Tyr-MIF-1 precipitates abstinence syndrome in morphine-dependent rats.

The endogenous neuropeptide Tyr-MIF-1 (Tyr-Pro-Leu-Gly-amide) has been shown to counteract various opiate actions. In the current study, third ventricular injection of 35 micrograms Tyr-MIF-1 protected by the enzyme inhibitor bestatin precipitated an abstinence syndrome in morphine-dependent rats, but not in opiate-naive rats. The results raise the possibility that Tyr-MIF-1 might participate in opiate dependence and opiate abstinence syndrome.