An involvement of the transient receptor potential vanilloid (TRPV) 1 channel in the regulation of body temperature (T b ) has not been established decisively. To provide decisive evidence for such an involvement and determine its mechanisms were the aims of the present study. We synthesized a new TRPV1 antagonist, AMG0347 [(E)-N-(7-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl)-3-(2-(piperidin-1-yl)-6-(trifluoromethyl)pyridin-3-yl)acrylamide], and characterized it in vitro. We then found that this drug is the most potent TRPV1 antagonist known to increase T b of rats and mice and showed (by using knock-out mice) that the entire hyperthermic effect of AMG0347 is TRPV1 dependent. AMG0347-induced hyperthermia was brought about by one or both of the two major autonomic cold-defense effector mechanisms (tail-skin vasoconstriction and/or thermogenesis), but it did not involve warmth-seeking behavior. The magnitude of the hyperthermic response depended on neither T b nor tail-skin temperature at the time of AMG0347 administration, thus indicating that AMG0347-induced hyperthermia results from blockade of tonic TRPV1 activation by nonthermal factors. AMG0347 was no more effective in causing hyperthermia when administered into the brain (intracerebroventricularly) or spinal cord (intrathecally) than when given systemically (intravenously), which indicates a peripheral site of action. We then established that localized intra-abdominal desensitization of TRPV1 channels with intraperitoneal resiniferatoxin blocks the T b response to systemic AMG0347; the extent of desensitization was determined by using a comprehensive battery of functional tests. We conclude that tonic activation of TRPV1 channels in the abdominal viscera by yet unidentified nonthermal factors inhibits skin vasoconstriction and thermogenesis, thus having a suppressive effect on T b .

We studied M8-B, a selective and potent antagonist of the transient receptor potential melastatin-8 (TRPM8) channel. In vitro, M8-B blocked cold-induced and TRPM8-agonist-induced activation of rat, human, and murine TRPM8 channels, including those on primary sensory neurons. In vivo, M8-B decreased deep body temperature (Tb) in Trpm8+/+ mice and rats, but not in Trpm8−/− mice, thus suggesting an on-target action. The intravenous administration of M8-B was more effective in decreasing Tb in rats than the intrathecal or intracerebroventricular administration, indicating a peripheral action. M8-B attenuated cold-induced c-Fos expression in the lateral parabrachial nucleus, thus indicating a site of action within the cutaneous cooling neural pathway to thermoeffectors, presumably on sensory neurons. A low intravenous dose of M8-B did not affect Tb at either a constantly high or a constantly low ambient temperature (Ta), but the same dose readily decreased Tb if rats were kept at a high Ta during the M8-B infusion and transferred to a low Ta immediately thereafter. These data suggest that both a successful delivery of M8-B to the skin (high cutaneous perfusion) and the activation of cutaneous TRPM8 channels (by cold) are required for the hypothermic action of M8-B. At tail skin temperatures < 23°C, the magnitude of the M8-B-induced decrease in Tb was inversely related to skin temperature, thus suggesting that M8-B blocks thermal (cold) activation of TRPM8. M8-B affected all thermoeffectors studied (thermopreferendum, tail skin vasoconstriction, and brown fat thermogenesis), thus suggesting that TRPM8 is a universal cold receptor in the thermoregulation system.

Transient receptor potential vanilloid-1 (TRPV1) antagonists are widely viewed as next-generation pain therapeutics. However, these compounds cause hyperthermia, a serious side effect. TRPV1 antagonists differentially block three modes of TRPV1 activation: by heat, protons, and chemical ligands (e.g., capsaicin). We asked what combination of potencies in these three modes of TRPV1 activation corresponds to the lowest potency of a TRPV1 antagonist to cause hyperthermia. We studied hyperthermic responses of rats, mice, and guinea pigs to eight TRPV1 antagonists with different pharmacological profiles and used mathematical modeling to find a relative contribution of the blockade of each activation mode to the development of hyperthermia. We found that the hyperthermic effect has the highest sensitivity to the extent of TRPV1 blockade in the proton mode (0.43 to 0.65) with no to moderate sensitivity in the capsaicin mode (Ϫ0.01 to 0.34) and no sensitivity in the heat mode (0.00 to 0.01). We conclude that hyperthermia-free TRPV1 antagonists do not block TRPV1 activation by protons, even if they are potent blockers of the heat mode, and that decreasing the potency to block the capsaicin mode may further decrease the potency to cause hyperthermia.

