| Objectives Although periventricular white matter injury is the leading causing of cognitive impairment and cerebral palsy, the relationship of myelination deficiency and long-term cognitive impairment is not well understand. The purpose of this study is to investigate the oligodendrocyte myelination and long-term cognitive impairment in a postnatal day 3(P3) rat model with hypoxia ischemia (HI).Methods The P3 SD rats had the right carotid artery ligation, and exposed to 6% oxygen (balanced with 94% N2) for 2.5 h to induce HI. The shame control was neither right carotid artery ligation nor hypoxia. Brain injury during early stage (24 h after HI) was evaluated by 04, glial fibrillary acidic protein (GFAP), CD68 immunostaining to investigate the expression of preoligodendrocytes (preOLs), astrocytes, activated microglia respectively. The brain during late stage (44 day after HI) was evaluated by myelin basic protein (MBP),2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), GFAP, CD68 immunostaining to investigate the expression of oligodendrocytes myelination, glial scaring, and activated microglia respectively. Spatial cognitive function was evaluated at P42 using the Morris Water Maze test followed by cresyl violet (CV) staining for histological evaluation.Results HI caused an increase in preOLs, astrocytes, and microglia in the ipsilateral white matter at 72 h after HI compared to contralateral regions and sham-operated controls (both p<0.05). There were significant decreases in MBP positive area and CNPase positive oligodendrocytes with GFAP labeled glial scarring in the ipsilateral periventricular white matter at P47 compared to contralateral regions and sham-operated controls (all p<0.05). The rats with HI had spatial learning deficits in navigation trials (longer escape latency and swimming distance) and memory dysfunction in probe trials (fewer number of platform crossings and percentage of time in the target quadrant) compared with sham-operated controls (p<0.05).The CV staining shows that the ratio of ipsilateral corpus callosum or hemisphere in HI group were lower than that of normal control group (both p<0.05). Couclusions In this neonatal rat model of HI, myelination deficiency induced by activated astrocytes and microglia during the early phase with subsequent glial scarring was associated with long-term spatial learning and memory dysfunction. Objectives:Emerging evidence shows that the premature brain are susceptible to inflammatory injury causing periventricular white matter injury accompanied with neuronal/axonal disease, however the molecular mechanism is not fully understood. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptors were reported to mediate various inflammatory responses in the central nervous degenerative diseases. However, little information is available regarding the expression of TRAIL and its receptors in the postnatal 3 (P3) rat brain after perinatal hypoxia ischemia (HI). The aim of this study is to investigate the expression of TRAIL and its receptors in the P3 rat immature brain after HI and evaluate the related neurofunctional deficits.Methods:P3 SD rats had the right common carotid artery ligation, and exposed to 6% humidified oxygen (balanced with 94% N2) for 2.5 h to induce HI. Sham-operated rat pups with 21% O2 exposure served as the control group. The expression of TRAIL and its receptors, Caspase-3, CD68 were evaluated at 24 h after HI (acute stage) by immunostaining, western blot, Real-time PCR, respectively. The delayed neuronal loss was evaluated by NeuN immunostaining at 7 day after HI (recovery stage). Meanwhile, the neuropathological change was evaluated by hematoxylin-eosin (HE) staining. The short-time neurobehavioral function (right reflex, gait reflex, cliff aversion and geotaxis reflex) was assessed at 24 h,72 h,5 day and 7 day after HI. The physical development was evaluated by the time of eye-opening after HI. The cognitive function was evaluated by the T-maze test at P60.Results:The TRAIL,DR5,DcR1,DcR2 and caspase 3-positive cells were abundant in the ipsilateral cortex than those in the contralateral part and control group at 24 h after HI (TRAIL:24±3 cells/hpf vs.3±1 cells/hpf and 2.8±0.7 cells/hpf; DR5:51±8 cells/hpf vs.16±4 cells/hpf and 12.1±3.8 cells/hpf; DcRl:36.6±7.7 cells/hpf vs.5.9±2.6 cells/hpf and 4.7±1.4 cells/hpf; DcR2:20.4±1.9 cells/hpf vs.15.3±1.5 cells/hpf and 15.1±1.0 cells/hpf; Caspase-3:35±7 cells/hpf vs.4±1 cells/hpf and 3.5±0.6 cells/hpf, all P<0.05), whereas the expression of DR4 was undetectable in both cortical and periventricular regions by immunostaining. The TRAIL and CD68 double labeled microglial cells were observed in cortical regions of ipsilateral hemisphere compared with the corresponding regions of the contralateral part and control group (P<0.05). Accordingly, the expression of TRAIL, DR5 protein was significantly upregulated at 24 h after HI. Meanwhile, the expression of TRAIL, DR5 and Caspase-3 mRNA was also significantly upregulated at 24 h after HI in the ipsilateral cortex. The neuronal loss was found in the ipsilateral cortex at 7 day after HI. Further, impaired short-time neurobehavioral development was observed from 72 h after HI in HI group compared to control (P<0.05).The delayed time of eye-opening and long-term cognitive deficiency were also observed in HI group.Conclusions:HI causes impaired neurobehavioral function and induces the neural cell apoptosis evidenced by the increased expression of TRAIL and death receptor 5 in the brain of newborn rats. The TRAIL-DR5 signal pathway may play an important role in the neuronal injury of HI rat brain. This may be one of the cellular mechanisms in delayed neurobehavioral development.
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