Electroacupuncture reduces microglial hyperactivity and synaptic phagocytosis in the medial prefrontal cortex to treat chronic pain comorbid with anxiety and depression

The role of dysfunctional microglial phagocytosis in the comorbidity of pain and affective disorders remains unclear. This study aimed to develop a potential therapeutic strategy targeting microglial phagocytosis. We established a mouse model of chronic constriction injury of the infraorbital nerve (CION) to induce pain and anxiety- and depressive-like behaviors simultaneously. Immunohistochemical analysis showed that CION led to increased density and aberrant morphology of microglia in the medial prefrontal cortex (mPFC), upregulation of lysosome-associated membrane protein 2 (LAMP2) and MER proto-oncogene tyrosine kinase (MERTK), and significant enhancement of phagocytosis of PSD-95-positive synaptic components by microglia. However, local injection of the microglia inhibitor minocycline into the mPFC markedly alleviated pain-induced anxiety-like behaviors. As a non-pharmacological intervention, electroacupuncture (EA) reduced the severity of pain-induced anxiety- and depressive-like behaviors, decreased the density of microglia and restored their morphology in the mPFC, and normalized MERTK expression levels. These results suggest that aberrant phagocytosis of excitatory synapses by microglia in the mPFC participates in regulating pain-induced anxiety-like behaviors, likely through MERTK. Pharmacological and non-pharmacological approaches (e.g., EA) targeting microglial phagocytosis in the mPFC may represent novel therapeutic strategies for chronic pain comorbid with anxiety and depression.