Articles: neuralgia.
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We have recently reported that the spinal angiotensin (Ang) converting enzyme (ACE)/Ang II/AT1 receptor axis and downstream p38 MAPK phosphorylation are activated in streptozotocin (STZ)-induced diabetic mice and lead to tactile hypersensitivity. Moreover, our previous results suggested that the intrathecal (i.t.) administration of Ang (1-7), an N-terminal fragment of Ang II, may attenuate the Ang II-induced nociceptive behaviour through the inhibition of p38 MAPK phosphorylation via Mas receptors. Here, we investigated whether the i.t. administration of Ang (1-7) can attenuate STZ-induced diabetic neuropathic pain. ⋯ The ACE2/Ang (1-7)/Mas receptor axis was down-regulated in the spinal cord of STZ mice and the i.t. administration of Ang (1-7) attenuated the STZ-induced diabetic neuropathic pain via Mas receptors. Therefore, the activation of this axis could be an effective therapeutic target to alleviate the neuropathic pain in diabetic patients.
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Chronic pain is associated with neuroplastic changes in the amygdala that may promote hyper-responsiveness to mechanical and thermal stimuli (allodynia and hyperalgesia) and/or enhance emotional and affective consequences of pain. Stress promotes dynorphin-mediated signaling at the kappa opioid receptor (KOR) in the amygdala and mechanical hypersensitivity in rodent models of functional pain. Here, we tested the hypothesis that KOR circuits in the central nucleus of the amygdala (CeA) undergo neuroplasticity in chronic neuropathic pain resulting in increased sensory and affective pain responses. ⋯ This effect was mediated through increased inhibitory postsynaptic currents, suggesting tonic disinhibition of CeA output neurons due to increased KOR activity as a possible mechanism promoting ongoing aversive aspects of neuropathic pain. Interestingly, this mechanism is not involved in SNL-induced mechanical allodynia. Kappa opioid receptor antagonists may therefore represent novel therapies for neuropathic pain by targeting aversive aspects of ongoing pain while preserving protective functions of acute pain.
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Peripheral nerve injury downregulates the expression of the μ-opioid receptor (MOR) and voltage-gated potassium channel subunit Kv1.2 by increasing their DNA methylation in the dorsal root ganglion (DRG). Ten-eleven translocation methylcytosine dioxygenase 1 (TET1) causes DNA demethylation. Given that DRG MOR and Kv1.2 downregulation contribute to neuropathic pain genesis, this study investigated the effect of DRG TET1 overexpression on neuropathic pain. ⋯ Mechanistically, TET1 microinjection rescued the expression of MOR and Kv1.2 by reducing the level of 5-methylcytosine and increasing the level of 5-hydroxymethylcytosine in the promoter and 5' untranslated regions of the Oprml1 gene (encoding MOR) and in the promoter region of the Kcna2 gene (encoding Kv1.2) in the DRG ipsilateral to SNL. These findings suggest that DRG TET1 overexpression mitigated neuropathic pain likely through rescue of MOR and Kv1.2 expression in the ipsilateral DRG. Virus-mediated DRG delivery of TET1 may open a new avenue for neuropathic pain management.
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Nerve stimulation is a reversible technique that is used successfully for the treatment of traumatic neuropathic pain, complex regional pain syndrome, and craniofacial neuropathic pain. Nerve field stimulation targets painful regions rather than a single nerve and has expanded indications, including axial low back pain. ⋯ Ongoing research is necessary to provide high-level evidence for the use of nerve stimulation. Most electrodes are primarily designed for spinal cord stimulation, hence the need to develop nerve electrodes dedicated for nerve stimulation.
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Amylin is a calcitonin gene-related peptide family member expressed by nociceptors. Amylin's expression is down-regulated following nerve damage, and studies suggested it affects nociception. We aimed at clarifying amylin's effects on chronic neuropathic pain and investigating its site of action. ⋯ Amylin modulated neuropathic pain by acting at different levels of the nervous system. Whereas supraspinal areas may be involved in amylin's induced pronociception, modulation of spinal cord amylin receptors by endogenous or pharmacological amylin doses triggers both pro- and antinociceptive effects.