PROLONGED ANALGESIA AFTER INTRACEREBROVENTRICULAR TYR-W-MIF-1 (TYR-PRO-TRP-GLY-NH2)

A peptide recently isolated from human and bovine brain, Tyr-W-MIF-1 ( Tyr-Pro-Trp-Gly-NH2), was tested for its effects on nociception in the tail-flick test after intracerebroventricular injection in the rat. T ail-Rick latencies were significantly increased with a rapid onset and remained significantly elevated for at least 50 min. Naloxone reverse d the effect of the peptide. indicating opiate receptor involvement in the response. Met-enkephalin at the same dose produced only slight an tinociception. Some animals showed 'barrel-rolling' behavior in additi on to the analgesia: this behavior was unusually short-lived, not a pr erequisite for the analgesia, and had no apparent persistent effects. The results show that, in addition to previously described opiate-like actions (binding to the mu-receptor and inhibition of electrically in duced contractions of the guinea pig ileum), Tyr-W-MIF-1 is capable of inducing significant analgesia.