1:国立遺伝研・初期発生 / Division of Molecular and Developmental Biology, National Institute of Genetics, Mishima, Shizuoka, Japan 2:総研大院遺伝学 / Department of Genetics, The Graduate University for Advanced Studies (SOKENDAI), Mishima, Shizuoka, Japan.
Zebrafish is a useful model vertebrate for neuroscience. We developed Tol-2 mediated transgenesis, enhancer trap, gene trap and Gal4-UAS methods, and generated transgenic zebrafish that express Gal4 in region-specific neural cells. These lines would be useful to elucidate cellular and molecular basis for learning and memory. However, behavior assay systems to study hippocampal learning are not well established in zebrafish. Here, we developed two behavior assay systems; temporal learning system and spatial learning system. For temporal learning, we employed a two-way trace active avoidance conditioning, in which CS (green light) and US (electrical shock) are given with a temporal gap between CS offset and US onset. We showed that wild type zebrafish learned in the temporal learning paradigm. For spatial learning, we made four compartments in a plastic box, and fed automatically at one of them. By performing the training, wild type zebrafish learned the place where food was given. Next, we analyzed the Gal4 expression patterns in the adult brain in our Gal4 enhancer trap and the gene trap lines, and isolated the transgenic line which expressed Gal4 in the dorsolateral telencephalon (Dl), since surgical study shows the Dl is a functional homolog of the mammalian hippocampus in goldfish (Portavella et al, 2004). To identify the importance of the neurons, we inhibited the neural activity of the Dl neurons by crossing the Dl-Gal4 driver line with the UAS:botulinum toxin effector line. We analyzed the behavior of the double transgenic fish in the learning paradigms, and found that the Dl-Gal4;UAS:botulinum toxin fish showed impairment in both the temporal learning paradigm and the spatial learning paradigm. From this study and the previous anatomical studies, we propose that some neurons in the Dl mediates hippocampal learning in zebrafish.