Abstract
Pavlovian olfactory learning in Drosophila produces two genetically distinct forms of intermediate-term memories: anesthesia-sensitive memory, which requires the amnesiac gene, and anesthesia-resistant memory (ARM), which requires the radish gene. In addition to the Amnesiac peptide required for anesthesia-sensitive memory formation, we report that ARM formation requires serotonin (5HT) released from only two dorsal paired medial (DPM) neurons onto the mushroom bodies (MBs), the olfactory learning and memory center in Drosophila. Long-term memory (LTM) formation requires time because information gradually accumulates across widely spaced learning episodes to a threshold that induces protein synthesis and synaptic changes. However, the neural mechanisms that determine this threshold remain obscure. Here, we report that LTM formation from a one-time experience is prevented by induction of new proteins in MB. Blocking protein synthesis in early alpha/beta MB neurons after a single training session induced LTM. Learning was accompanied by activation of molecules in early alpha/beta MB neurons and transcription of the serotonin receptor 5-HT1A, which increased the inhibitory constraints on the storage of LTM in the downstream circuits. We propose that learning induces sequential synthesis of new proteins at three different sites in the brain to inhibit, enhance, and consolidate LTM.