Glucocorticoids mediate stress-induced priming of microglial pro-inflammatory responses

Acute and chronic stress sensitizes or "primes" the neuroinflammatory response to a subsequent pro-inflammatory challenge. While prior evidence shows that glucocorticoids (GCs) play a pivotal role in stress-induced potentiation of neuroinflammatory responses, it remains unclear whether stress-induced GCs sensitize the response of key CNS immune substrates (i.e. microglia) to pro-inflammatory stimuli. An ex vivo approach was used to address this question. Here, stress-induced GC signaling was manipulated in vivo and hippocampal microglia challenged with the pro-inflammatory stimulus LPS ex vivo. Male Sprague-Dawley rats were either pretreated in vivo with the GC receptor antagonist RU486 or adrenalectomized (ADX). Animals were then exposed to an acute stressor (inescapable tailshock; IS) and 24 h later hippocampal microglia were isolated and challenged with LPS to probe for stress-induced sensitization of pro-inflammatory responses. Prior exposure to IS resulted in a potentiated pro-inflammatory cytokine response (e.g. IL-1β gene expression) to LPS in isolated microglia. Treatment in vivo with RU486 and ADX inhibited or completely blocked this IS-induced sensitization of the microglial pro-inflammatory response. The present results suggest that stress-induced GCs function to sensitize the microglial pro-inflammatory response (IL-1β, IL-6, NFκBIα) to immunologic challenges.