Neurobiology of early life stress and visceral pain: translational relevance from animal models to patient care

Paraventricular Mast Cell-Derived Histamine Activates CRH Neurons to Mediate Adult Visceral Hypersensitivity Induced by Neonatal Maternal Separation

Neonatal maternal separation (NMS) is an early-life stress (ELS) that can result in adult visceral hypersensitivity, which is usually manifested as chronic visceral pain. Although mast cells and corticotropin-releasing hormone (CRH) neurons are involved in stress response, whether there is an interaction between mast cells and CRH neurons in hypothalamic paraventricular nucleus (PVN) during the ELS-induced visceral hypersensitivity remains elusive. Herein, we established an NMS model by separating neonatal mice from their mothers, and observed that these mice presented visceral hypersensitivity in adulthood, as indicated by elevated abdominal withdrawal reflex and lowered visceral pain threshold. The NMS-induced adult visceral hypersensitivity was accompanied by activation of mast cells and CRH neurons in PVN. Also, NMS increased the histamine content (an inflammatory mediator mainly released by mast cells) and histamine H2 receptor (H2R) expression of CRH neurons in PVN. Remarkably, intra-PVN administration with mast cell stabilizer attenuated the NMS-induced CRH neuronal activation and adult visceral pain, while histamine administration showed the opposite effects. Moreover, intra-PVN injection with H2R antagonist alleviated the NMS-induced CRH neuronal activation, PKA and CREB phosphorylation, and importantly, adult visceral pain. Together, our findings revealed a role of an interaction between paraventricular mast cells and CRH neurons in NMS-induced adult visceral hypersensitivity, thereby providing a perspective for the management of visceral pain.

Glutamatergic and GABAergic anteroventral BNST projections to PVN CRH neurons regulate maternal separation-induced visceral pain

Early-life stress (ELS) is thought to cause the development of visceral pain disorders. While some individuals are vulnerable to visceral pain, others are resilient, but the intrinsic circuit and molecular mechanisms involved remain largely unclear. Herein, we demonstrate that inbred mice subjected to maternal separation (MS) could be separated into susceptible and resilient subpopulations by visceral hypersensitivity evaluation. Through a combination of chemogenetics, optogenetics, fiber photometry, molecular and electrophysiological approaches, we discovered that susceptible mice presented activation of glutamatergic projections or inhibition of GABAergic projections from the anteroventral bed nucleus of the stria terminalis (avBNST) to paraventricular nucleus (PVN) corticotropin-releasing hormone (CRH) neurons. However, resilience develops as a behavioral adaptation partially due to restoration of PVN SK2 channel expression and function. Our findings suggest that PVN CRH neurons are dually regulated by functionally opposing avBNST neurons and that this circuit may be the basis for neurobiological vulnerability to visceral pain.

Self-Perceived Stress Is Associated With Chest Pain and Personality in Patients With Refractory Functional Gastrointestinal Disorders

ABSTRACT

Stressful events are frequently associated with functional gastrointestinal disorders (FGID). This study aims to determine if the severity of self-perceived stress is associated with specific FGID and personality characteristics in 822 patients with FGID who have filled a Rome III questionnaire, Minnesota Multiphasic Personality Inventory 2 (MMPI-2), and a 10-point Likert scale for self-perceived stress. According to stress severity, the patients were divided into three groups: low (<4; n = 183), moderate (4-6; n = 283), and severe stress (>6; n = 356). Female sex was more frequent in the severe stress group than in the low stress group (p = 0.001). Stress severity was strongly correlated with the two MMPI-2 posttraumatic stress scales. Clinically, chest pain was more frequently reported by severe stress patients than moderate stress patients. MMPI-2 clinical scales vary significantly according to the severity of stress, and "mild stress" patients have increased hysteria and depression scales and showed a higher frequency of irritable bowel syndrome-diarrhea. This study shows that severe stress severity is associated with a higher frequency of noncardiac chest pain and correlated with most personality items.

