Sympathetic Release of Splenic Monocytes Promotes Recurring Anxiety Following Repeated Social Defeat

Chronic stress influences the macrophage M1-M2 polarization balance through β-adrenergic signaling in hepatoma mice

Chronic stress negatively affects the immune system and promotes tumor progression. Tumor-associated macrophage (TAM) is an important component of the tumor immune microenvironment. However, the influence of chronic stress on M1-M2 polarization of TAM is unclear. We used flow cytometry to measure the M1-M2 polarization of TAM in chronic stress hepatocellular carcinoma (HCC) bearing mice. We also measured the level of norepinephrine and blocked β-adrenergic signaling to explore the role of β-adrenergic receptor in the effect of chronic stress on M1-M2 polarization of TAM. We found that chronic stress disrupts the M1-M2 polarization in tumor tissues, increased the level of CD11b+Ly6C+CCR2+ monocyte and interleukin-1beta in blood and promoted the growth of HCC. Furthermore, chronic stress upregulated the level of CCL2 in tumor tissues. Finally, we found chronic stress increased norepinephrine level in serum and propranolol, a blocker of β-adrenergic signaling, inhibited HCC growth, recovered the M1-M2 polarization balance of TAM in tumor tissues, blocked the increase of CD11b+Ly6C+CCR2+ monocytes in blood, and blocked the increase of CCL2 in tumor tissues induced by chronic stress. Our study indicated that chronic stress disrupts the M1-M2 polarization balance of TAMs through β-adrenergic signaling, thereby promoting the growth of HCC.

Effects of social dominance and acute social stress on morphology of microglia and structural integrity of the medial prefrontal cortex

Chronic stress increases activity of the brain's innate immune system and impairs function of the medial prefrontal cortex (mPFC). However, whether acute stress triggers similar neuroimmune mechanisms is poorly understood. Across four studies, we used a Syrian hamster model to investigate whether acute stress drives changes in mPFC microglia in a time-, subregion-, and social status-dependent manner. We found that acute social defeat increased expression of ionized calcium binding adapter molecule 1 (Iba1) in the infralimbic (IL) and prelimbic (PL) and altered the morphology Iba1+ cells 1, 2, and 7 days after social defeat. We also investigated whether acute defeat induced tissue degeneration and reductions of synaptic plasticity 2 days post-defeat. We found that while social defeat increased deposition of cellular debris and reduced synaptophysin immunoreactivity in the PL and IL, treatment with minocycline protected against these cellular changes. Finally, we tested whether a reduced conditioned defeat response in dominant compared to subordinate hamsters was associated with changes in microglia reactivity in the IL and PL. We found that while subordinate hamsters and those without an established dominance relationships showed defeat-induced changes in morphology of Iba1+ cells and cellular degeneration, dominant hamsters showed resistance to these effects of social defeat. Taken together, these findings indicate that acute social defeat alters microglial morphology, increases markers of tissue degradation, and impairs structural integrity in the IL and PL, and that experience winning competitive interactions can specifically protect the IL and reduce stress vulnerability.

Innate and adaptive immune system consequences of post-traumatic stress disorder

In the field of psychiatry, biological markers are rarely, if ever, used in the diagnosis of mental health disorders. Clinicians rely primarily on patient histories and behavioral symptoms to identify specific psychopathologies, which makes diagnosis highly subjective. Moreover, therapies for mental health disorders are aimed specifically at attenuating behavioral manifestations, which overlooks the pathophysiological indices of the disease. This is highly evident in posttraumatic stress disorder (PTSD) where inflammation and immune system perturbations are becoming increasingly described. Further, patients with PTSD possess significantly elevated risks of developing comorbid inflammatory diseases such as autoimmune and cardiovascular diseases, which are likely linked (though not fully proven) to the apparent dysregulation of the immune system after psychological trauma. To date, there is little to no evidence that demonstrates current PTSD therapies are able to reverse the increased risk for psychological trauma-induced inflammatory diseases, which suggests the behavioral and somatic consequences of PTSD may not be tightly coupled. This observation provides an opportunity to explore unique mechanisms outside of the brain that contribute to the long-term pathology of PTSD. Herein, we provide an overview of neuroimmune mechanisms, describe what is known regarding innate and adaptive immunity in PTSD, and suggest new directions that are needed to advance the understanding, diagnosis, and treatment of PTSD moving forward.

Chronic stress alters lipid mediator profiles associated with immune-related gene expressions and cell compositions in mouse bone marrow and spleen

Despite the importance of lipid mediators in stress and depression and their link to inflammation, the influence of stress on these mediators and their role in inflammation is not fully understood. This study used RNA-seq, LC-MS/MS, and flow cytometry analyses in a mouse model subjected to chronic social defeat stress to explore the effects of acute and chronic stress on lipid mediators, gene expression, and cell population in the bone marrow and spleen. In the bone marrow, chronic stress induced a sustained transition from lymphoid to myeloid cells, accompanied by corresponding changes in gene expression. This change was associated with decreased levels of 15-deoxy-d12,14-prostaglandin J2, a lipid mediator that inhibits inflammation. In the spleen, chronic stress also induced a lymphoid-to-myeloid transition, albeit transiently, alongside gene expression changes indicative of extramedullary hematopoiesis. These changes were linked to lower levels of 12-HEPE and resolvins, both critical for inhibiting and resolving inflammation. Our findings highlight the significant role of anti-inflammatory and pro-resolving lipid mediators in the immune responses induced by chronic stress in the bone marrow and spleen. This study paves the way for understanding how these lipid mediators contribute to the immune mechanisms of stress and depression.

Enhanced fear memory after social defeat in mice is dependent on interleukin-1 receptor signaling in glutamatergic neurons

Chronic stress is associated with increased anxiety, cognitive deficits, and post-traumatic stress disorder. Repeated social defeat (RSD) in mice causes long-term stress-sensitization associated with increased microglia activation, monocyte accumulation, and enhanced interleukin (IL)-1 signaling in endothelia and neurons. With stress-sensitization, mice have amplified neuronal, immune, and behavioral responses to acute stress 24 days later. This is clinically relevant as it shares key aspects with post-traumatic stress disorder. The mechanisms underlying stress-sensitization are unclear, but enhanced fear memory may be critical. The purpose of this study was to determine the influence of microglia and IL-1R1 signaling in neurons in the development of sensitization and increased fear memory after RSD. Here, RSD accelerated fear acquisition, delayed fear extinction, and increased cued-based freezing at 0.5 day. The enhancement in contextual fear memory after RSD persisted 24 days later. Next, microglia were depleted with a CSF1R antagonist prior to RSD and several parameters were assessed. Microglia depletion blocked monocyte recruitment to the brain. Nonetheless, neuronal reactivity (pCREB) and IL-1β RNA expression in the hippocampus and enhanced fear memory after RSD were microglial-independent. Because IL-1β RNA was prominent in the hippocampus after RSD even with microglia depletion, IL-1R1 mediated signaling in glutamatergic neurons was assessed using neuronal Vglut2+/IL-1R1-/- mice. RSD-induced neuronal reactivity (pCREB) in the hippocampus and enhancement in fear memory were dependent on neuronal IL-1R1 signaling. Furthermore, single-nuclei RNA sequencing (snRNAseq) showed that RSD influenced transcription in specific hippocampal neurons (DG neurons, CA2/3, CA1 neurons) associated with glutamate signaling, inflammation and synaptic plasticity, which were neuronal IL-1R1-dependent. Furthermore, snRNAseq data provided evidence that RSD increased CREB, BDNF, and calcium signaling in DG neurons in an IL-1R1-dependent manner. Collectively, increased IL-1R1-mediated signaling (monocytes/microglia independent) in glutamatergic neurons after RSD enhanced neuronal reactivity and fear memory.

Esketamine mitigates cognitive impairment following exposure to LPS by modulating the intestinal flora/subdiaphragmatic vagus nerve/spleen axis

INTRODUCTION

Susceptibility to secondary infection often increases after primary infection. Secondary infections can lead to more severe inflammatory injuries; however, the underlying mechanisms are not yet fully elucidated.

OBJECTIVE

To investigate whether esketamine treatment immediately after primary lipopolysaccharide (LPS) exposure could alleviate cognitive impairment caused by secondary infection.

METHODS

Mice were injected intraperitoneally (IP) with LPS (5 mg/kg) 10 days apart. Esketamine (10, 15, or 30 mg/kg) was administered IP immediately after the primary LPS injection. Splenectomy or subdiaphragmatic vagotomy (SDV) was performed 7 days before secondary LPS exposure or broad-spectrum antibiotic administration.

RESULTS

Splenomegaly was observed after the primary LPS injection on Days 3 and 10. Splenomegaly was attenuated by treatment with 30 mg/kg esketamine. Esketamine treatment prevented increased plasma proinflammatory cytokines levels and cognitive dysfunction induced by secondary LPS exposure. Mice that underwent splenectomy or SDV had lower proinflammatory cytokines levels, higher hippocampal brain-derived neurotrophic factor (BDNF) levels, and improved cognitive function 1 day after secondary infection, which was not further improved by esketamine. Fecal microbiota transplantation (FMT) from endotoxic mice treated with esketamine attenuated hippocampal BDNF downregulation and cognitive dysfunction only in pseudo germ-free (PGF) mice without splenectomy. FMT with fecal suspensions from esketamine-treated endotoxic mice abrogated splenomegaly only in PGF mice without SDV. Blocking BDNF signaling blocked esketamine's ameliorating effects on secondary LPS exposure-induced cognitive dysfunction.

