Researchers used a cocktail of antibiotics to deplete gut microbes in mice. They found that metabolites in the gut differed in these mice compared with controls. In particular, metabolic pathways involved in making important neurotransmitters like serotonin were affected. Additionally, these mice showed abnormal day-night distribution in sleep/wake patterns, particularly the amount of REM sleep, and frequent transitions between REM and non-REM sleep episodes.
