Early-life inflammation with LPS delays fear extinction in adult rodents

A Rapid Heat-Enhanced Golgi-Cox Staining Method for Detailed Neuroanatomical Analysis Coupled With Immunostaining

The Golgi-Cox staining technique is renowned for its ability to delineate neuronal architecture with remarkable precision. However, the traditional protocol's lengthy processing timeline and limited compatibility with immunostaining and transgenic labeling have hindered its widespread adoption in modern neuroscience research. In the current study, we found that adjusting the incubation temperature to 55°C significantly reduced the staining duration to a mere 24 h for 100 µm-thick sections of mouse brain tissue. Importantly, our optimized protocol is compatible with immunostaining techniques and transgenic mouse models. In addition, using a lipopolysaccharides-induced mouse model of depression, we found a reduction in dendritic spines labeled by Golgi-Cox staining and an increase in the number of microglial cells labeled by immunofluorescence in the same samples, in addition, cross-talk between Golgi-Cox-stained neurons and microglial fibers were observed. In conclusion, the modified Golgi-Cox staining technique allows for the acquisition of a more comprehensive set of data from the same biological tissue with increased efficiency. This advancement promises to improve methodologies in histopathology and neurobiology, making advanced applications of Golgi-Cox staining more accessible in contemporary neuroscience research.

Peripherally-restricted recurrent infection by engineered E. coli strain modulates hippocampal proteome promoting memory impairments in a rat model

Commensal bacteria that breach endothelial barrier has been reported to induce low grade chronic inflammation producing disease symptoms in major peripheral tissues. In this study, we investigated the role of genetically modified cellular invasive form of commensal E. coli K12 (SK3842) in cognitive impairment. Low-grade systemic infection model was developed using recurring peripheral inoculation of live bacteria in Wistar rats. To examine memory parameters, Novel object recognition test and Radial arm maze test were performed. Differential protein expression profiling of rat hippocampus was carried out using LC-MS/MS and subsequently quantified using SWATH. HBA1/2, NEFH, PFN1 and ATP5d were chosen for validation using quantitative RT-PCR. Results showed drastic decline in Recognition memory of the SK3842 infected rats. Reference and Working Memory of the infected group were also significantly reduced in comparison to control group. Proteome analysis using LC-MS/MS coupled with SWATH revealed differential expression of key proteins that are crucial for the maintenance of various neurological functions. Moreover, expression of NEFH and PFN1transcripts were found to be in line with the proteomics data. Protein interaction network of these validated proteins generated by STRING database converged to RhoA protein. Thus, the present study establishes an association between peripheral infection of a hippocampal protein network dysregulation and overall memory decline.

Lipopolysaccharide-induced endotoxaemia during adolescence promotes stress vulnerability in adult mice via deregulation of nuclear factor erythroid 2-related factor 2 in the medial prefrontal cortex

RATIONALE

Sepsis is a severe inflammatory response to infection that leads to long-lasting cognitive impairment and depression after resolution. The lipopolysaccharide (LPS)-induced endotoxaemia model is a well-established model of gram-negative bacterial infection and recapitulates the clinical characteristics of sepsis. However, whether LPS-induced endotoxaemia during adolescence can modulate depressive and anxiety-like behaviours in adulthood remains unclear.

OBJECTIVES

To determine whether LPS-induced endotoxaemia in adolescence can modulate the stress vulnerability to depressive and anxiety-like behaviours in adulthood and explore the underlying molecular mechanisms.

METHODS

Quantitative real-time PCR was used to measure inflammatory cytokine expression in the brain. A stress vulnerability model was established by exposure to subthreshold social defeat stress (SSDS), and depressive- and anxiety-like behaviours were evaluated by the social interaction test (SIT), sucrose preference test (SPT), tail suspension test (TST), force swimming test (FST), elevated plus-maze (EPM) test, and open field test (OFT). Western blotting was used to measure Nrf2 and BDNF expression levels in the brain.

RESULTS

Our results showed that inflammation occurred in the brain 24 h after the induction of LPS-induced endotoxaemia at P21 but resolved in adulthood. Furthermore, LPS-induced endotoxaemia during adolescence promoted the inflammatory response and the stress vulnerability after SSDS during adulthood. Notably, the expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and BDNF in the mPFC were decreased after SSDS exposure in mice treated with LPS during adolescence. Activation of the Nrf2-BDNF signalling pathway by sulforaphane (SFN), an Nrf2 activator, ameliorated the effect of LPS-induced endotoxaemia during adolescence on stress vulnerability after SSDS during adulthood.

CONCLUSIONS

Our study identified adolescence as a critical period during which LPS-induced endotoxaemia can promote stress vulnerability during adulthood and showed that this effect is mediated by impairment of Nrf2-BDNF signalling in the mPFC.

Neuroinflammation is a susceptibility factor in developing a PTSD-like phenotype

Introduction

Post-Traumatic Stress Disorder (PTSD) is a psychological disorder that occurs after a traumatic event in a subset of exposed individuals. This implies the existence of susceptibility factors that foster the development of PTSD. Susceptibility factors are present before trauma and can contribute to the development and maintenance of PTSD after trauma. Manipulation of susceptibility factors may decrease the probability of developing PTSD. A putative susceptibility factor is inflammation. Patients with PTSD have been documented to have a higher pro-inflammatory profile compared to non-PTSD subjects. In addition, they are more likely to develop and die from cardiovascular disease which has a strong inflammation component. It is not known, however, whether inflammation plays a role in developing PTSD or whether reducing inflammation can prevent PTSD.

