Cellular and molecular bases of the initiation of fever

A novel peptide able to reduce PLA2 activity and modulate inflammatory cytokine production

Phospholipases A2 (PLA2s) are associated with inflammatory response, performing a complex process involving, specially, cytokines. The excess of pro-inflammatory cytokines induces a chronic inflammatory response and can cause several disorders in the body. Therefore, the inhibition or regulation of cytokines' signaling pathways is a target for new treatment development strategies. Thus, this study aimed to select PLA2 inhibitor mimetic peptides through phage display technology with anti-inflammatory activity. Specific mimetic peptides were selected using BpPLA2-TXI, a PLA2 isolated from Bothrops pauloensis, as a target, and γCdcPL, a PLA2 inhibitor isolated from Crotalus durissus collilineatus, which was used as a competitor during the elution step. We selected the peptide C2PD, which seems to play a pivotal role in the modulation of IL-6, IL-1β, and IL-10 cytokines in inflammatory cells. The C2PD showed a significant reduction in PLA2 activity. Furthermore, the synthetic peptide was tested in PBMC and showed a significant down-modulation of IL-6 and IL-1β release, whereas IL-10 responses were up-regulated. Our findings suggest that this novel peptide may be a potential therapeutic candidate for the treatment of inflammatory diseases, mainly due to its anti-inflammatory properties and absence of cytotoxicity.

The role of microglia in 67NR mammary tumor-induced suppression of brain responses to immune challenges in female mice

It is poorly understood how solid peripheral tumors affect brain neuroimmune responses despite the various brain-mediated side effects and higher rates of infection reported in cancer patients. We hypothesized that chronic low-grade peripheral tumor-induced inflammation conditions microglia to drive suppression of neuroinflammatory responses to a subsequent peripheral immune challenge. Here, Balb/c murine mammary tumors attenuated the microglial inflammatory gene expression responses to lipopolysaccharide (LPS) and live Escherichia coli (E. coli) challenges and the fatigue response to an E. coli infection. In contrast, the inflammatory gene expression in response to LPS or a toll-like receptor 2 agonist of Percoll-enriched primary microglia cultures was comparable between tumor-bearing and -free mice, as were the neuroinflammatory and sickness behavioral responses to an intracerebroventricular interleukin (IL)-1β injection. These data led to the hypothesis that Balb/c mammary tumors blunt the neuroinflammatory responses to an immune challenge via a mechanism involving tumor suppression of the peripheral humoral response. Balb/c mammary tumors modestly attenuated select circulating cytokine responses to LPS and E. coli challenges. Further, a second mammary tumor/mouse strain model (E0771 tumors in C57Bl/6 mice) displayed mildly elevated inflammatory responses to an immune challenge. Taken together, these data indicate that tumor-induced suppression of neuroinflammation and sickness behaviors may be driven by a blunted microglial phenotype, partly because of an attenuated peripheral signal to the brain, which may contribute to infection responses and behavioral side effects reported in cancer patients. Finally, these neuroimmune effects likely vary based on tumor type and/or host immune phenotype.

Microbial and Host Metabolites at the Backstage of Fever: Current Knowledge about the Co-Ordinate Action of Receptors and Molecules Underlying Pathophysiology and Clinical Implications

Fever represents an elevation of body temperature, that exerts a protective effect against pathogens. Innate immune cells and neurons are implicated in the regulation of body temperature. Pathogen-associated molecular patterns, i.e., lipopolysaccharides from Gram-negative bacteria and peptidoglycan and lipoteichoic acid from Gram-positive bacteria are exogenous pyrogens, that bind to Toll-like receptors on immune and non-immune cells. The subsequent release of pro-inflammatory cytokines [interleukin-1 (IL-1), IL-6 and Tumor necrosis factor-alpha] and their passage through the brain trigger the febrile response. In fact, neurons of the pre-optic area produce prostaglandin E2 (PGE2), that, in turn, bind to the PGE2 receptors; thus, generating fever. Apart from classical non-steroidal anti-inflammatory drugs, i.e., aspirin and acetaminophen, various botanicals are currently used as antipyretic agents and, therefore, their mechanisms of action will be elucidated.

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 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.

From Low-Grade Inflammation in Osteoarthritis to Neuropsychiatric Sequelae: A Narrative Review

Nowadays, osteoarthritis (OA), a common, multifactorial musculoskeletal disease, is considered to have a low-grade inflammatory pathogenetic component. Lately, neuropsychiatric sequelae of the disease have gained recognition. However, a link between the peripheral inflammatory process of OA and the development of neuropsychiatric pathology is not completely understood. In this review, we provide a narrative that explores the development of neuropsychiatric disease in the presence of chronic peripheral low-grade inflammation with a focus on its signaling to the brain. We describe the development of a pro-inflammatory environment in the OA-affected joint. We discuss inflammation-signaling pathways that link the affected joint to the central nervous system, mainly using primary sensory afferents and blood circulation via circumventricular organs and cerebral endothelium. The review describes molecular and cellular changes in the brain, recognized in the presence of chronic peripheral inflammation. In addition, changes in the volume of gray matter and alterations of connectivity important for the assessment of the efficacy of treatment in OA are discussed in the given review. Finally, the narrative considers the importance of the use of neuropsychiatric diagnostic tools for a disease with an inflammatory component in the clinical setting.

Lipopolysaccharide-induced hypothalamic inflammation in cancer cachexia-anorexia is amplified by tumour-derived prostaglandin E2

BACKGROUND

Cachexia-anorexia syndrome is a complex metabolic condition characterized by skeletal muscle wasting, reduced food intake and prominent involvement of systemic and central inflammation. Here, the gut barrier function was investigated in pancreatic cancer-induced cachexia mouse models by relating intestinal permeability to the degree of cachexia. We further investigated the involvement of the gut-brain axis and the crosstalk between tumour, gut and hypothalamus in vitro.

METHODS

Two distinct mouse models of pancreatic cancer cachexia (KPC and 4662) were used. Intestinal inflammation and permeability were assessed through fluorescein isothiocyanate dextran (FITC-dextran) and lipopolysaccharide (LPS), and hypothalamic and systemic inflammation through mRNA expression and plasma cytokines, respectively. To simulate the tumour-gut-brain crosstalk, hypothalamic (HypoE-N46) cells were incubated with cachexia-inducing tumour secretomes and LPS. A synthetic mimic of C26 secretome was produced based on its secreted inflammatory mediators. Each component of the mimic was systematically omitted to narrow down the key mediator(s) with an amplifying inflammation. To substantiate its contribution, cyclooxygenase-2 (COX-2) inhibitor was used.

