Change Of Neural Plasticity And Its Associated Inhibitory Factors After Hypoxic-Ischemic Brain Damage In Neonatal Rats

【Objective】1. Establish hypoxic-ischemic brain damage models in neonatal rats.2. Observe the change of neural plasticity after brain damage during developmental phase.3. Explore the relationship between the change of neural plasticity and the capability of learning and memory.4. Observe the change of neurocan after brain damage during developmental phase.5. Explore the effect of neurocan on neural plasticity.【Methods】1. 7 days neonatal SD rats were randomly divided into sham-operated group and HIBD group. Established HIBD models with improved Rice method, then screened through ethology and generally condition grading. Dissected the brain, then observed the change of neuron in histopathology and ultrastructure with HE staining and transmission electron microscopy respectively.2. The dynamic change of synaptophysin at 1, 4, 7, 14, 28 days after HIBD was detected in levels of proteinum and mRNA with reverse transcription-polymerase chain reaction and immunohistochemical method respectively to reflect the change of neural plasticity.3. Detected the change in capability of learning and memory with Y-maze training task after HIBD.4. The expression of neurocan was detected with reverse transcription- polymerase chain reaction and immunohistochemical method, respectively at 1, 4, 7, 14, 28 days after the operation.【Results】1. The brain lesion was found most severe at 4 days in HIBD group with HE staining, which was found that organizations necrosis and cell dissolved appeared in ligation side of the brain. Glial scar proliferation was found around the lesion at 7 days after HIBD. Much neuron was losed at 14, 28 days, and replaced by glial scar at last.2. It was observed that parts of the nuclear membrane was disappeared in HIBD group, mitochondrial swelling, nervous processes destruction were found in focal, the numbers of synapses and synaptic vesicles were decreased, and the structure were damaged in transmission electron microscopy.3. The expression of synaptophysin gradually increased with age in sham-operated group(P<0.05). While in HIBD group, synaptophysin immune activity increased at 4 days, and reached the peak level at 7 days, both were higher than that of sham-operated group (P<0.05); Then synaptophysin immune activity declined and have been significantly lower than that of sham-operated group at 14, 28days (P<0.05). The same results were found in the expression of synaptophysin mRNA with RT-PCR (P<0.05).4. It was found that the capability of learning and memory in HIBD group at 14, 28 days was weaker than that of sham-operated group in Y-maze training task. 5. The amount of neurocan reached a peak level after 7 days of the operation in sham-operated brains(P<0.05), then reduced. Expression of neurocan in HIBD brains at 4, 7days after the operation was lower than that of sham-operated brains(P<0.05), while was higher than that of sham-operated brains at 14, 28 days after the operation(P<0.05).【Conclusion】1. Improved Rice method is a simple and dependable approach to establish HIBD model in neonatal rat.2. Neural plasticity is strong within two weeks after brain damage during developmental phase. With neuron's further degeneration and necrosis, the brain injury is harder to restore because of exceeding the capability of plasticity compensation.3. Learning and memory are closely related to the plasticity of synaptic structure and function. The reduction of synaptophysin may be one of the neural mechanisms which cause learning and memory disorder after HIBD.4. The expression of neurocan is increase after two weeks of neonatal HIBD which will affect the neural plasticity. This prompt the best time for controlling neural plasticity associated inhibitory factors in brain damage during developmental phase is within two weeks.