Original Article Spinal Cord Transcriptomic and Metabolomic Analysis after Excitotoxic Injection Injury Model of Syringomyelia Ashley E. Mohrman, 1 Mahmoud Farrag, 2 He Huang, 3 Stephan Ossowski, 4 Stephanie Haft, 5 Leah P. Shriver, 3 and Nic D. Leipzig 1 Abstract Syringomyelia is a condition of the spinal cord in which a syrinx, or fluid-filled cavity, forms from trauma, malformation, or general disorder. Previous work has shown that in noncanalicular syringomyelia irregular flow and pressure conditions enhance the volumetric growth of syrinxes. A better understanding of the underlying molecular pathways associated with syrinx formation will unveil targets for treatments and possibly prevention of syringomyelia in the future. In this study, we performed an established surgical induction of a syrinx using quisqualic acid and kaolin injections in rats to characterize the injury at the molecular level by RNA sequencing and metabolomics techniques at three and six weeks post-injury. Syrinxes averaging nearly 10mm in length formed in the rats’ spinal cords; however, smaller syrinxes were also detected in saline injected surgical shams, complicating interpretation of results. Our current results indicate a robust immune response coupled with overall decreases in neuronal signal transmission of syrinx containing animals compared with controls. Although transcriptional changes indicated gliosis and loss of neurons, no neuropathic pain was detected by von Frey allodynia testing. Unique transporters were revealed to be highly dysregulated, including significant increases in betaine/glycine transporter (BGT-1), K+/Cl- co-transporter (KCC4), and aquaporin 1 (AQP1), along with the upregulation of small molecule osmolytes taurine and betaine. The identified metabolites are of particular interest because of their involvement in osmotic homeostasis and need to be investigated further for their specific involvement in trauma-induced syrinxes. Keywords: metabolomics; molecular transporters; spinal cord injury; syringomyelia; transcriptomics Introduction S yringomyelia results from the formation of a fluid-filled syrinx in the spinal cord and can be associated with several central nervous system (CNS) disorders including Chiari type I malformation, hydrocephalus, trauma, cancer, or spinal cord infec- tion. 1–4 The occurrence of syringomyelia changes across different ethnicities, and its detection rate is increasing because of the higher prevalence of magnetic resonance imaging (MRI), improvements in diagnostic imaging, or both. 5 Syrinxes are dynamic and sometimes asymptomatic, but large syrinxes often cause significant damage to the spinal cord, are often difficult to manage, and are debilitating to patients who experience pain, numbness, stiffness, or weakening of the limbs. 6 Reviews on syringomyelia, symptoms, and treatment options offer more in depth discussion. 1 Currently, syringomyelia is addressed mainly by managing the associated condition to halt formation or progression of a spinal cord cyst. 3 Treating those with Chiari or arachnoiditis often in- volves decompression of the skull or spine with or without expansive duraplasty, essentially creating space in which the cerebrospinal fluid (CSF) can flow properly. Idiopathic syringomyelia is addressed most commonly by managing symptoms or, in the worst cases, by shunting the syrinx. Recently, leading researchers in the field have highlighted the need for basic research and mechanistic insights into syringomyelia to improve both identification and treatments. 7 A clear grasp of the mechanisms responsible for syrinx initiation remains particularly elusive, even as the knowledge of hydrodynamic factors responsible for enlarging syrinxes has grown. Excitotoxic injury (EXC) is part of the initiation process in post-traumatic sy- ringomyelia and involves energy depletion and subsequent de- struction of neurons. 8 Studies have shown the importance of subarachnoid blockage in significantly expanding syrinx size and increasing damage to the syrinx parenchyma compared with syrinx size without arachnoiditis. 9–11 Preventing the formation of a syrinx within the spinal cord is paramount; however, many patients are asymptomatic with revers- ible pathology until the syrinx is of considerable size, so under- standing how to halt syrinx enlargement is also important. Additional Departments of 1 Chemical and Biomolecular Engineering, 2 Integrated Biosciences Program, 3 Chemistry, University of Akron, Akron, Ohio. 4 Centre for Genomic Regulation, The Barcelona Institute of Science and Technology, Barcelona, Spain. 5 Langley Porter Psychiatric Institute, University of California San Francisco, San Francisco, California. JOURNAL OF NEUROTRAUMA 33:1–14 (XXXX 00, 2016) ª Mary Ann Liebert, Inc. DOI: 10.1089/neu.2015.4341 1