Acute administration of MIF-1 or Tyr-MIF-1 inhibits haloperidol-induced catalepsy in rats.

The effects of MIF-1 (Pro-Leu-Gly-NH2) and Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) on haloperidol-induced catalepsy were studied in order to examine the influences of both peptides on central dopaminergic function. In the first experiment, several variables were tested. It was found that the optimal effect was achieved with a dose of 1.0 mg/kg haloperidol injected SC an hour before testing for catalepsy and 1.0 mg/kg MIF-1 injected SC 30 min before testing. In the second experiment, Tyr-MIF-1 as well as MIF-1 were injected as single injections at four doses. Catalepsy was inhibited in an inverted U-shape dose-response relationship with the maximal effect of each peptide occurring at 1.0 mg/kg. The results indicate that when careful attention is given to dose, both MIF-1 and Tyr-MIF-1 can activate dopaminergic neuronal activity after acute administration.