Maternal regulation of the infant's hypothalamic-pituitary-adrenal axis stress response: Seymour 'Gig' Levine's legacy to neuroendocrinology

The effect of tactile stimulation on spatial memory and hippocampal neuronal density in male rats with sensory deprivation during a critical period

It is well known that sensory information driven from whiskers serves as an example of tactile perception in rodents, and plays an important role in social behavior, environmental exploration, and decision-making processes, the influence of manipulations performed during the development of whiskers, on learning has been received little attention in the literature. This study aimed to evaluate the effect of tactile stimulation (TS) on spatial memory performance and neuronal density in the hippocampus during adulthood in early sensory-deprived rats. Wistar albino male rats were divided into four groups: control (CTL), bilateral whisker trimming (BWT), tactile stimulation (TS), and bilateral whisker trimming+tactile stimulation (BWT + TS). All whiskers were trimmed between P0-10, a critical period for whisker development. TS was applied from P3 to P21 using a soft brush. In this study, the 8-arm radial maze test was conducted from postnatal days 77 to 81 to assess spatial memory Animals sacrificed by intracardial perfusion and neuronal density in CA1, CA3, vDG, and dDG regions of the hippocampus were evaluated by Nissl staining. TS exposure negatively affected spatial memory performance and hippocampal neuronal density compared to BWT. We conclude that TS in healthy offspring can cause stress by interrupting maternal care, given the vulnerability of early development. On the contrary, the sensory deprivation protocol in this study was terminated at a time of high homeostatic plasticity and did not produce complete whisker deprivation, have triggered learning by inducing moderate stress early in development.

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.

Microbiota-immune-brain interactions: A new vision in the understanding of periodontal health and disease

This review highlights the significance of interactions between the microbiota, immune system, nervous and hormonal systems, and the brain on periodontal health and disease. Microorganisms in the microbiota, immune cells, and neurons communicate via homeostatic nervous and hormonal systems, regulating vital body functions. By modulating pro-inflammatory and anti-inflammatory adaptive immune responses, these systems control the composition and number of microorganisms in the microbiota. The strength of these brain-controlled responses is genetically determined but is sensitive to early childhood stressors, which can permanently alter their responsiveness via epigenetic mechanisms, and to adult stressors, causing temporary changes. Clinical evidence and research with humans and animal models indicate that factors linked to severe periodontitis enhance the responsiveness of these homeostatic systems, leading to persistent hyperactivation. This weakens the immune defense against invasive symbiotic microorganisms (pathobionts) while strengthening the defense against non-invasive symbionts at the gingival margin. The result is an increased gingival tissue load of pathobionts, including Gram-negative bacteria, followed by an excessive innate immune response, which prevents infection but simultaneously destroys gingival and periodontal tissues. Thus, the balance between pro-inflammatory and anti-inflammatory adaptive immunity is crucial in controlling the microbiota, and the responsiveness of brain-controlled homeostatic systems determines periodontal health.

Enduring Neurobiological Consequences of Early-Life Stress: Insights from Rodent Behavioral Paradigms

Stress profoundly affects physical and mental health, particularly when experienced early in life. Early-life stress (ELS) encompasses adverse childhood experiences such as abuse, neglect, violence, or chronic poverty. These stressors can induce long-lasting changes in brain structure and function, impacting areas involved in emotion regulation, cognition, and stress response. Consequently, individuals exposed to high levels of ELS are at an increased risk for mental health disorders like depression, anxiety, and post-traumatic stress disorders, as well as physical health issues, including metabolic disorders, cardiovascular disease, and cancer. This review explores the biological and psychological consequences of early-life adversity paradigms in rodents, such as maternal separation or deprivation and limited bedding or nesting. The study of these experimental models have revealed that the organism's response to ELS is complex, involving genetic and epigenetic mechanisms, and is associated with the dysregulation of physiological systems like the nervous, neuroendocrine, and immune systems, in a sex-dependent fashion. Understanding the impact of ELS is crucial for developing effective interventions and preventive strategies in humans exposed to stressful or traumatic experiences in childhood.

