# Microglia modulate stable wakefulness via the thalamic reticular nucleus in mice

## TL;DR

Microglia help maintain stable wakefulness in mice by regulating ceramide levels in the thalamic reticular nucleus.

## Contribution

This study reveals a novel role of microglia in modulating wakefulness via ceramide signaling in the thalamic reticular nucleus.

## Key findings

- Microglial depletion disrupts stable nighttime wakefulness in mice.
- Ceramide levels in the brain correlate with sleep-wake behavior and are regulated by microglia.
- Activating TRN neurons or inhibiting ceramide production restores stable wakefulness in microglia-depleted mice.

## Abstract

Microglia are important for brain homeostasis and immunity, but their role in regulating vigilance remains unclear. We employed genetic, physiological, and metabolomic methods to examine microglial involvement in the regulation of wakefulness and sleep. Microglial depletion decreased stable nighttime wakefulness in mice by increasing transitions between wakefulness and non-rapid eye movement (NREM) sleep. Metabolomic analysis revealed that the sleep-wake behavior closely correlated with diurnal variation of the brain ceramide, which disappeared in microglia-depleted mice. Ceramide preferentially influenced microglia in the thalamic reticular nucleus (TRN), and local depletion of TRN microglia produced similar impaired wakefulness. Chemogenetic manipulations of anterior TRN neurons showed that they regulated transitions between wakefulness and NREM sleep. Their firing capacity was suppressed by both microglial depletion and added ceramide. In microglia-depleted mice, activating anterior TRN neurons or inhibiting ceramide production both restored stable wakefulness. These findings demonstrate that microglia can modulate stable wakefulness through anterior TRN neurons via ceramide signaling.

Here, the authors show that microglia depletion results in unstable wakefulness and altered levels of ceramide, influencing microglia in the mouse thalamic reticular nucleus (TRN). Stable wakefulness can be restored by activation of the TRN or inhibition of ceramide production in the mouse brain.