Abstract
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 SPW-Rs peak power and prior hippocampal pyramidal cell activation. Moreover, lSuM SPW-R-active neurons show increased firing activity during theta and slow oscillations as compared to unchanged-neurons. SPW-R-active neurons are more active during high peak power SPW-Rs, whereas SPW-R-unchanged neurons are more active during long SPW-Rs. 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.
Footnotes
Key points Sharp-wave ripples (SPW-Rs) consist of a hippocampal fast field oscillation involved in memory consolidation.
Extra-hippocampal regions might participate in the expression of SPW-Rs.In the lateral supramammillary nucleus of the hypothalamus (lSuM), we found two neuronal populations: SPW-R-active neurons, which increased their firing during hippocampal SPW-Rs, and SPW R-unchanged neurons, which did not change their firing during SPW-Rs.
lSuM SPW-R-active neurons increased their firing prior SPW-Rs peak power and prior hippocampal pyramidal neurons activation.
lSuM SPW-R-active neurons showed a higher firing during theta and slow oscillations as compared to lSuM SPW-R-unchanged neurons.
These results provide new insight on the interaction between a lSuM neuronal population and hippocampus during SPW-Rs and suggest a role of lSuM in memory consolidation.