RESULTS

In vivo experiments showed FITC-dextran was enhanced in the KPC group (362.3 vs. sham 111.4 ng/mL, P < 0.001). LPS was increased to 140.9 ng/mL in the KPC group, compared with sham and 4662 groups (115.8 and 115.8 ng/mL, P < 0.05). Hypothalamic inflammatory gene expression of Ccl2 was up-regulated in the KPC group (6.3 vs. sham 1, P < 0.0001, 4662 1.3, P < 0.001), which significantly correlated with LPS concentration (r = 0.4948, P = 0.0226). These data suggest that intestinal permeability is positively related to the cachexic degree. Prostaglandin E2 (PGE2) was confirmed to be present in the plasma and PGE2 concentration (log10) in the KPC group was much higher than in 4662 group (1.85 and 0.56 ng/mL, P < 0.001), indicating a role for PGE2 in pancreatic cancer-induced cachexia. Parallel to in vivo findings, in vitro experiments revealed that the cachexia-inducing tumour secretomes (C26, LLC, KPC and 4662) amplified LPS-induced hypothalamic IL-6 secretion (419%, 321%, 294%, 160%). COX-2 inhibitor to the tumour cells reduced PGE2 content (from 10⁵ to 10²  pg/mL) in the secretomes and eliminated the amplified hypothalamic IL-6 production. Moreover, results could be reproduced by addition of PGE2 alone, indicating that the increased hypothalamic inflammation is directly related to the PGE2 from tumour.

CONCLUSIONS

PGE2 secreted by the tumour may play a role in amplifying the effects of bacteria-derived LPS on the inflammatory hypothalamic response. The cachexia-inducing potential of tumour mice models parallels the loss of intestinal barrier function. Tumour-derived PGE2 might play a key role in cancer-related cachexia-anorexia syndrome via tumour-gut-brain crosstalk.

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.

Xiang Qin Kang Gan Granules Treated the Human Coronavirus 229E Induced Pneumonia with Damp-Heat Syndrome in Mice

Coronavirus disease 2019 (COVID-19), which causes severe respiratory illness, was first reported in Wuhan, China. The etiology of the disease is a new novel coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which was reported to share the same origin as SARS-CoV, causing severe public health events in 2002. Unlike the SARS-CoV, which was conquered in the early summer of 2003, this virus was still contagious widely and reached a pandemic level. It can still spread fast even if the season's temperature is raised. Here, we made a model of pneumonia of human coronavirus 229E (HCoV-229E) with damp-heat syndrome treated by Xiangqin Kanggan granules to find a new medicine for treating these kinds of infectious diseases coronaviruses induced.

Pharmacological effects of berberine on models of ulcerative colitis: A meta-analysis and systematic review of animal studies

Berberine (BBR) is the main active constituent of the Rhizoma coptidis (Huanglian) and has multiple biological activities. Although current evidence suggests that the BBR has a multi-target effect in ulcerative colitis (UC), its action and mechanism are unclear. The purpose of this meta-analysis was to assess the pharmacological effects and potential mechanisms of BBR in UC models. Studies were searched from four databases (PubMed, Embase, Web of Science, and Cochrane Library) until March 2022. Standardized mean difference (SMD) and 95% confidence intervals (CI) were used for the adjudication of outcomes. Stata 15.0 software was used for statistical analysis. Twenty-eight publications and 29 studies involving 508 animals were included in the meta-analysis. The results showed that BBR reduced disease activity index (DAI) scores, alleviated UC-induced colon length (CL) loss, prevented weight loss, and reduced histological colitis score (HCS). Mechanistically, BBR was found to reduce myeloperoxidase (MPO) activity and malondialdehyde (MDA) levels, reduce levels of pro-inflammatory factors interleukin-1β (IL-1β), interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), interferon-γ (IFN-γ) and mRNA expression of interleukin 17, increase levels of anti-inflammatory factor interleukin 10 (IL-10), and to increase levels of tight junction protein zonula occludens-1 (ZO-1) and occludin, which may involve antioxidant, anti-apoptotic, neuromodulation, anti-fibrotic, anti-inflammatory, barrier protection, and flora regulation aspects. However, additional attention should be paid to these outcomes due to the heterogeneity and methodological quality of the studies.

Neural circuits mediating circulating interleukin-1β-evoked fever in the absence of prostaglandin E2 production

Infectious diseases and inflammatory conditions recruit the immune system to mount an appropriate acute response that includes the production of cytokines. Cytokines evoke neurally-mediated responses to fight pathogens, such as the recruitment of thermoeffectors, thereby increasing body temperature and leading to fever. Studies suggest that the cytokine interleukin-1β (IL-1β) depends upon cyclooxygenase (COX)-mediated prostaglandin E₂ production for the induction of neural mechanisms to elicit fever. However, COX inhibitors do not eliminate IL-1β-induced fever, thus suggesting that COX-dependent and COX-independent mechanisms are recruited for increasing body temperature after peripheral administration of IL-1β. In the present study, we aimed to build a foundation for the neural circuit(s) controlling COX-independent, inflammatory fever by determining the involvement of brain areas that are critical for controlling the sympathetic outflow to brown adipose tissue (BAT) and the cutaneous vasculature. In anesthetized rats, pretreatment with indomethacin, a non-selective COX inhibitor, did not prevent BAT thermogenesis or cutaneous vasoconstriction (CVC) induced by intravenous IL-1β (2 µg/kg). BAT and cutaneous vasculature sympathetic premotor neurons in the rostral raphe pallidus area (rRPa) are required for IL-1β-evoked BAT thermogenesis and CVC, with or without pretreatment with indomethacin. Additionally, activation of glutamate receptors in the dorsomedial hypothalamus (DMH) is required for COX-independent, IL-1β-induced BAT thermogenesis. Therefore, our data suggests that COX-independent mechanisms elicit activation of neurons within the DMH and rRPa, which is sufficient to trigger and mount inflammatory fever. These data provide a foundation for elucidating the brain circuits responsible for COX-independent, IL-1β-elicited fevers.

Investigations of the antipyretic effect and safety of Prasachandaeng, a traditional remedy from Thailand national list of essential medicines

Prasachandaeng (PSD) remedy from the Thailand National List of Essential Medicines (NLEM) has been used as an antipyretic for chronic fever in both adults and children for centuries. Its therapeutic effect in treating fever and its safety have not been studied in animal models. We evaluated its antipyretic activity on lipopolysaccharide (LPS)-induced fever and safety in the liver in comparison with acetaminophen (ACP). Correlation between biochemistry of liver function and the level of cytochrome P450 (CYP2E1) was also evaluated using an ELISA kit. All doses of PSD powder (PSDP) and a 95% ethanol extract of PSD (PSDE) (50, 200, and 400 mg/kg) showed a significant antipyretic effect (* p < 0.05) as compared to ACP. We investigated clinical biochemistry of liver and kidney functions, histopathology, and concentrations of CYP2E1. All treatment groups demonstrated a normal range of clinical biochemistry of liver and kidney functions in comparison with ACP on days 1, 3, 7, and 10. Serum AST, ALP, and LDH levels of PSDE and PSDP showed mean values less than that of ACP on the corresponding days (* p < 0.05). None of the treatment groups showed evidence of hepatocellular damage, nor did they affect CYPE21. The results of histopathology on liver tissue correlated with the biochemistry of liver functions which indicated no hepatotoxicity effect in liver tissue during the seven day treatment. These findings suggest that both forms of PSD remedy possessed marked antipyretic activity and were not hepatotoxic during the seven days of administration in rats.

Cytokines in the Brain and Neuroinflammation: We Didn’t Starve the Fire!

