Interleukin-1 receptor defect in autoimmune NZB mouse brain

Intermittent hypoxia exacerbated depressive and anxiety-like behaviors in the bleomycin-induced pulmonary fibrosis mice

Depression and anxiety are prevalent in patients with idiopathic pulmonary fibrosis (IPF). Recent researchers reveal that intermittent hypoxia (IH) increases the severity of bleomycin (BLM)-induced lung injury. However, experimental studies dealing with anxiety- and depression-like behavior in animal models of BLM-induced pulmonary fibrosis in a combination of IH are lacking, hence, this study aimed to investigate that. In this study, 80 C57BL/6J male mice were intratracheally injected with BLM or normal saline at day0 and then exposed to IH (alternating cycles of FiO₂ 21% for 60s and FiO₂ 10% for 30s, 40 cycles/hour, 8hours/day) or intermittent air (IA) for 21 days. Behavioral tests, including open field test (OFT), sucrose preference test (SPT) and tail suspension test (TST), were detected from day22 to day26. This study found that pulmonary fibrosis developed and lung inflammation were activated in BLM-induced mice, which were potentiated by IH. Significant less time in center and less frequency of entries in the centre arena in OFT were observed in BLM treated mice, and IH exposure further decreased that. Marked decreased percent of sucrose preference in SPT, and significant increased immobility time of the TST were detected in BLM treated mice and IH widen the gaps. The expression of ionized calcium-binding adaptor molecule (Iba1) was activated in the hippocampus of BLM instillation mice and IH enlarged it. Moreover, a positive correlation between hippocampal microglia activation and inflammatory factors was observed. Our results demonstrated that IH exacerbated depressive and anxiety-like behaviors in the BLM-induced pulmonary fibrosis mice. The changes in pulmonary inflammation-hippocampal microglia activation may be a potential mechanism in this phenomenon, which can be researched in future.

Neurogenic hypothesis of positive psychology in stress-induced depression: Adult hippocampal neurogenesis, neuroinflammation, and stress resilience

Stress is an important risk factor for depression. Emerging evidence supports the hypothesis that stress-mediated neuroinflammation destroys brain function and leads to anxiety-like and depression-like behaviors. Previous studies of stress-induced depression have mainly focused on pathological damage; however, the rise of positive psychology has attracted the interest of many researchers in environmental enrichment to promote stress resilience. The hippocampus is one of the most severely damaged brain regions in stress-induced depression. In addition, the hippocampus is one of the most unique regions in the brain, as new neurons are produced in the adult hippocampus, a process known as adult hippocampal neurogenesis (AHN). AHN is an important core component of the neurogenic hypothesis and has also become a major innovative breakthrough in positive psychology, in which environmental enrichment mediates stress resilience. Neuroinflammation, by activating microglia and releasing some proinflammatory cytokines, is increasingly shown to be one of the key determinant pathophysiological factors that negatively affects AHNand cognitive reserve. AHN is mainly related to remodeling stress response mechanisms, such as memory clearing, emotional control, and pattern separation, suggesting that a correlation may exist between neuroinflammation and AHN in stress resilience. Therefore, we summarized the previous research results to systematically expound on the relationship between AHN, stress resilience, and neuroinflammation. We hope this neurogenic hypothesis of positive psychology in stress-induced depression will provide a new perspective for the study of depression and antidepressant therapy.

Neuroprotection in Schizophrenia and Its Therapeutic Implications

Schizophrenia is a chronic and debilitating mental disorder. The persisting negative and cognitive symptoms that are unresponsive to pharmacotherapy reveal the impairment of neuroprotective aspects of schizophrenia. In this review, of the several neuroprotective factors, we mainly focused on neuroinflammation, neurogenesis, and oxidative stress. We conducted a narrative and selective review. Neuroinflammation is mainly mediated by pro-inflammatory cytokines and microglia. Unlike peripheral inflammatory responses, neuroinflammation has a role in various neuronal activities such as neurotransmission neurogenesis. The cross-talk between neuroinflammation and neurogenesis usually has beneficial effects in the CNS under physiological conditions. However, uncontrolled and chronic neuroinflammation exert detrimental effects such as neuronal loss, inhibited neurogenesis, and excessive oxidative stress. Neurogenesis is also a major component of neuroprotection. Adult neurogenesis mainly occurs in the hippocampal region, which has an important role in memory formation and processing. Impaired neurogenesis and an ineffective response to antipsychotics may be thought to indicate a deteriorating course of schizophrenia. Oxidative stress and excessive dopaminergic neurotransmission may create a vicious cycle and consequently disturb NMDA receptor-mediated glutamatergic neurotransmission. Based on the current evidences, several neuroprotective therapeutic approaches have been reported to be efficacious for improving psychopathology, but further longitudinal and large-sample based studies are needed.

