Electroacupuncture alleviates mechanical allodynia and anxiety-like behaviors induced by chronic neuropathic pain via regulating rostral anterior cingulate cortex-dorsal raphe nucleus neural circuit

Abstract

Aims: Epidemiological studies in patients with neuropathic pain have demonstrated a strong association between neuropathic pain and psychiatric conditions such as anxiety. Preclinical and clinical work has demonstrated that electroacupuncture (EA) effectively alleviates anxiety-like behaviors induced by chronic neuropathic pain. In this study, a potential neural circuitry underlying the therapeutic action of EA was investigated.

Methods: The effects of EA stimulation on mechanical allodynia and anxiety-like behaviors in animal models of spared nerve injury (SNI) were examined. EA plus chemogenetic manipulation of glutamatergic (Glu) neurons projecting from the rostral anterior cingulate cortex (rACC^Glu ) to the dorsal raphe nucleus (DRN) was used to explore the changes of mechanical allodynia and anxiety-like behaviors in SNI mice.

Results: Electroacupuncture significantly alleviated both mechanical allodynia and anxiety-like behaviors with increased activities of glutamatergic neurons in the rACC and serotoninergic neurons in the DRN. Chemogenetic activation of the rACC^Glu -DRN projections attenuated both mechanical allodynia and anxiety-like behaviors in mice at day 14 after SNI. Chemogenetic inhibition of the rACC^Glu -DRN pathway did not induce mechanical allodynia and anxiety-like behaviors under physiological conditions, but inhibiting this pathway produced anxiety-like behaviors in mice at day 7 after SNI; this effect was reversed by EA. EA plus activation of the rACC^Glu -DRN circuit did not produce a synergistic effect on mechanical allodynia and anxiety-like behaviors. The analgesic and anxiolytic effects of EA could be blocked by inhibiting the rACC^Glu -DRN pathway.

Conclusions: The role of rACC^Glu -DRN circuit may be different during the progression of chronic neuropathic pain and these changes may be related to the serotoninergic neurons in the DRN. These findings describe a novel rACC^Glu -DRN pathway through which EA exerts analgesic and anxiolytic effects in SNI mice exhibiting anxiety-like behaviors.

Keywords: anxiety-like behaviors; chronic neuropathic pain; dorsal raphe nucleus; electroacupuncture; neural circuit; rostral anterior cingulate cortex.