Effect of nonaversive and aversive stimulations in infancy on the acousticstartle response in adult rats

Two groups, each consisting of 8 three-week-old rat pups, were exposed to d ifferent behavioral treatments with the aim to determine how the experiment al manipulation influenced their adult emotional reactivity. Every day for two weeks the pups from the first group received 15 min of handling whereas the animals from the second group were exposed to various aversive stimuli , differing each day. Following these manipulations, after a 5-day break th e acoustic startle response (ASR) was measured in all animals and the testi ng was repeated after another four weeks. Statistical analysis of the data revealed significant differences between groups in the ASR parameters. Surp risingly, in the test which directly followed the treatment the mean ASR am plitudes were similar in both groups. Highly significant differences, howev er, were observed in the ASR amplitude four weeks later. The rats from the handling group responded with greater amplitudes. The latency of the ASR wa s significantly shorter in the nonaversive group compared with the second g roup exposed to aversive stimuli. The results suggest that early exposure t o aversive stimulation significantly decreases rats emotional reactivity wh ereas nonaversive and impoverished stimulation clearly elevates arousal lev els when the animal is placed in a novel situation.