Interleukin-1 (IL-1): a central regulator of stress responses

Microglia in neuronal plasticity: Influence of stress

The central nervous system (CNS) has previously been regarded as an immune-privileged site with the absence of immune cell responses but this dogma was not entirely true. Microglia are the brain innate immune cells and recent findings indicate that they participate both in CNS disease and infection as well as facilitate normal CNS function. Microglia are highly plastic and play integral roles in sculpting the structure of the CNS, refining neuronal circuitry and connectivity, and contribute actively to neuronal plasticity in the healthy brain. Interestingly, psychological stress can perturb the function of microglia in association with an impaired neuronal plasticity and the development of emotional behavior alterations. As a result it seemed important to describe in this review some findings indicating that the stress-induced microglia dysfunction may underlie neuroplasticity deficits associated to many mood disorders. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

The role of hepcidin in chronic mild stress-induced depression

Depression is one of the most prevalent challenges of mental conditions. Yet its exact etiology has not been clear. Chronic stress increases the production of cytokines, which can lead to depression. Hepcidin, an iron modulator, is involved in the inflammation process as well as iron homeostasis. This study was designed to investigate the role of hepcidin, on stress-induced depression. 60 male wistar rats were entered the experiment. We used a chronic unpredictable mild stress (for 28 days) as a rat model of depression. In stressed group, three subgroups were treated with three different doses of dalteparin (a hepcidin inhibitor): 70IU/kg, 100IU/kg and 140IU/kg daily, for 4 weeks. The animals in the stressed group had more depressive-like behavior than the control group. Moreover, chronic mild stress produced an increased serum interleukin-6 levels. These effects were accompanied by an obvious increase in hepcidin mRNA level and iron content in the hippocampus. These changes were blocked by the injection of dalteparin. In conclusion, inhibition of hepcidin may reduce many pathological changes seen in stress-induced depressive disorders.

Cytokine production as a putative biological mechanism underlying stress sensitization in high combat exposed soldiers

OBJECTIVE

Combat stress exposed soldiers may respond to post-deployment stressful life events (SLE) with increases in symptoms of posttraumatic stress disorder (PTSD), consistent with a model of stress sensitization. Several lines of research point to sensitization as a model to describe the relations between exposure to traumatic events, subsequent SLE, and symptoms of PTSD. Based on previous findings we hypothesized that immune activation, measured as a high in vitro capacity of leukocytes to produce cytokines upon stimulation, underlies stress sensitization.

METHODS

We assessed mitogen-induced cytokine production at 1 month, SLE at 1 year, and PTSD symptoms from 1 month up to 2 years post-deployment in soldiers returned from deployment to Afghanistan (N=693). Exploratory structural equation modeling as well as latent growth models were applied.

RESULTS

The data demonstrated significant three-way interaction effects of combat stress exposure, cytokine production, and post-deployment SLE on linear change in PTSD symptoms over the first 2 years following return from deployment. In soldiers reporting high combat stress exposure, both high mitogen-stimulated T-cell cytokine production and high innate cytokine production were associated with increases in PTSD symptoms in response to post-deployment SLE. In low combat stress exposed soldiers as well as those with low cytokine production, post-deployment SLE were not associated with increases in PTSD symptoms.

CONCLUSION

High stimulated T-cell and innate cytokine production may contribute to stress sensitization in recently deployed, high combat stress exposed soldiers. These findings suggest that detecting and eventually normalizing immune activation may potentially complement future strategies to prevent progression of PTSD symptoms following return from deployment.

Microglia activation regulates GluR1 phosphorylation in chronic unpredictable stress-induced cognitive dysfunction

Chronic stress is considered to be a major risk factor in the development of psychopathological syndromes in humans. Cognitive impairments and long-term potentiation (LTP) impairments are increasingly recognized as major components of depression, anxiety disorders and other stress-related chronic psychological illnesses. It seems timely to systematically study the potentially underlying neurobiological mechanisms of altered cognitive and synaptic plasticity in the course of chronic stress. In the present study, a rat model of chronic unpredictable stress (CUS) induced a cognitive impairment in spatial memory in the Morris water maze (MWM) test and a hippocampal LTP impairment. CUS also induced hippocampal microglial activation and attenuated phosphorylation of glutamate receptor 1 (GluR1 or GluA1). Moreover, chronic treatment with the selective microglial activation blocker, minocycline (120 mg/kg per day), beginning 3 d before CUS treatment and continuing through the behavioral testing period, prevented the CUS-induced impairments of spatial memory and LTP induction. Additional studies showed that minocycline-induced inhibition of microglia activation was associated with increased phosphorylation of GluR1. These results suggest that hippocampal microglial activation modulates the level of GluR1 phosphorylation and might play a causal role in CUS-induced cognitive and LTP disturbances.

Early post-stressor intervention with minocycline, a second-generation tetracycline, attenuates post-traumatic stress response in an animal model of PTSD

We assessed the effects of minocycline, a tetracycline with anti-inflammatory, anti-apoptotic and neuroprotective capacities, in an animal model of post-traumatic stress disorder (PTSD). Rats were exposed to psychogenic stress and treated 1h later with minocycline or saline. Behavioral measures included the elevated plus-maze (EPM) and acoustic startle response (ASR) 7 days post stress-exposure. One day after behavioral testing, animals were exposed to a trauma cue and freezing response was assessed. Local levels of cytokines interleukin-1 (IL-1), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in the hippocampus, frontal cortex (FC) and hypothalamus were then examined. Minocycline attenuated anxious-like behaviors in stress-exposed rats. In addition, decreased levels of cytokines were measured in exposed rats treated with minocycline compared to their counterparts treated with saline. This study suggests a potential use of minocycline in preventing physiological and behavioral alternations resulting from acute exposure to psychological stress. As this is the first study to report beneficial outcomes for minocycline treatment in an animal model of PTSD, further investigations of the use of minocycline in stress-related conditions with emphasis on PTSD is needed.

A review of the relationship between proinflammatory cytokines and major depressive disorder

BACKGROUND

Determining etiological factors and reviewing advances in diagnostic modalities sensitive and specific to Major Depressive Disorder (MDD) is of importance in its evaluation and treatment. The inflammatory hypothesis is one of the most prevalent topics concerning MDD and may provide insight into the pathogenesis of depression, development of biomarkers, and ultimately production of more effective depression therapies.

METHOD

We reviewed several studies to evaluate contemporary concepts concerning proinflammatory cytokines and their relationship to various depressive disorders, the use of anti-inflammatory therapies in MDD treatment, and the application of neuroimaging in conjunction with cytokine profiles from both plasma and CSF as possible diagnostic tools.

RESULTS

Proinflammatory cytokines in both plasma and CSF have been found to influence the progression and severity of depressive disorders in different populations. Studies have shown elevated serum levels of IL-1, IL-6, TNF-α, CRP, and MCP-1 in depressed patients, but have presented mixed results with IL-8 serum levels, and with IL-6 and MCP-1 CSF levels. Anti-inflammatory treatment of MDD may have adjuvant properties with current depression medications. MRI and NIRS neuroimaging confirm neurological abnormalities in the presence of elevated proinflammatory cytokines in depressed or stressed patients.

LIMITATIONS

Heterogeneity of MDD and limited CSF cytokine research complicate the study of MDD pathogenesis.

CONCLUSION

There is significant evidence that inflammatory processes influence the development and progression of MDD. Future studies with larger arrays of cytokine profiles aided by neuroimaging may provide more sensitive and specific modes of diagnostics in determining MDD etiology and provide guidance in individual therapies.

Let’s save our nurses and doctors!

Introduction: Several studies have shown that healthcare service is a dangerous workplace, but the reasons have been remained unexplained. Aim: The aim of the authors was to obtain data on the health condition of health care professionals and identify the underlying risk factors for the increased morbidity. Method: Health care data obtained from 276 bedside nurses in 2004 and 1250 hospital employees in 2009 were analysed. In addition, the fate of department directors of Szent György University Hospital in Székesfehérvár between 1979 and 2010 was recorded and the data were compared to those obtained from a smaller hospital in Budapest during the same time period. Results: The body mass index of bedside nurses between the age of 30–35 years reached the upper limit of normal (which occurred 5–10 years earlier as compared to the average population) and then it increased continuously above the average value. In hospital employees the increase of body mass index was accompanied by an increase in the frequency of chronic diseases such as hypertension, allergy, thyroid dysfunction, rheumatologic diseases, diabetes, peptic ulcer, cancer and depression. When the cause of death of the department directors who died between 1979 and 2010 was analyzed the authors found that cancer death occurred in 77% and 82% of department directors in Székesfehérvár and Budapest hospitals, respectively, while cancer death rate in 2011 was 25.4% in Hungary. Conclusions: The authors propose that continuous psychological stress, night shifts, nonstop standby and surcharge may all suppress the activity of the immune system. This proposal seems to be supported by novel psycho-neuro-immunological research data. The solution could be early prevention using stress control. Orv. Hetil., 2014, 155(52), 2082–2092.

