Pair Bonding Is Associated with Sexually Dimorphic Microglia Morphology in Prairie Voles (Microtus ochrogaster)

Microtus ochrogaster, monogamous prairie voles, are a translational animal model for studying monogamy and pair-bonding. Microglia, the resident immune cells of the brain, are one of several cell types still poorly understood in non-classical animal models. Microglia are known to play mechanistic roles in mediating social behaviors using inflammatory signaling, but the relationship between microglia reactivity and pair bonding has not yet been investigated. The present study first developed a robust protocol for quantitative histological visualization of microglia in Microtus ochrogaster. Second, it investigated differences in microglia morphology, a reliable index of microglia reactivity and function, in pair-bonded vs. unpaired voles. Sections containing prefrontal cortex (PFC) and anterior cingulate cortex (ACC) were stained for Ionized calcium-binding adaptor molecule I (Iba1) using immunohistochemistry (IHC). IHC results provided evidence for the successful use of murine histological protocols in prairie voles. Quantification results revealed a sexually dimorphic effect of pair-bonding on microglia: somas were significantly larger in pair-bonded vs. unpaired females, and somas were significantly smaller in pair-bonded vs. unpaired males. Additionally, somas were significantly larger in unpaired males than females. With larger somas indicating higher microglia reactivity, results elucidate how pair-bonding may influence microglia function in a sexually dimorphic manner.