Molecular mechanisms of fever and endogenous antipyresis

Behavioral responses during sickness in amphibians and reptiles: Concepts, experimental design, and implications for field studies

In ectothermic vertebrates, behavioral fever, where an individual actively seeks warmer areas, seems to be a primary response to pathogens. This is considered a broad and evolutionarily conserved response among vertebrates. Recent population declines in amphibians are associated with an increase of infectious disease driven largely by climate change, habitat degradation, and pollution. Immediate action through research is required to better understand and inform conservation efforts. The literature available, does not provide unifying concepts that can guide adequate experimental protocols and interpretation of data, especially when studying animals in the field. The aim of this review is to promote common understanding of terminology and facilitating improved comprehension and application of key concepts about the occurrence of both sickness behavior or behavioral fever in ectothermic vertebrates. We start with a conceptual synthesis of sickness behavior and behavioral fever, with examples in different taxa. Through this discussion we present possible paths to standardize terminology, starting from original use in endothermic tetrapods which was expanded to ectothermic vertebrates, particularly amphibians and reptiles. This conceptual expansion from humans (endothermic vertebrates) and then to ectothermic counterparts, gravitates around the concept of 'normality'. Thus, following this discussion, we highlight caveats with experimental protocols and state the need of a reference value considered normal (RVCN), which is different from experimental control and make recommendations regarding experimental procedures and stress the value of detailed documentation of behavioral responses. We also propose some future directions that could enhance interaction among disciplines, emphasizing relationships at different levels of biological organization. This is crucial given the increasing convergence of fields such as thermal physiology, immunology, and animal behavior due to emerging diseases and other global crises impacting biodiversity.

Fever of unknown origin associated with immune checkpoint inhibitors

Since the approval for the treatment of melanoma in 2014, immune checkpoint inhibitors (ICIs) have revolutionized the therapy pattern across various malignancies. Coinciding with their frequent usage, their adverse effects, including fever, cannot be neglected. In the context of cancer diseases and cancer treatments, fever of unknown origin (FUO), which has long posed a challenge for clinicians in terms of diagnosis and management, brings forth new connotation and significance. In this paper review, we present the concept of ICIs-associated FUO, consider activated immune system and elevated cytokines as common mechanisms by which ICIs induce fever and various immune-related adverse events (irAEs), summarize and compare the primary etiologies of ICI-associated FUO, and compare it with conventional types of FUO.

Current State of Knowledge on the Definition, Pathophysiology, Etiology, Outcomes, and Management of Fever in the Intensive Care Unit

Fever-an elevated body temperature-is a prominent feature of a wide range of disease conditions and is a common finding in intensive care, affecting up to 70% of patients in the intensive care unit (ICU). The causes of fever in the ICU are multifactorial, and it can be due to a number of infective and noninfective etiologies. The production of fever represents a complex physiological, adaptive host response that is beneficial for host defense and survival but can be maladaptive and harmful if left unabated. Despite any cause, fever is associated with a wide range of cellular, local, and systemic effects, including multiorgan dysfunction, systemic inflammation, poor neurological recovery, and an increased risk of mortality. This narrative review presents the current state-of-the-art knowledge on the definition, pathophysiology, etiology, and outcomes of fever in the ICU and highlights evidence-based findings regarding the management of fever in the intensive care setting.

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.

Non-inflammatory Physiology of "Inflammatory" Mediators - Unalamation, a New Paradigm

Many small molecules (mostly lipids derived from polyunsaturated fatty acids) and proteins (e. g., cytokines and chemokines) are labeled as inflammatory mediators for their role in eliciting physiological responses to injury. While acute inflammatory events are controlled by anti-inflammatory drugs, lasting damage to the tissues as a result of persistent inflammation is increasingly viewed as the root cause of many chronic diseases that include cardiovascular, neurological, and metabolic disorders, rheumatoid arthritis, and cancer. Interestingly, some of the “inflammatory” mediators also participate in normal developmental physiology without eliciting inflammation. Anti-inflammatory drugs that target the biosynthesis of these mediators are too indiscriminate to distinguish their two divergent physiological roles. A more precise definition of these two physiological processes partaken by the “inflammatory” mediators is warranted to identify their differences. The new paradigm is named “unalamation” ('ə‘n'əlAmāSH(ə)n) to distinguish from inflammation and to identify appropriate intervention strategies to mitigate inflammation associated pathophysiology without affecting the normal developmental physiology.

Insect Defense Proteins and Peptides

The composition of insect hemolymph can change depending on many factors, e.g. access to nutrients, stress conditions, and current needs of the insect. In this chapter, insect immune-related polypeptides, which can be permanently or occasionally present in the hemolymph, are described. Their division into peptides or low-molecular weight proteins is not always determined by the length or secondary structure of a given molecule but also depends on the mode of action in insect immunity and, therefore, it is rather arbitrary. Antimicrobial peptides (AMPs) with their role in immunity, modes of action, and classification are presented in the chapter, followed by a short description of some examples: cecropins, moricins, defensins, proline- and glycine-rich peptides. Further, we will describe selected immune-related proteins that may participate in immune recognition, may possess direct antimicrobial properties, or can be involved in the modulation of insect immunity by both abiotic and biotic factors. We briefly cover Fibrinogen-Related Proteins (FREPs), Down Syndrome Cell Adhesion Molecules (Dscam), Hemolin, Lipophorins, Lysozyme, Insect Metalloproteinase Inhibitor (IMPI), and Heat Shock Proteins. The reader will obtain a partial picture presenting molecules participating in one of the most efficient immune strategies found in the animal world, which allow insects to inhabit all ecological land niches in the world.

