? In mammals, serotonin (5HT) receptors modulate a variety of physiologic functions including craving, addiction, and feeding behavior. Given the important role of these receptors, the establishment of a simplified model system in which to identify genetic modifiers of serotonergic signaling would be an important advance. It is known that significant structural similarities exist between the mammalian and Drosophila proteins that comprise the serotonergic pathway (i.e. 5HT synthetic enzymes, transporters, and receptors). In contrast to mammals, 5HT receptor mediated function in the fly is not well defined. We have recently demonstrated that 5HT modulates food intake in flies thus establishing a functional parallel between Drosophila and mammals. We have shown that the administration of 5HT receptor agonists and antagonists significantly decreases and increases food intake, respectively. ? ? As an initial goal, we will determine which of the Drosophila 5HT receptor subtype(s) regulates food intake. In vitro cell based assays will be established to screen 5HT ligands to determine the subtype specificity of the compounds at each of the four fly 5HT receptors. These ligands will then be utilized in a larval food intake paradigm. The in vitro pharmacologic specificity will be correlated with in vivo receptor mediated effects to define which of the 5HT receptor subtype(s) underlies the serotonergic inhibition of feeding behavior. As a next step, flies in which the relevant receptor genetically down-regulated (i.e. RNAi flies) will be assessed for changes in food intake. Finally, these flies will be analyzed with gene expression profiling to identify novel genetic modifiers of serotonergic signaling. Genes with altered transcription in this genetic model will be prioritized for characterization using both in vitro and in vivo assays. ? ? ? ?
