Persistent Activity of Metabotropic Glutamate Receptor 5 in the Periaqueductal Gray Constrains Emergence of Chronic Neuropathic Pain

• DOI: 10.1016/j.cub.2020.09.008
• Publication Date: 2020-09-24T14:34:48Z
• Authors: Geehoon Chung; Hyun Geun Shim; Chae Young Kim; Hyun-Hee Ryu; Dong Cheol Jang; Seung Ha Kim; Jaegeon Lee; Chang-Eop Kim; Yu Kyeong Kim; Yong-Seok Lee; Jun Kim; Sun Kwang Kim; Paul F. Worley; Sang Jeong Kim
• Keywords: Male; 0303 health sciences; Receptor, Metabotropic Glutamate 5; Pain Perception; Rats; Disease Models, Animal; 03 medical and health sciences; Homer Scaffolding Proteins; Hyperalgesia; Gene Knockdown Techniques; Animals; Humans; Neuralgia; Periaqueductal Gray; Chronic Pain

Pain sensation is powerfully modulated by signal processing in the brain, and pain becomes chronic with the dysfunction of the pain modulatory system; however, the underlying mechanisms are unclear. We found that the metabotropic glutamate receptor 5 (mGluR5) in the periaqueductal gray (PAG), the key area of endogenous pain modulation, is persistently active in normal conditions to maintain an appropriate sensory perception. In the neuropathic pain condition, Homer1a, an activity-dependent immediate early gene product, disrupted the persistent mGluR5 activity resulting in chronic pain. Remarkably a single-time blockage of the mGluR5 resulted in chronic neuropathic pain-like symptoms even in the absence of nerve injury. The decline of mGluR5 activity induced the pain modulatory dysfunction with a profound reduction of excitability of PAG neurons. These findings uncover the role of the persistent mGluR5 activity in vivo and provide new insight into how pain becomes chronic with the maladaptive coping of the PAG to pain sensation.