CONCLUSION

The intestinal flora/subdiaphragmatic vagus nerve/spleen axis-mediated hippocampal BDNF downregulation significantly affected secondary LPS-induced systemic inflammation and cognitive dysfunction. Esketamine preserves cognitive function via this mechanism.

Spleen contributes to chronic restraint stress-induced lung injury through splenic CD11b+ cells

Chronic stress can induce lung injury. The spleen, as the largest peripheral immune organ, plays a crucial role in various lung diseases. Our previous study found that the spleen underwent significant changes during chronic restraint stress (CRS). However, the exact role of the spleen in CRS-induced lung injury remains unclear. In this study, we found that CRS could increase lung index. CRS could lead to alterations of the lungs such as destruction of alveolar wall, thickening of alveolar septa, dilation of pulmonary capillaries, and increased inflammatory cell infiltration. CRS increases the concentration of malondialdehyde (MDA), decreases the level of surfactant protein A (SP-A), and elevates the levels of pro-inflammatory factors (TNF-α, IL-6, and IL-1β) in the lungs. Additionally, CRS could increase the proportions and numbers of CD11b+Ly6ChiLy6G- monocytes in the lung, while cannot alter proportions and numbers of CD3-NK1.1+ NK cells, CD3+CD4+ T cells, CD3+CD8+ T cells, and CD11b+Ly6G+ neutrophils. Moreover, the levels of inflammatory markers in lung tissues were positively correlated with the proportion of CD11b+Ly6ChiLy6G- monocytes. Interestingly, splenectomy inhibited CRS-induced lung injury and attenuated the alteration in the proportion of CD11b+Ly6ChiLy6G- monocytes in the lungs induced by CRS. Moreover, splenic CD11b+ cells, rather than splenic CD11b- cells, transfused into splenectomized mice, and subsequently exposed to CRS, can cause lung injury. These results suggest that CRS could induce lung injury and CD11b+Ly6ChiLy6G- monocytes aggregation in the lung. The spleen could contribute to CRS-induced lung injury. Furthermore, splenic CD11b+ cells might play an important role in CRS-induced lung injury.

The mechanisms underlying alcohol-induced decreased splenic size: A network meta-analysis study

BACKGROUND

Organ weight change is widely accepted as a measure of toxicologic pathology. We and other groups have shown that excessive alcohol exposure leads to decreased spleen weight in rodents. This study explores the mechanisms underlying alcohol-induced splenic injury through a network meta-analysis.

METHODS

QIAGEN Ingenuity Pathway Analysis (IPA) and Mammalian Phenotype (MP) Ontology were used to identify alcohol-related molecules associated with the small spleen phenotype. Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and IPA bioinformatics tools were then used to analyze the biologic processes and enriched signaling pathways engaging these molecules. In addition, the "downstream effects analysis" algorithm was used to quantify alcohol's effects.

RESULTS

IPA identified 623 molecules affected by alcohol and a Venn diagram revealed that 26 of these molecules overlapped with those associated with the MP Ontology of small spleen. The 26 molecules are TGFB1, CASP8, MTOR, ESR1, CXCR4, CAMK4, NFKBIA, DRD2, BCL2, FAS, PEBP1, TRAF2, ATM, IGHM, EDNRB, MDM2, GLRA1, PRF1, TLR7, IFNG, ALOX5, FOXO1, IL15, APOE, IKBKG, and RORA. Some of the 26 molecules were also associated with the MP Ontology of abnormal white pulp and red pulp morphology of the spleen, abnormal splenic cell ratio, decreased splenocyte number, abnormal spleen physiology, increased splenocyte apoptosis, and reduced splenocyte proliferation. STRING and IPA "Core Analysis" showed that these molecules were mainly involved in pathways related to cell apoptosis, proliferation, migration, and immune responses. IPA's "Molecular Activity Predictor" tool showed that concurrent effects of activation and inhibition of these molecules led to decreased spleen size by modulating apoptosis, proliferation, and migration of splenocytes.

CONCLUSIONS

Our network meta-analysis revealed that excessive alcohol exposure can damage the spleen through a variety of molecular mechanisms, thereby affecting immune function and human health. We found that alcohol-mediated splenic atrophy is largely mediated by increased apoptosis signaling, migration of cells, and inhibition of splenocyte proliferation.

Antagonism of the brain P2X7 ion channel attenuates repeated social defeat induced microglia reactivity, monocyte recruitment and anxiety-like behavior in male mice

Chronic stress is linked to increased anxiety. Repeated social defeat (RSD) in mice causes anxiety that is dependent on activated neurons, reactive microglia, and accumulation of monocytes in the brain. This response requires interactions between the immune system and central nervous system (CNS). Neuronal activation within threat appraisal regions is a key response to RSD, however, it is unclear how microglia become activated. One potential explanation is that microglia express a purinergic non-selective ligand gated adenosine-triphosphate (ATP) receptor 7 (P2X7). Activation of P2X7 promotes the release of chemokines and cytokines, and recruitment of monocytes to the brain. Thus, the purpose of this study was to determine if a novel P2X7 antagonist blocked neuronal and microglia interactions and the corresponding anxiety following RSD. Male mice were administered (i.p.) a P2X7 antagonist, JNJ-54471300, prior to each cycle of RSD. Fourteen hours after RSD, behavioral deficits including social avoidance and anxiety-like were determined. Moreover, several immune parameters were assessed. RSD caused neuronal activation in stress-responsive regions, monocyte production and release, splenomegaly, and social avoidance. These parameters were unaffected by P2X7 antagonism. RSD-associated proportional area of Iba-1+ microglia, monocyte accumulation in the brain, IL-1β mRNA expression in enriched myeloid cells, plasma IL-6, and anxiety-like behavior were ameliorated by P2X7 antagonism. Gene expression analysis in the hippocampus and amygdala showed regional specific responses to RSD and some were reversed with P2X7 antagonism. Overall, blocking P2X7 activation attenuated RSD-induced microglia reactivity with corresponding reduction in neuroinflammation, monocyte accumulation, and anxiety-like behavior in male mice.

Ventromedial hypothalamus relays chronic stress inputs and exerts bidirectional regulation on anxiety state and related sympathetic activity

Chronic stress can induce negative emotion states, including anxiety and depression, leading to sympathetic overactivation and disturbed physiological homeostasis in peripheral tissues. While anxiety-related neural circuitry integrates chronic stress information and modulates sympathetic nervous system (SNS) activity, the critical nodes linking anxiety and sympathetic activity still need to be clarified. In our previous study, we demonstrated that the ventromedial hypothalamus (VMH) is involved in integrating chronic stress inputs and exerting influence on sympathetic activity. However, the underlying synaptic and electrophysiological mechanisms remain elusive. In this study, we combined in vitro electrophysiological recordings, behavioral tests, optogenetic manipulations, and SNS activity analyses to explore the role of VMH in linking anxiety emotion and peripheral SNS activity. Results showed that the VMH played an important role in bidirectionally regulating anxiety-like behavior and peripheral sympathetic excitation. Chronic stress enhanced excitatory inputs into VMH neurons by strengthening the connection with the paraventricular hypothalamus (PVN), hence promoting anxiety and sympathetic tone outflow, an important factor contributing to the development of metabolic imbalance in peripheral tissues and cardiovascular diseases.

Social stress induces autoimmune responses against the brain

Clinical studies have revealed a high comorbidity between autoimmune diseases and psychiatric disorders, including major depressive disorder (MDD). However, the mechanisms connecting autoimmunity and depression remain unclear. Here, we aim to identify the processes by which stress impacts the adaptive immune system and the implications of such responses to depression. To examine this relationship, we analyzed antibody responses and autoimmunity in the chronic social defeat stress (CSDS) model in mice, and in clinical samples from patients with MDD. We show that socially stressed mice have elevated serum antibody concentrations. We also confirm that social stress leads to the expansion of specific T and B cell populations within the cervical lymph nodes, where brain-derived antigens are preferentially delivered. Sera from stress-susceptible (SUS) mice exhibited high reactivity against brain tissue, and brain-reactive immunoglobulin G (IgG) antibody levels positively correlated with social avoidance behavior. IgG antibody concentrations in the brain were significantly higher in SUS mice than in unstressed mice, and positively correlated with social avoidance. Similarly, in humans, increased peripheral levels of brain-reactive IgG antibodies were associated with increased anhedonia. In vivo assessment of IgG antibodies showed they largely accumulate around blood vessels in the brain only in SUS mice. B cell-depleted mice exhibited stress resilience following CSDS, confirming the contribution of antibody-producing cells to social avoidance behavior. This study provides mechanistic insights connecting stress-induced autoimmune reactions against the brain and stress susceptibility. Therapeutic strategies targeting autoimmune responses might aid in the treatment of patients with MDD featuring immune abnormalities.

