Some analogs of Tyr-MIF-1 affect passive avoidance behavior but not motor activity in rats

The effects of three analogs of the brain peptide Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) were tested in several behavioral tests after peripheral injection in rats. In the passive avoidance test, rats injected SC with 1 mg/kg Ala-MIF-1 or Phe-MIF-1 entered the second compartment of two-chamber shuttle box significantly faster than did rats receiving diluent. Leu-MIF-1 failed to produce significantly faster entry compared to diluent. None of the peptides significantly affected ambulation, rearing, or defecation. Flinch and escape thresholds were not affected by Ala-MIF-1, the only analog tested for this behavior. The results demonstrate that some analogs of Tyr-MIF-1 can exert behavioral effects similar to those exerted by the parent compound whereas other analogs resemble MIF-1 in being inactive under these experimental conditions.