Adolescent psychosocial stress enhances sensitization to cocaine exposure in genetically vulnerable mice

Development of drug addictive behaviors is modulated by both genetic and environmental risk factors. However, the molecular mechanisms remain unknown. To address the role of adolescent stress in the development of drug addiction, we combined a transgenic mouse model in which a putative dominant-negative form of DISC1 under expressional control of the prion protein promoter is used as a genetic risk factor and adolescent social isolation stress as a gene-environmental interaction (GXE). Repeated cocaine exposure induced greater locomotion in the GXE group than in the other groups. In a conditioned place preference (CPP) test, GXE mice exhibited a significant place preference to the cocaine-conditioned area compared with the other groups. In the nucleus accumbens (NAc) of GXE mice, we found increased enzyme activity of phosphodiesterase-4 (PDE4), predominantly located in NAc D2-receptor-expressing neurons, and enhanced effects of the PDE4 inhibitor rolipram, but not the D1 agonist SKF81297, on the phosphorylation of DARPP-32 and GluA1 at PKA sites. Rolipram injection before cocaine exposure completely inhibited cocaine-induced hyperlocomotion and CPP in the GXE group. These results indicate that GXE enhances sensitivity to repeated cocaine exposure via an increase in PDE4 activity in NAc D2-recptor-expressing neurons, leading to the development of cocaine addictive behaviors.