Reactive Microglia-Mediated Synaptic Engulfment in the Basolateral Amygdala may Contribute to Preoperative Anxiety-Induced Postoperative Hyperalgesia.

Preoperative anxiety is closely associated with postoperative hyperalgesia, but the underlying neural mechanisms remain incompletely understood. The basolateral amygdala (BLA) is a key hub for processing negative emotions and pain. Emerging evidence indicates that microglial activation and synaptic engulfment contribute to the pathogenesis of neuropsychiatric and pain-related disorders. However, the role of BLA microglial activation-driven synaptic engulfment in preoperative anxiety-induced postoperative hyperalgesia remains unelucidated. A mouse model of preoperative anxiety-induced postoperative hyperalgesia was established by combining single prolonged stress (SPS) with plantar incision (I) surgery, designated as the SI model. Minocycline, a microglial inhibitor, was administered to investigate the role of microglial activation. The open field test (OFT) and elevated plus maze test (EPMT) were used to assess anxiety-like behaviors. Mechanical allodynia and thermal hyperalgesia tests were conducted to measure pain-related behaviors. Immunofluorescence (IF) staining for ionized calcium-binding adapter molecule 1 (IBA1), IBA1 + cluster of differentiation 68 (CD68), and IBA1 + synaptophysin (SYN) was performed to examine microglial reactivity, phagocytic activation, and synaptic engulfment in the BLA. Golgi staining was employed to quantify dendritic spine density of BLA neurons. Western blotting (WB) was employed to measure the expression levels of synaptic proteins, including postsynaptic density protein 95 (PSD95), SYN, and synapsin 1 (SYN1), in the BLA. SPS induced anxiety-like behaviors and exacerbated postoperative hyperalgesia in mice. Meanwhile, SI model mice exhibited increased microglial activation, phagocytic activity and synaptic engulfment in the BLA, accompanied by decreased dendritic spine density and reduced expression of synaptic proteins. Furthermore, minocycline treatment suppressed microglial activation and phagocytic activity, attenuated excessive synaptic engulfment, reversed the reductions in dendritic spine density and synaptic protein expression in the BLA, and ultimately alleviated both anxiety-like behaviors and postoperative hyperalgesia in SI mice. Our findings indicate that excessive microglial activation-mediated synaptic engulfment in the BLA is closely associated with preoperative anxiety-induced postoperative hyperalgesia. Targeting BLA microglial activation and associated synaptic engulfment may hold potential as a novel therapeutic strategy for mitigating preoperative anxiety-related postoperative hyperalgesia.