The effects of prior aversive stimulation on the behavioral and physiological responses to intense acoustic stimuli in the rat

Two experiments were conducted to assess the effects of intense, inescapable electric shock (preshock, PS) on the behavioral and physiological responses of rats to intense acoustic stimuli. In Experiment 1 startle amplitude, interstimulus activity and plasma corticosterone levels were compared in control and animals previously subjected to the PS treatment. In Experiment 2 heart rate (HR) responses were similarly compared. Results indicated that (1) startle amplitude was not affected by PS treatment (2) interstimulus activity was markedly suppressed and the plasma corticosterone response to startle testing elevated by the PS treatment, and (3) the initial presentations of startle stimuli elicited a dramatic HR deceleration in animals subjected to the PS treatment. These results were discussed in terms of (1) the relationship between arousal and startle and (2) the nature of the PS effect as revealed by the unusual HR response to the initial stimulus presentations.