Neuropharmacology
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Phα1β toxin is a peptide purified from the venom of the armed spider Phoneutria nigriventer, with markedly antinociceptive action in models of acute and persistent pain in rats. Similarly to ziconotide, its analgesic action is related to inhibition of high voltage activated calcium channels with more selectivity for N-type. In this study we evaluated the effect of Phα1β when injected peripherally or intrathecally in a rat model of spontaneous pain induced by capsaicin. ⋯ The simultaneous administration of Phα1β and SB366791 inhibited the capsaicin-induced Ca²⁺ transients that were additive suggesting that they act through different targets. Moreover, Phα1β did not inhibit capsaicin-activated currents in patch-clamp recordings of HEK293 cells that expressed TRPV1 receptors. Our results show that Phα1β may be effective as a therapeutic strategy for pain and this effect is not related to the inhibition of TRPV1 receptors.
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Comparative Study
Acetaminophen reduces lipopolysaccharide-induced fever by inhibiting cyclooxygenase-2.
Acetaminophen is one of the world's most commonly used drugs to treat fever and pain, yet its mechanism of action has remained unclear. Here we tested the hypothesis that acetaminophen blocks fever through inhibition of cyclooxygenase-2 (Cox-2), by monitoring lipopolysaccharide induced fever in mice with genetic manipulations of enzymes in the prostaglandin cascade. We exploited the fact that lowered levels of a specific enzyme make the system more sensitive to any further inhibition of the same enzyme. ⋯ However, when the same dose of acetaminophen was given to Cox-2 heterozygous mice, the febrile response to lipopolysaccharide was strongly attenuated, resulting in an almost normalized temperature curve, whereas no difference was seen between wild-type and heterozygous mPGES-1 mice. Furthermore, the fever to intracerebrally injected prostaglandin E₂ was unaffected by acetaminophen treatment. These findings reveal that acetaminophen, similar to aspirin and other non-steroidal anti-inflammatory drugs, is antipyretic by inhibiting cyclooxygenase-2, and not by inhibiting mPGES-1 or signaling cascades downstream of prostaglandin E₂.
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Comparative Study
Pleiotropic effect of histamine H4 receptor modulation in the central nervous system.
The histamine H4 receptor (H4R) is expressed primarily on cells involved in inflammation and immune responses. Recently, it has been reported the functional expression of H4R within neurons of the central nervous system, but their role has been poorly understood. The present study aimed to elucidate the physiopathological role of cerebral H4R in animal models by the intracerebroventricular administration of the H4R agonist VUF 8430 (20-40 μg per mouse). ⋯ Rotarod performance test was employed to demonstrate that the effects observed following the administration of VUF 8430 and JNJ 10191584 were not due to impaired motor function of animals. Furthermore, both compounds did not alter spontaneous mobility and exploratory activity in the hole board test. These results show the antinociceptive, antiamnesic, anxiolytic and anorexant effects induced by neuronal H4R agonism, suggesting that H4 modulators may have broader utility further the control of inflammatory and immune processes.
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Nitric oxide modulates pain development. However, there is no evidence on the effect of nitroxyl (HNO/NO⁻) in nociception. Therefore, we addressed whether nitroxyl inhibits inflammatory hyperalgesia and its mechanism using the nitroxyl donor Angeli's salt (AS; Na₂N₂O₃). ⋯ Furthermore, the analgesic effect of AS was prevented by treatment with ODQ (a soluble guanylate cyclase inhibitor), KT5823 (a protein kinase G [PKG] inhibitor) or glybenclamide (an ATP-sensitive K⁺ channel blocker), but not with naloxone (an opioid receptor antagonist). AS induced concentration-dependent increase in fluorescence intensity of DAF-treated neurons in a l-cysteine (nitroxyl scavenger) sensitive manner. l-cysteine did not affect the NO⁺ donor S-Nitroso-N-acetyl-DL- penicillamine (SNAP)-induced anti-hyperalgesia or fluorescence of DAF-treated neurons. This is the first study to demonstrate that nitroxyl inhibits inflammatory hyperalgesia by reducing cytokine production and activating the cGMP/PKG/ATP-sensitive K⁺ channel signaling pathway in vivo.
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Hemopressin is the first peptide ligand to be described for the CB₁ cannabinoid receptor. Hemopressin acts as an inverse agonist in vivo and can cross the blood-brain barrier to both inhibit appetite and induce antinociception. Despite being highly effective, synthetic CB₁ inverse agonists are limited therapeutically due to unwanted, over dampening of central reward pathways. ⋯ In contrast to AM251, there is a distinct lack of activation of the brain reward centres, such as the ventral tegmental area, nucleus accumbens and orbitofrontal cortex, which normally form a functional activity signature for the central action of synthetic CB₁ receptor inverse agonists. Thus, hemopressin modulates the function of key feeding-related brain nuclei of the mediobasal hypothalamus, and descending pain pathways of the PAG and DR, and not higher limbic structures. Thus, hemopressin may offer behaviourally selective effects on nociception and appetite, without engaging reward pathways.