Methods

We used the Revealing Individual Susceptibility to a PTSD-like phenotype (RISP) model to behaviorally classify male rats as resilient or susceptible before trauma and tested their serum and prefrontal cortical (mPFC) levels of IL-1β, IL-6, TNFα, IL-10, IFN IFNγ, and KC/GRO to determine whether inflammation represents a putative susceptibility factor for PTSD.

Results

We found elevated IL-6 levels in the mPFC, but not serum, of susceptible rats compared to resilient animals before trauma. Serum and mPFC levels were not correlated in any of the cytokines/chemokines. Rats with high anxiety-like behavior had elevated IL-6 and IL-10 mPFC levels. Acoustic startle responses were not associated with cytokine/chemokine levels.

Discussion

Neuroinflammation, rather than systemic inflammation exists in susceptible male rats before trauma and is thus a putative susceptibility factor for PTSD. Thus, susceptibility appears neurogenic in its pathogenesis. The lack of differences between susceptible and resilient rats in serum cytokine/chemokine levels infers that peripheral markers will not be useful in determining susceptibility. Chronic neuroinflammation appears more broadly associated with anxiety rather than startle responses.

New Insights into the Pivotal Role of the Amygdala in Inflammation-Related Depression and Anxiety Disorder

Depression and anxiety disorders are the two most prevalent psychiatric diseases that affect hundreds of millions of individuals worldwide. Understanding the etiology and related mechanisms is of great importance and might yield new therapeutic strategies to treat these diseases effectively. During the past decades, a growing number of studies have pointed out the importance of the stress-induced inflammatory response in the amygdala, a kernel region for processing emotional stimuli, as a potentially critical contributor to the pathophysiology of depression and anxiety disorders. In this review, we first summarized the recent progress from both animal and human studies toward understanding the causal link between stress-induced inflammation and depression and anxiety disorders, with particular emphasis on findings showing the effect of inflammation on the functional changes in neurons in the amygdala, at levels ranging from molecular signaling, cellular function, synaptic plasticity, and the neural circuit to behavior, as well as their contributions to the pathology of inflammation-related depression and anxiety disorders. Finally, we concluded by discussing some of the difficulties surrounding the current research and propose some issues worth future study in this field.

Severe inflammation in new-borns induces long-term cognitive impairment by activation of IL-1β/KCC2 signaling during early development

BACKGROUND

Neonatal sepsis can induce long-term cognitive impairment in adolescence or adulthood, but the underlying molecular mechanism is not fully understood. The expression of K⁺-Cl^- co-transporter 2 (KCC2) plays a pivotal role in the GABAergic shift from depolarizing to hyperpolarizing during early postnatal development. In this study, we aimed to determine whether neonatal severe inflammation-induced cognitive impairment was associated with the expression of KCC2 during early development.

METHODS

Neonatal severe inflammation was established by intraperitoneal injection of high dose lipopolysaccharide (LPS, 1 mg kg^-1) in postnatal day 3 (P3) rats. The Morris water maze task and fear conditioning test were used to investigate long-term cognitive functions. ELISA, RT-PCR and Western blotting were used to examine the expression levels of proinflammatory cytokines and KCC2. Perforated patch-clamping recordings were used to determine the GABAergic shift.

RESULTS

Neonatal severe inflammation led to long-term cognitive impairment in rats. Meanwhile, sustained elevation of interleukin-1 beta (IL-1β) levels was found in the hippocampus until P30 after LPS injection. Elevated expression of KCC2 and hyperpolarized GABA reversal potential (E_GABA) were observed in CA1 hippocampal pyramidal neurons from the P7-P10 and P14-P16 rats after LPS injection. Specific knockdown of IL-1β mRNA expression rescued the elevated expression of KCC2 and the hyperpolarized E_GABA at P7-P10 and P14-P16. Accordingly, specific knockdown of IL-1β or KCC2 expression improved the cognitive impairment induced by neonatal severe inflammation.

CONCLUSIONS

Sustained elevation of IL-1β in the hippocampus may induce cognitive impairment by upregulation of KCC2 during early development.

Inflammation-driven brain and gut barrier dysfunction in stress and mood disorders

Regulation of emotions is generally associated exclusively with the brain. However, there is evidence that peripheral systems are also involved in mood, stress vulnerability vs. resilience, and emotion-related memory encoding. Prevalence of stress and mood disorders such as major depression, bipolar disorder, and post-traumatic stress disorder is increasing in our modern societies. Unfortunately, 30%-50% of individuals respond poorly to currently available treatments highlighting the need to further investigate emotion-related biology to gain mechanistic insights that could lead to innovative therapies. Here, we provide an overview of inflammation-related mechanisms involved in mood regulation and stress responses discovered using animal models. If clinical studies are available, we discuss translational value of these findings including limitations. Neuroimmune mechanisms of depression and maladaptive stress responses have been receiving increasing attention, and thus, the first part is centered on inflammation and dysregulation of brain and circulating cytokines in stress and mood disorders. Next, recent studies supporting a role for inflammation-driven leakiness of the blood-brain and gut barriers in emotion regulation and mood are highlighted. Stress-induced exacerbated inflammation fragilizes these barriers which become hyperpermeable through loss of integrity and altered biology. At the gut level, this could be associated with dysbiosis, an imbalance in microbial communities, and alteration of the gut-brain axis which is central to production of mood-related neurotransmitter serotonin. Novel therapeutic approaches such as anti-inflammatory drugs, the fast-acting antidepressant ketamine, and probiotics could directly act on the mechanisms described here improving mood disorder-associated symptomatology. Discovery of biomarkers has been a challenging quest in psychiatry, and we end by listing promising targets worth further investigation.

