Microglia serve as a neuroimmune substrate for stress-induced potentiation of CNS pro-inflammatory cytokine responses

Associations of the immune system in aggression traits and the role of microglia as mediators

There is an important relationship between the immune system and aggressive behavior. Aggressive encounters acutely increase the levels of proinflammatory cytokines, and there are positive correlations between aggressive traits and peripheral proinflammatory cytokines. Endotoxin lipopolysaccharide (LPS) treatment, which results in peripheral immune activation, decreases aggressive behavior as one of the sickness behavioral symptoms. In contrast, certain brain infections and chronic interferon treatment are associated with increased aggression. Indeed, the effects of proinflammatory cytokines on the brain in aggressive behavior are bidirectional, depending on the type and dose of cytokine, target brain region, and type of aggression. Some studies have suggested that microglial activation and neuroinflammation influence intermale aggression in rodent models. In addition, pathological conditions as well as physiological levels of cytokines produced by microglia play an important role in social and aggressive behavior in adult animals. Furthermore, microglial function in early development is necessary for the establishment of the social brain and the expression of juvenile social behaviors, including play fighting. Overall, this review discusses the important link between the immune system and aggressive traits and the role of microglia as mediators of this link.

Prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in ovariectomized female rats

Stress is a major risk factor for several neuropsychiatric disorders in women, including postpartum depression. During the postpartum period, diminished ovarian hormone secretion increases susceptibility to developing depressive symptoms. Pleiotropic peptide hormones, like prolactin, are markedly released during lactation and suppress hypothalamic-pituitary-adrenal axis responses in women and acute stress-induced behavioral responses in female rodents. However, the effects of prolactin on chronic stress-induced maladaptive behaviors remain unclear. Here, we used chronic variable stress to induce maladaptive physiology in ovariectomized female rats and concurrently administered prolactin to assess its effects on several depression-relevant behavioral, endocrine, and neural characteristics. We found that chronic stress increased sucrose anhedonia and passive coping in saline-treated, but not prolactin-treated rats. Prolactin treatment did not alter stress-induced thigmotaxis, corticosterone (CORT) concentrations, hippocampal cell activation or survival. However, prolactin treatment reduced basal CORT concentrations and increased dopaminergic cells in the ventral tegmental area. Further, prolactin-treated rats had reduced microglial activation in the ventral hippocampus following chronic stress exposure. Together, these data suggest prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in hypogonadal females. Moreover, these findings imply neuroendocrine-immune mechanisms by which peptide hormones confer stress resilience during periods of low ovarian hormone secretion.

Cytokines IL-1β and IL-10 are required for Müller glia proliferation following light damage in the adult zebrafish retina

Zebrafish possess the ability to regenerate dying neurons in response to retinal injury, with both Müller glia and microglia playing integral roles in this response. Resident Müller glia respond to damage by reprogramming and undergoing an asymmetric cell division to generate a neuronal progenitor cell, which continues to proliferate and differentiate into the lost neurons. In contrast, microglia become reactive, phagocytose dying cells, and release inflammatory signals into the surrounding tissue following damage. In recent years, there has been increased attention on elucidating the role that microglia play in regulating retinal regeneration. Here we demonstrate that inflammatory cytokines are differentially expressed during retinal regeneration, with the expression of a subset of pro-inflammatory cytokine genes upregulated shortly after light damage and the expression of a different subset of cytokine genes subsequently increasing. We demonstrate that both cytokine IL-1β and IL-10 are essential for Müller glia proliferation in the light-damaged retina. While IL-1β is sufficient to induce Müller glia proliferation in an undamaged retina, expression of IL-10 in undamaged retinas only induces Müller glia to express gliotic markers. Together, these findings demonstrate the essential role of inflammatory cytokines IL-1β and IL-10 on Müller glia proliferation following light damage in adult zebrafish.

Unraveling the Role of the Blood-Brain Barrier in the Pathophysiology of Depression: Recent Advances and Future Perspectives

Depression is a highly prevalent psychological disorder characterized by persistent dysphoria, psychomotor retardation, insomnia, anhedonia, suicidal ideation, and a remarkable decrease in overall well-being. Despite the prevalence of accessible antidepressant therapies, many individuals do not achieve substantial improvement. Understanding the multifactorial pathophysiology and the heterogeneous nature of the disorder could lead the way toward better outcomes. Recent findings have elucidated the substantial impact of compromised blood-brain barrier (BBB) integrity on the manifestation of depression. BBB functions as an indispensable defense mechanism, tightly overseeing the transport of molecules from the periphery to preserve the integrity of the brain parenchyma. The dysfunction of the BBB has been implicated in a multitude of neurological disorders, and its disruption and consequent brain alterations could potentially serve as important factors in the pathogenesis and progression of depression. In this review, we extensively examine the pathophysiological relevance of the BBB and delve into the specific modifications of its components that underlie the complexities of depression. A particular focus has been placed on examining the effects of peripheral inflammation on the BBB in depression and elucidating the intricate interactions between the gut, BBB, and brain. Furthermore, this review encompasses significant updates on the assessment of BBB integrity and permeability, providing a comprehensive overview of the topic. Finally, we outline the therapeutic relevance and strategies based on BBB in depression, including COVID-19-associated BBB disruption and neuropsychiatric implications. Understanding the comprehensive pathogenic cascade of depression is crucial for shaping the trajectory of future research endeavors.

B cells and the stressed brain: emerging evidence of neuroimmune interactions in the context of psychosocial stress and major depression

The immune system has emerged as a key regulator of central nervous system (CNS) function in health and in disease. Importantly, improved understanding of immune contributions to mood disorders has provided novel opportunities for the treatment of debilitating stress-related mental health conditions such as major depressive disorder (MDD). Yet, the impact to, and involvement of, B lymphocytes in the response to stress is not well-understood, leaving a fundamental gap in our knowledge underlying the immune theory of depression. Several emerging clinical and preclinical findings highlight pronounced consequences for B cells in stress and MDD and may indicate key roles for B cells in modulating mood. This review will describe the clinical and foundational observations implicating B cell-psychological stress interactions, discuss potential mechanisms by which B cells may impact brain function in the context of stress and mood disorders, describe research tools that support the investigation of their neurobiological impacts, and highlight remaining research questions. The goal here is for this discussion to illuminate both the scope and limitations of our current understanding regarding the role of B cells, stress, mood, and depression.

Glucocorticoid receptor antagonist CORT113176 attenuates motor and neuropathological symptoms of Huntington's disease in R6/2 mice

Huntington's Disease (HD) is a progressive neurodegenerative disease caused by a mutation in the huntingtin gene. The mutation leads to a toxic gain of function of the mutant huntingtin (mHtt) protein resulting in cellular malfunction, aberrant huntingtin aggregation and eventually neuronal cell death. Patients with HD show impaired motor functions and cognitive decline. Elevated levels of glucocorticoids have been found in HD patients and in HD mouse models, and there is a positive correlation between increased glucocorticoid levels and the progression of HD. Therefore, antagonism of the glucocorticoid receptor (GR) may be an interesting strategy for the treatment of HD. In this study, we evaluated the efficacy of the selective GR antagonist CORT113176 in the commonly used R6/2 mouse model. In male mice, CORT113176 treatment significantly delayed the loss of grip strength, the development of hindlimb clasping, gait abnormalities, and the occurrence of epileptic seizures. CORT113176 treatment delayed loss of DARPP-32 immunoreactivity in the dorsolateral striatum. It also restored HD-related parameters including astrocyte markers in both the dorsolateral striatum and the hippocampus, and microglia markers in the hippocampus. This suggests that CORT113176 has both cell-type and brain region-specific effects. CORT113176 delayed the formation of mHtt aggregates in the striatum and the hippocampus. In female mice, we did not observe major effects of CORT113176 treatment on HD-related symptoms, with the exception of the anti-epileptic effects. We conclude that CORT113176 effectively delays several key symptoms related to the HD phenotype in male R6/2 mice and believe that GR antagonism may be a possible treatment option.

