European journal of pain : EJP
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Withdrawal from analgesic and addictive substances such as opioids or ethanol is associated with increased sensitivity to sensory stimulation in animal models. Here, we investigated perception of innocuous and noxious thermal or electric stimuli applied to the left hand or sternum in 30 male patients undergoing withdrawal from alcohol, 30 male abstained alcoholics and matched controls. The alcohol withdrawal scale and the Banger score were obtained to estimate the severity of withdrawal. ⋯ No differences were found between patients of the abstained group and control subjects for any pain parameter. In conclusion, we demonstrate withdrawal-induced hyperalgesia upon thermal stimulation in patients. Since the influence of affective symptoms on pain perception during withdrawal is remarkable, we assume that peripheral and central mechanisms might account for this finding, which should be assessed in detail in future studies.
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Peripheral nerve injury leading to neuropathic pain induces the upregulation of interleukin (IL)-6 and microglial CX3CR1 expression, and activation of p38 mitogen-activated protein kinase (MAPK) in the spinal cord. Here, we investigated whether IL-6 regulates CX3CR1 expression through p38 MAPK activation in the spinal cord in rats with chronic constriction injury (CCI) of the sciatic nerve. Similar temporal changes in the expression of IL-6, phosphorylated p38 MAPK and CX3CR1 were observed following CCI. ⋯ Furthermore, treatment with the p38 MAPK-specific inhibitor, SB203580, suppressed the increase in CX3CR1 expression induced by CCI or rrIL-6 treatment. Finally, blocking CX3CR1 or p38 MAPK activation prevented the development of mechanical allodynia and thermal hyperalgesia induced by CCI or rrIL-6 treatment. These results suggest a new mechanism of neuropathic pain, in which IL-6 induces microglial CX3CR1 expression in the spinal cord through p38 MAPK activation, enhancing the responsiveness of microglia to fractalkine in the spinal cord, thus playing an important role in neuropathic pain after peripheral nerve injury.
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Tricyclic antidepressants (TCAs) are among the first line treatments clinically recommended against neuropathic pain. However, the mechanism by which they alleviate pain is still unclear. Pharmacological and genetic approaches evidenced a critical role of delta-opioid receptors (DORs) in the therapeutic action of chronic TCA treatment. ⋯ Moreover, morphine induced an acute analgesia in control and in neuropathic wild-type mice, but was without effect in MOR-deficient mice. While MORs are crucial for morphine action, they are not critical for nortriptyline action. Our results highlight the functional difference between DORs and MORs in mechanisms of pain relief.
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Painful diabetic neuropathy may be due to impairments in descending modulation of nociceptive transmission at the spinal cord. In the present study, streptozotocin diabetic rats (STZ rats) with neuropathic symptoms (mechanical hypersensitivity) were used to perform a time-course evaluation of neuronal activity at the spinal dorsal horn and at the periaqueductal grey matter (PAG), a major brainstem area of pain modulation. The expression of Fos protein, a marker of nociceptive activation, progressively increased at the spinal dorsal horn at 4 and 10 weeks. ⋯ The present study shows that diabetic neuropathy is accompanied by a progressive increase of the spontaneous neuronal activity at the spinal cord. Changes in descending modulation of nociceptive transmission from the PAG are likely to occur during diabetic neuropathy, probably with exacerbation of facilitatory actions. The effects of gabapentin in reversing the behavioural signs of diabetic neuropathy and neuronal hyperactivity in the spinal cord and PAG reinforce the central causes of diabetic neuropathy and point to the central targets of the drug.