Articles: hyperalgesia.
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The molecular mechanisms responsible for sustained pain after tissue injury are largely unknown. The aim of this study was to clarify the role of exchange protein directly activated by cyclic adenosine monophosphate (EPAC) in sustained postincisional nociception, using tissue injury-induced nociceptor priming, and involvement of p38 mitogen-activated protein kinase (p38MAPK) in EPAC-mediated nociceptor priming. ⋯ Transient inflammatory stimulation causes long-lasting nociceptive hypersensitivity via nociceptor priming during the subacute period after incision. Acquired EPAC activity by p38MAPK in the dorsal root ganglion neurons is a key for this event.
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Temporomandibular disorders (TMDs) have the highest prevalence in women of reproductive age. The role of estrogen in TMDs and especially in TMDs related pain is not fully elucidated. Voltage-gated sodium channel 1.7 (Nav1.7) plays a prominent role in pain perception and Nav1.7 in trigeminal ganglion (TG) is involved in the hyperalgesia of inflamed Temporomandibular joint (TMJ). Whether estrogen could upregulate trigeminal ganglionic Nav1.7 expression to enhance hyperalgesia of inflamed TMJ remains to be explored. ⋯ Estradiol could upregulate trigeminal ganglionic Nav1.7 expression to contribute to hyperalgesia of inflamed TMJ.
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The current study investigated stretch variables and mechanical factors of lengthening contractions (LC) in the processes leading to muscular mechanical hyperalgesia in rats to understand mechanisms underpinning delayed onset muscle soreness (DOMS). ⋯ Mechanical hyperalgesia appears after LC in a stretch velocity- and range of motion-dependent manner. The rate of torque increase and integrated torque are the crucial factors. Neurotrophic factor-mediated peripheral pain mechanisms without robust inflammatory changes caused by myofibre damage were required for this mechanical hyperalgesia.
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The dorsal horn of the spinal cord is a crucial site for pain transmission and modulation. Dorsal horn neurons of the spinal cord express group I metabotropic glutamate receptors (group I mGluRs) that exert a complex role in nociceptive transmission. In particular, group I mGluRs promote the activation of L-type calcium channels, voltage-gated channels involved in short- and long-term sensitization to pain. ⋯ Surprisingly, in a model of persistent inflammation induced by complete Freund’s adjuvant, the activation of group I mGluRs induced an analgesia and a decrease in nociceptive field potentials. Among the group I mGluRs, mGluR1 promotes the activation of L-type calcium channels and increased nociceptive transmission while mGluR5 induces the opposite through the inhibitory network. These results suggest a functional switch exists in pathological conditions that can change the action of group I mGluR agonists into possible analgesic molecules, thereby suggesting new therapeutic perspectives to treat persistent pain in inflammatory settings.
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Accumulating evidence has demonstrated that epigenetic modification-mediated changes in pain-related gene expressions play an important role in the development and maintenance of neuropathic pain. Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, is involved in the development of chronic pain. Moreover, SIRT1 may be a novel therapeutic target for the prevention of type 2 diabetes mellitus (T2DM). ⋯ Concurrently, increased expressions of mGluR1/5 and H3 acetylation levels at Grm1/5 promoter regions were reversed by SIRT1 activation. In addition, knockdown of SIRT1 by Ad-SIRT1-shRNA induced pain behaviors and spinal neuronal activation in normal rats, which was accompanied by the increased expressions of mGluR1/5 and H3 acetylation levels at Grm1/5 promoter regions. Therefore, we concluded that SIRT1-mediated epigenetic regulation of mGluR1/5 expressions was involved in the development of neuropathic pain in type 2 diabetic rats.