Dopamine neurons in the midbrain play a central role in the rewarding and addictive effects of drugs of abuse. They are also important for appetite. Appetite is regulated by subsets of neurons in brain centers in the hypothalamus. However, it is not known whether these neurons transmit signals to midbrain dopamine neurons implicated in reward. In this proposal, I will examine how neurons linked to appetite transmit signals to dopamine neurons. Using a pseudorabies virus that can trace neural circuits, I will identify neuronal subsets upstream of midbrain dopamine neurons in brain regions linked to appetite behaviors. To identify neurotransmitters or neuromodulators expressed in appetite neurons presynaptic to dopamine neurons, I will dissociate fluorescently labeled appetite neuron subsets from the hypothalamus, isolate RNA and amplify cDNA after first-strand synthesis, and perform microarray analysis. After identifying candidate neurotransmitter and neuromodulator genes, I will perform dual immunofluorescent in situ hybridization to determine whether appetite neurons that are upstream of DA neurons express any of the candidate neurotransmitters, neuromodulators and biosynthetic enzymes genes. To identify receptors in midbrain dopamine neurons, I will dissociate live fluorescently labeled dopamine neurons, isolate RNA and amplify cDNA after first-strand synthesis, and perform a quantitative real-time PCR-based screen. From these results, I will construct an anatomical map of circuitry between upstream appetite centers and the dopamine neurons they convey signals to, and then superimpose onto that a cellular and molecular map. This kind of organization will provide a structure to understand the connections between the dopamine reward system and appetite, may implicate roles for dopamine in eating addictions, and could lay groundwork for novel drug targets for addictions and disorders.
Ventral midbrain dopamine neurons are responsible for the rewarding and addictive effects of drugs of abuse. They also are important for innate behaviors such as appetite behavior. The studies described here will clarify the relationship between appetite and rewards and addictions, and provide a platform for further studies in food addictions.