Pain
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Previous work demonstrated that, in rats, intrathecal GR89696, a putative kappa-2 opioid receptor agonist, inhibited hyperalgesia to noxious heat in an inflamed hind paw (anti-hyperalgesic effect). Non-inflamed paws were not influenced by kappa-2 receptor activation. The question addressed in this study was whether GR89696 was as effective in blocking hyperalgesia and allodynia in nerve injury models as it was in the inflammation model. ⋯ Naloxone (1 mg/kg, i.p.) reversed the anti-hyperalgesic and anti-allodynic effects of GR89696. The mu agonist DAMGO (6 nmoles, i.t.) and the kappa-1 agonist U69593 (100 nmoles, i.t.) only partially reversed hyperalgesia and allodynia. These findings suggest that kappa-2 opioid receptors may be a useful target for the pharmacological control of hyperalgesia and allodynia.