LAUSR

Abstract Numerous studies have shown that social defeat stress induces an increase in the rewarding effects of cocaine. In this study we have investigated the role played by the main hypothalamic stress hormone, corticotropin‐releasing factor (CRF), in the effects that repeated social defeat (RSD) induces in the conditioned rewarding effects and locomotor sensitization induced by cocaine. A total of 220 OF1 mice were divided into experimental groups according to the treatment received before each social defeat: saline, 5 or 10 mg/kg of the nonpeptidic corticotropin‐releasing factor CRF1 receptor antagonist CP‐154,526, or 15 or 30 &mgr;g/kg of the peptidic corticotropin‐releasing factor CRF2 receptor antagonist Astressin2‐B. Three weeks after the last defeat, conditioned place preference (CPP) induced by 1 mg/kg of cocaine was evaluated. Motor response to 10 mg/kg of cocaine was also studied after a sensitization induction. Blockade of corticotropin‐releasing factor CRF1 receptor reversed the increase in cocaine CPP induced by social defeat. Conversely, peripheral corticotropin‐releasing factor CRF2 receptor blockade produced similar effects to those observed in socially stressed animals. The effect of RSD on cocaine sensitization was again blocked by the corticotropin‐releasing factor CRF1 receptor antagonist, while peripheral CRF2 receptor antagonist did not show effect. Acute administration of Astressin2‐B induced an anxiogenic response. Our results confirm that CRF modulates the effects of social stress on reinforcement and sensitization induced by cocaine in contrasting ways. These findings highlight CRF receptors as potential therapeutic targets to be explored by research about stress‐related addiction problems.