MIF-1 facilitates passive avoidance retention.

MIF-1 (Pro-Leu-Gly-NH2) is an endogenous substance which seems to be involved in the regulation of some central nervous system functions. It was recently shown to affect learning and memory processes. In order to further clarify the role of MIF in these processes we used two different passive avoidance tests: one-trial step down (SD) and shock suppressed drinking (SSD). Z-Pro-Leu-Gly-NH2 was administered on the training day ip either 15 minutes before trial or immediately after. The doses used were as follows: SD--1.0 mg/kg, SSD--0.05 mg/kg (in the group injected before trial) and 1.0 mg/kg--SD and SSD, in the groups injected post-trial. Only the immediate post-training injection of peptide resulted in significant prolongation of the step-down latencies on the retention-day. Similarly, in the SSD procedure only post-training MIF markedly attenuated water intake on the day after training. In a separate experiment we have found that in the dose of 1.0 mg/kg, but not 0.1 mg/kg, MIF significantly inhibited water intake. These results suggest that this naturally occurring peptide can contribute to the processes of memory consolidation and water intake.