Spatio-temporal organization of cell assemblies in Nucleus Reuniens during slow oscillations

The nucleus reuniens (NR) is an important anatomical and functional relay between the medial prefrontal cortex (mPFC) and the hippocampus (HPC). Whether the NR controls neuronal assemblies - a hallmark of information exchange between the HPC and mPFC for memory transfer/consolidation - is not known. Using simultaneous LFP and unit recordings in NR, HPC and mPFC in rats during slow oscillations under anesthesia, we identified a reliable sequential activation of NR neurons at the beginning of UP states, which preceded mPFC ones. NR sequences were spatially organized, from dorsal to ventral NR. Chemical inactivation of the NR disrupted mPFC sequences at the onset of UP states as well as HPC sequences present during sharp-wave ripples. We conclude that the NR contributes to the coordination and stabilization of mPFC and HPC neuronal sequences during slow oscillations, possibly via the early activation of its own sequences.