Repeated social defeat stress leads to immunometabolic shifts in innate immune cells of the spleen

Psychosocial stress has been shown to prime peripheral innate immune cells, which take on hyper-inflammatory phenotypes and are implicated in depressive-like behavior in mouse models. However, the impact of stress on cellular metabolic states that are thought to fuel inflammatory phenotypes in immune cells are unknown. Using single cell RNA-sequencing, we investigated mRNA enrichment of immunometabolic pathways in innate immune cells of the spleen in mice subjected to repeated social defeat stress (RSDS) or no stress (NS). RSDS mice displayed a significant increase in the number of splenic macrophages and granulocytes (p < 0.05) compared to NS littermates. RSDS-upregulated genes in macrophages, monocytes, and granulocytes significantly enriched immunometabolic pathways thought to play a role in myeloid-driven inflammation (glycolysis, HIF-1 signaling, MTORC1 signaling) as well as pathways related to oxidative phosphorylation (OXPHOS) and oxidative stress (p < 0.05 and FDR<0.1). These results suggest that the metabolic enhancement reflected by upregulation of glycolytic and OXPHOS pathways may be important for cellular proliferation of splenic macrophages and granulocytes following repeated stress exposure. A better understanding of these intracellular metabolic mechanisms may ultimately help develop novel strategies to reverse the impact of stress and associated peripheral immune changes on the brain and behavior.

Ly6C-high monocytes alleviate brain injury in experimental subarachnoid hemorrhage in mice

BACKGROUND

Subarachnoid hemorrhage (SAH) is an uncommon type of potentially fatal stroke. The pathophysiological mechanisms of brain injury remain unclear, which hinders the development of drugs for SAH. We aimed to investigate the pathophysiological mechanisms of SAH and to elucidate the cellular and molecular biological response to SAH-induced injury.

METHODS

A cross-species (human and mouse) multiomics approach combining high-throughput data and bioinformatic analysis was used to explore the key pathophysiological processes and cells involved in SAH-induced brain injury. Patient data were collected from the hospital (n = 712). SAH was established in adult male mice via endovascular perforation, and flow cytometry, a bone marrow chimera model, qPCR, and microglial depletion experiments were conducted to explore the origin and chemotaxis mechanism of the immune cells. To investigate cell effects on SAH prognosis, murine neurological function was evaluated based on a modified Garcia score, pole test, and rotarod test.

RESULTS

The bioinformatics analysis confirmed that inflammatory and immune responses were the key pathophysiological processes after SAH. Significant increases in the monocyte levels were observed in both the mouse brains and the peripheral blood of patients after SAH. Ly6C-high monocytes originated in the bone marrow, and the skull bone marrow contribute a higher proportion of these monocytes than neutrophils. The mRNA level of Ccl2 was significantly upregulated after SAH and was greater in CD11b-positive than CD11b-negative cells. Microglial depletion, microglial inhibition, and CCL2 blockade reduced the numbers of Ly6C-high monocytes after SAH. With CCR2 antagonization, the neurological function of the mice exhibited a slow recovery. Three days post-SAH, the monocyte-derived dendritic cell (moDC) population had a higher proportion of TNF-α-positive cells and a lower proportion of IL-10-positive cells than the macrophage population. The ratio of moDCs to macrophages was higher on day 3 than on day 5 post-SAH.

CONCLUSIONS

Inflammatory and immune responses are significantly involved in SAH-induced brain injury. Ly6C-high monocytes derived from the bone marrow, including the skull bone marrow, infiltrated into mouse brains via CCL2 secreted from microglia. Moreover, Ly6C-high monocytes alleviated neurological dysfunction after SAH.

Social isolation and loneliness: Undervalued risk factors for disease states and mortality

Social isolation and loneliness are two common but undervalued conditions associated with a poor quality of life, decreased overall health and mortality. In this review, we aim to discuss the health consequences of social isolation and loneliness. We first provide the potential causes of these two conditions. Then, we explain the pathophysiological processes underlying the effects of social isolation and loneliness in disease states. Afterwards, we explain the important associations between these conditions and different non-communicable diseases, as well as the impact of social isolation and loneliness on health-related behaviours. Finally, we discuss the current and novel potential management strategies for these conditions. Healthcare professionals who attend to socially isolated and/or lonely patients should be fully competent in these conditions and assess their patients thoroughly to detect and properly understand the effects of isolation and loneliness. Patients should be offered education and treatment alternatives through shared decision-making. Future studies are needed to understand the underlying mechanisms better and to improve the treatment strategies for both social isolation and loneliness.

Divergent Spatial Learning, Enhanced Neuronal Transcription, and Blood-Brain Barrier Disruption Develop During Recovery from Post-Injury Sleep Fragmentation

Traumatic brain injury (TBI) causes pathophysiology that may significantly decrease quality of life over time. A major propagator of this response is chronic, maladaptive neuroinflammation, which can be exacerbated by stressors such as sleep fragmentation (SF). This study determined whether post-TBI SF had lasting behavioral and inflammatory effects even with a period of recovery. To test this, male and female mice received a moderate lateral fluid percussion TBI or sham surgery. Half the mice were left undisturbed, and half were exposed to daily SF for 30 days. All mice were then undisturbed between 30 and 60 days post-injury (DPI), allowing mice to recover from SF (SF-R). SF-R did not impair global Barnes maze performance. Nonetheless, TBI SF-R mice displayed retrogression in latency to reach the goal box within testing days. These nuanced behavioral changes in TBI SF-R mice were associated with enhanced expression of neuronal processing/signaling genes and indicators of blood-brain barrier (BBB) dysfunction. Aquaporin-4 (AQP4) expression, a marker of BBB integrity, was differentially altered by TBI and TBI SF-R. For example, TBI enhanced cortical AQP4 whereas TBI SF-R mice had the lowest cortical expression of perivascular AQP4, dysregulated AQP4 polarization, and the highest number of CD45+ cells in the ipsilateral cortex. Altogether, post-TBI SF caused lasting, divergent behavioral responses associated with enhanced expression of neuronal transcription and BBB disruption even after a period of recovery from SF. Understanding lasting impacts from post-TBI stressors can better inform both acute and chronic post-injury care to improve long-term outcome post-TBI.

Activation of cell-free mtDNA-TLR9 signaling mediates chronic stress-induced social behavior deficits

Inflammation and social behavior deficits are associated with a number of neuropsychiatric disorders. Chronic stress, a major risk factor for depression and other mental health conditions is known to increase inflammatory responses and social behavior impairments. Disturbances in mitochondria function have been found in chronic stress conditions, however the mechanisms that link mitochondrial dysfunction to stress-induced social behavior deficits are not well understood. In this study, we found that chronic restraint stress (RS) induces significant increases in serum cell-free mitochondrial DNA (cf-mtDNA) levels in mice, and systemic Deoxyribonuclease I (DNase I) treatment attenuated RS-induced social behavioral deficits. Our findings revealed potential roles of mitophagy and Mitochondrial antiviral-signaling protein (MAVS) in mediating chronic stress-induced changes in cf-mtDNA levels and social behavior. Furthermore, we showed that inhibition of Toll-like receptor 9 (TLR9) attenuates mtDNA-induced social behavior deficits. Together, these findings show that cf-mtDNA-TLR9 signaling is critical in mediating stress-induced social behavior deficits.

Traumatic brain injury stimulates sympathetic tone-mediated bone marrow myelopoiesis to favor fracture healing

Traumatic brain injury (TBI) accelerates fracture healing, but the underlying mechanism remains largely unknown. Accumulating evidence indicates that the central nervous system (CNS) plays a pivotal role in regulating immune system and skeletal homeostasis. However, the impact of CNS injury on hematopoiesis commitment was overlooked. Here, we found that the dramatically elevated sympathetic tone accompanied with TBI-accelerated fracture healing; chemical sympathectomy blocks TBI-induced fracture healing. TBI-induced hypersensitivity of adrenergic signaling promotes the proliferation of bone marrow hematopoietic stem cells (HSCs) and swiftly skews HSCs toward anti-inflammation myeloid cells within 14 days, which favor fracture healing. Knockout of β3- or β2-adrenergic receptor (AR) eliminate TBI-mediated anti-inflammation macrophage expansion and TBI-accelerated fracture healing. RNA sequencing of bone marrow cells revealed that Adrb2 and Adrb3 maintain proliferation and commitment of immune cells. Importantly, flow cytometry confirmed that deletion of β2-AR inhibits M2 polarization of macrophages at 7th day and 14th day; and TBI-induced HSCs proliferation was impaired in β3-AR knockout mice. Moreover, β3- and β2-AR agonists synergistically promote infiltration of M2 macrophages in callus and accelerate bone healing process. Thus, we conclude that TBI accelerates bone formation during early stage of fracture healing process by shaping the anti-inflammation environment in the bone marrow. These results implicate that the adrenergic signals could serve as potential targets for fracture management.