An immunogenomic phenotype predicting behavioral treatment response: Toward precision psychiatry for mothers and children with trauma exposure

Inflammatory pathways predict antidepressant treatment non-response among individuals with major depression; yet, this phenomenon may have broader transdiagnostic and transtherapeutic relevance. Among trauma-exposed mothers (M_age = 32 years) and their young children (M_age = 4 years), we tested whether genomic and proteomic biomarkers of pro-inflammatory imbalance prospectively predicted treatment response (PTSD and depression) to an empirically-supported behavioral treatment. Forty-three mother-child dyads without chronic disease completed Child Parent Psychotherapy (CPP) for roughly 9 months. Maternal blood was drawn pre-treatment, CD14 + monocytes isolated, gene expression derived from RNA sequencing (n = 34; Illumina HiSeq 4000;TruSeqcDNA library), and serum assayed (n = 43) for C-Reactive Protein (CRP) and interleukin-1ß (IL-1ß). Symptoms of PTSD and depression decreased significantly from pre- to post-treatment for both mothers and children (all p's < 0.01). Nonetheless, a higher pre-treatment maternal pro-inflammatory imbalance of M1-like versus M2-like macrophage-associated RNA expression (M1/M2) (ß = 0.476, p = .004) and IL-1ß (ß=0.333, p = .029), but not CRP, predicted lesser improvements in maternal PTSD symptoms, unadjusted and adjusting for maternal age, BMI, ethnicity, antidepressant use, income, education, and US birth. Only higher pre-treatment M1/M2 predicted a clinically-relevant threshold of PTSD non-response among mothers (OR = 3.364, p = .015; ROC-AUC = 0.78). Additionally, higher M1/M2 predicted lesser decline in maternal depressive symptoms (ß = 0.556, p = .001), though not independent of PTSD symptoms. For child outcomes, higher maternal IL-1ß significantly predicted poorer PTSD and depression symptom trajectories (ß's = 0.318-0.429, p's < 0.01), while M1/M2 and CRP were marginally associated with poorer PTSD symptom improvement (ß's = 0.295-0.333, p's < 0.056). Pre-treatment pro-inflammatory imbalance prospectively predicts poorer transdiagnostic symptom response to an empirically-supported behavioral treatment for trauma-exposed women and their young children.

Early Life Painful Procedures: Long-Term Consequences and Implications for Farm Animal Welfare

Farm animals routinely undergo painful husbandry procedures early in life, including disbudding and castration in calves and goat kids, tail docking and castration in piglets and lambs, and beak trimming in chicks. In rodents, inflammatory events soon after birth, when physiological systems are developing and sensitive to perturbation, can profoundly alter phenotypic outcomes later in life. This review summarizes the current state of research on long-term phenotypic consequences of neonatal painful procedures in rodents and farm animals, and discusses the implications for farm animal welfare. Rodents exposed to early life inflammation show a hypo-/hyper-responsive profile to pain-, fear-, and anxiety-inducing stimuli, manifesting as an initial attenuation in responses that transitions into hyperresponsivity with increasing age or cumulative stress. Neonatal inflammation also predisposes rodents to cognitive, social, and reproductive deficits, and there is some evidence that adverse effects may be passed to offspring. The outcomes of neonatal inflammation are modulated by injury etiology, age at the time of injury and time of testing, sex, pain management, and rearing environment. Equivalent research examining long-term phenotypic consequences of early life painful procedures in farm animals is greatly lacking, despite obvious implications for welfare and performance. Improved understanding of how these procedures shape phenotypes will inform efforts to mitigate negative outcomes through reduction, replacement, and refinement of current practices.

Rapidly Growing Mycobacterium Species: The Long and Winding Road from Tuberculosis Vaccines to Potent Stress-Resilience Agents

Inflammatory diseases and stressor-related psychiatric disorders, for which inflammation is a risk factor, are increasing in modern Western societies. Recent studies suggest that immunoregulatory approaches are a promising tool in reducing the risk of suffering from such disorders. Specifically, the environmental saprophyte Mycobacterium vaccae National Collection of Type Cultures (NCTC) 11659 has recently gained attention for the prevention and treatment of stress-related psychiatric disorders. However, effective use requires a sophisticated understanding of the effects of M. vaccae NCTC 11659 and related rapidly growing mycobacteria (RGMs) on microbiome–gut–immune–brain interactions. This historical narrative review is intended as a first step in exploring these mechanisms and provides an overview of preclinical and clinical studies on M. vaccae NCTC 11659 and related RGMs. The overall objective of this review article is to increase the comprehension of, and interest in, the mechanisms through which M. vaccae NCTC 11659 and related RGMs promote stress resilience, with the intention of fostering novel clinical strategies for the prevention and treatment of stressor-related disorders.

Early-life inflammation promotes depressive symptoms in adolescence via microglial engulfment of dendritic spines

Early-life inflammation increases the risk for depression in later life. Here, we demonstrate how early-life inflammation causes adolescent depressive-like symptoms: by altering the long-term neuronal spine engulfment capacity of microglia. For mice exposed to lipopolysaccharide (LPS)-induced inflammation via the Toll-like receptor 4/NF-κB signaling pathway at postnatal day (P) 14, ongoing longitudinal imaging of the living brain revealed that later stress (delivered during adolescence on P45) increases the extent of microglial engulfment around anterior cingulate cortex (ACC) glutamatergic neuronal (ACCGlu) spines. When the ACC microglia of LPS-treated mice were deleted or chemically inhibited, the mice did not exhibit depressive-like behaviors during adolescence. Moreover, we show that the fractalkine receptor CX3CR1 mediates stress-induced engulfment of ACCGlu neuronal spines. Together, our findings establish that early-life inflammation causes dysregulation of microglial engulfment capacity, which encodes long-lasting maladaptation of ACCGlu neurons to stress, thus promoting development of depression-like symptoms during adolescence.

