ABSTRACT
Objective:To establish Sprague-Dawley (SD) rat models of cognitive impairment through repeated stimulation of lipopolysaccharide (LPS) in the early brain development, and to inquire into the effect of " multi-hits" mediated by inflammatory response on the histology and behavior of SD rat models and related molecular mechanisms.Methods:This study adopted a group design for experiments.The " multi-hits" SD rat models were established by intraperitoneal injection of LPS.According to the random number table method, 24 pregnant rats were randomly divided into 4 groups: control group, LPS1 group, LPS2 group and LPS3 group, 6 rats in each group.In the control group, saline was intraperitoneally injected into rats with gestational age of 18 days and 20-day-old neonatal rats.Rats with gestational age of 18 days were intraperitoneally injected with saline in the LPS1 group, 0.05 mg/kg LPS in the LPS2 group, and 0.1 mg/kg LPS in the LPS3 group.The pups in LPS1-3 groups were all injected intraperitoneally with 1 mg/kg LPS at the postnatal age of 20 days.The motor and cognitive function of the pups were evaluated overall by behavioral experiments such as forelimb suspension tests, grid tests and water maze tests.The relative expression of glial fibrillary acidic protein (GFAP), Notch1 and Jagged1 in brain tissue of pups was mainly detected by Western blot (WB) and histological experiments.One-way ANOVA analysis of variance and independent samples t- test were used to compare data among groups and between groups, respectively. Results:(1) Behavioral experiments: compared with the control group, LPS1-3 groups showed progressive decrease in forelimb suspension time [(34.81±5.66) s, (22.47±4.35) s, and (13.20±4.25) s vs.(43.88 ± 4.85) s], and the number of missteps in the grid experiment increased progressively (16.13±2.90, 20.75±3.10, 25.13±4.45 vs.9.00±2.72). The differences were statistically significant ( F=69.77, 35.59, all P<0.001). Both the escape latency and total distance in Morri′s water maze test increased progressively ( P<0.05). (2) WB experiment: the relative expression levels of GFAP, Notch1 and Jagged1 proteins in LPS1-3 groups were significantly higher than that in the control group ( P<0.05). (3) Hematoxylin-eosin (HE) staining and electron microscope pathology: compared with the control group, LPS1-3 groups had more loosely arranged frontal cortices and more obvious cell pyknosis.Under the electron microscope, the cytoplasm was swelling to varying degrees, mitochondrial cristae were broken, and part of the nuclear membrane was damaged. Conclusions:In the " multi-hits" cognitive impairment model, the damage to the brain tissue structure and behavioral changes of pups may be related to the up-regulation of Notch1/Jagged1 pathway mediated by repeated exposure to LPS.