Dynorphin‐related peptides cause motor dysfunction in the rat through a non‐opiate action

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Abstract
1 We compared effects on motor function of four peptides belonging to the dynorphin family -dynorphin-(1–17) (DYN-(1–17)), dynorphin-(1–13) (DYN-(1–13)), dynorphin-(1–8) (DYN-(1–8)) and α-neo-endorphin (αNE). 2 After intrathecal administration, each of these peptides produced dose-related, flaccid, hindlimb paralysis, with the order of potency being DYN-(1–17) > DYN-(1–13) > αNE ≏DYN-(1–8). 3 This motor dysfunction was not reversed or blocked by the opiate receptor antagonist naloxone and was not produced by a variety of other κ-selective agonists. 4 However, paralysis was produced by des-Tyr-dynorphin (DYN-(2–17)), which does not act at the opioid receptor. 5 Taken together, the present studies show that dynorphin-related peptides, uniquely amongst opioids, produce motor dysfunction, an action which does not appear to be mediated by opioid receptors.