Shock sensitization of startle in the developing rat.

Rats given a series of shocks exhibit a potentiated startle response to a loud acoustic stimulus compared to nonshocked animals. Experiment 1 showed that this shock sensitization of startle, like conditioned fear potentiation of startle to discrete cues, emerges relatively late in development (i.e., 23 days of age). Although different testing procedures were used in Experiment 2, preweanling rats still failed to exhibit the shock sensitization of startle effect. The failure to observe the shock sensitization of startle effect in preweanling rats was not due to age differences in contextual conditioning produced by the shock treatment (Experiment 3). The results of this study are discussed in terms of (a) the emergence of fear potentiation of startle during development, and (b) the relation between conditioned freezing and startle potentiation.