Social transmission of inflammation in mice.

The ability to detect and respond to sickness in others promotes survival. Here we show that mouse dams respond to immune challenged pups by mirroring their inflammatory response. Dams with pups subjected to immune challenge displayed a marked induction of inflammatory mediators in both the brain and the periphery, accompanied by an increase in maternal behaviors and corticosterone levels. This social transmission of inflammation did not require physical contact, and it contributed to the stress hormone response in the dams. In adult dyads, interaction with an immune challenged cagemate did not elicit robust inflammatory signaling but induced an increased responsiveness to a subsequent immune challenge. The identification of social transmission of inflammation, or inflammatory responsiveness, may open new avenues for research on social behavior, just like the description of similar phenomena such as observational fear and transmitted pain has done.

Melanocortin-4 receptors on neurons in the parabrachial nucleus mediate inflammation-induced suppression of food-seeking behavior.

Anorexia is a common symptom during infectious and inflammatory disease. Here we examined the role of melanocortin-4 receptors (MC4Rs) in inflammation-induced anorexia. Mice with transcriptional blockage of the MC4Rs displayed the same reduction of food intake following peripheral injection of lipopolysaccharide as wild type mice but were protected against the anorexic effect of the immune challenge in a test in which fasted animals were to use olfactory cues to find a hidden cookie. By using selective virus-mediated receptor re-expression we demonstrate that the suppression of the food-seeking behavior is subserved by MC4Rs in the brain stem parabrachial nucleus, a central hub for interoceptive information involved in the regulation of food intake. Furthermore, the selective expression of MC4R in the parabrachial nucleus also attenuated the body weight increase that characterizes MC4R KO mice. These data extend on the functions of the MC4Rs and show that MC4Rs in the parabrachial nucleus are critically involved in the anorexic response to peripheral inflammation but also contribute to body weight homeostasis during normal conditions.

Prostaglandin production in brain endothelial cells during the initiation of fever.

The initiation of fever has been a matter of controversy. Based on observations of little or no induction of prostaglandin synthesizing enzymes in the brain during the first phase of fever it was suggested that fever is initiated by prostaglandin released into the circulation from cells in the liver and lungs. Here we show in the mouse that prostaglandin synthesis is rapidly induced in the brain after immune challenge. These data are consistent with our recent findings in functional experiments that prostaglandin production in brain endothelial cells is both necessary and sufficient for the generation of all phases of fever.

Prostaglandin E2 Production by Brain Endothelial Cells and the Generation of Fever.

We recently demonstrated that prostaglandin production in brain endothelial cells is both necessary and sufficient for the generation of fever during systemic immune challenge. I here discuss this finding in light of the previous literature and point to some unresolved issues.

Prostaglandin production selectively in brain endothelial cells is both necessary and sufficient for eliciting fever.

Fever is known to be elicited by prostaglandin E2 acting on the brain, but its origin has remained disputed. We show in mice that selective deletion of prostaglandin synthesis in brain endothelial cells, but not in neural cells or myeloid cells, abolished fever induced by intravenous administration of lipopolysaccharide and that selective rescue of prostaglandin synthesis in brain endothelial cells reinstated fever. These data demonstrate that prostaglandin production in brain endothelial cells is both necessary and sufficient for eliciting fever.

Fever During Localized Inflammation in Mice Is Elicited by a Humoral Pathway and Depends on Brain Endothelial Interleukin-1 and Interleukin-6 Signaling and Central EP3 Receptors.

We examined the signaling route for fever during localized inflammation in male and female mice, elicited by casein injection into a preformed air pouch. The localized inflammation gave rise to high concentrations of prostaglandins of the E species (PGE2) and cytokines in the air pouch and elevated levels of these inflammatory mediators in plasma. There were also elevated levels of PGE2 in the cerebrospinal fluid, although there was little evidence for PGE2 synthesis in the brain. Global deletion of the PGE2 prostaglandin E receptor 3 (EP3) abolished the febrile response as did deletion of the EP3 receptor in neural cells, whereas its deletion on peripheral nerves had no effect, implying that PGE2 action on this receptor in the CNS elicited the fever. Global deletion of the interleukin-1 receptor type 1 (IL-1R1) also abolished the febrile response, whereas its deletion on neural cells or peripheral nerves had no effect. However, deletion of the IL-1R1 on brain endothelial cells, as well as deletion of the interleukin-6 receptor α on these cells, attenuated the febrile response. In contrast, deletion of the PGE2 synthesizing enzymes cyclooxygenase-2 and microsomal prostaglandin synthase-1 in brain endothelial cells, known to attenuate fever evoked by systemic inflammation, had no effect. We conclude that fever during localized inflammation is not mediated by neural signaling from the inflamed site, as previously suggested, but is dependent on humoral signaling that involves interleukin actions on brain endothelial cells, probably facilitating PGE2 entry into the brain from the circulation and hence representing a mechanism distinct from that at work during systemic inflammation.

