演題番号 : P1-m07
西島 さおり / Saori Nishijima:1 天野 恭志 / Hisayuki Amano:1 丸山 一郎 / Ichiro Maruyama:1
1:沖縄科学技術研究基盤整備機構・情報処理生物学ユニット / Information Process Biology Unit, Okinawa Institute of Science and Technology, Okinawa
Learning and memory are essential for all animals to survive and reproduce. C. elegans is an excellent model organism for the study of learning and memory for a number of reasons. For instance, the C. elegans nervous system consists of only 302 neurons. The neural circuits of these invariant neurons have completely been reconstructed from serial thin sections using electron microscopy. The body is transparent throughout the life so that neural activities can be observed using Ca2+- and voltage-sensitive fluorescent proteins in living animals. In this study, we developed a paradigm for the study on learning and memory in C. elegans by classical conditioning of worms with nonanol, as a conditioned stimulus (CS), and potassium chloride (KCl) as an unconditioned stimulus (US).Before the training, worms avoided nonanol, an aversive olfactory stimulus, and were attracted by KCl, an appetitive gustatory stimulus, in chemotaxis assay. In contrast, trained worms were attracted to nonanol after eight-cycle massed (without intertrial intervals, ITI) or spaced (with 10-min ITI) training. Memory induced by the massed training was extinguished within an hour, while the spaced training induced the memory which was retained for 24 hours. Worms treated with cycloheximide or actinomycin D failed to form the long-lasting memory by the spaced training, whereas the memory induced by the massed training was not significantly affected. These results indicated that the memory formation by the spaced training, but not by the massed training, required protein synthesis and mRNA transcription. Therefore, the memories induced by the massed and spaced training are classified as short-term and long-term memories, respectively. In support of this, C. elegans mutants defective in nmr-1 encoding an NMDA receptor subunit failed to form both of the short-term and long-term memory, while mutations in crh-1 encoding the CREB transcription factor affected only on the formation of the long-term memory.