Cytokines, prostaglandins and nitric oxide in the regulation of stress-response systems

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is accepted as one of the fundamental biological mechanisms that underlie major depression. This hyperactivity is caused by diminished feedback inhibition of glucocorticoid (GC)-induced reduction of HPA axis signaling and increased corticotrophin-releasing hormone (CRH) secretion from the hypothalamic paraventricular nucleus (PVN) and extra-hypothalamic neurons. During chronic stress-induced inhibition of systemic feedback, cytosolic glucocorticoid receptor (GR) levels were significantly changed in the prefrontal cortex (PFC) and hippocampus, both structures known to be deeply involved in the pathogenesis of depression. Cytokines secreted by both immune and non-immune cells can markedly affect neurotransmission within regulatory brain circuits related to the expression of emotions; cytokines may also induce hormonal changes similar to those observed following exposure to stress. Proinflammatory cytokines, including interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) are implicated in the etiologies of clinical depression and anxiety disorders. Prolonged stress responses and cytokines impair neuronal plasticity and stimulation of neurotransmission. Exposure to acute stress and IL-1β markedly increased IL-1β levels in the PFC, hippocampus and hypothalamus, as well as overall HPA axis activity. Repeated stress sensitized the HPA axis response to IL-1β. Inflammatory responses in the brain contribute to cellular damage associated with neuropsychiatric diseases related to stress. Physical, psychological or combined-stress conditions evoke a proinflammatory response in the brain and other systems, characterized by a complex release of several inflammatory mediators including cytokines, prostanoids, nitric oxide (NO) and transcription factors. Induced CRH release involves IL-1, IL-6 and TNF-α, for stimulation adrenocorticotropic hormone (ACTH) release from the anterior pituitary. NO also participates in signal transduction pathways that result in the release of corticosterone from the adrenal gland. NO participates in multiple interactions between neuroendocrine and neuroimmune systems in physiological and pathological processes. Neuronal NO synthase (nNOS) modulates learning and memory and is involved in development of neuropsychiatric diseases, including depression. Nitric oxide generated in response to stress exposure is associated with depression-like and anxiety-like behaviors. In the central nervous system (CNS), prostaglandins (PG) generated by the cyclooxygenase (COX) enzyme are involved in the regulation of HPA axis activity. Prior exposure to chronic stress alters constitutive (COX-1) and inducible (COX-2) cyclooxygenase responses to homotypic stress differently in the PFC, hippocampus and hypothalamus. Both PG and NO generated within the PVN participate in this modulation. Acute stress affects the functionality of COX/PG and NOS/NO systems in brain structures. The complex responses of central and peripheral pathways to acute and chronic stress involve cytokines, NO and PG systems that regulate and turn off responses that would be potentially harmful for cellular homeostasis and overall health.

Social defeat promotes a reactive endothelium in a brain region-dependent manner with increased expression of key adhesion molecules, selectins and chemokines associated with the recruitment of myeloid cells to the brain

Repeated social defeat (RSD) in mice causes myeloid cell trafficking to the brain that contributes to the development of prolonged anxiety-like behavior. Myeloid cell recruitment following RSD occurs in regions where neuronal and microglia activation is observed. Thus, we hypothesized that crosstalk between neurons, microglia, and endothelial cells contributes to brain myeloid cell trafficking via chemokine signaling and vascular adhesion molecules. Here we show that social defeat caused an exposure- and brain region-dependent increase in several key adhesion molecules and chemokines involved in the recruitment of myeloid cells. For example, RSD induced distinct patterns of adhesion molecule expression that may explain brain region-dependent myeloid cell trafficking. VCAM-1 and ICAM-1 mRNA expression were increased in an exposure-dependent manner. Furthermore, RSD-induced VCAM-1 and ICAM-1 protein expression were localized to the vasculature of brain regions implicated in fear and anxiety responses, which spatially corresponded to previously reported patterns of myeloid cell trafficking. Next, mRNA expression of additional adhesion molecules (E- and P-selectin, PECAM-1) and chemokines (CXCL1, CXCL2, CXCL12, CCL2) were determined in the brain. Social defeat induced an exposure-dependent increase in mRNA levels of E-selectin, CXCL1, and CXCL2 that increased with additional days of social defeat. While CXCL12 was unaffected by RSD, CCL2 expression was increased by six days of social defeat. Last, comparison between enriched CD11b(+) cells (microglia/macrophages) and enriched GLAST-1(+)/CD11b(-) cells (astrocytes) revealed RSD increased mRNA expression of IL-1β, CCL2, and CXCL2 in microglia/macrophages but not in astrocytes. Collectively, these data indicate that key mediators of leukocyte recruitment were increased in the brain vasculature following RSD in an exposure- and brain region-dependent manner.

A role for tissue plasminogen activator in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease characterized by generalized microvascular occlusion. TTP has been related to severe deficiency of ADAMTS13, an enzyme that cleaves von Willebrand factor multimers into less adhesive molecules. However, ADAMTS13 deficiency correlates poorly with severity of thrombocytopenia or microangiopathic hemolysis, with the frequency of neurologic complications or the response to plasma exchange. Also, some patients with severe hereditary ADAMTS13 deficiency consistently relapse every few weeks, whereas others remain asymptomatic into their forties. Taken together, these findings suggest that an additional element is missing in the pathophysiology of TTP. We postulate that both low ADAMTS13 activity and low tissue-plasminogen activator activity are required to trigger TTP attacks. Tissue-plasminogen activator end product, plasmin, extensively degrades von Willebrand factor, breaking-down the bonds between platelets and the blood vessel wall, so that low tissue-plasminogen activator activity prevents a mechanism similar to that of ADAMTS13. The hypothesis that low tissue-plasminogen activator activity plays an important role in TTP pathogenesis is further substantiated by TTP comorbidity. Problems prevalent in patients with TTP attacks or with long-term TTP remission, including increased body mass index, major depression, cognitive abnormalities, hypertension, and premature death, are somehow associated with low tissue-plasminogen activator activity.

Dietary broccoli mildly improves neuroinflammation in aged mice but does not reduce lipopolysaccharide-induced sickness behavior

Aging is associated with oxidative stress and heightened inflammatory response to infection. Dietary interventions to reduce these changes are therefore desirable. Broccoli contains glucoraphanin, which is converted to sulforaphane (SFN) by plant myrosinase during cooking preparation or digestion. Sulforaphane increases antioxidant enzymes including NAD(P)H quinone oxidoreductase and heme oxygenase I and inhibits inflammatory cytokines. We hypothesized that dietary broccoli would support an antioxidant response in brain and periphery of aged mice and inhibit lipopolysaccharide (LPS)-induced inflammation and sickness. Young adult and aged mice were fed control or 10% broccoli diet for 28 days before an intraperitoneal LPS injection. Social interactions were assessed 2, 4, 8, and 24 hours after LPS, and mRNA was quantified in liver and brain at 24 hours. Dietary broccoli did not ameliorate LPS-induced decrease in social interactions in young or aged mice. Interleukin-1β (IL-1β) expression was unaffected by broccoli consumption but was induced by LPS in brain and liver of adult and aged mice. In addition, IL-1β was elevated in brain of aged mice without LPS. Broccoli consumption decreased age-elevated cytochrome b-245 β, an oxidative stress marker, and reduced glial activation markers in aged mice. Collectively, these data suggest that 10% broccoli diet provides a modest reduction in age-related oxidative stress and glial reactivity, but is insufficient to inhibit LPS-induced inflammation. Thus, it is likely that SFN would need to be provided in supplement form to control the inflammatory response to LPS.

