Articles: hyperalgesia.
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This study evaluated the impact of sex on the short term consequences of different periods of sleep deprivation and the effect of the respective sleep recovery periods on nociceptive responses. Male and female C57BL/6J mice were assigned to the following groups: paradoxical sleep deprived (PSD) for 72 h, sleep restricted (SR) for 15 days, exposed to respective recovery periods for 24 h, or untreated home-cage controls (CTRL). Mice were submitted to a noxious thermal stimulus to evaluate their nociceptive response after PSD, SR, or recovery periods. ⋯ Our study revealed that PSD and SR induce hyperalgesia in mice. The SR groups showed marked changes in the nociceptive response, and the females were more sensitive to these alterations. This finding indicates that, although different periods of sleep deprivation change the nociceptive sensitivity in male and female mice, sex could influence hyperalgesia induced by chronic sleep loss.
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Interleukin-4 (IL-4) is an anti-inflammatory and analgesic cytokine that induces opioid receptor transcription. We investigated IL-4 knockout (ko) mice to characterize their pain behavior before and after chronic constriction injury (CCI) of the sciatic nerve as a model for neuropathic pain. We investigated opioid responsivity and measured cytokine and opioid receptor gene expression in the peripheral and central nervous system (PNS, CNS) of IL-4 ko mice in comparison with wildtype (wt) mice. ⋯ The compensatory overexpression of the anti-inflammatory and analgesic cytokines IL-10 and IL-13 in the spinal cord of IL-4 ko mice may explain the lack of genotype differences for pain behavior after CCI. Additionally, CCI induced gene expression of μ, κ, and δ opioid receptors in the contralateral cortex and thalamus of IL-4 ko mice, paralleled by fast onset of morphine analgesia, but not in wt mice. We conclude that a lack of IL-4 leads to mechanical sensitivity; the compensatory hyperexpression of analgesic cytokines and opioid receptors after CCI, in turn, protects IL-4 ko mice from enhanced pain behavior after nerve lesion.
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Neuroinflammation and nitroxidative stress are implicated in the pathophysiology of neuropathic pain. In view of both processes, microglial and astroglial activation in the spinal dorsal horn play a predominant role. The present study investigated the severity of neuropathic pain and the degree of glial activation in an inflammatory- and nitroxidative-prone animal model. ⋯ Taken together, our findings show that exacerbated microglial activation and subsequent inflammatory and nitroxidative processes are associated with the severity of neuropathic pain symptoms.
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The prefrontal cortex may be a promising target for transcranial magnetic stimulation (TMS) in the management of pain. It is not clear how prefrontal TMS affects pain perception, but previous findings suggest that ventral lateral and medial prefrontal circuits may comprise an important part of a circuit of perceived controllability regarding pain, stress, and learned helplessness. Although the left dorsolateral prefrontal cortex is a common TMS target for treating clinical depression as well as modulating pain, little is known about whether TMS over this area may affect perceived controllability. ⋯ Although it is not clear whether this cortical area is directly involved with modulating perceived controllability or whether downstream effects are responsible for the present findings, it appears possible that left dorsolateral prefrontal TMS may produce analgesic effects by acting through a cortical perceived-control circuit regulating limbic and brainstem areas of the pain circuit. Despite evidence that prefrontal TMS can have analgesic effects, fast left prefrontal TMS appears to acutely suppress analgesia associated with perceived-control. This effect may be limited to the emotional dimension of pain experience.
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The aim of this study was to assess any interaction between ondansetron and paracetamol on a model of post-fracture pain in mice. ⋯ We found that paracetamol 100 mg kg⁻¹ blocked the development of hyperalgesia and allodynia after fracture pain and ondansetron did not modify the antinociceptive effect of paracetamol in this model.