Septal cholinergic neurons gate hippocampal output to entorhinal cortex via oriens lacunosum moleculare interneurons

Significance

Memory formation is a complex process that involves information transfer to the hippocampus for temporary storage (i.e., encoding) and the reciprocal circuit that relays the temporary information back to the neocortex for long-term storage (i.e., consolidation). Acetylcholine has been shown to play a critical role in memory function by differentially modulating encoding and consolidation, but the underlying mechanism is yet unclear. We found that acetylcholine suppresses the hippocampus–entorhinal cortex pathway, which is the gateway to the consolidation pathway. We show that this inhibition is mediated by oriens lacunosum moleculare interneurons and that the ablation of these interneurons impairs proper memory encoding. We provide evidence that demonstrates how acetylcholine tones down the memory consolidation pathway for efficient memory encoding.

Abstract

Neuromodulation of neural networks, whereby a selected circuit is regulated by a particular modulator, plays a critical role in learning and memory. Among neuromodulators, acetylcholine (ACh) plays a critical role in hippocampus-dependent memory and has been shown to modulate neuronal circuits in the hippocampus. However, it has remained unknown how ACh modulates hippocampal output. Here, using in vitro and in vivo approaches, we show that ACh, by activating oriens lacunosum moleculare (OLM) interneurons and therefore augmenting the negative-feedback regulation to the CA1 pyramidal neurons, suppresses the circuit from the hippocampal area CA1 to the deep-layer entorhinal cortex (EC). We also demonstrate, using mouse behavior studies, that the ablation of OLM interneurons specifically impairs hippocampus-dependent but not hippocampus-independent learning. These data suggest that ACh plays an important role in regulating hippocampal output to the EC by activating OLM interneurons, which is critical for the formation of hippocampus-dependent memory.