Inflammation in the pathogenesis of depression: a disorder of neuroimmune origin

There are several hypotheses concerning the underlying pathophysiological mechanisms of major depression, which centre largely around adaptive changes in neuronal transmission and plasticity, neurogenesis, and circuit and regional connectivity. The immune and endocrine systems are commonly implicated in driving these changes. An intricate interaction of stress hormones, innate immune cells and the actions of soluble mediators of immunity within the nervous system is described as being associated with the symptoms of depression. Bridging endocrine and immune processes to neurotransmission and signalling within key cortical and limbic brain circuits are critical to understanding depression as a disorder of neuroimmune origins. Emergent areas of research include a growing recognition of the adaptive immune system, advances in neuroimaging techniques and mechanistic insights gained from transgenic animals. Elucidation of glial-neuronal interactions is providing additional avenues into promising areas of research, the development of clinically relevant disease models and the discovery of novel therapies. This narrative review focuses on molecular and cellular mechanisms that are influenced by inflammation and stress. The aim of this review is to provide an overview of our current understanding of depression as a disorder of neuroimmune origin, focusing on neuroendocrine and neuroimmune dysregulation in depression pathophysiology. Advances in current understanding lie in pursuit of relevant biomarkers, as the potential of biomarker signatures to improve clinical outcomes is yet to be fully realised. Further investigations to expand biomarker panels including integration with neuroimaging, utilising individual symptoms to stratify patients into more homogenous subpopulations and targeting the immune system for new treatment approaches will help to address current unmet clinical need.

Association between immune cells in peripheral blood and psychiatric symptoms

Background

There are bidirectional associations between immunological dysfunction and psychiatric symptoms. However, the associations between the levels of immune cells in the peripheral blood and psychiatric symptoms remain unclear. The present study aimed to evaluate levels of immune cells in peripheral blood in people with positive psychiatric symptoms.

Methods

This retrospective study analyzed data from routine blood tests and psychopathology and sleep quality assessments. Data were compared between a group of 45 patients with de novo psychological symptoms and 225 matched controls.

Results

Patients with psychiatric symptoms had higher white blood cell and neutrophil counts compared with controls. However, in a subgroup analysis, neutrophil counts were significantly higher than in controls only in patients with multiple psychiatric symptoms. Furthermore, monocyte counts were significantly higher in patients with multiple psychiatric symptoms than in controls. Further, sleep quality was lower in patients with psychiatric symptoms than in controls.

Conclusion

White blood cell and neutrophil counts in the peripheral blood of patients with psychiatric symptoms were significantly higher and sleep quality was significantly lower than in controls. Participants with multiple psychiatric symptoms showed more significant differences in peripheral blood immune cell counts than other subgroups. These results provided evidence for the relationship between psychiatric symptoms, immunity, and sleep.

Oleoylethanolamide restores stress-induced prepulse inhibition deficits and modulates inflammatory signaling in a sex-dependent manner

RATIONALE

Social stress contributes to the development of depressive and anxiety symptomatology and promotes pro-inflammatory signaling in the central nervous system. In this study, we explored the effects of a lipid messenger with anti-inflammatory properties - oleoylethanolamide (OEA) - on the behavioral deficits caused by social stress in both male and female mice.

METHODS

Adult mice were assigned to an experimental group according to the stress condition (control or stress) and treatment (vehicle or OEA, 10 mg/kg, i.p.). Male mice in the stress condition underwent a protocol consisting of four social defeat (SD) encounters. In the case of female mice, we employed a procedure of vicarious SD. After the stress protocol resumed, anxiety, depressive-like behavior, social interaction, and prepulse inhibition (PPI) were assessed. In addition, we characterized the stress-induced inflammatory profile by measuring IL-6 and CX3CL1 levels in the striatum and hippocampus.

RESULTS

Our results showed that both SD and VSD induced behavioral alterations. We found that OEA treatment restored PPI deficits in socially defeated mice. Also, OEA affected differently stress-induced anxiety and depressive-like behavior in male and female mice. Biochemical analyses showed that both male and female stressed mice showed increased levels of IL-6 in the striatum compared to control mice. Similarly, VSD female mice exhibited increased striatal CX3CL1 levels. These neuroinflammation-associated signals were not affected by OEA treatment.

CONCLUSIONS

In summary, our results confirm that SD and VSD induced behavioral deficits together with inflammatory signaling in the striatum and hippocampus. We observed that OEA treatment reverses stress-induced PPI alterations in male and female mice. These data suggest that OEA can exert a buffering effect on stress-related sensorimotor gating behavioral processing.

Microglial synaptic pruning in the nucleus accumbens during adolescence sex-specifically influences splenic immune outcomes

Strong social support promotes a variety of positive health outcomes in humans and rodent models, while social isolation in rodents shortens lifespan, perceived social isolation (i.e. loneliness) can increase mortality by up to 50% in humans. How social relationships lead to these drastic health effects is unclear, but may involve modulation of the peripheral immune system. The reward circuitry of the brain and social behaviors undergo a critical period of development during adolescence. We published that microglia-mediated synaptic pruning occurs in the nucleus accumbens (NAc) reward region during adolescence to mediate social development in male and female rats. We hypothesized that if reward circuitry activity and social relationships directly impact the peripheral immune system, then natural developmental changes in the reward circuitry and social behaviors during adolescence should also directly impact the peripheral immune system. To test this, we inhibited microglial pruning in the NAc during adolescence, and then collected spleen tissue for mass spectrometry proteomic analysis and ELISA validation. We found that the global proteomic consequences of inhibiting microglial pruning in the NAc were similar between the sexes, but target-specific examination suggests that NAc pruning impacts Th1 cell-related immune markers in the spleen in males, but not females, and broad neurochemical systems in the spleen in females, but not males.

Social isolation produces a sex- and brain region-specific alteration of microglia state

Social isolation is a profound form of psychological stress that impacts the mental health of a large proportion of society. Other experimental models of stress have demonstrated a microglia response that serves either a protective or pathological function. However, the effect of adult social isolation on microglia has not been thoroughly investigated. We measured microglia territory, branching, end points and phagocytic-lysosomal activity in group housed C57Bl/6 mice and mice that were socially isolated for 2 weeks. Our results show that the dorsomedial hypothalamus and hippocampal CA2 region of adult male mice undergo increased microglia volume, territory and endpoints following social isolation, whereas females exhibit this increase in the hypothalamus only. Males exhibited decreases in the phagocytic-lysosomal marker CD68 in microglia in these regions, whereas females showed an increase in CD68 in the hypothalamus suggesting sexually dimorphic and brain region-specific change in microglia state in response to social isolation. The prefrontal cortex, central amygdala, nucleus accumbens shell and visual cortex did not exhibit changes in microglia structure in either male or female mice. These data show that microglia in different brain regions undergo a distinct response to social isolation which may account for changes in cognition and behaviour associated with this prevalent form of psychological stress.

IL-1 Receptor-1 on Vglut2 + neurons in the hippocampus is critical for neuronal and behavioral sensitization after repeated social stress

Myriad findings connect stress and inflammation to mood disorders. Social defeat in mice promotes the convergence of neuronal, central inflammatory (microglia), and peripheral immune (monocytes) pathways causing anxiety, social avoidance, and "stress-sensitization." Stress-sensitization results in augmented inflammation and the recurrence of anxiety after re-exposure to social stress. Different cell compartments, including neurons, may be uniquely sensitized by social defeat-induced interleukin-1 (IL-1) signaling. Therefore, the aim of this study was to determine if glutamatergic neuronal IL-1 receptor signaling was essential in promoting stress-sensitization after social defeat. Here, wild-type (IL-1R1+/+) mice and mice with IL-1 receptor-1 deleted selectively in glutamatergic neurons (Vglut2-IL-1R1-/-) were stress-sensitized by social defeat (6-cycles) and then exposed to acute defeat (1-cycle) at day 30. Acute defeat-induced neuronal activation (ΔFosB and phospo-CREB) in the hippocampus of stress-sensitized mice was dependent on neuronal IL-1R1. Moreover, acute defeat-induced social withdrawal and working memory impairment in stress-sensitized mice were also dependent on neuronal IL-1R1. To address region and time dependency, an AAV2-IL-1 receptor antagonist construct was administered into the hippocampus after sensitization, but prior to acute defeat at day 30. Although stress-sensitized mice had increased hippocampal pCREB and decreased working memory after stress re-exposure, these events were not influenced by AAV2-IL-1 receptor antagonist. Hippocampal ΔFosB induction and corresponding social withdrawal in stress-sensitized mice after stress re-exposure were prevented by the AAV2-IL-1 receptor antagonist. Collectively, IL-1 signaling in glutamatergic neurons of the hippocampus was essential in neuronal-sensitization after social defeat and the recall of social withdrawal.

Neuroimmune mechanisms in fear and panic pathophysiology

Panic disorder (PD) is unique among anxiety disorders in that the emotional symptoms (e.g., fear and anxiety) associated with panic are strongly linked to body sensations indicative of threats to physiological homeostasis. For example, panic attacks often present with feelings of suffocation that evoke hyperventilation, breathlessness, or air hunger. Due to the somatic underpinnings of PD, a major focus has been placed on interoceptive signaling and it is recognized that dysfunctional body-to-brain communication pathways promote the initiation and maintenance of PD symptomatology. While body-to-brain signaling can occur via several pathways, immune and humoral pathways play an important role in communicating bodily physiological state to the brain. Accumulating evidence suggests that neuroimmune mediators play a role in fear and panic-associated disorders, although this has not been systematically investigated. Currently, our understanding of the role of immune mechanisms in the etiology and maintenance of PD remains limited. In the current review, we attempt to summarize findings that support a role of immune dysregulation in PD symptomology. We compile evidence from human studies and panic-relevant rodent paradigms that indicate a role of systemic and brain immune signaling in the regulation of fear and panic-relevant behavior and physiology. Specifically, we discuss how immune signaling can contribute to maladaptive body-to-brain communication and conditioned fear that are relevant to spontaneous and conditioned symptoms of PD and identify putative avenues warranting future investigation.