Unraveling the Influence of Litter Size, Maternal Care, Exercise, and Aging on Neurobehavioral Plasticity and Dentate Gyrus Microglia Dynamics in Male Rats

This study explores the multifaceted influence of litter size, maternal care, exercise, and aging on rats' neurobehavioral plasticity and dentate gyrus microglia dynamics. Body weight evolution revealed a progressive increase until maturity, followed by a decline during aging, with larger litters exhibiting lower weights initially. Notably, exercised rats from smaller litters displayed higher body weights during the mature and aged stages. The dentate gyrus volumes showed no significant differences among groups, except for aged sedentary rats from smaller litters, which exhibited a reduction. Maternal care varied significantly based on litter size, with large litter dams showing lower frequencies of caregiving behaviors. Behavioral assays highlighted the detrimental impact of a sedentary lifestyle and reduced maternal care/large litters on spatial memory, mitigated by exercise in aged rats from smaller litters. The microglial dynamics in the layers of dentate gyrus revealed age-related changes modulated by litter size and exercise. Exercise interventions mitigated microgliosis associated with aging, particularly in aged rats. These findings underscore the complex interplay between early-life experiences, exercise, microglial dynamics, and neurobehavioral outcomes during aging.

One day away from mum has lifelong consequences on brain and behaviour

This chapter presents a brief overview of attachment theory and discusses the importance of the neonatal period in shaping an individual's physiological and behavioural responses to stress later in life, with a focus on the role of the parent-infant relationship, particularly in rodents. In rodents, the role of maternal behaviours goes far beyond nutrition, thermoregulation and excretion, acting as hidden regulators of the pup's physiology and development. In this review, we will discuss the inhibitory role of specific maternal behaviours on the ACTH and corticosterone (CORT) stress response. The interest of our group to explore the long-term consequences of maternal deprivation for 24 h (DEP) at different ages (3 days and 11 days) in rats was sparked by its opposite effects on ACTH and CORT levels. In early adulthood, DEP3 animals (males and females alike) show greater negative impact on affective behaviours and stress related parameters than DEP11, indicating that the latter is more resilient in tests of anxiety-like behaviour. These findings create an opportunity to explore the neurobiological underpinnings of vulnerability and resilience to stress-related disorders. The chapter also provides a brief historical overview and highlights the relevance of attachment theory, and how DEP helps to understand the effects of childhood parental loss as a risk factor for depression, schizophrenia, and PTSD in both childhood and adulthood. Furthermore, we present the concept of environmental enrichment (EE), its effects on stress responses and related behavioural changes and its benefits for rats previously subjected to DEP, along with the clinical implications of DEP and EE.

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

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

A Novel Early Life Stress Model Affects Brain Development and Behavior in Mice

Early life stress (ELS) in developing children has been linked to physical and psychological sequelae in adulthood. In the present study, we investigated the effects of ELS on brain and behavioral development by establishing a novel ELS model that combined the maternal separation paradigm and mesh platform condition. We found that the novel ELS model caused anxiety- and depression-like behaviors and induced social deficits and memory impairment in the offspring of mice. In particular, the novel ELS model induced more enhanced depression-like behavior and memory impairment than the maternal separation model, which is the established ELS model. Furthermore, the novel ELS caused upregulation of arginine vasopressin expression and downregulation of GABAergic interneuron markers, such as parvalbumin (PV), vasoactive intestinal peptide, and calbindin-D_28k (CaBP-28k), in the brains of the mice. Finally, the offspring in the novel ELS model showed a decreased number of cortical PV-, CaBP-28k-positive cells and an increased number of cortical ionized calcium-binding adaptors-positive cells in their brains compared to mice in the established ELS model. Collectively, these results indicated that the novel ELS model induced more negative effects on brain and behavioral development than the established ELS model.

Points of divergence on a bumpy road: early development of brain and immune threat processing systems following postnatal adversity

Lifelong indices of maladaptive behavior or illness often stem from early physiological aberrations during periods of dynamic development. This is especially true when dysfunction is attributable to early life adversity (ELA), when the environment itself is unsuitable to support development of healthy behavior. Exposure to ELA is strongly associated with atypical sensitivity and responsivity to potential threats-a characteristic that could be adaptive in situations where early adversity prepares individuals for lifelong danger, but which often manifests in difficulties with emotion regulation and social relationships. By synthesizing findings from animal research, this review will consider threat sensitivity through the lenses of associated corticolimbic brain circuitry and immune mechanisms, both of which are immature early in life to maximize adaptation for protection against environmental challenges to an individual's well-being. The forces that drive differential development of corticolimbic circuits include caretaking stimuli, physiological and psychological stressors, and sex, which influences developmental trajectories. These same forces direct developmental processes of the immune system, which bidirectionally communicates with sensory systems and emotion regulation circuits within the brain. Inflammatory signals offer a further force influencing the timing and nature of corticolimbic plasticity, while also regulating sensitivity to future threats from the environment (i.e., injury or pathogens). The early development of these systems programs threat sensitivity through juvenility and adolescence, carving paths for probable function throughout adulthood. To strategize prevention or management of maladaptive threat sensitivity in ELA-exposed populations, it is necessary to fully understand these early points of divergence.

