Effects of Unpredictable and Uncontrollable Aversive Stimulus upon Long-term Adaptive Behavior in Rats

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The effects of predictable/unpredictable grid-shocks upon rats' long-term adaptive behavior were studied in three experiments using two boxes named KGbox-24. In each experiment, rats were run in a pair and brief inescapable shocks were given to both rats of a pair with a VT-6 min schedule over 24 hours a day for 20 days. To one rat of each pair, shocks were always given preceded by a 1-min tone, but to the other rat, shocks were given unsignaled. This stress phase was preceded by a baseline phase of 8-10 days, during which no shocks were given. In the KGbox-24, eating and drinking, as well as locomotion and rearing, of rats were continuously measured in 1-min units under the condition of 12:12-h light:dark cycle. All three experiments were of essentially the same nature, but in Experiments 2 and 3, a home-cage control group was prepared and the body weight of shock-free control rats was measured daily at the noon time. The body weight of rats run in the experimental boxes was also meas … More ured daily at the noon time, taking them out temporarily from the boxes.In Experiments 2 and 3, the hody weight of rats run in the KGbox-24 decreased substantially during the stress phase compared with that of those kept in the shock-free home cages. Of those run in the experimental boxes, rats exposed to the predictable shocks lost relatively more body weight than those exposed to the unpredictable shocks in all three experiments. This fact of greater stressfulness of predictable shocks over unpredictable shocks contrasts sharply with the opposite effect usually found in short-term experiments. But the fact is in line with the suggestion made recently by Abbott et al (1984) who distinguished the short-term effects and long-term effects of predictable/unpredictable shocks upon stress. The results of more detailed analyses of other behaviors are presented elsewhere.A study on the effects of controllable/uncontrollable shocks upon long-term adaptive behavior of rats had been originally planned but was not conducted because of shortage of time. Less