Proteomic study of left ventricle and cortex in rats after myocardial infarction

Myocardial infarction (MI) induces neuroinflammation indirectly, chronic neuroinflammation may cause neurodegenerative diseases. Changes in the proteomics of heart and brain tissue after MI may shed new light on the mechanisms involved in neuroinflammation. This study explored brain and heart protein changes after MI with a data-independent acquisition (DIA) mode proteomics approach. Permanent ligation of the left anterior descending coronary artery (LAD) was performed in the heart of rats, and the immunofluorescence of microglia in the brain cortex was performed at 1d, 3d, 5d, and 7d after MI to detect the neuroinflammation. Then proteomics was accomplished to obtain the vital proteins in the heart and brain post-MI. The results show that the number of microglia was significantly increased in the Model-1d group, the Model-3d group, the Model-5d group, and the Model-7d group compared to the Sham group. Various proteins were obtained through DIA proteomics. Linking to key targets of brain disease, 14 proteins were obtained in the brain cortex. Among them, elongation of very long chain fatty acids protein 5 (ELOVL5) and ATP-binding cassette subfamily G member 4 (ABCG4) were verified through western blotting (WB). The results of WB were consistent with the proteomics results. Therefore, these proteins may be related to the pathogenesis of neuroinflammation after MI.

Chronically stressed male and female mice show a similar peripheral and central pro-inflammatory profile after an immune challenge

Although acute stressors are known for stimulating the production of glucocorticoids and pro-inflammatory cytokines in rodents, the effects of chronic stressors on cytokine levels and the activation of the hypothalamic-pituitary-adrenal (HPA) axis, especially in response to a subsequent challenge, are less clear. In this study, male and female mice were exposed to 6 weeks of chronic variable stress (CVS) and the peripheral and central levels of IL-1β, IL-6, and TNF-α, as well as the HPA axis reactivity, were measured after an acute injection of LPS. The findings indicate that the pro-inflammatory profile in the plasma, regardless of stress exposure, was similar between male and female animals, whereas there was a region-, sex-, and stress-dependent pattern in the brain. Exposure to chronic stressors blunted the HPA reactivity to the LPS challenge, indicating a modulatory effect on the stress axis responsiveness.

Effect of a multi-strain probiotic mixture consumption on anxiety and depression symptoms induced in adult mice by postnatal maternal separation

BACKGROUND

Intestinal microbial composition not only affects the health of the gut but also influences centrally mediated systems involved in mood, through the "gut-brain" axis, a bidirectional communication between gut microbiota and the brain. In this context, the modulation of intestinal microbiota and its metabolites through the administration of probiotics seems to represent a very promising approach in the treatment of the central nervous system alterations. Early postnatal life is a critical period during which the brain undergoes profound and essential modulations in terms of maturation and plasticity. Maternal separation (MS), i.e., the disruption of the mother-pup interaction, represents a pivotal paradigm in the study of stress-related mood disorders, by inducing persistent changes in the immune system, inflammatory processes, and emotional behavior in adult mammals.

RESULTS

We conducted experiments to investigate whether sustained consumption of a multi-strain probiotic formulation by adult male mice could mitigate the effects of maternal separation. Our data demonstrated that the treatment with probiotics was able to totally reverse the anxiety- and depressive-like behavior; normalize the neuro-inflammatory state, by restoring the resting state of microglia; and finally induce a proneurogenic effect. Mice subjected to maternal separation showed changes in microbiota composition compared to the control group that resulted in permissive colonization by the administered multi-strain probiotic product. As a consequence, the probiotic treatment also significantly affected the production of SCFA and in particular the level of butyrate.

CONCLUSION

Gut microbiota and its metabolites mediate the therapeutic action of the probiotic mix on MS-induced brain dysfunctions. Our findings extend the knowledge on the use of probiotics as a therapeutic tool in the presence of alterations of the emotional sphere that significantly impact on gut microbiota composition. Video Abstract.

Keratinocyte-Derived Cytokine in the Hippocampus Disrupts Extinction of Conditioned Fear Memory in Tumor-Bearing Mice

While patients with cancer show a higher prevalence of psychiatric disorders than the general population, the mechanism underlying this interaction remains unclear. The present study examined whether tumor-bearing (TB) mice show psychological changes using the conditioned fear paradigm and the role of cytokines in these changes. TB mice were established by transplantation with mouse osteosarcoma AXT cells. These TB mice were then found to exhibit disruption in extinction of conditioned fear memory. Eighteen cytokines in serum were increased in TB mice, among which i.c.v. injection of interleukin (IL)-1β and IL-6 strengthened fear memory in normal mice. Contents of IL-17 and keratinocyte-derived cytokine (KC) in the amygdala and KC in the hippocampus were increased in TB mice. KC mRNA in both the amygdala and hippocampus was also increased in TB mice, and i.c.v. injection of KC dose-dependently strengthened fear memory in normal mice. In addition, injection of IL-1β, but not IL-6, increased KC mRNA in the amygdala and hippocampus. In TB mice KC mRNA was increased in both astrocytes and microglia of the amygdala and hippocampus. The microglia inhibitor minocycline, but not the astrocyte inhibitor fluorocitrate, alleviated disruption in extinction of conditioned fear memory in TB mice. Microinjection of KC into the hippocampus, but not into the amygdala, increased fear memory in normal mice. These findings indicate that TB mice show an increase in serum cytokines, including IL-1β, that increases KC production in microglia of the hippocampus, which then disrupts extinction of fear memory.

Prenatal exposure to maternal disadvantage-related inflammatory biomarkers: associations with neonatal white matter microstructure

Prenatal exposure to heightened maternal inflammation has been associated with adverse neurodevelopmental outcomes, including atypical brain maturation and psychiatric illness. In mothers experiencing socioeconomic disadvantage, immune activation can be a product of the chronic stress inherent to such environmental hardship. While growing preclinical and clinical evidence has shown links between altered neonatal brain development and increased inflammatory states in utero, the potential mechanism by which socioeconomic disadvantage differentially impacts neural-immune crosstalk remains unclear. In the current study, we investigated associations between socioeconomic disadvantage, gestational inflammation, and neonatal white matter microstructure in 320 mother-infant dyads over-sampled for poverty. We analyzed maternal serum levels of four cytokines (IL-6, IL-8, IL-10, TNF-α) over the course of pregnancy in relation to offspring white matter microstructure and socioeconomic disadvantage. Higher average maternal IL-6 was associated with very low socioeconomic status (SES; INR < 200% poverty line) and lower neonatal corticospinal fractional anisotropy (FA) and lower uncinate axial diffusivity (AD). No other cytokine was associated with SES. Higher average maternal IL-10 was associated with lower FA and higher radial diffusivity (RD) in corpus callosum and corticospinal tracts, higher optic radiation RD, lower uncinate AD, and lower FA in inferior fronto-occipital fasciculus and anterior limb of internal capsule tracts. SES moderated the relationship between average maternal TNF-α levels during gestation and neonatal white matter diffusivity. When these interactions were decomposed, the patterns indicated that this association was significant and positive among very low SES neonates, whereby TNF-α was inversely and significantly associated with inferior cingulum AD. By contrast, among the more advantaged neonates (lower-to-higher SES [INR ≥ 200% poverty line]), TNF-α was positively and significantly associated with superior cingulum AD. Taken together, these findings suggest that the relationship between prenatal cytokine exposure and white matter microstructure differs as a function of SES. These patterns are consistent with a scenario where gestational inflammation's effects on white matter development diverge depending on the availability of foundational resources in utero.