Paracetamol analogues conjugated by FAAH induce TRPV1-mediated antinociception without causing acute liver toxicity.

Paracetamol, one of the most widely used pain-relieving drugs, is deacetylated to 4-aminophenol (4-AP) that undergoes fatty acid amide hydrolase (FAAH)-dependent biotransformation into N-arachidonoylphenolamine (AM404), which mediates TRPV1-dependent antinociception in the brain of rodents. However, paracetamol is also converted to the liver-toxic metabolite N-acetyl-p-benzoquinone imine already at therapeutic doses, urging for safer paracetamol analogues. Primary amine analogues with chemical structures similar to paracetamol were evaluated for their propensity to undergo FAAH-dependent N-arachidonoyl conjugation into TRPV1 activators both in vitro and in vivo in rodents. The antinociceptive and antipyretic activity of paracetamol and primary amine analogues was examined with regard to FAAH and TRPV1 as well as if these analogues produced acute liver toxicity. 5-Amino-2-methoxyphenol (2) and 5-aminoindazole (3) displayed efficient target protein interactions with a dose-dependent antinociceptive effect in the mice formalin test, which in the second phase was dependent on FAAH and TRPV1. No hepatotoxicity of the FAAH substrates transformed into TRPV1 activators was observed. While paracetamol attenuates pyrexia via inhibition of brain cyclooxygenase, its antinociceptive FAAH substrate 4-AP was not antipyretic, suggesting separate mechanisms for the antipyretic and antinociceptive effect of paracetamol. Furthermore, compound 3 reduced fever without a brain cyclooxygenase inhibitory action. The data support our view that analgesics and antipyretics without liver toxicity can be derived from paracetamol. Thus, research into the molecular actions of paracetamol could pave the way for the discovery of analgesics and antipyretics with a better benefit-to-risk ratio.

NF-κB signaling in tanycytes mediates inflammation-induced anorexia.

OBJECTIVES: Infections, cancer, and systemic inflammation elicit anorexia. Despite the medical significance of this phenomenon, the question of how peripheral inflammatory mediators affect the central regulation of food intake is incompletely understood. Therefore, we have investigated the sickness behavior induced by the prototypical inflammatory mediator IL-1ß. METHODS: IL-1ß was injected intravenously. To interfere with IL-1ß signaling, we deleted the essential modulator of NF-κB signaling (Nemo) in astrocytes and tanycytes. RESULTS: Systemic IL-1ß increased the activity of the transcription factor NF-κB in tanycytes of the mediobasal hypothalamus (MBH). By activating NF-κB signaling, IL-1ß induced the expression of cyclooxygenase-2 (Cox-2) and stimulated the release of the anorexigenic prostaglandin E2 (PGE2) from tanycytes. When we deleted Nemo in astrocytes and tanycytes, the IL-1ß-induced anorexia was alleviated whereas the fever response and lethargy response were unchanged. Similar results were obtained after the selective deletion of Nemo exclusively in tanycytes. CONCLUSIONS: Tanycytes form the brain barrier that mediates the anorexic effect of systemic inflammation in the hypothalamus.

Sagittal Alignment After Laminectomy Without Fusion as Treatment for Cervical Spondylotic Myelopathy: Follow-up of Minimum 4 Years Postoperatively.

OBJECTIVES: The aims of this study were to evaluate the incidence of sagittal malalignment including kyphosis following cervical laminectomy without fusion as treatment for cervical spondylotic myelopathy and to assess any correlation between malalignment and clinical outcome. STUDY DESIGN: Retrospective cohort study. METHODS: In all, 60 patients were followed up with conventional radiography at an average of 8 years postoperatively. The cervical lordosis (C2-C7 Cobb angle), C2-C7 sagittal vertical axis (cSVA) and C7 slope were measured on both preoperative and postoperative images. Patients completed a questionnaire covering Neck Disability Index (NDI), visual analogue scale for neck pain, and general health (EQ-5D). RESULTS: Mean C2-C7 Cobb angle was 8.6° (SD 9.0) preoperatively, 3.4° (10.7) postoperatively and 9.6° (14.5) at follow-up. Ultimately, 3 patients showed >20° cervical kyphosis. Mean cSVA was 16.3 mm (SD 10.2) preoperatively, 20.6 mm (11.8) postoperatively, and 31.6 mm (11.8) at follow-up. Mean C7 slope was 20.4° (SD 8.9) preoperatively, 18.4° (9.4) postoperatively, and 32.6° (10.2) at follow-up. The preoperative to follow-up increase in cSVA and C7 slope was statistically significant (both P < .0001), but not for cervical lordosis. The preoperative to follow-up change in cSVA correlated moderately with preoperative cSVA (r = 0.43, P = .002), as did the corresponding findings regarding C7 slope (r = 0.52, P = .0001). A comparison of radiographic measurements with clinical outcome showed no strong correlations. CONCLUSIONS: No preoperative to follow-up change in cervical lordosis was found in this group; 5.0% developed >20° kyphosis. No clear correlation between sagittal alignment and clinical outcome was shown.