This study aimed at determining the thermoregulatory phenotype of mice lacking transient receptor potential vanilloid-1 (TRPV1) channels. We used Trpv1 knockout (KO) mice and their genetically unaltered littermates to study diurnal variations in deep body temperature (Tb) and thermoeffector activities under basal conditions, as well as thermoregulatory responses to severe heat and cold. Only subtle alterations were found in the basal Tb of Trpv1 KO mice or in their Tb responses to thermal challenges. The main thermoregulatory abnormality of Trpv1 KO mice was a different pattern of thermoeffectors used to regulate Tb. On the autonomic side, Trpv1 KO mice were hypometabolic (had a lower oxygen consumption) and hypervasoconstricted (had a lower tail skin temperature). In agreement with the enhanced skin vasoconstriction, Trpv1 KO mice had a higher thermoneutral zone. On the behavioral side, Trpv1 KO mice preferred a lower ambient temperature and expressed a higher locomotor activity. Experiments with pharmacological TRPV1 agonists (resiniferatoxin and anandamide) and a TRPV1 antagonist (AMG0347) confirmed that TRPV1 channels located outside the brain tonically inhibit locomotor activity. With age (observed for up to 14 months), the body mass of Trpv1 KO mice exceeded that of controls, sometimes approaching 60 g. In summary, Trpv1 KO mice possess a distinct thermoregulatory phenotype, which is coupled with a predisposition to age-associated overweight and includes hypometabolism, enhanced skin vasoconstriction, decreased thermopreferendum, and hyperkinesis. The latter may be one of the primary deficiencies in Trpv1 KO mice. We propose that TRPV1-mediated signals from the periphery tonically suppress the general locomotor activity.

DL, Romanovsky AA. Cyclooxygenase-1 or -2-which one mediates lipopolysaccharide-induced hypothermia? Am J Physiol Regul Integr Comp Physiol 297: R485-R494, 2009. First published June 10, 2009 doi:10.1152/ajpregu.91026.2008.-Systemic inflammation is associated with either fever or hypothermia. Fever, a response to mild systemic inflammation, is mediated by cyclooxygenase (COX)-2 and not by COX-1. However, it is still disputed whether COX-2, COX-1, neither, or both mediate(s) responses to severe systemic inflammation, and, in particular, the hypothermic response. We compared the effects of SC-236 (COX-2 inhibitor) and SC-560 (COX-1 inhibitor) on the deep body temperature (Tb) of rats injected with a lower (10 g/kg iv) or higher (1,000 g/kg iv) dose of LPS at different ambient temperatures (Tas). At a neutral Ta (30°C), the rats responded to LPS with a polyphasic fever (lower dose) or a brief hypothermia followed by fever (higher dose). SC-236 (2.5 mg/kg iv) blocked the fever induced by either LPS dose, whereas SC-560 (5 mg/kg iv) altered neither the febrile response to the lower LPS dose nor the fever component of the response to the higher dose. However, SC-560 blocked the initial hypothermia caused by the higher LPS dose. At a subneutral T a (22°C), the rats responded to LPS with early (70 -90 min, nadir) dose-dependent hypothermia. The hypothermic response to either dose was enhanced by SC-236 but blocked by SC-560. The hypothermic response to the higher LPS dose was associated with a fall in arterial blood pressure. This hypotensive response was attenuated by either SC-236 or SC-560. At the onset of LPS-induced hypothermia and hypotension, the functional activity of the COX-1 pathway (COX-1-mediated PGE2 synthesis ex vivo) increased in the spleen but not liver, lung, kidney, or brain. The expression of splenic COX-1 was unaffected by LPS. We conclude that COX-1, but not COX-2, mediates LPS hypothermia, and that both COX isoforms are required for LPS hypotension. body temperature; thermoregulation; fever; inflammation SO STRONGLY IS SYSTEMIC INFLAMMATION associated with changes in deep body temperature (T b ) that every clinical definition of the systemic inflammatory response syndrome includes a change in T b (11,48). Whereas the majority (ϳ90%) of patients with systemic inflammation have an increased T b , a number of them (ϳ10%) have a lowered T b (6, 17). Thermoregulatory manifestations are also present in animal models of systemic inflammation. In a rat model of systemic inflammation induced by bacterial LPS, the pattern of T b change depends on the ambient temperature (T a ) and the LPS dose. At a neutral or supraneutral T a (warm environment), fever is the prevailing response; the fever is monophasic when the dose of LPS is low (just suprathreshold), but it turns polyphasic as the dose increases (66, 68, 69, 71, 79); a mild hypothermia may precede the polyphasic fever when the dose of LPS is high (68). At a subneutral T a (cool environment), hypothermia followed by fever is the predominant response; th...

