[Passive avoidance in two inbred strains of mice: conditioned emotional response and specific avoidance]

Specific response inhibition and generalized behavioral suppression (conditioned emotional response) contributions to a step-through passive avoidance performance are tested in two inbred strains of mice. For this purpose response contingent (0 sec.) and delayed punishment (from 5 to 60 sec.) are used in the learning session. The results of the test session (24 hr later) show that in the BALB/c strain, the response contingent component is very important (i.e. delaying the punishment produces a rapid decrease of the step-through latency). On the otherhand the latency remains unaffected in C57 BL/6 mice, showing that conditioned emotional response is the major determinant of the passive avoidance performance in this strain. These results might at least partially explain some contradictory results about memory differences between inbred strains of mice. Moreover they show that more sophisticated behavioral analysis is necessary whenever interstrain comparisons or genetic analysis are used for studying learning and memory.