The neuroimmunology of social-stress-induced sensitization

Myriad clinical findings provide links between chronic stressors, inflammation, and mood disorders. Furthermore, traumatic or chronic exposure to psychological stressors may promote stress sensitization, in which individuals have long-term complications, including increased vulnerability to subsequent stressors. Post-traumatic stress disorder (PTSD) is a clinically relevant example of stress sensitization. PTSD alters neuronal circuitry and mood; however, the mechanisms underlying long-term stress sensitization within this disorder are unclear. Rodent models of chronic social defeat recapitulate several key physiological, immunological, and behavioral responses associated with psychological stress in humans. Repeated social defeat (RSD) uniquely promotes the convergence of neuronal, central inflammatory (microglial), and peripheral immune (monocyte) pathways, leading to prolonged anxiety, social withdrawal, and cognitive impairment. Moreover, RSD promotes stress sensitization, in which mice are highly sensitive to subthreshold stress exposure and recurrence of anxiety weeks after the cessation of stress. Therefore, the purpose of this Review is to discuss the influence of social-defeat stress on the immune system that may underlie stress sensitization within three key cellular compartments: neurons, microglia, and monocytes. Delineating the mechanisms of stress sensitization is critical in understanding and treating conditions such as PTSD.

Neurobiology, Stem Cell Biology, and Immunology: An Emerging Triad for Understanding Tissue Homeostasis and Repair

The peripheral nervous system (PNS) endows animals with the remarkable ability to sense and respond to a dynamic world. Emerging evidence shows the PNS also participates in tissue homeostasis and repair by integrating local changes with organismal and environmental changes. Here, we provide an in-depth summary of findings delineating the diverse roles of peripheral nerves in modulating stem cell behaviors and immune responses under steady-state conditions and in response to injury and duress, with a specific focus on the skin and the hematopoietic system. These examples showcase how elucidating neuro-stem cell and neuro-immune cell interactions provides a conceptual framework that connects tissue biology and local immunity with systemic bodily changes to meet varying demands. They also demonstrate how changes in these interactions can manifest in stress, aging, cancer, and inflammation, as well as how these findings can be harnessed to guide the development of new therapeutics.

Adolescent microglia stimulation produces long-lasting protection against chronic stress-induced behavioral abnormalities in adult male mice

Our previous studies had reported that microglia activation one day before stress exposure prevented the behavioral abnormalities induced by chronic stress in adult mice, and a 10-day interval between microglia stimulation and stress exposure can abolish the prophylactic effect of LPS preinjection on the behavioral abnormalities induced by chronic stress, which, however, could be rescued by repeated LPS injection. This suggests that increased stimulation of microglia results in animals developing a strong ability to prevent deleterious stress stimuli. Because microglia in the adolescent brain exhibit flexible immunological plasticity, we hypothesize that a single low-dose LPS injection during adolescence may provide long-lasting protection against behavioral abnormalities induced by chronic stress in adult mice. As expected, our results showed that a single injection of LPS (100 μg/kg) at post-natal day 28 (PND 28) prevented the development of abnormal behaviors and shifted neuroinflammatory responses toward an anti-inflammatory phenotype in adult mice treated with CSDS at their different stages of the age (PND 56, 140, and 252). Moreover, pretreatment with minocycline or PLX3397 to inhibit microglial activation abolished the prophylactic effect of LPS preinjection after PND 28 on behavioral abnormalities and neuroinflammatory responses induced by CSDS in adult mice at their different stages of the age, PND 56, 140, and 252. These results indicate that stimulation of microglia in adolescence may confer long-lasting protection against neuroinflammatory responses and behavioral abnormalities induced by chronic stress in adult mice. This may offer the potential for the development of a "vaccine-like strategy" to prevent mental disorders.

Psychological stress creates an immune suppressive environment in the lung that increases susceptibility of aged mice to Mycobacterium tuberculosis infection

Age is a major risk factor for chronic infections, including tuberculosis (TB). Elderly TB patients also suffer from elevated levels of psychological stress. It is not clear how psychological stress impacts immune response to Mycobacterium tuberculosis (M.tb). In this study, we used social disruption stress (SDR) to investigate effects of psychological stress in young and old mice. Unexpectedly, we found that SDR suppresses lung inflammation in old mice as evidenced by lower pro-inflammatory cytokine levels in bronchial lavage fluid and decreased cytokine mRNA expression by alveolar macrophages. To investigate effects of stress on M.tb infection, mice were subjected to SDR and then infected with M.tb. As previously reported, old mice were better at controlling infection at 30 days than young mice. This control was transient as CFUs at 60 days were higher in old control mice compared to young mice. Consistently, SDR significantly increased M.tb growth at 60 days in old mice compared to young mice. In addition, SDR in old mice resulted in accumulation of IL-10 mRNA and decreased IFN-γ mRNA at 60 days. Also, confocal microscopy of lung sections from old SDR mice showed increased number of CD4 T cells which express LAG3 and CD49b, markers of IL-10 secreting regulatory T cells. Further, we also demonstrated that CD4 T cells from old SDR mice express IL-10. Thus, we conclude that psychological stress in old mice prior to infection, increases differentiation of IL-10 secreting T cells, which over time results in loss of control of the infection.

Granulocyte-macrophage colony-stimulating factor-triggered innate immune tolerance against chronic stress-induced behavioral abnormalities in mice

Pre-stimulation of the innate immune is considered a potential strategy to prevent chronic stress-induced behavioral abnormalities in animals. In this study, we investigated whether granulocyte-macrophage colony-stimulating factor (GM-CSF), an immunostimulant used in the clinic to treat diseases of the hematopoietic system, can prevent chronic stress-induced behavioral abnormalities in mice. Our results showed that a single intraperitoneal injection of GM-CSF (100 μg/kg) one day before stress exposure prevented the depression- and anxiety-like behaviors induced by chronic social defeat stress (CSDS) in mice, including preventing the CSDS-induced increase in the immobility time in the tail suspension test and forced swimming test and decrease in the time spent in the interaction zone in the social interaction test, as well as preventing the CSDS-induced decrease in the time spent (i) in open arms in the elevated plus maze test, (ii) on the illuminated side in the light-dark test, and (iii) in the central region of the open field test. The single GM-CSF preinjection (100 μg/kg) also prevented the CSDS-induced increase in the expression levels of interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-α (TNF-α) mRNA in the hippocampus and medial prefrontal cortex of the mice. Further analysis showed that the preventive effect of GM-CSF on CSDS-induced depression- and anxiety-like behaviors and neuroinflammatory responses was abolished by pretreatment with minocycline (an innate immune inhibitor). These results indicate that a single low dose of GM-CSF before injection could be a potential way to prevent behavioral abnormalities induced by chronic stress in mice.

Interactions between the Autonomic Nervous System and the Immune System after Stroke

Acute stroke is one of the leading causes of morbidity and mortality worldwide. Stroke-induced immune-inflammatory response occurs in the perilesion areas and the periphery. Although stroke-induced immunosuppression may alleviate brain injury, it hinders brain repair as the immune-inflammatory response plays a bidirectional role after acute stroke. Furthermore, suppression of the systemic immune-inflammatory response increases the risk of life-threatening systemic bacterial infections after acute stroke. Therefore, it is essential to explore the mechanisms that underlie the stroke-induced immune-inflammatory response. Autonomic nervous system (ANS) activation is critical for regulating the local and systemic immune-inflammatory responses and may influence the prognosis of acute stroke. We review the changes in the sympathetic and parasympathetic nervous systems and their influence on the immune-inflammatory response after stroke. Importantly, this article summarizes the mechanisms on how ANS regulates the immune-inflammatory response through neurotransmitters and their receptors in immunocytes and immune organs after stroke. To facilitate translational research, we also discuss the promising therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response to promote neurologic recovery after stroke. © 2022 American Physiological Society. Compr Physiol 12:3665-3704, 2022.

Alpha-Ketoglutarate Attenuates Colitis in Mice by Increasing Lactobacillus Abundance and Regulating Stem Cell Proliferation via Wnt-Hippo Signaling

SCOPE

Inflammatory bowel disease is an inflammatory gastrointestinal disorder associated with intestinal barrier damage, cell proliferation disorder, and dysbiosis of the intestinal microbiota. It remains unknown whether alpha-ketoglutarate (α-KG) can alleviate colitis in mice.

