Identification of a dopamine circuit mediating day eating and diet-induced obesity in mice - Project Summary
Excess body fat significantly increases the risk for a range of maladies including diabetes,
cancer, and cardiovascular diseases. An estimated 45 million adult Americans go on diets and
spend over $30 billion on weight loss products each year. Most of these interventions fail, leaving
individuals overweight and susceptible to metabolic disorders like type 2 diabetes. This trend is
likely due to the easy availability of palatable, energy-rich foods which incentivizes food
consumption for pleasure regardless of the energy need (hedonic feeding). Dopaminergic neurons
of the ventral tegmental area (VTA) compute the potential value of food reward and release
dopamine (DA) to tune the activity of downstream targets. One of the results of this reward
computation is the encoding of the necessary drive for retrieval and consumption of food.
Uncoupling food consumption from energy need guided by the reward circuitry leads to continuous
snacking rather than a meal-based pattern of feeding. Mounting evidence suggests that in addition
to increased caloric intake, this type of irregular meal timing promotes desynchrony of precisely
timed metabolic processes, which further contributes to the maladaptive effects of overeating.
Indeed, disorganization of mealtimes by manipulation of circadian rhythms is correlated with weight
gain and metabolic syndrome in humans and animal models. How do rewarding foods influence
meal timing? The suprachiasmatic nucleus (SCN) is the primary regulator of circadian rhythms and
integrates sensory and physiologic information to synchronize homeostatic functions to the
day/night cycles. The basis for how reward, feeding and circadian circuitry interact to promote
normal and pathological feeding represents a significant gap in our knowledge. Here, we propose
to test the hypothesis that dopaminergic input from a select group of VTA-DA neurons to the SCN is
an integral part of the hedonic feeding neurocircuitry. We will genetically and anatomically define
the subpopulation of VTA neurons that releases DA in the SCN in response to palatable foods. We
will ablate DA production in these select neurons to validate their direct functional SCN input. This
proposal employs innovative approaches while leveraging our expertise in mouse genetics,
stereotaxic viral delivery, and functional neural circuitry mapping strategies. Using these tools, we
will identify the group of DA neurons that govern feeding behavior by modulating the activity of
central circadian clock neurons. This work will have broad implications for understanding how
reward circuitry overcomes homeostatic control while providing unique avenues for therapeutic
approaches against the obesity epidemic.
