pregnancy decreased scores for all three ASD-related behavioral responses, resulting in an overall significant prevention of the ASD-like phenotype. These findings highlight the potential of broad-spectrum cannabidiol oil as a complementary and integrative approach for prevention of stressor-induced sequelae relevant to development of an ASD-like phenotype.

Enhancing translation: A need to leverage complex preclinical models of addictive drugs to accelerate substance use treatment options

Preclinical models of addictive drugs have been developed for decades to model aspects of the clinical experience in substance use disorders (SUDs). These include passive exposure as well as volitional intake models across addictive drugs and have been utilized to also measure withdrawal symptomatology and potential neurobehavioral mechanisms underlying relapse to drug seeking or taking. There are a number of Food and Drug Administration (FDA)-approved medications for SUDs, however, many demonstrate low clinical efficacy as well as potential sex differences, and we also note gaps in the continuum of care for certain aspects of clinical experiences in individuals who use drugs. In this review, we provide a comprehensive update on both frequently utilized and novel behavioral models of addiction with a focus on translational value to the clinical experience and highlight the need for preclinical research to follow epidemiological trends in drug use patterns to stay abreast of clinical treatment needs. We then note areas in which models could be improved to enhance the medications development pipeline through efforts to enhance translation of preclinical models. Next, we describe neuroscience efforts that can be leveraged to identify novel biological mechanisms to enhance medications development efforts for SUDs, focusing specifically on advances in brain transcriptomics approaches that can provide comprehensive screening and identification of novel targets. Together, the confluence of this review demonstrates the need for careful selection of behavioral models and methodological parameters that better approximate the clinical experience combined with cutting edge neuroscience techniques to advance the medications development pipeline for SUDs.

The lateral habenula integrates age and experience to promote social transitions in developing rats

Early caregiving adversity (ECA) is associated with social behavior deficits and later development of psychopathology. However, the infant neural substrates of ECA are poorly understood. The lateral habenula (LHb), a highly conserved brain region with consistent links to adult psychopathology, is understudied in development, when the brain is most vulnerable to environmental impacts. Here, we describe the structural and functional ontogeny of the LHb and its behavioral role in infant and juvenile rat pups. We show that the LHb promotes a developmental transition in social approach behavior under threat as typically reared infants mature. By contrast, we show that ECA disrupts habenular ontogeny, including volume, protein expression, firing properties, and corticohabenular connectivity. Furthermore, inhibiting a specific corticohabenular projection rescues infant social approach deficits following ECA. Together, these results identify immediate biomarkers of ECA in the LHb and highlight this region as a site of early social processing and behavior control.

Integrating developmental neuroscience with community-engaged approaches to address mental health outcomes for housing-insecure youth: Implications for research, practice, and policy

One in three children in the United States is exposed to insecure housing conditions, including unaffordable, inconsistent, and unsafe housing. These exposures have detrimental impacts on youth mental health. Delineating the neurobehavioral pathways linking exposure to housing insecurity with children's mental health has the potential to inform interventions and policy. However, in approaching this work, carefully considering the lived experiences of youth and families is essential to translating scientific discovery to improve health outcomes in an equitable and representative way. In the current paper, we provide an introduction to the range of stressful experiences that children may face when exposed to insecure housing conditions. Next, we highlight findings from the early-life stress literature regarding the potential neurobehavioral consequences of insecure housing, focusing on how unpredictability is associated with the neural circuitry supporting cognitive and emotional development. We then delineate how community-engaged research (CEnR) approaches have been leveraged to understand the effects of housing insecurity on mental health, and we propose future research directions that integrate developmental neuroscience research and CEnR approaches to maximize the impact of this work. We conclude by outlining practice and policy recommendations that aim to improve the mental health of children exposed to insecure housing.