In spite of the brain-protecting tissues of the skull, meninges, and blood-brain barrier, some forms of injury to or infection of the CNS can give rise to cerebral cytokine production and action and result in drastic changes in brain function and behavior. Interestingly, peripheral infection-induced systemic inflammation can also be accompanied by increased cerebral cytokine production. Furthermore, it has been recently proposed that some forms of psychological stress may have similar CNS effects. Different conditions of cerebral cytokine production and action will be reviewed here against the background of neuroinflammation. Within this context, it is important to both deepen our understanding along already taken paths as well as to explore new ways in which neural functioning can be modified by cytokines. This, in turn, should enable us to put forward different modes of cerebral cytokine production and action in relation to distinct forms of neuroinflammation.

The hyperthermic effect of central cholecystokinin is mediated by the cyclooxygenase-2 pathway

Cholecystokinin (CCK) increases core body temperature via CCK₂ receptors when administered intracerebroventricularly (icv). The mechanisms of CCK-induced hyperthermia are unknown, and it is also unknown whether CCK contributes to the fever response to systemic inflammation. We studied the interaction between central CCK signaling and the cyclooxygenase (COX) pathway. Body temperature was measured in adult male Wistar rats pretreated with intraperitoneal infusion of the nonselective COX enzyme inhibitor metamizol (120 mg/kg) or a selective COX-2 inhibitor, meloxicam, or etoricoxib (10 mg/kg for both) and, 30 min later, treated with intracerebroventricular CCK (1.7 µg/kg). In separate experiments, CCK-induced neuronal activation (with and without COX inhibition) was studied in thermoregulation- and feeding-related nuclei with c-Fos immunohistochemistry. CCK increased body temperature by ∼0.4°C from 10 min postinfusion, which was attenuated by metamizol. CCK reduced the number of c-Fos-positive cells in the median preoptic area (by ∼70%) but increased it in the dorsal hypothalamic area and in the rostral raphe pallidus (by ∼50% in both); all these changes were completely blocked with metamizol. In contrast, CCK-induced satiety and neuronal activation in the ventromedial hypothalamus were not influenced by metamizol. CCK-induced hyperthermia was also completely blocked with both selective COX-2 inhibitors studied. Finally, the CCK₂ receptor antagonist YM022 (10 µg/kg icv) attenuated the late phases of fever induced by bacterial lipopolysaccharide (10 µg/kg; intravenously). We conclude that centrally administered CCK causes hyperthermia through changes in the activity of "classical" thermoeffector pathways and that the activation of COX-2 is required for the development of this response.NEW & NOTEWORTHY An association between central cholecystokinin signaling and the cyclooxygenase-prostaglandin E pathway has been proposed but remained poorly understood. We show that the hyperthermic response to the central administration of cholecystokinin alters the neuronal activity within efferent thermoeffector pathways and that these effects are fully blocked by the inhibition of cyclooxygenase. We also show that the activation of cyclooxygenase-2 is required for the hyperthermic effect of cholecystokinin and that cholecystokinin is a modulator of endotoxin-induced fever.

Thermal dysregulation in patients with multiple sclerosis during SARS-CoV-2 infection. The potential therapeutic role of exercise

Thermoregulation is a homeostatic mechanism that is disrupted in some neurological diseases. Patients with multiple sclerosis (MS) are susceptible to increases in body temperature, especially with more severe neurological signs. This condition can become intolerable when these patients suffer febrile infections such as coronavirus disease-2019 (COVID-19). We review the mechanisms of hyperthermia in patients with MS, and they may encounter when infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Finally, the thermoregulatory role and relevant adaptation to regular physical exercise are summarized.

A hypothalamomedullary network for physiological responses to environmental stresses

Various environmental stressors, such as extreme temperatures (hot and cold), pathogens, predators and insufficient food, can threaten life. Remarkable progress has recently been made in understanding the central circuit mechanisms of physiological responses to such stressors. A hypothalamomedullary neural pathway from the dorsomedial hypothalamus (DMH) to the rostral medullary raphe region (rMR) regulates sympathetic outflows to effector organs for homeostasis. Thermal and infection stress inputs to the preoptic area dynamically alter the DMH → rMR transmission to elicit thermoregulatory, febrile and cardiovascular responses. Psychological stress signalling from a ventromedial prefrontal cortical area to the DMH drives sympathetic and behavioural responses for stress coping, representing a psychosomatic connection from the corticolimbic emotion circuit to the autonomic and somatic motor systems. Under starvation stress, medullary reticular neurons activated by hunger signalling from the hypothalamus suppress thermogenic drive from the rMR for energy saving and prime mastication to promote food intake. This Perspective presents a combined neural network for environmental stress responses, providing insights into the central circuit mechanism for the integrative regulation of systemic organs.

The Anti-Nociceptive Potential of Tulathromycin against Chemically and Thermally Induced Pain in Mice

The present study was conducted to evaluate the analgesic potential of the new triamilide macrolide antibiotic, tulathromycin, at 20 and 40 mg/kg of body weight (BW), subcutaneously against acute pain in mice. Acute pain was induced either chemically (using acetic acid-induced writhing and formalin-induced pain tests) or thermally (using hot-plate, and tail-flick tests). In the acetic acid-induced writhing test, tulathromycin induced a dose-dependent and significant decrease in the number of writhes compared with the control group. In the late phase of the formalin test, a significant decline in hind paw licking time compared with the control group was observed. In the hot-plate and tail-flick tests, tulathromycin caused a dose-dependent and significant prolongation of latency of nociceptive response to heat stimuli, compared with the control group. These findings may indicate that tulathromycin possesses significant peripheral and central analgesic potentials that may be valuable in symptomatic relief of pain, in addition to its well-established antibacterial effect.

Pathophysiology of Fever and Application of Infrared Thermography (IRT) in the Detection of Sick Domestic Animals: Recent Advances

Body-temperature elevations are multifactorial in origin and classified as hyperthermia as a rise in temperature due to alterations in the thermoregulation mechanism; the body loses the ability to control or regulate body temperature. In contrast, fever is a controlled state, since the body adjusts its stable temperature range to increase body temperature without losing the thermoregulation capacity. Fever refers to an acute phase response that confers a survival benefit on the body, raising core body temperature during infection or systemic inflammation processes to reduce the survival and proliferation of infectious pathogens by altering temperature, restriction of essential nutrients, and the activation of an immune reaction. However, once the infection resolves, the febrile response must be tightly regulated to avoid excessive tissue damage. During fever, neurological, endocrine, immunological, and metabolic changes occur that cause an increase in the stable temperature range, which allows the core body temperature to be considerably increased to stop the invasion of the offending agent and restrict the damage to the organism. There are different metabolic mechanisms of thermoregulation in the febrile response at the central and peripheral levels and cellular events. In response to cold or heat, the brain triggers thermoregulatory responses to coping with changes in body temperature, including autonomic effectors, such as thermogenesis, vasodilation, sweating, and behavioral mechanisms, that trigger flexible, goal-oriented actions, such as seeking heat or cold, nest building, and postural extension. Infrared thermography (IRT) has proven to be a reliable method for the early detection of pathologies affecting animal health and welfare that represent economic losses for farmers. However, the standardization of protocols for IRT use is still needed. Together with the complete understanding of the physiological and behavioral responses involved in the febrile process, it is possible to have timely solutions to serious problem situations. For this reason, the present review aims to analyze the new findings in pathophysiological mechanisms of the febrile process, the heat-loss mechanisms in an animal with fever, thermoregulation, the adverse effects of fever, and recent scientific findings related to different pathologies in farm animals through the use of IRT.

