Red light exaggerated sepsis-induced learning impairments and anxiety-like behaviors.

Light exerts critical non-visual effects on a multitude of physiological processes and behaviors, including sleep-wake behavior and cognitive function. In this study, we investigated the effects of continued exposure to different colors of light on cognitive function after sepsis in old mice. We found that exposure to red light, but not green light, exaggerated learning impairments and anxiety-like behaviors after sepsis. Red light also induced remarkable splenomegaly and altered the diversity and composition of the fecal microbiota. Pseudo germ-free mice transplanted with fecal bacteria from septic mice exposed to red light developed the same behavioral defects and splenomegaly as their donors. Intriguingly, splenectomy and subdiaphragmatic vagotomy reversed the learning impairments and anxiety-like behaviors resulting from red light exposure after sepsis. After subdiaphragmatic vagotomy, no differences in behavior or spleen size were observed among pseudo germ-free mice transplanted with fecal bacteria from septic mice exposed to different colors of light. Our results suggested that red light exposure after sepsis in old mice causes gut microbiota dysfunction, thus stimulating signaling through the subdiaphragmatic vagus nerve that induces splenomegaly and aggravates learning impairments and anxiety-like behaviors.