Neonatal Exposure to Bacterial Lipopolysaccharide Affects Behavior and Expression of Ionotropic Glutamate Receptors in the Hippocampus of Adult Rats after Psychogenic Trauma

According to the two-hit hypothesis of psychoneuropathology formation, infectious diseases and other pathological conditions occurring during the critical periods of early ontogenesis disrupt normal brain development and increase its susceptibility to stress experienced in adolescence and adulthood. It is believed that these disorders are associated with changes in the functional activity of the glutamatergic system in the hippocampus. Here, we studied expression of NMDA (GluN1, GluN2a, GluN2b) and AMPA (GluA1, GluA2) glutamate receptor subunits, as well as glutamate transporter EAAT2, in the ventral and dorsal regions of the hippocampus of rats injected with LPS during the third postnatal week and then subjected to predator stress (contact with a python) in adulthood. The tests were performed 25 days after the stress. It was found that stress altered protein expression in the ventral, but not in the dorsal hippocampus. Non-stressed LPS-treated rats displayed lower levels of the GluN2b protein in the ventral hippocampus vs. control animals. Stress significantly increased the content of GluN2b in the LPS-treated rats, but not in the control animals. Stress also affected differently the exploratory behavior of LPS-injected and control rats. Compared to the non-stressed animals, stressed control rats demonstrated a higher locomotor activity during the 1st min of the open field test, while the stressed LPS-injected rats displayed lower locomotor activity than the non-stressed rats. In addition, LPS-treated stressed and non-stressed rats spent more time in the open arms of the elevated plus maze and demonstrated reduced blood levels of corticosterone. To summarize the results of our study, exposure to bacterial LPS in the early postnatal ontogenesis affects the pattern of stress-induced changes in the behavior and hippocampal expression of genes coding for ionotropic glutamate receptor subunits after psychogenic trauma suffered in adulthood.

What animal models can tell us about long-term cognitive dysfunction following sepsis: A systematic review

Survivors of sepsis often develop long-term cognitive impairments. This review aimed at exploring the results of the behavioral tools and tests which have been used to evaluate cognitive dysfunction in different animal models of sepsis. Two independent investigators searched for sepsis- and cognition-related keywords. 6323 publications were found, of which 355 were selected based on their title, and 226 of these were chosen based on manuscript review. LPS was used to induce sepsis in 171 studies, while CLP was used in 55 studies. Inhibitory avoidance was the most widely used method for assessing aversive memory, followed by fear conditioning and continuous multi-trial inhibitory avoidance. With regard to non-aversive memory, most studies used the water maze, open-field, object recognition, Y-maze, plus maze, and radial maze tests. Both CLP and LPS models of sepsis were effective in inducing short- and long-term behavioral impairment. Our findings help elucidate the mechanisms involved in the pathophysiology of sepsis-induced cognitive changes, as well as the available methods and tests used to study this in animal models.

Increased Excitatory Synaptic Transmission Associated with Adult Seizure Vulnerability Induced by Early-Life Inflammation in Mice

Early-life inflammatory stress increases seizure susceptibility later in life. However, possible sex- and age-specific differences and the associated mechanisms are largely unknown. C57BL/6 mice were bred in house, and female and male pups were injected with lipopolysaccharide (LPS; 100 μg/kg, i.p.) or vehicle control (saline solution) at postnatal day 14 (P14). Seizure threshold was assessed in response to pentylenetetrazol (1% solution, i.v.) in adolescence (∼P40) and adulthood (∼P60). We found that adult, but not adolescent, mice treated with LPS displayed ∼34% lower seizure threshold compared with controls. Females and males showed similar increased seizure susceptibility, suggesting that altered brain excitability was age dependent, but not sex dependent. Whole-cell recordings revealed no differences in excitatory synaptic activity onto CA1 pyramidal neurons from control or neonatally inflamed adolescent mice of either sex. However, adult mice of both sexes previously exposed to LPS displayed spontaneous EPSC frequency approximately twice that of controls, but amplitude was unchanged. Although these changes were not associated with alterations in dendritic spines or in the NMDA/AMPA receptor ratio, they were linked to an increased glutamate release probability from Schaffer collateral, but not temporoammonic pathway. This glutamate increase was associated with reduced activity of presynaptic GABA_B receptors and was independent of the endocannabinoid-mediated suppression of excitation. Our new findings demonstrate that early-life inflammation leads to long-term increased hippocampal excitability in adult female and male mice associated with changes in glutamatergic synaptic transmission. These alterations may contribute to enhanced vulnerability of the brain to subsequent pathologic challenges such as epileptic seizures.SIGNIFICANCE STATEMENT Adult physiology has been shown to be affected by early-life inflammation. Our data reveal that early-life inflammation increases excitatory synaptic transmission onto hippocampal CA1 pyramidal neurons in an age-dependent manner through disrupted presynaptic GABA_B receptor activity on Schaffer collaterals. This hyperexcitability was seen only in adult, and not in adolescent, animals of either sex. The data suggest a maturation process, independent of sex, in the priming action of early-life inflammation and highlight the importance of studying mature brains to reveal cellular changes associated with early-life interventions.

