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 [1, 2]. Electric shock reinforcement is mediated by dopaminergic neurons [3-5], and it converges with the odor signal in the mushroom body (MB) [2, 6-8]. Dopamine is synthesized in similar to 280 neurons that form distinct cell clusters [9-11] and is involved in a variety of brain functions [9, 12-20]. Recently, one of the dopaminergic clusters (PPL1) that includes MB-projecting neurons was shown to signal reinforcement for aversive odor memory [21]. As each dopaminergic cluster contains multiple types of neurons with different projections and physiological characteristics [11, 20], 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.