Microglial Morphological Complexity in the Piriform Cortex Is Associated with Olfactory Aversion Following Chronic Stress.

Olfactory anhedonia and heightened aversion to unpleasant odors are well-documented features of depression in humans, yet the neural mechanisms linking chronic stress to altered olfactory perception remain poorly understood. We used the unpredictable chronic mild stress (UCMS) paradigm to examine how chronic stress affects olfactory avoidance behavior and glial cell morphology across multiple olfactory brain regions in male and female mice. UCMS-treated mice showed increased avoidance of aversive odorants in an odorized light/dark box assay, consistent with heightened aversive reactivity to odors following chronic stress. Using immunohistochemistry, we assessed microglial morphology and astrocyte density across six olfactory and limbic brain regions. Chronic stress produced region-specific glial remodeling: astrocyte counts were selectively elevated in the medial amygdala, and microglial process complexity was increased in the anterior olfactory nucleus and anterior piriform cortex. Microglial morphological complexity in the anterior piriform cortex was correlated with individual odor avoidance scores. These findings reveal that chronic stress induces regionally specific glial plasticity within olfactory sensory and affective networks and suggest that microglial remodeling in piriform cortex may contribute to stress-related changes in olfactory perception.