Maternal probiotic Lactocaseibacillus rhamnosus HN001 treatment alters postpartum anxiety, cortical monoamines, and the gut microbiome

Peripartum mood and anxiety disorders (PMADs) affect 15-20% of peripartum women and are well known to disrupt infant caregiving. A recent study in humans reported that anxiety and depressive symptoms were alleviated by peripartum treatment with the probiotic, Lactocaseibacillus rhamnosus HN001. The current study determined the effects of chronic Lactocaseibacillus rhamnosus HN001 (HN001) treatment on postpartum affective and caregiving behaviors in a laboratory rodent model. Female rats were given probiotic overnight in their drinking water, or untreated water, from the first day of pregnancy through postpartum day 10. To determine whether the HN001 effects were influenced by a background of stress, half the females underwent chronic variable pregnancy stress and the other half remained undisturbed. The results revealed that, even without pregnancy stress, HN001 reduced postpartum anxiety-related behavior, increased variability in behavioral fragmentation when dams interacted with pups, increased time away from pups, and decreased prefrontal cortex norepinephrine (NE), dopamine (DA) and serotonin (5-HT). Probiotic plus stress consistently reduced the latency to float in the forced swim test, increased DA and 5-HT turnovers in the prefrontal cortex, increased hippocampal NE, and reduced hypothalamic DA. Fecal microbe alpha and beta diversities were lower postpartum than prepartum, which was prevented by the probiotic treatment and/or stress. Across the entire sample lower postpartum anxiety behavior was associated with lower fecal Bacteroides dorei. This study reveals novel information about how L. rhamnosus HN001 influences postpartum behavior and microbiota-gut-brain physiology in female laboratory rats, with implications for probiotic supplement use by pregnant and postpartum women.

Early-Life Resource Scarcity in Mice Does Not Alter Adult Corticosterone or Preovulatory Luteinizing Hormone Surge Responses to Acute Psychosocial Stress

Early-life stressors can affect reproductive development and change responses to adult stress. We tested if resource scarcity in the form of limited bedding and nesting (LBN) from postnatal days (PND) 4 to 11 delayed sexual maturation in male and female mice and/or altered the response to an acute, layered, psychosocial stress (ALPS) in adulthood. Contrary to the hypotheses, age and mass at puberty were unaffected by the present application of LBN. Under basal conditions and after ALPS, corticosterone concentrations in males, diestrous females, and proestrous females reared in standard (STD) or LBN environments were similar. ALPS disrupts the luteinizing hormone (LH) surge in most mice when applied on the morning of proestrus; this effect was not changed by resource scarcity. In this study, the paucity of effects in the offspring may relate to a milder response of CBA dams to the paradigm. While LBN dams exited the nest more often and their offspring were smaller than STD-reared offspring on PND11, dam corticosterone concentrations were similar on PND11. To test if ALPS disrupts the LH surge by blunting the increase in excitatory GABAergic input to gonadotropin-releasing hormone (GnRH) neurons on the afternoon of proestrus, we conducted whole-cell voltage-clamp recordings. The frequency of GABAergic postsynaptic currents in GnRH neurons was not altered by LBN, ALPS, or their interaction. It remains possible that ALPS acts at afferents of GnRH neurons, changes response of GnRH neurons to input, and/or alters pituitary responsiveness to GnRH and that a more pronounced resource scarcity would affect the parameters studied.

Long-term effects of Preweaning environmental impoverishment on neurobehavioral and neurocognitive outcomes in Sprague Dawley rats: An early environmental stress model

Developmental stress, including low socioeconomic status (SES), can induce dysregulation of the hypothalamic-pituitary-adrenal axis and result in long-term changes in stress reactivity. Children in lower SES conditions often experience more stress than those in other SES groups. There are multiple model systems of early environmental stress (EES), one of which is reduced cage bedding. Here we tested the effects of both prenatal and lactational EES in rats on a range of long-term behavioral and cognitive outcomes. There were persistent reductions in body weight in the EES rats in both sexes. The behavioral results showed no effects on learning and memory using tests of spatial learning or cognitive flexibility in the Morris water maze, egocentric learning in the Cincinnati water maze, or working memory in the radial-arm maze. There were no effects on basic open-field activity, elevated zero-maze, or forced swim test, but EES rats had reduced time in the dark side of the light/dark test. When rats were drug challenged in the open-field with d-amphetamine or MK-801, there were no differential responses to d-amphetamine, but the EES group under responded compared with the drug-induced hyperactivity in the control group in both males and females. The objective was to establish a developmental stress model that induced cognitive deficits and to the extent that this method did not cause such effects it was not the model we sought. However, the data showed several long-term effects of EES, including the reduced response to the irreversible NMDA antagonist MK-801. This effect merits further investigation.

