Cell Reports
Volume 30, Issue 2, 14 January 2020, Pages 432-441.e3
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Article
Hippocampal Ripple Coordinates Retrosplenial Inhibitory Neurons during Slow-Wave Sleep

https://doi.org/10.1016/j.celrep.2019.12.038Get rights and content
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Highlights

  • Both the hippocampus and RSC play indispensable roles in memory formation

  • The RSC displays a pre-ripple activation and fast oscillation

  • Hippocampal ripple activates RSC interneurons and inhibits RSC principal neurons

  • The hippocampus may overshadow the RSC in supporting memory functions

Summary

The hippocampus and retrosplenial cortex (RSC) play indispensable roles in memory formation, and importantly, a hippocampal oscillation known as ripple is key to consolidation of new memories. However, it remains unclear how the hippocampus and RSC communicate and the role of ripple oscillation in coordinating the activity between these two brain regions. Here, we record from the dorsal hippocampus and RSC simultaneously in freely behaving mice during sleep and reveal that the RSC displays a pre-ripple activation associated with slow and fast oscillations. Immediately after ripples, a subpopulation of RSC putative inhibitory neurons increases firing activity, while most RSC putative excitatory neurons decrease activity. Consistently, optogenetic stimulation of this hippocampus-RSC pathway activates and suppresses RSC putative inhibitory and excitatory neurons, respectively. These results suggest that the dorsal hippocampus mainly inhibits RSC activity via its direct innervation of RSC inhibitory neurons, which overshadows the RSC in supporting learning and memory functions.

Keywords

hippocampus
retrosplenial cortex
sharp-wave ripple
neural oscillation
memory consolidation
memory formation
slow-wave sleep
optogenetic stimulation
in vivo recording
neural ensemble

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