Fever and breast cancer: A critical review of the literature and possible underlying mechanisms

Fever is a common feature in various pathological conditions that manifests a series of molecular events in the internal milieu. Much less attention has been paid to the clinical importance and the management of fever in breast cancer patients. However, several studies have reported an association between postoperative fever and poor treatment outcomes in breast cancer patients. The fever is a side effect of chemotherapy and a manifestation of cancer recurrence. The postmenopausal breast cancer patients experience another body temperature disturbance that is known as a hot flashes. Here, we reviewed the literature regarding postoperative fever and the possible underlying molecular and cellular mechanisms. Then the efficacy of non-steroidal anti-inflammatory drugs was discussed as a therapeutic option to control postoperative fever. Finally, we reviewed the chemotherapy-induced neutropenic fever and cancer vaccination-induced fever.

N-acylethanolamine regulation of TLR3-induced hyperthermia and neuroinflammatory gene expression: A role for PPARα

Increasing evidence suggests that SARS-CoV-2, the virus responsible for the COVID-19 pandemic, is associated with increased risk of developing neurological or psychiatric conditions such as depression, anxiety or dementia. While the precise mechanism underlying this association is unknown, aberrant activation of toll-like receptor (TLR)3, a viral recognizing pattern recognition receptor, may play a key role. Synthetic cannabinoids and enhancing cannabinoid tone via inhibition of fatty acid amide hydrolase (FAAH) has been demonstrated to modulate TLR3-induced neuroimmune responses and associated sickness behaviour. However, the role of individual FAAH substrates, and the receptor mechanisms mediating these effects, are unknown. The present study examined the effects of intracerebral or systemic administration of the FAAH substrates N-oleoylethanolamide (OEA), N-palmitoylethanolamide (PEA) or the anandamide (AEA) analogue meth-AEA on hyperthermia and hypothalamic inflammatory gene expression following administration of the TLR3 agonist, and viral mimetic, poly I:C. The data demonstrate that meth-AEA does not alter TLR3-induced hyperthermia or hypothalamic inflammatory gene expression. In comparison, OEA and PEA attenuated the TLR3-induced hyperthermia, although only OEA attenuated the expression of hyperthermia-related genes (IL-1β, iNOS, COX2 and m-PGES) in the hypothalamus. OEA, but not PEA, attenuated TLR3-induced increases in the expression of all IRF- and NFκB-related genes examined in the hypothalamus, but not in the spleen. Antagonism of PPARα prevented the OEA-induced attenuation of IRF- and NFκB-related genes in the hypothalamus following TLR3 activation but did not significantly alter temperature. PPARα agonism did not alter TLR3-induced hyperthermia or hypothalamic inflammatory gene expression. These data indicate that OEA may be the primary FAAH substrate that modulates TLR3-induced neuroinflammation and hyperthermia, effects partially mediated by PPARα.

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.

A leukotriene-dependent spleen-liver axis drives TNF production in systemic inflammation

Production of the proinflammatory cytokine tumor necrosis factor (TNF) must be precisely regulated for effective host immunity without the induction of collateral tissue damage. Here, we showed that TNF production was driven by a spleen-liver axis in a rat model of systemic inflammation induced by bacterial lipopolysaccharide (LPS). Analysis of cytokine expression and secretion in combination with splenectomy and hepatectomy revealed that the spleen generated not only TNF but also factors that enhanced TNF production by the liver, the latter of which accounted for nearly half of the TNF secreted into the circulation. Using mass spectrometry-based lipidomics, we identified leukotriene B₄ (LTB₄) as a candidate blood-borne messenger in this spleen-liver axis. LTB₄ was essential for spleen-liver communication in vivo, as well as for humoral signaling between splenic macrophages and Kupffer cells in vitro. LPS stimulated the splenic macrophages to secrete LTB₄, which primed Kupffer cells to secrete more TNF in response to LPS in a manner dependent on LTB₄ receptors. These findings provide a framework to understand how systemic inflammation can be regulated at the level of interorgan communication.

Fever and Antipyretic Supported by Traditional Chinese Medicine: A Multi-Pathway Regulation

The coronavirus disease, 2019 (COVID-19), has spread rapidly around the world and become a major public health problem facing the world. Traditional Chinese medicine (TCM) has been fully committed to treat COVID-19 in China. It improved the clinical symptoms of patients and reduced the mortality rate. In light of the fever was identified as one of leading clinical features of COVID-19, this paper will first analyze the material basis of fever, including pyrogenic cytokines and a variety of the mediators of fever. Then the humoral and neural pathways of fever signal transmission will be described. The scattered evidences about fever recorded in recent years are connected in series. On this basis, the understanding of fever is further deepened from the aspects of pathology and physiology. Finally, combining with the chemical composition and pharmacological action of available TCM, we analyzed the mechanisms of TCMs to play the antipyretic effect through multiple ways. So as to further provide the basis for the research of antipyretic compound preparations of TCMs and explore the potential medicines for the prevention and treatment of COVID-19.

The Systemic and Cellular Metabolic Phenotype of Infection and Immune Response to Listeria monocytogenes

It is widely accepted that infection and immune response incur significant metabolic demands, yet the respective demands of specific immune responses to live pathogens have not been well delineated. It is also established that upon activation, metabolic pathways undergo shifts at the cellular level. However, most studies exploring these issues at the systemic or cellular level have utilized pathogen associated molecular patterns (PAMPs) that model sepsis, or model antigens at isolated time points. Thus, the dynamics of pathogenesis and immune response to a live infection remain largely undocumented. To better quantitate the metabolic demands induced by infection, we utilized a live pathogenic infection model. Mice infected with Listeria monocytogenes were monitored longitudinally over the course of infection through clearance. We measured systemic metabolic phenotype, bacterial load, innate and adaptive immune responses, and cellular metabolic pathways. To further delineate the role of adaptive immunity in the metabolic phenotype, we utilized two doses of bacteria, one that induced both sickness behavior and protective (T cell mediated) immunity, and the other protective immunity alone. We determined that the greatest impact to systemic metabolism occurred during the early immune response, which coincided with the greatest shift in innate cellular metabolism. In contrast, during the time of maximal T cell expansion, systemic metabolism returned to resting state. Taken together, our findings demonstrate that the timing of maximal metabolic demand overlaps with the innate immune response and that when the adaptive response is maximal, the host has returned to relative metabolic homeostasis.

