Gabapentin Effects on PKC-ERK1/2 Signaling in the Spinal Cord of Rats with Formalin-Induced Visceral Inflammatory Pain

October Gabapentin Effects on PKC-ERK1/2 Signaling in the Spinal Cord of Rats with Formalin- Induced Visceral Inflammatory Pain Yan-bo Zhang 0 1 Zheng-dong Guo 0 1 Mei-yi Li 0 1 Peter Fong 0 1 Ji-guo Zhang 0 1 Can- wen Zhang 0 1 Ke-rui Gong 0 1 Ming-feng Yang 0 1 Jing-zhong Niu 0 1 Xun-ming Ji 0 1 Guo-wei Lv 0 1 0 1 Department of Neurology, Affiliated Hospital of Taishan Medical University , Taian , China , 2 Department of Endocrinology, Affiliated Hospital of Taishan Medical University , Taian , China , 3 Department of Neurology, Shandong Taishan Chronic Disease Hospital , Taian , China , 4 Department of Neurology, University of California San Francisco , San Francisco, CA , United States of America, 5 Department of Pharmacology, College of Pharmacy, Taishan Medical University , Taian , China , 6 Department of Oral and Maxillofacial Surgery, University of California San Francisco , San Francisco, CA , United States of America, 7 Hypoxia Medical Institute, Xuanwu Hospital, Capital Medical University , Beijing , China 1 Editor: Yvette Tache, University of California , Los Angeles, UNITED STATES Currently, the clinical management of visceral pain remains unsatisfactory for many patients suffering from this disease. While preliminary animal studies have suggested the effectiveness of gabapentin in successfully treating visceral pain, the mechanism underlying its analgesic effect remains unclear. Evidence from other studies has demonstrated the involvement of protein kinase C (PKC) and extracellular signal-regulated kinase1/2 (ERK1/ 2) in the pathogenesis of visceral inflammatory pain. In this study, we tested the hypothesis that gabapentin produces analgesia for visceral inflammatory pain through its inhibitory effect on the PKC-ERK1/2 signaling pathway. Intracolonic injections of formalin were performed in rats to produce colitis pain. Our results showed that visceral pain behaviors in these rats decreased after intraperitoneal injection of gabapentin. These behaviors were also reduced by intrathecal injections of the PKC inhibitor, H-7, and the ERK1/2 inhibitor, PD98059. Neuronal firing of wide dynamic range neurons in L6-S1 of the rat spinal cord dorsal horn were significantly increased after intracolonic injection of formalin. This increased firing rate was inhibited by intraperitoneal injection of gabapentin and both the individual and combined intrathecal application of H-7 and PD98059. Western blot analysis also revealed that PKC membrane translocation and ERK1/2 phosphorylation increased significantly following formalin injection, confirming the recruitment of PKC and ERK1/2 during visceral inflammatory pain. These effects were also significantly reduced by intraperitoneal injection of gabapentin. Therefore, we concluded that the analgesic effect of gabapentin on visceral inflammatory pain is mediated through suppression of PKC and ERK1/2 signaling pathways. Furthermore, we found that the PKC inhibitor, H-7, significantly diminished ERK1/2 phosphorylation levels, implicating the involvement of PKC and ERK1/2 in the same signaling pathway. Thus, our results suggest a novel mechanism of gabapentin- - Funding: This study was supported by the National Science and Technology Support Program in China (2013BAI07B01), the Natural Science Foundation of Shandong Province in China (ZR2012HQ014, ZR2011HM044), and Shandong Province Medical and Health Plan (2014WSB32015). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. mediated analgesia for visceral inflammatory pain through a PKC-ERK1/2 signaling pathway that may be a future therapeutic target for the treatment of visceral inflammatory pain. Visceral pain is characterized by inaccurate positioning, an imprecise nature of pain, and the frequent occurrence of referred pain. Approximately 10–40% of the general population suffers from visceral pain [1]. Recently, clinical examples of visceral pain, including inflammatory bowel disease and cancer-related visceral pain have become more prevalent, prompting greater interest in the mechanism and treatment of visceral pain. While the conduction of visceral pain is similar to that of somatic pain, both are categorized by different characteristics and clinical treatments. In contrast to the extensive literature of somatic pain, studies addressing the mechanism of visceral pain currently remain preliminary. Furthermore, the clinical therapeutic management of visceral pain remains less satisfactory than that of somatic pain, and studies investigating the mechanism of visceral pain with the aim of identifying new therapeutic targets have produced little success [1–5]. In 2002, the USA Food and Drug Administration approved gabapentin, a γ-aminobutyric acid derivative, for clinical use in the treatment of neuropathic pain. Since then, gabapentin has been extensively (...truncated)