Octopamine neuron dependent aggression requires dVGLUT from dual-transmitting neurons

Neuromodulators such as monoamines are often expressed in neurons that also release at least one fast-acting neurotransmitter. The release of a combination of transmitters provides both "classical" and "modulatory" signals that could produce diverse and/or complementary effects in associated circuits. Here, we establish that the majority of Drosophila octopamine (OA) neurons are also glutamatergic and identify the individual contributions of each neurotransmitter on sex-specific behaviors. Males without OA display low levels of aggression and high levels of inter-male courtship. Males deficient for dVGLUT solely in OA-glutamate neurons (OGNs) also exhibit a reduction in aggression, but without a concurrent increase in inter-male courtship. Within OGNs, a portion of VMAT and dVGLUT puncta differ in localization suggesting spatial differences in OA signaling. Our findings establish a previously undetermined role for dVGLUT in OA neurons and suggests that glutamate uncouples aggression from OA-dependent courtship-related behavior. These results indicate that dual neurotransmission can increase the efficacy of individual neurotransmitters while maintaining unique functions within a multi-functional social behavior neuronal network. Author summary Neurons communicate with each other via electrical events and the release of chemical signals. An emerging challenge in understanding neuron communication is the realization that many neurons release more than one type of chemical signal or neurotransmitter. Here we ask how does the release of more than one neurotransmitter from a single neuron impact circuits that control behavior? We determined the monoamine octopamine and the classical transmitter glutamate are co-expressed in the Drosophila adult CNS. By manipulating the release of glutamate in OA-glutamate neurons, we demonstrated glutamate has both separable actions and complementary actions with OA on aggression and reproductive behaviors respectively. Aggression is a behavior that is highly conserved between organisms and present in many human disease states, including depression and Alzheimer's disease. Our results show that aggressive behavior requires the release of both neurotransmitters in dual-transmitting neurons and suggests within this set of neurons, glutamate may provide a new therapeutic target to modulate aggression in pathological conditions.