Articles: chronic-pain.
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We examined the analgesic effect of the selective kappa opioid receptor agonist SA14867 and the balance of its antinociceptive and sedative effects. The ED(50) values of SA14867 after oral administration for acetic acid-induced writhing, first and second phases of the formalin test, and rotarod test in mice were 6.1, 9.3, 2.7, and 19.5mg/kg, respectively. These values were smaller than those of the conventional kappa receptor agonists asimadoline and U-50488H. ⋯ Subcutaneously administered morphine (0.1-1mg/kg) improved the decreased pain threshold in a SART-stressed model; on the contrary, morphine did not inhibit the arthritis-induced decrease in the pain threshold. Moreover, orally administered SA14867 (0.1-1mg/kg) strongly attenuated mechanical allodynia and thermal hyperalgesia in a sciatic nerve ligation model. These results suggest that SA14867 has analgesic effects on chronic pain and may serve as a new therapeutic agent for pain treatment.
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Comparative Study
Engagement of descending inhibition from the rostral ventromedial medulla protects against chronic neuropathic pain.
A puzzling observation is why peripheral nerve injury results in chronic pain in some, but not all, patients. We explored potential mechanisms that may prevent the expression of chronic pain. Sprague Dawley (SD) or Holtzman (HZ) rats showed no differences in baseline sensory thresholds or responses to inflammatory stimuli. ⋯ Thus, expression of nerve injury-induced pain may ultimately depend on descending modulation. Engagement of descending inhibition protects in the transition from acute to chronic pain. These unexpected findings might provide a mechanistic explanation for medications that engage descending inhibition or mimic its consequences.