Chronic restraint stress and social transfer of stress produce tactile allodynia mediated by the HMGB1/TNFα/TNFR1 pathway in female and male rats

Previous studies have shown the relevance of high mobility group box 1 protein (HMGB1) and tumor necrosis factor α (TNFα) in nerve or tissue injury-induced nociception. However, the role of these proteins in chronic stress and social transfer of stress (STS)-induced dysfunctional pain is not entirely known. The aim of this study was to determine the participation of the spinal HMGB1-TNFα signaling pathway and TNFα receptor 1 (TNFR1) in rats subjected to chronic restraint stress (CRS) and STS. Non-stressed female and male rats in contact with CRS rats increased sniffing behavior of the anogenital area, behavior related to STS. Rats subjected to CRS and STS reduced 50 % withdrawal threshold and reached the value of tactile allodynia after 21 days of stress. Rats return to the basal withdrawal threshold after 30 days without stress and return to allodynia values in only 5 days of stress sessions (priming). Female and male rats subjected to 28 days of CRS or STS were intrathecal injected with glycyrrhizin (inhibitor of HMGB1), thalidomide (inhibitor of the TNFα synthesis), and R7050 (TNFR1 antagonist), in all the cases, an antiallodynic effect was observed. Rats under CRS or STS enhanced HMGB1 and TNFR1 protein expression in DRG and dorsal spinal cord. Data suggest that the spinal HMGB1/TNFα/TNFR1 signaling pathway plays a relevant role in the maintenance of CRS and STS-induced nociceptive hypersensitivity in rats. These proteins could be helpful in developing pain treatments for fibromyalgia in humans.

Peripheral and central biomarkers associated with inflammation in antipsychotic naïve first episode psychosis: Pilot studies

BACKGROUND

Elevated serum pro-inflammatory molecules have been reported in early psychosis. What is not known is whether peripheral inflammatory biomarkers are associated with CNS biomarkers. In the brain, release of pro-inflammatory molecules by microglial hyperactivity may lead to neuronal apoptosis seen in neurodegenerative disorders and account for loss of brain tissue observed in psychotic disorders. Neurochemical changes, including elevated glutamate levels, are also associated with neuroinflammation, present in early psychosis and change with antipsychotic treatment.

METHODS

Antipsychotic naïve patients with first episode psychosis (FEP) were studied as part of a collaborative project of neuroinflammation. In Study 1 we explored associations between plasma inflammatory molecules and neurometabolites in the dorsal caudate using magnetic resonance spectroscopy (1H-MRS) in N = 13 FEP participants. Study 2 examined the relationship between inflammatory molecules in the Plasma and CSF in N = 20 FEP participants.

RESULTS

In Study 1, the proinflammatory chemokine MDC/CCL22 and IL10 were significantly positively correlated with Glutamate and Glx (glutamate + glutamine) levels in the dorsal caudate. In Study 2, plasma inflammatory molecules (MIP1β/CCL4, MCP1/CCL2, Eotaxin-1/CCL11 and TNFα) were significantly correlated with CSF MIP1β/CCL4, IL10, MCP1/CCL2 and Fractalkine/CX3CL1 and symptoms ratings.

DISCUSSION

Plasma inflammatory biomarkers are elevated in early psychosis, associated with neurochemical markers as well as CSF inflammatory molecules found in neurodegenerative disorders. Future studies are needed that combine both peripheral and central biomarkers in both FEP and HC to better understand a potential neuroinflammatory subtype of psychosis likely to respond to targeted interventions.

Clinical value and mechanistic analysis of HIIT on modulating risk and symptoms of depression: A systematic review

Background

The exact causal mechanisms of depression remain unclear due to the complexity of the triggers, which has led to limitations in treating depression using modern drugs. High-intensity interval training (HIIT) is as effective as medication in treating depression without toxic side effects. Typically, HIIT requires less time commitment (i.e., shorter exercise duration) and exhibits pronounced benefits on depressive symptoms than other forms of physical exercise. This review summarizes the risk reduction and clinical effects of HIIT for depression and discusses the underlying mechanisms, providing a theoretical basis for utilizing HIIT in treating depression.

Methods

A database search was conducted in PubMed, Embase, Web of Science, and Scopus from inception up to October 2022. The methodological quality of the included literature was evaluated by the physiotherapy evidence database (PEDro) scale criteria. The review focused on evaluating the changes in depression risk or symptoms of HIIT interventions in healthy individuals, patients with depression, and patients with other disorders co-morbid with depression. Consequently, the mechanisms associated with depression related HIIT were summarized.

Results

A total of 586 participants (52 % female; mean age: 43.58±8.93 years) from 22 studies were included. Implementing HIIT using different exercise types alleviates depressive symptoms in individuals with depression and in individuals with depression who have exhibited comorbidities and reduced depression scale scores in subjects immediately after acute exercise. In addition, the long-interval HIIT and short-interval HIIT in the treatment of patients with cardiovascular or psychiatric disorders may reduce depressive symptoms via complex exercise-related changes on several levels, including by effecting the following measures: releasing monoamines, reducing neuronal death, inducing neurogenesis, modulating the functional homeostasis of the HPA axis, and enhancing the level of inflammation in the body.

Conclusion

HIIT is a relatively safe and effective antidepressant, which may involve multiple neurobiological mechanisms (release of monoamines, reducing neuronal death, inducing neurogenesis, modulating the functional homeostasis of the HPA axis, and enhancing the level of inflammation in the body), thereby reducing the risk or symptoms of depression in participants.

Developmental and adult stress: effects of steroids and neurosteroids

In humans, exposure to early life adversity has profound implications for susceptibility to developing neuropsychiatric disorders later in life. Studies in rodents have shown that stress experienced during early postnatal life can have lasting effects on brain development. Glucocorticoids and sex steroids are produced in endocrine glands and the brain from cholesterol; these molecules bind to nuclear and membrane-associated steroid receptors. Unlike other steroids that can also be made in the brain, neurosteroids bind specifically to neurotransmitter receptors, not steroid receptors. The relationships among steroids, neurosteroids, and stress are multifaceted and not yet fully understood. However, studies demonstrating altered levels of progestogens, androgens, estrogens, glucocorticoids, and their neuroactive metabolites in both developmental and adult stress paradigms strongly suggest that these molecules may be important players in stress effects on brain circuits and behavior. In this review, we discuss the influence of developmental and adult stress on various components of the brain, including neurons, glia, and perineuronal nets, with a focus on sex steroids and neurosteroids. Gaining an enhanced understanding of how early adversity impacts the intricate systems of brain steroid and neurosteroid regulation could prove instrumental in identifying novel therapeutic targets for stress-related conditions.

Behavior, synaptic mitochondria, and microglia are differentially impacted by chronic adolescent stress and repeated endotoxin exposure in male and female rats

Early life adversity and chronic inflammation have both been associated with cognitive impairment and neural compromise. In this study, we investigated the interactions between a history of chronic adolescent stress (CAS) and repeated endotoxin exposure on behavior, synaptic mitochondria, and microglia in adult male and female Wistar rats. Adult rats from chronic stress and control conditions were exposed to either repeated endotoxin (lipopolysaccharide; LPS) or saline injections every 3 days for 9 weeks. In both sexes, repeated LPS, regardless of stress history, impaired working memory in the Y maze. Regarding spatial memory, LPS impaired function for females; whereas, CAS altered function in males. Although males had an increase in anxiety-like behavior shortly after CAS, there were no long-term effects on anxiety-like behavior or social interaction observed in males or females. Stress did not alter synaptic mitochondrial function in either sex. Repeated LPS altered synaptic mitochondrial function such that ATP production was increased in females only. There were no observed increases in IBA-1 positive cells within the hippocampus for either sex. However, LPS and CAS altered microglia morphology in females. Impact of repeated LPS was evident at the terminal endpoint with increased spleen weight in both sexes and decreased adrenal weight in males only. Circulating cytokines were not impacted by repeated LPS at the terminal endpoint, but evidence of CAS effects on cytokines in females were evident. These data suggest a long-term impact of chronic stress and an impact of repeated endotoxin challenge in adulthood; however, not all physiological and behavioral metrics examined were impacted by the paradigm employed in this study and the two environmental challenges rarely interacted.

