IL-4 Knock Out Mice Display Anxiety-Like Behavior.

Inflammation is a recognized antecedent and coincident factor when examining the biology of anxiety. Little is known, however, about how reductions in endogenous anti-inflammatory mediators impact anxiety. Therefore, mood- cognition- and anxiety-associated/like behaviors were examined in IL-4 knock out (KO) mice and wild-type (WT) mice. In comparison to WT mice, IL-4 KO mice demonstrated decreased burrowing and increased social exploration. No differences were seen in forced swim or saccharine preference testing. IL-4 KO mice had similar performance to WT mice in the Morris water maze and during object location and novel object recognition. In the elevated zero-maze, IL-4 KO mice, in comparison to WT mice, demonstrated anxiety-like behavior. Anxiety-like behavior in IL-4 KO mice was not observed, however, during open-field testing. Taken together, these data indicate that IL-4 KO mice display state, but not trait, anxiety suggesting that reductions in endogenous anti-inflammatory bioactives can engender subtypes of anxiety.

Adenosine through the A2A adenosine receptor increases IL-1ß in the brain contributing to anxiety.

Anxiety is one of the most commonly reported psychiatric conditions, but its pathogenesis is poorly understood. Ailments associated with activation of the innate immune system, however, are increasingly linked to anxiety disorders. In adult male mice, we found that adenosine doubled caspase-1 activity in brain by a pathway reliant on ATP-sensitive potassium (KATP) channels, protein kinase A (PKA) and the A2A adenosine receptor (AR). In addition, adenosine-dependent activation of caspase-1 increased interleukin (IL)-1ß in the brain by 2-fold. Peripheral administration of adenosine in wild-type (WT) mice led to a 2.3-fold increase in caspase-1 activity in the amygdala and to a 33% and 42% reduction in spontaneous locomotor activity and food intake, respectively, that were not observed in caspase-1 knockout (KO), IL-1 receptor type 1 (IL-1R1) KO and A2A AR KO mice or in mice administered a caspase-1 inhibitor centrally. Finally, adenosine administration increased anxiety-like behaviors in WT mice by 28% in the open field test and by 55% in the elevated zero-maze. Caspase-1 KO mice, IL-1R1 KO mice, A2A AR KO mice and WT mice treated with the KATP channel blocker, glyburide, were resistant to adenosine-induced anxiety-like behaviors. Thus, our results indicate that adenosine can act as an anxiogenic by activating caspase-1 and increasing IL-1ß in the brain.

Sickness behavior induced by endotoxin can be mitigated by the dietary soluble fiber, pectin, through up-regulation of IL-4 and Th2 polarization.

Peripheral activation of the immune system by infectious agents triggers the brain-cytokine system causing sickness behaviors which profoundly impact well-being. Dietary fiber is a beneficial foodstuff that, from a gastrointestinal tract perspective, exists in both insoluble and soluble forms. We show that a diet rich in soluble fiber protects mice from endotoxin-induced sickness behavior by polarizing mice Th2 when compared to a diet containing only insoluble fiber. Mice fed soluble fiber became less sick and recovered faster from endotoxin-induced sickness behaviors than mice fed insoluble fiber. In response to intraperitoneal endotoxin, mice fed soluble fiber had up-regulated IL-1RA and reduced IL-1beta and TNF-alpha in the brain as compared to mice fed insoluble fiber. Importantly, mice fed soluble fiber had a basal increase in IL-4 in the ileum and spleen which was absent in MyD88 knockout mice. Con-A stimulated splenocytes from mice fed soluble fiber showed increased IL-4 and IL-5 and decreased IL-2, IL-12 and IFN-gamma when compared to mice fed insoluble fiber. Likewise, endotoxin-stimulated macrophages from mice fed soluble fiber demonstrated decreased IL-1beta, TNF-alpha, IFN-gamma, IL-12 and nitrate and increased IL-1RA, arginase 1 and Ym1 when compared to mice fed insoluble fiber. Finally, the behavioral protection afforded by feeding mice soluble fiber was reduced in IL-4 knockout mice, as was the impact of soluble fiber on Con-A stimulated splenocytes and endotoxin activated macrophages. These data show that a diet rich in soluble fiber protects against endotoxin-induced sickness behavior by polarizing mice Th2 and promoting alternative activation of macrophages.