Lipoteichoic acid, a cell wall component of Gram-positive bacteria, induces sleep and fever and suppresses feeding

Fragments of the bacterial cell wall are bioactive microbial molecules that have profound effects on the function of the brain. Some of the cell wall constituents are common to both Gram-positive and Gram-negative bacteria, e.g., peptidoglycans, while other cell wall components are specific to either Gram-positive or Gram-negative microbes. Lipopolysaccharide (LPS), also called endotoxin, is found exclusively in Gram-negative bacteria, while lipoteichoic acid (LTA) is specific to Gram-positive bacteria. The effects of peptidoglycans, their fragments, and LPS are well characterized, they induce sleep, fever and anorexia. In the present study, we investigated the sleep, body temperature and food intake modulating effects of LTA. We found that intraperitoneal injection of 100 and 250 μg LTA from B. subtilis and S. aureus increases non-rapid-eye movement sleep (NREMS) in mice. The effects were dose-dependent, and the changes were accompanied by decreased motor activity and feeding as well as febrile responses. Intraperitoneal injection of 10 μg LTA induced monophasic increases in body temperature, while 100 and 250 μg LTA from B. subtilis induced initial hypothermia followed by fever. Treatment with 250 μg LTA from S. aureus elicited monophasic hypothermia. Administration of 300 μg/kg LTA from S. aureus directly into the portal vein elicited similar sleep responses in rats but did not affect body temperature. The sleep-modulating effects of LTA were similar to that of LPS in mice, although LTA appears to be less potent. These findings suggest that the role of LTA in signaling by Gram-positive bacteria in the host body is analogous to the role of LPS/endotoxin in signaling by Gram-negative microbes. LTA may play a role in the development of sickness response in clinically manifest Gram-positive bacterial infections and may contribute to sleep signaling by the commensal intestinal microbiota.

Nutraceutical Status and Scientific Strategies for Enhancing Production of Omega-3 Fatty Acids from Microalgae and their Role in Healthcare

Adherence to Omega-3 fatty acids (O3FAs) as Nutraceuticals for medicinal applications provides health improvement. The prevention and treatment of diseases with O3FAs hold promise in clinical therapy and significantly reduces the risk of chronic disorders. Polyunsaturated fatty acids (PUFA) O3FAs have beneficial effects in the treatment of cardiovascular disorders, diabetic disease, foetal development, Alzheimer's disease, retinal problem, growth and brain development of infants and antitumor effects. Association to current analysis promotes the application of algal biomass for production of O3FAs, mode of action, fate, weight management, immune functions, pharmaceutical and therapeutic applications serving potent sources in healthcare management. A search of the literature was conducted in the databases of WHO website, Sci.org, PubMed, academics and Google. The authors performed search strategies and current scenario of O3FAs in health associated disorders. Promising outcomes and future strategies towards O3FAs may play a pivotal role in Nutraceutical industries in the cure of human health in the future.

Neurons and astrocytes of the chicken hypothalamus directly respond to lipopolysaccharide and chicken interleukin-6

In 4-5-month-old chicken, intravenous injections of bacterial lipopolysaccharide (LPS) induced a dose-dependent fever response and a pronounced increase of circulating interleukin-6 (IL-6). To assess a possible role for IL-6 in the brain of birds, a hypothalamic neuro-glial primary culture from 1-day-old chicken was established. Each well of cultured hypothalamic cells contained some 615 neurons, 1350 astrocytes, and 580 microglial cells on average. Incubation of chicken hypothalamic primary cultures with 10 or 100 µg/ml LPS induced a dose-dependent release of bioactive IL-6 into the supernatant. Populations of hypothalamic neurons (4%) and astrocytes (12%) directly responded to superfusion with buffer containing 10 µg/ml LPS with a transient increase of intracellular calcium, a sign of direct cellular activation. Stimulation of hypothalamic cultures with buffer containing 50 ng/ml chicken IL-6 induced calcium signaling in 11% of neurons and 22% of astrocytes investigated. These results demonstrate that IL-6 is produced in the periphery and in the hypothalamus in response to LPS in chicken. The observed cellular responses of hypothalamic cells to chicken IL-6 indicate that this cytokine may readily be involved in the manifestation of fever in the avian hypothalamus.

The Impact of Different Augmentative Methods on the Expression of Inflammatory Factors

Many animal studies show that an intact periosteum plays an important role in osseous regeneration. The potential effect of an in vivo periosteal barrier membrane on the expression of specific proteins has not been examined sufficiently. The aim of the present study is to investigate the influence of the flap preparation method and collagen membrane on the emission of inflammatory factors. This study examines 20 patients with dental implants who had previously undergone an augmentation. A soft tissue sample was taken during augmentation and 3 months later from the same location. Samples were always taken from the margins of a previously prepared mucoperiosteal flap. The flap was raised with a conventional periosteal elevator in the control group and with a piezoelectric device in the test group. In both groups, we covered half of the augmented bone with a native collagen membrane (NCM; Geistlich Bio-Gide). This allowed us to examine the same incision area with and without a membrane. An immunohistochemical analysis was performed for collagen IV, fibronectin, and inflammatory factors such as cluster of differentiation 31 (CD31), cyclooxygenase-2 (COX-2), and interleukin 6 (IL-6). There was a clear difference in the expression of specific proteins after the piezoelectric device and the periosteal elevator were used. The expression of fibronectin, IL-6, and COX-2 was higher after preparation with the periosteal elevator than after piezoelectric periosteum dissection. The expression of collagen IV was higher after the piezoelectric procedure. No difference was observed for CD31. The membrane had no effect on the expression of collagen IV, fibronectin, IL-6, and COX-2. The type of periosteal preparation influences the expression of specific proteins. With regard to the factors examined here, NCM did not appear to influence the wound healing cascade.

A new cationic palladium(II) dithiocarbamate exhibits anti-inflammatory, analgesic, and antipyretic activities through inhibition of inflammatory mediators in in vivo models

Inflammation is being a protective mechanism of the body towards the injury. However, chronic and progressive inflammation may lead to some chronic diseases. Due to the serious unwanted effects associated with available drugs, new and safe anti-inflammatory agents are still required. Therefore, the present study was designed to investigate the anti-inflammatory, analgesics, and antipyretic properties of a new compound (4-benzylpiperidine-1-carbodithioato-κ2S,S')(1,4-bis-(diphenylphosphino)butane)palladium(II)chloride monohydrate (compound-1) in albino mice models. Compound-1 was characterized by elemental analysis, FT-IR, and multinuclear NMR spectroscopy. Initially, compound-1 was evaluated for cytotoxicity, anti-inflammatory, and analgesic activities by performing MTT assay, carrageenan-, histamine-, serotonin-, and CFA-induced paw edema, mechanical hyperalgesia, thermal hyperalgesia, and mechanical allodynia (0.1, 1, and 10 mg/kg, b.w). Antipyretic activity was evaluated in brewer's yeast-induced model. The pro-inflammatory cytokines were measured by using commercially available ELISA kits. Additionally, nitrite production, antioxidant enzymes, H&E staining, muscle activity and motor coordination, and kidney and liver function tests were also determined. The results demonstrated that compound-1 significantly inhibited inflammation, pain, and febrile responses in all models at a dose of 10 mg/kg without effecting viability of cells in vitro at concentrations up to 100 μM. Similarly, the data clearly demonstrated significant reduction in the pro-inflammatory cytokines and nitrite production while enhancing antioxidant enzymes. Furthermore, pretreatment with compound-1 did not produce any prominent side effect on kidney, liver, stomach, and muscles. These findings suggest that compound-1 has potent anti-inflammatory-, pain-, and pyrexia-relieving properties. Hence, compound-1 might be a potential candidate for the therapeutic management of chronic inflammation and pain.

