Single Serotonergic Neurons that Modulate Aggression in Drosophila

Monoamines, including dopamine (DA), have been linked to aggres-sion in various species. However, the precise role or roles served bythe amine in aggression have been dif ficult to define becausedopaminergic systems influence many behaviors, and all can bealtered by changing the function of dopaminergic neurons. In thefruit fly, with the powerful genetic tools available, small subsets ofbrain cells can be reliably manipulated, offering enormous advan-tages for exploration of how and where amine neurons fitintothecircuits involved with aggression. By combining the GAL4/upstreamactivating sequence (UAS) binary system with the Flippase (FLP) re-combination technique, we were able to restrict the numbers oftargeted DA neurons down to a single-cell level. To explore thefunction of these individual dopaminergic neurons, we inactivatedthem with the tetanus toxin light chain, a genetically encoded in-hibitor of neurotransmitter release, or activated them with dTrpA1,a temperature-sensitive cation channel. We found two sets of dopa-minergic neurons that modulate aggression, one from the T1 clusterand another from the PPM3 cluster. Both activation and inactivationof these neurons resulted in an increase in aggression. We demon-strate that the presynaptic terminals of the identi fied T1 and PPM3dopaminergic neurons project to different parts of the central com-plex, overlapping with the receptor fields of DD2R and DopR DAreceptor subtypes, respectively. These data suggest that the twotypes of dopaminergic neurons may in fluence aggression throughinteractions in thecentral complex regionof the brain involvingtwodifferent DA receptor subtypes.