[Electroacupuncture alleviates neuropathic pain hyperalgesia and anxiety-like behaviors via the dorsal raphe nucleus-basolateral amygdala circuit].

Objectives: This study aims to investigate the intervention effects of electroacupuncture on neuropathic pain and anxiety-like behavior, and to explore the underlying mechanisms of the DRN^5-HT-BLA (dorsal raphe nucleus serotoninergic - basolateral amygdala) neural circuit.

Methods: Male C57BL/6J mice were selected, and a neuropathic pain model was established through spared nerve injury (SNI) surgery. Electroacupuncture (100 Hz, 0.3 mA, 30 min) was applied to bilateral "Zusanli" (ST36) and "Sanyinjiao"(SP6). Anxiety-like behavior was assessed using the elevated plus maze (EPM) and open field (OF) tests, while mechanical allodynia was evaluated using the Von-Frey test. Viral tracing was used to confirm the anatomical connection between DRN^5-HT and BLA. Immunofluorescence was used to assess the activity of 5-HT neurons in the DRN. Chemogenetic and calcium imaging techniques were employed to observe changes in the activity of 5-HT neurons in the DRN of DRN^5-HT-BLA. Chemogenetics were used to observe the effect of inhibiting DRN^5-HT-BLA on electroacupuncture.

Results: SNI model mice showed a significant decrease in mechanical pain threshold (P<0.000 1) and exhibited marked anxiety-like behavior in both the EPM and OF tests (P<0.01, P<0.05). Compared to the model group, electroacupuncture significantly increased the mechanical pain threshold in the electroacupuncture group (P<0.000 1). The EPM and OF results indicated that electroacupuncture significantly reduced anxiety-like behavior (P<0.05, P<0.001) without affecting spontaneous activity. Virus tracing results confirmed the anatomical connection between 5-HT neurons in the DRN and the BLA. Immunofluorescence results showed that the activity of 5-HT neurons in the DRN was significantly reduced (P<0.000 1) in SNI model mice, which was significantly reversed by electroacupuncture (P<0.01). Calcium imaging revealed that in SNI model mice, the excitability of 5-HT neurons in the DRN^5-HT-BLA circuit was decreased, and electroacupuncture treatment restored their excitability. After chemogenetic inhibition of the DRN^5-HT-BLA circuit, electroacupuncture failed to improve mechanical allodynia and anxiety-like behavior in the SNI model mice (P<0.05, P<0.001, P<0.01).

Conclusions: 5-HT neurons in the DRN^5-HT-BLA circuit play a crucial role in the mechanical allodynia and associated anxiety-like behavior in neuropathic pain. Electroacupuncture activates this circuit, enhancing the activity of 5-HT neurons in the DRN, thereby alleviating mechanical allodynia and anxiety-like behavior in SNI model mice.