METHODS AND RESULTS

Six-week-old male C57BL/6 mice supplemented with or without 0.5% α-KG (delivered in the form of sodium salt) are subjected to drinking water or 2.5% DSS to induce colitis. The results show that α-KG administration is attenuated the severity of colitis, as is indicated by reduced body-weight loss, colon shortening and colonic hyperplasia, and repressed proinflammatory cytokine secretion in DSS-challenged mice. Additionally, DSS-induced increases in malondialdehyde (MDA) and hydrogen peroxide (H₂ O₂ ), and decreases in glutathione (GSH) levels are attenuated by α-KG administration. Further study shows that the protective effect of α-KG is associated with restoring gut barrier integrity by enhancing the expression of tight junction proteins, increasing Lactobacillus levels, and regulating gut hyperplasia by the Wnt-Hippo signaling pathway in DSS-induced colitis.

CONCLUSION

Collectively, the data provided herein demonstrate that α-KG administration is attenuated mucosal inflammation, barrier dysfunction, and gut microflora dysbiosis. This beneficial effect is associated with increased Lactobacillus levels and regulated colon hyperplasia by the Wnt-Hippo signaling pathway.

Dynamic Interleukin-1 Receptor Type 1 Signaling Mediates Microglia-Vasculature Interactions Following Repeated Systemic LPS

Introduction

Lipopolysaccharide (LPS) preconditioning involves repeated, systemic, and sub-threshold doses of LPS, which induces a neuroprotective state within the CNS, thus preventing neuronal death and functional losses. Recently, proinflammatory cytokine, Interleukin-1 (IL-1), and its primary signaling partner, interleukin-1 receptor type 1 (IL-1R1), have been associated with neuroprotection in the CNS. However, it is still unknown how IL-1/IL-1R1 signaling impacts the processes associated with neuroprotection.

Methods

Using our IL-1R1 restore genetic mouse model, mouse lines were generated to restrict IL-1R1 expression either to endothelia (Tie2-Cre-Il1r1^r/r) or microglia (Cx3Cr1-Cre-Il1r1 ^r/r), in addition to either global ablation (Il1r1 ^r/r) or global restoration of IL-1R1 (Il1r1 ^GR/GR). The LPS preconditioning paradigm consisted of four daily i.p. injections of LPS at 1 mg/kg (4d LPS). 24 hrs following the final i.p. LPS injection, tissue was collected for qPCR analysis, immunohistochemistry, or FAC sorting.

Results

Following 4d LPS, we found multiple phenotypes that are dependent on IL-1R1 signaling such as microglia morphology alterations, increased microglial M2-like gene expression, and clustering of microglia onto the brain vasculature. We determined that 4d LPS induces microglial morphological changes, clustering at the vasculature, and gene expression changes are dependent on endothelial IL-1R1, but not microglial IL-1R1. A novel observation was the induction of microglial IL-1R1 (mIL-1R1) following 4d LPS. The induced mIL-1R1 permits a unique response to central IL-1β: the mIL-1R1 dependent induction of IL-1R1 antagonist (IL-1RA) and IL-1β gene expression. Analysis of RNA sequencing datasets revealed that mIL-1R1 is also induced in neurodegenerative diseases.

Discussion

Here, we have identified cell type-specific IL-1R1 mediated mechanisms, which may contribute to the neuroprotection observed in LPS preconditioning. These findings identify key cellular and molecular contributors in LPS-induced neuroprotection.

Stressor-Induced Reduction in Cognitive Behavior is Associated with Impaired Colonic Mucus Layer Integrity and is Dependent Upon the LPS-Binding Protein Receptor CD14

Purpose

Commensal microbes are impacted by stressor exposure and are known contributors to cognitive and social behaviors, but the pathways through which gut microbes influence stressor-induced behavioral changes are mostly unknown. A murine social stressor was used to determine whether host-microbe interactions are necessary for stressor-induced inflammation, including neuroinflammation, that leads to reduced cognitive and social behavior.

Methods

C57BL/6 male mice were exposed to a paired fighting social stressor over a 1 hr period for 6 consecutive days. Y-maze and social interaction behaviors were tested following the last day of the stressor. Serum cytokines and lipopolysaccharide binding protein (LBP) were measured and the number and morphology of hippocampal microglia determined via immunohistochemistry. Intestinal mucous thickness and antimicrobial peptide expression were determined via fluorescent staining and real-time PCR (respectively) and microbial community composition was assessed using 16S rRNA gene amplicon sequencing. To determine whether the microbiota or the LBP receptor (CD14) are necessary for stressor-induced behavioral changes, experiments were performed in mice treated with a broad-spectrum antibiotic cocktail or in CD14-/- mice.

Results

The stressor reduced Y-maze spontaneous alternations, which was accompanied by increased microglia in the hippocampus, increased circulating cytokines (eg, IL-6, TNF-α) and LBP, and reduced intestinal mucus thickness while increasing antimicrobial peptides and cytokines. These stressor-induced changes were largely prevented in mice given broad-spectrum antibiotics and in CD14-/- mice. In contrast, social stressor-induced alterations of social behavior were not microbe-dependent.

Conclusion

Stressor-induced cognitive deficits involve enhanced bacterial interaction with the intestine, leading to low-grade, CD14-dependent, inflammation.

Childhood Violence Exposure, Inflammation, and Cardiometabolic Health

Exposure to interpersonal violence during childhood, a severe and often traumatic form of social stress, is an enduring problem that an emerging body of work suggests may be relevant to cardiometabolic health and the progression of cardiovascular disease (CVD) across the life course. Less is known about this association causally, and consequently, the biological mechanisms that may confer risk for, and resilience to, poor health outcomes in the aftermath of violence are not well understood. Drawing on recent theoretical insights and empirical research in both humans and non-human animal models, the current paper articulates a hypothesis for one way that childhood violence could get "under the skin" to influence CVD. Based on this emerging literature, one plausible way that childhood violence exposure could increase susceptibility to CVD in later life is by sensitizing stress-response neurobiology and immune processes that regulate and promote inflammation, which is a key pathogenic mechanism in CVD. This is inherently a developmental process that begins in early life and that unfolds across the life course, although less is known about the specific mechanisms through which this occurs. The goal of this paper is to articulate some of these plausible mechanisms and to suggest areas for future research that aims to reduce the burden of disease among individuals who are exposed to violence.

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.

Electroacupuncture improves repeated social defeat stress-elicited social avoidance and anxiety-like behaviors by reducing Lipocalin-2 in the hippocampus

Background

Post-traumatic stress disorder (PTSD) is a trauma-related disorder that is associated with pro-inflammatory activation and neurobiological impairments in the brain and leads to a series of affective-like behaviors. Electroacupuncture (EA) has been proposed as a clinically useful therapy for several brain diseases. However, the potential role of EA treatment in PTSD and its molecular and cellular mechanisms has rarely been investigated.

Methods

We used an established preclinical social defeat stress mouse model to study whether EA treatment modulates PTSD-like symptoms and understand its underlying mechanisms. To this end, male C57BL/6 mice were subjected to repeated social defeat stress (RSDS) for 6 consecutive days to induce symptoms of PTSD and treated with EA at Baihui (GV 20) and Dazhui (GV 14) acupoints.

Results

The stimulation of EA, but not needle insertion at Baihui (GV 20) and Dazhui (GV 14) acupoints effectively improved PTSD-like behaviors such as, social avoidance and anxiety-like behaviors. However, EA stimulation at the bilateral Tianzong (SI11) acupoints did not affect the PTSD-like behaviors obtained by RSDS. EA stimulation also markedly inhibited astrocyte activation in both the dorsal and ventral hippocampi of RSDS-treated mice. Using next-generation sequencing analysis, our results showed that EA stimulation attenuated RSDS-enhanced lipocalin 2 expression in the hippocampus. Importantly, using double-staining immunofluorescence, we observed that the increased lipocalin 2 expression in astrocytes by RSDS was also reduced by EA stimulation. In addition, intracerebroventricular injection of mouse recombinant lipocalin 2 protein in the lateral ventricles provoked social avoidance, anxiety-like behaviors, and the activation of astrocytes in the hippocampus. Interestingly, the overexpression of lipocalin 2 in the brain also altered the expression of stress-related genes, including monoamine oxidase A, monoamine oxidase B, mineralocorticoid receptor, and glucocorticoid receptor in the hippocampus.

Conclusions

This study suggests that the treatment of EA at Baihui (GV 20) and Dazhui (GV 14) acupoints improves RSDS-induced social avoidance, anxiety-like behaviors, astrocyte activation, and lipocalin 2 expression. Furthermore, our findings also indicate that lipocalin 2 expression in the brain may be an important biomarker for the development of PTSD-related symptoms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13041-021-00860-0.

Glucocorticoid resistance and β2-adrenergic receptor signaling pathways promote peripheral pro-inflammatory conditions associated with chronic psychological stress: A systematic review across species

Activation of the HPA-axis and SNS are widely accepted to link chronic stress with elevated levels of peripheral pro-inflammatory markers in blood. Yet, empirical evidence showing that peripheral levels of glucocorticoids and/or catecholamines mediate this effect is equivocal. Recent attention has turned to the possibility that cellular sensitivity to these ligands may contribute to inflammatory mediators that accompany chronic stress. We review current evidence for the association of chronic stress with glucocorticoid receptor (GR) and β-adrenergic receptor (β-AR) signaling sensitivity. Across 15 mouse, 7 primate, and 19 human studies, we found that chronic stress reliably associates with downregulation in cellular GR sensitivity, alterations in intracellular β-AR signaling, and upregulation in pro-inflammatory biomarkers in peripheral blood. We also present evidence that alterations in GR and β-AR signaling may be specific to myeloid progenitor cells such that stress-related signaling promotes release of cells that are inherently less sensitive to glucocorticoids and differentially sensitive to catecholamines. Our findings have broad implications for understanding mechanisms by which chronic stress may contribute to pro-inflammatory phenotypes.

