Development of Threat Expression Following Infant Maltreatment: Infant and Adult Enhancement but Adolescent Attenuation

Developmental impacts of deprivation and threat on emotion recognition

Dimensional models of early adversity propose developmental mechanisms by which threat and deprivation confer risk for psychopathology. Exposure to violent environments may influence social information processing biases, and limited access to complex learning environments might be associated with general challenges in emotion recognition. We examined associations of adversity measured early in development (6-36 months) and emotion recognition in early (72 months) and middle (96 months) childhood in a sample of 92 mother-child dyads. Low cognitive stimulation negatively predicted early childhood emotion recognition (β = -0.32, p = .01). Moreover, experiences of intimate-partner violence were associated with anger bias, but not global emotion recognition, in early (β = 0.24, p = .01), and middle (β = 0.18, p = .04) childhood. This pattern suggests that while the lack of exposure to complex learning experiences might impact children's conceptual knowledge of emotions, children who experience violence show biases that facilitate threat detection.

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.

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.

Developmental mechanisms linking deprivation and threat to psychopathology and school outcomes

BACKGROUND

Decades of evidence have elucidated associations between early adversity and risk for negative outcomes. However, traditional conceptualizations of the biologic embedding of adversity ignore neuroscientific principles which emphasize developmental plasticity. Dimensional models suggest that separate dimensions of experiences shape behavioral development differentially. We hypothesized that deprivation would be associated with higher psychopathology and lower academic achievement through executive function and effortful control, while threat would do so through observed, and parent reported emotional reactivity.

METHODS

In this longitudinal study of 206 mother-child dyads, we test these theories across the first 7 years of life. Threat was measured by the presence of domestic violence, and deprivation by the lack of cognitive stimulation within the parent-child interaction. We used path analyses to test associations between deprivation and threat with psychopathology and school outcomes through cognition and emotional reactivity.

RESULTS

We show that children who experienced more deprivation showed poor academic achievement through difficulties with executive function, while children who experienced more threat had higher levels of psychopathology through increased emotional reactivity.

CONCLUSION

These observations are consistent with work in adolescence and reflect how unique adverse experiences have differential effects on children's behavior and subsequently long-term outcomes.

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.

Homeostatic NREM sleep and salience network function in adult mice exposed to ethanol during development

Developmental exposure to ethanol is a leading cause of cognitive, emotional and behavioral problems, with fetal alcohol spectrum disorder (FASD) affecting more than 1:100 children. Recently, comorbid sleep deficits have been highlighted in these disorders, with sleep repair a potential therapeutic target. Animal models of FASD have shown non-REM (NREM) sleep fragmentation and slow-wave oscillation impairments that predict cognitive performance. Here we use a mouse model of perinatal ethanol exposure to explore whether reduced sleep pressure may contribute to impaired NREM sleep, and compare the function of a brain network reported to be impacted by insomnia-the Salience network-in developmental ethanol-exposed mice with sleep-deprived, saline controls. Mice were exposed to ethanol or saline on postnatal day 7 (P7) and allowed to mature to adulthood for testing. At P90, telemetered cortical recordings were made for assessment of NREM sleep in home cage before and after 4 h of sleep deprivation to assess basal NREM sleep and homeostatic NREM sleep response. To assess Salience network functional connectivity, mice were exposed to the 4 h sleep deprivation period or left alone, then immediately sacrificed for immunohistochemical analysis of c-Fos expression. The results show that developmental ethanol severely impairs both normal rebound NREM sleep and sleep deprivation induced increases in slow-wave activity, consistent with reduced sleep pressure. Furthermore, the Salience network connectome in rested, ethanol-exposed mice was most similar to that of sleep-deprived, saline control mice, suggesting a sleep deprivation-like state of Salience network function after developmental ethanol even without sleep deprivation.

