Specific Dopaminergic Neurons for the Formation of Labile Aversive Memory

A paired presentation of an odor and electric shock induces aversive odor memory in Drosophila melanogaster. Electric shock reinforcement is mediated by dopaminergic neurons, and it converges with the odor signal in the mushroom body (MB). Dopamine is synthesized in approximately 280 neurons that form distinct cell clusters and is involved in a variety of brain functions. Recently, one of the dopaminergic clusters (PPL1) that includes MB-projecting neurons was shown to signal reinforcement for aversive odor memory. As each dopaminergic cluster contains multiple types of neurons with different projections and physiological characteristics, functional understanding of the circuit for aversive memory requires cellular identification. Here, we show that MB-M3, a specific type of dopaminergic neurons in the PAM cluster, is preferentially required for the formation of labile memory. Strikingly, flies formed significant aversive odor memory without electric shock when MB-M3 was selectively stimulated together with odor presentation. In addition, we identified another type of dopaminergic neurons in the PPL1 cluster, MB-MP1, which can induce aversive odor memory. As MB-M3 and MB-MP1 target the distinct subdomains of the MB, these reinforcement circuits might induce different forms of aversive memory in spatially segregated synapses in the MB.