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Updated: Aug 3, 2025
Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents
Published on: January 24, 2013
Ablation of microglia does not alter circadian rhythm of locomotor activity
Futaba Matsui1, Sho T Yamaguchi1, Riho Kobayashi1
1Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
Abstract:
Microglia, as macrophages in the brain, are responsible for immune responses and synaptic remodeling. Although the function of microglia is regulated by circadian rhythms, it is still unclear whether microglia are involved in the generation and light entrainment of circadian rhythms of behavior. Here, we report that microglial depletion does not alter behavioral circadian rhythms. We depleted ~ 95% of microglia in the mouse brain by PLX3397, a CSF1R inhibitor, and analyzed the effect on the spontaneous behaviors of mice. We found that neither the free-running period under constant darkness nor light entrainment under jet-lag circumstances were influenced by the ablation of microglia. Our results demonstrate that the circadian rhythms of locomotor activity, an important output of the circadian clock in the brain, are likely a phenomenon not produced by microglia.
Insights
Microglia, the brain's immune cells, do not generate or regulate behavioral circadian rhythms. Depleting microglia in mice did not affect their daily activity patterns or light entrainment.
Area of Science:
- Neuroscience
- Immunology
- Chronobiology
Background:
- Microglia are brain-resident macrophages involved in immune surveillance and synaptic plasticity.
- Microglial functions are known to be influenced by circadian rhythms.
- The specific role of microglia in generating and entraining behavioral circadian rhythms remains largely unknown.
Purpose of the Study:
- To investigate whether microglia are essential for the generation and light entrainment of circadian rhythms in behavior.
- To determine if the ablation of microglia impacts the free-running period or light responsiveness of circadian locomotor activity.
Main Methods:
- Utilized PLX3397, a colony-stimulating factor 1 receptor (CSF1R) inhibitor, to deplete approximately 95% of microglia in the mouse brain.
- Analyzed the spontaneous locomotor behaviors of microglia-depleted mice under constant darkness (free-running period) and simulated jet-lag conditions (light entrainment).
Main Results:
- Microglial depletion did not alter the free-running period of circadian locomotor activity under constant darkness.
- Light entrainment of behavioral rhythms under simulated jet-lag conditions was unaffected by the absence of microglia.
- The circadian rhythms of locomotor activity, a key output of the central circadian clock, were maintained despite near-complete microglial ablation.
Conclusions:
- Microglia are not required for the generation or maintenance of circadian rhythms of locomotor activity in mice.
- The study suggests that the neural circuits governing circadian behavior are independent of microglial cells.
- These findings clarify the role of microglia in the context of circadian biology, indicating they are not primary drivers of behavioral rhythms.