Microglia and their CX3CR1 signaling are involved in hippocampal- but not olfactory bulb-related memory and neurogenesis

Recent studies demonstrate that microglia play an important role in cognitive and neuroplasticity processes, at least partly via microglial CX3C receptor 1 (CX3CR1) signaling. Furthermore, microglia are responsive to environmental enrichment (EE), which modulates learning, memory and neurogenesis. In the present study we examined the role of microglial CX3CR1 signaling in hippocampal- and olfactory-bulb (OB)-related memory and neurogenesis in homozygous mice with microglia-specific transgenic expression of GFP under the CX3CR1 promoter (CX3CR1(-/-) mice), in which the CX3CR1 gene is functionally deleted, as well as heterozygous CX3CR1(+/-) and WT controls. We report that the CX3CR1-deficient mice displayed better hippocampal-dependent memory functioning and olfactory recognition, along with increased number and soma size of hippocampal microglia, suggestive of mild activation status, but no changes in OB microglia. A similar increase in hippocampal-dependent memory functioning and microglia number was also induced by pharmacological inhibition of CX3CR1 signaling, using chronic (2weeks) i.c.v. administration of CX3CR1 blocking antibody. In control mice, EE improved hippocampal-dependent memory and neurogenesis, and increased hippocampal microglia number and soma size, whereas odor enrichment (OE) improved olfactory recognition and OB neurogenesis without changing OB microglia status. In CX3CR1-deficient mice, EE and OE did not produce any further improvement in memory functioning or neurogenesis and had no effect on microglial status. These results support the notion that in the hippocampus microglia and their interactions with neurons via the CX3CR1 play an important role in memory functioning and neurogenesis, whereas in the OB microglia do not seem to be involved in these processes.

Anti-interleukin-1β antibody prevents the occurrence of repeated restraint stress-induced alterations in synaptic transmission and long-term potentiation in the rat frontal cortex

BACKGROUND

The mechanisms of the influence of prolonged stress on glutamatergic transmission and synaptic plasticity in the cerebral cortex remain poorly understood. The purpose of this study was to determine an involvement of interleukin-1β (IL-1β) in the effects of repeated restraint stress on excitatory synaptic transmission and long-term potentiation (LTP) in the rat frontal cortex.

METHODS

The effects of restraint stress lasting for 10 min, repeated twice daily for 3 consecutive days were studied ex vivo in the rat frontal cortex slices prepared 24h after the last stress session. Rats received intraperitoneal injections of interleukin-1β antibody. In a separate experimental group, rats received injections of IL-1β. Field potentials were recorded in the cortical layer II/III.

RESULTS

In slices originating from stressed animals, the amplitude of field potentials was increased. Consistent with the previous studies, restraint stress resulted in a reduced magnitude of LTP. Similar effects were evident after administration of IL-1β. Stress-induced modifications of the glutamatergic transmission and synaptic plasticity were prevented by interleukin-1β antibody, which was administered 15 min before each restraint session.

CONCLUSIONS

These data point to an involvement of peripherally produced IL-1β in mediating the influence of repeated restraint stress on the functions of the frontal cortex.

Iptakalim confers an antidepressant effect in a chronic mild stress model of depression through regulating neuro-inflammation and neurogenesis

Depression is a serious mental disorder in the world, but the underlying mechanisms remain unclear and the effective cures are scarce. Iptakalim (Ipt), an ATP-sensitive potassium (K-ATP) channel opener that can cross the blood-brain barrier freely, has been demonstrated to inhibit neuro-inflammation and enhance adult hippocampal neurogenesis. But it is unknown whether Ipt is beneficial to therapy of depression by modulating neurogenesis and neuro-inflammation. This study aimed to determine the potential antidepressant efficacy of Ipt in a chronic mild stress (CMS) mouse model of depression. We showed that treatment with Ipt (10 mg/kg/day, i.p) for 4 wk restored the decrease of sucrose preference and shortened the immobile time in forced swimming tests (FST) and tail suspension tests (TST) in CMS model mice. We further found that Ipt reversed the CMS-induced reduction of the adult hippocampal neurogenesis and improved cerebral insulin signalling in the CMS mice. Furthermore, Ipt negatively regulated nod-like receptor protein 3 (NLRP3) expression and, in turn, inhibited microglia-mediated neuro-inflammation by suppressing the activation of NLRP3-inflammasome/caspase-1/interleukin 1β axis in the hippocampus of CMS mice. Taken together, our findings demonstrate that Ipt plays a potential antidepressant role in CMS model mice through regulating neuro-inflammation and neurogenesis, which will provide potential for Ipt in terms of opening up novel therapeutic avenues for depression.

Early postnatal exposure to ultrafine particulate matter air pollution: persistent ventriculomegaly, neurochemical disruption, and glial activation preferentially in male mice

BACKGROUND

Air pollution has been associated with adverse neurological and behavioral health effects in children and adults. Recent studies link air pollutant exposure to adverse neurodevelopmental outcomes, including increased risk for autism, cognitive decline, ischemic stroke, schizophrenia, and depression.

OBJECTIVES

We sought to investigate the mechanism(s) by which exposure to ultrafine concentrated ambient particles (CAPs) adversely influences central nervous system (CNS) development.

METHODS

We exposed C57BL6/J mice to ultrafine (< 100 nm) CAPs using the Harvard University Concentrated Ambient Particle System or to filtered air on postnatal days (PNDs) 4-7 and 10-13, and the animals were euthanized either 24 hr or 40 days after cessation of exposure. Another group of males was exposed at PND270, and lateral ventricle area, glial activation, CNS cytokines, and monoamine and amino acid neurotransmitters were quantified.

RESULTS

We observed ventriculomegaly (i.e., lateral ventricle dilation) preferentially in male mice exposed to CAPs, and it persisted through young adulthood. In addition, CAPs-exposed males generally showed decreases in developmentally important CNS cytokines, whereas in CAPs-exposed females, we observed a neuroinflammatory response as indicated by increases in CNS cytokines. We also saw changes in CNS neurotransmitters and glial activation across multiple brain regions in a sex-dependent manner and increased hippocampal glutamate in CAPs-exposed males.

CONCLUSIONS

We observed brain region- and sex-dependent alterations in cytokines and neurotransmitters in both male and female CAPs-exposed mice. Lateral ventricle dilation (i.e., ventriculomegaly) was observed only in CAPs-exposed male mice. Ventriculomegaly is a neuropathology that has been associated with poor neurodevelopmental outcome, autism, and schizophrenia. Our findings suggest alteration of developmentally important neurochemicals and lateral ventricle dilation may be mechanistically related to observations linking ambient air pollutant exposure and adverse neurological/neurodevelopmental outcomes in humans.

On the time course, generality, and regulation of plasma progesterone release in male rats by stress exposure

Although progesterone is most commonly regarded in terms of its role in the female estrous cycle, reproductive behavior, and pregnancy, progesterone is also a precursor to corticosterone (CORT) and is released from the adrenal glands of both sexes in response to stress. However, the relationship between plasma CORT and progesterone during times of stress has not been well established. To better characterize dynamic changes in progesterone release as a result of stressor exposure, plasma progesterone levels were measured using enzyme immunoassay under multiple conditions, including after stress exposure (footshock, restraint, and forced swim), manipulations of the hypothalamic-pituitary-adrenal axis (injection of metyrapone or dexamethasone, or adrenalectomy), and in response to CRH and ACTH injections. When plasma levels of ACTH, CORT, and progesterone were analyzed across studies, CORT and progesterone were found to be highly correlated and rarely dissociated. Additionally, it appears that in male rats, the adrenal glands are the principle source of circulating progesterone in response to stress. Interestingly, a detailed time course indicated lack of a circadian rhythm of progesterone secretion, despite a robust rhythm of circulating CORT. The current studies provide critical new information on the coincident release of progesterone and CORT in response to stress and their somewhat paradoxical dissociation across the circadian rhythm. These findings provide an important foundation for future studies that will examine the role of stress-induced progesterone in behavioral, neuroimmune, and neuroendocrine responses to stress.

Cerebrospinal fluid markers of neuroinflammation in delirium: a role for interleukin-1β in delirium after hip fracture

OBJECTIVE

Exaggerated central nervous system (CNS) inflammatory responses to peripheral stressors may be implicated in delirium. This study hypothesised that the IL-1β family is involved in delirium, predicting increased levels of interleukin-1β (IL-1β) and decreased IL-1 receptor antagonist (IL-1ra) in the cerebrospinal fluid (CSF) of elderly patients with acute hip fracture. We also hypothesised that Glial Fibrillary Acidic Protein (GFAP) and interferon-γ (IFN-γ) would be increased, and insulin-like growth factor 1 (IGF-1) would be decreased.