A Nontarget Mechanism to Explain Carcinogenesis Following α-Irradiation

This commentary highlights the published data on the metabolic processes that lead to the development of cancer following intakes of asbestos and chemical agents. Following exposure to both, the key initiating event is cell injury leading to cell death that may further lead to inflammation, fibrosis, and cancer. Since α-particle transits also kill cells, it is suggested that cell death and inflammation will also trigger carcinogenesis within tissues irradiated by these particles. Such an explanation would be consistent with the inflammation and fibrosis seen in tumor-bearing tissues irradiated by radon-222, radium-226, thorium-232, plutonium-239, and other α-emitting radionuclides. It would also provide an explanation for dose-related changes in latency and in the similar dose-responses for the same tissue in differently sized species.

High mobility group box 1 protein released in the course of aseptic necrosis of tissues sensitizes rats to pyrogenic effects of lipopolysaccharide

It is still an open question as to whether or not aseptic injuries affect the generation of fever due to exogenous pyrogens including bacterial products. Therefore, in the present paper we have investigated the course of endotoxin fever in rats induced with lipopolysaccharide (LPS; given intraperitoneally in a dose of 50 μg/kg) 48 h after subcutaneous administration of turpentine oil (TRP; 0.1 mL per rat) that causes aseptic necrosis of tissues. We found that febrile response was significantly augmented in the animals pre-treated with turpentine compared to control rats (pre-treated with saline), and that observed excessive elevation of body temperature (Tb) was accompanied by enhanced release of fever mediators: interleukin-6 (IL-6) and prostaglandin E₂ (PGE₂) into plasma. Moreover, we found that sensitization to pyrogenic effects of lipopolysaccharide was associated with the increase in plasma level of high mobility group box 1 protein (HMGB1), one of the best-known damage-associated molecular patterns (DAMP), which was recently discovered as inflammatory mediator. Since the injection of anti-HMGB1 antibodies weakened observed hyperpyrexia in the animals pre-treated with turpentine, we conclude that HMGB1 is a plasma-derived factor released in the course of aseptic injury that enhances pyrogenic effects of LPS.

An evaluation of the anti-inflammatory, antipyretic and analgesic effects of hydroethanol leaf extract of Albizia zygia in animal models

CONTEXT

The leaves of Albizia zygia (DC.) J.F. Macbr. (Leguminosae-Mimosoideae) are used in Ghanaian traditional medicine for the treatment of pain, inflammatory disorders and fever (including malaria).

OBJECTIVES

The present study evaluated the anti-inflammatory, antipyretic and analgesic effects of the hydroethanol leaf extract of Albizia zygia (AZE) in animal models.

MATERIALS AND METHODS

The anti-inflammatory and antipyretic effects of AZE were examined in the carrageenan-induced foot oedema model and the baker's yeast-induced pyrexia test respectively. The analgesic effect and possible mechanisms of action were also assessed in the formalin test.

RESULTS

AZE (30-300 mg/kg, p.o.), either preemptively or curatively, significantly inhibited carrageenan-induced foot edema in 7-day-old chicks (ED₅₀ values; preemptive: 232.9 ± 53.33 mg/kg; curative: 539.2 ± 138.28 mg/kg). Similarly, the NSAID diclofenac (10-100 mg/kg, i.p.) significantly reduced the oedema in both preemptive (ED₅₀: 21.16 ± 4.07 mg/kg) and curative (ED₅₀: 44.28 ± 5.75 mg/kg) treatments. The extract (30-300 mg/kg, p.o.) as well as paracetamol (150 mg/kg, p.o.) also showed significant antipyretic activity in the baker's yeast-induced pyrexia test (ED₅₀ of AZE: 282.5 ± 96.55 mg/kg). AZE and morphine (1-10 mg/kg, i.p.; positive control), exhibited significant analgesic activity in the formalin test. The analgesic effect was partly or wholly reversed by the systemic administration of naloxone, theophylline and atropine.

CONCLUSION

The results suggest that AZE possesses anti-inflammatory, antipyretic and analgesic properties, which justifies its traditional use. Also, the results show the involvement of the opioidergic, adenosinergic and the muscarinic cholinergic pathways in the analgesic effects of AZE.

Protein-bound polysaccharides from Coriolus versicolor attenuate LPS-induced synthesis of pro-inflammatory cytokines and stimulate PBMCs proliferation

Protein-bound polysaccharides (PBP) isolated from Coriolus versicolor (CV) are classified as biological response modifiers capable of exhibiting various biological activities, such as anti-tumour and immunopotentiating activity. Since we have found in vivo studies that the tested PBP induced prolongation of endotoxin fever in rats, the aim of the present study was to investigate the in vitro effect of the PBP on the production of pro-inflammatory cytokines by the lipolysaccharide (LPS)-stimulated rat peripheral blood mononuclear cells (PBMCs). The results showed that the PBP affect the immunomodulating properties of the LPS-treated PBMCs by the enhancement of mitogenic activity and attenuation of the LPS-induced production of interleukin (IL)-1β and IL-6. Moreover, the tested polysaccharides peptides themselves also exhibit immunomodulatory properties manifested in the increased cell proliferation and pro-inflammatory cytokine release from PBMCs. The effect of PBP on the both phenomena was time-dependent and occurred in the U-shaped dose response manner. These findings are significant when considering the use of commercially available PBP from CV extract by cancer patients suffering from immunodeficiency, who may experience microbial infections during therapy.