Chd8 haploinsufficiency impacts rearing experience in C57BL/6 mice

Mutations in CHD8 are one of the highest genetic risk factors for autism spectrum disorder. Studies in mice that investigate underlying mechanisms have shown Chd8 haploinsufficient mice display some trait disruptions that mimic clinical phenotypes, although inconsistencies have been reported in some traits across different models on the same strain background. One source of variation across studies may be the impact of Chd8 haploinsufficiency on maternal-offspring interactions. While differences in maternal care as a function of Chd8 genotype have not been studied directly, a previous study showed that pup survival was reduced when reared by Chd8 heterozygous dams compared with wild-type (WT) dams, suggesting altered maternal care as a function of Chd8 genotype. Through systematic observation of the C57BL/6 strain, we first determined the impact of Chd8 haploinsufficiency in the offspring on WT maternal care frequencies across preweaning development. We next determined the impact of maternal Chd8 haploinsufficiency on pup care. Compared with litters with all WT offspring, WT dams exhibited less frequent maternal behaviors toward litters consisting of offspring with mixed Chd8 genotypes, particularly during postnatal week 1. Dam Chd8 haploinsufficiency decreased litter survival and increased active maternal care also during postnatal week 1. Determining the impact of Chd8 haploinsufficiency on early life experiences provides an important foundation for interpreting offspring outcomes and determining mechanisms that underlie heterogeneous phenotypes.

Early movement restriction affects the acquisition of neurodevelopmental reflexes in rat pups

Childhood is a period of construction of the organism, during which interactions with the environment and regular physical activity are necessary for the maturation of the neuronal networks. An atypical sensorimotor activity during childhood (due to bed-rest or neurodevelopmental disorders) impacts the development of the neuromuscular system. A model of sensorimotor restriction (SMR) developed in rats has shown that casting pups' hind limbs from postnatal day 1 (P1) to P28 induced a severe perturbation of motor behavior, due to muscle weakness as well as disturbances within the central nervous system. In the present study, our objective was to determine whether SMR affects the early postnatal ontogenesis. We explored the neuromuscular development through the determination of the age for achievement of the main neurodevelopmental reflexes, which represent reliable indicators of neurological and behavioral development. We also evaluated the maturation of postural control. Our results demonstrate that SMR induces a delay in the motor development, illustrated by a several days delay in the acquisition of a mature posture and in the acquisition reflexes: hind limb grasping, righting, hind limb placing, cliff avoidance, negative geotaxis. In conclusion, impaired physical activity and low interactions with environment during early development result in altered maturation of the nervous system.

Early resource scarcity causes cortical astrocyte enlargement and sex-specific changes in the orbitofrontal cortex transcriptome in adult rats

Astrocyte morphology affects function, including the regulation of glutamatergic signaling. This morphology changes dynamically in response to the environment. However, how early life manipulations alter adult cortical astrocyte morphology is underexplored. Our lab uses brief postnatal resource scarcity, the limited bedding and nesting (LBN) manipulation, in rats. We previously found that LBN augments maternal behaviors and promotes later resilience to adult addiction-related behaviors, reducing impulsivity, risky decision-making, and morphine self-administration. These behaviors rely on glutamatergic transmission in the medial orbitofrontal (mOFC) and medial prefrontal (mPFC) cortex. Here we tested whether LBN changed astrocyte morphology in the mOFC and mPFC of adult rats using a novel viral approach that, unlike traditional markers, fully labels astrocytes. Prior exposure to LBN causes an increase in the surface area and volume of astrocytes in the mOFC and mPFC of adult males and females relative to control-raised rats. We next used bulk RNA sequencing of OFC tissue to assess transcriptional changes that could increase astrocyte size in LBN rats. LBN caused mainly sex-specific changes in differentially expressed genes. Pathway analysis revealed that OFC glutamatergic signaling is altered by LBN in males and females, but the gene changes in that pathway differed across sex. This may represent a convergent sex difference where glutamatergic signaling, which affects astrocyte morphology, is altered by LBN via sex-specific mechanisms. Collectively, these studies highlight that astrocytes may be an important cell type that mediates the effect of early resource scarcity on adult brain function.