A Theoretical Endogenous Opioid Neurobiological Framework for Co-occurring Pain, Trauma, and Non-suicidal Self-injury

PURPOSE OF REVIEW

Individuals with chronic pain are significantly more likely to have experienced overwhelming trauma early and often in key developmental years. There is increasing acknowledgment that childhood trauma disrupts how individuals process and cope with both physical and emotional pain. Emerging studies acknowledge elevated rates of non-suicidal self-injury (NSSI) in chronic pain populations. This review provides a theoretical framework to understand the relationship between NSSI behavior and pain experience in persons with chronic pain and childhood trauma histories. We discuss how NSSI may act to regulate neurobiological (e.g., endogenous opioid systems) and psychological (e.g., heightened negative affect and emotion dysregulation) systems affected by childhood trauma, leading to temporary pain relief and a cycle of negative reinforcement perpetuating NSSI. As these concepts are greatly understudied in pain populations, this review focuses on key areas relevant to chronic pain that may provide a testable, conceptual framework to support hypothesis generation, future empirical investigation, and intervention efforts.

RECENT FINDINGS

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Corticotropin-releasing factor receptor 1 (CRF-R1) antagonists: Promising agents to prevent visceral hypersensitivity in irritable bowel syndrome

Corticotropin-releasing factor (CRF) is a 41-amino acid polypeptide that coordinates the endocrine system, autonomic nervous system, immune system, and physiological behavior. CRF is a signaling regulator in the neuro-endocrine-immune (NEI) network that mediates visceral hypersensitivity. Rodent models to simulate changes in intestinal motility similar to those reported in the irritable bowel syndrome (IBS), demonstrate that the CRF receptor 1 (CRF-R1) mediates intestinal hypersensitivity under many conditions. However, the translation of preclinical studies into clinical trials has not been successful possibly due to the lack of sufficient understanding of the multiple variants of CRF-R1 and CRF-R1 antagonists. Investigating the sites of action of central and peripheral CRF is critical for accelerating the translation from preclinical to clinical studies.

A Monoclonal Anti-Calcitonin Gene-Related Peptide Antibody Decreases Stress-Induced Colonic Hypersensitivity

Irritable bowel syndrome (IBS) is a brain-gut disorder characterized by abdominal pain and altered bowel habits. Although the etiology of IBS remains unclear, stress in adulthood or in early life has been shown to be a significant factor in the development of IBS symptomatology. Evidence suggests that aberrant calcitonin gene-related peptide (CGRP) signaling may be involved in afferent sensitization and visceral organ hypersensitivity. Here, we used a monoclonal anti-CGRP divalent antigen-binding fragment [F(ab')₂] antibody to test the hypothesis that inhibition of peripheral CGRP signaling reverses colonic hypersensitivity induced by either chronic adult stress or early life stress. A cohort of adult male rats was exposed to repeated water avoidance stress. Additionally, a second cohort consisting of female rats was exposed to a female-specific neonatal odor-attachment learning paradigm of unpredictable early life stress. Colonic sensitivity was then assessed in adult animals via behavioral responses to colorectal distension (CRD). To analyze spinal nociceptive signaling in response to CRD, dorsal horn extracellular signal-regulated kinase (ERK) 1/2 phosphorylation was measured via immunohistochemistry. Repeated psychologic stress in adulthood or unpredictable stress in early life induced colonic hypersensitivity and enhanced evoked ERK1/2 phosphorylation in the spinal cord after CRD in rats. These phenotypes were reversed by administration of a monoclonal anti-CGRP F(ab')₂ fragment antibody. Stress-induced changes in visceral sensitivity and spinal nociceptive signaling were reversed by inhibition of peripheral CGRP signaling, which suggests a prominent role for CGRP in central sensitization and the development of stress-induced visceral hypersensitivity. SIGNIFICANCE STATEMENT: Targeting peripheral calcitonin gene-related peptide (CGRP) with a monoclonal anti-CGRP divalent antigen-binding fragment antibody reduced central sensitization and attenuated colonic hypersensitivity induced by either chronic adult stress or early life stress. CGRP-targeting antibodies are approved for migraine prevention, and the results of this study suggest that targeting CGRP may provide a novel treatment strategy for irritable bowel syndrome-related, stress-induced visceral pain.