The role of pro-inflammatory cytokines in neuroinflammation, neurogenesis and the neuroendocrine system in major depression

Cytokines are pleiotropic molecules with important roles in inflammatory responses. Pro-inflammatory cytokines and neuroinflammation are important not only in inflammatory responses but also in neurogenesis and neuroprotection. Sustained stress and the subsequent release of pro-inflammatory cytokines lead to chronic neuroinflammation, which contributes to depression. Hippocampal glucocorticoid receptors (GRs) and the associated hypothalamus-pituitary-adrenal (HPA) axis have close interactions with pro-inflammatory cytokines and neuroinflammation. Elevated pro-inflammatory cytokine levels and GR functional resistance are among the most widely investigated factors in the pathophysiology of depression. These two major components create a vicious cycle. In brief, chronic neuroinflammation inhibits GR function, which in turn exacerbates pro-inflammatory cytokine activity and aggravates chronic neuroinflammation. On the other hand, neuroinflammation causes an imbalance between oxidative stress and the anti-oxidant system, which is also associated with depression. Although current evidence strongly suggests that cytokines and GRs have important roles in depression, they are essential components of a whole system of inflammatory and endocrine interactions, rather than playing independent parts. Despite the evidence that a dysfunctional immune and endocrine system contributes to the pathophysiology of depression, much research remains to be undertaken to clarify the cause and effect relationship between depression and neuroinflammation.

Interleukin-6 facilitates lipopolysaccharide-induced disruption in working memory and expression of other proinflammatory cytokines in hippocampal neuronal cell layers

Proinflammatory cytokines inhibit learning and memory but the significance of interleukin-6 (IL-6) in acute cognitive deficits induced by the peripheral innate immune system is not known. To examine the functional role of IL-6 in hippocampus-mediated cognitive impairments associated with peripheral infections, C57BL6/J (IL-6(+/+)) and IL-6 knock-out (IL-6(-/-)) mice were trained in a matching-to-place version of the water maze. After an acquisition phase, IL-6(+/+) mice injected intraperitoneally with lipopolysaccharide (LPS) exhibited deficits in working memory. However, IL-6(-/-) mice were refractory to the LPS-induced impairment in working memory. To determine the mechanism by which IL-6 deficiency conferred protection from disruption in working memory, plasma IL-1beta and tumor necrosis factor alpha (TNFalpha), c-Fos immunoreactivity in the nucleus of the solitary tract (NTS), and steady-state levels of IL-1beta and TNFalpha mRNA in neuronal layers of the hippocampus were determined in IL-6(+/+) and IL-6(-/-) mice after injection of LPS. Plasma IL-1beta and TNFalpha and c-Fos immunoreactivity in the NTS were increased similarly in IL-6(+/+) and IL-6(-/-) mice after LPS, indicating high circulating levels of IL-1beta and TNFalpha and activation of vagal afferent pathways were not sufficient to disrupt working memory in the absence of IL-6. However, the LPS-induced upregulation of IL-1beta and TNFalpha mRNA that was evident in hippocampal tissue of IL-6(+/+) mice was greatly attenuated or entirely absent in IL-6(-/-) mice. Collectively, these data suggest that humoral and neural immune-to-brain communication pathways are intact in IL-6-deficient mice but that, in the absence of IL-6, the central cytokine compartment is hyporesponsive.