Maternal immune activation: reporting guidelines to improve the rigor, reproducibility, and transparency of the model

The 2017 American College of Neuropychopharmacology (ACNP) conference hosted a Study Group on 4 December 2017, Establishing best practice guidelines to improve the rigor, reproducibility, and transparency of the maternal immune activation (MIA) animal model of neurodevelopmental abnormalities. The goals of this session were to (a) evaluate the current literature and establish a consensus on best practices to be implemented in MIA studies, (b) identify remaining research gaps warranting additional data collection and lend to the development of evidence-based best practice design, and (c) inform the MIA research community of these findings. During this session, there was a detailed discussion on the importance of validating immunogen doses and standardizing the general design (e.g., species, immunogenic compound used, housing) of our MIA models both within and across laboratories. The consensus of the study group was that data does not currently exist to support specific evidence-based model selection or methodological recommendations due to lack of consistency in reporting, and that this issue extends to other inflammatory models of neurodevelopmental abnormalities. This launched a call to establish a reporting checklist focusing on validation, implementation, and transparency modeled on the ARRIVE Guidelines and CONSORT (scientific reporting guidelines for animal and clinical research, respectively). Here we provide a summary of the discussions in addition to a suggested checklist of reporting guidelines needed to improve the rigor and reproducibility of this valuable translational model, which can be adapted and applied to other animal models as well.

The role of neutrophil granulocytes in immune-to-brain communication

Immune-to-brain communication has been studied in a variety of experimental models. Crucial insights into signalling and mechanisms were previously revealed in studies investigating fever induction pathways. The scientific community has primarily focused on neuronal and humoral pathways in the manifestation of this response. Emerging evidence has now shown that immune-to-brain signalling via immune cells is pivotal for normal brain function and brain pathology. The present manuscript aims to provide a brief overview on the current understanding of how immune cells signal to the brain. Insights are summarized on the potential physiological significance of some immune cells signalling from the periphery to the brain. A particular focus is laid on the role of neutrophil granulocytes. As such, IL-1β expressing neutrophil granulocytes have been shown to transfer inflammatory information to the brain and contribute to prolonged behavioural changes due to septic encephalopathy in rats during severe systemic inflammation induced by the bacterial component and TLR4 agonist lipopolysaccharide. Modulation of immune cell recruitment to the brain is discussed by various confounding factors including sleep, exercise, the nutritional status e.g. obesity, leptin and omega 3 fatty acids, and psychological or inflammatory stressors. The physiological significance of immune cell mediated communication between the immune system and the brain is highlighted by the fact that systemic inflammatory insults can exacerbate ongoing brain pathologies via immune cell trafficking. New insights into mechanisms and mediators of immune cell mediated immune-to-brain communication are important for the development of new therapeutic strategies and the better understanding of existing ones. Abbreviations: ACTH: adrenocorticotropic hormone; BBB: blood-brain barrier; BBI: blood-brain interface; CD: cluster of differentiation; CINC: cytokine-induced neutrophil chemoattractant; CRH: corticotropin releasing hormone; CVOs: circumventricular organs; CXCR: chemokine receptor; DAPI: 40:6-diamidino-2-phenylindole dilactate; DHA: docosahexaenoid acid; ICAM: intracellular adhesion molecule; IL: interleukin; i.p.: intraperitoneal; i.v.: intravenous; KC: keratinocytes-derived chemokine; LPS: lipopolysaccharide; MIP: macrophage inflammatory protein; MS: multiple sclerosis; NFκB: nuclear factor kappa B; NF-IL6: nuclear factor IL-6; PCTR: protectin conjugates in tissue regeneration; PG: prostaglandin; p.i.: post injection; PVN: paraventricular nucleus; ra: receptor antagonist; STAT3: signal transducer and activator of transcription 3; TIMP: tissue inhibitors of metalloproteinases; TLR: toll-like receptor; TNFα: tumor necrosis factor alpha.

Central Mechanisms for Thermoregulation

Maintenance of a homeostatic body core temperature is a critical brain function accomplished by a central neural network. This orchestrates a complex behavioral and autonomic repertoire in response to environmental temperature challenges or declining energy homeostasis and in support of immune responses and many behavioral states. This review summarizes the anatomical, neurotransmitter, and functional relationships within the central neural network that controls the principal thermoeffectors: cutaneous vasoconstriction regulating heat loss and shivering and brown adipose tissue for heat production. The core thermoregulatory network regulating these thermoeffectors consists of parallel but distinct central efferent pathways that share a common peripheral thermal sensory input. Delineating the neural circuit mechanism underlying central thermoregulation provides a useful platform for exploring its functional organization, elucidating the molecular underpinnings of its neuronal interactions, and discovering novel therapeutic approaches to modulating body temperature and energy homeostasis.

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.

Prostaglandin Transporter OATP2A1/SLCO2A1 Is Essential for Body Temperature Regulation during Fever

Prostaglandin E₂ (PGE₂) in the hypothalamus is a principal mediator of the febrile response. However, the role of organic anion transporting polypeptide 2A1 (OATP2A1/SLCO2A1), a prostaglandin transporter, in facilitating this response is unknown. Here, we investigated the effect of Slco2a1 deficiency on the body core temperature (Tc) and on the PGE₂ concentration in hypothalamus interstitial fluid (C_isf) and CSF (C_csf) of lipopolysaccharide (LPS; 100 μg/kg, i.p.)-treated mice of both sexes. Slco2a1^-/- mice did not develop a febrile response. C_csf was increased in Slco2a1^+/+ and Slco2a1^-/- mice, and C_csf of Slco2a1^-/- mice was well maintained at 5 h after LPS injection (1160 pg/ml) compared with Slco2a1^+/+ mice (316 pg/ml). A microdialysis study revealed that C_isf peaked at 2 h after LPS injection in Slco2a1^+/+ mice (841 pg/ml), whereas the increase in C_isf was negligible in Slco2a1^-/- mice. The PGE₂ plasma concentration in Slco2a1^-/- mice (201 pg/ml) was significantly higher than that in Slco2a1^+/+ mice (54 pg/ml) at 1 h after LPS injection, whereas the two groups showed similar PGE₂ concentrations in the hypothalamus. Strong Oatp2a1 immunoreactivity was observed in F4/80-positive microglia and perivascular cells and in brain capillary endothelial cells. The changes in Tc and C_isf seen in LPS-injected Slco2a1^+/+ mice were partially attenuated in monocyte-/macrophage-specific Slco2a1^-/- (Slco2a1^Fl/Fl/LysM^Cre/+) mice. Thus, OATP2A1 facilitates the LPS-induced febrile response by maintaining a high level of C_isf, possibly by regulating PGE₂ secretion from F4/80-positive glial cells and/or facilitating PGE₂ transport across the blood-brain barrier. These findings suggest that OATP2A1 is a useful therapeutic target for neuroinflammation.SIGNIFICANCE STATEMENT Fever is a physiological response caused by pyrogen-induced release of prostaglandin E₂ (PGE₂) in the hypothalamus, which plays a central role in regulating the set-point of body temperature. However, it is unclear whether the prostaglandin transporter OATP2A1/SLCO2A1 is involved in this response. We show here that LPS-induced fever is associated with increased PGE₂ concentration in hypothalamus interstitial fluid (C_isf), but not in CSF (C_csf), by means of a microdialysis study in global Slco2a1-knock-out mice and monocyte-/macrophage-specific Slco2a1-knock-out mice. The results suggest that OATP2A1 serves as a regulator of C_isf in F4/80-positive glial cells. OATP2A1 was detected immunohistochemically in brain capillary endothelial cells and, therefore, may also play a role in PGE₂ transport across the blood-brain barrier.