Neurobiological mechanisms involved in maternal deprivation-induced behaviours relevant to psychiatric disorders

Parental care is essential for proper development of stress response and emotion-related behaviours. Epidemiological studies show that parental loss in childhood represents a major risk factor for the development of mental disorders throughout the lifespan, including schizophrenia, depression, and anxiety. In most mammalian species, the mother is the main source of care and maternal behaviours regulate several physiological systems. Maternal deprivation (DEP) for 24 h is a paradigm widely used to disinhibit the hypothalamic-pituitary-adrenal axis response to stress during the stress hyporesponsive period. In this mini-review we will highlight the main DEP-induced neurobiological and behavioural outcomes, including alterations on stress-related hormones, neurogenesis, neurotransmitter/neuromodulatory systems and neuroinflammation. These neurobiological changes may be reflected by aberrant behaviours, which are relevant to the study of mental disorders. The evidence indicates that DEP consequences depend on the sex, the age when the DEP takes place and the age when the animals are evaluated, reflecting dynamic plasticity and individual variability. Individual variability and sex differences have a great relevance for the study of biological factors of stress resilience and vulnerability and the DEP paradigm is a suitable model for evaluation of phenotypes of stress- and emotion-related psychopathologies.

Comparison of LPS and MS-induced depressive mouse model: behavior, inflammation and biochemical changes

Depression is a mental disease involving complex pathophysiological mechanisms, and there are many ways to establish depressive mouse models. The purpose of this study is to comprehensively compare the behavioral changes and its mechanism induced by two different models. This study established two depressive mouse models by maternal separation (MS) or lipopolysaccharide (LPS) administration, and added fluoxetine treatment group respectively for comparison. MS induced more apparent anxiety-like behavior while LPS induced more apparent depressive-like behavior. LPS increased peripheral inflammatory factors more apparent, which were mitigated by fluoxetine. MS inhibited the 5-HT system more obviously and was relieved by fluoxetine. LPS triggered stronger immune response in the hippocampus and prefrontal cortex (PFC). MS significantly reduced the expression of neurotrophic proteins and was alleviated by fluoxetine. Overall, LPS induced stronger system inflammation, while MS impaired the function of HPA axis and 5-HT system. Our results will contribute to a deeper understanding of the pathophysiology of different stress-induced depression and will also help researchers select appropriate models of depression for their own needs.

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

Resilience to stress and social touch

Modern lifestyle and adversities such as the COVID-19 pandemic pose challenges for our physical and mental health. Hence, it is of the utmost importance to identify mechanisms by which we can improve resilience to stress and quickly adapt to adversity. While there are several factors that improve stress resilience, social behavior—primarily in the form of social touch—is especially vital. This article provides an overview of how the somatosensory system plays a key role in translating the socio-emotional information of social touch into active coping with stress. Important future directions include evaluating in humans whether stress resilience can be modulated through the stimulation of low-threshold C-fiber mechanoreceptors and using this technology in the prevention of stress-related neuropsychiatric disorders such as major depressive disorder.

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

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

Early Adverse Experiences and Repeated Wheezing From 6 to 30 Months of Age: Investigating the Roles of Hypothalamic-Pituitary-Adrenal Axis Functioning, Child Sex, and Caregiving Sensitivity

This study examined associations among early adversity, diurnal cortisol, child sex, and caregiver sensitivity at age 6 months in relation to wheezing in children (47% male) followed to 30 months. Analyses included 676 mother-child dyads, 393 of whom completed an observational caregiver sensitivity measure. Participants were primarily ethnic minorities (42.7% Black, 25.4% Hispanic); 22.1% of children had ≥ 1 wheezing episode. Higher adversity was associated with increased wheeze frequency and blunted diurnal cortisol slope. The indirect effect of adversity on wheezing through cortisol slope was significant for females, but not males. Higher caregiver sensitivity was protective against wheezing for males, but not females, with high cortisol. Findings suggest complex associations among adversity, cortisol, child sex, and caregiver sensitivity in predicting wheezing.

Early life stress alters emotional learning in a sex- and age-dependent manner with no impact on emotional behaviors

Neonatal adversity can impact neurodevelopmental trajectories. This study examined the long-term effects of maternal deprivation on day 9 (DEP9), associated or not to a stressor (saline injection [SAL]), on contextual fear conditioning (Experiment 1) and emotional behaviors (Experiment 2) in Wistar rats. Whole litters were either assigned to DEP9 or control groups, and on day 10, half of the litters in each group received an SAL or not (NSAL). DEP9-SAL male adolescents showed the longest freezing time and DEP9 adult males froze more than females. Females exhibited less anxiety-like behavior than males; DEP9-SAL females spent more time in the open arms and DEP9 males visited less the extremity of the open arm in the elevated plus maze. Early life stress increased conditioned and innate fear in males, but not in females, indicating a clear sexual dimorphism in the response to potentially threatening stimuli.