Switching from a high-fat cellulose diet to a high-fat pectin diet reverses certain obesity-related morbidities.

BACKGROUND: Reducing caloric intake is a proven intervention for mitigating and modulating morbidities associated with overnutrition. Caloric restriction is difficult to affect clinically, therefore, dietary interventions that ameliorate the adverse consequences of overnutrition in the presence of a high-calorie diet would be of value. METHODS: Mice were fed an obesogenic diet containing 60% fat + 10% cellulose (HFC), or a control diet containing 10% fat + 10% cellulose (LFC) for 12 wks. Subgroups of mice were then switched from HFC to each of the following diets for an additional 5 wks: 1) 60% fat + 10% pectin (HFP), 2) LFC or 3) 10% fat + 10% pectin (LFP). To test for statistical differences, one-way or two-way ANOVAs were used with or without repeated measurements as needed. RESULTS: In comparison to HFC, HFP prevented additional weight gain while LFC and LFP triggered weight loss of 22.2 and 25.4%, respectively. Mice continued on HFC experienced a weight increase of 26% during the same 5 wk. interval. After 12 wks, HFC decreased mouse locomotion by 18% when compared to control diet, but a diet switch to LFC or LFP restored mouse movement. Importantly, HFP, LFC, and LFP reduced fasting blood glucose when compared to HFC. Likewise, HFP, LFC and LFP improved glucose tolerance and decreased fatty liver by 37.9, 49.8, 53.6 and 20.2%, 37.2, 43.7%, respectively. CONCLUSIONS: Taken together, the results indicate that the dietary fiber pectin can mitigate some adverse consequences of overnutrition even in the presence of high-fat.

The saturated fatty acid, palmitic acid, induces anxiety-like behavior in mice.

OBJECTIVES: Excess fat in the diet can impact neuropsychiatric functions by negatively affecting cognition, mood and anxiety. We sought to show that the free fatty acid (FFA), palmitic acid, can cause adverse biobehaviors in mice that last beyond an acute elevation in plasma FFAs. METHODS: Mice were administered palmitic acid or vehicle as a single intraperitoneal (IP) injection. Biobehaviors were profiled 2 and 24 h after palmitic acid treatment. Quantification of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their major metabolites was performed in cortex, hippocampus and amygdala. FFA concentration was determined in plasma. Relative fold change in mRNA expression of unfolded protein response (UPR)-associated genes was determined in brain regions. RESULTS: In a dose-dependent fashion, palmitic acid rapidly reduced mouse locomotor activity by a mechanism that did not rely on TLR4, MyD88, IL-1, IL-6 or TNFα but was dependent on fatty acid chain length. Twenty-four hours after palmitic acid administration mice exhibited anxiety-like behavior without impairment in locomotion, food intake, depressive-like behavior or spatial memory. Additionally, the serotonin metabolite 5-HIAA was increased by 33% in the amygdala 24h after palmitic acid treatment. CONCLUSIONS: Palmitic acid induces anxiety-like behavior in mice while increasing amygdala-based serotonin metabolism. These effects occur at a time point when plasma FFA levels are no longer elevated.

Fasting Induces IL-1 Resistance and Free-Fatty Acid-Mediated Up-Regulation of IL-1R2 and IL-1RA.