Exposure to bacterial lipopolysaccharidein early life affects the expression of ionotropic glutamate receptor genes and is accompanied by disturbances in long-term potentiation and cognitive functions in young rats

Infections in childhood play an essential role in the pathogenesis of cognitive and psycho-emotional disorders. One of the possible mechanisms of these impairments is changes in the functional properties of NMDA and AMPA glutamate receptors in the brain. We suggest that bacterial infections during the early life period, which is critical for excitatory synapse maturation, can affect the subunit composition of NMDA and AMPA receptors. In the present study, we investigated the effect of repetitive lipopolysaccharide (LPS) intraperitoneal (i.p.) administration (25 μg/kg/day on P14, 16, and 18), mimicking an infectious disease, on the expression of subunits of NMDA and AMPA receptors in young rats. We revealed a substantial decrease of GluN2B subunit expression in the hippocampus at P23 using Western blot analysis and real-time polymerase chain reaction assay. Moderate changes were also found in GluN1, GluN2A, and GluA1 mRNA expression. The LPS-treated rats exhibited decreased exploratory and locomotor activity in the open field test and the impairment of spatial learning in the Morris water maze. Behavioral impairments were accompanied by a significant reduction in long-term hippocampal synaptic potentiation. Our data indicate that LPS-treatment in the critical period for excitatory synapse maturation alters ionotropic glutamate receptor gene expression, disturbs synaptic plasticity, and alters behavior.

Dysregulation of inflammation, neurobiology, and cognitive function in PTSD: an integrative review

Compelling evidence from animal and human research suggest a strong link between inflammation and posttraumatic stress disorder (PTSD). Furthermore, recent findings support compromised neurocognitive function as a key feature of PTSD, particularly with deficits in attention and processing speed, executive function, and memory. These cognitive domains are supported by brain structures and neural pathways that are disrupted in PTSD and which are implicated in fear learning and extinction processes. The disruption of these supporting structures potentially results from their interaction with inflammation. Thus, the converging evidence supports a model of inflammatory dysregulation and cognitive dysfunction as combined mechanisms underpinning PTSD symptomatology. In this review, we summarize evidence of dysregulated inflammation in PTSD and further explore how the neurobiological underpinnings of PTSD, in the context of fear learning and extinction acquisition and recall, may interact with inflammation. We then present evidence for cognitive dysfunction in PTSD, highlighting findings from human work. Potential therapeutic approaches utilizing novel pharmacological and behavioral interventions that target inflammation and cognition also are discussed.

Impact of chemotherapy on the association between fear of cancer recurrence and the gut microbiota in breast cancer survivors

BACKGROUND

Dysfunctional processing of fear memory may be involved in the pathophysiology of fear of cancer recurrence (FCR), which is cited as the major unmet psychological need of cancer survivors. Emerging evidence has shown that the microbiota-gut-brain (MGB) axis affects depressive and anxiety disorders, and chemotherapy-associated psychological distress. We therefore hypothesized that the gut microbiota is associated with FCR in cancer survivors.

METHODS

This cross-sectional study enrolled women diagnosed with invasive breast cancer who were not currently undergoing chemotherapy. Fecal samples were obtained to assess the gut microbiota. FCR grade was assessed using the Concerns About Recurrence Scale (CARS).

RESULTS

Mean age of the participants (n = 126) was 58 years; 47% had stage I disease. Multiple regression analysis with adjustment for possible confounders showed that the relative abundance of the Bacteroides genus (beta = 0.180, p = 0.03) was significantly and directly associated with FCR. In the 57 participants with a history of chemotherapy, higher FCR was associated with lower microbial diversity (p = 0.04), lower relative abundance of Firmicutes (p = 0.03) and higher relative abundance of Bacteroidetes (p = 0.04) at the phylum level, and higher relative abundance of Bacteroides (p < 0.01) and lower relative abundance of Lachnospiraceae.g (p = 0.03) and Ruminococcus (p = 0.02) at the genus level.

CONCLUSION

Our findings provide the first evidence of an association between the gut microbiota and FCR and suggest that chemotherapy-induced changes in gut microbiota can influence FCR. Further studies should examine the effects of the gut microbiota on FCR using a prospective design.

Early Neonatal Pain-A Review of Clinical and Experimental Implications on Painful Conditions Later in Life

Modern health care has brought our society innumerable benefits but has also introduced the experience of pain very early in life. For example, it is now routine care for newborns to receive various injections or have blood drawn within 24 h of life. For infants who are sick or premature, the pain experiences inherent in the required medical care are frequent and often severe, with neonates requiring intensive care admission encountering approximately fourteen painful procedures daily in the hospital. Given that much of the world has seen a steady increase in preterm births for the last several decades, an ever-growing number of babies experience multiple painful events before even leaving the hospital. These noxious events occur during a critical period of neurodevelopment when the nervous system is very vulnerable due to immaturity and neuroplasticity. Here, we provide a narrative review of the literature pertaining to the idea that early life pain has significant long-term effects on neurosensory, cognition, behavior, pain processing, and health outcomes that persist into childhood and even adulthood. We refer to clinical and pre-clinical studies investigating how early life pain impacts acute pain later in life, focusing on animal model correlates that have been used to better understand this relationship. Current knowledge around the proposed underlying mechanisms responsible for the long-lasting consequences of neonatal pain, its neurobiological and behavioral effects, and its influence on later pain states are discussed. We conclude by highlighting that another important consequence of early life pain may be the impact it has on later chronic pain states-an area of research that has received little attention.