Salivary cortisol reactivity in 6-month-old infants of mothers with severe psychiatric disorders: findings from the face-to-Face Still-Face paradigm

Background.

Maternal psychopathology is associated with altered HPA axis functioning in offspring. Most studies have focused on mildly affected populations, but less is known about the effect of severe maternal psychopathology. In our explorative study we investigated in a heterogenic sample of mothers with severe and long-lasting psychiatric disorders, if a diagnosis of depression and severity of general maternal psychiatric symptomatology were associated with infant salivary cortisol reactivity to the Face-to-Face Still-Face (FFSF) paradigm at 6 months of age.

Methods.

A clinical sample of 36 mother-infant dyads was explored. All mothers fulfilled criteria for a severe psychiatric disorder and had psychiatric complaints for the last two consecutive years. Maternal diagnosis was established during pregnancy using a diagnostic interview and general maternal psychiatric symptom severity was established by self-report at the time of the FFSF procedure. The FFSF paradigm was used to assess infants’ response to social stress at the age of 6 months. Infant saliva samples were collected at three time points: 5 min before and 15 and 30 min after the social stressor. Cortisol reactivity was operationalized as incremental Area Under the Curve (AUCi). Potential confounders were identified and adjusted for.

Results.

In regression analyses, a negative relationship was found between infant cortisol reactivity (AUCi) during the FFSF paradigm at 6 months and general maternal symptom severity at time of the FFSF paradigm (unadjusted n = 36, ß = −0.331, B = −9.758, SE 4.8, p = .048; adjusted n = 36, ß = −0.335, B = −9.868, SE 4.5, p = .039) and for diagnosis of perinatal depression at trend level (unadjusted n = 36, ß = −0.293, B = −8.640, SE 4.8, p = .083; adjusted n = 36, ß = −0.317, B = −9.347, SE 4.6, p = .052). Analyses were adjusted for gestational age.

Conclusions.

Preliminary results on cortisol reactivity in 6-month-old infants of mothers with severe and long-lasting psychiatric disorders show a significant reduction in the group of mothers who experienced a high level of psychiatric symptoms in the post-partum period, compared to mothers with lower levels of psychiatric symptomatology. The same trend was found for mothers with and without a diagnosis of perinatal depression. Since these infants are considered to be at increased risk for later psychopathology, our study suggests that future longitudinal studies should investigate whether reduced cortisol reactivity in babies could be a marker for any adverse outcomes, besides other possible risk factors (e.g. (epi)genetic phenomena).

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Psychiatric symptom severity in mothers might affect infant cortisol reactivity during the Face-to-Face-Still-Face (FFSF) paradigm.

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Infants of mothers with a diagnosis of depression show borderline diminished reactivity of cortisol during the FFSF paradigm.

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Under-activation of cortisol reactivity in infants of severely affected mothers might point to early patterns of blunted HPA-axis functioning.

Collaboration to Improve Neuroprotection and Neuropromotion in the NICU: Team Education and Family Engagement

The number of babies born extremely low birth weight surviving to be discharged home after experiencing the NICU continues to improve. Unfortunately, early sensory development for these babies occurs in an environment vastly different from the intended in-utero environment and places them at high risk of long-term neurodevelopmental and neurocognitive challenges. Our goal in the NICU must transition from simply discharge home to supporting the neurosensory development necessary for a thriving lifetime. To accomplish a goal of thriving families and thriving babies, it is clear the NICU interprofessional team must share an understanding of neurosensory development, the neuroprotective strategies safeguarding development, the neuropromotive strategies supporting intended maturational development, and the essential nature of family integration in these processes. We share the educational endeavors of 11 center collaboratives in establishing the foundational knowledge necessary to support preterm babies and their families.

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

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

How early maternal deprivation changes the brain and behavior?

Early life stress can adversely influence brain development and reprogram brain function and consequently behavior in adult life. Adequate maternal care in early childhood is therefore particularly important for the normal brain development, and adverse early life experiences can lead to altered emotional, behavioral, and neuroendocrine stress responses in the adulthood. As a form of neonatal stress, maternal deprivation/separation is often used in behavioral studies to examine the effects of early life stress and for modeling the development of certain psychiatric disorders and brain pathologies in animal models. The temporary loss of maternal care during the critical postpartum periods remodels the offspring's brain and provokes long-term effects on learning and cognition, the development of mental disorders, aggression, and an increased tendency for the drug abuse. Early life stress through maternal deprivation affects neuroendocrine responses to stress in adolescence and adulthood by dysregulating the hypothalamic-pituitary-adrenal axis and permanently disrupts stress resilience. In this review, we focused on how improper maternal care during early postnatal life affects brain development resulting in modified behavior later in life.