METHODS

Participants with acute hip fracture aged >60 (N=43) were assessed for delirium before and 3-4 days after surgery. CSF samples were taken at induction of spinal anaesthesia. Enzyme-linked immunosorbent assays (ELISA) were used for protein concentrations.

RESULTS

Prevalent delirium was diagnosed in eight patients and incident delirium in 17 patients. CSF IL-1β was higher in patients with incident delirium compared to never delirium (incident delirium 1.74 pg/ml (1.02-1.74) vs. prevalent 0.84 pg/ml (0.49-1.57) vs. never 0.66 pg/ml (0-1.02), Kruskal-Wallis p=0.03). CSF:serum IL-1β ratios were higher in delirious than non-delirious patients. CSF IL-1ra was higher in prevalent delirium compared to incident delirium (prevalent delirium 70.75 pg/ml (65.63-73.01) vs. incident 31.06 pg/ml (28.12-35.15) vs. never 33.98 pg/ml (28.71-43.28), Kruskal-Wallis p=0.04). GFAP was not increased in delirium. IFN-γ and IGF-1 were below the detection limit in CSF.

CONCLUSION

This study provides novel evidence of CNS inflammation involving the IL-1β family in delirium and suggests a rise in CSF IL-1β early in delirium pathogenesis. Future larger CSF studies should examine the role of CNS inflammation in delirium and its sequelae.

Broken or maladaptive? Altered trajectories in neuroinflammation and behavior after early life adversity

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This paper reviews how early life adversity alters neuroimmune mechanisms.

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Neuroimmune sensitization from early life adversity impacts circuitry at discrete life stages.

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Neuroimmune and neurodevelopmental influences can impact behavior and vulnerability.

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Sexual dimorphism in immune and brain development yield distinct effects of early life adversity.

Exposure to adversity and stress early in development yields vulnerability to mental illnesses throughout the lifespan. Growing evidence suggests that this vulnerability has mechanistic origins involving aberrant development of both neurocircuitry and neuro-immune activity. Here we review the current understanding of when and how stress exposure initiates neuroinflammatory events that interact with brain development. We first review how early life adversity has been associated with various psychopathologies, and how neuroinflammation plays a role in these pathologies. We then summarize data and resultant hypotheses describing how early life adversity may particularly alter neuro-immune development with psychiatric consequences. Finally, we review how sex differences contribute to individualistic vulnerabilities across the lifespan. We submit the importance of understanding how stress during early development might cause outright neural or glial damage, as well as experience-dependent plasticity that may insufficiently prepare an individual for sex-specific or life-stage specific challenges.

Neuroimmunomodulation in depression: a review of inflammatory cytokines involved in this process

Depression is a debilitating mental disease that affects a large number of people globally; however the pathophysiological mechanisms of this disease remain incompletely understood. Some studies have shown that depression is associated with inflammatory activity, and the mode of action of several antidepressants appears to involve immunomodulation. In this case, the induction of a pro-inflammatory state in healthy or depressive subjects induces a 'sickness behaviour' resembling depressive symptomatology. Potential mechanisms of pro-inflammatory cytokines are effects on monoamine levels, disruption of the hypothalamic-pituitary-adrenal axis, activation of the pathological microglial cells, such as the macrophages and alterations in neuroplasticity and brain functions. Thus, this review will highlight the role of inflammation in depression, the possible mechanisms involved, and also explore effective treatments that act on the immune system.

Inflammatory cytokine-associated depression

Inflammatory cytokines can sometimes trigger depression in humans, are often associated with depression, and can elicit some behaviors in animals that are homologous to major depression. Moreover, these cytokines can affect monoaminergic and glutamatergic systems, supporting an overlapping pathoetiology with major depression. This suggests that there could be a specific major depression subtype, inflammatory cytokine-associated depression (ICAD), which may require different therapeutic approaches. However, most people do not develop depression, even when exposed to sustained elevations in inflammatory cytokines. Thus several vulnerabilities and sources of resilience to inflammation-associated depression have been identified. These range from genetic differences in neurotrophic and serotonergic systems to sleep quality and omega-3 fatty acid levels. Replicating these sources of resilience as treatments could be one approach for preventing "ICAD". This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Interleukin-1β-immunoreactive neurons in the hippocampus and paraventricular nucleus of the hypothalamus after stress stimulation in aged versus adult rats

It is believed that the impact of stress on interleukin-1β (IL-1β) depends on the ontogenetic age. This study examines the influence of acute or chronic exposure to forced-swim (FS) stress or high-light open-field (HL-OF) stimulation on the expression of IL-1β. Double immunofluorescence staining was used to reveal the density of IL-1β/NeuN (NeuN is a neuronal nuclear marker)-immunoreactive (-ir) cells in the hippocampal subfields CA1 and CA3, dentate gyrus (DG), and paraventricular nucleus (PVN) of the hypothalamus. Adult postnatal day 90 (P90) and aged (P720) rats were used in this experiment. The data showed a significant increase in the density of IL-1β/NeuN-ir cells in the CA1, CA3, DG, and PVN in P720 nonstressed rats in relation to P90 control animals. Neither FS nor HL-OF acute stimulation caused alteration in the density of IL-1β-ir neurons in any of the investigated structures in P90 and P720 rats in comparison with control groups. However, chronic FS caused a significant increase in CA3 and DG of P720 rats, and chronic HL-OF led to a significant increase in the density of IL-1β-ir neurons in the PVN of P90 rats and in all hippocampal subfields of P720 animals. These results indicate that chronic HL-OF stimulation is a factor that induces changes in the number of IL-1β-ir neurons in the PVN of adult rats, whereas both chronic FS and HL-OF are aggravating factors for the hippocampus of aged (P720) animals.

Dynamic microglial alterations underlie stress-induced depressive-like behavior and suppressed neurogenesis

The limited success in understanding the pathophysiology of major depression may result from excessive focus on the dysfunctioning of neurons, as compared with other types of brain cells. Therefore, we examined the role of dynamic alterations in microglia activation status in the development of chronic unpredictable stress (CUS)-induced depressive-like condition in rodents. We report that following an initial period (2-3 days) of stress-induced microglial proliferation and activation, some microglia underwent apoptosis, leading to reductions in their numbers within the hippocampus, but not in other brain regions, following 5 weeks of CUS exposure. At that time, microglia displayed reduced expression of activation markers as well as dystrophic morphology. Blockade of the initial stress-induced microglial activation by minocycline or by transgenic interleukin-1 receptor antagonist overexpression rescued the subsequent microglial apoptosis and decline, as well as the CUS-induced depressive-like behavior and suppressed neurogenesis. Similarly, the antidepressant drug imipramine blocked the initial stress-induced microglial activation as well as the CUS-induced microglial decline and depressive-like behavior. Treatment of CUS-exposed mice with either endotoxin, macrophage colony-stimulating factor or granulocyte-macrophage colony-stimulating factor, all of which stimulated hippocampal microglial proliferation, partially or completely reversed the depressive-like behavior and dramatically increased hippocampal neurogenesis, whereas treatment with imipramine or minocycline had minimal or no anti-depressive effects, respectively, in these mice. These findings provide direct causal evidence that disturbances in microglial functioning has an etiological role in chronic stress-induced depression, suggesting that microglia stimulators could serve as fast-acting anti-depressants in some forms of depressive and stress-related conditions.