From circuits to behavior: Amygdala dysfunction in fragile X syndrome

Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by a repeat expansion mutation in the promotor region of the FMR1 gene resulting in transcriptional silencing and loss of function of fragile X messenger ribonucleoprotein 1 protein (FMRP). FMRP has a well-defined role in the early development of the brain. Thus, loss of the FMRP has well-known consequences for normal cellular and synaptic development leading to a variety of neuropsychiatric disorders including an increased prevalence of amygdala-based disorders. Despite our detailed understanding of the pathophysiology of FXS, the precise cellular and circuit-level underpinnings of amygdala-based disorders is incompletely understood. In this review, we discuss the development of the amygdala, the role of neuromodulation in the critical period plasticity, and recent advances in our understanding of how synaptic and circuit-level changes in the basolateral amygdala contribute to the behavioral manifestations seen in FXS.

The lifetime impact of stress on fear regulation and cortical function

A variety of stressful experiences can influence the ability to form and subsequently inhibit fear memory. While nonsocial stress can impact fear learning and memory throughout the lifespan, psychosocial stressors that involve negative social experiences or changes to the social environment have a disproportionately high impact during adolescence. Here, we review converging lines of evidence that suggest that development of prefrontal cortical circuitry necessary for both social experiences and fear learning is altered by stress exposure in a way that impacts both social and fear behaviors throughout the lifespan. Further, we suggest that psychosocial stress, through its impact on the prefrontal cortex, may be especially detrimental during early developmental periods characterized by higher sociability. This article is part of the Special Issue on 'Fear, Anxiety and PTSD'.

Neurobiology of Infant Fear and Anxiety: Impacts of Delayed Amygdala Development and Attachment Figure Quality

Anxiety disorders are the most common form of mental illness and are more likely to emerge during childhood compared with most other psychiatric disorders. While research on children is the gold standard for understanding the behavioral expression of anxiety and its neural circuitry, the ethical and technical limitations in exploring neural underpinnings limit our understanding of the child's developing brain. Instead, we must rely on animal models to build strong methodological bridges for bidirectional translation to child development research. Using the caregiver-infant context, we review the rodent literature on early-life fear development to characterize developmental transitions in amygdala function underlying age-specific behavioral transitions. We then describe how this system can be perturbed by early-life adversity, including reduced efficacy of the caregiver as a safe haven. We suggest that greater integration of clinically informed animal research enhances bidirectional translation to permit new approaches to therapeutics for children with early onset anxiety disorders.

Elevated infant cortisol is necessary but not sufficient for transmission of environmental risk to infant social development: Cross-species evidence of mother-infant physiological social transmission

Environmental adversity increases child susceptibility to disrupted developmental outcomes, but the mechanisms by which adversity can shape development remain unclear. A translational cross-species approach was used to examine stress-mediated pathways by which poverty-related adversity can influence infant social development. Findings from a longitudinal sample of low-income mother-infant dyads indicated that infant cortisol (CORT) on its own did not mediate relations between early-life scarcity-adversity exposure and later infant behavior in a mother-child interaction task. However, maternal CORT through infant CORT served as a mediating pathway, even when controlling for parenting behavior. Findings using a rodent "scarcity-adversity" model indicated that pharmacologically blocking pup corticosterone (CORT, rodent equivalent to cortisol) in the presence of a stressed mother causally prevented social transmission of scarcity-adversity effects on pup social behavior. Furthermore, pharmacologically increasing pup CORT without the mother present was not sufficient to disrupt pup social behavior. Integration of our cross-species results suggests that elevated infant CORT may be necessary, but without elevated caregiver CORT, may not be sufficient in mediating the effects of environmental adversity on development. These findings underscore the importance of considering infant stress physiology in relation to the broader social context, including caregiver stress physiology, in research and interventional efforts.

