Genetic variation in heroin‐induced changes in behaviour: effects of B6 strain dose on conditioned reward and locomotor sensitization in 129‐B6 hybrid mice

Substantial interindividual variability exists in the propensity to develop opiate addiction. Genetic variation in opiate reward may contribute to this variability. A large body of evidence indicates genetic variation in mice for several effects of opiate drugs. The present study examined heroin‐induced place conditioning and locomotor sensitization in the two strains of mice employed most frequently in the generation of transgenic animals, C57BL/6J (B6) and 129X1/sVJ (129), as well as in groups of B6‐129 hybrid mice, differing in their amount of B6 genetic background. Four pairings of 100 µg/kg of heroin elicited robust place conditioning and locomotor sensitization in B6 controls and in N 10 congenic B6‐129 hybrid mice. In comparison, the identical treatment produced no locomotor sensitization and induced place aversion in 129 controls. No heroin‐induced changes in the behaviour of N 3 congenic B6‐129 hybrid mice or F5‐8 non‐congenic B6‐129 hybrid mice were observed. The expression of place conditioning was not facilitated in any group by the administration of a heroin‐priming injection prior to testing. These data indicate that genetic variation exists in mice for the rewarding and locomotor‐sensitizing effects of heroin and that the capacity of heroin to induce conditioned reward and locomotor sensitization can be modulated in a B6 strain dose‐dependent manner in B6‐129 hybrid mice. Thus, strain differences in heroin responsiveness should be considered when examining transgenic lines on B6‐129 backgrounds for opiate‐induced changes in behaviour that may be relevant for addiction.