[Sequential structure of behavior and its modification in inbred strains of mice in a passive avoidance situation]

Behavior in a shuttle-box of four inbred strains of mice (BALB, C3H, C57BL and DBA) was observed by time-sampling method with 11 behavioral items in order to determine how their dyadic sequential structure of the items would be modified under a passive avoidance procedure. Mice in the safe-compartment could enter freely into the shock-compartment, the grid of which was electrified during Days 1-5. A common structure mainly composed of six items was found in every strain on Day 0 when the grid floor was not electrified. The structure was modified on Days 1-5. Entries into the shock-compartment were greatly reduced in all strains as the shock-experience increased, indicating the establishment of passive-avoidance. However, the way they avoided shocks was quite different between BALB and the other strains. In the latter the transitions between 'locomotion' and 'peeping' and between 'sniffing' and 'peeping' did not extinguish, while in BALB these transitions extinguished after Day 1, which means they avoided even 'peeping' into the shock-compartment. It was concluded that the passive avoidance strategy may be different among inbred strains.