Complement activation in the peripheral nervous system following the spinal nerve ligation model of neuropathic pain

Neuroinflammatory and neuroimmune mechanisms, as exemplified by infiltrating immune cells and activation of resident endothelial/glial cells, respectively, are known to be involved in the establishment and maintenance of chronic pain. An immune system pathway that may be involved in the activation of both immune and glial cells is complement. The complement pathway is made up of a large number of distinct plasma proteins which react with one another to opsonize pathogens and induce a series of inflammatory responses to help fight infection. Cleaved products and complexes produced by complement activation are responsible for a range of effects including mediation of immune infiltration, activation of phagocytes, opsonization/lysis of pathogens and injured cells, and production of vasoactive amines such as histamine and serotonin. Gene-expression microarray-analysis was performed on the rat spinal nerve ligation (SNL) model of neuropathic pain Keywords: organ type comparison, disease state analysis and drug treatment For gene expression analysis, rats from five experimental groups were sacrificed 19–21 days after surgery: (1)Naïve+ vehicle; (2) Naïve + GPN; (3) sham + vehicle; (4) SNL + vehicle; (5) SNL + GPN. Tissue was collected from whole brain, hemisected spinal cord, mid thigh sciatic nerve, and L4, L5 and L6 dorsal root ganglia (DRG), both ipsilateral(ipsi) and contralateral (contra) to the injury. In addition,‘‘organ recital’’ tissues were harvested from naı ¨ve animals: adrenal,aorta, fetal brain, kidney, liver, quadriceps muscle, spleen,submaxillary gland, and testis and 15 other tissues.For each experimental group and tissue, samples rapidly frozen on dry ice were separated into two pools(Pool 1 and Pool 2), consisting of half or 4-6 animals each.Pool 1 total RNA was subjected to standard methods on Affymetrix GeneChip Arrays using rat U34 A, B, and C.