Early Life Trauma Has Lifelong Consequences for Sleep And Behavior

Sleep quality varies widely across individuals, especially during normal aging, with impaired sleep contributing to deficits in cognition and emotional regulation. Sleep can also be impacted by a variety of adverse events, including childhood adversity. Here we examined how early life adverse events impacted later life sleep structure and physiology using an animal model to test the relationship between early life adversity and sleep quality across the life span. Rat pups were exposed to an Adversity-Scarcity model from postnatal day 8–12, where insufficient bedding for nest building induces maternal maltreatment of pups. Polysomnography and sleep physiology were assessed in weaning, early adult and older adults. Early life adversity induced age-dependent disruptions in sleep and behavior, including lifelong spindle decreases and later life NREM sleep fragmentation. Given the importance of sleep in cognitive and emotional functions, these results highlight an important factor driving variation in sleep, cognition and emotion throughout the lifespan that suggest age-appropriate and trauma informed treatment of sleep problems.

During infant maltreatment, stress targets hippocampus, but stress with mother present targets amygdala and social behavior

Infant maltreatment increases vulnerability to physical and mental disorders, yet specific mechanisms embedded within this complex infant experience that induce this vulnerability remain elusive. To define critical features of maltreatment-induced vulnerability, rat pups were reared from postnatal day 8 (PN8) with a maltreating mother, which produced amygdala and hippocampal deficits and decreased social behavior at PN13. Next, we deconstructed the maltreatment experience to reveal sufficient and necessary conditions to induce this phenotype. Social behavior and amygdala deficits (volume, neurogenesis, c-Fos, local field potential) required combined chronic high corticosterone and maternal presence (not maternal behavior). Hippocampal deficits were induced by chronic high corticosterone regardless of social context. Causation was shown by blocking corticosterone during maltreatment and suppressing amygdala activity during social behavior testing. These results highlight (1) that early life maltreatment initiates multiple pathways to pathology, each with distinct causal mechanisms and outcomes, and (2) the importance of social presence on brain development.

Infant Trauma Alters Social Buffering of Threat Learning: Emerging Role of Prefrontal Cortex in Preadolescence

Within the infant-caregiver attachment system, the primary caregiver holds potent reward value to the infant, exhibited by infants' strong preference for approach responses and proximity-seeking towards the mother. A less well-understood feature of the attachment figure is the caregiver's ability to reduce fear via social buffering, commonly associated with the notion of a "safe haven" in the developmental literature. Evidence suggests this infant system overlaps with the neural network supporting social buffering (attenuation) of fear in the adults of many species, a network known to involve the prefrontal cortex (PFC). Here, using odor-shock conditioning in young developing rats, we assessed when the infant system transitions to the adult-like PFC-dependent social buffering of threat system. Rat pups were odor-shock conditioned (0.55 mA-0.6 mA) at either postnatal day (PN18; dependent on mother) or 28 (newly independent, weaned at PN23). Within each age group, the mother was present or absent during conditioning, with PFC assessment following acquisition using 14C 2-DG autoradiography and cue testing the following day. Since the human literature suggests poor attachment attenuates the mother's ability to socially buffer the infants, half of the pups at each age were reared with an abusive mother from PN8-12. The results showed that for typical control rearing, the mother attenuated fear in both PN18 and PN28 pups, although the PFC [infralimbic (IL) and ventral prelimbic (vPL) cortices] was only engaged at PN28. Abuse rearing completely disrupted social buffering of pups by the mother at PN18. The results from PN28 pups showed that while the mother modulated learning in both control and abuse-reared pups, the behavioral and PFC effects were attenuated after maltreatment. Our data suggest that pups transition to the adult-like PFC social support circuit after independence from the mother (PN28), and this circuit remains functional after early-life trauma, although its effectiveness appears reduced. This is in sharp contrast to the effects of early life trauma during infancy, where social buffering of the infant is more robustly impacted. We suggest that the infant social buffering circuit is disengaged by early-life trauma, while the adolescent PFC-dependent social buffering circuit may use a safety signal with unreliable safety value.