N-Acetyl-l-cysteine exacerbates generation of IL-10 in cells stimulated with endotoxin in vitro and produces antipyresis via IL-10 dependent pathway in vivo

N-Acetyl-l-cysteine (NAC) is a well-known medication, primarily used as a mucolytic agent in pulmonary disease. Recently, we have found that NAC possesses antipyretic properties. The aim of the present study was to investigate the mechanism by which NAC attenuates fever. The concentration of interleukin (IL)-10 and prostaglandin (PG) E2 were measured using ELISA kit in the supernatants aspirated after stimulation of peripheral blood mononuclear cells (PBMCs) with lipopolysaccharide (LPS, 1μg/mL) and NAC (10mM). The body temperature of the Wistar rats was measured using biotelemetry system. To inhibit endotoxic fever, NAC (200mg/kg; i.p.) was injected into the rats one hour prior to the LPS administration (50μg/kg; i.p.). The pre-treatment of LPS-stimulated PBMCs with NAC resulted in a significant decrease in PGE2 concentration in comparison to the cells treated with LPS alone (PGE2 level was 386.1±61.9pg/mL vs. 2078.9±157.9pg/mL, respectively, p<0.001). Furthermore, in these cells we observed a significant increase in IL-10 level (142.1±2.62pg/mL in NAC+LPS stimulated cells vs. 54.4±0.6pg/mL in LPS stimulated cells, p<0.001). The injection of anti-IL-10 antibody into the rats abolished antipyretic properties of NAC. Body temperature in animals treated with anti-IL-10+NAC/LPS was 38.28±0.12°C vs. 37.73±0.06°C in IgG+NAC/LPS rats (p<0.001) and 38.31±0.20°C in NaCl/LPS-treated animals (n.s.). Based on these data, we conclude that NAC acts as an antipyretic via IL-10 stimulation. This finding provides a new insight into the immunopharmacology of NAC, and we believe that in a future it will contribute to the new and/or more accurate application of NAC in medicine.

What We Talk About When We Talk About Evolution

Currently, the biologic sciences are a Tower of Babel, having become so highly specialized that one discipline cannot effectively communicate with another. A mechanism for evolution that integrates development and physiologic homeostasis phylogenetically has been identified—cell-cell interactions. By reducing this process to ligand-receptor interactions and their intermediate down-stream signaling partners, it is possible, for example, to envision the functional homologies between such seemingly disparate structures and functions as the lung alveolus and kidney glomerulus, the skin and brain, or the skin and lung. For example, by showing the continuum of the lung phenotype for gas exchange at the cell-molecular level, being selected for increased surface area by augmenting lung surfactant production and function in lowering surface tension, we have determined an unprecedented structural-functional continuum from proximate to ultimate causation in evolution. It is maintained that tracing the changes in structure and function that have occurred over both the short-term history of the organism (as ontogeny), and the long-term history of the organism (as phylogeny), and how the mechanisms shared in common can account for both biologic stability and novelty, will provide the key to understanding the mechanisms of evolution. We need to better understand evolution from its unicellular origins as the Big Bang of biology.

Silver nanoparticles augment releasing of pyrogenic factors by blood cells stimulated with LPS

Silver nanoparticles (AgNPs) have cytotoxic properties via generation of reactive oxygen species which are involved in the generalized sickness behavior of the host, including fever and lethargy among others. The aim of the present study was to investigate the impact of AgNPs on the ability of rat peripheral blood mononuclear cells (PBMCs) to release fever mediating factors after stimulation with lipopolysaccharide (LPS). Body temperature and motor activity of the Wistar rats were measured by biotelemetry system. Rat PBMCs were stimulated with LPS and after that the cells were washed and incubated alone or with AgNPs. The final supernatants were injected intraperitoneally. The levels of endogenous pyrogens such as interleukin-1β (IL−1β), IL-6 and tumor necrosis factor-α (TNF-α) released from the PBMCs into the final supernatants were also estimated. The results indicated that injection of the supernatants from the cells stimulated with LPS induced fever and inhibited motor activity. These effects were potentiated by the presence of AgNPs during the final incubation. The presence of the AgNPs also resulted in significant increases in levels of endogenous pyrogens. The augmentation of fever in the rats by the AgNPs treatment of the cultures seemed to be primarily associated with the changes in interleukin-1β levels.

Polysaccharide peptide induces a tumor necrosis factor-α-dependent drop of body temperature in rats

Polysaccharide peptide (PSP) extracted from the Coriolus versicolor mushroom is frequently suggested as an adjunct to the chemo- or radiotherapy in cancer patients. It improves quality of the patients' life by decreasing pain, fatigue, loss of appetite, nausea, and vomiting. However, the effect of PSP on body temperature has not thus far been studied, although it is well known that treatment with other polysaccharide adjuvants, such as lipopolysaccharides, may induce fever. The aim of the present study, therefore, was to investigate the influence of PSP on temperature regulation in rats. We report that intraperitoneal injection of PSP provoked a dose-dependent decrease of temperature in male Wistar rats equipped with biotelemetry devices to monitor deep body temperature (Tb). The response was rapid (i.e., with latency of 15-20min), transient (lasting up to 5h post-injection), and accompanied by a significant elevation of the blood tumor necrosis factor-α (TNF-α) level. Pretreatment of the rats with anti-TNF-α antibody prevented the PSP-induced drop in Tb. Based on these data, we conclude that rats may develop an anapyrexia-like response to the injection of peptidopolysaccharide rather than fever, and the response was TNF-α-dependent.

