Differences in acquisition of discrete lever-press and shuttle avoidance responses in 6 strains of mice.

Characteristics of the acquisition processes of discrete lever-press and shuttle avoidance responses (intertrial interval = 25 sec, warning duration = 5 sec with an escape contingency, and 1 session = 1 hr training/day) as well as those of the ambulatory activity were investigated in 6 strains of mice (dd, ICR, BALB/c, C57BL/6, C3H/He and DBA/2). In the lever-press avoidance situation, the dd, BALB/c and DBA/2 strains demonstrated a good avoidance response, showing average avoidance rates of higher than 80% within 10-15 sessions of the training. The C3H/He also demonstrated a good avoidance response, though 20 sessions or more of the training were required to attain to the level. The ICR and C57BL/6 strains demonstrated a poorer avoidance response than the other 4 strains, and achieved average avoidance rates of 30-40%. The dd, BALB/c, C3H/He and DBA/2 strains also demonstrated a good shuttle avoidance response when they were trained in an experimental box of 50 cm in width. In contrast, the ICR and C57BL/6 strains demonstrated an extremely poor avoidance response in this situation, showing an average avoidance rate of less than 10%. However, when the dd, ICR and C57BL/6 strains were trained in a shuttle box of 30 cm in width, they rapidly acquired the avoidance response, and the average avoidance rates finally achieved were much higher than those of the mice trained in the shuttle box of 50 cm in width. In particular, the C57BL/6 strain exhibited the best avoidance response among the 3 strains. The ambulatory activity of the C57BL/6 strain was less than those of the other 5 strains.