OBJECTIVE: Weight-loss is a near societal obsession and many diet programs use significant calorie restriction including fasting/short term starvation to generate rapid effects. Fasting is also a well-recognized cause of immunosuppression especially within the innate immune system. In this study, we sought to determine if the IL-1 arm of the neuroimmune system was down-regulated by a 24 h fast and how fasting might generate this effect. DESIGN: Mice were allowed ad libitum access to food or had food withheld for 24 h. Expression of the endogenous IL-1 antagonists, IL-1 receptor type 2 (IL-1R2), and IL-1 receptor antagonist (IL-1RA) was determined as were sickness behaviors before and after IL-1ß administration. RESULTS: Fasting markedly increased gene expression of IL-1R2 (83-fold in adipose tissue, 9.5-fold in liver) and IL-1RA (68-fold in liver). Fasted mice were protected from IL-1ß-induced weight-loss, hypoglycemia, loss of locomotor, and social anxiety. These protections were coupled to a large positive interaction of fasting and IL-1ß on IL-1R2 gene expression in adipose tissue and liver (2.6- and 1.6-fold, respectively). Fasting not only increased IL-1RA and IL-1R2 protein 2.5- and 3.2-fold, respectively, in liver but also increased IL-1R2 1.8-fold in adipose tissue. Fasting, in turn, triggered a 2.4-fold increase in plasma free-fatty acids (FFAs) and a 2.1-fold increase in plasma corticosterone. Inhibition, of glucocorticoid action with mifepristone did not impact fasting-dependent IL-1R2 or IL-1RA gene expression. Administration of the FFA, palmitate, to mice increased liver IL-1R2 and IL-1RA gene expression by 14- and 11-fold, respectively. CONCLUSION: These findings indicate that fasting augments expression of endogenous IL-1 antagonists inducing IL-1 resistance. Fasting-induced increases in plasma FFAs appears to be a signal that drives immunosuppression during fasting/short term starvation.

Macrophages make me sick: how macrophage activation states influence sickness behavior.

The macrophage (MΦ) is an essential cellular first responder in the innate immune system, sensing, alerting, removing and destroying intrinsic and extrinsic pathogens. While congenital aplasia of granulocytes, T or B lymphocytes leads to serious disease, lack of MΦs is incompatible with life. The MΦ, however, is not a monomorphic entity. These constructers, repairers and defenders of the body are diverse in form and function. What controls MΦ phenotype is beginning to be understood and involves a complex interplay of origination, location and microenvironment. Common to all MΦ developmental pathways are pro-inflammatory and anti-inflammatory cytokines. MΦs respond to these bioactives in distinct ways developing recently recognized activation phenotypes that canonically support bacterial clearance (classical activation), parasite defense/tissue repair (alternative activation) and anti-inflammation (deactivation). Critically, the same cytokines which orchestrate immune defense and homeostasis dramatically impact sense of well being and cognition by eliciting sickness symptoms. Such behaviors are the manifestation of pro/anti-inflammatory cytokine action in the brain and are a direct consequence of MΦ function. This review describes the "new" archetypal MΦ activation states, delineates microglia phenotypic plasticity and explores the importance of these macrophage activation states to sickness behavior.

Fasting induces an anti-inflammatory effect on the neuroimmune system which a high-fat diet prevents.

The neuroimmunological and behavioral consequences of a high-fat diet (HFD) are not well delineated. This is especially true when short term (24 h) fasting is used as a physiologic stressor. In this study, we examined the impact of a HFD on learning and memory and depressive-like behaviors to understand how fasting impacts neuroimmunity and whether obesity modulates the response. Mice were fed diets containing either 10% (low-fat diet (LFD) mice) or 60% (HFD mice) calories from fat for 10-12 weeks. Gene transcripts for 26 pro-/anti-inflammatory cytokines and markers of macrophage activation were examined in adipose tissue and whole brain. Mouse learning and memory (spontaneous alternation, novel object) and depressive-like behaviors (saccharin preference, burrowing, forced swim) were studied in the fed and fasted state as were gene transcripts for F4/80, CD11b, interleukin-1α (IL-1α), IL-1ß, IL-1R1, IL-1R2, IL-1RA, IL-6 and tumor necrosis factor-α in cortex, hippocampus and hypothalamus. In the fed state, HFD mice compared to LFD mice had reduced locomotor activity, and were adverse to saccharin and burrowed less. After fasting, LFD mice vs. HFD mice lost 18 vs. 5% of their body weight, respectively. In addition, HFD mice failed to downregulate gene transcripts for the myeloid-cell associated proteins F4/80, CD11b and IL-1α in the brain, failed to appropriately explore a novel object, failed to reduce locomotor activity and had increased saccharin consumption and burrowing. These data indicate that fasting induces an anti-inflammatory effect on the neuroimmune system which a HFD prevents. This breakdown appears linked to the IL-1 system because of the association of this cytokine with memory and learning.