Subsequently enhanced CPP to morphine following chronic but not acute footshock stress associated with corticosterone mechanism in rats.

The purpose of this study was to determine the morphine-induced place preference in rats pre-exposed to footshock stress and corticosterone (CORT). The authors also studied the involvement of dopamine mechanisms in the CORT-induced place preference. The results showed that chronic footshock or CORT exposure but not acute footshock or CORT exposure similarly potentiated the conditioned place preference to morphine. The CORT-induced conditioned place preference were established only with high and middle dose (5, 3 mg/kg) CORT. The dopamine levels in NAc of rats injected with CORT (5, 3, 1 mg/kg, i.p.) increased significantly. The findings suggest that the increase of dopamine levels in NAc induced by CORT might be the medium between stress and morphine.