Study of the effects of chronic stress and the rapid-acting antidepressant psilocybin in primary murine microglia

Stress is a major risk factor for depression and is associated with immune dysregulation and increased inflammation. The emergence of rapid-acting antidepressants such as ketamine has renewed interest in psychedelics, including psilocybin, which has shown rapid antidepressant effects and enhanced brain plasticity in both clinical and preclinical studies. Recent evidence shows that psilocybin reduces inflammatory markers and modulates immune responses, suggesting that immunomodulation may contribute to its therapeutic effects. Microglia play a key role in maintaining brain homeostasis and regulating neuroinflammation, and its dysfunction has been implicated in depression. However, the mechanisms linking stress, microglia, and the antidepressant effects of psilocybin remain poorly understood. Here, we used primary microglia cultures to establish an in vitro model of chronic stress based on repeated doses of corticosterone to study microglial molecular and morphological changes and the effects of psilocybin. Immunofluorescence experiments followed by microscopy and image analysis with Fiji software confirmed culture purity and highlighted specific morphological features in naïve conditions. Further, the expression of the macrophage tetraspan Ms4a4a in microglia was confirmed. Finally, MTT assay identified critical corticosterone concentrations associated with increased toxicity. Future studies will investigate Ms4a4a role in stress response and the effects of psilocybin.