Epistemology of the origin of cancer: a new paradigm

Background

Carcinogenesis is widely thought to originate from somatic mutations and an inhibition of growth suppressors, followed by cell proliferation, tissue invasion, and risk of metastasis. Fewer than 10% of all cancers are hereditary; the ratio in gastric (1%), colorectal (3-5%) and breast (8%) cancers is even less. Cancers caused by infection are thought to constitute some 15% of the non-hereditary cancers. Those remaining, 70 to 80%, are called “sporadic,” because they are essentially of unknown etiology. We propose a new paradigm for the origin of the majority of cancers.

Presentation of hypothesis

Our paradigm postulates that cancer originates following a sequence of events that include (1) a pathogenic stimulus (biological or chemical) followed by (2) chronic inflammation, from which develops (3) fibrosis with associated changes in the cellular microenvironment. From these changes a (4) pre-cancerous niche develops, which triggers the deployment of (5) a chronic stress escape strategy, and when this fails to resolve, (6) a transition of a normal cell to a cancer cell occurs. If we are correct, this paradigm would suggest that the majority of the findings in cancer genetics so far reported are either late events or are epiphenomena that occur after the appearance of the pre-cancerous niche.

Testing the hypothesis

If, based on experimental and clinical findings presented here, this hypothesis is plausible, then the majority of findings in the genetics of cancer so far reported in the literature are late events or epiphenomena that could have occurred after the development of a PCN. Our model would make clear the need to establish preventive measures long before a cancer becomes clinically apparent. Future research should focus on the intermediate steps of our proposed sequence of events, which will enhance our understanding of the nature of carcinogenesis. Findings on inflammation and fibrosis would be given their warranted importance, with research in anticancer therapies focusing on suppressing the PCN state with very early intervention to detect and quantify any subclinical inflammatory change and to treat all levels of chronic inflammation and prevent fibrotic changes, and so avoid the transition from a normal cell to a cancer cell.

Implication of the hypothesis

The paradigm proposed here, if proven, spells out a sequence of steps, one or more of which could be interdicted or modulated early in carcinogenesis to prevent or, at a minimum, slow down the progression of many cancers.

Long-lasting impact of early life immune stress on neuroimmune functions

Fever is one major cardinal sign of disease. It results from an intricate interplay between the immune system and the central nervous system. Bacterial or viral infections activate peripheral immune competent organs which send inflammatory signals to the brain and lead to an increase in body temperature. The increased body temperature creates a conducive environment to optimize the body's fight against the infection. A large body of experimental evidence suggests that early life bacterial or viral infections can lead to a long-lasting impact on this natural febrile response. The early life pathogenic encounter heightens the hypothalamic-pituitary-adrenal axis response, dampens the innate immune system, and consequently reduces the febrile response to a subsequent immune challenge during adulthood. This 'programming' effect operates only when such early life immune challenges occur during a critical window of either prenatal or postnatal development. In this review, the mechanisms underlying the long-lasting impact of perinatal immune challenge on adult fever are addressed.

Treatment of fever after stroke: conflicting evidence

Approximately 50% of patients hospitalized for stroke develop fever. In fact, experimental evidence suggests that high body temperature is significantly correlated to initial stroke severity, lesion size, mortality, and neurologic outcome. Fever occurring after stroke is associated with poor outcomes. We investigated the etiology of fever after stroke and present evidence evaluating the efficacy and safety of interventions used to treat stroke-associated fever. Oral antipyretics are only marginally effective in lowering elevated body temperature in this population and may have unintended adverse consequences. Nonpharmacologic approaches to cooling have been more effective in achieving normothermia, but whether stroke outcomes can be improved remains unclear. We recommend using body temperature as a biomarker and a catalyst for aggressive investigation for an infectious etiology. Care must be taken not to exceed the new standard of a maximum acetaminophen dose of 3 g/day to avoid patient harm.

Epoxygenated fatty acids and soluble epoxide hydrolase inhibition: novel mediators of pain reduction

The soluble epoxide hydrolase (sEH) enzyme was discovered while investigating the metabolism of xenobiotic compounds in the Casida laboratory. However, an endogenous role of sEH is to regulate the levels of a group of potent bioactive lipids, epoxygenated fatty acids (EFAs), that have pleiotropic biological activities. The EFAs, in particular the arachidonic acid derived epoxy eicosatrienoic acids (EETs), are established autocrine and paracrine messengers. The most recently discovered outcome of inhibition of sEH and increased EFAs is their effects on the sensory system and in particular their ability to reduce pain. The inhibitors of sEH block both inflammatory and neuropathic pain. Elevation of EFAs, in both the central and peripheral nervous systems, blocks pain. Several laboratories have now published a number of potential mechanisms of action for the pain-reducing effects of EFAs. This paper provides a brief history of the discovery of the sEH enzyme and argues that inhibitors of sEH through several independent mechanisms display pain-reducing effects.

