Experimental Study Of White Matter Damage In Newborn Rats And The Diagnostic Value Investigation Of Dwi In Premature White Matter Damage

ObjectWhite matter damage(WMD) was considered to be the important reason of neonatal death, as well as the most significant risk factors that associated with cerebral palsy. However,the its mechanism involved in white matter damage is still not clear at present, the epidemiologic evidence and the animal experiments supported the viewpoint that the infants which exposed to intrauterine infection were at high risk for WMD. But the role of the early detection is quite limited with cranial conventional MRI or US. Diffusion Weighted Imaging has been universally acknowledged in the early diagnosis of the acute brain injury. In current study,we developed a model of intrauterine infection in rats using Lipopolysaccharide as the inflammatory stimulus to observation effects of intrauterine infection on Glial fibrillary acidic protein and myelin basic protein in the neonatal rat brain and the immunological mechanisms mediating of them. Basing on the light and electron pathology and the following early imaging evidences,we suggested the important value of the DWI and conventional MRI in the early detection of White matter damage.Methods Twenty Pregnant rats on gestation day18were randomly divided in the infection group(n=6) and the control group(n=14).The infection group was established by injecting Lipopolysaccharide (450μg·kg-1·d-1) in pregnant rats for two consecutive days when gestation at18days. The control group was treated with normal saline.Then,we observed two groups delivery time、the birth weight and state. We removed the rats which delivery before22days.We killed the rats on the postnatal hour6(P6h),P3,P7and P25,respectively. Hematoxylineosin(HE) staining and immuno histoehemistry were used for evaluation of GEAP and MBP expression in neonatal rat brains at P1,P3,P7andP25,with the cerebral white matter damage of neonatal rat,as well as electron pathology and DWI.We studied the prematures at postnatal4weeks or term、3months、8months and12months by using conventional MRI and DWI in our NICU form September2010to February2011,as well as the assays of blood routine test、CRP、boold sugar、blood culture and serum ions.ResultsOne was died after intrauterine infection. The experimental group has received only58pups and control group for71only. The survival rate of the experimental and control groups was85%and100%,respectively.Intrauterine Lipopolysaccharide infection produced inflammation of uterine and placenta in all Pregnant mice of experimental group, but all cases of control group had no intrauterine infection. The skin of the experimental group pups were purple and their weight low than control group. The pups born average weight of experimental group and control group have significant differences (P<0.05). The major histopathologic changes in experimental group at P7after birth were weak staining and rarefaction of cerebral white matter. GFAP-positive cells were not observed in both the control and the experimental groups of P6h and P3. The numbers of GFAP-positive cells of the experimental group were marked inerea-sed in periventricular white matter and hippocampus at P7and P25compared with the control group(P<0.05). The integrate density (ID) of MBP-Positive staining of the experimental group were marked decreased in periven-tricular white matter and corpus callosum at P7and P25compared with the control group,except the periventricular white matter at P7(P>0.05). Brain pathological result under electron microscope:at6hP and3P groups,we can observed the organelles of oligodendrocytes swollen noticeably in all pups,including mitochondria、endoplasmic reticulum and the Golgi apparatus. The number of organelles in most pups decreased compared with control group.Vacuolated mitochondria were seen in same pups and we can observed degranulated rough endoplasmic in another pups.Furthermore, the apoptotic cells can be seen in experimental group.At7P and25P groups,we can observed that the oligodendrocyte generally displayed karyopycnosis and karyolysis in experimental group.No myelogenesis of white matter in3P experimental group.the sparse myelogenesis in the7P and25P experimental group and normal myelogenesis in control group were observed. Therefore, intrauterine infection could cause weal staining of cerebral white matter、the sparse myelogenesis、early oligodendrocytes and astrocytes necrosis and the alteration of expression of GFAP and MBP in the brain of experiment pups.MRI:we only observed the significant anomalous signals in DWI images of pups from the experimental6hP group.However, the difference of ADC values were obviously through measuring in ADC chart.In the6hP and3P group,the ADC values were significantly lower than that of brain in the control group (F(6hP)=0.001; P(3dp)=0.002), meanwhile, the degree and the area of organization dispersion limited were more noticeably compared with control group. However,7P and25P group has not seen the definite abnormalities compared with control group (P(7d组)=0.080;P(25d组)=0.176)In the premature infants imagings,28cases of DWI has not seen the high signal change on the first time in all premature infants.The changes of regular MRI:punctate short T1signal and slightly shorter T2signal were observed in27(27/40) cases in Periventrieular white matter,8cases has not seen the obvious abnormity.12infants (12/40) with lesions in clusters in bothsides of periventricular、frontal and parietal lobe on DWI.what’s more,we can see point flake and strip signals which increased on T1-weighted images and decreased on T2-weighted images in7cases(7/12) from the12infants in regular MRI.5cases(5/12) has not seen the obvious abnormity in regular MRI. The signal on DWI that symmetric、diffuse high signal intensity can been the earliest evidence of PVL.DWI was demonstrated to had better be performed in one week after birth.Time from the initial examination to the follow-up examination ranged from3to22months.22infants(22/27) in DWI normal group with lesions in clusters showed no abnormal intensity on follow-up MRI. Time from the initial examination to the follow-up examination ranged from1to22months.5infants(5/12) in DWI unnormal group but with no lesions in regular MRI showed irregularly high,low mixed signal on DWI and punctuate high signal intensity on T1-weighted imaging and slightly lower signal on T2-weighted imaging after two weeks.After Correct gestational age, the cerebral white matter reduced and dilation of ventricle of bothside can be seen in4infants(4/12) on conventional MRI. Four months later,DWI showed cystic low signal intensity where conventional MRI showed low signal intensity on T1-weighted and high signal intensity on T2-weighted imaging (cystic PVL) in8infants (8/12).2cases accorded with the diagnosis of bad brain development(2/12).Conclusion1. Injecting Lipopolysaccharide as the inflammatory stimulus could lead to inflammation of uterine and placenta and the model of intrauterine infection in rats were established successfully.2. Intrauterine infection could cause neonatal white matter damage.DWI can dynamic to reflected the variation of organization pathophysiological after the brain damage. Furthermore,the ADC values for display model rat regional brain oedema after brain damage circumstance have higher sensitivity.3. DWI can show a higher correlation with subsequent evidence of PVL than conventional MRI imaging.DWI was supposed to be a preferred technique in the early detection of PVL infant.4. The premature infant who suspected of brain white matter risk factors could make a MRI as soon as possible. On the one hand,they can provide corresponding scientific basis to the clinical diagnosis and treatment, on the other hand, they can reduce the occurrence of poor outcome as far as possible.