INESCAPABLE FOOTSHOCKS INDUCE PROGRESSIVE AND LONG-LASTING BEHAVIORAL-CHANGES IN MALE-RATS

Long-term behavioural consequences of exposure to a brief (I 5 min) session of inescapable footshocks (10 X 6 s, 1 mA) were investigated in male rats. The time course of the effects of inescapable footshocks was assessed by studying the behaviour of groups of rats at different post-stress intervals. Footshocked rats (S) did not differ from control (C) rats (exposed to the shock box for 15 min) in their behavioural response to an open field whether tested 1 h or 4 h post-stress. However, one day after shocks, S rats showed less locomotion and rearing, and more immobility and attention as compared to C rats. At 7 days or 14 days post-stress, S rats exhibited decreased locomotion, rearing, sniffing. and grooming, and increased immobility, attention, and defecation relative to C rats. In a second experiment, we investigated whether footshocks affect the behavioural response to a sudden drop in background noise during exposure to a novel environment. At 21 days post-stress, S rats showed a markedly enhanced immobility response to this stimulus as compared to C rats. In order to investigate whether rats could be exposed repeatedly to the open field without affecting the differences in behaviour between the two treatment groups. C and S rats were tested in an open field for the first time at 7 days post-stress, which yielded the typical effects of footshocks. When these rats were exposed to a second open-field test one week later, the behavioural responses of C and S rats were not different. However, the typical long-lasting effects of footshocks were still present when the same rats were exposed to a noise test at 2 1 days post-stress. Qualitatively similar effects were found when the reverse experiment was conducted (first noise test at 14 days, and the second noise test at 2 1 days, and finally an open-field test at 28 days post-stress). The present results demonstrate that exposure of rats to a short session of inescapable footshocks induces a gradually developing and long-lasting change in behavioural responses to novel environmental stimuli. It is suggested that footshock-induced long-lasting behavioural changes may serve as a model of affective disorders in man.