The lateral habenula integrates age and experience to promote social transitions in developing rats

Social behavior deficits are an early-emerging marker of psychopathology and are linked with early caregiving quality. However, the infant neural substrates linking early care to social development are poorly understood. Here, we focused on the infant lateral habenula (LHb), a highly-conserved brain region at the nexus between forebrain and monoaminergic circuits. Despite its consistent links to adult psychopathology, this brain region has been understudied in development when the brain is most vulnerable to environmental impacts. In a task combining social and threat cues, suppressing LHb principal neurons had opposing effects in infants versus juveniles, suggesting the LHb promotes a developmental switch in social approach behavior under threat. We observed that early caregiving adversity (ECA) disrupts typical growth curves of LHb baseline structure and function, including volume, firing patterns, neuromodulatory receptor expression, and functional connectivity with cortical regions. Further, we observed that suppressing cortical projections to the LHb rescued social approach deficits following ECA, identifying this microcircuit as a substrate for disrupted social behavior. Together, these results identify immediate biomarkers of ECA in the LHb and highlight this region as a site of early social processing and behavior control.

Dentate Gyrus Microstructure Is Associated With Resilience After Exposure to Maternal Stress Across Two Human Cohorts

BACKGROUND

Maternal stress (MS) is a well-documented risk factor for impaired emotional development in offspring. Rodent models implicate the dentate gyrus (DG) of the hippocampus in the effects of MS on offspring depressive-like behaviors, but mechanisms in humans remain unclear. Here, we tested whether MS was associated with depressive symptoms and DG micro- and macrostructural alterations in offspring across 2 independent cohorts.

METHODS

We analyzed DG diffusion tensor imaging-derived mean diffusivity (DG-MD) and volume in a three-generation family risk for depression study (TGS; n = 69, mean age = 35.0 years) and in the Adolescent Brain Cognitive Development (ABCD) Study (n = 5196, mean age = 9.9 years) using generalized estimating equation models and mediation analysis. MS was assessed by the Parenting Stress Index (TGS) and a measure compiled from the Adult Response Survey from the ABCD Study. The Patient Health Questionnaire-9 and rumination scales (TGS) and the Child Behavior Checklist (ABCD Study) measured offspring depressive symptoms at follow-up. The Schedule for Affective Disorders and Schizophrenia-Lifetime interview was used to assign depression diagnoses.

RESULTS

Across cohorts, MS was associated with future symptoms and higher DG-MD (indicating disrupted microstructure) in offspring. Higher DG-MD was associated with higher symptom scores measured 5 years (in the TGS) and 1 year (in the ABCD Study) after magnetic resonance imaging. In the ABCD Study, DG-MD was increased in high-MS offspring who had depressive symptoms at follow-up, but not in offspring who remained resilient or whose mother had low MS.

CONCLUSIONS

Converging results across 2 independent samples extend previous rodent studies and suggest a role for the DG in exposure to MS and offspring depression.

Chronic Stress in Early Development and Effects on Traumatic Brain Injury Outcome

In recent years, significant advances have been made in the study of mild traumatic brain injury (mTBI). Complete recovery from mTBI normally requires days to weeks, yet a subset of the population suffers from symptoms for weeks to months after injury. The risk factors for these prolonged symptoms have not yet been fully understood. In this chapter, we address one proposed risk factor, early life stress (ELS) and its influence on mTBI recovery. To study the effects of ELS on mTBI recovery, accepted animal models of ELS, including maternal separation, limited bedding and nesting, and chronic unpredictable stress, have been implemented. Combining these ELS models with standardized mTBI models, such as fluid percussion injury or controlled cortical impact, has allowed for a deeper understanding of the neuronal, hormonal, and cognitive changes that occur after mTBI following ELS. These preclinical findings are being used to understand how adverse childhood experiences may predispose a subset of individuals to poorer recovery after mTBI.

Peripheral clock gene oscillations are perturbed in neonatal and adult rat offspring raised under adverse limited bedding conditions

Circadian (24-h) rhythms in the suprachiasmatic nucleus (SCN) are established in utero in rodents, but rhythmicity of peripheral circadian clocks appears later in postnatal development. Since peripheral oscillators can be influenced by maternal feeding and behavior, we investigated whether exposure to the adverse environmental conditions of limited bedding (LB) during postnatal life would alter rhythmicity in the SCN, adrenal gland and liver in neonatal (postnatal day PND10), juvenile (PND28) and adult rats. We also examined locomotor activity in adults. Limited bedding increased nursing time and slightly increased fragmentation of maternal behavior. Exposure to LB reduced the amplitude of Per2 in the SCN on PND10. Adrenal clock gene expression (Bmal1, Per2, Cry1, Rev-erbα, Dbp) and corticosterone secretion were rhythmic at all ages in NB offspring, whereas rhythmicity of Bmal1, Cry1 and corticosterone was abolished in neonatal LB pups. Circadian gene expression in the adrenal and liver was well established by PND28. In adults, liver expression of several circadian genes was increased at specific daytimes by LB and the microstructure of locomotor behavior was altered. Thus, changes in maternal care and behavior might provide important signals to the maturing peripheral oscillators and modify, in particular their output functions in the long-term.

