Experimental Study On Protective Effects Of Magnesium Sulfate On Secondary Spinal Cord Injury

Objective: Through studying the changes of the contentsH2O,Ca²⁺,Mg²⁺ in spinal cord tissues after SCI, observingthe changes of histopathology and apoptosis, to investigatethe possible mechanism on protective effects of magnesiumsulfate on the injured spinal cord in rabbits so as to seek anew way to alleviate the secondary spinal cord injury.Methods: Thirty six Newzealand white rabbits wererandomly assigned to three groups: Sham(Group A n=12);Spinal cord injury (SCI) (Group B n=12); SCI withmagnesium sulfate treatment group (Group C n=12).Therabbits were injected 3% nembutal(1ml/kg)intraperitoneally.Secondly, cut L1-3 spinous process and neural scute to exposedura. Group A is laminectomy-only and no trauma. The SCIanimals were made by using an improved Allen'sweight-drop device. 270g-cm contusion injury wasintroduced to Group B and Group C. After thirty minutes theanimals of group B were injected 600mg/kg physiologicSaline through intraperitoneum and group C were injected600mg/kg magnesium sulfate. Ten rabbits were choosed tokill from every group randomly after 48 hours. Spinal cordsamples were obtained from original wound center. Everysample is 0.8cm.The samples were divided two parts fromcenter. One half was placed in 10% formalin. After 24 hoursthey were taken out to make the dyeing of HE and observedthe histopathology through light microscope. Another halfwere used to examined the contents of H2O,Mg²⁺,Ca²⁺.Onehistopathologic slice of every rabbit was choosen radomly tomake the dyeing of TUNEL (TdT mediated dUTP-biotin nickend labeling). The apoptosis cells are russet. The positive cellswere quantitated by a computer image analysis system. Thetwo-remainder rabbits of every group were perfused andtaken the spinal cord samples to make TEM slices. The sliceswere observed and taken photos through H-7500 TEM. Alldata were express as means±SD. The result was analyzedthrough SAS6.12 software. Analysis of variance(ANOVA)and q-test were used for the contents of H2O,Ca²⁺,Mg²⁺. Thet-test of two samples was used for apoptosis cells statisticalevaluation. Statistical significance for the test was set atp<0.01.Result: The H2O and Ca²⁺ contents of injured spinalcord tissues in each SCI group were significantly increasedcompared to the Sham (P<0.01), but group C was less thangroup B (P<0.05). The Mg²⁺ contents were significantlydecreased (P<0.01) in the injured spinal cord tissues than thebaseline level. Light and electronic microscope observationshowed that the damage of structure in group C was lessserious than group B. Through light microscope we can seethe boundary of white and gray matter were dim, there werelamellar hemorrhage,edema and zone of necrosis,theneurons in gray matter decreased, many Nissl's bodies andnucleus vanished, the white matter presenteddictyo-demyelination in group B and group C. But thedamage in group C is much better than group B. The numberof apoptosis cell in group B was more than group C(P<0.01).Through TEM we can see the nucleus were fragmentary,nuclear membrane were blur and disfiguration, nucleolusvacuolization, mitochondria engorgement,crista disappeared,endoplasmic reticulum extension, ribosome reduction, theplank layer construction of posterior funiculus myelin sheathwere crushed, neuraxis were not clear in group B. Thechanges in group C were better than group B.Conclusions: The magnesium sulfate is a kind of excitingamino acid receptor antagonist. Magnesium, anoncompetitive NMDA antagonist, would block the ionchannel of NMDA receptors and decrease the release ofexciting amino acid. So magnesium sulfate can lessen thedamage of exciting amino acid in SCI. In addition, themagnesium ion protection functions to SCI also depend onthe antagonism to calcium ion. Mg2+ can hold down the insideblowing of Ca2+ through competing the binding site of cellmembrane with Ca2+. Mg²⁺ also can contain the exchange ofCa²⁺—Na⁺ through Mg²⁺—Na⁺ to decrease the inside blowingof Ca²⁺,increase the outside blowing of Ca²⁺ through...