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.

The Neurokinin-1 Receptor Contributes to the Early Phase of Lipopolysaccharide-Induced Fever via Stimulation of Peripheral Cyclooxygenase-2 Protein Expression in Mice

Neurokinin (NK) signaling is involved in various inflammatory processes. A common manifestation of systemic inflammation is fever, which is usually induced in animal models with the administration of bacterial lipopolysaccharide (LPS). A role for the NK1 receptor was shown in LPS-induced fever, but the underlying mechanisms of how the NK1 receptor contributes to febrile response, especially in the early phase, have remained unknown. We administered LPS (120 µg/kg, intraperitoneally) to mice with the Tacr1 gene, i.e., the gene encoding the NK1 receptor, either present (Tacr1^+/+ ) or absent (Tacr1^-/- ) and measured their thermoregulatory responses, serum cytokine levels, tissue cyclooxygenase-2 (COX-2) expression, and prostaglandin (PG) E₂ concentration. We found that the LPS-induced febrile response was attenuated in Tacr1^-/- compared to their Tacr1^+/+ littermates starting from 40 min postinfusion. The febrigenic effect of intracerebroventricularly administered PGE₂ was not suppressed in the Tacr1^-/- mice. Serum concentration of pyrogenic cytokines did not differ between Tacr1^-/- and Tacr1^+/+ at 40 min post-LPS infusion. Administration of LPS resulted in amplification of COX-2 mRNA expression in the lungs, liver, and brain of the mice, which was statistically indistinguishable between the genotypes. In contrast, the LPS-induced augmentation of COX-2 protein expression was attenuated in the lungs and tended to be suppressed in the liver of Tacr1^-/- mice compared with Tacr1^+/+ mice. The Tacr1^+/+ mice responded to LPS with a significant surge of PGE₂ production in the lungs, whereas Tacr1^-/- mice did not. In conclusion, the NK1 receptor is necessary for normal fever genesis. Our results suggest that the NK1 receptor contributes to the early phase of LPS-induced fever by enhancing COX-2 protein expression in the periphery. These findings advance the understanding of the crosstalk between NK signaling and the "cytokine-COX-2-prostaglandin E₂" axis in systemic inflammation, thereby open up the possibilities for new therapeutic approaches.

Fever and hypothermia in systemic inflammation

Systemic inflammation-associated syndromes (e.g., sepsis and septic shock) often have high mortality and remain a challenge in emergency medicine. Systemic inflammation is usually accompanied by changes in body temperature: fever or hypothermia. In animal studies, systemic inflammation is often modeled by administering bacterial lipopolysaccharide, which triggers autonomic and behavioral thermoeffector responses and causes either fever or hypothermia, depending on the dose and ambient temperature. Fever and hypothermia are regulated changes of body temperature, which correspond to mild and severe forms of systemic inflammation, respectively. Mediators of fever and hypothermia are called endogenous pyrogens and cryogens; they are produced when the innate immune system recognizes an infectious pathogen. Upon an inflammatory challenge, hepatic and pulmonary macrophages (and later brain endothelial cells) start to release lipid mediators, of which prostaglandin (PG) E₂ plays the key role, and cytokines. Blood PGE₂ enters the brain and triggers fever. At later stages of fever, PGE₂ synthesized within the blood-brain barrier maintains fever. In both cases, PGE₂ is synthesized by cyclooxygenase-2 and microsomal PGE₂synthase-1. Mediators of hypothermia are not well established. Both fever and hypothermia are beneficial host defense responses. Based on evidence from studies in laboratory animals and clinical trials in humans, fever is beneficial for fighting mild infection. Based mainly on animal studies, hypothermia is beneficial in severe systemic inflammation and infection.

Efferent thermoregulatory pathways regulating cutaneous blood flow and sweating

Cutaneous vasoconstrictor nerves regulate heat retention, and are activated by falls in skin or core temperature. The efferent pathways controlling this process originate within the preoptic area. A descending GABAergic pathway, activated by warm skin or core, indirectly inhibits sympathetic premotor neurons in the medullary raphé. Those premotor neurons drive cutaneous vasoconstriction via excitatory glutamatergic and serotonergic connections to spinal preganglionic neurons. Cold skin and/or cold core temperatures activate a direct preoptic-to-raphé excitatory pathway. The balance of inhibitory and excitatory influences reaching the medullary raphé determines cutaneous blood flow. During fever, prostaglandin E₂ inhibits preoptic GABAergic neurons, resulting in disinhibition of the excitatory preoptic-to-raphé pathway, and hence, cutaneous vasoconstriction. A weaker, parallel source of descending excitatory drive reaches cutaneous preganglionic neurons from the rostral ventrolateral medulla. Sweating follows local heating of the preoptic area in cats and monkeys, and heated humans show sweating-related activation of this same region in functional magnetic resonance imaging (fMRI) studies. A descending pathway that drives sweating has been traced in cats from the hypothalamus to putative premotor neurons in the parafacial region at the pontomedullary junction. The homologous parafacial region in humans also shows sweating-related activation in fMRI studies. The central pathways that drive active vasodilatation in human nonacral skin remain unknown.

Antipyretic therapy: clinical pharmacology

Fever depends on a complex physiologic response to infectious agents and other conditions. To alleviate fever, many medicinal agents have been developed over a century of trying to improve upon aspirin, which was determined to work by inhibiting prostaglandin synthesis. We present the process of fever induction through prostaglandin synthesis and discuss the development of pharmaceuticals that target enzymes and receptors involved in prostaglandin-mediated signal transduction, including prostaglandin H₂ synthase (also known as cyclooxygenase), phospholipase A₂, microsomal prostaglandin E₂ synthase-1, EP receptors, and transient potential cation channel subfamily V member 1. Clinical use of established antipyretics will be discussed as well as medicinal agents under clinical trials and future research.

