Given that drug dependence (i.e., "addiction") is a significant threat to personal and public health, the research in my laboratory seeks to identify the kinds of specific neurobiological and behavioral changes that may occur in a drug using individual as they transition from occasional use of a psychoactive drug of abuse to drug addiction. Ongoing research in my laboratory tests the hypothesis that escalation of cocaine consumption is mediated through activation of the glutamate system, specifically through activation of NMDA receptors. These studies use an animal model of drug-taking behavior called the drug self-administration procedure, which can be used to reveal escalations of cocaine intake over time. This model provides a valuable preclinical tool for assessing the neurobiological changes that take place during this transition. Additionally, research in my laboratory seeks to describe the pharmacological, neurobiological, and behavioral mechanisms that contribute to the abuse potential of some psychoactive drugs. To this end, we are currently testing the roles of drug efficacy and receptor selectivity in the motivational effects of mixed action opioid analgesics.