What's Next? Advances and Challenges in Understanding How Environmental Predictability Shapes the Development of Cognitive Control

Forming predictions about what will happen next in the world happens early in development, without instruction, and across species. Some environments support more accurate predictions. These more predictable environments also support what appear to be positive developmental trajectories, including increases in cognitive control over thoughts and actions. Such consequences of predictable environments have broad-reaching implications for society and have been explained across ecological, psychological, computational, and neural frameworks. However, many challenges remain in understanding the effects of environmental predictability, including adaptive responses to unpredictable environments and the mechanisms underlying the effects of predictable environments on developmental trajectories. Future work addressing different dimensions of predictability -- across time scales, locations, actions, people, and outcomes -- and their interactions will advance the ability to understand, predict, and support developmental trajectories.

Vulnerability and resilience to prenatal stress exposure: behavioral and molecular characterization in adolescent rats

Exposure to stress can lead to long lasting behavioral and neurobiological consequences, which may enhance the susceptibility for the onset of mental disorders. However, there are significant individual differences in the outcome of stress exposure since only a percentage of exposed individuals may show pathological consequences, whereas others appear to be resilient. In this study, we aimed to characterize the effects of prenatal stress (PNS) exposure in rats at adolescence and to identify subgroup of animals with a differential response to the gestational manipulation. PNS adolescent offspring (regardless of sex) showed impaired emotionality in different pathological domains, such as anhedonia, anxiety, and sociability. However, using cluster analysis of the behavioral data we could identify 70% of PNS-exposed animals as vulnerable (PNS-vul), whereas the remaining 30% were considered resilient (PNS-res). At the molecular level, we found that PNS-res males show a reduced basal activation of the ventral hippocampus whereas other regions, such as amygdala and dorsal hippocampus, show significant PNS-induced changes regardless from vulnerability or resilience. Taken together, our results provide evidence of the variability in the behavioral and neurobiological effects of PNS-exposed offspring at adolescence. While these data may advance our understanding of the association between exposure to stress during gestation and the risk for psychopathology, the investigation of the mechanisms associated to stress vulnerability or resilience may be instrumental to develop novel strategies for therapeutic intervention.

Perinatal Depression and the Role of Synaptic Plasticity in Its Pathogenesis and Treatment

Emerging evidence indicates that synaptic plasticity is significantly involved in the pathophysiology and treatment of perinatal depression. Animal models have demonstrated the effects of overstimulated or weakened synapses in various circuits of the brain in causing affective disturbances. GABAergic theory of depression, stress, and the neuroplasticity model of depression indicate the role of synaptic plasticity in the pathogenesis of depression. Multiple factors related to perinatal depression like hormonal shifts, newer antidepressants, mood stabilizers, monoamine systems, biomarkers, neurotrophins, cytokines, psychotherapy and electroconvulsive therapy have demonstrated direct and indirect effects on synaptic plasticity. In this review, we discuss and summarize the various patho-physiology-related effects of synaptic plasticity in depression. We also discuss the association of treatment-related aspects related to psychotropics, electroconvulsive therapy, neuromodulation, psychotherapy, physical exercise and yoga with synaptic plasticity in perinatal depression. Future insights into newer methods of treatment directed towards the modulation of neuroplasticity for perinatal depression will be discussed.

