The sinonasal microbiota, neural signaling, and depression in chronic rhinosinusitis

Background The complex relationships between the human microbiota, the immune system, and the brain play important roles in both health and disease, and have been of increasing interest in the study of chronic inflammatory mucosal conditions. We hypothesized that the sinonasal microbiota may act as a modifier of interkingdom neural signaling and, subsequently, mental health, in the upper respiratory inflammatory condition chronic rhinosinusitis (CRS). In this study we investigated associations between the sinonasal microbiota; local concentrations of the neurotransmitters serotonin, dopamine, and γ‐aminobutyric acid (GABA); and depression severity in a cohort of 14 CRS patients and 12 healthy controls. Methods Subject demographics, clinical severity scores, depression index scores, and sinonasal swab and mucus samples were collected at the time of surgery. Bacterial communities were characterized from swabs by 16S rRNA gene‐targeted sequencing and quantified by quantitative polymerase chain reaction. Mucus concentrations of the neurotransmitters serotonin, dopamine, and GABA were quantified by enzyme‐linked immunosorbent assay. Results Several commonly “health‐associated” sinonasal bacterial taxa were positively associated with higher neurotransmitter concentrations and negatively associated with depression severity. In contrast, several taxa commonly associated with an imbalanced sinonasal microbiota negatively associated with neurotransmitters and positively with depression severity. Few significant differences were identified when comparing between control and CRS subject groups, including neurotransmitter concentrations, depression scores, or sinonasal microbiota composition or abundance. Conclusion The findings obtained lend support to the potential for downstream effects of the sinonasal microbiota on neural signaling and, subsequently, brain function and behavior.