MSH/ACTH4-10 influences on the CAR in human subjects: a negative finding.

Twenty normal, male, paid volunteers were randomly assigned to MSH/ACTH4-10 or diluent control groups. Following a subcutaneous injection of either 30 mg MSH/ACTH4-10 or diluent, all subjects were placed in an active conditioned avoidance response situation where they learned to avoid a painful electric shock by pressing a key during a safe interval between a warning signal (light) and shock onset. MSH/ACTH4-10 did not influence any parameter of the acquisition or extinction process. The between subjects' variability of autonomic variables was significantly less for the MSH/ACTH4-10 group. Results indicate that inhibition of extinction of conditioned avoidance responding does not generalize across species from rat to man.