Corticosteroids limit microglial activation occurring during acute stress

Our previous studies demonstrated that exposure of animals to acute stress immediately induced morphological microglial activation in the brain. Here we investigated the effects of adrenal corticoids on microglial activation following acute stress. We compared microglial activation in vivo in adrenalectomized (ADX), Sham-operated (SHM), and adrenalectomy plus corticosterone (CORT) administered rats exposed to a 2-h period of acute water restraint stress. We found that: (1) acute stress induced microglial activation in SHM rats; (2) acute stress robustly enhanced microglial activation in ADX rats; (3) CORT treatment significantly reduced the effects of adrenalectomy. Thus, while acute stress has the ability to activate microglia, the magnitude of activation is negatively regulated by CORT. Glucocorticoids may serve as an important endogenous suppressive signal limiting neuroinflammation that might otherwise occur during stress.

► The present study investigated the effects of corticosteroids on microglia in the rat brain following acute stress.
► Acute stress induced microglial activation in Sham-operated rats.
► Acute stress in adrenalectomized rats robustly enhanced microglial activation.
► Corticosterone treatment in adrenalectomized rats significantly reduced the effects of adrenalectomy.
► Corticosteroids may provide suppressive signals for the microglial activation in the brain.