Prior experience with behavioral control over stress facilitates social dominance

Dominance status has extensive effects on physical and mental health, and an individual's relative position can be shaped by experiential factors. A variety of considerations suggest that the experience of behavioral control over stressors should produce winning in dominance tests and that winning should blunt the impact of later stressors, as does prior control. To investigate the interplay between competitive success and stressor control, we first examined the impact of stressor controllability on subsequent performance in a warm spot competition test modified for rats. Prior experience of controllable, but not physically identical uncontrollable, stress increased later effortful behavior and occupation of the warm spot. Controllable stress subjects consistently ranked higher than did uncontrollable stress subjects. Pharmacological inactivation of the prelimbic (PL) cortex during behavioral control prevented later facilitation of dominance. Next, we explored whether repeated winning experiences produced later resistance against the typical sequelae of uncontrollable stress. To establish dominance status, triads of rats were given five sessions of warm spot competition. The development of stable dominance was prevented by reversible inactivation of the PL or NMDA receptor blockade in the dorsomedial striatum. Stable winning blunted the later stress-induced increase in dorsal raphe nucleus serotonergic activity, as well as prevented uncontrollable stress-induced social avoidance. In contrast, endocrine and neuroimmune responses to uncontrollable stress were unaffected, indicating a selective impact of prior dominance. Together, these data demonstrate that instrumental control over stress promotes later dominance, but also reveal that winning experiences buffer against the neural and behavioral outcomes of future adversity.

Neurometabolic alterations in children and adolescents with functional neurological disorder

OBJECTIVES

In vivo magnetic resonance spectroscopy (MRS) was used to investigate neurometabolic homeostasis in children with functional neurological disorder (FND) in three regions of interest: supplementary motor area (SMA), anterior default mode network (aDMN), and posterior default mode network (dDMN). Metabolites assessed included N-acetyl aspartate (NAA), a marker of neuron function; myo-inositol (mI), a glial-cell marker; choline (Cho), a membrane marker; glutamate plus glutamine (Glx), a marker of excitatory neurotransmission; γ-aminobutyric acid (GABA), a marker of inhibitor neurotransmission; and creatine (Cr), an energy marker. The relationship between excitatory (glutamate and glutamine) and inhibitory (GABA) neurotransmitter (E/I) balance was also examined.

METHODS

MRS data were acquired for 32 children with mixed FND (25 girls, 7 boys, aged 10.00 to 16.08 years) and 41 healthy controls of similar age using both short echo point-resolved spectroscopy (PRESS) and Mescher-Garwood point-resolved spectroscopy (MEGAPRESS) sequences in the three regions of interest.

RESULTS

In the SMA, children with FND had lower NAA/Cr, mI/Cr (trend level), and GABA/Cr ratios. In the aDMN, no group differences in metabolite ratios were found. In the pDMN, children with FND had lower NAA/Cr and mI/Cr (trend level) ratios. While no group differences in E/I balance were found (FND vs. controls), E/I balance in the aDMN was lower in children with functional seizures-a subgroup within the FND group. Pearson correlations found that increased arousal (indexed by higher heart rate) was associated with lower mI/Cr in the SMA and pDMN.

CONCLUSIONS

Our findings of multiple differences in neurometabolites in children with FND suggest dysfunction on multiple levels of the biological system: the neuron (lower NAA), the glial cell (lower mI), and inhibitory neurotransmission (lower GABA), as well as dysfunction in energy regulation in the subgroup with functional seizures.

MLKL deficiency alleviates neuroinflammation and motor deficits in the α-synuclein transgenic mouse model of Parkinson's disease

Parkinson's disease (PD), one of the most devastating neurodegenerative brain disorders, is characterized by the progressive loss of dopaminergic neurons in the substantia nigra (SN) and deposits of α-synuclein aggregates. Currently, pharmacological interventions for PD remain inadequate. The cell necroptosis executor protein MLKL (Mixed-lineage kinase domain-like) is involved in various diseases, including inflammatory bowel disease and neurodegenerative diseases; however, its precise role in PD remains unclear. Here, we investigated the neuroprotective role of MLKL inhibition or ablation against primary neuronal cells and human iPSC-derived midbrain organoids induced by toxic α-Synuclein preformed fibrils (PFFs). Using a mouse model (Tg-Mlkl-/-) generated by crossbreeding the SNCA A53T synuclein transgenic mice with MLKL knockout (KO)mice, we assessed the impact of MLKL deficiency on the progression of Parkinsonian traits. Our findings demonstrate that Tg-Mlkl-/- mice exhibited a significant improvement in motor symptoms and reduced phosphorylated α-synuclein expression compared to the classic A53T transgenic mice. Furthermore, MLKL deficiency alleviated tyrosine hydroxylase (TH)-positive neuron loss and attenuated neuroinflammation by inhibiting the activation of microglia and astrocytes. Single-cell RNA-seq (scRNA-seq) analysis of the SN of Tg-Mlkl-/- mice revealed a unique cell type-specific transcriptome profile, including downregulated prostaglandin D synthase (PTGDS) expression, indicating reduced microglial cells and dampened neuron death. Thus, MLKL represents a critical therapeutic target for reducing neuroinflammation and preventing motor deficits in PD.

Noteworthy perspectives on microglia in neuropsychiatric disorders

Microglia are so versatile that they not only provide immune surveillance for central nervous system, but participate in neural circuitry development, brain blood vessels formation, blood-brain barrier architecture, and intriguingly, the regulation of emotions and behaviors. Microglia have a profound impact on neuronal survival, brain wiring and synaptic plasticity. As professional phagocytic cells in the brain, they remove dead cell debris and neurotoxic agents via an elaborate mechanism. The functional profile of microglia varies considerately depending on age, gender, disease context and other internal or external environmental factors. Numerous studies have demonstrated a pivotal involvement of microglia in neuropsychiatric disorders, including negative affection, social deficit, compulsive behavior, fear memory, pain and other symptoms associated with major depression disorder, anxiety disorder, autism spectrum disorder and schizophrenia. In this review, we summarized the latest discoveries regarding microglial ontogeny, cell subtypes or state spectrum, biological functions and mechanistic underpinnings of emotional and behavioral disorders. Furthermore, we highlight the potential of microglia-targeted therapies of neuropsychiatric disorders, and propose outstanding questions to be addressed in future research of human microglia.

Effects of physical activity in child and adolescent depression and anxiety: role of inflammatory cytokines and stress-related peptide hormones

Depression and anxiety are the most common mental illnesses affecting children and adolescents, significantly harming their well-being. Research has shown that regular physical activity can promote cognitive, emotional, fundamental movement skills, and motor coordination, as a preventative measure for depression while reducing the suicide rate. However, little is known about the potential role of physical activity in adolescent depression and anxiety. The studies reviewed in this paper suggest that exercise can be an effective adjunctive treatment to improve depressive and anxiety symptoms in adolescents, although research on its neurobiological effects remains limited.

Chemokine receptor 5 signaling in PFC mediates stress susceptibility in female mice

Chronic stress induces changes in the periphery and the central nervous system (CNS) that contribute to neuropathology and behavioral abnormalities associated with psychiatric disorders. In this study, we examined the impact of peripheral and central inflammation during chronic social defeat stress (CSDS) in female mice. Compared to male mice, we found that female mice exhibited heightened peripheral inflammatory response and identified C-C motif chemokine ligand 5 (CCL5), as a stress-susceptibility marker in females. Blocking CCL5 signaling in the periphery promoted resilience to CSDS. In the brain, stress-susceptible mice displayed increased expression of C-C chemokine receptor 5 (CCR5), a receptor for CCL5, in microglia in the prefrontal cortex (PFC). This upregulation was associated with microglia morphological changes, their increased migration to the blood vessels, and enhanced phagocytosis of synaptic components and vascular material. These changes coincided with neurophysiological alterations and impaired blood-brain barrier (BBB) integrity. By blocking CCR5 signaling specifically in the PFC were able to prevent stress-induced physiological changes and rescue social avoidance behavior. Our findings are the first to demonstrate that stress-mediated dysregulation of the CCL5-CCR5 axis triggers excessive phagocytosis of synaptic materials and neurovascular components by microglia, resulting in disruptions in neurotransmission, reduced BBB integrity, and increased stress susceptibility. Our study provides new insights into the role of cortical microglia in female stress susceptibility and suggests that the CCL5-CCR5 axis may serve as a novel sex-specific therapeutic target for treating psychiatric disorders in females.