Prospective Associations of Frequent Pain Symptoms With Suicidal Behavior in Adolescents

Chronic pain and suicidal behavior are prevalent in adolescents. This longitudinal study examined the associations between pain symptoms and suicidal behavior in adolescents. A total of 7,072 adolescents participated in a follow-up study of behavior and health in Shandong, China. A self-administered structured questionnaire was used to assess pain symptoms (headache, stomachache, and other nonspecific pain), insomnia, anxiety/depression, substance use, stressful life events, prior suicidal behavior, and family environment in November-December in 2015. One year later, a follow-up survey was conducted. Mean age of the sample was 14.6 years, and half were female. Of the sample, 44.8% and 8.4% reported having one or more pain symptoms "sometimes" and "often", respectively. A total of 22.4% and 10.6% reported having lifetime suicidal behavior at baseline and subsequent suicidal behavior over the 1-year follow-up, respectively. Frequent pain was significantly associated with increased risk of suicidal behavior at baseline (OR=1.64, 95%CI=1.32-2.03) and during the subsequent year (OR=1.50, 95%CI=1.17-1.93) while adjusting for adolescent individual and family covariates. Among adolescents without a history of prior suicidal behavior, frequent pain was significantly associated with an approximately 70% increased risk of incident suicidal behavior (OR= 1.69, 95%CI=1.14-2.51). In conclusion, frequent pain appears to be predictive of adolescent suicidal behavior one year later. PERSPECTIVE: This article presents the prospective associations of frequent pain symptoms with suicidal behavior in adolescents. Frequent pain was associated with a 50-70% increased risk of suicidal behavior 1 year later. The finding underscores the importance of pain assessment and treatment in comprehensive suicide prevention efforts in adolescents.

Irritable bowel syndrome in midlife women: a narrative review

Midlife women between the ages of 40 and 65 years have reported multiple challenges due to menopausal, developmental, and situational transitions from younger to older adulthood. During the midlife period, many women seek health care for gastrointestinal symptoms and irritable bowel syndrome (IBS). Multiple factors including stress, poor sleep, diet, and physical inactivity may contribute to IBS or gastrointestinal symptoms in midlife women. As such, a comprehensive assessment and treatment approach is needed for midlife women suffering gastrointestinal symptoms. This article reviews the main aspects of the menopausal transition, sex hormonal changes, abdominal and pelvic surgery, psychosocial distress, behavioral factors, and gut microbiome, as well as their relevance on IBS and gastrointestinal symptoms in midlife women. Also, management strategies for IBS in midlife women are discussed. To date, gastrointestinal symptoms during midlife years remain a critical area of women’s health. Additional research is needed to better understand the contributors to gastrointestinal symptoms in this group. Such efforts may provide a new window to refine or develop treatments of gastrointestinal symptoms for midlife women.

Histamine-dependent interactions between mast cells, glia, and neurons are altered following early-life adversity in mice and humans

