CHRONIC TWO-PHOTON CALCIUM IMAGING OF ASTROCYTES, PYRAMIDAL CELLS AND INTERNEURONS DURING NATURAL AROUSAL AND OPTOGENETIC STIMULATION OF LOCUS COERULEUS

During arousal, the locus coeruleus (LC) releases noradrenaline (NA) throughout the brain. Here, we investigate how LC-mediated NA release is distributed across layers of hippocampal CA1, and how it contributes to the cellular response profiles observed during natural arousal. To this end, we use optogenetic stimulation of LC while performing simultaneous two-photon calcium imaging of all major cell types of the brain – astrocytes, pyramidal cells, and interneurons – in the hippocampus of awake head-fixed mice. We find that natural arousal robustly activated all three major cell types on a population level. In contrast, stimulation of the LC alone resulted in a slow inhibition of pyramidal cells and interneurons. A subset of interneurons were consistently activated by LC stimulation and were found in distinct laminar positions in CA1. However, these LC-responsive subpopulations of interneurons did not reliably map onto response subpopulations defined by activity patterns during natural arousal. Astrocytes were strongly activated by both natural arousal and LC stimulation, but single-cell responses of astrocytes to LC stimulation only partially aligned with their activity during natural arousal responses. These results show that LC-driven NA release produces distinct, cell-specific effects that do not align with hippocampal dynamics during natural arousal.