| PrefaceTraumatic injury to the spinal cord results in tissue necrosis and loss of function, and some axons are directly damaged by the physical deformation of the spinal cord (primary injury). However, it is likely that a large number of axons are lost due to a cascade of pathochemical and/or pathophysiological events (secondary injury) that are initiated by the original insult. It is this secondary injury that would appear to be susceptible to pharmacological intervention. To explain this delayed tissue damage, numerous pathophysiological mechanisms have been postulated. It has been suggested that one of the most important factors precipitating posttraumatic degeneration in the spinal cord is oxygen free radical-induces lipid peroxidation.Methylprednisolone has been used extensively as a pharmacological tool in the treatment of experimental traumatic Spinal Cord Injury( SCI). In clinical trials , methylprednisolone has been shown to be an effective agent for the treatment of acute SCI. Numerous investigators have postulated that the neuroprotctive mechanism of action of steroids is the inhibition of lipid peroxidation rather than glucocorticoid receptor activation. When administered in large doses, methylprednisolone has been shown to be a powerful antioxidant.The pinel hormone melatonin is also a very potent free radical scavenger that has likewise been shown to enter the cell and nucleus. However, methylprednisolone possesses its neuroprotective effect by a direct membrane action. In previous studies, melatonin has been shown to potect against nucleic acid damage via an action involving generation of oxygen-based free radicals produced by the administration of chemical carcinogen safrole and ionizing radiation. Althoughmany studies have been published in which the effectiveness of methylpred-nisolone has been proven, such a therapeutic benefit for melatonin in SCI has not been previously demonstrated. In the present study, we examined the possible potential protective effect of melatonin in experimental acute SCI. We compared the effects of melatonin with methylprednisolone, which has been suggested to protect the spinal cord from secondary injury from traumatized spinal cord tissue.Materials and Methods72 Male Wistar rats weighing 230 to 280 g were used for the study. The rats, housed one in a cage,were given free access to food and water. The rats were pinned in the prone position. Following T5 -12 midline skin incision, spi-nous processes and laminar arcs of T8 — 10 were removed with the assistance of a surgical microscope after paravertebral muscle dissection. Trauma was produced by the method described by Allen in 1911. The animals were subjected to 50 -g/cm impact to the dorsal surface of the spinal cord, rendering them severly wounded and paraplegic. The force was applied via a stainless steel rod that was rounded at the surface, which made contact with the spinal cord after being dropped vertically through a calibrated tube. The injury apparatus was a 10 - cm guide tube that was positioned perpendicular to the center of the spinal cord.The rats were randomly allocated into four groups: trauma group of 18 rats in which, following surgical and traumatic interventions, 1 - cm injured spinal cord samples were removed at 2,24,72 hours posttrauma; melatonin group of 18 rats in which a 100 - mg/kg single dose of melatonin was given intraperitoneally 10 minutes after trauma, and 1 - cm samples of injured spinal cord were removed at 2,24,72 hours posttrauma; methylprednisolone group of 18 animals in which a 30 - mg/kg single dose of methylprednisolone was administered intraperitoneally 10 minutes after trauma,and 1 -cm samples of injured spinal cord were removed at 2,24,72 hours posttrauma; vehicle-treated group of 18 animals in which a same single dose of vehicle was administered intraperitoneally 10 minutes after trauma,and 1 - cm samples of injured spinal cord were removed at 2,24,72 hours posttrauma.Samples obtained from all groups were used for further study, such as the immunohistochemistry of Glial Fibrillary Acid Protein ( GFAP). Statistical significance between experiment groups was defined by using SPSS analysis.ResultsThe difference between melatonin-treated group and trauma group was statistically significant (P =0.019,0.004 and 0.009 for samples obtained at 2,24 and 72 hours postinjury, respectively ). The difference between methylpred-nisolone-treated group and trauma group was statistically significant ( P =0.016, 0.016 and 0.004 for samples obtained at 2,24 and 72 hours postinjury,respectively). But the difference between melatonin-treated group and methylpred-nisolone-treated group was not statistically significant ( P =0.927, 0.520 and 0. 712 for samples obtained at 2,24 and 72 hours postinjury, respectively). The difference between vehicle-treated group and trauma group was not statistically significant (P =0. 889,0. 828 and 0. 711 for samples obtained at 2,24 and 72 hours postinjury, respectively ).DiscussionTraumatic injury to the spinal cord results in tissue necrosis and loss of function, include primary injury and secondary injury. It is this secondary injury that would appear to be susceptible to pharmacological intervention, such as the expression of GFAP.Methylprednisolone has been used extensively as a pharmacological tool in the treatment of experimental traumatic SCI. In clinical trials, methylprednisolone has been shown to be an effective agent for the treatment of acute SCI. Numerous investigators have postulated that the neuroprotective mechanism of action of steroids is the inhibition of lipid peroxidation rather than glucocorticoid receptor activation. When administered in large doses, methylprednisolone has been shown to be a powerful antioxidant.Melatonin, N-acetil-5-methoxytriptamine, is a hormonal product of pineal gland. Until recently it was generally thought that melatonin' s action in the oranism depended on its exclusive interaction with specific receptors on cells. Certainly, the interactions of melatonin with these membrane-bound receptors are believed to mediate the endocrinological function and the circadian rhythm of melatonin. It has been recently discovered that melatonin is a very potent free radical scavenger as well as an electron donor. Thus,potentially,the indolamine not only protects biomolecules from free radical damage, but it may also repair e-lectron-deficient biomolectiles by donating an electron to them. Melatonin' s efficacy as a free radical scavenger has been compared with mannitol and glutathi-one, the most effective exogenous and endogenous hydroxyl radical ( OH) scavenger. The free radical quenching activity of melatonin does not require a receptor,and it enters all cells and passes all morphophysiological barriers. It is nontoxic, it is both lipophylic and hydrophilic, is rapidly absorbed, easy to produce , and it is inexpensive. Melatonin' s extreme diffusability is important for its scavenging action because this feature allows it to enter all cells and every sub-celluar compartent. It has also been shown that it may be bound in the nucleus, thereby providing on-side protection to DNA.Because of its antioxidant effect, methylprednisolone has been shown to be very effective in protecting the spinal cord from secondary injury and, when administered to animals or humans in antioxidant doses, improves chronic neurological recovery after SCI. This activity of methylprednisolone is independent of the steroid' s glucocorticoid receptor mediated activity. Unlike melatonin, it is known that the neuroprotective effect of methylprednisolone is by a direct membrane action.Interperitoneal administration of melatonin and methylprednisolone was shown to decrease remarkably levels of lipid peroxide at all time periods. Al-thought melatonin was shown to decrease lipid peroxidation in the 2nd hour more than methylprednisolone, this difference was not statistically significant. This difference between trauma group and vehicle-treated group was not statistically significant. |