Anxiety, aggression, reward sensitivity, and forebrain dopamine receptor expression in a laboratory rat model of early-life disadvantage

Despite early-life disadvantage (ELD) in humans being a highly heterogenous construct, it consistently predicts negative neurobehavioral outcomes. The numerous environmental contributors and neural mechanisms underlying ELD remain unclear, though. We used a laboratory rat model to evaluate the effects of limited resources and/or heavy metal exposure on mothers and their adult male and female offspring. Dams and litters were chronically exposed to restricted (1-cm deep) or ample (4-cm deep) home cage bedding postpartum, with or without lead acetate (0.1%) in their drinking water from insemination through 1-week postweaning. Restricted-bedding mothers showed more pup-directed behaviors and behavioral fragmentation, while lead-exposed mothers showed more nestbuilding. Restricted bedding-raised male offspring showed higher anxiety and aggression. Either restricted bedding or lead exposure impaired goal-directed performance in a reinforcer devaluation task in females, whereas restricted bedding alone disrupted it in males. Lead exposure, but not limited bedding, also reduced sucrose reward sensitivity in a progressive ratio task in females. D1 and D2 receptor mRNA in the medial prefrontal cortex and nucleus accumbens (NAc) were each affected by the early-life treatments and differently between the sexes. Most notably, adult males (but not females) exposed to both early-life treatments had greatly increased D1 receptor mRNA in the NAc core. These results illuminate neural mechanisms through which ELD threatens neurobehavioral development and highlight forebrain dopamine as a factor.

Automated maternal behavior during early life in rodents (AMBER) pipeline

Mother-infant interactions during the early postnatal period are critical for infant survival and the scaffolding of infant development. Rodent models are used extensively to understand how these early social experiences influence neurobiology across the lifespan. However, methods for measuring postnatal dam-pup interactions typically involve time-consuming manual scoring, vary widely between research groups, and produce low density data that limits downstream analytical applications. To address these methodological issues, we developed the Automated Maternal Behavior during Early life in Rodents (AMBER) pipeline for quantifying home-cage maternal and mother-pup interactions using open-source machine learning tools. DeepLabCut was used to track key points on rat dams (32 points) and individual pups (9 points per pup) in postnatal day 1-10 video recordings. Pose estimation models reached key point test errors of approximately 4.1-10 mm (14.39 pixels) and 3.44-7.87 mm (11.81 pixels) depending on depth of animal in the frame averaged across all key points for dam and pups respectively. Pose estimation data and human-annotated behavior labels from 38 videos were used with Simple Behavioral Analysis (SimBA) to generate behavior classifiers for dam active nursing, passive nursing, nest attendance, licking and grooming, self-directed grooming, eating, and drinking using random forest algorithms. All classifiers had excellent performance on test frames, with F1 scores above 0.886. Performance on hold-out videos remained high for nest attendance (F1 = 0.990), active nursing (F1 = 0.828), and licking and grooming (F1 = 0.766) but was lower for eating, drinking, and self-directed grooming (F1 = 0.534-0.554). A set of 242 videos was used with AMBER and produced behavior measures in the expected range from postnatal 1-10 home-cage videos. This pipeline is a major advancement in assessing home-cage dam-pup interactions in a way that reduces experimenter burden while increasing reproducibility, reliability, and detail of data for use in developmental studies without the need for special housing systems or proprietary software.

Postpartum scarcity-adversity inflicts sex-specific cerebellar adaptations and reward behaviors in adolescence

Early life adversity in the form of poor postnatal care is a major developmental stressor impacting behavior later in life. Previous studies have shown the impact of early life stress on neurobehavioral abnormalities. Specifically, research has demonstrated how limited bedding and nesting (LBN) materials can cause behavioral deficits in adulthood. There is, however, a limited understanding of how LBN influences sex-specific neurobehavioral adaptation in adolescence, a developmental stage susceptible to psychiatric diseases including substance use disorder. LBN and stress-naive c57BL/6 adolescent male and female mouse offspring were tested for a battery of behaviors including open field, novel object recognition, elevated plus maze, social preference, and morphine-induced conditioned place preference. There was a significant sex-specific deficit in social preference in male mice exposed to LBN compared to stress-naïve counterparts and both LBN males and females had a higher preference towards the drug-paired chamber in the morphine-induced conditioned place preference test. These behavioral deficits were concomitant with sex-specific increases in the transcription factor, Klf9 in the deep cerebellar nuclei (DCN) of males. Further, mRNA levels of the circadian gene Bmal1, which is known to be transcriptionally regulated by Klf9, were decreased in the DCN. Since Bmal1 has recently been implicated in extracellular matrix modulation, we examined perineuronal nets (PNN) and observed depleted PNN in the DCN of males but not female LBN mice. Overall, we provide a novel understanding of how postpartum adversity impinges on the cerebellar extracellular matrix homeostasis, likely, through disruption of the circadian axis by Klf9 that might underlie sex-specific behavioral adaptations in adolescence.

