The Dopamine Transporter in Eating Disorders: Uncovering New Therapeutic Targets

Although eating disorders are complex and their etiology unclear, dysregulation of dopamine neurotransmission is a consistent finding. A vital regulator of dopamine neurotransmission is the dopamine transporter (DAT). DAT terminates dopamine neurotransmission by uptake of dopamine from extracellular fluid and because of this DAT is a primary determinant of both the strength and duration of dopamine signaling. In spite of its critical role in maintaining dopamine homeostasis, there have been no investigations of DAT function, per se, in eating disorders. Using neurochemical, cellular and behavioral approaches, we have shown that DAT activity is highly sensitive to diet and food intake, strongly supporting the notion that DAT activity is dysregulated in individuals with eating disorders. However, studies so far have been in adult, male rodents. Anorexia, bulimia and binge eating are most common in teenage girls. What is lacking in our fundamental understanding of DAT is how its activity varies as a function of age and sex and, importantly, how age and sex interact to contribute to 'disordered eating'. In turn, how does aberrant DAT activity contribute to 'disordered eating'? Here we will begin to fill these critical knowledge gaps. We will make use of the 'activity-based anorexia' (ABA) model in rats to determine how age, sex and 'eating disorder' influence DAT function and how manipulations of DAT activity modify eating behavior. The ABA model recapitulates key characteristics of anorexia in humans, including reduced food intake in the presence of hunger, weight loss, hyperactivity, and increased insulin sensitivity. Importantly, in this model rats must 'choose' between eating and another rewarding condition, exercise. Thus, food intake is controlled by the rat and not artificially by the experimenter, offering a powerful translational model system. We will explore phosphotidylinositol 3-kinase (PI3K) and extracellular signal-regulated protein kinase (ERK), regulators of DAT activity that we have identified as putative targets to restore normal DAT function, as novel targets for therapeutic intervention to prevent, or lessen the severity of ABA. Given the well-established role of dopamine in reward and motivation, these studies will not only provide mechanistic insight into dysregulation of dopamine neurotransmission in eating disorders, but also other illnesses, including addiction and depression, which are often co-morbid with eating disorders. PUBLIC HEALTH RELEVANCE: Eating disorders, including anorexia, bulimia nervosa and binge eating, are major public health concerns, particularly prevalent in adolescent girls, and are compounded by a lack of effective treatments. Dysfunction of dopaminergic neurotransmission is implicated in these illnesses, but studies investigating the relationship between the dopamine transporter, a primary regulator of dopamine neurotransmission, and eating disorders during adolescence and adulthood are lacking. These studies will begin to fill critical knowledge gaps, with the long-term goal to elucidate novel targets for the treatment of these debilitating and ofte fatal disorders.