Heat shock alters the expression of schizophrenia and autism candidate genes in an induced pluripotent stem cell model of the human telencephalon

Schizophrenia (SZ) and autism spectrum disorders (ASD) are highly heritable neuropsychiatric disorders, although environmental factors, such as maternal immune activation (MIA), play a role as well. Cytokines mediate the effects of MIA on neurogenesis and behavior in animal models. However, MIA stimulators can also induce a febrile reaction, which could have independent effects on neurogenesis through heat shock (HS)-regulated cellular stress pathways. However, this has not been well-studied. To help understand the role of fever in MIA, we used a recently described model of human brain development in which induced pluripotent stem cells (iPSCs) differentiate into 3-dimensional neuronal aggregates that resemble a first trimester telencephalon. RNA-seq was carried out on aggregates that were heat shocked at 39°C for 24 hours, along with their control partners maintained at 37°C. 186 genes showed significant differences in expression following HS (p<0.05), including known HS-inducible genes, as expected, as well as those coding for NGFR and a number of SZ and ASD candidates, including SMARCA2, DPP10, ARNT2, AHI1 and ZNF804A. The degree to which the expression of these genes decrease or increase during HS is similar to that found in copy loss and copy gain copy number variants (CNVs), although the effects of HS are likely to be transient. The dramatic effect on the expression of some SZ and ASD genes places HS, and perhaps other cellular stressors, into a common conceptual framework with disease-causing genetic variants. The findings also suggest that some candidate genes that are assumed to have a relatively limited impact on SZ and ASD pathogenesis based on a small number of positive genetic findings, such as SMARCA2 and ARNT2, may in fact have a much more substantial role in these disorders - as targets of common environmental stressors.

Knockdown of interleukin-1 receptor type-1 on endothelial cells attenuated stress-induced neuroinflammation and prevented anxiety-like behavior

Interleukin-1β (IL-1β) is an inflammatory cytokine that plays a prominent role in stress-induced behavioral changes. In a model of repeated social defeat (RSD), elevated IL-1β expression in the brain was associated with recruitment of primed macrophages that were necessary for development of anxiety-like behavior. Moreover, microglia activation and anxiety-like behavior associated with RSD did not occur in IL-1 receptor type-1 knock-out (IL-1R1(KO)) mice. Therefore, the objective of this study was to examine the role of IL-1 signaling in RSD-induced macrophage trafficking to the brain and anxiety-like behavior. Initial studies revealed that RSD did not increase circulating myeloid cells in IL-1R1(KO) mice, resulting in limited macrophage trafficking to the brain. In addition, IL-1R1(KO) bone marrow-chimera mice showed that IL-1R1 expression was essential for macrophage trafficking into the brain. To differentiate cellular mediators of stress-induced IL-1 signaling, endothelial-specific IL-1R1 knock-down (eIL-1R1kd) mice were used. Both wild-type (WT) and eIL-1R1kd mice had increased circulating monocytes, recruitment of macrophages to the brain, and altered microglia activation after RSD. Nonetheless, RSD-induced expression of IL-1β, TNF-α, and IL-6 mRNA in brain CD11b(+) cells was attenuated in eIL-1R1kd mice compared with WT. Moreover, anxiety-like behavior did not develop in eIL-1R1kd mice. Collectively, these findings demonstrated that there was limited RSD-induced priming of myeloid cells in IL-1R1(KO) mice and disrupted propagation of neuroinflammatory signals in the brain of eIL-1R1kd mice. Furthermore, these data showed that transduction of IL-1 signaling by endothelial cells potentiates stress-induced neuroinflammation and promotes anxiety-like behavior.

cRGD mediated liposomes enhanced antidepressant-like effects of edaravone in rats

The delayed onset of therapeutic outcomes is a major drawback of the current antidepressants. The blood-brain barrier is the most important bottleneck impeding drug transport into the brain. Therefore, development of novel antidepressant medications with rapid onset and sustained activity is urgent. RGD liposomes showed an excellent effect of brain-targeting drug delivery and increased the entering rate to the brain. In the present study, we prepared cyclic RGD liposomes loaded with edaravone (cRGD-ERLs) and evaluated the potential antidepressant-like effects of this drug delivery system in rats. The results showed single injection of cRGD-ERLs produced significant antidepressant-like effects in both forced swim and novelty suppressed feeding test. Moreover, acute cRGD-ERLs increased the expression of c-fos in the medial prefrontal cortex, suggesting that cRGD-ERLs could activate the neuronal function. Furthermore, cRGD-ERLs reversed the increase of lipopolysaccharides (LPS)-induced plasma cytokine IL-1β and IL-6, suggesting that normalization of cytokine level might be involved in the behavioral response of cRGD-ERLs. Finally, cRGD-ERLs prevented the increase of immobility induced by LPS in the forced swim test. Overall, the current data revealed a novel brain-target drug delivery system, which can be used to improve the therapeutic outcomes of antidepressants by increase of crossing rate to the brain.

Biomarkers of epileptogenesis: psychiatric comorbidities (?)

The last decade has witnessed a significant shift on our understanding of the relationship between psychiatric disorders and epilepsy. While traditionally psychiatric disorders were considered as a complication of the underlying seizure disorder, new epidemiologic data, supported by clinical and experimental research, have suggested the existence of a bidirectional relation between the two types of conditions: not only are patients with epilepsy at greater risk of experiencing a psychiatric disorder, but patients with primary psychiatric disorders are at greater risk of developing epilepsy. Do these data suggest that some of the pathogenic mechanisms operant in psychiatric comorbidities play a role in epileptogenesis? The aim of this article is to review the epidemiologic data that demonstrate that primary psychiatric disorders are more frequent in people who develop epilepsy, before the onset of the seizure disorder than among controls. The next question looks at the available data of pathogenic mechanisms of primary mood disorders and their potential for facilitating the development and/or exacerbation in the severity of epileptic seizures. Finally, we review data derived from experimental studies in animal models of depression and epilepsy that support a potential role of pathogenic mechanisms of mood disorders in the development of epileptic seizures and epileptogenesis. The data presented in this article do not yet establish conclusive evidence of a pathogenic role of psychiatric comorbidities in epileptogenesis, but raise important research questions that need to be investigated in experimental, clinical, and population-based epidemiologic research studies.

Hippocampal dysfunctions in tumor-bearing mice

Individuals with cancer are particularly susceptible to depression and cognitive impairment. However, the precise mechanisms underlying cancer-induced hippocampal dysfunction are poorly understood. We investigated the effects of a peripheral tumor on emotional behavior, hippocampus-dependent memory and associated molecular and cellular features using an experimental animal model. Behavioral alterations were examined; stress-related parameters measured; hippocampal neurogenesis evaluated; and the levels of pro-inflammatory cytokines, brain-derived neurotrophic factor (BDNF) and cyclooxygenase-2 (COX-2) assayed, 2 weeks after inoculation of adult BALB/c mice with cells of a colon carcinoma cell line (CT26). As the tumors developed, CT26-inoculated mice showed significant increases in the depression-like behavior (measured using the tail suspension test) and memory impairment (in terms of object recognition) compared with vehicle-inoculated controls. The presence of a peripheral tumor significantly elevated the hippocampal levels of mRNAs encoding interleukin-6 (IL-6) and tumor necrosis factor-α, as well as plasma IL-6 and corticosterone levels. Additionally, the adrenal glands became enlarged, and the numbers of Ki-67-positive proliferating hippocampal cells and doublecortin-positive immature progenitor neurons, as well as the constitutive levels of mRNAs encoding BDNF and COX-2 were significantly reduced. Therefore, a peripheral tumor alone may be sufficient to induce hippocampal dysfunction, possibly by reducing the rate of neurogenesis and the levels of BDNF and COX-2 in that tissue and also by increasing stress-related parameters and the circulating levels of pro-inflammatory cytokines.

Influence of a probiotic lactobacillus strain on the intestinal ecosystem in a stress model mouse

Daily exposure to stressful situations affects the health of humans and animals. It has been shown that psychological stress affects the immune system and can exacerbate diseases. Probiotics can act as biological immunomodulators in healthy people, increasing both intestinal and systemic immune responses. The use of probiotics in stress situations may aid in reinforcing the immune system. The aim of this study was to evaluate the effect of a probiotic bacterium on the gut immune system of mice that were exposed to an experimental model of stress induced by food and mobility restriction. The current study focused on immune cells associated with the lamina propria of the intestine, including CD4+ and CD8+ T lymphocytes, CD11b+ macrophages, CD11c+ dendritic cells, and IgA+ B lymphocytes, as well as the concentrations of secretory IgA (S-IgA) and cytokine interferon gamma (INF-γ in intestinal fluid. We also evaluated the probiotic's influence on the gut microbiota. Probiotic administration increased IgA producing cells, CD4+ cells in the lamina propria of the small intestine, and S-IgA in the lumen; it also reduced the levels of IFN-γ that had increased during stress and improved the intestinal microbiota as measured by an increase in the lactobacilli population. The results obtained from administration of the probiotic to stressed mice suggest that the use of food containing these microorganisms may work as a palliative to reinforce the immune system.