Early Life Inflammation Increases CA1 Pyramidal Neuron Excitability in a Sex and Age Dependent Manner through a Chloride Homeostasis Disruption

Early life, systemic inflammation causes long-lasting changes in behavior. To unmask possible mechanisms associated with this phenomenon, we asked whether the intrinsic membrane properties in hippocampal neurons were altered as a consequence of early life inflammation. C57BL/6 mice were bred in-house and both male and female pups from multiple litters were injected with lipopolysaccharide (LPS; 100 μg/kg, i.p.) or vehicle at postnatal day (P)14, and kept until adolescence (P35-P45) or adulthood (P60-P70), when brain slices were prepared for whole-cell and perforated-patch recordings from CA1 hippocampal pyramidal neurons. In neurons of adult male mice pretreated with LPS, the number of action potentials elicited by depolarizing current pulses was significantly increased compared with control neurons, concomitant with increased input resistance, and a lower action potential threshold. Although these changes were not associated with changes in relevant sodium channel expression or differences in capacitance or dendritic architecture, they were linked to a mechanism involving intracellular chloride overload, revealed through a depolarized GABA reversal potential and increased expression of the chloride transporter, NKCC1. In contrast, no significant changes were observed in neurons of adult female mice pretreated with LPS, nor in adolescent mice of either sex. These data uncover a potential mechanism involving neonatal inflammation-induced plasticity in chloride homeostasis, which may contribute to early life inflammation-induced behavioral alterations.SIGNIFICANCE STATEMENT Early life inflammation results in long-lasting changes in many aspects of adult physiology. In this paper we reveal that a brief exposure to early life peripheral inflammation with LPS increases excitability in hippocampal neurons in a sex- and age-dependent manner through a chloride homeostasis disruption. As this hyperexcitability was only seen in adult males, and not in adult females or adolescent animals of either sex, it raises the possibility of a hormonal interaction with early life inflammation. Furthermore, as neonatal inflammation is a normal feature of early life in most animals, as well as humans, these findings may be very important for the development of animal models of disease that more appropriately resemble the human condition.

Inflammatory neonatal pain disrupts maternal behavior and subsequent fear conditioning in a rodent model

Infants spending extended time in the neonatal intensive care unit are at greater risk of developing a variety of mental health problems later in life, possibly due to exposure to painful/stressful events. We used a rodent model of inflammatory neonatal pain to explore effects on fear conditioning, somatosensory function and maternal behavior. Hindpaw injections of 2% λ-carrageenan on postnatal days 1 and 4 produced an attenuation in conditioned freezing during the postweaning period, similar to our previous work with acute pain, but did not cause lasting impacts on contextual freezing nor somatosensory function. Additionally, we assessed maternal behavior to observe dam-pup interactions during the neonatal period. Results showed dams of litters which experienced pain spent similar amounts of time with pups as undisturbed controls. However, the specific behaviors differed per condition. Dams of pain litters exhibited less time licking/grooming, but more time nursing than controls. These results suggest changes in maternal care following pain could be a contributing factor underlying the long-term effects of neonatal trauma. Furthermore, our laboratory has previously shown acute, but not inflammatory pain, disrupted conditioned freezing; the current experiment observed the long-term effects of neonatal inflammatory pain on conditioned fear using a weak conditioning protocol.

Prenatal Inflammation Dampens Neurogenesis and Enhances Serotonin Transporter Expression in the Hippocampus of Adult Female Rats

BACKGROUND/AIMS

Prenatal exposure to lipopolysaccharide (LPS) dampens hippocampal neurogenesis. This effect is associated with increased anxiety-like behavior in adult offspring. Furthermore, blocking serotonin transporters (SERT) promotes adult neurogenesis. Previous studies were performed largely in males. Therefore, we explored the impact of prenatal LPS on neurogenesis, SERT expression in the hippocampus, and anxiety-like behavior in female rats during prepubertal and adulthood stages.

MATERIALS AND METHODS

Timed pregnant rats were injected with either saline or LPS (100 µg/kg, i.p.) on gestational days 15, 17, and 19. Newly born neurons were monitored by immunohistochemistry, and anxiety-like behavior was monitored using the elevated plus maze and open-field test. SERT expression in the hippocampus was assessed by Western blot and immunofluorescence.

RESULTS

Prenatal LPS led to reduced hippocampal neurogenesis in adult but not in prepubertal female offspring. This reduced neurogenesis was associated with enhanced hippocampal expression of SERT protein. However, there was no significant impact of prenatal LPS on anxiety-like behavior.

CONCLUSIONS

Prenatal LPS-induced reduction in neurogenesis was dissociated from anxiety-like behavior in adult female rats. Furthermore, the long-lasting impact of prenatal LPS on neurogenesis in female offspring was age-dependent.

Adverse neuropsychiatric development following perinatal brain injury: from a preclinical perspective

Perinatal brain injury is a leading cause of death and disability in young children. Recent advances in obstetrics, reproductive medicine and neonatal intensive care have resulted in significantly higher survival rates of preterm or sick born neonates, at the price of increased prevalence of neurological, behavioural and psychiatric problems in later life. Therefore, the current focus of experimental research shifts from immediate injury processes to the consequences for brain function in later life. The aetiology of perinatal brain injury is multi-factorial involving maternal and also labour-associated factors, including not only placental insufficiency and hypoxia-ischaemia but also exposure to high oxygen concentrations, maternal infection yielding excess inflammation, genetic factors and stress as important players, all of them associated with adverse long-term neurological outcome. Several animal models addressing these noxious stimuli have been established in the past to unravel the underlying molecular and cellular mechanisms of altered brain development. In spite of substantial efforts to investigate short-term consequences, preclinical evaluation of the long-term sequelae for the development of cognitive and neuropsychiatric disorders have rarely been addressed. This review will summarise and discuss not only current evidence but also requirements for experimental research providing a causal link between insults to the developing brain and long-lasting neurodevelopmental disorders.

