RSEP1 is a novel gene with functional involvement in neuropathic pain behaviour Xidao Wang, 1,2, * Yuqiu Zhang, 3,4, * Lingwei Kong, 1 Zhiqin Xie, 1 Zhixin Lin, 2 Ning Guo, 4 Judith A. Strong, 4 Johanna T. A. Meij, 4 Zhiqi Zhao, 3 Naihe Jing 1 and Lei Yu 4 1 Laboratory of Molecular Cell Biology, Laboratory of Stem Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China 2 School of Life Science and Biotechnology, Shanghai Jiao Tong University, 1954 Hua-Shan Road, Shanghai 200030, China 3 Institute of Neurobiology, Fudan University, 220 Han-Dan Road, Shanghai 200433, China 4 Department of Cell Biology, Neurobiology & Anatomy, University of Cincinnati College of Medicine, 3125 Eden Avenue, Cincinnati, OH 45267–0521, USA Keywords: allodynia, chronic constriction injury of the sciatic nerve, hyperalgesia, neuropathic pain, rat, spinal cord Abstract Neuropathic pain from nerve injury by trauma, disease or surgery often causes prolonged suffering. To explore the molecular mechanisms that underlie neuropathic pain, we used mRNA from the L4–5 segments of the lumbar spinal cord of rats with chronic constriction injury (CCI)-induced neuropathic pain, and differentially screened a cDNA library from the rat brain. A novel gene, termed RSEP1 (Rat Spinal cord Expression Protein 1), was identified. Northern blots revealed that RSEP1 was expressed mainly in the central nervous system including the cerebral cortex, hippocampus, brainstem and spinal cord, as well as in the kidney and ovary. In situ hybridization showed a high level of RSEP1 expression in the CA1, CA3 and dentate gyrus regions of the hippocampus and the small sensory neurons in the dorsal horn, as well as the large neurons in the ventral horn of the spinal cord. Intrathecal injection of RSEP1 antisense oligonucleotide into the spinal cord lumbar enlargement attenuated neuropathic pain behaviours in CCI rats, suggesting a functional involvement of RSEP1 in neuropathic pain. Introduction Neuropathic pain is a chronic painful condition that can result from nerve injury caused by trauma, disease or surgery accidents. Effective treatment for this debilitating condition is still lacking (Merskey & Bogduk, 1994). Symptoms include spontaneous burning or stabbing pain, exaggerated responses to light touch (tactile allodynia) and painful stimuli (hyperalgesia). Most evidence indicates that the spinal and supraspinal structures are involved in processing neuropathic pain (Iadarola et al., 1998; Peyron et al., 1998), and many genes are involved in the process of neuropathic pain formation (Malmberg et al., 1997; Boucher et al., 2000). In addition, studies have shown that aspects of neuropathic pain involve certain neuromodulators of pain processing such as tachykinins (Zieglgansberger et al., 2005) and endogenous opioid peptides (Jones et al., 2004). However, the molecular mechanisms underlying the neuropathic pain are still poorly understood. In this study, we undertook a differential screening strategy to explore novel genes that may be involved in neuropathic pain. The chronic constriction injury (CCI) model is one of the most commonly used to study the mechanisms of the neuropathic pain (Bennett & Xie, 1988). We used mRNAs from the spinal cords of CCI rats to differentially screen a cDNA library from the rat brain. We identified a novel gene, RSEP1 (Rat Spinal cord Expression Protein 1), that appeared to have a cause–effect relationship with the neuropathic pain behaviours. Materials and methods Experimental animals Adult male Sprague–Dawley rats (from either Shanghai Laboratory Animal Centre, Shanghai, China, or Harlem Laboratory Animals, Indianapolis, IN, USA; 200–280 g) were housed one or two per cage with free access to water and standard rat chow, with a 12 : 12 h day : night cycle and at a constant room temperature of 21 °C. All experimental protocols and animal handling procedures were consis- tent with the National Institutes of Health Guide for the Care and Use of Laboratory Animals, as well as the PRC national standards for laboratory animal quality and the Chinese guidelines for care and use of laboratory animals. All efforts were made to minimize the number of animals used. CCI model A peripheral mononeuropathy was produced by loosely ligating the sciatic nerve (a CCI) according to a method described previously (Bennett & Xie, 1988). Briefly, under pentobarbital sodium anaes- thesia (40 mg ⁄ kg, i.p.), the sciatic nerves were exposed bilaterally at mid-thigh level by blunt dissection through the biceps femoris muscle. Correspondence: Dr Z. Zhao, Dr N. Jing and Dr L. Yu, all as above. E-mail: zqzhao@fudan.edu.cn, njing@sibs.ac.cn and lei.yu@uc.edu *X. W. and Y. Z. contributed equally to this work. Received 28 March 2005, revised 1 June 2005, accepted 1 June 2005 European Journal of Neuroscience, Vol. 22, pp. 1090–1096, 2005 ª Federation of European Neuroscience Societies doi:10.1111/j.1460-9568.2005.04282.x