Intra-hippocampal transplantation of neural precursor cells with transgenic over-expression of IL-1 receptor antagonist rescues memory and neurogenesis impairments in an Alzheimer's disease model

Ample evidence implicates neuroinflammatory processes in the etiology and progression of Alzheimer's disease (AD). To assess the specific role of the pro-inflammatory cytokine interleukin-1 (IL-1) in AD we examined the effects of intra-hippocampal transplantation of neural precursor cells (NPCs) with transgenic over-expression of IL-1 receptor antagonist (IL-1raTG) on memory functioning and neurogenesis in a murine model of AD (Tg2576 mice). WT NPCs- or sham-transplanted Tg2576 mice, as well as naive Tg2576 and WT mice served as controls. To assess the net effect of IL-1 blockade (not in the context of NPCs transplantation), we also examined the effects of chronic (4 weeks) intra-cerebroventricular (i.c.v.) administration of IL-1ra. We report that 12-month-old Tg2576 mice exhibited increased mRNA expression of hippocampal IL-1β, along with severe disturbances in hippocampal-dependent contextual and spatial memory as well as in neurogenesis. Transplantation of IL-1raTG NPCs 1 month before the neurobehavioral testing completely rescued these disturbances and significantly increased the number of endogenous hippocampal cells expressing the plasticity-related molecule BDNF. Similar, but less-robust effects were also produced by transplantation of WT NPCs and by i.c.v. IL-1ra administration. NPCs transplantation produced alterations in hippocampal plaque formation and microglial status, which were not clearly correlated with the cognitive effects of this procedure. The results indicate that elevated levels of hippocampal IL-1 are causally related to some AD-associated memory disturbances, and provide the first example for the potential use of genetically manipulated NPCs with anti-inflammatory properties in the treatment of AD.

Serotonin and its implication in the side-effects of interferon-based treatment of patients with chronic viral hepatitis: Pharmacological interventions

Depression is a frequent side-effect of interferon-based treatment of patients with chronic viral hepatitis, that may lead to reduction or discontinuation of treatment. Clinical trials data showed the importance of therapy of psychiatric disorders for a successful antiviral treatment. Emerging evidence suggests that interferon may cause depression affecting serotonin synthesis via increased activity of indoleamine 2,3-dioxygenase. Serotonin reuptake inhibitors significantly improve mood disorders, but the use of these drugs requires caution because some studies reported the emergence of mania in patients treated for depression during antiviral therapy. Therefore, this review will examine and discuss the putative role of serotonin and its metabolism in the development of depression during antiviral therapy, focusing on pharmacological interventions to reduce side-effects.

The effects of ryanodine receptor 1 (RYR1) mutation on plasma cytokines and catecholamines during prolonged restraint in pigs

In the current study, plasma cytokines, including interleukin (IL) 1, IL-2, IL-6, IL-10, IL-12, interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) and catecholamines (adrenaline and noradrenaline) were evaluated during 4h restraint and recovery phase in 60 male pigs. Blood samples were collected from three groups of pigs representing different RYR1 genotypes, namely NN homozygotes (wild-type), Nn heterozygous and nn homozygous (mutant). The 4h restraint evoked an increase in plasma cytokine concentrations in each of the RYR1 genotype groups. During the restraint, the greatest concentrations of plasma IL-6, IL-10, IL-12 and TNF-α in nn homozygous pigs and IFN-γ in NN homozygous were observed. Interleukin 1, IL-2, IL-10, and TNF-α measures were positively intercorrelated in each of the three RYR1 genotype group. A positive correlation was seen between all measured cytokines (with the exception of IL-6) and plasma catecholamine concentrations in Nn heterozygous and nn homozygous pigs. The results suggest that of the cytokine parameters evaluated, IL-6, IL-10, IL-12 and TNF-α of the nn homozygous group seem to show a stronger stress-related response as compared with those of the other two (NN and Nn) groups.

Involvement of inflammasome activation in lipopolysaccharide-induced mice depressive-like behaviors

AIMS

The NLRP3 inflammasome is a cytoplasmic multiprotein complex of the innate immune system that regulates the cleavage of interleukin-1β and interleukin-18 precursors. It can detect a wide range of danger signals and trigger a series of immune-inflammatory reactions. There were plenty of studies indicating that activation of the immune system played pivotal roles in depression. However, the underlying mechanisms of immune-depression interactions remained elusive and there was no report about the involvement of inflammasome activation in depression.

METHODS

We established an acute depression mouse model with lipopolysaccharide to explore the involvement of inflammasome activation in depression.

RESULTS

The lipopolysaccharide-treated mice displayed depressive-like behaviors and pro-inflammatory cytokine interleukin-1β protein and mRNA levels significantly increased. The NLRP3 inflammasome mRNA expression level also significantly elevated in depressed mice brain. Pretreatment with the NLRP3 inflammasome inhibitor Ac-YVAD-CMK significantly abrogated the depressive-like behaviors induced by lipopolysaccharide.

CONCLUSION

These data suggest for the first time that the NLRP3 inflammasome is involved in lipopolysaccharide-induced mice depressive-like behaviors. The NLRP3 inflammasome may be a central mediator between immune activation and depression, which raises the possibility that it may be a more specific target for the depression treatments in the near future.

Stress-induced recruitment of bone marrow-derived monocytes to the brain promotes anxiety-like behavior

Social stress is associated with altered immunity and higher incidence of anxiety-related disorders. Repeated social defeat (RSD) is a murine stressor that primes peripheral myeloid cells, activates microglia, and induces anxiety-like behavior. Here we show that RSD-induced anxiety-like behavior corresponded with an exposure-dependent increase in circulating monocytes (CD11b(+)/SSC(lo)/Ly6C(hi)) and brain macrophages (CD11b(+)/SSC(lo)/CD45(hi)). Moreover, RSD-induced anxiety-like behavior corresponded with brain region-dependent cytokine and chemokine responses involved with myeloid cell recruitment. Next, LysM-GFP(+) and GFP(+) bone marrow (BM)-chimeric mice were used to determine the neuroanatomical distribution of peripheral myeloid cells recruited to the brain during RSD. LysM-GFP(+) mice showed that RSD increased recruitment of GFP(+) macrophages to the brain and increased their presence within the perivascular space (PVS). In addition, RSD promoted recruitment of GFP(+) macrophages into the PVS and parenchyma of the prefrontal cortex, amygdala, and hippocampus of GFP(+) BM-chimeric mice. Furthermore, mice deficient in chemokine receptors associated with monocyte trafficking [chemokine receptor-2 knockout (CCR2(KO)) or fractalkine receptor knockout (CX3CR1(KO))] failed to recruit macrophages to the brain and did not develop anxiety-like behavior following RSD. Last, RSD-induced macrophage trafficking was prevented in BM-chimeric mice generated with CCR2(KO) or CX3CR1(KO) donor cells. These findings indicate that monocyte recruitment to the brain in response to social stress represents a novel cellular mechanism that contributes to the development of anxiety.

Natural killer cell cytotoxicity, cytokine and neuroendocrine responses to opioid receptor blockade during prolonged restraint in pigs

This study evaluated porcine natural killer cell cytotoxicity (NKCC), plasma cytokines including interleukin (IL) 1β, IL-6, IL-10, IL-12 and tumor necrosis factor-α and plasma stress-related hormones including prolactin (PRL), growth hormone (GH), β-endorphin (BEND), ACTH and cortisol (COR) during a 4h restraint and recovery phase after saline or naloxone (1mg/kg BW) administration. The restraint preceded with saline altered NKCC and IL-12 concentration (an early from 15 to 60 min increase followed by a decrease) and increased other measured cytokines and hormones concentrations. Naloxone pretreatment blocked the suppressive effects of the restraint on NKCC and IL-12 and altered IL-10, IL-6, TNF-α, PRL and ACTH concentrations. Furthermore, in naloxone-injected pigs, a positive correlation was found between NKCC and all measured cytokines (with the exception of IL-6) and BEND, ACTH and COR. Results suggest that naloxone-sensitive opioid pathways could influence the mechanisms underlying the immune system (including NKCC) response during stress.

