Sex-specific gut microbiota modulation of aversive conditioning and basolateral amygdala dendritic spine density

Gut microbiota influence numerous aspects of host biology, including brain structure and function. Growing evidence implicates gut microbiota in aversive conditioning and anxiety-related behaviors, but research has focused almost exclusively on males. To investigate sex-dependent effects of gut dysbiosis on aversive learning and memory, adult male and female C57BL/6N mice were orally administered a moderate dose of antimicrobials (ATMs) or a control over 10 days. Changes in microbiome composition were analyzed by 16S rRNA sequencing. Open field behavior, cued aversive learning, context recall, and cued recall were assessed. Following behavioral testing, the morphology of principal neuron dendrites and spines in the basolateral amygdala (BLA) was characterized. Results revealed that ATMs induced a similar pattern of gut dysbiosis in both sexes. Only treated males exhibited altered locomotor and anxiety-like behavior in the novel open field. ATMs impaired aversive memory acquisition and cued recall in females, but not males. Context recall remained intact, as did dendritic structure of BLA principal neurons. However, treatment exerted sex-specific effects on spine density. A second experiment was conducted to isolate gut perturbation to cued recall. Results revealed no effect of ATMs on recall of a previously consolidated fear memory, indicating that ATMs preferentially impact aversive learning. These data shed new light on how gut microbiota interact with sex to influence aversive conditioning, anxiety-like behavior, and BLA dendritic spine architecture.