Peripheral lipopolysaccharide administration impairs two-way active avoidance conditioning in C57BL/6J mice

Peripheral administration of lipopolysaccharide (LPS) or interleukin-1 (IL-1) may lead to alterations of CNS function and behavioral changes designated "sickness behavior." Further, some experiments show evidence of LPS- and cytokine-mediated alterations in learning and memory. The current series of experiments examined the effects of a single or repeated intraperitoneal LPS injections, at a number of doses and time points before or after test sessions, on behavior in a two-way active avoidance conditioning paradigm. Subjects were able to avoid the mild shock stimulus, escape it, or fail to respond to it. Subjects treated with LPS at many, but not all, of the time points sampled showed impaired learning, by exhibiting significantly fewer avoidance responses than controls. Furthermore, an LPS-induced increase in non-cued inter-trial interval crossings was observed during the later days of testing, suggesting that a greater percentage of their avoidance responses was not conditioned and their behavior was less efficient. Taken together, the results suggest that LPS-treated animals showed a diminished association between conditioned stimulus (CS) and unconditioned stimulus (US). These results support the theory that peripheral immune stimuli may induce deleterious effects on learning, and extend the work to a negatively reinforced operant procedure.

Animal models of neuroimmune interactions in inflammatory diseases

Animal models have been used successfully to study various aspects of neural-immune interactions. Although different approaches carry certain advantages and disadvantages, current high sensitivity screening and manipulation methods coupled with molecular and genetic approaches can be successfully used to tease out the neural pathways that regulate inflammatory disease and the effects of immune molecules, such as interleukins, on neuronal function and pathology. Newer methodologies that measure gene expression of thousands of genes will in the future add to the ability to evaluate complex systems interactions in whole animal models. This review addresses the advantages and disadvantages of some of these approaches in the context of application to neural-immune interactions.

[Psychoimmunology: a questionable model?]

INTRODUCTION

The concept of "psychoimmunology" that had long been supported by clinical observation and common sense, has acquired a sound scientific basis in the last two decades. The discovery of neuro-mediators and cytokines and their receptors shared by the central nervous system and the immune system has prompted research work using reliable methodologies to study the relationship between a 'hard' scientific field, such as immunology, and a 'soft' one, such as the behavioral sciences.

CURRENT KNOWLEDGE AND KEY POINTS

The complexity of the studies on stress and immunity lies upon the choice of immunological measurements and the development of reproducible stress protocols. Models of stress in experimental animals may address acute versus chronic stress, and individual versus social stress. In humans, typical situations such as academic exams, and care given to patients with dementia, for instance, have been chosen to study large groups of subjects. The development of self-questionnaires for a reliable evaluation of stress and its consequences has led to more accurate measurements of psychosocial events. In animals, acute stress usually drives the immune response towards a Th2, grossly 'immunosuppressive,' profile. In humans, acute stress associates an endocrine response (characterized by glucocorticoid secretion and hyperprolectinemia) with an immunosuppression. Chronic stress is more likely to induce a range of effects, depending on the capacity of the subject to cope with stress, and on his/her social environment. Among the numerous mediators of the hypothalamo-pituitary cascade, Corticotropin Releasing Hormone is a key factor in the stress-immunity relationship. Several studies in humans have demonstrated the influence of stress on the susceptibility to infections (including HIV infection) and on survival in malignant diseases. In autoimmune diseases, a high prevalence of depression, as well as a particular sensitivity to stressful events, seem to modify the course of conditions such as systemic lupus erythematosus, rhumatoid arthritis or Sjögren's disease. The relationship between stress and diseases is based on the pathogenic model which involves the following chain of events: stressor, reaction to stress, neuro-endocrine changes, abnormalities of the immune response, and occurrence (or aggravation) of a disease. The evolution from health to disease could be associated, at least partially, with a 'passive' immunosuppressive mode of response, mediated by the pituitary-adrenal axis, typically the opposite of an 'active,' immunostimulant mode of response, mediated by adrenergic stimulation.

FUTURE PROSPECTS AND PROJECTS

Concept-related problems still remain to be solved: adaptation to stress ('coping'), is both genetically and socially mediated; the significance and interpretation of stress-related abnormalities and their precise involvement in the pathogenesis of diseases may be ambiguous. However, available epidemiological and pathophysiological evidence is currently sufficient to allow physicians in their everyday practice to take stress and depression into account in order to markedly improve the prognosis of many diseases related to immune responses. Prospective studies of neuropsychological intervention, using either pharmacologic or behavioral approaches, should be made to provide the necessary rational to a psychoimmunological management of patients.