The generation of immune-induced fever and emotional stress-induced hyperthermia in mice does not involve brown adipose tissue thermogenesis.

We examined the role of brown adipose tissue (BAT) for fever and emotional stress-induced hyperthermia. Wild-type and uncoupling protein-1 (UCP-1) knockout mice were injected with lipopolysaccharide intraperitoneally or intravenously, or subjected to cage exchange, and body temperature monitored by telemetry. Both genotypes showed similar febrile responses to immune challenge and both displayed hyperthermia to emotional stress. Neither procedure resulted in the activation of BAT, such as the induction of UCP-1 or peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) mRNA, or reduced BAT weight and triglyceride content. In contrast, in mice injected with a ß3 agonist, UCP-1 and PGC-1α were strongly induced, and BAT weight and triglyceride content reduced. Both lipopolysaccharide and the ß3 agonist, and emotional stress, induced UCP-3 mRNA in skeletal muscle. A ß3 antagonist did not attenuate lipopolysaccharide-induced fever, but augmented body temperature decrease and inhibited BAT activation when mice were exposed to cold. An α1 /α2b antagonist or a 5HT1A agonist, which inhibit vasoconstriction, abolished lipopolysaccharide-induced fever, but had no effect on emotional stress-induced hyperthermia. These findings demonstrate that in mice, UCP-1-mediated BAT thermogenesis does not take part in inflammation-induced fever, which is dependent on peripheral vasoconstriction, nor in stress-induced hyperthermia. However, both phenomena may involve UCP-3-mediated muscle thermogenesis.

IL-6R expressed on CNS vascular endothelial cells contributes to the development of experimental autoimmune encephalomyelitis in mice.

Experimental autoimmune encephalomyelitis (EAE) is the most common model for studying the molecular mechanisms of multiple sclerosis (MS). Here, we examined the CNS-restricted effects of classical interleukin (IL)-6 signaling on the development of EAE, using mice with cell-type specific deletion of the IL-6 receptor (IL-6R). We found that IL-6R deletion in CNS vascular endothelial cells, but not in microglia, ameliorated symptoms of EAE. The milder clinical symptoms in the gene-deleted mice were associated with less demyelination and immune cell infiltration/activation, and lower mRNA levels of the cytokines IL-17 and IL-1ß, as well as the cell adhesion molecules VCAM-1, ICAM-1 and ICAM-2 than what was seen in WT mice. These findings demonstrate that classical IL-6 signaling via endothelial cells of the CNS contributes substantially to the development of MS-like pathology, which should be taken into consideration when conceptualizing future therapeutic approaches.

Interleukin-1 reduces food intake and body weight in rat by acting in the arcuate hypothalamus.

A reduction in food intake is commonly observed after bacterial infection, a phenomenon that can be reproduced by peripheral administration of Gram-negative bacterial lipopolysaccharide (LPS) or interleukin-1beta (IL-1ß), a pro-inflammatory cytokine released by LPS-activated macrophages. The arcuate nucleus of the hypothalamus (ARH) plays a major role in food intake regulation and expresses IL-1 type 1 receptor (IL-1R1) mRNA. In the present work, we tested the hypothesis that IL-1R1 expressing cells in the ARH mediate IL-1ß and/or LPS-induced hypophagia in the rat. To do so, we developed an IL-1ß-saporin conjugate, which eliminated IL-R1-expressing neurons in the hippocampus, and micro-injected it into the ARH prior to systemic IL-1ß and LPS administration. ARH IL-1ß-saporin injection resulted in loss of neuropeptide Y-containing cells and attenuated hypophagia and weight loss after intraperitoneal IL-1ß, but not LPS, administration. In conclusion, the present study shows that ARH NPY-containing neurons express functional IL-1R1s that mediate peripheral IL-1ß-, but not LPS-, induced hypophagia. Our present and previous findings indicate that the reduction of food intake after IL-1ß and LPS are mediated by different neural pathways.

Acute maternal separation potentiates the gene expression and corticosterone response induced by inflammation.