Maternal behavior and the neonatal HPA axis in the Wistar Audiogenic Rat (WAR) strain: Early-life implications for a genetic animal model in epilepsy

Epileptogenesis is a multistage process and seizure susceptibility can be influenced by stress early in life. Wistar Audiogenic Rat (WAR) strain is an interesting model to study the association between stress and epilepsy, since it is naturally susceptible to seizures and present changes in the hypothalamus-pituitary-adrenal (HPA) axis activity. All these features are related to the pathogenic mechanisms usually associated with psychiatric comorbidities present in epilepsy. Therefore, the current study aimed to evaluate the neonate HPA axis function and maternal care under control and stress conditions in the WAR strain. Maternal behavior and neonate HPA axis were evaluated in Wistar and WAR strains under rest and after the presence of stressors. We observed that WAR pups present higher plasmatic corticosterone concentration as compared to Wistar pups. Although WAR dams do not show significant altered maternal behavior at rest, there is a higher latency to recover the litter in the pup retrieval test, while some did not recover all the litter. Wistar Audiogenic Rat dams presented similar behaviors to Wistar dams to a female intruder and maternal care with the pups in the maternal defense test. Taken together, these findings indicate that the WAR strain could show HPA axis disruption early in life and dams present altered maternal behavior under stressful events. Those alterations make the WAR strain an interesting model to evaluate vulnerability to epilepsy and its associated neuropsychiatric comorbidities.

Chronic Escitalopram Treatment Does Not Alter the Effects of Neonatal Stress on Hippocampal BDNF Levels, 5-HT1A Expression and Emotional Behaviour of Male and Female Adolescent Rats

Early life stress is considered a risk factor for the development of long-term psychiatric disorders. Maternal deprivation (MD) is a useful paradigm to understand the neurobiological underpinnings of early stress-induced changes in neurodevelopment trajectory. The goal of the present study was to examine the effects of a chronic treatment with escitalopram (ESC) on the hippocampal levels of BDNF and neuropeptide Y (NPY), expression of serotonin type 1A receptor (5-HT1A), plasma corticosterone levels and emotional behaviours in male and female adolescent rats submitted to MD at 9 days of life (group DEP9) and challenged with a brief and mild stress (saline injection (SAL)) at the end of MD. Whole litters were kept with mothers (CTL) or submitted to MD (DEP9). Within each group, pups were stress-challenged (CTL-SAL and DEP9-SAL) or not (CTL-NSAL and DEP9-NSAL). ESC or vehicle treatments began at weaning and lasted 24 days, when animals were sacrificed for determination of neurobiological variables or submitted to a battery of tests for evaluation of emotional behaviours. The results showed that BDNF levels were higher in SAL-challenged males and in DEP9-SAL females, whereas 5-HT1A receptor expression was reduced in DEP9 males and in SAL-challenged females. There were no changes in NPY or corticosterone levels. In the forced swim test, SAL-challenged males and DEP9 females displayed less immobility and ESC only increased social motivation in males. The results indicated that neonatal stress led to sex-dependent changes in neurobiology and behaviour and that chronic ESC treatment had minor effects on these parameters.

Maternal immune activation in rats attenuates the excitability of monoamine-secreting neurons in adult offspring in a sex-specific way

Higher risk of depression and schizophrenia in descendants of mothers experienced acute infection during the pregnancy has been reported. Since monoamines are fundamental in mentioned psychopathologies, it is possible that maternal immune activation leads to impaired functioning of serotonin (5-HT), noradrenaline, and dopamine neurons in offspring. To test this hypothesis, we examined the effect of maternal immune activation by lipopolysaccharide (LPS) in rats on the excitability of monoamine-secreting neurons in the offspring. LPS was administered during days 15-19 of the gestation in the rising doses of 20-80 µg/kg; control dams received vehicle. During days 53-63 postpartum, rats were anesthetized and electrodes were inserted into the dorsal raphe nucleus, locus coeruleus, and ventral tegmental area for in vivo excitability assessment of 5-HT, noradrenaline, and dopamine neurons. Maternal immune activation suppressed the firing rate of 5-HT neurons in both sexes and stimulated the firing rate of dopamine neurons in males. Decrease in the firing rate of 5-HT neurons was accompanied with an increase, and increase in the firing rate of dopamine neurons with a decrease, in the density of spontaneously active cells. Maternal immune activation also decreased the variability of interspike intervals in 5-HT and dopamine neurons. It is possible that the alteration of excitability of 5-HT and dopamine neurons by maternal immune activation is involved in the psychopathologies induced by infectious disease during the pregnancy. Stimulation of dopamine excitability in males might be a compensatory mechanism secondary to the maternal immune challenge-induced suppression of 5-HT neurons.

