Post-training corticosterone opposingly modulates fear conditioning of high and low anxiety rats

The activity of hypothalamic-pituitary-adrenal (HPA) axis is paralleled with the behavioral disturbances of individuals with high anxiety and has been conceptualized to involve a fear conditioning process. We investigated the effect of modulating HPA axis activity on fear conditioning for high (HA) and low (LA) anxiety individuals. Firstly, male Sprague-Dawley rats received open field test. According to a criterion of normalized factor scores obtained by factor analysis for open field behaviors, the rats were separated into two colonies: HA and LA. After one week, they successively received classical tone-cued fear conditioning training and a post-training intraperitoneal injection of corticosterone (CORT). After 48 hours, fear expression test were operated. The CORT was found to have no effect on fear conditioning in totally. However, when the rats were separated into LA and HA, the CORT dose dependently enhanced fear conditioning in LA rats, but inverted U-shaped dependently reduced freezing in HAs. Our findings suggest that post-training CORT has an opposite effects on fear expression in rats as a function of their pre-existing anxiety.