ASTROGLIAL CALCIUM DYNAMICS IN HIPPOCAMPAL RHYTHMS DURING SLEEP

Sleep plays a critical role in memory consolidation. In the hippocampus, spatial information encoded by place cells during exploration is replayed in sleep during fast oscillations (sharp-wave ripples, SWRs). SWRs provide optimal temporal windows for synaptic plasticity, particularly long-term potentiation, and their disruption causally impairs spatial memory. However, the cellular and molecular mechanisms that regulate this network activity in relation to learning remain poorly understood.
While neurons have long been considered the only drivers of information processing, mounting evidence suggests a key role for glial cells, particularly astrocytes, in modulating neural circuits and behaviour. Though considered electrically silent, astrocytes display dynamic intracellular calcium signaling in response to local and global brain states, including sleep and wakefulness. Recent studies show that astrocytic calcium activity can encode expected reward locations in spatial contexts. Yet, how astrocytes interact with hippocampal network rhythms during sleep-dependent memory consolidation remains unexplored in vivo.
To investigate this, we performed simultaneous large-scale astrocytic calcium imaging and extracellular recordings of neuronal activity in freely behaving mice during learning tasks and subsequent sleep. Preliminary results suggest that specific temporal calcium dynamics of hippocampal astrocytes are associated with brain rhythms during sleep. In addition, our data point to a contribution of local calcium signaling in hippocampal astrocytes to different types of memory, associated with specific brain rhythms.
These findings suggest that hippocampal astrocytes actively respond and modulate hippocampal rhythms critical for memory.