Maternal Undernutrition Modulates Neonatal Rat Cerebrovascular Structure, Function, and Vulnerability to Mild Hypoxic-Ischemic Injury via Corticosteroid-Dependent and -Independent Mechanisms

The present study explored the hypothesis that an adverse intrauterine environment caused by maternal undernutrition (MUN) acted through corticosteroid-dependent and -independent mechanisms to program lasting functional changes in the neonatal cerebrovasculature and vulnerability to mild hypoxic-ischemic (HI) injury. From day 10 of gestation until term, MUN and MUN-metyrapone (MUN-MET) group rats consumed a diet restricted to 50% of calories consumed by a pair-fed control; and on gestational day 11 through term, MUN-MET groups received drinking water containing MET (0.5 mg/mL), a corticosteroid synthesis inhibitor. P9/P10 pups underwent unilateral carotid ligation followed 24 h later by 1.5 h exposure to 8% oxygen (HI treatment). An ELISA quantified MUN-, MET-, and HI-induced changes in circulating levels of corticosterone. In P11/P12 pups, MUN programming promoted contractile differentiation in cerebrovascular smooth muscle as determined by confocal microscopy, modulated calcium-dependent contractility as revealed by cerebral artery myography, enhanced vasogenic edema formation as indicated by T2 MRI, and worsened neurobehavior MUN unmasked HI-induced improvements in open-field locomotion and in edema resolution, alterations in calcium-dependent contractility and promotion of contractile differentiation. Overall, MUN imposed multiple interdependent effects on cerebrovascular smooth muscle differentiation, contractility, edema formation, flow-metabolism coupling and neurobehavior through pathways that both required, and were independent of, gestational corticosteroids. In light of growing global patterns of food insecurity, the present study emphasizes that infants born from undernourished mothers may experience greater risk for developing neonatal cerebral edema and sensorimotor impairments possibly through programmed changes in neonatal cerebrovascular function.

Pubertal recalibration of cortisol reactivity following early life parent-child separation

BACKGROUND

The hypothalamic-pituitary-adrenocortical (HPA) axis had been proved to calibrate to early-life adversity and puberty may reverse the calibration. This study examines the consequences of prolonged parent-child separation on HPA axis reactivity and the pubertal recalibration hypothesis.

METHODS

Totally of 144 participants aged 8.75 to 15.25 (mean age 12.50 years, SD: 1.32) were enrolled from rural areas of Chizhou city, Anhui Province of China in 2019. Data on parent-child separation was collected from parents. Self-reported Peterson Pubertal Development Scale was used to assess pubertal maturation and HPA axis stress reactivity was measured using the Trier Social Stress Test for Children.

RESULTS

For children at early stage of puberty, childhood parent-child separation experiences were associated with blunted HPA axis reactivity (B = -1.888, p = 0.034); while for those at later stage of puberty, HPA axis reactivity was similar between children experienced early childhood separation and those without separation (AUCi: B = -0.426, p = 0.878). In contrast, for children experienced persistent parent-child separation, blunted HPA axis reactivity was observed (all p < 0.05).

LIMITATIONS

Due to the cross-sectional nature of this study, conclusions about causality remain speculative.

CONCLUSIONS

The effect of parent-child separation on dysregulation of HPA axis acts in a time-dependent manner. This finding provides support for the pubertal recalibration hypothesis suggesting that a focus of improving environment in adolescence would help those individuals reared initially in non-supportive conditions.

Effects of Early-Life Stress on the Brain and Behaviors: Implications of Early Maternal Separation in Rodents

Early-life stress during the prenatal and postnatal periods affects the formation of neural networks that influence brain function throughout life. Previous studies have indicated that maternal separation (MS), a typical rodent model equivalent to early-life stress and, more specifically, to child abuse and/or neglect in humans, can modulate the hypothalamic-pituitary-adrenal (HPA) axis, affecting subsequent neuronal function and emotional behavior. However, the neural basis of the long-lasting effects of early-life stress on brain function has not been clarified. In the present review, we describe the alterations in the HPA-axis activity-focusing on serum corticosterone (CORT)-and in the end products of the HPA axis as well as on the CORT receptor in rodents. We then introduce the brain regions activated during various patterns of MS, including repeated MS and single exposure to MS at various stages before weaning, via an investigation of c-Fos expression, which is a biological marker of neuronal activity. Furthermore, we discuss the alterations in behavior and gene expression in the brains of adult mice exposed to MS. Finally, we ask whether MS repeats itself and whether intergenerational transmission of child abuse and neglect is possible.

