Articles: neuropathic-pain.
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Patients with chronic pain conditions such as neuropathic pain frequently experience delays in diagnosis and treatment. Ideally, all patients should be treated in a timely manner, but in those patients with more established disease it is important to know that approved treatments remain effective. ⋯ Pregabalin significantly improves pain irrespective of the length of time since onset of neuropathic pain.
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Neuropathic pain, a maladaptive and chronic condition that can develop after a lesion or disease affecting the somatosensory system, is characterized by allodynia, hyperalgesia and spontaneous pain, and comorbidities such as sleep deprivation, depression and anxiety. The activation of microglial cells in response to nerve injury has been implicated in the development of neuropathic pain. Mediators such as Neuregulin-1, matrix metalloproteinase (MMP)-2, MMP-9, The chemokine (C-C motif) ligand 2 (CCL2) and fractalkine are released after nerve injury and are involved in the activation of microglial cells. ⋯ It is becoming increasingly apparent that an intricate network of cytokines and cellular signalling mechanisms underpin the complex relationship between microglia and various cell types including neurones, astrocytes, oligodendrocytes, mast cells and T-cells. Although the precise mechanism of action of microglial cells in producing neuropathic pain has not been completely elucidated, research into these different activating factors and cytokines is providing further insight into the role of microglial cells in the development and maintenance of neuropathic pain. Further studies also are required to elucidate how "pain" mediators act on neurones and how the interactions between these mediators, or between neurones and glia in the presence of these mediators occur, in order to develop effective therapies for the management of neuropathic pain.
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Whereas neurovascular interactions in spinal neuropathic pain models have been well characterized, little attention has been given to such neurovascular interactions in orofacial neuropathic pain models. This study investigated in male Sprague-Dawley rats the vascular changes following chronic constriction injury (CCI) of the infraorbital nerve (IoN), a broadly validated preclinical model of orofacial neuropathic pain. Following IoN-CCI, an early downregulation of tight junction proteins Claudin-1 and Claudin-5 was observed within the endoneurium and perineurium, associated with increased local accumulation of sodium fluorescein (NaFlu) within the IoN parenchyma, as compared with sham animals. ⋯ A significant upregulation of immunocytes (CD3, CD11b) and innate immunity (TLR2, TLR4) mRNA markers was also observed, suggestive of increased local inflammation. Finally, a significant downregulation of Hedgehog pathway readouts Patched-1 and Gli-1 was observed within the IoN after CCI and local injections of cyclopamine, a Hedgehog pathway inhibitor, replicated in naïve rats the molecular, vascular, and behavioral changes observed following IoN-CCI. These results suggest a major role of Hedgehog pathway inhibition in mediating local increased endoneurial and perineurial vascular permeability following trigeminal nerve injury, thus facilitating immunocytes infiltration, neuroinflammation development, and neuropathic pain-like aversive behavior.