Central NO-cGMP pathway in thermoregulation and survival rate during polymicrobial sepsis

Sepsis induces production of inflammatory mediators such as nitric oxide (NO) and causes physiological alterations, including changes in body temperature (Tb). We evaluated the involvement of the central NO-cGMP pathway in thermoregulation during sepsis induced by cecal ligation and puncture (CLP), and analyzed its effect on survival rate. Male Wistar rats with a Tb probe inserted in their abdomen were intracerebroventricularly injected with 1 microL NG-nitro-L-arginine methyl ester (L-NAME, 250 microg), a nonselective NO synthase (NOS) inhibitor; or aminoguanidine (250 microg), an inducible NOS inhibitor; or 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 0.25 microg), a guanylate cyclase inhibitor. Thirty minutes after injection, sepsis was induced by cecal ligation and puncture (CLP), or the rats were sham operated. The animals were divided into 2 groups for determination of Tb for 24 h and assessment of survival during 3 days. The drop in Tb seen in the CLP group was attenuated by pretreatment with the NOS inhibitors (p < 0.05) and blocked with ODQ. CLP rats pretreated with either of the inhibitors showed higher survival rates than vehicle injected groups (p < 0.05), and were even higher in the ODQ pretreated group. Our results showed that the effect of NOS inhibition on the hypothermic response to CLP is consistent with the role of nitrergic pathways in thermoregulation.

Food deprivation alters thermoregulatory responses to lipopolysaccharide by enhancing cryogenic inflammatory signaling via prostaglandin D2

We tested the hypothesis that food deprivation alters body temperature (T(b)) responses to bacterial LPS by enhancing inflammatory signaling that decreases T(b) (cryogenic signaling) rather than by suppressing inflammatory signaling that increases T(b) (febrigenic signaling). Free-feeding or food-deprived (24 h) rats received LPS at doses (500 and 2,500 microg/kg iv) that are high enough to activate both febrigenic and cryogenic signaling. At these doses, LPS caused fever in rats at an ambient temperature of 30 degrees C, but produced hypothermia at an ambient temperature of 22 degrees C. Whereas food deprivation had little effect on LPS fever, it enhanced LPS hypothermia, an effect that was particularly pronounced in rats injected with the higher LPS dose. Enhancement of hypothermia was not due to thermogenic incapacity, since food-deprived rats were fully capable of raising T(b) in response to the thermogenic drug CL316,243 (1 mg/kg iv). Neither was enhancement of hypothermia associated with altered plasma levels of cytokines (TNF-alpha, IL-1beta, and IL-6) or with reduced levels of an anti-inflammatory hormone (corticosterone). The levels of PGD(2) and PGE(2) during LPS hypothermia were augmented by food deprivation, although the ratio between them remained unchanged. Food deprivation, however, selectively enhanced the responsiveness of rats to the cryogenic action of PGD(2) (100 ng icv) without altering the responsiveness to febrigenic PGE(2) (100 ng icv). These findings support our hypothesis and indicate that cryogenic signaling via PGD(2) underlies enhancement of LPS hypothermia by food deprivation.

Temperature management in acute neurologic disorders

Temperature management in acute neurologic disorders has received considerable attention in the last 2 decades. Numerous trials of hypothermia have been performed in patients with head injury, stroke, and cardiac arrest. This article reviews the physiology of thermoregulation and mechanisms responsible for hyperpyrexia. Detrimental effects of fever and benefits of normalizing elevated temperature in experimental models are discussed. This article presents a detailed analysis of trials of induced hypothermia in patients with acute neurologic insults and describes methods of fever control.

The dorsomedial hypothalamus: a new player in thermoregulation

Neurons in the dorsomedial hypothalamus (DMH) play key roles in physiological responses to exteroceptive (“emotional”) stress in rats, including tachycardia. Tachycardia evoked from the DMH or seen in experimental stress in rats is blocked by microinjection of the GABAA receptor agonist muscimol into the rostral raphe pallidus (rRP), an important thermoregulatory site in the brain stem, where disinhibition elicits sympathetically mediated activation of brown adipose tissue (BAT) and cutaneous vasoconstriction in the tail. Disinhibition of neurons in the DMH also elevates core temperature in conscious rats and sympathetic activity to least significant difference interscapular BAT (IBAT) and IBAT temperature in anesthetized preparations. The latter effects are blocked by microinjection of muscimol into the rRP, while microinjection of muscimol into either the rRP or DMH suppresses increases in sympathetic nerve activity to IBAT, IBAT temperature, and core body temperature elicited either by microinjection of PGE2 into the preoptic area (an experimental model for fever), or central administration of fentanyl. Neurons concentrated in the dorsal region of the DMH project directly to the rRP, a location corresponding to that of neurons transsynaptically labeled from IBAT. Thus these neurons control nonshivering thermogenesis in rats, and their activation signals its recruitment in diverse experimental paradigms. Evidence also points to a role for neurons in the DMH in thermoregulatory cutaneous vasoconstriction, shivering, and endocrine adjustments. These directions provide intriguing avenues for future exploration that may expand our understanding of the DMH as an important hypothalamic site for the integration of autonomic, endocrine, and behavioral responses to diverse challenges.