Chronic postnatal chemogenetic activation of forebrain excitatory neurons evokes persistent changes in mood behavior

Early adversity is a risk factor for the development of adult psychopathology. Common across multiple rodent models of early adversity is increased signaling via forebrain Gq-coupled neurotransmitter receptors. We addressed whether enhanced Gq-mediated signaling in forebrain excitatory neurons during postnatal life can evoke persistent mood-related behavioral changes. Excitatory hM3Dq DREADD-mediated chemogenetic activation of forebrain excitatory neurons during postnatal life (P2–14), but not in juvenile or adult windows, increased anxiety-, despair-, and schizophrenia-like behavior in adulthood. This was accompanied by an enhanced metabolic rate of cortical and hippocampal glutamatergic and GABAergic neurons. Furthermore, we observed reduced activity and plasticity-associated marker expression, and perturbed excitatory/inhibitory currents in the hippocampus. These results indicate that Gq-signaling-mediated activation of forebrain excitatory neurons during the critical postnatal window is sufficient to program altered mood-related behavior, as well as functional changes in forebrain glutamate and GABA systems, recapitulating aspects of the consequences of early adversity.

Stress and adversity in early childhood can have long-lasting effects, predisposing people to mental illness and mood disorders in adult life. The weeks immediately before and after birth are critical for establishing key networks of neurons in the brain. Therefore, any disruption to these neural circuits during this time can be detrimental to emotional development. However, it is still unclear which cellular mechanisms cause these lasting changes in behavior.

Studies in animals suggest that these long-term effects could result from abnormalities in a few signaling pathways in the brain. For example, it has been proposed that overstimulating the cells that activate circuits in the forebrain – also known as excitatory neurons – may contribute to the behavioral changes that persist into adulthood.

To test this theory, Pati et al. used genetic engineering to modulate a signaling pathway in male mice, which is known to stimulate excitatory neurons in the forebrain. The experiments showed that prolonged activation of excitatory neurons in the first two weeks after birth resulted in anxious and despair-like behaviors as the animals aged. The mice also displayed discrepancies in how they responded to certain external sensory information, which is a hallmark of schizophrenia-like behavior. However, engineering the same changes in adolescent and adult mice had no effect on their mood-related behaviors.

This animal study reinforces just how critical the first few weeks of life are for optimal brain development. It provides an insight into a possible mechanism of how disruption during this time could alter emotional behavior. The findings are also relevant to psychiatrists interested in the underlying causes of mental illness after early childhood adversity.

Social buffering enhances extinction of conditioned fear responses by reducing corticosterone levels in male rats

The presence of an affiliative conspecific reduces stress responses to a wide variety of stimuli, which is termed "social buffering." We previously reported that social buffering in male rats ameliorated behavioral responses, as well as hypothalamic-pituitary-adrenal axis activation, elicited by an auditory conditioned stimulus (CS). In addition, subjects that experienced social buffering did not show stress responses when re-exposed to the CS the next day in the absence of an accompanying rat. However, the mechanisms underlying this enhancement of between-session extinction are poorly understood. In Experiment 1, we compared corticosterone levels at 0, 10, and 15 min after extinction training. Subjects that experienced social buffering had lower corticosterone levels than subjects that trained alone at the end of extinction training. However, corticosterone levels at 10 and 15 min after training were not affected by the experience of social buffering. These results suggest that a lower level of corticosterone during extinction training had an important role in the enhancement of extinction. To directly assess this, in Experiment 2, we manipulated the corticosterone level during extinction training. We found that a subcutaneous injection of corticosterone before extinction training blocked the enhancement of extinction by social buffering. These results demonstrate that the enhancement is caused by a low level of corticosterone during the training. Taken together, we suggest that social buffering enhances extinction of conditioned fear responses by reducing corticosterone levels in male rats.

