Modulation of Comorbid Chronic Neuropathic Pain and Anxiety-Like Behaviors by Glutamatergic Neurons in the vlPAG and the Analgesic and Anxiolytic Effects of EA.

Abstract

Comorbid chronic neuropathic pain and anxiety is a common disease that represents a major clinical challenge. The underlying mechanisms of chronic neuropathic pain and anxiety are not entirely understood, which limits the exploration of effective treatment methods. Glutamatergic neurons in the ventrolateral periaqueductal gray (vlPAG) have been implicated in regulating pain, but the potential roles of the vlPAG in neuropathic pain-induced anxiety have not been investigated. Herein, whole-cell recording and immunofluorescence showed that the excitability of CamkIIα neurons in the vlPAG (vlPAGCamkIIα+ neurons) was decreased in mice with spared nerve injury (SNI), while electroacupuncture (EA) activated these neurons. We also showed that chemogenetic inhibition of vlPAGCamkIIα+ neurons resulted in allodynia and anxiety-like behaviors in naive mice. Furthermore, chemogenetic activation of vlPAGCamkIIα+ neurons reduced anxiety-like behaviors and allodynia in mice with SNI, and EA had a similar effect in alleviating these symptoms. Nevertheless, EA combined with chemogenetic activation failed to further relieve allodynia and anxiety-like behaviors. Artificial inhibition of vlPAGCamkIIα+ neurons abolished the analgesic and anxiolytic effects of EA. Overall, our study reveals a novel mechanism of neuropathic pain-induced anxiety and shows that EA may relieve comorbid chronic neuropathic pain and anxiety by activating vlPAGCamkIIα+ neurons.Significance Statement Neuropathic pain is clinically accompanied by anxiety. Both glutamatergic neurons in the ventrolateral periaqueductal gray (vlPAG) and electroacupuncture (EA) have demonstrated analgesic properties. However, the efficacy of these interventions in addressing neuropathic pain and its concomitant anxiety has yet to be fully elucidated. In a mice model of spared nerve injury (SNI), we observed a decreased excitability of vlPAG CamkIIα neurons. Remarkably, EA treatment significantly enhanced the excitability of these neurons. Further, chemogenetic activation of vlPAGCamkIIα+ neurons not only resulted in analgesia but also mitigated anxiety-like behaviors in SNI mice, mirroring the effects observed with EA treatment. Conversely, inhibition of vlPAGCamkIIα+ neurons activity in naive mice reduced pain thresholds and induced anxiety-like behavior, while also negating the beneficial effects of EA. These findings provide novel insights into the mechanistic interplay between chronic neuropathic pain and anxiety, highlighting the therapeutic potential of targeting vlPAG glutamatergic neurons in these conditions.