Cyclooxygenase-2 Expression In Traumatic Rat Spinal Cord And The Effect Of Methylprednisolone

Backgrounds: Research and medical treatment efforts devoted to the therapy of acute spinal cord injury have contributed to significant reduction of the mortality from spinal cord injury. But, the prognosis for neurologic recovery after spinal cord injury remains bleak. There is presently no cure for spinal cord injury. Approaches to treatment can be broadly categorized into two main groups, namely neuroprotection and neurorepair. Both approaches rely on the further understanding of the pathophysiological mechanisms underlying acute spinal cord injury. There are a number of evidence that prostaglandins (PGs) play a driving role in central nerve system injuries. PGs are involved in most of secondary pathways of acute traumatic spinal cord, especially membrane lipid peroxidation, release of excitatory amino acid, inflammatory response, etc. The pharmacological mechanisms of methylprednisolone(MP) on spinal cord injury are ameliorate progression of these secondary pathways. MP also lowers PGs concentrations in spinal cord after acute injury. Cyclooxygenase(COX) is the obligate, rate-limiting enzyme for the conversion of arachidonic acid into PGs. So, COX must be an important mediator in secondary pathways and inhibition of COX expression and activity must be one of mechanisms which contribute to the curative effect of MP on acute spinal cord injury.Objects: We sought to characterize the localization and regulation of COX in thoracic spinal cord before and after acute contusion and the effect of MP.Methods: One hundred and ninety-two Sprague Dawley rats, 250~300g of weight, were used for the study. Rats spinal cord injury were induced at T8~9 level by dropping a 10.24g weight form a height of 50mm(Allen's model). All spinal cord injury or drug pretreatment animals were sacrificed at time points ranging from 2 to 48 hours(2,4, 8,16, 24, and 48 hours) after management. COX-1 and COX-2 expression in normal and injuried thoracic spinal cord were studied with immunohistochemistry and in situ hybridization. The production of COX-2 mRNA and protein in thoracic spinal cord before and after injury were studied with reverse transcriptase polymerase chain reaction(RT-PCR) and Western blotting. The effect of MP, which is administrated 30 minutes before and after spinal cord injury, on the localization and production of COX-2 in the injuried thoracic spinal cord were evaluated by the four methods. The effect of MP on the COX-2 expression in normal spinal cord was studied too.Results:1. COX-1 immunoreactivity was found to constitutively express in cytoplasm of glial cells and neuropils in white matter. There are tiny COX-1 immunoreactivity was found in glial cells, neuropils and neurons in the gray, not only ventral horn, but also dorsal. It was found that COX-2 immunolabeling expressed constitutively in cytoplasm and closely surrounding the nucleus of neurons in both ventral and dorsal horn. Results of RT-PCR and Western blotting also show that COX-2 mRNA and protein constitutively expressed in normal thoracic spinal cord.2. Contusion to the spinal cord did not result in changes of COX-1 mRNA and protein localization and expression evaluated by immunohistochemistry and in situ hybridization. COX-2 mRNA expression was detected in neurons after 2 hours following impaction, and COX-2 immunoreactivity which improved only in neurons after 4 hours following impaction. The positive COX-2 mRNA and protein reactivity all reach the most after 24 hours after contusion.3. COX-2 mRNA level increased after 2 hours following impaction and reached the highest concentration at 24 hours, then reduced to the baseline at 48 hours. COX-2 protein level increased 4 hours after contusion, reached the highest at 24 hours and remained debated for 48 hours.4. MP administrated pre- and post-injury could reduce the production level of COX-2 mRNA and protein in thoracic spinal cord, and postponed the point of level pinnacle occurred. The effect of MP pretreatment was significantly stronger than administrated postinjury. MP administration could al...