Drug-social interactions in the reinforcing property of methamphetamine in mice.

There are many examples of the social facilitation of drug effects. This study focused on the pharmacological state of social partners and reports the effects of drug injections in mice whose cage mates were also, or were not, injected with the drug. The reinforcing property of methamphetamine was examined in a social context using a conditioned place preference (CPP) paradigm in mice. The paired and control-paired groups both received CPP training with a cage mate. In the paired group, both mice were either injected with methamphetamine (2 mg/kg), or with saline. The control-paired group received CPP training with their cage mate but treatment was reversed: when one mouse was injected with the drug the other was injected with saline. For the paired group, the methamphetamine injection enhanced the reinforcing effect of the drug in comparison with the mice that had undergone conventional CPP in a single-mouse design. In contrast, the control-paired group did not show such a social enhancement effect. These results suggest that sharing the same experience is crucial for the social enhancement of the methamphetamine reinforcing effect.