? Because food and drugs activate some of the same areas of the brain, it is hypothesized that the common ability to activate the mesolimbic dopamine system may underlie the observed relationship between substance abuse and eating disorders. The proposed experiments are based on a review of current literature and research in our laboratory that shows that rats previously exposed to cocaine demonstrate faster latencies to complete sessions on a fixed-ratio (FR) 30 schedule of reinforcement for sucrose than rats exposed to saline. It is hypothesized that exposure to cocaine sensitizes rats to the rewarding properties of sucrose and vice-versa. The first four proposed experiments will explore how previous cocaine exposure increases the value of sucrose as measured by an increased willingness to work for sucrose reward (Experiment 1) and increased consumption of sucrose (Experiments 2 & 3). Experiments 4 and 5 will examine whether exposure to sucrose produces cross-sensitization to cocaine. The findings of these experiments are intended to increase current understanding of how drug use affects the rewarding properties of natural reinforcers and how previous experience with natural reinforcers affects subsequent drug reward. ? ? ? ?