The role of medullary astrocytes in breathing and arousal: insights into glial regulation of respiratory function.

Astrocytes play vital roles in regulating brain states across organisms. Specifically, they serve several roles in regulating breathing behaviors and associated brain states, including facilitating transitions between phases of breathing by sensing small changes in O2 and CO2 levels, regulating the sleep-wake cycle, and impacting arousal and wakefulness. Here, we tested the hypothesis that astrocytes in the ventral respiratory column (VRC) are important for arousal and sigh generation in alert mice (Aldh1l1Cre). Using calcium imaging we show that some Aldh1l1 cells are phase-locked with sigh generation and are activated in the VRC by hypoxia. Optogenetic activation (AAV-CAG-ChR2-EYFP) of astrocytes in the VRC increased the probability of evoking sighs and arousal while awake and during non-rapid eye movement (NREM) sleep. Depletion of astrocytes in the VRC by an AAV-CAG-Caspase3 virus (ablation of 77%) does not impact the probability of sigh generation in any sleep-wake state under control conditions. However following the depletion of astrocytes, arousal and sigh generation is significantly delayed in response to hypoxia (65.3 ± 5.5 vs. control: 21.7 ± 1.9 seconds). We conclude that medullary astrocytes play a critical role in the generation of arousal and sighs particularly in response to hypoxia.