Genetic Tagging Uncovers a Robust, Selective Activation of the Thalamic Paraventricular Nucleus by Adverse Experiences Early in Life

Background

Early-life adversity (ELA) is associated with increased risk for mood disorders, including depression and substance use disorders. These disorders are characterized by impaired reward-related behaviors, suggesting compromised operations of reward-related brain circuits. However, the brain regions engaged by ELA that mediate these enduring consequences of ELA remain largely unknown. In an animal model of ELA, we identified aberrant reward-seeking behaviors, a discovery that provides a framework for assessing the underlying circuits.

Methods

Employing TRAP2 (targeted recombination in active populations) male and female mice, in which neurons activated within a defined time frame are permanently tagged, we compared ELA- and control-reared mice, assessing the quantity and distribution of ELA-related neuronal activation. After validating the TRAP2 results using native c-Fos labeling, we defined the molecular identity of this population of activated neurons.

Results

We uniquely demonstrated that the TRAP2 system is feasible and efficacious in neonatal mice. Surprisingly, the paraventricular nucleus of the thalamus was robustly and almost exclusively activated by ELA and was the only region distinguishing ELA from typical rearing. Remarkably, a large proportion of ELA-activated paraventricular nucleus of the thalamus neurons expressed CRF1, the receptor for the stress-related peptide, corticotropin-releasing hormone, but these neurons did not express corticotropin-releasing hormone itself.

Conclusions

The paraventricular nucleus of the thalamus, an important component of reward circuits that is known to encode remote, emotionally salient experiences to influence future motivated behaviors, encodes adverse experiences as remote as those occurring during the early postnatal period and is thus poised to contribute to the enduring deficits in reward-related behaviors consequent to ELA.

Father's care uniquely influences male neurodevelopment

Mammalian infants depend on parental care for survival, with numerous consequences for their behavioral development. We investigated the epigenetic and neurodevelopmental mechanisms mediating the impact of early biparental care on development of alloparenting behavior, or caring for offspring that are not one's own. We find that receiving high parental care early in life leads to slower epigenetic aging of both sexes and widespread male-specific differential expression of genes related to synaptic transmission and autism in the nucleus accumbens. Examination of parental care composition indicates that high-care fathers promote a male-specific increase in excitatory synapses and increases in pup retrieval behavior as juveniles. Interestingly, females raised by high-care fathers have the opposite behavioral response and display fewer pup retrievals. These results support the concept that neurodevelopmental trajectories are programmed by different features of early-life parental care and reveal that male neurodevelopmental processes are uniquely sensitive to care by fathers.

Early resource scarcity causes cortical astrocyte enlargement and sex-specific changes in the orbitofrontal cortex transcriptome in adult rats

Astrocyte morphology affects function, including the regulation of glutamatergic signaling. This morphology changes dynamically in response to the environment. However, how early life manipulations alter adult cortical astrocyte morphology is underexplored. Our lab uses brief postnatal resource scarcity, the limited bedding and nesting (LBN) manipulation, in rats. We previously found that LBN promotes later resilience to adult addiction-related behaviors, reducing impulsivity, risky decision-making, and morphine self-administration. These behaviors rely on glutamatergic transmission in the medial orbitofrontal (mOFC) and medial prefrontal (mPFC) cortex. Here we tested whether LBN changed astrocyte morphology in the mOFC and mPFC of adult rats using a novel viral approach that, unlike traditional markers, fully labels astrocytes. Prior exposure to LBN causes an increase in the surface area and volume of astrocytes in the mOFC and mPFC of adult males and females relative to control-raised rats. We next used bulk RNA sequencing of OFC tissue to assess transcriptional changes that could increase astrocyte size in LBN rats. LBN caused mainly sex-specific changes in differentially expressed genes. However, Park7, which encodes for the protein DJ-1 that alters astrocyte morphology, was increased by LBN across sex. Pathway analysis revealed that OFC glutamatergic signaling is altered by LBN in males and females, but the gene changes in that pathway differed across sex. This may represent a convergent sex difference where glutamatergic signaling, which affects astrocyte morphology, is altered by LBN via sex-specific mechanisms. Collectively, these studies highlight that astrocytes may be an important cell type that mediates the effect of early resource scarcity on adult brain function.

