Effects Of Enriched Environment On Neurofilament Protein Expression And Ultrastructure Of Neonatal Rats With Hypoxic-ischemic Brain Damage

Background and objective: Hypoxic-ischemic brain damage (HIBD) in the human perinatal period is a common disease which severely influence the health of neonates, and even cause disability and severe the quality of children's life. Unfortunately there is no ideal therapy to treat it up to now. The common view at present is that early interference is helpful to the recovery of brain injury. The early environment interference include early touch and various stimuli, and the latter can influence the morphology and function of the brain, increase neuronal plasticity, improve the brain functions and promote the recovery from brain damage. In our experiment the content of neurofilament protein(NFP) in rats brain and the number and ultrastructure change of live neurons in hippocampus were examined after early environment interference, which aimed to explore the possible mechanism of the recovery of HIBD and the reconstruction of the brain nervous net enhanced by the early touch and various stimuli, and provide theoretical basis and clinic instruction for its application with HIBD neonates.Methods: The Sprague-Dawley (SD) rat's models of HIBD were established by the method of Rice. Then the rats were divided into 3 groups at random: normal control group, hypoxic-ischemic(HI) group and enriched environment(EE) group. The early touch and enriched environment interference were administrated to the rats since the 2nd day after HIBD. On the 28th day, Morris water maze was used to evaluate the learning and memory ability, also the weight and cerebral weight of rats were measured. The HE stain and the Nissl stain were respectively employed to observe the morphopathologic changes and the number of live neurons in the left-sided hippocampus of the rats. The immunohistochemical stain was used to detect the ratios of left-to-right hemispheric integrated optical density (IOD) values of the neurofilament protein(NFP) in the hippocampus(L: R_RF), the transmission electron microscope(TEM) was used to observe the ultramicrorstructure change of the left hippocampus. Results:1. The water maze scores of EE group in place navigation test and spatial probe test were much higher than that of HI group (P<0.001), there was no significant difference compared EE group with the normal control group (P>0.05)2. The weight of EE group was much higher than that of HI group (P<0.01), there was no significant difference compared EE group with normal control group (P>0.05). The cerebral weight of EE group was still higher than that of HI group(P<0.001), but was lower than control group(P<0.05).3. HE stain displayed that the left-sided hippocampus of EE group was minimal abnormal with the slightly disorganized neurons and some cells lost; while the morphology of HI group was obviously abnormal with reduced cell layers, disorganized and sparse neurons, increased cellular gap, obscure nucleolus, karyopyknosis and nuclear fragmentation; the morphology of normal control group was normal4. The Nissl stain showed that the number of live neurons in the left-sided hippocampus of EE group was much more than that of HI group (P<0.01). There was no significant difference compared EE group with normal control group (P>0.05).5. Immunohistochemical analysis showed that the expression of NF-H in left-sided hippocampus of EE group significantly increased as compared with that of HI group (P<0.01), and there was no obvious difference compared EE group with the normal control group(P>0.05).6. The transmission electron microscope(TEM) displayed neuronal shrinkage and swelling mitochondrium in the left- sided hippocampus neurons of HI group, the number of neurofilament was decreased, the alinement was in rarement, the amount of synapse was diminished, the synaptic cleft was widened, the synaptic vesicles were reduced, the postsynapse density was slining; while the neurons and synapses of EE group and normal control group was normal.Conclusions:1. The reduction of NF-H protein expression and the number of neurons in the injured side brain tissue of HIBD neonatal rats indicated that not only gray matter but also whiter matter was vulnerable to hypoxia-ischemia.2. The decreased neuron damage and alleviation of poor NFP expression in the injured side brain tissue of HIBD neonatal rats implied that the enriched environment could protect both the neuron and the axon.3. Enriched environmental inteference could be used to alleviate the ultrastructure change of neurofilament and synapse, it also improved the plasticity of nervous system.4. The neonatal rats with HIBD had disturbance with the ability of long- term learning and memory, while the enriched environmental inteference can markedly improve this ability, which indicated that early environmental inteference had great benefit to the protection of long- term learning and memory.