INFLAMMASOME BLOCKADE PREVENTS MICROBIOTA-INDUCED ANXIETY AND HIPPOCAMPAL MICROGLIA–PERINEURONAL NETS REMODELING

Gut microbiota has been implicated in anxiety-related phenotypes, yet the neural substrates remain unclear. We aimed to test whether microbiota from the anxiety-prone 129S1/SvImJ mice strain (S1) can transfer behavioral and neuroimmune features to C57BL/6J mice. Baseline profiling revealed marked strain differences in fecal microbial composition and short-chain fatty acids. Recipient C57BL/6J mice received fecal microbiota transplantation (FMT) from S1 donors once daily for 5 days. Anxiety-like behavior was assessed the following day in the light-dark box and in the elevated plus maze (EPM) tests, followed by cued fear conditioning and extinction. FMT recipients displayed increased anxiety-like behavior, as revealed reduced exploration of the light compartment and open arms in the EPM, whereas fear extinction remained unchanged. In the same FMT recipients, immunofluorescence in hippocampal subfields (CA1, CA3 and dentate gyrus) showed reduced parvalbumin (PV) interneurons and perineuronal nets (PNNs) density. Concurrently, Iba1-positive microglia exhibited increased soma area and perimeter in the same brain regions, suggesting microglia activation. A separate cohort of C57BL/6J mice received the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome inhibitor MCC950 or saline during fecal microbiota transplantation. MCC950 prevented the FMT-induced anxiety-like phenotype and normalized microglial morphology and PV/PNNs density. Together, these results suggest that short-term microbiota transfer is sufficient to increase anxiety and remodel hippocampal microglia and inhibitory circuit markers, supporting a gut-brain pathway linking microbial communities and anxiety-related behavior.