Maternal immune activation and role of placenta in the prenatal programming of neurodevelopmental disorders

Maternal infection during pregnancy, leading to maternal immune activation (mIA) and cytokine release, increases the offspring risk of developing a variety of neurodevelopmental disorders (NDDs), including schizophrenia. Animal models have provided evidence to support these mechanistic links, with placental inflammatory responses and dysregulation of placental function implicated. This leads to changes in fetal brain cytokine balance and altered epigenetic regulation of key neurodevelopmental pathways. The prenatal timing of such mIA-evoked changes, and the accompanying fetal developmental responses to an altered in utero environment, will determine the scope of the impacts on neurodevelopmental processes. Such dysregulation can impart enduring neuropathological changes, which manifest subsequently in the postnatal period as altered neurodevelopmental behaviours in the offspring. Hence, elucidation of the functional changes that occur at the molecular level in the placenta is vital in improving our understanding of the mechanisms that underlie the pathogenesis of NDDs. This has notable relevance to the recent COVID-19 pandemic, where inflammatory responses in the placenta to SARS-CoV-2 infection during pregnancy and NDDs in early childhood have been reported. This review presents an integrated overview of these collective topics and describes the possible contribution of prenatal programming through placental effects as an underlying mechanism that links to NDD risk, underpinned by altered epigenetic regulation of neurodevelopmental pathways.

Early and recent exposure to adversity, TLR-4 stimulated inflammation, and diurnal cortisol in women with interstitial cystitis/bladder pain syndrome: A MAPP research network study

Both early (ELA) and recent life adversity (RLA) have been linked with chronic pain conditions and persistent alterations of neuroendocrine and inflammatory responses. Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS) is a chronic urologic disorder characterized by bladder and/or pelvic pain, and excessive urinary frequency and/or urgency. IC/BPS has been associated with high levels of ELA as well as a distinct inflammatory signature. However, associations between ELA and RLA with inflammatory mechanisms in IC/BPS that might underlie the link between adversity and symptoms have not been examined. Here we investigated ELA and RLA in women with IC/BPS as potential risk factors for inflammatory processes and hypothalamic-pituitaryadrenal (HPA) abnormalities using data from the Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network. Women with IC/BPS and healthy controls (n = 154 and 32, respectively) completed surveys, collected salivary cortisol at awakening and bedtime for 3 days, and gave a blood sample which was analyzed for 7 LPS-stimulated cytokines and chemokines (IL-6, TNFα, IL-1β, MIP1α, MCP1, IL-8, and IL-10). Two cytokine/chemokine composites were identified using principal components analysis. Patients with greater exposure to RLA or cumulative ELA and RLA of at least moderate severity showed elevated levels of a composite of all cytokines, adjusting for age, body mass index, and study site. Furthermore, there was a trending relationship between ELA and the pro-inflammatory composite score. Nocturnal cortisol and cortisol slope were not associated with ELA, RLA, or inflammation. The present findings support the importance of adverse events in IC/BPS via a biological mechanism and suggest that ELA and RLA should be assessed as risk factors for inflammation as part of a clinical workup for IC/BPS.

Prior experience with behavioral control over stress facilitates social dominance

Dominance status has extensive effects on physical and mental health, and an individual's relative position can be shaped by experiential factors. A variety of considerations suggest that the experience of behavioral control over stressors should produce winning in dominance tests and that winning should blunt the impact of later stressors, as does prior control. To investigate the interplay between competitive success and stressor control, we first examined the impact of stressor controllability on subsequent performance in a warm spot competition test modified for rats. Prior experience of controllable, but not physically identical uncontrollable, stress increased later effortful behavior and occupation of the warm spot. Controllable stress subjects consistently ranked higher than did uncontrollable stress subjects. Pharmacological inactivation of the prelimbic (PL) cortex during behavioral control prevented later facilitation of dominance. Next, we explored whether repeated winning experiences produced later resistance against the typical sequelae of uncontrollable stress. To establish dominance status, triads of rats were given five sessions of warm spot competition. Reversible inactivation of the PL or NMDA receptor blockade in the dorsomedial striatum led to a long-term reduction in social rank. Stable dominance blunted the later stress-induced increase in dorsal raphe nucleus serotonergic activity, as well as prevented stress-induced social avoidance. In contrast, endocrine and neuroimmune responses to uncontrollable stress were unaffected, indicating a selective impact of prior dominance. Together, these data demonstrate that instrumental control over stress promotes later dominance, but also reveal that winning experiences buffer against the neural and behavioral outcomes of future adversity.

Stressed Microglia: Neuroendocrine-Neuroimmune Interactions in the Stress Response

Stressful life experiences are associated with the development of neuropsychiatric disorders like depression. Emerging evidence indicates that microglia, the specialized resident macrophages of the brain, may be a key mediator of the relationship between psychosocial stressor exposure and adaptive or maladaptive responses at the level of synaptic, circuit, and neuroimmune alterations. Here, we review current literature regarding how psychosocial stressor exposure changes microglial structure and function, thereby altering behavioral and brain outcomes, with a particular focus on age- and sex-dependent effects. We argue that additional emphasis should be placed in future research on investigating sex differences and the impacts of stressor exposure during sensitive periods of development, as well as going beyond traditional morphological measurements to interrogate microglial function. The bidirectional relationship between microglia and the stress response, particularly the role of microglia in the neuroendocrine control of stress-related circuits, is also an important area for future investigation. Finally, we discuss emerging themes and future directions that point to the possibility of the development of novel therapeutics for stress-related neuropsychiatric disorders.

From helplessness to controllability: toward a neuroscience of resilience

"Learned helplessness" refers to debilitating outcomes, such as passivity and increased fear, that follow an uncontrollable adverse event, but do not when that event is controllable. The original explanation argued that when events are uncontrollable the animal learns that outcomes are independent of its behavior, and that this is the active ingredient in producing the effects. Controllable adverse events, in contrast, fail to produce these outcomes because they lack the active uncontrollability element. Recent work on the neural basis of helplessness, however, takes the opposite view. Prolonged exposure to aversive stimulation per se produces the debilitation by potent activation of serotonergic neurons in the brainstem dorsal raphe nucleus. Debilitation is prevented with an instrumental controlling response, which activates prefrontal circuitry detecting control and subsequently blunting the dorsal raphe nucleus response. Furthermore, learning control alters the prefrontal response to future adverse events, thereby preventing debilitation and producing long-term resiliency. The general implications of these neuroscience findings may apply to psychological therapy and prevention, in particular by suggesting the importance of cognitions and control, rather than habits of control.

Impact of exercise on brain-bone marrow interactions in chronic stress: potential mechanisms preventing stress-induced hypertension

We examined the effect of chronic restraint stress and the counteractive effects of daily exercise on the molecular basis of the brain-bone marrow (BM) interactions, by especially focusing on the paraventricular nucleus (PVN) of the hypothalamus. Male Wistar rats were assigned into control, restraint stress, and stress + daily spontaneous exercise (SE) groups. BM and hypothalamic gene expression profiles were examined through the undertaking of RT-PCR and microarrays, respectively. The inflammatory blood cell population was investigated through flow cytometry. Through the use of immunohistochemistry, we examined the presence of BM-derived C-C chemokine receptor type 2 (CCR2)-expressing microglial cells in the rat PVN. The gene expression levels of BM inflammatory factors such as those of interleukin 1 beta and CCR2, and the inflammatory blood cell population were found to be significantly higher in both restrained groups compared with control group. Interestingly, chronic restraint stress alone activated the recruitment of BM-derived CCR2-expressing microglial cells into the PVN, whereas daily spontaneous exercise prevented it. A notable finding was that restraint stress upregulated relative gene expression of hypothalamic matrix metalloproteinase 3 (MMP3), which increases the permeability of the blood-brain barrier (BBB), and that exercise managed to normalize it. Moreover, relative expression of some hypothalamic genes directly involved in the facilitation of cell migration was downregulated by daily exercise. Our findings suggest that daily spontaneous exercise can reduce the numbers of BM-derived CCR2-expressing microglial cells into the PVN through the prevention of stress-induced changes in the hypothalamic gene expression.NEW & NOTEWORTHY Chronic restraint stress can upregulate MMP3 gene expression in the rat hypothalamus, whereas daily spontaneous exercise can prevent this stress-induced effect. Stress-induced BM-derived inflammatory cell recruitment into the rat PVN can be prevented by daily spontaneous exercise. Stress-induced increase of hypothalamic MMP3 gene expression may be responsible for BBB injury, thereby allowing for BM-derived inflammatory cells to be recruited and to accumulate in the rat PVN, and to be subsequently involved in the onset of stress-induced hypertension.

