PERIPHERAL KAPPA(1)-OPIOID RECEPTOR-MEDIATED ANALGESIA IN MICE

When injected directly into the tail, U50,488H is a potent analgesic i n the tailflick assay (ED(50) 3.1 mu g). The analgesic activity is los t if the radiant heat is focused 1 cm away from the site of injection. The Kappa(1)-opioid receptor antagonist nor-binaltorphimine given sys temically reverses the local analgesic response of U50,488H, but the a ntagonist is 100-fold more potent when injected directly into the tail . Intrathecal antisense treatment with a probe targeting the mRNA enco ding the Kappa(1)-opioid receptor blocks the local analgesic actions o f U50,488H in the tail, suggesting that U50,488H is acting on dorsal g anglia neurons.