Social experiences affect reinstatement of cocaine-induced place preference in mice.

RATIONALE: Drug addiction is a multifactorial disorder resulting from an interaction between genetic and environmental factors, and negative and positive environmental conditions may increase or reduce, respectively, vulnerability to drug addiction.
OBJECTIVES: The influence of different social experiences on the acquisition, extinction, and reinstatement of a cocaine-induced conditioned place preference (CPP) was evaluated.
METHODS: In experiment 1, adolescent and adult male OF1 mice housed under four different conditions (grouped, isolated, crowded, and cohabitating with a female) were conditioned with 50, 12.5, or 3.125 mg/kg of cocaine. All mice underwent extinction sessions until the CPP was extinguished. The effects of cocaine priming injections on the reinstatement of CPP were then evaluated. In experiment 2, the effect of different social experiences on the maintenance and reinstatement of cocaine-CPP in adult mice was studied.
RESULTS: Although housing conditions did not affect the acquisition of cocaine-CPP, it did modify reinstatement after extinction. Adolescent mice living in crowded conditions or cohabitating with a female did not present reinstatement after cocaine priming. Similarly, neither isolated adult mice nor adults cohabitating with a female presented reinstatement. In grouped adult mice, isolation after acquisition of the CPP and social defeat before reinstatement increased the vulnerability to reinstatement induced by cocaine priming. Conversely, both exposure to females and a brief social interaction undermined cocaine-induced reinstatement.
CONCLUSIONS: Social experiences modify vulnerability to reinstatement, acting as prevention or risk factors in the development of drug addiction.