Peripheral BDNF Regulates Somatosensory–Sympathetic Coupling in Brachial Plexus Avulsion-Induced Neuropathic Pain
Hang Xian1 · Huan Guo2,4 · Yuan‑Ying Liu3,4 · Jian‑Lei Zhang1 · Wen‑Chao Hu4,5 · Ming‑Jun Yu6 · Rui Zhao1 · Rou‑Gang Xie4 · Hang Zhang1 · Rui Cong1 1 Department of Orthopedics, Xijing Hospital, The Air Force Medical University, Xi’an 710032, China
2 Pain and Related Diseases Research Laboratory, Medical College of Shantou University, Shantou 515041, China
3 School of Life Science and Research Center for Resource Peptide Drugs, Shaanxi Engineering and Technological Research Center for Conversation and Utilization of Regional Biological Resources, Yanan University, Yanan 716000, China
4 Department of Neurobiology, School of Basic Medicine, The Air Force Medical University, Xi’an 710032, China
5 The Sixth Regiment, School of Basic Medicine, The Air Force Medical University, Xi’an 710032, China
6 The Tenth Squadron of the Third Regiment, School of Basic Medicine, The Air Force Medical University, Xi’an 710032, China
Abstract
Brachial plexus avulsion (BPA) is a combined injury involving the central and peripheral nervous systems. Patients with BPA often experience severe neuropathic pain (NP) in the affected limb. NP is insensitive to the existing treatments, which makes it a challenge to researchers and clinicians. Accumulated evidence shows that a BPA-induced pain state is often accompanied by sympathetic nervous dysfunction, which suggests that the excitation state of the sympathetic nervous system is correlated with the existence of NP. However, the mechanism of how somatosensory neural crosstalk with the sympathetic nerve at the peripheral level remains unclear. In this study, through using a novel BPA C7 root avulsion mouse model, we found that the expression of BDNF and its receptor TrκB in the DRGs of the BPA mice increased, and the markers of sympathetic nervous system activity including α1 and α2 adrenergic receptors (α1-AR and α2-AR) also increased after BPA. The phenomenon of superexcitation of the sympathetic nervous system, including hypothermia and edema of the affected extremity, was also observed in BPA mice by using CatWalk gait analysis, an infrared thermometer, and an edema evaluation. Genetic knockdown of BDNF in DRGs not only reversed the mechanical allodynia but also alleviated the hypothermia and edema of the affected extremity in BPA mice. Further, intraperitoneal injection of adrenergic receptor inhibitors decreased neuronal excitability in patch clamp recording and reversed the mechanical allodynia of BPA mice. In another branch experiment, we also found the elevated expression of BDNF, TrκB, TH, α1-AR, and α2-AR in DRG tissues from BPA patients compared with normal human DRGs through western blot and immunohistochemistry. Our results revealed that peripheral BDNF is a key molecule in the regulation of somatosensory-sympathetic coupling in BPA-induced NP. This study also opens a novel analgesic target (BDNF) in the treatment of this pain with fewer complications, which has great potential for clinical transformation.
Keywords
Brachial plexus avulsion; Neuropathic pain; Sympathetic nervous system; Brain-derived neurotrophic factor; Peripheral sensitization; Mechanical allodynia
