The Experimental Study On Pathological Changes And Proton Magnetic Resonance Spectroscopy In The Early Stage Of Diffuse Axonal Injury In Rats

Diffuse axonal injury(DAI) is very common in various kinds of traumatic brain injury(TBI) from mild to severe. It is found in more than 50% of head-injury cases. Thus DAI may play an important role in modern TBI. In the early stage of DAI, although its morphology unchanged, the neurochemical metabolite changed obviously. Recently, utilization of Megnetic Resonance Spectroscopy(MRS) techniques could accurately observe change of metabolite (N-acetylaspartate , NAA; Choline , Cho; Creatine ,Cr, et al)after DAI in vivo, which is very useful for early diagnosis of DAI. The purpose of the presenting study is to detect the changes of neurochemical matter in the early stage after DAI in rats by MRS, and discuss what time in the early stage after DAI is optimal for MRS detection to provide help for clinical diagnosis.Methods In this experiment, DAI was induced by a rotational acceleration device in 16 Sprague-Dawley(SD) rats. MRS was used to detect those 16 self-control rats of injury group in pre-trauma, 2 hours and 3 hours post-trauma. The changes of metabolite were observed, and the data was analysed statistically. The 16 rats of injury group were sacrificed by decapitation at 3 hours and 6 hours post-trauma, while the other 8 rats of sham group were put to death after 24 hours. The samples of the rat brain were stained with hematoxylin and eosin(HE), Bielschowsky, Luxol Fast Blue for histologicalexamination, and withP ?APP for inmunohisto- chemistry in order to detect the early stage pathological changes of subcortex white matter, hippocampal, corpus callosum and brain stem in different time points.Result At the MRS evaluation , we observed significantly lower ratios of NAA/Cr in 3 hours injury group compared to the sham group in corpus callosum, and no significantly different in 2 hours injury group compared to the sham group in the same area, there were significant difference in the NAA/Cr ratios between 2 hours and 3 hours group. The same result was found in Cho/Cr ratios in the same area .The NAA/Cr ratios in the injury group were found to be significantly lower than in control group in brain stem at 2 hours and 3 hours measured, while that of ratio between 2 and 3 hours had no any significant differentiation. The Cho/Cr ratios.on the other hand ,indicated no difference between 2 hours injury group and control group in brain stem , and significant difference between 3 hours injury group and control group in the same area. Axon and myeline swelling were found within 6 hours after injury, with a few retraction balls detected. The ?桝PP expression was positive at 3 hours and was particularly stronge at 6 hours after injury. The results of semi-quantitative analysis showed the significant differentiation of 3 hours and 6 hours in the inmuno-positive expression of brain stem, corpus callosum and hippocampal. Histological results demonstrated that DAI occoured in all rats of injury group.Conclusion These results suggest that (1) MRS techniques provides high sensitivity in diagnosing microscopic pathology following DAI. (2) The acute decline in NAA/Cr ratios occurs at 2-3 hours following experimental brain trauma, potentially marking deficits of neuronal or axonal function. (3) Theacute decrease in Cho level may be relevant to catabolism of membrance, especially in early stage at 3 hours after trauma. (4) It is speculated that 2-3 hours after trauma are probably the best time for MRS detection in early stage of DAI.