Post-traumatic Stress Disorder: Focus on Neuroinflammation

Post-traumatic stress disorder (PTSD), gaining increasing attention, is a multifaceted psychiatric disorder that occurs following a stressful or traumatic event or series of events. Recently, several studies showed a close relationship between PTSD and neuroinflammation. Neuroinflammation, a defense response of the nervous system, is associated with the activation of neuroimmune cells such as microglia and astrocytes and with changes in inflammatory markers. In this review, we first analyzed the relationship between neuroinflammation and PTSD: the effect of stress-derived activation of the hypothalamic-pituitary-adrenal (HPA) axis on the main immune cells in the brain and the effect of stimulated immune cells in the brain on the HPA axis. We then summarize the alteration of inflammatory markers in brain regions related to PTSD. Astrocytes are neural parenchymal cells that protect neurons by regulating the ionic microenvironment around neurons. Microglia are macrophages of the brain that coordinate the immunological response. Recent studies on these two cell types provided new insight into neuroinflammation in PTSD. These contribute to promoting comprehension of neuroinflammation, which plays a pivotal role in the pathogenesis of PTSD.

Modeling integrated stress, sleep, fear and neuroimmune responses: Relevance for understanding trauma and stress-related disorders

Sleep and stress have complex interactions that are implicated in both physical diseases and psychiatric disorders. These interactions can be modulated by learning and memory, and involve additional interactions with the neuroimmune system. In this paper, we propose that stressful challenges induce integrated responses across multiple systems that can vary depending on situational variables in which the initial stress was experienced, and with the ability of the individual to cope with stress- and fear-inducing challenges. Differences in coping may involve differences in resilience and vulnerability and/or whether the stressful context allows adaptive learning and responses. We provide data demonstrating both common (corticosterone, SIH and fear behaviors) and distinguishing (sleep and neuroimmune) responses that are associated with an individual's ability to respond and relative resilience and vulnerability. We discuss neurocircuitry regulating integrated stress, sleep, neuroimmune and fear responses, and show that responses can be modulated at the neural level. Finally, we discuss factors that need to be considered in models of integrated stress responses and their relevance for understanding stress-related disorders in humans.

Effects of Current Psychotropic Drugs on Inflammation and Immune System

The immune system and inflammation are involved in the pathological progression of various psychiatric disorders such as depression or major depressive disorder (MDD), generalized anxiety disorder (GAD) or anxiety, schizophrenia, Alzheimer's disease (AD), and Huntington's disease. It is observed that levels of inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and other markers are highly increased in the abovementioned disorders. The inflammation and immune component also lead to enhance the oxidative stress. The oxidative stress and increased production of reactive oxygen species (ROS) are considered as important factors that are involved in pathological progression of psychiatric disorders. Increase production of ROS is associated with excessive inflammation followed by cell necrosis and death. The psychotropic drugs are mainly work through modulations of neurotransmitter system. However, it is evident that inflammation and immune modulation are also having important role in the progression of psychiatric disorders. Rationale of the use of current psychotropic drugs is modulation of immune system by them. However, the effects of psychotropic drugs on the immune system and how these might contribute to their efficacy remain largely unclear. The drugs may act through modification of inflammation and related markers. The main purpose of this book chapter is to address the role of current psychotropic drugs on inflammation and immune system. Moreover, it will also address the role of inflammation in the progression of psychiatric disorders.

Immunization with a heat-killed preparation of Mycobacterium vaccae NCTC 11659 enhances auditory-cued fear extinction in a stress-dependent manner

Stress-related psychiatric disorders including anxiety disorders, mood disorders, and trauma and stressor-related disorders, such as posttraumatic stress disorder (PTSD), affect millions of people world-wide each year. Individuals with stress-related psychiatric disorders have been found to have poor immunoregulation, increased proinflammatory markers, and dysregulation of fear memory. The "Old Friends" hypothesis proposes that a lack of immunoregulatory inputs has led to a higher prevalence of inflammatory disorders and stress-related psychiatric disorders, in which inappropriate inflammation is thought to be a risk factor. Immunization with a soil-derived saprophytic bacterium with anti-inflammatory and immunoregulatory properties, Mycobacterium vaccae NCTC 11659, can lower proinflammatory biomarkers, increase stress resilience, and, when given prior to or after fear conditioning in a rat model of fear-potentiated startle, enhance fear extinction. In this study, we investigated whether immunization with heat-killed M. vaccae NCTC 11659 would enhance fear extinction in contextual or auditory-cued fear conditioning paradigms and whether M. vaccae NCTC 11659 would prevent stress-induced exaggeration of fear expression or stress-induced resistance to extinction learning. Adult male Sprague Dawley rats were immunized with M. vaccae NCTC 11659 (subcutaneous injections once a week for three weeks), and underwent either: Experiment 1) one-trial contextual fear conditioning; Experiment 2) two-trial contextual fear conditioning; Experiment 3) stress-induced enhancement of contextual fear conditioning; Experiment 4) stress-induced enhancement of auditory-cued fear conditioning; or Experiment 5) stress-induced enhancement of auditory-cued fear conditioning exploring short-term memory. Immunizations with M. vaccae NCTC 11659 had no effect on one- or two-trial contextual fear conditioning or contextual fear extinction, with or without exposure to inescapable stress. However, inescapable stress increased resistance to auditory-cued fear extinction. Immunization with M. vaccae NCTC 11659 prevented the stress-induced increase in resistance to auditory-cued fear extinction learning. Finally, in an auditory-cued fear conditioning paradigm exploring short-term memory and fear acquisition, immunization with M. vaccae did not prevent fear acquisition, either with or without exposure to inescapable stress, consistent with the hypothesis that M. vaccae NCTC 11659 has no effect on fear acquisition but enhances fear extinction. These data are consistent with the hypothesis that increased immunoregulation following immunization with M. vaccae NCTC 11659 promotes stress resilience, in particular by preventing stress-induced resistance to fear extinction, and may be a potential therapeutic intervention for trauma- and stressor-related disorders such as PTSD.

An evaluation of the rat intestinal monoamine biogeography days following exposure to acute stress

Stress-induced abnormalities in gut monoamine levels (e.g., serotonin, dopamine, norepinephrine) have been linked to gastrointestinal (GI) dysfunction, as well as the worsening of symptoms in GI disorders. However, the influence of stress on changes across the entire intestinal monoamine biogeography has not been well-characterized, especially in the days following stress exposure. Therefore, the aim of this study was to comprehensively assess changes to monoamine neurochemical signatures across the entire rat intestinal tract days after exposure to an acute stressor. To the end, adult male F344 rats were subjected to an episode of unpredictable tail shocks (acute stress) or left undisturbed. Forty-eight hours later rats were euthanized either following a 12 h period of fasting or 30 min of food access to evaluate neurochemical profiles during the peri- and early postprandial periods. Monoamine-related neurochemicals were measured via UHPLC in regions of the small intestine (duodenum, jejunum, ileum), large intestine (cecum, proximal colon, distal colon), cecal contents, fecal contents, and liver. The results suggest a relatively wide-spread increase in measures of serotonin activity across intestinal regions can be observed 48 h after exposure to acute stress, however some evidence was found supporting localized differences in serotonin metabolization. Moreover, acute stress exposure reduced catecholamine-related neurochemical concentrations most notably in the ileum, and to a lesser extent in the cecal contents. Next, stress-related fecal serotonin concentrations were consistent with intestinal profiles. However, fecal dopamine was elevated in association with stress, which did not parallel findings in any other intestinal area. Finally, stress exposure and the food access period together only had minor effects on intestinal monoamine profiles. Taken together, these data suggest nuanced differences in monoaminergic profiles exist across intestinal regions the days following exposure to an acute stressor, highlighting the importance of assessments that consider the entire intestinal tract biogeography when investigating stress-related biological outcomes that may be relevant to GI pathophysiology.