Bundling the haystack to find the needle: Challenges and opportunities in modeling risk and resilience following early life stress

Various forms of early life adversity (ELA) have been linked with increased risk for negative health outcomes, including neuropsychiatric disorders. Understanding how the complex interplay between types, timing, duration, and severity of ELA, together with individual differences in genetic, socio-cultural, and physiological differences can mediate risk and resilience has proven difficult in population based studies. Use of animal models provides a powerful toolset to isolate key variables underlying risk for altered neural and behavioral maturational trajectories. However, a lack of clarity regarding the unique features of differing forms of adversity, lab differences in the implementation and reporting of methods, and the ability compare across labs and types of ELA has led to some confusion. Here, we highlight the diversity of approaches available, current challenges, and a possible ways forward to increase clarity and drive more meaningful and fruitful implementation and comparison of these approaches.

The behavioral phenotype of early life adversity: A 3-level meta-analysis of rodent studies

Altered cognitive performance is considered an intermediate phenotype mediating early life adversity (ELA) effects on later-life development of mental disorders, e.g. depression. Whereas most human studies are limited to correlational conclusions, rodent studies can prospectively investigate how ELA alters cognitive performance in several domains. Despite the volume of reports, there is no consensus on i) the behavioral domains being affected by ELA and ii) the extent of these effects. To test how ELA (here: aberrant maternal care) affects specific behavioral domains, we used a 3-level mixed-effect meta-analysis, and thoroughly explored heterogeneity with MetaForest, a novel machine-learning approach. Our results are based on >400 independent experiments, involving ∼8600 animals. Especially in males, ELA promotes memory formation during stressful learning but impairs non-stressful learning. Furthermore, ELA increases anxiety-like and decreases social behavior. The ELA phenotype was strongest when i) combined with other negative experiences ("hits"); ii) in rats; iii) in ELA models of ∼10days duration. All data is easily accessible with MaBapp (https://osf.io/ra947/), allowing researchers to run tailor-made meta-analyses, thereby revealing the optimal choice of experimental protocols and study power.

Access to a high resource environment protects against accelerated maturation following early life stress: A translational animal model of high, medium and low security settings

Early life exposure to a low security setting, characterized by a scarcity of resources and limited food access, increases the risk for psychiatric illness and metabolic dysfunction. We utilized a translational rat model to mimic a low security environment and determined how this manipulation affected offspring behavior, metabolism, and puberty. Because food insecurity in humans is associated with reduced access to healthy food options the "low security" rat manipulation combined a Western diet with exposure to a limited bedding and nesting manipulation (WD-LB). In this setting, dams were provided with limited nesting materials during the pups' early life (P2-P10). This manipulation was contrasted with standard rodent caging (SD) and environmental enrichment (EE), to model "medium security" and "high security" environments, respectively. To determine if transitioning from a low to high security environment improved outcomes, some juvenile WD-LB offspring were exposed to EE. Maternal care was impacted by these environments such that EE dams engaged in high quality care when on the nest, but spent less time on the nest than SD dams. Although WD-LB dams excessively chased their tails, they were very attentive to their pups, perhaps to compensate for limited resources. Offspring exposed to WD-LB only displayed subtle changes in behavior. However, WD-LB exposure resulted in significant metabolic dysfunction characterized by increased body weight, precocious puberty and alterations in the hypothalamic kisspeptin system. These negative effects of WD-LB on puberty and weight regulation were mitigated by EE exposure. Collectively, these studies suggest that both compensatory maternal care and juvenile enrichment can reduce the impact of a low security environment. Moreover, they highlight how utilizing diverse models of resource (in)stability can reveal mechanisms that confer vulnerability and resilience to early life stress.

Energy Medicine: Current Status and Future Perspectives

Current practices in allopathic medicine measure different types of energy in the human body by using quantum field dynamics involved in nuclear medicine, radiology, and imaging diagnostics. Once diagnosed, current treatments revert to biochemistry instead of using biophysics therapies to treat the disturbances in subtle energies detected and used for diagnostics. Quantum physics teaches us there is no difference between energy and matter. All systems in the human being, from the atomic to the molecular level, are constantly in motion-creating resonance. This resonance is important to understanding how subtle energy directs and maintains health and wellness in the human being. Energy medicine (EM), whether human touch or device-based, is the use of known subtle energy fields to therapeutically assess and treat energetic imbalances, bringing the body's systems back to homeostasis (balance). The future of EM depends on the ability of allopathic medicine to merge physics with biochemistry. Biophoton emissions as well as signal transduction and cell signaling communication systems are widely accepted in today's medicine. This technology needs to be expanded to include the existence of the human biofield (or human energy field) to better understand that disturbances in the coherence of energy patterns are indications of disease and aging. Future perspectives include understanding cellular voltage potentials and how they relate to health and wellness, understanding the overlap between the endocrine and chakra systems, and understanding how EM therapeutically enhances psychoneuroimmunology (mind-body) medicine.