Gypenosides attenuate lipopolysaccharide-induced neuroinflammation and anxiety-like behaviors in rats

Neuroinflammation is considered a major factor in several neuropsychiatric disorders. Gypenosides (GPS) have pharmacological properties with multiple beneficial effects including antiinflammatory, antioxidative, and protective properties. The present study was performed to examine whether GPS shows anxiolytic-like effects in a model of chronic inflammation induced by injection of lipopolysaccharide (LPS) into the rat hippocampus. The effects of GPS on inflammatory factors in the hippocampus and the downstream mechanisms of these effects were also examined. Introduction of LPS into the lateral ventricle caused inflammatory reactions and anxiety-like symptoms in the rats. Daily treatment with GPS (25, 50, and 100 mg/kg) for 21 consecutive days significantly increased the time spent and number of visits to the open arm in the elevated plus maze test, and significantly increased the number of central zone crossings in the open field test. Moreover, GPS administration significantly reduced the freezing response to contextual fear conditioning, and significantly decreased the levels of proinflammatory mediators, such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and nuclear factor-kappaB (NF-κB), levels in the brain. Furthermore, GPS reduced LPS-induced elevated levels of Toll-like receptor 4 (TLR4) mRNA and inhibition of brain-derived neurotrophic factor (BDNF) mRNA levels. Taken together, these results suggest that GPS may have anxiolytic-like effects and may have novel therapeutic potential for anxiety-like behaviors caused by neuroinflammation. GPS may be useful for developing an agents for the treatment of neuropsychiatric disorders, such as anxiety, due to its antiinflammatory activities and the modulation of NF-κB/iNOS/TLR4/BDNF.

Comorbid epilepsy in autism spectrum disorder: Implications of postnatal inflammation for brain excitability

OBJECTIVE

In different cohorts, 5%-30% of individuals with autism spectrum disorder (ASD) also have epilepsy. The high co-occurrence of these disorders suggests that a common mechanistic link may exist. The underlying pathophysiology of this comorbidity remains unknown. To investigate the mechanism(s) involved in the pathogenesis of ASD and epilepsy, we developed and validated a novel mouse model that concurrently exhibits hallmark features of both disorders.

METHODS

We utilized inbred BTBR T+ Itpr3tf/J (BTBR) mice that exhibit the core behavioral characteristics of ASD (ie, impaired sociability, altered vocalizations, and restricted interests). BTBR mice received a lipopolysaccharide (LPS) or sterile saline injection at postnatal day (P)7, P14, or P21. Cytokine expression was analyzed for interleukin (IL)-1β, IL-10, IL-6, and tumor necrosis factor α in brain tissue of P7 and adult BTBR mice. Adult BTBR mice were behaviorally analyzed for seizure susceptibility, sociability, communication deficits, and motor stereotypies, and monitored using chronic video-electroencephalography (EEG).

RESULTS

Adult male and female BTBR mice treated at P7-P14 with LPS were more sensitive to pentylenetetrazol-induced seizures than saline-treated controls. ASD-like behaviors and hippocampal cytokine levels were unchanged between P7 LPS-treated BTBR mice and controls. EEG recordings from the dorsal hippocampus revealed a significant increase in number and frequency of seizures over the 4-week recording period (P60-P88) in BTBR mice postnatally treated with LPS at P7. These results indicate the presence of a comorbid epileptic phenotype in BTBR mice.

SIGNIFICANCE

These findings suggest that an early postnatal immune challenge can increase brain excitability in adult BTBR mice and reveal an underlying epilepsy phenotype. This novel animal model may enable the elucidation of specific molecular alterations that are associated with the concurrent presentation of ASD and epilepsy, which could facilitate the development of targeted therapies for individuals affected by this comorbidity.

Neonatal pain and stress disrupts later-life pavlovian fear conditioning and sensory function in rats: Evidence for a two-hit model

Early life trauma has been linked to increased risks for anxiety, depression, and chronic pain. We used rodent models of acute and inflammatory neonatal pain to explore effects on fear conditioning and somatosensory function. Hindpaw needle pricks or handling on postnatal days (PNDs) 1-7 caused lasting impacts on affective and somatosensory function when assessed at later ages, PNDs 24 (postweaning), 45 (adolescence), or 66 (adulthood). First, auditory, but not contextual, freezing was mildly disrupted regardless of age. Second, a profound postfear conditioning tactile hypersensitivity was observed in neonatally stressed, postweaning rats. In the absence of fear conditioning, the mechanical hypersensitivity was not observed, consistent with a two-hit model of psychopathology. Injections of 2% α-carrageenan did not have the same lasting impact but was slightly protective against observed effects of neonatal vehicle injections. Basal and elicited corticosterone levels postweaning were not altered by neonatal pain or handling. These data demonstrate that neonatal adversity can have lasting impacts on affective and somatosensory function that differs regardless of age.

