Microglial Engulfment of Spines in the Ventral Zona Incerta Regulates Anxiety-Like Behaviors in a Mouse Model of Acute Pain.

Although activation of microglial cells is critical in developing brain disorders, their role in anxiety-like behaviors in pain is still vague. This study indicates that alteration of microglia's neuronal spine engulfment capacity in ventral zona incerta (ZI V ) leads to significant pain and anxiety-like behaviors in mice 1-day post-injection of Complete Freud's Adjuvant (CFA1D). Performing whole-cell patch-clamp recordings in GABAergic neurons in the ZI V (ZI V GABA ) in brain slices, we observed decreased activity in ZIv GABA and reduced frequency of the miniature excitatory postsynaptic currents (mEPSCs) in ZI V GABA of CFA1D mice compared with the saline1D mice. Besides, chemogenetic activation of ZI V GABA significantly relieved pain and anxiety-like behaviors in CFA1D mice. Conversely, in naïve mice, chemogenetic inhibition of ZI V GABA induced pain and anxiety-like behaviors. Interestingly, we found changes in the density and morphology of ZI V Microglia and increased microglial engulfment of spines in ZI V of CFA1D mice. Furthermore, pain sensitization and anxiety-like behaviors were reversed when the ZI V Microglia of CFA1D-treated mice were chemically inhibited by intra-ZI V minocycline injection, accompanied by the recovery of decreased ZI V GABA excitability. Conclusively, our results provide novel insights that dysregulation of microglial engulfment capacity encodes maladaptation of ZI V GABA , thus promoting the development of anxiety-like behaviors in acute pain.