Dopamine and ecdysone acutely modulate AKH signaling during physiological stress in Drosophila. Jason T. Braco, Greg E. Alberto, Emily L. Gillespie, Erik C. Johnson. Biology, Wake Forest University, Winston-Salem, NC.

   The link between dopamine (DA) and stress response has been well established in both vertebrates and invertebrates. However, the precise mechanisms of how dopamine is modulating behavioral and physiological responses to stress are unknown. In Drosophila, we show that genetic and pharmacological manipulations that increase levels of dopamine cause elevated locomotion during physiological stress and a concomitant decrease in survivorship. Conversely, manipulations that decrease dopamine signaling cause blunted locomotor responses and longer survival during physiological stress. To identify underlying mechanisms of dopamine action, we performed these manipulations in different mutant backgrounds. Notably, manipulations of dopamine levels in flies with altered Adipokinetic Hormone (AKH) signaling implicate epistatic interactions. AKH is required for stress- induced hyperactivity, and the mobilization of energy from stores, and we have previously evaluated the role of AKH as a stress hormone. We next tested whether DA exerts its effects directly on AKH cells, through employing the fluorescent Ca2+ reporter, GCaMP, to examine AKH cell activation. Application of dopamine leads to heightened calcium levels, in an energy-independent manner. To identify the dopamine receptor subtypes that mediate DA responses, we selectively introduced RNAi elements targeting the four different DA receptors present in Drosophila. RNAi elements targeting the DopEcR result in behavioral phenotypes consistent with DA activation and we confirmed the expression of this receptor with RNAseq. Notably, this receptor is inhibited by ecdysone, and co-application of DA and ecdysone results in a loss of GCaMP responsiveness. These results suggest a complex neuroendocrine circuit involving DA and ecdysone convergence that regulate AKH signaling during physiological stress.