Microglia inflammatory responses are controlled by an intrinsic circadian clock

Highlights • There are temporal differences in sickness behavior in rats. • Changes in sickness behavior are reflected in hippocampal cytokine and microglial responses. • Microglia show dramatic differences in immune activation throughout the day, with peak activation during the light phase. • Microglia rhythms are entrained by, but oscillate independent of, glucocorticoids. • These results suggest time-of-day should be considered when planning procedures that induce neuroinflammation.