What microglia depletion approaches tell us about the role of microglia on synaptic function and behavior

Microglia are dynamic cells, constantly surveying their surroundings and interacting with neurons and synapses. Indeed, a wealth of knowledge has revealed a critical role of microglia in modulating synaptic transmission and plasticity in the developing brain. In the past decade, novel pharmacological and genetic strategies have allowed the acute removal of microglia, opening the possibility to explore and understand the role of microglia also in the adult brain. In this review, we summarized and discussed the contribution of microglia depletion strategies to the current understanding of the role of microglia on synaptic function, learning and memory, and behavior both in physiological and pathological conditions. We first described the available microglia depletion methods highlighting their main strengths and weaknesses. We then reviewed the impact of microglia depletion on structural and functional synaptic plasticity. Next, we focused our analysis on the effects of microglia depletion on behavior, including general locomotor activity, sensory perception, motor function, sociability, learning and memory both in healthy animals and animal models of disease. Finally, we integrated the findings from the reviewed studies and discussed the emerging roles of microglia on the maintenance of synaptic function, learning, memory strength and forgetfulness, and the implications of microglia depletion in models of brain disease.

Microglia as Central Protagonists in the Chronic Stress Response

Chronic stress is a major risk factor for developing psychiatric conditions. In addition to elevating the levels of stress hormones released in the body, chronic stress activates the immune system, resulting in increased levels of proinflammatory cytokines and innate immune cells in the circulation of rodents and humans. Furthermore, exposure to chronic stress alters the phenotype of microglia, a population of innate immune cells that reside in the CNS parenchyma. In rodent models, chronic stress activates microglia in defined brain regions and induces changes in their phenotype and functional properties. In this review, we discussed how microglia are activated in stressful situations. Furthermore, we described how microglia affect the CNS environment during chronic stress, through the production of cytokines, the induction of reactive oxygen species, and phagocytosis. We suggested that, due to their strategic location as immune cells within the CNS, microglia are important players in the induction of psychopathologies after chronic stress.

Stress- and drug-induced neuroimmune signaling as a therapeutic target for comorbid anxiety and substance use disorders

Stress and substance use disorders remain two of the most highly prevalent psychiatric conditions and are often comorbid. While individually these conditions have a debilitating impact on the patient and a high cost to society, the symptomology and treatment outcomes are further exacerbated when they occur together. As such, there are few effective treatment options for these patients, and recent investigation has sought to determine the neural processes underlying the co-occurrence of these disorders to identify novel treatment targets. One such mechanism that has been linked to stress- and addiction-related conditions is neuroimmune signaling. Increases in inflammatory factors across the brain have been heavily implicated in the etiology of these disorders, and this review seeks to determine the nature of this relationship. According to the "dual-hit" hypothesis, also referred to as neuroimmune priming, prior exposure to either stress or drugs of abuse can sensitize the neuroimmune system to be hyperresponsive when exposed to these insults in the future. This review completes an examination of the literature surrounding stress-induced increases in inflammation across clinical and preclinical studies along with a summarization of the evidence regarding drug-induced alterations in inflammatory factors. These changes in neuroimmune profiles are also discussed within the context of their impact on the neural circuitry responsible for stress responsiveness and addictive behaviors. Further, this review explores the connection between neuroimmune signaling and susceptibility to these conditions and highlights the anti-inflammatory pharmacotherapies that may be used for the treatment of stress and substance use disorders.

Infections and schizophrenia

This paper provides a critical review of the literature, demonstrating a certain pathogenetic role of various infections, primarily viruses from the herpes and chlamydia groups, in the development and progression of schizophrenia, including published results of the authors’ own long-term studies.

Immune signaling as a node of interaction between systems that sex-specifically develop during puberty and adolescence

Adolescence is pivotal for neural and behavioral development across species. During this period, maturation occurs in several biological systems, the most well-recognized being activation of the hypothalamic-pituitary-gonadal axis marking pubertal onset. Increasing comparative studies of sex differences have enriched our understanding of systems integration during neurodevelopment. In recent years, immune signaling has emerged as a key node of interaction between a variety of biological signaling processes. Herein, we review the age- and sex-specific changes that occur in neural, hypothalamic-pituitary, and microbiome systems during adolescence. We then describe how immune signaling interacts with these systems, and review recent preclinical evidence indicating that immune signaling may play a central role in integrating changes in their typical and atypical development during adolescence. Finally, we discuss the translational relevance of these preclinical studies to human health and wellness.

Identification of hyper-ramified microglia in the CA1 region of the mouse hippocampus potentially associated with stress resilience

Recent studies have indicated that some individuals are less affected by stress, and such individuals are called resilient. This study aimed to determine whether the specific phenotype of microglia might be involved in resilience using the social defeat stress paradigm. Male C57BL/6J (B6) mice were attacked by aggressive male ICR mice for five consecutive days. After stress exposure, the social behaviour was reduced in about half of the B6 mice (vulnerable), whereas no such change was observed in the remaining half of the B6 mice (resilient). Anxiety-like behaviour was increased in vulnerable mice compared with resilient mice and non-stressed controls. However, depression-related behaviour was comparable between the three groups. The morphological characteristics of microglia in the CA1 region of the dorsal hippocampus in non-stressed controls and resilient mice differed from those in vulnerable mice. Interestingly, the voxel densities of GABAergic and glutamatergic synaptic puncta colocalized with microglia were higher in resilient mice than in non-stressed controls and vulnerable mice. Microglia were then objectively classified into three morphological types by hierarchical cluster analysis. The appearance of type I microglia resembled the so-called resting ramified microglia and represented the major population of microglia in non-stressed controls. Type II microglia exhibited a de-ramified morphology and accounted for 60% of the microglia in vulnerable mice. Type III microglia showed a hyper-ramified morphology and represented more than half of the microglia in resilient mice. These results suggest that hyper-ramified microglia in the hippocampus may be associated with stress resilience via the modulation of synaptic transmission.

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.

Effects of Social Isolation on the Development of Anxiety and Depression-Like Behavior in Model Experiments in Animals

This review describes the role of social isolation in the development of anxiety and depression-like behavior in rodents. The duration of social isolation, age from onset of social isolation, sex, species, and strain of animals, the nature of the model used, and other factors have been shown to have influences. The molecular-cellular mechanisms of development of anxiety and depression-like behavior under the influence of social isolation and the roles of the HHAS, oxidative and nitrosative stress, neuroinflammation, BDNF, neurogenesis, synaptic plasticity, as well as monoamines in these mechanisms are discussed. This review presents data on sex differences in the effects of social isolation, along with the effects of interactions with other types of stress, and the roles of an enriched environment and other factors in ameliorating the negative sequelae of social isolation.

The role of the immune system in posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) develops in a subset of individuals upon exposure to traumatic stress. In addition to well-defined psychological and behavioral symptoms, some individuals with PTSD also exhibit elevated concentrations of inflammatory markers, including C-reactive protein, interleukin-6, and tumor necrosis factor-α. Moreover, PTSD is often co-morbid with immune-related conditions, such as cardiometabolic and autoimmune disorders. Numerous factors, including lifetime trauma burden, biological sex, genetic background, metabolic conditions, and gut microbiota, may contribute to inflammation in PTSD. Importantly, inflammation can influence neural circuits and neurotransmitter signaling in regions of the brain relevant to fear, anxiety, and emotion regulation. Given the link between PTSD and the immune system, current studies are underway to evaluate the efficacy of anti-inflammatory treatments in those with PTSD. Understanding the complex interactions between PTSD and the immune system is essential for future discovery of diagnostic and therapeutic tools.

