Early fear as a predictor of avoidance in a rat model of post-traumatic stress disorder

Exposure of humans and animals to an intensely fearful experience can lead to an enduring behavioral profile involving fear and avoidance. The present study examined if rats that show more fear to a novel tone one day after exposure to footshocks exhibit more avoidance-like responses over a 4-week period. Rats were exposed to an episode of moderately intense footshock (5 x 2s episodes of 1.5 mA presented randomly over 3 min). Shock rats that exhibited a high level of fear (HR) to a novel tone one day after the shock exposure showed more avoidance of open spaces and novel rats when compared to shock rats that exhibited a lower level of fear to the novel tone (LR). Similarly, HR emitted more ultrasonic vocalization in the dysphoric range (20-30 kHz) when placed in a novel chamber or the chamber in which shock was given. This study highlights the importance of early fear as a contributing factor for the development of lasting changes in avoidance. These results also support the view that the presence of an intense peritraumatic stress response may be a predictor of the subsequent development of a lasting negative emotional state in humans exposed to trauma. (C) 2011 Elsevier B.V. All rights reserved.