Selection for two-way avoidance deficit inhibits shock-induced fighting in the rat

Matched pairs of male and female, Roman high- and low-avoidance (RHA/Verh and RLA/Verh) rats were tested for shock-induced fighting, and single rats were tested for comparative sensitivity to footshocks. The main finding was that the RLA/Verh rats showed a total absence of shock-induced fighting or posturing. The females of both selected lines showed lower flinch-, shuffle- and jump-shock thresholds than did the males. Although the RHA/Verh rats had lower shuffle and jump thresholds than did the RLA/Verh rats, there was no significant difference in the initial detection of foot-shocks by either group (flinch threshold), and all 3 levels of threshold values for both were well below the 3 mA shock level used in the shock-induced fighting experiment. It was concluded that the genetically-based response suppression (freezing behavior) seen with RLA/Verh rats under these and all shock-stress conditions played a greater role in the inhibition of shock-induced fighting than did sensitivity to footshocks per se.