Early-life adversity contributes to the development of functional bowel disorders later in life through unresolved mechanisms. Here, we tested the hypothesis that early-life adversity alters anatomical and functional interactions between mast cells and enteric glia. The effects of early-life stress were studied using the neonatal maternal separation (NMS) stress mouse model. Anatomical relationships between mast cells and enteric glia were assessed using immunohistochemistry and mast cell reporter mice (Mcpt5^Cre;GCaMP5g-tdT). Immunohistochemistry was used to assess the expression of histamine, histamine 1 (H1) receptors, and glial fibrillary acidic protein. Functional responses of glia to mast cell mediators were assessed in calcium imaging experiments using Sox10^CreERT2;GCaMP5g-tdT mice and cultured human enteric glial cells. NMS increases mast cell numbers at the level of the myenteric plexus and their proximity to myenteric ganglia. Myenteric glia respond to mediators released by activated mast cells that are blocked by H1 receptor antagonists in mice and humans and by blocking neuronal activity with tetrodotoxin in mouse tissue. Histamine replicates the effects of mast cell supernatants on enteric glia, and NMS increases histamine production by mast cells. NMS reduces glial responses to mast cell mediators in mouse tissue, while potentiating responses in cultured human enteric glia. NMS increases myenteric glial fibrillary acidic protein expression and reduces glial process length but does not cause neurodegeneration. Histamine receptor expression is not altered by NMS and is localized to neurons in mice, but glia in humans. Early-life stress increases the potential for interactions between enteric glia and mast cells, and histamine is a potential mediator of mast cell-glial interactions through H1 receptors. We propose that glial-mast cell signaling is a mechanism that contributes to enteric neuroplasticity driven by early-life adversity.NEW & NOTEWORTHY Early-life adversity places an individual at risk for developing functional gastrointestinal disorders later in life through unknown mechanisms. Here, we show that interactions between mast cells and glia are disrupted by early-life stress in mice and that histamine is a potential mediator of mast cell-glial interactions.

Disinhibition of PVN-projecting GABAergic neurons in AV region in BNST participates in visceral hypersensitivity in rats

Ample evidence suggests that early life stress (ELS) is a high-risk factor for the development of visceral pain disorders, whereas the mechanism underlying neuronal circuit remains elusive. Herein, we employed neonatal colorectal distension (CRD) to induce visceral hypersensitivity in rats. A combination of electrophysiology, pharmacology, behavioral test, molecular biology, chemogenetics and optogenetics confirmed that CRD in neonatal rats could predispose the elevated firing frequency of the parvocellular corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus of hypothalamus (PVN) in adulthood, with the CRH neurons activated and the frequency of spontaneous inhibitory postsynaptic currents (sIPSC) diminished, both contributing to chronic visceral hypersensitivity. Moreover, following administration of exogenous GABA (300 mM/0.5 μL) and GABA_A receptor agonist muscimol (3 mM/0.5 μL) in PVN, visceral hyperalgesia was abrogated. In addition, the PVN-projecting GABAergic neurons were mainly distributed in the anterior ventral (AV) region in the bed nucleus of stria terminalis (BNST), and the excitability of these GABAergic neurons was weakened in visceral hypersensitivity. Specific depletion of the GABAergic neurons in AV region precipitated visceral hyperalgesia. Moreover, chemogenetic activation of the PVN-projecting neurons alleviated the visceral hypersensitivity. Photoactivation of PVN-projecting GABAergic neurons abated the visceral hypersensitivity in neonatal-CRD rats, whereas photoinhibition evoked visceral hyperalgesia in naïve rats. Our findings demonstrated that disinhibition of the PVN-projecting GABAergic neurons in AV region contributed to the excitation of CRH neurons, thereby mediating visceral hypersensitivity. Our study might provide a novel insight into the neuronal circuits involved in the ELS-induced visceral hypersensitivity.

Reprogramming of the Immune System by Stress and Faulty Hormonal Imprinting

PURPOSE

Hormonal imprinting is taking place perinatally at the first encounter between the developing hormone receptors and their target hormones. However, in this crucial period when the developmental window for physiological imprinting is open, other molecules, such as synthetic hormones and endocrine disruptors can bind to the receptors, leading to faulty imprinting with life-long consequences, especially to the immune system. This review presents the factors of stress and faulty hormonal imprinting that lead to reprogramming of the immune system.

METHODS

Relevant publications from Pubmed since 1990 were reviewed and synthesized.