A cytokine network involving brain-borne IL-1β, IL-1ra, IL-18, IL-6, and TNFα operates during long-term potentiation and learning

We have previously shown that long-term potentiation (LTP) induces hippocampal IL-1β and IL-6 over-expression, and interfering their signalling either inhibits or supports, respectively, LTP maintenance. Consistently, blockade of endogenous IL-1 or IL-6 restricts or favours hippocampal-dependent memory, effects that were confirmed in genetically manipulated mice. Since cytokines are known for their high degree of mutual crosstalk, here we studied whether a network of cytokines with known neuromodulatory actions is activated during LTP and learning. We found that, besides IL-1β and IL-6, also IL-1 receptor antagonist (IL-1ra) and IL-18, but not TNFα are over-expressed during LTP maintenance in freely moving rats. The increased expression of these cytokines is causally related to an increase in synaptic strength since it was abrogated when LTP was interfered by blockade of NMDA-glutamate receptors. Likewise, IL-1 and IL-6 were found to be over-expressed in defined regions of the hippocampus during learning a hippocampus-dependent task. However, during learning, changes in IL-18 were restricted to the dorsal hippocampus, and no differences in TNFα and IL1-ra expression were noticed in the hippocampus. Noticeably, IL-1ra transcripts were significantly reduced in the prefrontal cortex. The relation between cytokine expression and learning was causal because such changes were not observed in animals from a pseudo-trained group that was subject to the same manipulation but could not learn the task. Taken together with previous studies, we conclude that activation of a cytokine network in the brain is a physiologic relevant phenomenon not only for LTP maintenance but also for certain types of learning.

Learning and memory ... and the immune system

The nervous system and the immune system are two main regulators of homeostasis in the body. Communication between them ensures normal functioning of the organism. Immune cells and molecules are required for sculpting the circuitry and determining the activity of the nervous system. Within the parenchyma of the central nervous system (CNS), microglia constantly monitor synapses and participate in their pruning during development and possibly also throughout life. Classical inflammatory cytokines, such as interleukin (IL)-1β and tumor necrosis factor (TNF), are released during neuronal activity and play a crucial role in regulating the strength of synaptic transmission. Systemically, proper functioning of the immune system is critical for maintaining normal nervous system function. Disruption of the immune system functioning leads to impairments in cognition and in neurogenesis. In this review we provide examples of the communication between the nervous and the immune systems in the interest of normal CNS development and function.

IL-32γ Inhibits Acetaminophen-Induced Acute Hepatotoxicity through Inactivation of NF-κB and Stat1 Signals

Although several studies have shown physiological functions of interleukin (IL)-32, the role of IL-32 in liver has not yet been reported. This study was initiated to examine the effects of IL-32γ on APAP-induced acute hepatic failure in IL-32γ transgenic mice. IL-32Γ overexpressing and non-transgenic mice received 500 mg/kg Acetoaminophen (APAP) intraperitoneally. Serum alanine transaminase and aspartate transaminase were significantly lower in the APAP treated IL-32γ overexpressing mice compared with those APAP-treated non-transgenic. IL-32γ markedly reduced a restricted area of the necrosis and inflammation. APAP-induced reduced glutathione depletion, induction of nitric oxide and lipid peroxidation, and cytochrome P4502E1 expression was significantly lowered in the IL-32γ overexpressing mice. Elevation of Kupffer cells and natural killer cells by APAP were reduced in the IL-32γ overexpressing mice. The expression of IL-1α, IL-1rα, macrophage inflammatory protein-2, C-C motif chemokine ligand 5 and tissue inhibitor of metalloproteinase-1 was increased by APAP in non-transgenic mice, and were lowered in the IL-32γ overexpressing mice. Moreover, APAP-induced nuclear transcription factor-kappa B (NF-κB) and signal transducers and activators of transcription 1 (STAT1) activities were greatly lowered in the IL-32γ overexpressing mice. The results indicate that IL-32γ could effectively inhibit drug-induced hepatic failure, and reduce the number of cytotoxic immune cells and pro-inflammatory cytokine production through reduced activities of NF-κB and STAT1. This might be attributable to lowering APAP-induced liver toxicity in IL-32γ overexpressing mice.

Cause of idiopathic sudden sensorineural hearing loss: The stress response theory

The stress response theory is a relatively new concept about the cause of idiopathic sudden sensorineural hearing loss (ISHL). A number of possible etiologies have been proposed in the literature, as discussed in this paper, but each proposed etiology has been both supported and refuted in the literature. However, the stress response theory can integrate hypotheses that have been advocated so far. The word “stress” refers to a constellation of physical and psychological stimuli including systemic viral and bacterial illness, systemic inflammatory disorders, and physical, mental or metabolic stress. Numerous studies have demonstrated adverse effects of systemic stress on health. Stress causes changes in the immune system and cytokine network through activation of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system. Several types of catecholamine and cytokine receptors are in the cochlea cells other than capillary cells, and then they can respond to systemic stressors. However, there are few studies examining how systemic stress is associated with cochlear dysfunction. The stress response theory addresses this question. In the theory, a variety of stressors and risk factors contribute to the onset of ISHL in varying degrees. The lateral wall of the cochlea has very unique responses to systemic stressors. It plays a critical role in causing ISHL. Systemic stressors converge at the lateral wall and trigger pathological activation of nuclear factor κ-light-chain-enhancer of activated B cells, a transcriptional factor known as a stress sensor. This activation enhances local expression of genes associated with immune and inflammatory system, resulting in cochlear dysfunction. We review the original stress response theory advocated by Adams et al and the integrative stress response theory that integrates our knowledge about the etiologies of ISHL so far.

New Insights in the Immunobiology of IL-1 Family Members

The interleukin-1 (IL 1) family of ligands is associated with acute and chronic inflammation, and plays an essential role in the non-specific innate response to infection. The biological properties of IL 1 family ligands are typically pro-inflammatory. The IL 1 family has 11 family members and can be categorized into subfamilies according to the length of their precursor and the length of the propiece for each precursor (Figure 1). The IL 1 subfamily consists of IL 1α, IL 1β, and IL 33, with the longest propieces of the IL 1 family. IL 18 and IL 37 belong to the IL 18 subfamily and contain smaller propieces than IL 1 and IL-33. Since IL 37 binds to the IL 18Rα chain it is part of the IL 18 subfamily, however it remains to be elucidated how the propiece of IL 37 is removed. IL 36α, β, and γ as well as IL 36 Ra belong to the IL 36 subfamily. In addition, IL 38 likely belongs to this family since it has the ability to bind to the IL 36R. The IL 36 subfamily has the shortest propiece. The one member of the IL 1 family that cannot be categorized in these subfamilies is IL 1 receptor antagonist (IL 1Ra), which has a signal peptide and is readily secreted. In the present review we will describe the biological functions of the IL-1F members and new insights in their biology.

The inflammasome: pathways linking psychological stress, depression, and systemic illnesses

Stress is a common occurrence in everyday life and repeated or traumatic stress can be a precipitating factor for illnesses of the central nervous system, as well as peripheral organ systems. For example, severe or long-term psychological stress can not only induce depression, a leading illness worldwide, but can also cause psychosomatic diseases such as asthma and rheumatoid arthritis. Related key questions include how psychological stress influences both brain and peripheral systems, and what detection mechanisms underlie these effects? A clue is provided by the discovery of the pathways underlying the responses to host "danger" substances that cause systemic diseases, but can also contribute to depression. The inflammasome is a protein complex that can detect diverse danger signals and produce the accompanying immune-inflammatory reactions. Interestingly, the inflammasome can detect not only pathogen-associated molecules, but also cell damage-associated molecules such as ATP. Here, we propose a new inflammasome hypothesis of depression and related comorbid systemic illnesses. According to this hypothesis, the inflammasome is a central mediator by which psychological and physical stressors can contribute to the development of depression, and as well as a bridge to systemic diseases. This hypothesis includes an explanation for how psychological stress can influence systemic diseases, and conversely how systemic diseases can lead to psychiatric illnesses. The evidence suggests that the inflammasome may be a new target for the development of treatments for depression, as well as psychosomatic and somato-psycho diseases.

