Articles: neuropathic-pain.
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Earlier studies indicate that the central nucleus of the amygdala (CeA) contributes to neuropathic pain. Here we studied whether amygdaloid administration of antioxidants or antagonists of TRPA1 that is among ion channels activated by oxidative stress attenuates nociceptive or affective pain in experimental neuropathy, and whether this effect involves amygdaloid astrocytes or descending serotonergic pathways acting on the spinal 5-HT1A receptor. The experiments were performed in rats with spared nerve injury (SNI). ⋯ The results suggest that injury-induced amygdaloid oxidative stress that drives TRPA1 promotes neuropathic pain behavior. This pronociceptive effect involves suppression of medullospinal serotonergic feedback-inhibition acting on the spinal 5-HT1A receptor. While the CeA is involved in mediating the nerve injury-induced pronociception, it may not be a critical relay for the recruitment of medullospinal feedback-inhibition.
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CD137L (4-1BBL) is a costimulatory molecule whose signaling can promote monocyte/macrophage functions; however, CD137L-mediated microglial response and its role in neuropathic pain remain unknown. We investigated CD137L following peripheral nerve injury-induced neuropathic pain using a spinal nerve L5 transection (L5Tx) murine model in both sexes. First, C57BL/6_CD137L knock-out (KO) mice displayed decreased mechanical and diminished heat hypersensitivity compared to wild-type (WT) controls, beginning on day 3 to up to day 35 post-L5Tx. ⋯ Following L5Tx, female CD137L KO mice did not show increased iNOS mRNA and had reduced numbers of IL-1β+ cells compared to WT. At 21 d post-surgery, CD137L KO mice had higher total numbers of arginase (Arg)-1+ cells and Arg-1+ microglia. Altogether, results indicate that spinal cord CD137L contributes to the development of peripheral nerve injury-induced neuropathic pain, which may be in part mediated through CD137L's modulation of the pro- and anti-inflammatory balance within the spinal cord.
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Neuropathic pain affects multiple brain functions, including motivational processing. However, little is known about the structural and functional brain changes involved in the transition from an acute to a chronic pain state. Here we combined behavioral phenotyping of pain thresholds with multimodal neuroimaging to longitudinally monitor changes in brain metabolism, structure and connectivity using the spared nerve injury (SNI) mouse model of chronic neuropathic pain. ⋯ Similarly, all global and local network changes that occurred following pain induction disappeared over time, with two notable exceptions: the nucleus accumbens, which played a more dominant role in the global network in a chronic pain state and the prefrontal cortex and hippocampus, which showed lower connectivity. These changes in connectivity were accompanied by enhanced glutamate levels in the hippocampus, but not in the prefrontal cortex. We suggest that hippocampal hyperexcitability may contribute to alterations in synaptic plasticity within the nucleus accumbens, and to pain chronification.
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In DRG an increase in miR-133b-3p, miR-143-3p, and miR-1-3p correlates with the lack of development of neuropathic pain following a peripheral nerve injury. Using lentiviral (LV) vectors we found that a single injection of LV-miR-133b-3p or LV-miR-143-3p immediately after a peripheral nerve injury prevented the development of sustained mechanical and cold allodynia. Injection of LV-miR-133b-3p or LV-miR-143-3p by themselves or in combination, on day 3 post-injury produced a partial and transient reduction in mechanical allodynia and a sustained decrease in cold allodynia. ⋯ LV-miR133b-3p and LV-miR-143-3p reduced TRPM8-mRNA. LV-miR-133b-3p and LV-miR-143-3p prevent the development of chronic pain when injected immediately after the injury, but are only partially effective when injected at later times. LV-miR-1a-3p had no effect on pain, but complemented the actions of LV-miR-133b-3p or LV-miR-143-3p resulting in a sustained reversal of pain when co-injected 3 days following nerve injury.