FINDINGS

The developing immune system is rather sensitive to hormonal effects. Faulty hormonal imprinting is able to reprogram the original developmental program present in a given cell, with lifelong consequences, manifested in alteration of hormone binding by receptors, susceptibility to certain (non-infectious) diseases, and triggering of other diseases. As stress mobilizes the hypothalamic-pituitary-adrenal axis if it occurred during gestation or perinatally, it could lead to faulty hormonal imprinting in the immune system, manifested later as allergic and autoimmune diseases or weakness of normal immune defenses. Hormonal imprinting is an epigenetic process and is carried to the offspring without alteration of DNA base sequences. This means that any form of early-life stress alone or in association with hormonal imprinting could be associated with the developmental origin of health and disease (DOHaD). As puberty is also a period of reprogramming, stress or faulty imprinting can change the original (developmental) program, also with life-long consequences.

IMPLICATIONS

Considering the continuous differentiation of immune cells (from blast-cells) during the whole life, there is a possibility of late-imprinting or stress-activated reprogramming in the immune system at any periods of life, with later pathogenetic consequences.

Early life esophageal acid exposure reduces expression of NMDAR1 in the adult rat dorsal hippocampus and medial prefrontal cortex: Potential relationship with hyperlocomotion

OBJECTIVE

Early life esophageal acid exposure causes long-term molecular alterations in the rostral cingulate cortex; however, whether it induces behavioral changes remains unverified. Little is known about the molecular changes resulting from this event in the developing hippocampus and medial prefrontal cortex (mPFC). This study aimed to investigate the influence of early life esophageal acid exposure on spontaneous locomotor behavior and N-methyl-D-aspartate receptor (NMDAR), expression in these brain regions of adult rats.

METHODS

Male Sprague-Dawley rats were administered with an esophageal acid or saline infusion once per day (postnatal days 7-14). Some of these rats were given acute esophageal acid rechallenge in adulthood (postnatal day 60). The spontaneous locomotor behavior and expressions of esophageal epithelial caludin-1 and NMDAR subunits in the dorsal hippocampus (DH), ventral hippocampus (VH) and mPFC of the adult rats were recorded.

RESULTS

Neonatal esophageal acid stimulation caused long-term impairment of the tight junctions in the adult esophagus. Simultaneously, hyperlocomotion and reduced expression of NMDAR1 subunits in both the DH and mPFC were observed, but not in the VH regions. Adult acute acid rechallenge reversed the decreased NMDAR1 expression in the DH and mPFC. The glycine ligand to NMDAR1 subunits was also changed.

CONCLUSIONS

Peripheral visceral stimulation such as esophageal acid exposure during cerebral development induces increased locomotor activity, which may be related to the alteration of central sensitivity via NMDAR1 subunit reduction in the DH and mPFC. The impairment of tight junctions in the esophageal epithelium may contribute to the formation of central neuroplasticity.

Behavioural medicine and gastrointestinal disorders: the promise of positive psychology

Psychosocial risk factors linked to brain-gut dysregulation are prevalent across the spectrum of gastrointestinal disorders and are associated with poor patient outcomes. Robust and reproducible data in the areas of behavioural intervention science and the brain-gut axis have led to major advances in patient care, including the routine use of brain-gut psychotherapies to manage digestive symptoms and optimize coping. The logical next step for the emerging field of psychogastroenterology is to develop a scientific framework that enables the identification of those individual characteristics and coping styles that buffer patients against the negative psychological effects of chronic gastrointestinal disorders. A shift towards a strength-based, positive psychological science of gastrointestinal disorders could facilitate the integration of early, effective psychological care into gastroenterology practice. In this Perspective, I discuss the potential role of three human strengths with relevance to gastrointestinal health - resilience, optimism and self-regulation - and how these three constructs can be cultivated through existing or emerging brain-gut psychotherapies.

