Chronic Inflammatory Pain Impairs mGluR5-Mediated Depolarization-Induced Suppression of Excitation in the Anterior Cingulate Cortex.

The anterior cingulate cortex (ACC) is a critical hub for nociceptive perception and pain-related anxiety. Long-term synaptic plasticity in ACC was found to be important for chronic inflammatory pain and pain-related anxiety. As short-term synaptic plasticity, depolarization-induced suppression of excitation (DSE) is involved in several conditions, such as chronic stress, epilepsy, and autism. However, it is still unknown whether DSE in the ACC is involved in the central sensitization of pain and anxiety. Using a whole-cell patch clamp, calcium imaging, western blot, and behavioral testing, we found that DSE was induced by a 2 s depolarization in postsynaptic pyramidal cells in ACC. DSE was mediated by endocannabinoid signaling and modulated by metabotropic glutamate receptor 5 (mGluR5). DSE was impaired by decreasing expression and dysfunction of mGluR5 in a mouse model of inflammatory pain induced by complete Freund's adjuvant. CDPPB, an mGluR5-positive allosteric modulator, could rescue hypersensitivity and anxiety-like behavior in this pain model. Our results demonstrated that mGluR5-mediated short-term plasticity in ACC may be a critical mechanism for chronic pain, and mGluR5 may potentially serve as a target of pain therapy, including treatments for hyperalgesia and anxiety.