Mechanisms underlying the effects of n-3 polyunsaturated fatty acids on fear memory processing and their hypothetical effects on fear of cancer recurrence in cancer survivors

The relationship of n-3 polyunsaturated fatty acids (PUFAs) and gut microbiota with brain function has been extensively reported. Here, we review how n-3 polyunsaturated fatty acids affect fear memory processing. n-3 PUFAs may improve dysfunctional fear memory processing via immunomodulation/anti-inflammation, increased BDNF, upregulated adult neurogenesis, modulated signal transduction, and microbiota-gut-brain axis normalization. We emphasize how n-3 PUFAs affect this axis and also focus on the hypothetical effects of PUFAs in fear of cancer recurrence (FCR), the primary psychological unmet need of cancer survivors. Its pathophysiology may be similar to that of post-traumatic stress disorder (PTSD), which involves dysfunctional fear memory processing. Due to fewer adverse effects than psychotropic drugs, nutritional interventions involving n-3 PUFAs should be acceptable for physically vulnerable cancer survivors. We are currently studying the relationship of FCR with n-3 PUFAs and gut microbiota in cancer survivors to provide them with a nutritional intervention that protects against FCR.

Dynamic Patterns of Threat-Associated Gene Expression in the Amygdala and Blood

Stress and trauma profoundly influence psychiatric biobehavioral outcomes. The identification of treatment and biomarker targets would be accelerated by a broad understanding of the biological responses to these events. The goal of this study was to determine genes responsive to auditory fear conditioning (FC), a well-characterized amygdala-dependent rodent model of threat-exposure, in the presence or absence of prior stress history, providing insight into the physiological processes underlying response to trauma. RNA-sequencing was performed in blood and amygdala from mice that underwent fear conditioning with (Immo+FC) and without (FC) prior immobilization stress, a paradigm that induces HPA axis, and behavioral stress sensitization. In the amygdala, 607 genes were regulated by FC vs. home-cage (HC) controls, and 516 genes differed in stress-sensitized mice (Immo+FC vs. FC). In the former, we observed an enhancement of specific biological processes involved in learning and synaptic transmission, and in the latter processes associated with cell proliferation and the cellular response to drugs. In the blood of stress-sensitized animals, 468 genes were dynamically regulated when compared to FC, and were enriched for the biological pathways of inflammation and cytokine signaling. This study identified genes and pathways that respond to threat in the amygdala and blood of mice with and without a prior stress history and reveals the impact of stress history on subsequent inflammation. Future studies will be needed to examine the role of these dynamically regulated genes may play in human clinical stress and trauma-related disorders.

Preimmunization with a heat-killed preparation of Mycobacterium vaccae enhances fear extinction in the fear-potentiated startle paradigm

The hygiene hypothesis or "Old Friends" hypothesis proposes that inflammatory diseases are increasing in modern urban societies, due in part to reduced exposure to microorganisms that drive immunoregulatory circuits, and a failure to terminate inappropriate inflammatory responses. Inappropriate inflammation is also emerging as a risk factor for trauma-related, anxiety, and affective disorders, including posttraumatic stress disorder (PTSD), which is characterized as persistent re-experiencing of the trauma after a traumatic experience. Traumatic experiences can lead to long-lasting fear memories and exaggerated fear potentiation of the acoustic startle reflex. The acoustic startle reflex is an ethologically relevant reflex and can be potentiated in both humans and rats through Pavlovian conditioning. Mycobacterium vaccae NCTC 11659 is a soil-derived bacterium with immunoregulatory and anti-inflammatory properties that has been demonstrated to confer stress resilience in mice. Here we immunized adult male Sprague Dawley rats 3×, once per week, with a heat-killed preparation of M. vaccae NCTC 11659 (0.1mg, s.c., in 100µl borate-buffered saline) or vehicle, and, then, 3weeks following the final immunization, tested them in the fear-potentiated startle paradigm; controls were maintained under home cage control conditions throughout the experiment (n=11-12 per group). Rats were tested on days 1 and 2 for baseline acoustic startle, received fear conditioning on days 3 and 4, and underwent fear extinction training on days 5-10. Rats were euthanized on day 11 and brain tissue was sectioned for analysis of mRNA expression for genes important in control of brain serotonergic signaling, including tph2, htr1a, slc6a4, and slc22a3, throughout the brainstem dorsal and median raphe nuclei. Immunization with M. vaccae had no effect on baseline acoustic startle or fear expression on day 5. However, M. vaccae-immunized rats showed enhanced between-session and within-session extinction on day 6, relative to vehicle-immunized controls. Immunization with M. vaccae and fear-potentiated startle altered serotonergic gene expression in a gene- and subregion-specific manner. These data are consistent with the hypothesis that immunoregulatory strategies, such as preimmunization with M. vaccae, have potential for prevention of stress- and trauma-related psychiatric disorders.

Perinatal programming by inflammation

Since Levine and then Barker's seminal work mid to late last century demonstrating the importance of early life environment, intensive research has revealed the plasticity, vulnerability and resilience of the developing brain to environmental challenges. In particular, early exposure to infectious pathogens and inflammatory stimuli has a lasting impact on brain and behavior. These data establish clear effects on vulnerability to later disease and neuroinflammatory injury, cognitive function and emotionality, and even responses to pain and susceptibility to metabolic disorders. They also highlight the issues with defining rodent models of complex diseases like autism spectrum disorders and schizophrenia, as well as the complexity of experimental design, for instance when deciding the appropriate allocation of subjects to experimental groups when dealing with whole-litter manipulations in rodents. The studies presented in this special issue of Brain Behavior and Immunity are a collection of the very latest advances in the science of perinatal inflammation and its implications for perinatal programming of brain and behavior.