Behavioral consequences of predictable vs. unpredictable shocks in rats

Adult, male, Sprague-Dawley rats were given either predictable or unpredictable footshocks coupled with predictable or unpredictable warning stimuli in a factorially designed experiment. The effect of footshocks on different parameters of motility was studied immediately, 1 h and 24 h later. Footshock-induced stress caused increases in the motility of rats, and this increase persisted for 24 h. Of the parameters studied, distance travelled and time spent in ambulatory behavior were significantly affected, but there was no difference between the predictably and unpredictably shocked animals in the pattern or time course of stress-induced locomotion changes. The defecation scores recorded in footshocked rats were lower than in controls in both the predictably and unpredictably shocked groups, but there was no difference between the predictably and unpredictably shocked groups. Lack of differences in motility and defecation between the two groups limits the usefulness of these parameters in behavioral experiments based on predictability of noxious stimuli.