He uses a combination of behavioral (conditioned place preference (CPP) and behavioral sensitization that mimic some aspects of drug seeking and craving in humans), molecular and neurochemical approaches to determine the role of endogenous neuropeptides, in particular orphanin FQ/nociceptin (OFQ/N) and endogenous opioid peptides, in the reinforcing and addictive actions of cocaine and morphine. He is also interested in the role of (1) the OFQ/N/ORL-1 receptor system in the analgesic and reinforcing actions of buprenorphine and morphine and (2) the endogenous opioid peptides in stress-mediated analgesia and in cross-sensitization between stress and cocaine.