Maternal care is crucial for infants and profoundly affects their responses to different kinds of stressors. Here, we examined how maternal separation affects inflammatory gene expression and the corticosterone response to an acute immune challenge induced by lipopolysaccharide (LPS; 40 µg/kg ip) in mouse pups, 8-9 days old. Maternal separation initially attenuated LPS-induced hypothalamic pro-inflammatory gene expression, but later, at 3 h after immune challenge, robustly augmented such gene expression and increased serum corticosterone levels. Providing the pups with a warm and soft object prevented the separation-induced augmented hypothalamic-pituitary-adrenal (HPA)-axis response. It also prevented the potentiated induction of some, but not all, inflammatory genes to a similar extent as did the dam. Our results show that maternal separation potentiates the inflammatory response and the resulting HPA-axis activation, which may have detrimental effects if separation is prolonged or repeated.

Motivational valence is determined by striatal melanocortin 4 receptors.

It is critical for survival to assign positive or negative valence to salient stimuli in a correct manner. Accordingly, harmful stimuli and internal states characterized by perturbed homeostasis are accompanied by discomfort, unease, and aversion. Aversive signaling causes extensive suffering during chronic diseases, including inflammatory conditions, cancer, and depression. Here, we investigated the role of melanocortin 4 receptors (MC4Rs) in aversive processing using genetically modified mice and a behavioral test in which mice avoid an environment that they have learned to associate with aversive stimuli. In normal mice, robust aversions were induced by systemic inflammation, nausea, pain, and κ opioid receptor-induced dysphoria. In sharp contrast, mice lacking MC4Rs displayed preference or indifference toward the aversive stimuli. The unusual flip from aversion to reward in mice lacking MC4Rs was dopamine dependent and associated with a change from decreased to increased activity of the dopamine system. The responses to aversive stimuli were normalized when MC4Rs were reexpressed on dopamine D1 receptor-expressing cells or in the striatum of mice otherwise lacking MC4Rs. Furthermore, activation of arcuate nucleus proopiomelanocortin neurons projecting to the ventral striatum increased the activity of striatal neurons in an MC4R-dependent manner and elicited aversion. Our findings demonstrate that melanocortin signaling through striatal MC4Rs is critical for assigning negative motivational valence to harmful stimuli.

The antipyretic effect of paracetamol occurs independent of transient receptor potential ankyrin 1-mediated hypothermia and is associated with prostaglandin inhibition in the brain.

The mode of action of paracetamol (acetaminophen), which is widely used for treating pain and fever, has remained obscure, but may involve several distinct mechanisms, including cyclooxygenase inhibition and transient receptor potential ankyrin 1 (TRPA1) channel activation, the latter being recently associated with paracetamol's propensity to elicit hypothermia at higher doses. Here, we examined whether the antipyretic effect of paracetamol was due to TRPA1 activation or cyclooxygenase inhibition. Treatment of wild-type and TRPA1 knockout mice rendered febrile by immune challenge with LPS with a dose of paracetamol that did not produce hypothermia (150 mg/kg) but is known to be analgetic, abolished fever in both genotypes. Paracetamol completely suppressed the LPS-induced elevation of prostaglandin E2 in the brain and also reduced the levels of several other prostanoids. The hypothermia induced by paracetamol was abolished in mice treated with the electrophile-scavenger N-acetyl cysteine. We conclude that paracetamol's antipyretic effect in mice is dependent on inhibition of cyclooxygenase activity, including the formation of pyrogenic prostaglandin E2, whereas paracetamol-induced hypothermia likely is mediated by the activation of TRPA1 by electrophilic metabolites of paracetamol, similar to its analgesic effect in some experimental paradigms.-Mirrasekhian, E., Nilsson, J. L. Å., Shionoya, K., Blomgren, A., Zygmunt, P. M., Engblom, D., Högestätt, E. D., Blomqvist, A. The antipyretic effect of paracetamol occurs independent of transient receptor potential ankyrin 1-mediated hypothermia and is associated with prostaglandin inhibition in the brain.

Neural Mechanisms of Inflammation-Induced Fever.

Fever is a common symptom of infectious and inflammatory disease. It is well-established that prostaglandin E2 is the final mediator of fever, which by binding to its EP3 receptor subtype in the preoptic hypothalamus initiates thermogenesis. Here, we review the different hypotheses on how the presence of peripherally released pyrogenic substances can be signaled to the brain to elicit fever. We conclude that there is unequivocal evidence for a humoral signaling pathway by which proinflammatory cytokines, through their binding to receptors on brain endothelial cells, evoke fever by eliciting prostaglandin E2 synthesis in these cells. The evidence for a role for other signaling routes for fever, such as signaling via circumventricular organs and peripheral nerves, as well as transfer into the brain of peripherally synthesized prostaglandin E2 are yet far from conclusive. We also review the efferent limb of the pyrogenic pathways. We conclude that it is well established that prostaglandin E2 binding in the preoptic hypothalamus produces fever by disinhibition of presympathetic neurons in the brain stem, but there is yet little understanding of the mechanisms by which factors such as nutritional status and ambient temperature shape the response to the peripheral immune challenge.