Interleukin-1 receptor on hippocampal neurons drives social withdrawal and cognitive deficits after chronic social stress

Chronic stress contributes to the development of psychiatric disorders including anxiety and depression. Several inflammatory-related effects of stress are associated with increased interleukin-1 (IL-1) signaling within the central nervous system and are mediated by IL-1 receptor 1 (IL-1R1) on several distinct cell types. Neuronal IL-1R1 is prominently expressed on the neurons of the dentate gyrus, but its role in mediating behavioral responses to stress is unknown. We hypothesize that IL-1 acts on this subset of hippocampal neurons to influence cognitive and mood alterations with stress. Here, mice subjected to psychosocial stress showed reduced social interaction and impaired working memory, and these deficits were prevented by global IL-1R1 knockout. Stress-induced monocyte trafficking to the brain was also blocked by IL-1R1 knockout. Selective deletion of IL-1R1 in glutamatergic neurons (nIL-1R1^-/-) abrogated the stress-induced deficits in social interaction and working memory. In addition, viral-mediated selective IL-1R1 deletion in hippocampal neurons confirmed that IL-1 receptor in the hippocampus was critical for stress-induced behavioral deficits. Furthermore, selective restoration of IL-1R1 on glutamatergic neurons was sufficient to reestablish the impairments of social interaction and working memory after stress. RNA-sequencing of the hippocampus revealed that stress increased several canonical pathways (TREM1, NF-κB, complement, IL-6 signaling) and upstream regulators (INFγ, IL-1β, NF-κB, MYD88) associated with inflammation. The inductions of TREM1 signaling, complement, and leukocyte extravasation with stress were reversed by nIL-1R1^-/-. Collectively, stress-dependent IL-1R1 signaling in hippocampal neurons represents a novel mechanism by which inflammation is perpetuated and social interactivity and working memory are modulated.

Juvenile social defeat stress exposure favors in later onset of irritable bowel syndrome-like symptoms in male mice

Irritable bowel syndrome (IBS) is the most common functional gastrointestinal disorder. Traumatic stress during adolescence increases the risk of IBS in adults. The aim of this study was to characterize the juvenile social defeat stress (SDS)-associated IBS model in mice. Juvenile mice were exposed to an aggressor mouse for 10 min once daily for 10 consecutive days. Behavioral tests, visceral sensitivity, immune responses, and fecal bacteria in the colon were evaluated in 5 weeks after SDS exposure. Social avoidance, anxiety- and depression-like behavior, and visceral hypersensitivity were observed. Juvenile SDS exposure significantly increased the number of 5-HT-containing cells and calcitonin gene-related peptide-positive neurons in the colon. The gut microbiota was largely similar between the control and juvenile SDS groups. The alterations in fecal pellet output, bead expulsion time, plasma corticosterone concentration, and colonic 5-HT content in response to restraint stress were exacerbated in the juvenile SDS group compared with the control group. The combination of juvenile SDS and restraint stress increased the noradrenaline metabolite 3-Methoxy-4-hydroxyphenylglycol (MHPG) content and MHPG/noradrenaline ratio in the amygdala when compared with restraint stress in control mice. These results suggest that juvenile SDS exposure results in later onset of IBS-like symptoms.

Type 1 interferon mediates chronic stress-induced neuroinflammation and behavioral deficits via complement component 3-dependent pathway

Chronic stress is a major risk factor in the pathophysiology of many neuropsychiatric disorders. Further, chronic stress conditions can promote neuroinflammation and inflammatory responses in both humans and animal models. Type I interferons (IFN-I) are critical mediators of the inflammatory response in the periphery and responsible for the altered mood and behavior. However, the underlying mechanisms are not well understood. In the present study, we investigated the role of IFN-I signaling in chronic stress-induced changes in neuroinflammation and behavior. Using the chronic restraint stress model, we found that chronic stress induces a significant increase in serum IFNβ levels in mice, and systemic blockade of IFN-I signaling attenuated chronic stress-induced infiltration of macrophages into prefrontal cortex and behavioral abnormalities. Furthermore, complement component 3 (C3) mediates systemic IFNβ-induced changes in neuroinflammation and behavior. Also, we found significant increases in the mRNA expression levels of IFN-I stimulated genes in the prefrontal cortex of depressed suicide subjects and significant correlation with C3 and inflammatory markers. Together, these findings from animal and human postmortem brain studies identify a crucial role of C3 in IFN-I-mediated changes in neuroinflammation and behavior under chronic stress conditions.

Association between cellular immune response and spleen weight in mice with hepatocellular carcinoma

The spleen is an important site for extramedullary hematopoiesis and tumor immunotolerance. Spleen weight varies with tumor progression and may be a predictor of tumor recurrence. However, to the best of our knowledge, the association between spleen weight and tumor progression remains unclear. The present study revealed a novel role for the spleen in predicting the cellular immune response in tumor-bearing mice. A murine H22 subcutaneous hepatoma model was established. The spleen weight and tumor weight were measured. The proportion of immune cells in peripheral blood and spleen were detected by flow cytometry. The results demonstrated that the spleen weight of tumor-bearing mice at day 21 was higher than that of the controls. In addition, spleen weight was identified to be positively correlated with tumor weight. The percentages of CD4⁺ and CD8⁺ T lymphocytes in the spleen were decreased at day 21 after tumor cell inoculation, while those of monocytic-like myeloid-derived suppressor cells (M-MDSCs) and CD11b⁺F4/80⁺ macrophages were increased at day 21 after tumor cell inoculation. Similarly, the percentage of polymorphonuclear-like MDSCs (PMN-MDSCs) in the spleen of tumor-bearing mice was increased at days 7, 14 and 21 after tumor cell inoculation. Notably, spleen weight was negatively correlated with the percentages of CD4⁺ and CD8⁺ T lymphocytes in the spleen, although spleen and tumor weight were positively correlated with the percentages of M-MDSCs and PMN-MDSCs in the spleen. Similarly, the percentages of CD8⁺ T lymphocytes in the peripheral blood were decreased, and programmed cell death protein 1 expression on CD8⁺ T lymphocytes was increased at day 21 after tumor cell inoculation. Furthermore, the percentages of M-MDSCs were increased at day 21 and PMN-MDSCs in the peripheral blood were increased at days 7, 14 and 21 after tumor cell inoculation. Additionally, spleen and tumor weight were also positively correlated with the percentages of M-MDSC and PMN-MDSCs in the peripheral blood of tumor-bearing mice. Collectively, the findings of the present study suggested that spleen weight may be a predictor of tumor prognosis, since it was directly correlated with tumor weight and the percentages of M-MDSC and PMN-MDSCs in tumor-bearing mice.

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.

Adolescent stress sensitizes the adult neuroimmune transcriptome and leads to sex-specific microglial and behavioral phenotypes

Adolescent exposure to chronic stress, a risk factor for mood disorders in adulthood, sensitizes the neuroinflammatory response to a subsequent immune challenge. We previously showed that chronic adolescent stress (CAS) in rats led to distinct patterns of neuroimmune priming in adult male and female rats. However, sex differences in the neuroimmune consequences of CAS and their underlying mechanisms are not fully understood. Here we hypothesized that biological sex would dictate differential induction of inflammation-related transcriptomic pathways and immune cell involvement (microglia activation and leukocyte presence) in the hippocampus of male and female rats with a history of CAS. Adolescent rats underwent CAS (six restraint and six social defeat episodes during postnatal days 38-49), and behavioral assessments were conducted in adolescence and adulthood. Neuroimmune measures were obtained following vehicle or a systemic lipopolysaccharide (LPS) challenge in adulthood. CAS led to increased time in the corners of the open field in adolescence. In males, CAS also increased social avoidance. As adults, CAS rats displayed an exaggerated enrichment of the nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) pathway and chemokine induction following LPS challenge, and increased number of perivascular CD45⁺ cells in the hippocampus. However, CAS females, but not males, showed exaggerated glucocorticoid receptor (GR) pathway enrichment and increased microglial complexity. These results provide further insight to the mechanisms by which peripheral immune events may influence neuroimmune responses differentially among males and females and further demonstrate the importance of adolescent stress in shaping adult responses.