The role of vitamin D in osteomineral metabolism is well known. Several studies have suggested its action on different biological mechanisms, such as nociceptive sensitivity and sleep-wake cycle modulation. Sleep is an important biological process regulated by different regions of the central nervous system, mainly the hypothalamus, in combination with several neurotransmitters. Pain, which can be classified as nociceptive, neuropathic and psychological, is regulated by both the central and peripheral nervous systems. In the peripheral nervous system, the immune system participates in the inflammatory process that contributes to hyperalgesia. Sleep deprivation is an important condition related to hyperalgesia, and recently it has also been associated with vitamin

Non-technical summary Systemic inflammation and related disorders, including sepsis, are leading causes of death in hospitalized patients. In most severe cases, systemic inflammation is accompanied by a drop in body temperature (hypothermia). We know that inflammation-associated hypothermia is a brain-mediated response, but mechanisms of this response are unknown. We administered a bacterial product (endotoxin) to rats to cause systemic inflammation and hypothermia. We then used a variety of pharmacological tools to probe whether three different receptors are involved in this hypothermia. We have found that one of the receptors studied, the so-called cannabinoid-1 (CB1) receptor, is crucial for the development of hypothermia. This is the same receptor that is responsible for many effects of marihuana (cannabis). We further show that hypothermia associated with inflammation depends on CB1 receptors located inside the brain. These novel findings suggest that brain CB1 receptors should be studied as potential therapeutic targets in systemic inflammation and sepsis.Abstract Hypothermia occurs in the most severe cases of systemic inflammation, but the mechanisms involved are poorly understood. This study evaluated whether the hypothermic response to bacterial lipopolysaccharide (LPS) is modulated by the endocannabinoid anandamide (AEA) and its receptors: cannabinoid-1 (CB1), cannabinoid-2 (CB2) and transient receptor potential vanilloid-1 (TRPV1). In rats exposed to an ambient temperature of 22• C, a moderate dose of LPS (25-100 μg kg −1 I.V.) induced a fall in body temperature with a nadir at ∼100 min postinjection. This response was not affected by desensitization of intra-abdominal TRPV1 receptors with resiniferatoxin (20 μg kg −1 I.P.), by systemic TRPV1 antagonism with capsazepine (40 mg kg −1 I.P.), or by systemic CB2 receptor antagonism with SR144528 (1.4 mg kgHowever, CB1 receptor antagonism by rimonabant (4.6 mg kg −1 I.P.) or SLV319 (15 mg kgblocked LPS hypothermia. The effect of rimonabant was further studied. Rimonabant blocked LPS hypothermia when administered I.C.V. at a dose (4.6 μg) that was too low to produce systemic effects. The blockade of LPS hypothermia by I.C.V. rimonabant was associated with suppression of the circulating level of tumour necrosis factor-α. In contrast to rimonabant, the I.C.V. administration of AEA (50 μg) enhanced LPS hypothermia. Importantly, I.C.V. AEA did not evoke hypothermia in rats not treated with LPS, thus indicating that AEA modulates LPS-activated pathways in the brain rather than thermoeffector pathways. In conclusion, the present study reveals a novel, critical role of brain CB1 receptors in LPS hypothermia. Brain CB1 receptors may constitute a new therapeutic target in systemic inflammation and sepsis.

Studies in young rodents have shown that the transient receptor potential vanilloid-1 (TRPV1) channel plays a suppressive role in the systemic inflammatory response syndrome (SIRS) by inhibiting production of tumor necrosis factor (TNF)α and possibly by other mechanisms. We asked whether the anti-inflammatory role of TRPV1 changes with age. First, we studied the effect of AMG517, a selective and potent TRPV1 antagonist, on aseptic, lipopolysaccharide (LPS)-induced SIRS in young (12 wk) mice. In agreement with previous studies, AMG517 increased LPS-induced mortality in the young. We then studied the effects of TRPV1 antagonism (AMG517 or genetic deletion of TRPV1) on SIRS in middle-aged (43-44 wk) mice. Both types of TRPV1 antagonism delayed and decreased LPS-induced mortality, indicating a reversal of the anti-inflammatory role of TRPV1 with aging. In addition, deletion of TRPV1 decreased the serum TNFα response to LPS, suggesting that the suppressive control of TRPV1 on TNFα production is also reversed with aging. In contrast to aseptic SIRS, polymicrobial sepsis (induced by cecal ligation and puncture) caused accelerated mortality in aged TRPV1-deficient mice as compared with wild-type littermates. The recovery of TRPV1-deficient mice from hypothermia associated with the cecal ligation and puncture procedure was delayed. Hence, the reversal of the anti-inflammatory role of TRPV1 found in the aged and their decreased systemic inflammatory response are coupled with suppressed defense against microbial infection. These results caution that TRPV1 antagonists, widely viewed as new-generation painkillers, may decrease the resistance of older patients to infection and sepsis.