Interactions Between Stress and Sex in Microbial Responses Within the Microbiota-Gut-Brain Axis in a Mouse Model.

Objective: Animal models are frequently used to examine stress response, but experiments seldom include females. The connection between the microbiota-gut-brain axis and behavioral stress response is investigated here using a mixed-sex mouse cohort.

Methods: CF-1 mice underwent alternating days of restraint and forced swim for 19 days (male n = 8, female n = 8) with matching numbers of control animals at which point the 16S rRNA genes of gut microbiota were sequenced. Mixed linear models accounting for stress status and sex with individuals nested in cage to control for cage effects evaluated these data. Murine behaviors in elevated plus-maze, open-field, and light/dark box were investigated.

Results: Community-level associations with sex, stress, and their interaction were significant. Males had higher microbial diversity than females (p = .025). Of the 638 operational taxonomic units detected in at least 25% of samples, 94 operational taxonomic units were significant: 31 (stress), 61 (sex), and 34 (sex-stress interaction). Twenty of the 39 behavioral measures were significant for stress, 3 for sex, and 6 for sex-stress. However, no significant associations between behavioral measures and specific microbes were detected.

Conclusions: These data suggest sex influences stress response and the microbiota-gut-brain axis and that studies of behavior and the microbiome therefore benefit from consideration of how sex differences drive behavior and microbial community structure. Host stress resilience and absence of associations between stress-induced behaviors with specific microbes suggests that hypothalamic-pituitary-adrenal axis activation represents a threshold for microbial influence on host behavior. Future studies are needed in examining the intersection of sex, stress response, and the microbiota-gut-brain axis.