Sex differences in stress-induced alcohol intake: a review of preclinical studies focused on amygdala and inflammatory pathways

Clinical studies suggest that women are more likely than men to relapse to alcohol drinking in response to stress; however, the mechanisms underlying this sex difference are not well understood. A number of preclinical behavioral models have been used to study stress-induced alcohol intake. Here, we review paradigms used to study effects of stress on alcohol intake in rodents, focusing on findings relevant to sex differences. To date, studies of sex differences in stress-induced alcohol drinking have been somewhat limited; however, there is evidence that amygdala-centered circuits contribute to effects of stress on alcohol seeking. In addition, we present an overview of inflammatory pathways leading to microglial activation that may contribute to alcohol-dependent behaviors. We propose that sex differences in neuronal function and inflammatory signaling in circuits centered on the amygdala are involved in sex-dependent effects on stress-induced alcohol seeking and suggest that this is an important area for future studies.

The Role of Microglia in the (Mal)adaptive Response to Traumatic Experience in an Animal Model of PTSD

The present study investigates whether predator scent-stress (PSS) shifts the microglia from a quiescent to a chronically activated state and whether morphological alterations in microglial activation differ between individuals displaying resilient vs. vulnerable phenotypes. In addition, we examined the role that GC receptors play during PSS exposure in the impairment of microglial activation and thus in behavioral response. Adult male Sprague Dawley rats were exposed to PSS or sham-PSS for 15 min. Behaviors were assessed with the elevated plus-maze (EPM) and acoustic startle response (ASR) paradigms 7 days later. Localized brain expression of Iba-1 was assessed, visualized, and classified based on their morphology and stereological counted. Hydrocortisone and RU486 were administered systemically 10 min post PSS exposure and behavioral responses were measured on day 7 and hippocampal expression of Ionized calcium-binding adaptor molecule 1 (Iba-1) was subsequently evaluated. Animals whose behavior was extremely disrupted (PTSD-phenotype) selectively displayed excessive expression of Iba-1 with concomitant downregulation in the expression of CX3C chemokine receptor 1 (CX3CR1) in hippocampal structures as compared with rats whose behavior was minimally or partially disrupted. Changes in microglial morphology have also been related only to the PTSD-phenotype group. These data indicate that PSS-induced microglia activation in the hippocampus serves as a critical mechanistic link between the HPA-axis and PSS-induced impairment in behavioral responses.

Sex-Dependent Effects of Chronic Microdrive Implantation on Acquisition of Trace Eyeblink Conditioning

Neuroscience techniques, including in vivo recording, have allowed for a great expansion in knowledge; however, this technology may also affect the very phenomena researchers set out to investigate. Including both female and male mice in our associative learning experiments shed light on sex differences on the impact of chronic implantation of tetrodes on learning. While previous research showed intact female mice acquired trace eyeblink conditioning faster than male and ovariectomized females, implantation of chronic microdrive arrays showed sexually dimorphic effects on learning. Microdrive implanted male mice acquired the associative learning paradigm faster than both intact and ovariectomized females. These effects were not due to the weight of the drive alone, as there were no significant sex-differences in learning of animals that received "dummy drive" implants without tetrodes lowered into the brain. Tandem mass tag mass spectrometry and western blot analysis suggest that significant alterations in the MAPK pathway, acute inflammation, and brain derived neurotrophic factor may underlie these observed sex- and surgery-dependent effects on learning.

The role of the stress system in recovery after traumatic brain injury: A tribute to Bruce S. McEwen

Traumatic brain injury (TBI) represents a major public health concern. Although the majority of individuals that suffer mild-moderate TBI recover relatively quickly, a substantial subset of individuals experiences prolonged and debilitating symptoms. An exacerbated response to physiological and psychological stressors after TBI may mediate poor functional recovery. Individuals with TBI can suffer from poor stress tolerance, impairments in the ability to evaluate stressors, and poor initiation (and cessation) of neuroendocrine stress responses, all of which can exacerbate TBI-mediated dysfunction. Here, we pay tribute to the pioneering neuroendocrinologist Dr. Bruce McEwen by discussing the ways in which his work on stress physiology and allostatic loading impacts the TBI patient population both before and after their injuries. Specifically, we will discuss the modulatory role of hypothalamic-pituitary-adrenal axis responses immediately after TBI and later in recovery. We will also consider the impact of stressors and stress responses in promoting post-concussive syndrome and post-traumatic stress disorders, two common sequelae of TBI. Finally, we will explore the role of early life stressors, prior to brain injuries, as modulators of injury outcomes.

Is there a relationship between morphological and functional platelet changes and depressive disorder?

BACKGROUND

Blood platelets, due to shared biochemical and functional properties with presynaptic serotonergic neurons, constituted, over the years, an attractive peripheral biomarker of neuronal activity. Therefore, the literature strongly focused on the investigation of eventual structural and functional platelet abnormalities in neuropsychiatric disorders, particularly in depressive disorder. Given their impact in biological psychiatry, the goal of the present paper was to review and critically analyze studies exploring platelet activity, functionality, and morpho-structure in subjects with depressive disorder.

METHODS

According to the PRISMA guidelines, we performed a systematic review through the PubMed database up to March 2020 with the search terms: (1) platelets in depression [Title/Abstract]"; (2) "(platelets[Title]) AND depressive disorder[Title/Abstract]"; (3) "(Platelet[Title]) AND major depressive disorder[Title]"; (4) (platelets[Title]) AND depressed[Title]"; (5) (platelets[Title]) AND depressive episode[Title]"; (6) (platelets[Title]) AND major depression[Title]"; (7) platelet activation in depression[All fields]"; and (8) platelet reactivity in depression[All fields]."

RESULTS

After a detailed screening analysis and the application of specific selection criteria, we included in our review a total of 106 for qualitative synthesis. The studies were classified into various subparagraphs according to platelet characteristics analyzed: serotonergic system (5-HT2A receptors, SERT activity, and 5-HT content), adrenergic system, MAO activity, biomarkers of activation, responsivity, morphological changes, and other molecular pathways.

CONCLUSIONS

Despite the large amount of the literature examined, nonunivocal and, occasionally, conflicting results emerged. However, the findings on structural and metabolic alterations, modifications in the expression of specific proteins, changes in the aggregability, or in the responsivity to different pro-activating stimuli, may be suggestive of potential platelet dysfunctions in depressed subjects, which would result in a kind of hyperreactive state. This condition could potentially lead to an increased cardiovascular risk. In line with this hypothesis, we speculated that antidepressant treatments would seem to reduce this hyperreactivity while representing a potential tool for reducing cardiovascular risk in depressed patients and, maybe, in other neuropsychiatric conditions. However, the problem of the specificity of platelet biomarkers is still at issue and would deserve to be deepened in future studies.

Shedding light on biological sex differences and microbiota-gut-brain axis: a comprehensive review of its roles in neuropsychiatric disorders

Women and men are suggested to have differences in vulnerability to neuropsychiatric disorders, including major depressive disorder (MDD), generalized anxiety disorder (GAD), schizophrenia, eating disorders, including anorexia nervosa, and bulimia nervosa, neurodevelopmental disorders, such as autism spectrum disorder (ASD), and neurodegenerative disorders including Alzheimer’s disease, Parkinson’s disease. Genetic factors and sex hormones are apparently the main mediators of these differences. Recent evidence uncovers that reciprocal interactions between sex-related features (e.g., sex hormones and sex differences in the brain) and gut microbiota could play a role in the development of neuropsychiatric disorders via influencing the gut–brain axis. It is increasingly evident that sex–microbiota–brain interactions take part in the occurrence of neurologic and psychiatric disorders. Accordingly, integrating the existing evidence might help to enlighten the fundamental roles of these interactions in the pathogenesis of neuropsychiatric disorders. In addition, an increased understanding of the biological sex differences on the microbiota–brain may lead to advances in the treatment of neuropsychiatric disorders and increase the potential for precision medicine. This review discusses the effects of sex differences on the brain and gut microbiota and the putative underlying mechanisms of action. Additionally, we discuss the consequences of interactions between sex differences and gut microbiota on the emergence of particular neuropsychiatric disorders.

The human microbiome is a unique set of organisms affecting health via the gut–brain axis.

Neuropsychiatric disorders, eating disorders, neurodevelopmental disorders, and neurodegenerative disorders are regulated by the microbiota–gut–brain axis in a sex-specific manner.

Understanding the role of the microbiota–gut–brain axis and its sex differences in various diseases can lead to better therapeutic methods.