Articles: neuralgia.
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This study aimed to establish a practical method for assessing pain symptomatology and develop criteria for quantifying small fiber functions using laser speckle contrast analysis (LASCA). ⋯ Pain-related small fiber functions and symptomatology (two-in-one method) can be assessed via histamine- or capsaicin-evoked axon flare responses in as little as 15 minutes. The reduction of small fiber functions are characterized by decrease in flare size/intensity at 5 minutes after stimulation and prolongation/abolishment of the latency to reach 3-fold higher levels of baseline skin microcirculation. LASCA may be applied in the clinic to aid early diagnosis, monitor disease progression, and objectively assess treatment efficacy in patients with neuropathic pain.
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Peripheral delta opioid (DOP) receptors are essential for the antiallodynic effect of the tricyclic antidepressant nortriptyline. However, the population of DOP-expressing cells affected in neuropathic conditions or underlying the antiallodynic activity of antidepressants remains unknown. Using a mouse line in which DOP receptors were selectively ablated in cells expressing Nav1.8 sodium channels (DOP cKO), we established that these DOP peripheral receptors were mandatory for duloxetine to alleviate mechanical allodynia in a neuropathic pain model based on sciatic nerve cuffing. ⋯ These changes were not present in nerve-injured mice chronically treated with oral duloxetine. In addition, increased DOPeGFP translocation to the plasma membrane was observed in neuropathic conditions but not in duloxetine-treated neuropathic mice, which may represent an additional level of control of the neuronal activity by DOP receptors. Our results therefore established a parallel between changes in the expression profile of peripheral DOP receptors and mechanical allodynia induced by sciatic nerve cuffing.
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Downregulation of the potassium chloride cotransporter type 2 (KCC2) after a spinal cord injury (SCI) disinhibits motoneurons and dorsal horn interneurons causing spasticity and neuropathic pain, respectively. We showed recently (Bos et al., 2013) that specific activation of 5-HT2A receptors by TCB-2 [(4-bromo-3,6-dimethoxybenzocyclobuten-1-yl)methylamine hydrobromide] upregulates KCC2 function, restores motoneuronal inhibition and reduces SCI-induced spasticity. Here, we tested the potential analgesic effect of TCB-2 on central (thoracic hemisection) and peripheral [spared nerve injury (SNI)] neuropathic pain. ⋯ This analgesic effect was associated with an increase in dorsal horn membrane KCC2 expression and was prevented by pharmacological blockade of KCC2 with an intrathecal injection of DIOA [(dihydroindenyl)oxy]alkanoic acid]. In contrast, the SNI-induced neuropathic pain was not attenuated by TCB-2 although there was a slight increase of membrane KCC2 expression in the dorsal horn ipsilateral to the lesion. Up-regulation of KCC2 function by targeting 5-HT2A receptors, therefore, has therapeutic potential in the treatment of neuropathic pain induced by SCI but not by SNI.
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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.