Temperature Management in Acute Neurologic Disorders

Temperature management in acute neurologic disorders has received considerable attention in the last 2 decades. Numerous trials of hypothermia have been performed in patients with head injury, stroke, and cardiac arrest. This article reviews the physiology of thermoregulation and mechanisms responsible for hyperpyrexia. Detrimental effects of fever and benefits of normalizing elevated temperature in experimental models are discussed. This article presents a detailed analysis of trails of induced hypothermia in patients with acute neurologic insults and describes methods of fever control.

Stress-induced cardiac stimulation and fever: Common hypothalamic origins and brainstem mechanisms

Our past results provide considerable evidence that activation of neurons somewhere in the region of the dorsomedial hypothalamus (DMH) plays a key role in the generation of many of the effects typically seen in "emotional" stress in rats, including activation of the hypothalamic-pituitary-adrenal (HPA) axis, the neuroendocrine hallmark of the generalized response to stress, and sympathetically mediated tachycardia. More recently, we demonstrated that (1) the tachycardia resulting either from chemical stimulation of the DMH or from experimental stress is markedly attenuated by microinjection of the GABAA receptor agonist muscimol, a neuronal inhibitor, into the medullary raphe pallidus (RP); and (2) the specific subregion of the DMH mediating stimulation-induced tachycardia corresponds to the dorsal hypothalamic area (DHA), a site where neurons projecting to the RP are densely concentrated. Thus, the pathway from neurons in the DHA to sympathetic premotor neurons in the RP may constitute a key relay mediating the increases in heart rate seen in emotional stress--a role that had never been proposed previously for either of these regions. Instead, sympathetic premotor neurons were known to exist in the RP but had been most closely associated with sympathetic thermoregulatory mechanisms, including activation of brown fat, the principal means for nonshivering thermogenesis in rats, and cutaneous vasoconstriction in the tail, an important method of conserving body heat in this species. These sympathetic effects serve to maintain body temperature in a cold environment or to increase it in fever--and are typically accompanied by tachycardia. Interestingly, we and others have now shown that (1) disinhibition of neurons in the DMH also increases body temperature, at least in part through activation of brown fat, (2) microinjection of the neuronal inhibitor muscimol into the DMH reduces experimental fever and the associated tachycardia in rats. We hypothesize that activation of neurons in the DMH mediates both the increased body temperature and cardiac stimulation produced in rats by experimental "emotional" stress and fever, and that these effects are mediated in large part through direct projections to sympathetic premotor neurons in the RP. Thus, this pathway may constitute a common effector circuit upon which a variety of forebrain inputs converge in response to diverse environmental challenges.

Impacts of fever on locust life-history traits: costs or benefits?

Fever, like other mechanisms for defence against pathogens, may have positive and negative consequences for host fitness. In ectotherms, fever can be attained through modified behavioural thermoregulation. Here we examine potential costs of behavioural fever by holding adult, gregarious desert locusts at elevated temperatures simulating a range of fever intensities. We found no effect of fever temperatures on primary fitness correlates of survival and fecundity. However, flight capacity and mate competition were reduced, although there was no relation between time spent at fever temperatures and magnitude of the response. While these effects could indicate a direct cost of fever, they are also consistent with a shift towards the solitaria phase state that, in a field context, could be considered an adaptive life-history response to limit the impact of disease. These conflicting interpretations highlight the importance of considering complex defence mechanisms and trade-offs in an appropriate ecological context.

Immunological role of neuronal receptor vanilloid receptor 1 expressed on dendritic cells

Capsaicin (CP), the pungent component of chili pepper, acts on sensory neurons to convey the sensation of pain. The CP receptor, vanilloid receptor 1 (VR1), has been shown to be highly expressed by nociceptive neurons in dorsal root and trigeminal ganglia. We demonstrate here that the dendritic cell (DC), a key cell type of the vertebrate immune system, expresses VR1. Engagement of VR1 on immature DCs such as by treatment with CP leads to maturation of DCs as measured by up-regulation of antigen-presenting and costimulatory molecules. This effect is present in DCs of VR1+/+ but not VR1-/- mice. In VR1+/+ mice, this effect is inhibited by the VR1 antagonist capsazepine. Further, intradermal administration of CP leads to migration of DCs to the draining lymph nodes in VR1+/+ but not VR1-/- mice. These data demonstrate a powerful influence of a neuroactive ligand on a central aspect of immune function and a commonality of mechanistic pathways between neural and immune functions.

The effect of fever‐like temperatures on neutrophil signaling

The effect of fever on neutrophils has not been explored. We tested the hypothesis that fever-like temperature spikes affect neutrophil signaling and function. Prior 60 min, 42 degrees C heat exposure inhibited p38 MAPK, ERK, PI3-Kinase/Akt, and NF-kappaB activation in TNF-alpha-challenged suspended neutrophils. Using pharmacological inhibitors and an inhibitory peptide transduced into neutrophils by a HIV-TAT sequence, we found that p38 MAPK and NF-kappaB mediate TNF-alpha-mediated delayed apoptosis in suspended neutrophils. Heat exposure (39-42 degrees C) did not affect constitutive apoptosis but abrogated TNF-alpha-delayed apoptosis in these suspended cells. In contrast, adhesion-dependent functions were not inhibited. Furthermore, we found that heat exposure neither blocked p38 MAPK, ERK, and NF-kappaB activation in neutrophils on fibronectin nor prevented delayed apoptosis by TNF-alpha when cells interacted with fibronectin. Above and beyond apoptosis, TNF-alpha initiated NF-kappaB-dependent gene transcription. Heat exposure blocked this effect in suspended neutrophils but not in neutrophils on fibronectin. Finally, we show that beta2-integrins, which are not necessary for TNF-alpha-induced NF-kappaB activation at 37 degrees C, transduce costimulatory signals allowing NF-kappaB activation after heat exposure. The effect could protect circulating neutrophils from TNF-alpha activation, while not interfering with activation of adherent neutrophils. Fever could make neutrophils more parsimonious.