Anxiety is associated with increased risk for atrial cardiopathy

Anxiety is common in patients with atrial fibrillation (AF). The mutual causal effect between anxiety and AF is expected with limited evidence. Atrial cardiopathy is a term to describe structural or electrophysiological atrium abnormality that precedes the onset of AF. This study aimed to investigate the association of anxiety with atrial cardiopathy, giving a clue to the causal relationship of this mind-heart link. This cross-sectional study analyzed 532 patients who were free of AF, atrial flutter, stroke, acute coronary syndrome and valvular heart disease. Atrial cardiopathy was defined as P-wave terminal force in lead V1 > 5000 μV·ms on electrocardiogram or severe left atrial enlargement on echocardiogram. Generalized anxiety disorder was ascertained by a score of > 17/56 on Hamilton anxiety rating scale. Multivariable logistic regression was used to explore the association of anxiety with atrial cardiopathy. A total of 65(12.2%) patients had atrial cardiopathy and 53(10.0%) had generalized anxiety disorder, respectively. Those with atrial cardiopathy were older (74.0 vs 67.0, P < 0.001), had a bigger left ventricular posterior wall thickness (10.1 vs 9.7 mm, P = 0.030), and had a higher prevalence of hypertension (83.1% vs 65.5%, P = 0.005), premature complexes (20.0% vs 6.2%, P < 0.001), and generalized anxiety disorder (20.0% vs 8.6%, P = 0.004), respectively. Multivariable logistic regression showed the significant association of anxiety with atrial cardiopathy (OR 2.788; 95% CI 1.304-5.960, P = 0.008), independent of confounding factors. Anxiety is independently associated with atrial cardiopathy. This association indicates the triggering effect of anxiety on atrial remodeling.

Potential role of primed microglia during obesity on the mesocorticolimbic circuit in autism spectrum disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental disease which involves functional and structural defects in selective central nervous system (CNS) regions that harm function and individual ability to process and respond to external stimuli. Individuals with ASD spend less time engaging in social interaction compared to non-affected subjects. Studies employing structural and functional magnetic resonance imaging reported morphological and functional abnormalities in the connectivity of the mesocorticolimbic reward pathway between the nucleus accumbens and the ventral tegmental area (VTA) in response to social stimuli, as well as diminished medial prefrontal cortex in response to visual cues, whereas stronger reward system responses for the non-social realm (e.g., video games) than social rewards (e.g., approval), associated with caudate nucleus responsiveness in ASD children. Defects in the mesocorticolimbic reward pathway have been modulated in transgenic murine models using D2 dopamine receptor heterozygous (D2+/-) or dopamine transporter knockout mice, which exhibit sociability deficits and repetitive behaviors observed in ASD phenotypes. Notably, the mesocorticolimbic reward pathway is modulated by systemic and central inflammation, such as primed microglia, which occurs during obesity or maternal overnutrition. Therefore, we propose that a positive energy balance during obesity/maternal overnutrition coordinates a systemic and central inflammatory crosstalk that modulates the dopaminergic neurotransmission in selective brain areas of the mesocorticolimbic reward pathway. Here, we will describe how obesity/maternal overnutrition may prime microglia, causing abnormalities in dopamine neurotransmission of the mesocorticolimbic reward pathway, postulating a possible immune role in the development of ASD.

Emotional Impairments and Neuroinflammation are Induced in Male Mice Invulnerable to Repeated Social Defeat Stress

Prolonged stress triggers neuroinflammation, which plays a significant role in the development of depression; however, stressed people do not always suffer from depression because of individual differences in stress vulnerability. Negative cognitive bias (NCB) toward pessimistic judgment often underlies depressive episodes. However, a relationship between stress vulnerability, neuroinflammation, and NCB remains elusive. In addition, an animal model with all the traits would be a powerful tool for studying the etiology of depression and its therapeutic approaches. Accordingly, this study evaluated the effect of stress vulnerability on neuroinflammation and depression-related behaviors, including NCB in males, using a modified version of repeated social defeat stress (mRSDS) paradigm, a validated animal model of psychosocial stress. Exposure to mRSDS, consisting of 5 min of social defeat by unfamiliar CD-1 aggressor mice for five consecutive days, caused NCB, which co-occurred with depressive- and anxiety-like behaviors, and neuroinflammation in male BALB/c mice. Treatment with minocycline, an antibiotic with anti-inflammatory property, blocked mRSDS-induced depressive-like behaviors and neuroinflammation, but not NCB, indicating the limited effect of an anti-inflammatory intervention. In addition, marked differences were found in neuroinflammatory profiles and hippocampal gene expression patterns between resilient and unstressed mice, as well as between susceptible and resilient mice. Therefore, mice resilient to mRSDS are indeed not intact. Our findings provide insights into the unique features of the mRSDS model in male BALB/c mice, which could be used to investigate the etiological mechanisms underlying depression as well as bridge the gap in the relationship between stress vulnerability, neuroinflammation, and NCB in males.

A history of juvenile mild malaria exacerbates chronic stress-evoked anxiety-like behavior, neuroinflammation, and decline of adult hippocampal neurogenesis in mice

Children residing in high malaria transmission regions are particularly susceptible to malaria. This early-life window is also a critical period for development and maturation of the nervous system, and inflammatory insults during this period may evoke a persistent increase in vulnerability for psychopathology. We employed a two-hit model of juvenile mild malaria and a two-week chronic unpredictable mild stress (CUMS) regime, commencing 60 days post-parasite clearance, to assess whether a history of juvenile infection predisposed the mice towards mood-related behavioral alterations and neurocognitive deficits. We showed that adult mice with a history of juvenile malaria (A-H/JMAL) exhibited heightened CUMS-associated anxiety-like behavior, with no observable change in cognitive behavior. In contrast, mice with a history of adult malaria did not exhibit such enhanced stress vulnerability. At baseline, A-H/JMAL mice showed increased activated microglia within the hippocampal dentate gyrus subfield. This was accompanied by a decrease in proliferating neuronal progenitors, with total number of immature hippocampal neurons unaltered. This neuroinflammatory and neurogenic decline was further exacerbated by CUMS. At day-14 post-CUMS, hippocampi of A-H/JMAL mice showed significantly higher microglial activation, and a concomitant decrease in progenitor proliferation and number of immature neurons. Taken together, these results suggest that a history of juvenile mild malaria leaves a neuroinflammatory mark within the hippocampal niche, and this may contribute to a heightened stress response in adulthood. Our findings lend credence to the idea that the burden of malaria in early-life results in sustained CNS changes that could contribute to increased vulnerability to adult-onset neuronal insults.

Sleep Disruption Exacerbates and Prolongs the Inflammatory Response to Traumatic Brain Injury

Traumatic brain injury (TBI) alters stress responses, which may influence neuroinflammation and behavioral outcome. Sleep disruption (SD) is an understudied post-injury environmental stressor that directly engages stress-immune pathways. Thus, we predicted that maladaptive changes in the hypothalamic-pituitary-adrenal (HPA) axis after TBI compromise the neuroendocrine response to SD and exacerbate neuroinflammation. To test this, we induced lateral fluid percussion TBI or sham injury in female and male C57BL/6 mice aged 8-10 weeks that were then left undisturbed or exposed to 3 days of transient SD. At 3 days post-injury (DPI) plasma corticosterone (CORT) was reduced in TBI compared with sham mice, indicating altered HPA-mediated stress response to SD. This response was associated with approach-avoid conflict behavior and exaggerated cortical neuroinflammation. Post-injury SD specifically enhanced neutrophil trafficking to the injured brain in conjunction with dysregulated aquaporin-4 (AQP4) polarization. Delayed and persistent effects of post-injury SD were determined 4 days after SD concluded at 7 DPI. SD prolonged anxiety-like behavior regardless of injury and was associated with increased cortical Iba1 labeling in both sham and TBI mice. Strikingly, TBI SD mice displayed an increased number of CD45+ cells near the site of injury, enhanced cortical glial fibrillary acidic protein (GFAP) immunolabeling, and persistent expression of Trem2 and Tlr4 7 DPI compared with TBI mice. These results support the hypothesis that post-injury SD alters stress-immune pathways and inflammatory outcomes after TBI. These data provide new insight to the dynamic interplay between TBI, stress, and inflammation.

The spleen mediates chronic sleep restriction-mediated enhancement of LPS-induced neuroinflammation, cognitive deficits, and anxiety-like behavior

Chronic sleep restriction promotes neuroinflammation and cognitive deficits in neurodegenerative and neurobehavioral diseases. The spleens of mice exposed to chronic and repeated psychological stress serve as a reservoir of inflammatory myeloid cells that are released into the blood and brain following secondary acute stress. Here, we tested whether chronic and repeated short-term sleep restriction (CRSR) would exacerbate lipopolysaccharide (LPS)-induced neuroinflammation, cognitive deficits, and anxiety-like behavior in a spleen-dependent manner. LPS was administered to aged mice 14 days after exposure to CRSR consisting of three cycles of 7 days of sleep restriction with 7-day intervals in between. CRSR increased plasma proinflammatory cytokine levels, blood-brain barrier permeability, hippocampal proinflammatory cytokine levels, and transition of microglia to the M1 phenotype 24 h after LPS treatment. This in turn led to cognitive deficits and anxiety-like behavior. Interestingly, removal of the spleen 14 days prior to CRSR abrogated the enhancement of LPS-induced increases in systemic inflammation, neuroinflammation, cognitive deficits, and anxiety-like behavior. These data indicate that the spleen was essential for CRSR-induced exacerbation of LPS-induced brain damage.