Inflammatory cytokines in depression: neurobiological mechanisms and therapeutic implications

Mounting evidence indicates that inflammatory cytokines contribute to the development of depression in both medically ill and medically healthy individuals. Cytokines are important for development and normal brain function, and have the ability to influence neurocircuitry and neurotransmitter systems to produce behavioral alterations. Acutely, inflammatory cytokine administration or activation of the innate immune system produces adaptive behavioral responses that promote conservation of energy to combat infection or recovery from injury. However, chronic exposure to elevated inflammatory cytokines and persistent alterations in neurotransmitter systems can lead to neuropsychiatric disorders and depression. Mechanisms of cytokine behavioral effects involve activation of inflammatory signaling pathways in the brain that results in changes in monoamine, glutamate, and neuropeptide systems, and decreases in growth factors, such as brain-derived neurotrophic factor. Furthermore, inflammatory cytokines may serve as mediators of both environmental (e.g. childhood trauma, obesity, stress, and poor sleep) and genetic (functional gene polymorphisms) factors that contribute to depression's development. This review explores the idea that specific gene polymorphisms and neurotransmitter systems can confer protection from or vulnerability to specific symptom dimensions of cytokine-related depression. Additionally, potential therapeutic strategies that target inflammatory cytokine signaling or the consequences of cytokines on neurotransmitter systems in the brain to prevent or reverse cytokine effects on behavior are discussed.

Interleukin-1 beta converting enzyme is necessary for development of depression-like behavior following intracerebroventricular administration of lipopolysaccharide to mice

Background

Interleukin-1 beta converting enzyme (ICE, caspase 1) is a cysteine protease that processes immature pro-IL-1β into active mature IL-1β. IL-1β is a pro-inflammatory cytokine that mediates many of the physiological and behavioral responses to inflammation. Genetic deletion of ICE has previously been shown to prevent some negative physiologic responses to lipopolysaccharide (LPS)-induced inflammation.

Methods

Here we used a preclinical murine model to test the hypothesis that ICE is necessary for development of depression-like behaviors following intracerebroventricular (ICV) treatment with LPS. Adult male ICE knockout (ICE KO) and congenic wild-type C57BL/6 J (WT) mice were administered LPS either ICV at 100 ng/mouse or intraperitoneally (IP) at 830 μg/kg body weight or an equal volume of saline as controls. Mice were monitored up to 48 h after treatment for both sickness and depression-like behaviors.

Results

LPS given ICV induced a loss of body weight in both WT and ICE KO mice. This sickness response was similar between WT and ICE KO mice. As expected, LPS administered ICV increased immobility in the forced swim test (FST) and decreased sucrose preference in WT mice but no change in either of these two depression-like behaviors was observed in ICE KO mice. Expression of TNF-α and CD11b in brain was lower in ICE-KO mice at 24 h following ICV administration of LPS compared to WT mice. In contrast, when LPS was given systemically, sickness response, depression-like behaviors, and expression of these genes were similar between the two strains of mice.

Conclusions

These findings indicate that ICE plays a specific role in depression-like behavior induced by a central inflammatory stimuli even though it is not required when LPS is administered systemically.

The effects of central pro-and anti-inflammatory immune challenges on depressive-like behavior induced by chronic forced swim stress in rats

Although increasing evidence demonstrates that both chronic stressors and inflammatory immune activation contribute to pathophysiology and behavioral alterations associated with major depression, little is known about the interaction effect of central inflammatory immune activation and stress on depressive-like behavior. Our previous work has shown that 14-day chronic forced swim stress induces significant depressive-like behavior. The present investigation assessed whether pro-inflammatory cytokine and anti-inflammatory cytokine challenges have differential interaction effect on depressive-like behavior induced by chronic forced swim stress in rats. The pro-inflammatory and anti-inflammatory immune challenges were achieved respectively by central administration of lipopolysaccharide (LPS), a pro-inflammatory cytokine inducer, and interleukin-10 (IL-10), an anti-inflammatory cytokine. It was found that either central LPS treatment alone or chronic forced swim stress alone significantly induced depressive-like behavior, including reduced body weight gain, reduced saccharin preference and reduced locomotor activity. However, there was no significant synergistic or additive effect of central LPS treatment and stress on depressive-like behavior. LPS treatment did not exacerbate the depressive-like behavior induced by forced swim stress. Nevertheless, IL-10 reversed depressive-like behavior induced by forced swim stress, a finding indicating that IL-10 has antidepressant effect on behavioral depression induced by stress. The present findings provide new insight into the complexity of the immunity-inflammation hypothesis of depression.

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Microglial activation, increased TNF and SERT expression in the prefrontal cortex define stress-altered behaviour in mice susceptible to anhedonia

A chronic stress paradigm comprising exposure to predation, tail suspension and restraint induces a depressive syndrome in C57BL/6J mice that occurs in some, but not all, animals. Here, we sought to extend our behavioural studies to investigate how susceptibility (sucrose preference<65%) or resilience (sucrose preference>65%) to stress-induced anhedonia affects the 5HT system and the expression of inflammation-related genes. All chronically stressed animals, displayed increased level of anxiety, but susceptible mice exhibited an increased propensity to float in the forced swim test and demonstrate hyperactivity under stressful lighting conditions. These changes were not present in resilient or acutely stressed animals. Compared to resilient animals, susceptible mice showed elevated expression of tumour necrosis factor alpha (TNF) and the 5-HT transporter (SERT) in the pre-frontal area. Enhanced expression of 5HT(2A) and COX-1 in the pre-frontal area was observed in all stressed animals. In turn, indoleamine-2,3-dioxygenase (IDO) was significantly unregulated in the raphe of susceptible animals. At the cellular level, increased numbers of Iba-1-positive microglial cells were also present in the prefrontal area of susceptible animals compared to resilient animals. Consequently, the susceptible animals display a unique molecular profile when compared to resilient, but anxious, animals. Unexpectedly, this altered profile provides a rationale for exploring anti-inflammatory, and possibly, TNF-targeted therapy for major depression.

Lack of pro-inflammatory cytokine mobilization predicts poor prognosis in patients with acute heart failure

AIMS

The aim of this study was to gain insight in the inflammatory response in acute heart failure (AHF) by assessing (1) plasma cytokine profiles and (2) prognostic value of circulating cytokines in AHF patients.

METHODS AND RESULTS

Plasma levels of 26 cytokines were quantified by multiplex protein arrays in 36 patients with congestive AHF, characterized by echocardiographic, radiologic, and clinical examinations on admission, during hospitalization and at discharge. Recurrent AHF leading to death or readmission constituted the combined end point, and all patients were followed for 120 days after discharge. Levels of 15 of the measured cytokines were higher in AHF than in healthy subjects (n=22) on admission. Low levels of MCP-1, IL-1β and a low IL-1β/IL-1ra ratio predicted fatal and non-fatal AHF within 120 days. Patients with low circulating levels of IL-1β had lower left ventricular ejection fraction and higher levels of N-terminal pro-B-type natriuretic peptide, while patients with low levels of MCP-1 had higher E/E' and inferior caval vein diameter, than patients with high levels.

CONCLUSION

Immune activation, reflected in increased cytokine levels, is present in AHF patients. Interestingly, failure to increase secretion of IL-1β and MCP-1 during AHF is associated with poor outcome.

Interleukin-1β inhibits the differentiation of hippocampal neural precursor cells into serotonergic neurons

Interleukin-1 beta (IL-1β) is one of pro-inflammatory cytokines. Recent studies have shown that IL-1β impairs hippocampal neurogenesis, mediates proliferation and differentiation of multipotent neural precursor cells (NPCs), and exerts effects of anti-proliferation, anti-neurogenesis, and pro-gliogenesis on embryonic hippocampal NPCs. The aim of this study was to examine the effect of IL-1β on the differentiation of hippocampal NPCs into functional serotonergic neurons, which play important roles in the pathophysiology and treatment of depression. Hippocampal NPCs were prepared from the hippocampus of neonatal rats (within 24h after birth). After three passages and phenotyping, hippocampal NPCs were cultured in a differentiating medium with various concentrations (5, 10, and 20 ng/mL) of IL-1β for 7 days. At the endpoint, the serotonergic differentiation of hippocampal NPCs in IL-1β-treated cultures decreased in a dose-dependent manner and this effect was blocked by IL-1ra, an IL-1 receptor antagonist capable of blocking the effects of IL-1 by binding to the same receptor (IL-1R1) without triggering signaling; serotonin in the lysate of the differentiated hippocampal NPCs decreased in IL-1β-treated cultures; and levels of Bcl-2 and phosphorylated extracellular-regulated kinase (pERK) were also lower in differentiated hippocampal NPCs with IL-1β treatment. These results support the hypothesis that IL-1β is an important factor in the stress-associated neuropathology and psychopathology and has relevance to the treatment of depressive symptoms in patients with depression.