Brain Circuits for Water Reward Memory in Drosophila (I)

The secrets of memory forming processes in the brain have tantalized people for centuries. Here, we found thirsty fruit flies, Drosophila melanogaster, can be trained with a specific odors paired with water to form memory. Only a single 2-min training conditioning pairing odor with water reinforcement forms memory, which lasts for more than 24 hours. Target expressed shibirets transgene, a mutant dynamin, in water receptor PPK28 neurons abolished the association of water reward learning. Genetically labeled two color images and behavioral experiments suggest the information of water reinforcement from PPK28 neurons to tyrosine decarboxylase (dtdc2) neurons. The dtdc2 neurons connect to dopaminergic protocerebral anterior medial (PAM) neurons and finally transmit water signal to the mushroom body (MB), the learning and memory center in Drosophila. In addition, only the 24-hour water reward memory is disrupted by protein synthesis inhibitor cycloheximide (CXM), the LTM-specific mutations (radish, crammer, and tequila) or the expression of CREB blocker (creb2b) in MB, suggesting this long-lasting memory belongs to long-term memory (LTM). We also revealed that distinct dopaminergic PAM clusters deliver the water reinforcement into different MB compartments to form water reward STM (delivered by PAM-y4 and -y5 clusters) and aP neuron subsets and LTM (delivered by PAM-p i cluster), respectively. Finally, water reward STM requires MB y neuronal activity during memory retrieval, whereas water reward LTM requires MB y and aP neuronal activity during memory retrieval suggesting that the parallel storage of STM and LTM in water rewarding process. There are some specific aims we are going to achieve. (1) Identify whether different inputs of dopaminergic PAM circuits modulate initial learning (0 hour), early short-term memory, STM (3-hour), and late LTM (24-hour), respectively. (2) Identify the dopamine receptors in which MB neurons is required for STM and LTM (3) Identify the neuronal activity in which subset of MB neurons is required for STM, and which subset is required for LTM. (4) Identify which subset of MB neurons is involved in CREB-dependent water reward LTM. (5) Identify de no^ve protein synthesis in which MB neuron subsets require for water reward LTM, and compare the difference with sugar reward LTM. (6) Identify the possible MB output circuits for water reward STM and LTM. (7) Propose a model of brain circuits specific for water reward STM and LTM. We believe through our systematic analysis in the current study will reveal a comprehensive brain circuits and molecule mechanism regarding the short- and long-term water reward memory in Drosophila and paves the way for understanding our own memory.

Project ID:PC10408-1817
External Project ID:MOST104-2321-B182-008