“Starve a fever and feed a cold”: feeding and anorexia may be adaptive behavioral modulators of autonomic and T helper balance

Anorexia is a common symptom accompanying infections, but the teleology of the phenomenon remains unexplained. We hypothesize that anorexia may represent a prehistoric behavioral adaptation to fight infection by maintaining T helper (Th)2 bias, which is particularly vital in fighting bacterial pathogens. Specifically, we propose that anorexia may avert the reduction of Th2/Th1 ratio by preventing feeding-induced neurohormonal and vagal output from the gut. Emerging evidence suggests that the vagal and neurohormonal output of the gut during feeding promotes Th1 function, which is desirable in fighting viral infections. Since fever may be an adaptation to fight bacteria and "colds" are generally viral in origin, the adage "starve a fever and feed a cold" may reflect a sensible behavioral strategy to tilt autonomic and Th balance in directions that are optimal for fighting the particular type of infection. The ability to modulate T helper balance through the neurohormonal and autonomic axis by adjusting food intake may be the mechanism behind other unexplained clinical observations such as the improved outcomes of ICU patients after enteric versus parenteric feedings. Compared to the prehistoric period when bacterial infection was commonplace, the anorexic response may be less adaptive today when viruses and cancers have become common triggers of anorexia. By promoting host anorexia, cachexia, and insomnia, cancers and viruses can deter behaviors such as digestion and sleep that would raise vagal and Th1 activity against tumors and viruses. Hydration and sleep, unexplained but widely accepted recommendations for flu patients, may also work by promoting vagal and Th1 functions. Modulating feeding, hydration, and sleep may prove beneficial in treating other conditions associated with abnormal autonomic and Th balance.

Shivering in acutely ill vulnerable populations

The hazards of thermoregulatory shivering in the critically ill are often overlooked by caregivers. Shivering may accompany heat loss from bathing, dressing, transport, and many therapeutic activities. Febrile shivering is common during chills of fever, blood product transfusions, administration of antigenic drugs, and chemotherapy. Many patients are at risk for shivering and its negative consequences that increase oxygen expenditure and cardiorespiratory effort. Learning how underlying thermoregulatory mechanisms are involved in shivering clarifies how temperature gradients and environmental stimuli induce the shivering response. Knowledge of the anatomical progression of shivering equips the nurse to recognize or prevent this energy-consuming response. This article discusses measures to prevent shivering as well as evidence-based interventions to manage shivering during fever, aggressive cooling, and postoperative recovery. Detailed information is presented on assessment and documentation of the extent and severity of shivering.

Epstein-Barr virus-encoded dUTPase modulates immune function and induces sickness behavior in mice

Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis (IM). In addition, latent infections with EBV are associated with nasopharyngeal carcinoma (NPC) and Burkitt's Lymphoma (BL). Antibodies to several EBV-encoded early antigens (EA) are often observed in patients with NPC and BL, however, the role of EBV-encoded proteins in the etiology of these and other EBV-associated diseases is not completely understood. The EA complex encodes for at least six different viral enzymes including deoxyuridine triphosphate nucleotidohydrolase (dUTPase). dUTPase has recently been shown to modulate activation of human peripheral blood mononuclear cells in vitro (unpublished data). Therefore, these studies were designed to test whether dUTPase would modulate immune function in an in vivo model. Mice were injected with purified EBV dUTPase, and baseline immune function and sickness behaviors were measured. EBV dUTPase treatment inhibited replication of mitogen-stimulated lymphocytes obtained from treated mice. These lymphocytes were also less able to synthesize interferon-gamma after re-stimulation. In addition, treatment with dUTPase induced sickness behaviors. For example, as compared to control animals, dUTPase-treated animals lost body mass, had elevated body temperature, and displayed diminished locomotor activity. These data suggest that individual viral proteins may play a role in the pathophysiology of EBV associated disease.

Stress-induced fever after postischemic rectal temperature measurements in the gerbil

Postischemic temperature, which modulates brain injury, is commonly determined via a rectal temperature (Trec) probe. This procedure causes a stress-induced fever (SIF) in rodents that may aggravate injury or diminish the efficacy of a neuroprotectant. We continually measured core temperature (Tcore) via an implanted telemetry probe and made 16 Trec measurements over 4 days in sham and ischemic gerbils (5 min bilateral carotid artery occlusion). Controls did not have Trec sampled, but Tcore was measured. Rectal temperature measurements predicted Tcore in sham and ischemic gerbils. The Trec measurements caused a SIF (1 degrees C peak) in shams that did not habituate, whereas the SIF was initially absent and then increased over days in ischemic gerbils. Ischemic groups had similar CA1 injury (approximately 32% remaining), presumably because Trec measurements only resulted in a significant SIF starting on day 2 postischemia, when cell death is less sensitive to hyperthermia. Caution is warranted with Trec measurements, since the resultant SIF occurs to different extents in normal and ischemic rodents. Furthermore, the SIF could vary according to many other factors, such as the type and severity of insult, the time and frequency of measurement, and drug treatment. Accordingly, postischemic Trec measurements should be replaced with telemetry probes.

