Effects of prior aversive stimulation on heart rate responses to open field exposure in the rat.

Heart rate (HR) responses to open field (OF) exposure were compared between rats previously exposed to intense, inescapable electric shock (preshock, PS) and Controls. Results indicated that (1) Control animals showed a steady increase in HR across a 3 min exposure on each of 4 days of testing, while PS animals showed an initial HR deceleration followed by partial recovery on each day; (2) the HR response of PS animals in the OF was not related to any HR response to shock during treatment; and (3) the HR responses of both PS and Control animals were specific to the OF situation, with both groups showing steady HR deceleration across 3 min after being placed in their home cages. Results were discussed in terms of (1) the apparently altered perception of environmental change produced by PS, and (2) the possible role of HR acceleration in Controls in terms of minimizing the impact of aversive stimulation.