INTRAVENOUS SELF-ADMINISTRATION OF HEROIN, COCAINE, AND THE COMBINATION IN BALB C MICE/

Polydrug abuse, including the abuse of cocaine + heroin combinations ( or 'speedballs') is an increasingly significant problem. The use of ge netically defined populations of mice has the potential to add conside rably to the study of polydrug abuse. Balb/cByJ (Balb/c) mice have bee n shown to self-administer opiates, but not cocaine, therefore these m ice were chosen for the initial characterization of intravenous self-a dministration of cocaine + heroin combinations. Mice were implanted wi th chronic indwelling jugular catheters and given the opportunity to s elf-administer heroin, cocaine or heroin + cocaine combinations. Heroi n was self-administered, while, under the same conditions, none of the mice tested acquired cocaine self-administration. However, heroin + c ocaine combinations were self-administered in naive mice as well as in mice that had failed to self-administer cocaine alone. The heroin + c ocaine combination dose-effect curve resembled the heroin dose-effect curve. It is hypothesized that heroin may interact with effects of coc aine that function to limit self-administration in Balb/c mice, facili tating the acquisition and maintenance of self-administration of cocai ne + heroin combinations.