Novelty facilitates formation of memories. The detection of novelty and storage of contextual memories are both mediated by the hippocampus, yet the mechanisms that link these two functions remain to be defined. Dentate granule cells (GCs) of the dorsal hippocampus fire upon novelty exposure forming engrams of contextual memory. However, their key excitatory inputs from the entorhinal cortex are not responsive to novelty and are insufficient to make dorsal GCs fire reliably. Here we uncover a powerful glutamatergic pathway to dorsal GCs from ventral hippocampal mossy cells (MCs) that relays novelty, and is necessary and sufficient for driving dorsal GCs activation. Furthermore, manipulation of ventral MCs activity bidirectionally regulates novelty-induced contextual memory acquisition. Our results show that ventral MCs activity controls memory formation through an intra-hippocampal interaction mechanism gated by novelty.
We thank Peter Jonas and Peter Somogyi for critically reading the manuscript, Satoshi Kida for helpful discussion, Taijia Makinen for providing the Prox1-creERT2 mouse line, and Hiromu Yawo for the VAMP2-Venus construct. We also thank Vivek Jayaraman, Ph.D.; Rex A. Kerr, Ph.D.; Douglas S. Kim, Ph.D.; Loren L. Looger, Ph.D.; and Karel Svoboda, Ph.D. from the GENIE Project, Janelia Farm Research Campus, Howard Hughes Medical Institute for the viral constructs used for GCaMP6s expression. We also thank Jacqueline Montanaro, Vanessa Zheden, David Kleindienst, and Laura Burnett for technical assistance, as well as Robert Beattie for imaging assistance. This work was supported by a European Research Council Advanced Grant 694539 to R.S.
Fredes Tolorza FA, Silva Sifuentes MA, Koppensteiner P, Kobayashi K, Jösch MA, Shigemoto R. Ventro-dorsal hippocampal pathway gates novelty-induced contextual memory formation. Current Biology. doi:10.1016/j.cub.2020.09.074
Fredes Tolorza, F. A., Silva Sifuentes, M. A., Koppensteiner, P., Kobayashi, K., Jösch, M. A., & Shigemoto, R. (n.d.). Ventro-dorsal hippocampal pathway gates novelty-induced contextual memory formation. Current Biology. Elsevier. https://doi.org/10.1016/j.cub.2020.09.074
Fredes Tolorza, Felipe A, Maria A Silva Sifuentes, Peter Koppensteiner, Kenta Kobayashi, Maximilian A Jösch, and Ryuichi Shigemoto. “Ventro-Dorsal Hippocampal Pathway Gates Novelty-Induced Contextual Memory Formation.” Current Biology. Elsevier, n.d. https://doi.org/10.1016/j.cub.2020.09.074.
F. A. Fredes Tolorza, M. A. Silva Sifuentes, P. Koppensteiner, K. Kobayashi, M. A. Jösch, and R. Shigemoto, “Ventro-dorsal hippocampal pathway gates novelty-induced contextual memory formation,” Current Biology. Elsevier.
Fredes Tolorza FA, Silva Sifuentes MA, Koppensteiner P, Kobayashi K, Jösch MA, Shigemoto R. Ventro-dorsal hippocampal pathway gates novelty-induced contextual memory formation. Current Biology.
Fredes Tolorza, Felipe A., et al. “Ventro-Dorsal Hippocampal Pathway Gates Novelty-Induced Contextual Memory Formation.” Current Biology, Elsevier, doi:10.1016/j.cub.2020.09.074.
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