The Role of Diet in the Treatment of Irritable Bowel Syndrome: A Systematic Review

Irritable bowel syndrome (IBS) is a multifaceted illness involving maladaptive shifts in the gut microbiota that affect the enteric nervous and immune systems, mucosal barrier function, the balance of neurotransmitters and hormones, and emotional well-being. There is abundant evidence indicating that certain foods elicit symptoms in IBS. Numerous elimination-type diets have been shown to alleviate symptoms. However, among these, the most controversial is a group of foods called fructo, oligo-, di-, and monosaccharides and polyols (FODMAPs). This paper reviews the role of diet and systematically analyze the literature for the role of FODMAPs in IBS.

Mechanisms of Stress-induced Visceral Pain

Evidence suggests that long-term stress facilitates visceral pain through sensitization of pain pathways and promotes chronic visceral pain disorders such as the irritable bowel syndrome (IBS). This review will describe the importance of stress in exacerbating IBS-induced abdominal pain. Additionally, we will briefly review our understanding of the activation of the hypothalamic-pituitary-adrenal axis by both chronic adult stress and following early life stress in the pathogenesis of IBS. The review will focus on the glucocorticoid receptor and corticotropin-releasing hormone-mediated mechanisms in the amygdala involved in stress-induced visceral hypersensitivity. One potential mechanism underlying persistent effects of stress on visceral sensitivity could be epigenetic modulation of gene expression. While there are relatively few studies examining epigenetically mediated mechanisms involved in stress-induced visceral nociception, alterations in DNA methylation and histone acetylation patterns within the brain, have been linked to alterations in nociceptive signaling via increased expression of pro-nociceptive neurotransmitters. This review will discuss the latest studies investigating the long-term effects of stress on visceral sensitivity. Additionally, we will critically review the importance of experimental models of adult stress and early life stress in enhancing our understanding of the basic molecular mechanisms of nociceptive processing.

Irritable Bowel Syndrome and Stress-Related Psychiatric Co-morbidities: Focus on Early Life Stress

Irritable bowel syndrome is a functional gastrointestinal disorder, with stress playing a major role in onset and exacerbation of symptoms such as abdominal pain and altered bowel movements. Stress-related disorders including anxiety and depression often precede the development of irritable bowel syndrome and vice versa. Stressor exposure during early life has the potential to increase an individual's susceptibility to both irritable bowel syndrome and psychiatric disease indicating that there may be a common origin for these disorders. Moreover, adverse early life events significantly impact upon many of the communication pathways within the brain-gut-microbiota axis, which allows bidirectional interaction between the central nervous system and the gastrointestinal tract. This axis is proposed to be perturbed in irritable bowel syndrome and studies now indicate that dysfunction of this axis is also seen in psychiatric disease. Here we review the co-morbidity of irritable bowel syndrome and psychiatric disease with their common origin in mind in relation to the impact of early life stress on the developing brain-gut-microbiota axis. We also discuss the therapeutic potential of targeting this axis in these diseases.

Psychological and physical pain as predictors of suicide risk: evidence from clinical and neuroimaging findings

PURPOSE OF REVIEW

Suicide is a multidimensional clinical phenomenon with complex biological, social and psychological risk factors. Therefore, it is imperative for studies to focus on developing a unified understanding of suicide risk that integrates current clinical and neurobiological findings. A recent line of research has implicated different classifications of pain in understanding suicide risk, including the concepts of psychache and pain tolerance. Although psychache is defined as the experience of unbearable psychological pain, pain tolerance refers to the greatest duration or intensity of painful stimuli that one is able to bear. This review will focus on integrating current clinical and neurobiological findings by which psychache and pain tolerance confer suicide risk.

RECENT FINDINGS

Results indicate that psychache has been identified as a significant risk factor for suicide and that psychache may be associated with the neurocircuitry involved in the modulation of physical pain. Converging evidence has also been found linking pain tolerance to self-injurious behaviours and suicide risk. The experience of psychache and physical pain in relation to other predictors of suicide, including reward processing, hopelessness and depression, are further discussed.

SUMMARY

Future research examining the pain-suicide connection is required to understand the mechanism behind clinically relevant risk factors for suicide, which can ultimately inform the construction of empirically supported suicide risk assessment and intervention techniques.