Effects of limited bedding and nesting on postpartum mood state in rats

This study examined the effect of limited bedding and nesting (LBN) stress on postpartum anhedonia, maternal behaviors, anxiety-like behaviors, and neuroendocrine and neuroimmune function as a potential model of postpartum depression. Dams underwent sucrose preference tests prior to breeding, during gestation and again postpartum, to examine the potential onset of anhedonia. On embryonic day 19, dams were placed into either a LBN or control housing condition. Contrary to our predictions, LBN stress had no effect on postpartum sucrose preference. We also found no effect of LBN condition on fecal estradiol or corticosterone levels, both of which increased at birth and decreased postpartum. Regardless of housing conditions, approximately 40% of new mothers exhibited a decrease in sucrose preference, while others show no change, suggesting an individual susceptibility to postpartum anhedonia. In a separate cohort of LBN and control dams, we measured pup retrieval, hoarding behavior, elevated plus maze (EPM), and marble burying. LBN dams exhibited increased anxiety, associated with decreased time spent in the open arms of the EPM. We also measured a significant increase in IL-6 expression in the dorsal hippocampus and medial prefrontal cortex of postpartum dams compared to nonpregnant dams. These findings suggest that while LBN stress has effects on anxiety and maternal care, it does not induce postpartum anhedonia. Rather, there are inherent differences in susceptibility to anhedonia in individual dams, and future studies should be conducted to better understand individual vulnerability and resilience to postpartum anhedonia.

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

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

Developmental Brain Injury and Social Determinants of Health: Opportunities to Combine Preclinical Models for Mechanistic Insights into Recovery

Epidemiological studies show that social determinants of health are among the strongest factors associated with developmental outcomes after prenatal and perinatal brain injuries, even when controlling for the severity of the initial injury. Elevated socioeconomic status and a higher level of parental education correlate with improved neurologic function after premature birth. Conversely, children experiencing early life adversity have worse outcomes after developmental brain injuries. Animal models have provided vital insight into mechanisms perturbed by developmental brain injuries, which have indicated directions for novel therapeutics or interventions. Animal models have also been used to learn how social environments affect brain maturation through enriched environments and early adverse conditions. We recognize animal models cannot fully recapitulate human social circumstances. However, we posit that mechanistic studies combining models of developmental brain injuries and early life social environments will provide insight into pathways important for recovery. Some studies combining enriched environments with neonatal hypoxic injury models have shown improvements in developmental outcomes, but further studies are needed to understand the mechanisms underlying these improvements. By contrast, there have been more limited studies of the effects of adverse conditions on developmental brain injury extent and recovery. Uncovering the biological underpinnings for early life social experiences has translational relevance, enabling the development of novel strategies to improve outcomes through lifelong treatment. With the emergence of new technologies to analyze subtle molecular and behavioral phenotypes, here we discuss the opportunities for combining animal models of developmental brain injury with social construct models to deconvolute the complex interactions between injury, recovery, and social inequity.

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.

Developmental Manipulation-Induced Changes in Cognitive Functioning

Schizophrenia is a complex neurodevelopmental disorder with as-yet no identified cause. The use of animals has been critical to teasing apart the potential individual and intersecting roles of genetic and environmental risk factors in the development of schizophrenia. One way to recreate in animals the cognitive impairments seen in people with schizophrenia is to disrupt the prenatal or neonatal environment of laboratory rodent offspring. This approach can result in congruent perturbations in brain physiology, learning, memory, attention, and sensorimotor domains. Experimental designs utilizing such animal models have led to a greatly improved understanding of the biological mechanisms that could underlie the etiology and symptomology of schizophrenia, although there is still more to be discovered. The implementation of the Research and Domain Criterion (RDoC) has been critical in taking a more comprehensive approach to determining neural mechanisms underlying abnormal behavior in people with schizophrenia through its transdiagnostic approach toward targeting mechanisms rather than focusing on symptoms. Here, we describe several neurodevelopmental animal models of schizophrenia using an RDoC perspective approach. The implementation of animal models, combined with an RDoC framework, will bolster schizophrenia research leading to more targeted and likely effective therapeutic interventions resulting in better patient outcomes.

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.