Pain
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Patients with chronic pain often have accompanying cognitive deficiency, which may reduce their quality of life and hamper efficient medical treatment. Alteration of extracellular glycine concentration may affect cognitive function and spinal pain signaling. In the present study, we assessed recognition memory by novel-object recognition and found that mice developing mechanical hypersensitivity after peripheral nerve injury exhibited impaired recognition ability for novelty, which was never observed in mice provided the selective glycine transporter 1 (GlyT1) inhibitor N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl]sarcosine (NFPS) systemically. ⋯ These findings imply that chronic pain has a crucial influence on hippocampal plasticity related to cognitive function, and strongly suggest that increasing the extracellular level of glycine via blockade of GlyT1 is a potential therapeutic approach for chronic pain with memory impairment. Chronic pain crucially influences hippocampal plasticity related to cognitive function. Increasing the extracellular level of glycine via blockade of GlyT1 is a potential therapeutic approach for chronic pain with memory impairment.
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Neuropathic pain is a severe health problem for which there is a lack of effective therapy. A frequent underlying condition of neuropathic pain is a sustained overexcitability of pain-sensing (nociceptive) sensory fibres. Therefore, the identification of mechanisms for such abnormal neuronal excitability is of utmost importance for understanding neuropathic pain. ⋯ Behavioural experiments demonstrated that neuropathic hyperalgesia following PSNL developed faster than the downregulation of Kcnq2 expression could be detected, suggesting that this transcriptional mechanism may contribute to the maintenance rather than the initiation of neuropathic pain. Importantly, the decrease in the peripheral M channel abundance could be functionally compensated by peripherally applied M channel opener flupirtine, which alleviated neuropathic hyperalgesia. Our work suggests a novel mechanism for neuropathic overexcitability and brings focus on M channels and REST as peripheral targets for the treatment of neuropathic pain.
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Neuropathic pain is associated with reorganization of spinal synaptic circuits, implying that adhesion proteins that normally build and modify synapses must be involved. The adhesion proteins E- and N-cadherin delineate different synapses furnished by nociceptive primary afferents, but dynamic aspects of cadherin localization in relationship to onset, maintenance or reversibility of neuropathic pain are uncharacterized. Here, we find very different responses of these cadherins to L5 spinal nerve transection (SNT)-induced mechanical allodynia and to intrathecal glial derived neurotrophic factor (GDNF), which has potent analgesic effects in this pain model. ⋯ Patterns of immunolabeling for GDNF receptor components GFRα1, NCAM, and RET after L5 SNT suggest that GFRα1 and NCAM are the principal receptors operative in this model. In addition, GFRα1 codistributes with E-cadherin, but not N-cadherin, profiles. Together, these data indicate strikingly divergent patterns of temporal and molecular regulation of different cadherins at distinct nociceptive circuits in response to spinal nerve injury, suggesting that the two cadherins and the circuits with which they are affiliated participate in different aspects of synaptic and circuit reorganization associated with neuropathic pain.