CONDITIONED TASTE AVOIDANCE PREDICTS MORPHINE, BUT NOT COCAINE, SELF-ADMINISTRATION: A ROLE OF DRUG AVERSION IN DRUG TAKING

Drugs of abuse are complex pharmacological compounds that produce multiple effects, not all of which are rewarding or positively reinforcing. Drugs of abuse have also been described in terms of their aversive effects, evidenced by their ability to suppress consumption of a taste stimulus with which they were previously paired. This ability to condition taste avoidance has been described for all major drugs of abuse, including morphine and cocaine. In the present series of experiments, the relationship between the ability of morphine and cocaine to condition taste avoidance or place preference and support self-administration was assessed. There was a significant negative relationship between the aversive effects of morphine and morphine self-administration, such that rats most sensitive to the aversive effects of morphine self-administered less drug than rats least sensitive to morphine's aversive effects. Interestingly, no such relationship was found with cocaine. Moreover, there was no relationship between the ability of either morphine or cocaine to produce place preference and support self-administration. The present results are discussed in the context of the theoretical position that the balance of drug reward and aversion determines drug self-administration.