Sites of analgesic action of dynorphin.

Analgesic effects of dynorphin and dynorphin-(1-13) injected into various regions of the CNS of rats were investigated using the tail pinch method. Dynorphin and dynorphin-(1-13) produced a dose-dependent analgesic effect when injected into the third ventricle (3rd vent.) or the nuclei reticularis gigantocellularis and paragigantocellularis (NRGC-NRPG) and the analgesic activity of dynorphin was 3 to 5 times more potent than that of dynorphin-(1-13). These peptides in higher doses elicited transient "barrel-rolling" and rigidity in behavior. On the other hand, when injected intrathecally, dynorphin exerted an analgesia accompanied by paralysis of hindlimbs which were long lasting. But its analgesic activity was less effective as compared with the 3rd vent. and NRGC-NRPG injections.