| Objectives:1. To explore the regulatory mechanism of N-methyl-D-aspartic acid receptor subunits NR2 A and NR2 B on the synaptic after cerebral ischemia, so as to reveal the regulatory mechanism of NR2 A and NR2 B subunits on the long-term potentiation of synaptic plasticity of cranial nerves.2. To investigate the changes of growth associated protein-43(GAP-43),postsynaptic density protein-95(PSD-95) and synaptophysin(Syn) contents related to synaptic plasticity at the time of cerebral ischemia as well as their relationships with the neurological brain synapses.Methods:120 Wistar rats were selected and randomly divided into control group(60 rats) and cerebral ischemia group(60 rats) according to the random number table. The chronic cerebral ischemia model of rats was built with the improved two-vessel-occlusion(2VO)method, while the vessels and vagus nurves of rats in the control group would not be occluded. Then, the expression levels of N-methyl-D-aspartic acid receptor subunits NR2 A and NR2 B in the hippocampus of rats in the cerebral ischemia groups were detected with western blot. The formation of long-term potentiation in hippocampal CA1 region was induced with the low frequency stimulation of 5Hz/16 s as threshold stimulation and the high frequency stimulation of 100Hx/s, and the change process of field potential was recorded through the amplification of neural signals.After that, immunohistochemical staining was made to the PSD, Syn and GAP, and the cellular morphologies of relevant matters were observed with the microscope. Then,the changes of relevant matters in the bodies of rats after cerebral ischemia were evaluated through the comparison of above indexes in cerebral ischemia groups and control group, and then the indexes of the corresponding matters and the mechanism of neural synaptic plasticity were analyzed and elaborated.Results:1. The NR2 A expression level in the hippocampus of rats within 0-12 h after the chronic cerebral ischemia was reduced in all ischemia groups, and the NR2 A expression level after 12 h of cerebral ischemia was significantly lower than those at 0h and 4h(P<0.01); the NR2 B level reached its peak value at 4h of cerebral ischemia and the lowest point at 12 h.2. The long-term potentiation could not be formed no matter with what kind of stimulation way(high frequency or low frequency), and results indicated that NR2 B had certain inhibiting effect on the formation of long-term potentiation induced by conditioned stimulus; however, NR2 A was of promotion role to the formation of long-term potentiation induced by conditioned stimulus.3. No cell with obvious positive expression was found in the control group, while the positive expression appeared in the rats of ischemia groups at 1h, and the positive cells were increased obviously compared to the control group(P<0.05). Also, in the ischemia groups, the positive particles at 12 h were more than those at 4h and 1h, with significant statistical differences(P<0.05).4. The cells with obvious positive expression of PSD-95 were seen in the control group, while the PSD-95 positive expressions in cerebral ischemia groups at 12 h were significantly reduced than those at 4h and 1h, with obvious statistical different(P<0.05);the PSD-95 positive cells in the cerebral ischemia groups at 4h were significantly lower than those at 1h(P<0.05); it could be seen with the electron microscope that: PSD-95 was mainly distributed in cyton, dendrite and axon fiber, the positive cells could be seen as circular, oval or triangular in the control group, the dendrite fibers had many branches,and the axon fibers presented the long and thin forms; it could be found with the microscope that, swelling appeared in the nerve cells of cerebral ischemia groups, the branches of dendrites disappeared, and some cell nucleuses were deeply stained.5. The Syn P38 contents in cerebral ischemia groups were significantly lower than that of control group, with significant statistical difference(P<0.05); in the cerebral ischemia groups, the Syn P38 content at 12 h was significantly reduced compared to those at 4h and 1h, with significant statistical difference(P<0.05); also, in the cerebral ischemia groups, the P38 positive cells at 4h were obviously fewer than those at 1h(P<0.05); under the microscope, the P38 immunoreactive products in the hippocampal area of rats in control group were in brown or yellow particles and dots, mainly located in neuropil, the inclusions of nerve cells were slightly stained, and the glial cells, white matters and blood vessels were not stained; in the cerebral ischemia groups, it could be seen that, the reactive particles were reduced, they were relatively sparse and fine, their staining was light and shallow, and the average optical of immunoreactive products was gradually reduced along with the passage of time.Conclusions:1. NR2 B has inhibiting effect on the formation of long-term potentiation induced by conditioned stimulus, while NR2 A could promote the formation of long-term potentiation induced by conditioned stimulus.2. GAP-43 is possibly an important matter actively promoting the repair after brain tissue damage caused by cerebral ischemia and having positive regulation to the neuronal synaptic plasticity.3. PSD-95 is possibly the matter playing important role in the long-term potentiation mechanism in neural synapse under the stress state of cerebral ischemia.4. The Syn P38 might be the important matter taking part in neuronal synaptic plasticity. |
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