Journal of pharmacological sciences
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Oxidative stress plays pivotal roles in aging, neurodegenerative disease, and pathological conditions such as ischemia. We investigated the effect of sulforaphane and 6-(methysulfinyl) hexyl isothiocyanate (6-HITC), a naturally occurring isothiocyanate, on oxidative stress-induced cytotoxicity using primary neuronal cultures of rat striatum. Pretreatment with sulforaphane and 6-HITC significantly protected against H(2)O(2)- and paraquat-induced cytotoxicity in a concentration-dependent manner. ⋯ In contrast, sulforaphane and 6-HITC increased heme oxygenase-1 (HO-1) expression in neurons. However, zinc-protophorphyrin IX, a competitive inhibitor of HO-1, did not influence the protective effects of sulforaphane and 6-HITC. These results suggest that sulforaphane and 6-HITC prevent oxidative stress-induced cytotoxicity in rat striatal cultures by raising the intracellular glutathione content via an increase in γ-GCS expression induced by the activation of the Nrf2-antioxidant response element pathway.
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We investigated the effects of gabapentin and pregabalin on the itch-associated response in a mouse model of chronic dermatitis induced by the repeated application of 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one (oxazolone). Challenging the mice with oxazolone-induced chronic dermatitis with the oxazolone evoked severe and transient scratching behavior until 1 h after the application of oxazolone. Thereafter, a more mild and continuous scratching behavior was also observed for at least 8 h. ⋯ Gabapentin failed to suppress the scratching behavior induced by the intradermal injection of compound 48/80 in normal mice. The expression of the α₂δ-1 subunit in dorsal root ganglion (DRG) from mice following repeated application of oxazolone was significantly higher than that from normal mice. These results suggest that gabapentin and pregabalin show an anti-pruritic activity through α₂δ-subunit binding, and the up-regulation of the α₂δ-1 subunit in DRG may therefore play an important role in its anti-pruritic activity.
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G protein-coupled receptors, in particular, Ca(2+)-mobilizing G(q)-coupled receptors have been reported to be targets for anesthetics. Opioids are commonly used analgesics in clinical practice, but the effects of anesthetics on the opioid mu-receptors (muOR) have not been systematically examined. We report here an electrophysiological assay to analyze the effects of anesthetics and ethanol on the functions of muOR in Xenopus oocytes expressing a muOR fused to chimeric Galpha protein G(qi5) (muOR-G(qi5)). ⋯ Propofol and halothane inhibited the DAMGO-induced currents only at higher concentrations. These findings suggest that ketamine and ethanol may inhibit muOR functions in clinical practice. We propose that the electrophysiological assay in Xenopus oocytes expressing muOR-G(qi5) would be useful for analyzing the effects of anesthetics and analgesics on opioid receptor function.
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Linopirdine is a well known blocker of voltage-gated potassium channels from the Kv7 (or KCNQ) family that generate the so called M current in mammalian neurons. Kv7 subunits are also expressed in pain-sensing neurons in dorsal root ganglia, in which they modulate neuronal excitability. In this study we demonstrate that linopirdine acts as an agonist of TRPV1 (transient receptor potential vanilloid type 1), another ion channel expressed in nociceptors and involved in pain signaling. ⋯ Linopirdine also activates an inward current in TRPV1-expressing HEK293 cells that is almost completely blocked by the selective TRPV1 antagonist capsazepine. At low concentrations linopirdine sensitizes both recombinant and native TRPV1 channels to heat, in a manner that is not prevented by the Kv7-channel opener flupirtine. Taken together, these results indicate that linopirdine exerts an excitatory action on mammalian nociceptors not only through inhibition of the M current but also through activation of the capsaicin receptor TRPV1.
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Development of next-generation analgesics requires a better understanding of the molecular and cellular mechanisms underlying pathological pain. Accumulating evidence suggests that the activation of glia contributes to the central sensitization of pain signaling in the spinal cord. The role of microglia in pathological pain has been well documented, while that of astrocytes still remains unclear. ⋯ Although astrocyte-to-neuron signals implicated in pathological pain is poorly understood, activated astrocytes, as well as microglia, produce proinflammatory cytokines and chemokines, which lead to adaptation of the dorsal horn neurons. Furthermore, it has been suggested that glial glutamate transporters in the spinal astrocytes are down-regulated in pathological pain and that up-regulation or functional enhancement of these transporters prevents pathological pain. This review will briefly discuss novel findings on the role of spinal astrocytes in pathological pain and their potential as a therapeutic target for novel analgesics.