Stress-induced hyperthermia and hypothermia

Stress affects core body temperature (T_c). Many kinds of stress induce transient, monophasic hyperthermia, which diminishes gradually if the stressor is terminated. Stronger stressors produce a longer-lasting effect. Repeated/chronic stress induces anticipatory hyperthermia, reduces diurnal changes in T_c, or slightly increases T_c throughout the day. Animals that are exposed to chronic stress or a cold environment exhibit an enhanced hyperthermic response to a novel stress. These changes persist for several days after cessation of stress exposure. In contrast, long-lasting inescapable stress sometimes induces hypothermia. In healthy humans, psychologic stress induces slight increases in T_c, which are within the normal range of T_c or just above it. Some individuals, however, develop extremely high T_c (up to 41°C) when they are exposed to emotional events or show persistent low-grade high T_c (37-38°C) during or after chronic stress situations. In addition to the nature of the stressor itself, such stress-induced thermal responses are modulated by sex, age, ambient temperature, cage mates, past stressful experiences and cold exposure, and coping. Stress-induced hyperthermia is driven by mechanisms distinct from infectious fever, which requires inflammatory mediators. However, both stress and infection activate the dorsomedial hypothalamus-rostral medullary raphe region-sympathetic nerve axis to increase T_c.

Afferent pathways for autonomic and shivering thermoeffectors

Body core temperature of mammals is regulated by the central nervous system, in which the preoptic area (POA) of the hypothalamus plays a pivotal role. The POA receives peripheral and central thermosensory neural information and provides command signals to effector organs to elicit involuntary thermoregulatory responses, including shivering thermogenesis, nonshivering brown adipose tissue thermogenesis, and cutaneous vasoconstriction. Cool-sensory and warm-sensory signals from cutaneous thermoreceptors, monitoring environmental temperature, are separately transmitted through the spinal-parabrachial-POA neural pathways, distinct from the spinothalamocortical pathway for perception of skin temperature. These cutaneous thermosensory inputs to the POA likely impinge on warm-sensitive POA neurons, which monitor body core (brain) temperature, to alter thermoregulatory command outflows from the POA. The cutaneous thermosensory afferents elicit rapid thermoregulatory responses to environmental thermal challenges before they impact body core temperature. Peripheral humoral signals also act on neurons in the POA to transmit afferent information of systemic infection and energy storage to induce fever and to regulate energy balance, respectively. This chapter describes the thermoregulatory afferent mechanisms that convey cutaneous thermosensory signals to the POA and that integrate the neural and humoral afferent inputs to the POA to provide descending command signals to thermoregulatory effectors.

Immune-Induced Fever Is Dependent on Local But Not Generalized Prostaglandin E2 Synthesis in the Brain

Fever occurs upon binding of prostaglandin E₂ (PGE₂) to EP₃ receptors in the median preoptic nucleus of the hypothalamus, but the origin of the pyrogenic PGE₂ has not been clearly determined. Here, using mice of both sexes, we examined the role of local versus generalized PGE₂ production in the brain for the febrile response. In wild-type mice and in mice with genetic deletion of the prostaglandin synthesizing enzyme cyclooxygenase-2 in the brain endothelium, generated with an inducible CreER^T2 under the Slco1c1 promoter, PGE₂ levels in the CSF were only weakly related to the magnitude of the febrile response, whereas the PGE₂ synthesizing capacity in the hypothalamus, as reflected in the levels of cyclooxygenase-2 mRNA, showed strong correlation with the immune-induced fever. Histological analysis showed that the deletion of cyclooxygenase-2 in brain endothelial cells occurred preferentially in small- and medium-sized vessels deep in the brain parenchyma, such as in the hypothalamus, whereas larger vessels, and particularly those close to the neocortical surface and in the meninges, were left unaffected, hence leaving PGE₂ synthesis largely intact in major parts of the brain while significantly reducing it in the region critical for the febrile response. Furthermore, injection of a virus vector expressing microsomal prostaglandin E synthase-1 (mPGES-1) into the median preoptic nucleus of fever-refractive mPGES-1 knock-out mice, resulted in a temperature elevation in response to LPS. We conclude that the febrile response is dependent on local release of PGE₂ onto its target neurons and not on the overall PGE₂ production in the brain.SIGNIFICANCE STATEMENT By using mice with selective deletion of prostaglandin synthesis in brain endothelial cells, we demonstrate that local prostaglandin E₂ (PGE₂) production in deep brain areas, such as the hypothalamus, which is the site of thermoregulatory neurons, is critical for the febrile response to peripheral inflammation. In contrast, PGE₂ production in other brain areas and the overall PGE₂ level in the brain do not influence the febrile response. Furthermore, partly restoring the PGE₂ synthesizing capacity in the anterior hypothalamus of mice lacking such capacity with a lentiviral vector resulted in a temperature elevation in response to LPS. These data imply that the febrile response is dependent on the local release of PGE₂ onto its target neurons, possibly by a paracrine mechanism.

Behavioral fever in ectothermic vertebrates

Fever is an evolutionary conserved defense mechanism which is present in both endothermic and ectothermic vertebrates. Ectotherms in response to infection can increase their body temperature by moving to warmer places. This process is known as behavioral fever. In this review, we summarize the current knowledge on the mechanisms of induction of fever in mammals. We further discuss the evolutionary conserved mechanisms existing between fever of mammals and behavioral fever of ectothermic vertebrates. Finally, the experimental evidences supporting an adaptive value of behavioral fever expressed by ectothermic vertebrates are summarized.

G-CSF-induced sympathetic tone provokes fever and primes antimobilizing functions of neutrophils via PGE2

Granulocyte colony-stimulating factor (G-CSF) is widely used for peripheral blood stem/progenitor mobilization. G-CSF causes low-grade fever that is ameliorated by nonsteroidal anti-inflammatory drugs (NSAIDs), suggesting the activation of arachidonic acid (AA) cascade. How G-CSF regulated this reaction was assessed. G-CSF treatment in mice resulted in fever, which was canceled in prostaglandin E synthase (mPGES-1)-deficient mice. Mobilization efficiency was twice as high in chimeric mice lacking mPGES-1, specifically in hematopoietic cells, suggesting that prostaglandin E₂ (PGE₂) from hematopoietic cells modulated the bone marrow (BM) microenvironment. Neutrophils from steady-state BM constitutively expressed mPGES-1 and significantly enhanced PGE₂ production in vitro by β-adrenergic stimulation, but not by G-CSF, which was inhibited by an NSAID. Although neutrophils expressed all β-adrenergic receptors, only β3-agonist induced this phenomenon. Liquid chromatography-tandem mass spectrometry traced β-agonist-induced PGE₂ synthesis from exogenous deuterium-labeled AA. Spontaneous PGE₂ production was highly efficient in Gr-1^high neutrophils among BM cells from G-CSF-treated mice. In addition to these in vitro data, the in vivo depletion of Gr-1^high neutrophils disrupted G-CSF-induced fever. Furthermore, sympathetic denervation eliminated both neutrophil priming for PGE₂ production and fever during G-CSF treatment. Thus, sympathetic tone-primed BM neutrophils were identified as one of the major PGE₂ producers. PGE₂ upregulated osteopontin, specifically in preosteoblasts, to retain progenitors in the BM via EP4 receptor. Thus, the sympathetic nervous system regulated neutrophils as an indispensable PGE₂ source to modulate BM microenvironment and body temperature. This study provided a novel mechanistic insight into the communication of the nervous system, BM niche components, and hematopoietic cells.