Dr. Randy Seeley of the University of Cincinnati College of Medicine described research analyzing neurotransmitters that have been linked to food intake in order to discern which of the transmitters are more important than others in regulating food intake. The precise location of the opioid receptors that are important in influencing the activity of these systems is unknown. Also unknown is the relationship of the classic reward circuits involved in the dopamine system and their ability to interact with various peptide systems. These are critical issues in terms of understanding natural rewards, and of understanding why the dietary environment that we live in leads us to the propensity to gain weight.

Rapid Dopamine Signaling: Cocaine vs. "Natural" Rewards
Regina M. Carelli, Ph.D., University of North Carolina

Dr. Regina Carelli of the University of North Carolina described experiments examining the role of dopamine in reward. Rat self-administration studies showed that increases in dopamine took place before an operant response, were relative to the cues given, and reflected learned associations for both cocaine and a "natural" reward (sucrose). From these experiments, Carelli’s team concluded that rapid dopamine signaling appears to promote goal-directed behaviors regardless of reinforcer type.

Emotional Feelings, Drug Addictions, and Social Processes
Jaak Panksepp, Ph.D., Bowling Green State University

Dr. Jaak Panksepp discussed his theory that, in order to understand drug addiction, researchers must understand the nature of affective processes. Further, affective states of the nervous system are emergent evolutionary properties of complex neural dynamics that should be conceptualized properly and linked to the concrete, multidimensional brain processes from which they emerge. Panksepp summarized a variety of research on affective processes and concluded that an understanding of these processes may be necessary to understanding addictions.

The Expression of a Simple Appetitive Response Becomes Dopamine-Independent with Overlearning
Jon Horvitz, Ph.D., Boston College

Dr. Jon Horvitz described a series of head-entry experiments that showed that once a reward-directed behavior becomes habit, the expression of the response seems to become dopamine independent. Further, dopamine is needed to execute internally-generated responses, but not to respond to an overlearned conditioned stimulus. Horvitz noted that when a person goes to a clinic for treatment, dopamine antagonist drugs are surprisingly ineffective at reducing drug-seeking behavior. Horvitz proposed that by the time a person goes to a clinic, the drug-seeking behavior has been repeated so many times and has been tied so strongly to eliciting stimulae that the behavior actually becomes independent of dopamine transmission.