Diurnal and sleep-wake dependent variations of soluble TNF- and IL-2 receptors in healthy volunteers

There is very little published information on the diurnal variation of cytokines and their receptors, in healthy individuals during normal sleep-wake patterns or during sustained wakefulness. The aim of the current investigation was to characterize concentrations of soluble tumor necrosis factor receptors (sTNF-Rs) and interleukin-2 receptor (sIL-2R) during normal sleep and wakefulness, as well as during a 24 h vigil. Plasma levels of the sTNF-R p55, sTNF-R p75, and sIL-2R did not differ significantly between nocturnal sleep and nocturnal wakefulness. Rhythmic analysis (2-h intervals) revealed significant diurnal variations for both sTNF-R p55 and sTNF-R p75, but not levels of sIL-2R. Diurnal variations of both sTNF-Rs were characterized by a single cosine curve with an average peak near 06:00 h in the morning. This peak occurred well before that of cortisol, and fluctuated inversely with the diurnal rhythm of temperature. These diurnal variations in sTNF-Rs levels are consistent with the hypothesis that the TNF system plays a role in normal diurnal temperature regulation.

A novel antipyretic action of 15-deoxy-Delta12,14-prostaglandin J2 in the rat brain

Fever is an important part of the host defense response, yet fever can be detrimental if it is uncontrolled. We provide the first evidence that 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), an endogenous ligand for peroxisome proliferator-activated receptor gamma (PPARgamma), can attenuate the febrile response to lipopolysaccharide (LPS) in rats via an action on the brain. Furthermore, we show that PPARgamma is expressed in the hypothalamus, an important locus in the brain for fever generation. In addition, 15d-PGJ2 and its synthesizing enzyme (PGD2 synthase) were present in rat cerebrospinal fluid, and their levels were enhanced in response to systemic injection of LPS. The antipyretic effect of 15d-PGJ2 was associated with reduction in LPS-stimulated cyclooxygenase-2 expression in the hypothalamus but not in p44/p42 mitogen-activated protein kinase phosphorylation or in the expression of the PPARgamma. Thus it is likely that there is a parallel induction of an endogenous prostanoid pathway in the brain capable of limiting deleterious actions of the proinflammatory prostaglandin E2-dependent pathway.

Gene expression profiling of melanocortin system in neuropathic rats supports a role in nociception

The melanocortin (MC) system is involved in several biological functions. Its possible role in nociception has recently attracted attention in the field. Published data suggest that melanocortin antagonists are analgesic and agonists are hyperalgesic. Gene expression information about the MC system components (receptor, agonist and antagonist) in pain relevant areas is at present limited. To deepen our knowledge, we studied the expression of MC system components in nai;ve, sham and neuropathic rat spinal cord and dorsal root ganglia (DRG) by PCR and quantitative real-time PCR. MC4 receptor, proopiomelanocortin (POMC) and agouti-related protein (AgRP) transcripts were detected in both spinal cord and DRG, whereas MC3 receptor was detected only in the spinal cord. To study the relationship between the MC system and chronic pain, we used the chronic constriction injury model and gene expression analysis was performed in rats showing both tactile allodynia and thermal hyperalgesia. MC4 and POMC transcript were upregulated in the spinal cord of neuropathic rats, whereas MC3 and AgRP expression were unaffected. Thus, this study demonstrates for the first time the presence of AgRP in the spinal cord and DRG, suggesting that it could play a role in the regulation of MC system activity. In addition, the upregulation of POMC and MC4, in parallel with the presence of tactile allodynia and thermal hyperalgesia, further supports the idea of MC system involvement in nociception.

The role of melanocortins and their receptors in inflammatory processes, nerve regeneration and nociception

The melanocortins are a family of bioactive peptides derived from proopiomelanocortin. Those peptides, included among hormones and comprising ACTH, alpha-MSH, beta-MSH and gamma-MSH, are best known mainly for their physiological effects, such as the control of skin pigmentation by alpha-MSH, and ACTH effects on pigmentation and steroidogenesis. Melanocortins are released in various sites in the central nervous system and in peripheral tissues, and participate in the regulation of multiple physiological functions. They are involved in grooming behavior, food intake and thermoregulation processes, and can also modulate the response of the immune system in inflammatory states. Research of the past decade provided evidence that melanocortins could elicit their diverse biological effects by binding to a distinct family of G protein-coupled receptors with seven transmembrane domains. To date, five melanocortin receptor genes have been cloned and characterized. Those receptors differ in their tissue distribution and in their ability to recognize various melanocortins. These advances have opened up new horizons for exploring the significance of melanocortins, their ligands and their receptors for a variety of important physiological functions. We reviewed the origin of MSH peptides, the function and distribution of melanocortin receptors and their endogenous and exogenous ligands and the role of melanocortins and their receptors in inflammatory processes, nerve regeneration and nociception. Moreover, we analyzed their interaction with opioid peptides and finally, we discussed the postulated role of the melanocortin system in pain transmission at the spinal cord level.