In Vivo Characterization of Neurophysiological Diversity in the Lateral Supramammillary Nucleus during Hippocampal Sharp-wave Ripples of Adult Rats

•Extra-hippocampal regions might participate in the expression of sharp-wave ripples (SPW-Rs).•We found two neuronal populations in the lSuM: SPW-R-active (increased firing during SPW-Rs), and SPW-R-unchanged neurons.•lSuM SPW-R-active neurons increased their firing prior to SPW-Rs peak power and hippocampal excitatory neurons.•lSuM SPW-R-active neurons showed a higher firing during theta and slow oscillations compared to SPW-R-unchanged neurons.•These results provide new insight on the interaction between a lSuM neuronal population and hippocampus during SPW-Rs. The extent of the networks that control the genesis and modulation of hippocampal sharp-wave ripples (SPW-Rs), which are involved in memory consolidation, remains incompletely understood. Here, we performed a detailed in vivo analysis of single cell firing in the lateral supramammillary nucleus (lSuM) during theta and slow oscillations, including SPW-Rs, in anesthetized rats. We classified neurons as SPW-R-active and SPW-R-unchanged according to whether or not they increased their firing during SPW-Rs. We show that lSuM SPW-R-active neurons increase their firing prior to SPW-Rs peak power and prior to hippocampal excitatory cell activation. Moreover, lSuM SPW-R-active neurons show increased firing activity during theta and slow oscillations as compared to unchanged neurons. These results suggest that a sub-population of lSuM neurons can interact with the hippocampus during SPW-Rs, raising the possibility that the lSuM may modulate memory consolidation.