| With the aging of the world population growing,the incidence of cerebrovascular diseases is increasing,and the high mortality and morbidity rates of them pose a serious threat to human health and survival.Cerebral ischemia is one of the important reasons for the diseases.As the complexity of cerebral ischemia,there is no effective method for cure.Enriched environment attested to be one of the effective methods to get well,and can leave caducity,enhance intellect.Clinical acute cerebral ischemia induced central nervous system injury,but has varying degrees of spontaneous recovery after reperfusion,relate with the central nervous system in a certain extent,in particular with the compensatory ability of organize which is adjacent to ischemia zone. Synaptic is a structure have plasticity,and sensitivity to the inside and outside stimulation of cells,and thus change the effectiveness of the transfer function.Synaptic plasticity is an important mechanism for neural reconstruction,and has important effection in neurological function recovery after cerebral ischemia.Post synaptic density(PSD)contains all kinds of receptors,signaling proteins,the scaffolding protein and cytoskeletal protein.When stimulated by the extracellular signal,they dynamic combined,and make effect for cell signal transduction,cell skeleton anchored,receptor transit,specificly activation on downsteam signal transduction pathway,thereby affecting nerve conduction function.PSD-95 is one of the most representative scaffold protein in PSD,regulating the synaptie activity by the integration of the signal transduction.Therefore,it is assume that if enriched environment can affect the structural changed of synaptic interface caused by cerebral ischemia,then the expression of PSD-95 which is an important molecular of scaffold protein changed or not? This study used MCAO cerebral ischemia model of rats,to discuss the above questions.In the present study,open field behavior,suspension test hanging,Morris water maze,jumping stand test,and paraffin section techniques,transmission electron microscope,agarose gel electrophoresis techniques,reverse transcription polymerase chain reaction(RT-PCR)amplification techniques were used to investigate the mechanism underlying cerebral ischemia-induced learning-memory damage,further to study the protection of enriched environment against cerebral ischemia.The spontaneous behavior and inquire actions of cerebral ischemia were first tested using open field.The results showed that the spontaneous behavior and inquire actions were significantly reduced by cerebral ischemia(P＜0.01,P＜0.05).Enriched environment can significantly enhanced these behaviors(P＜0.01,P＜0.05).Suspension test hanging showed that there were no differences occurred by transient focal cerebral ischemia or enriched environment.The results of Morris water maze showed that the ability of spatial learning and memory were significantly damaged on the transient focal cerebral ischemia rats and 3 days after global cerebral repeated ischemia-reperfusion mice(P＜0.01,P＜0.05).The environmental enrichment significantly improved the memory of transient focal cerebral ischemia rats and 7 days after global cerebral repeated ischemia-reperfusion mice(P＜0.01,P＜0.05).Meanwhile,enhanced the learning and memory of sham rats(P＜0.01).The escape learning and memory ability were reduced by transient focal cerebral ischemia(P＜0.05),and enriched environment enhanced it(P＜0.05)were got in jumping stand test.The results suggest that,either transient focal cerebral ischemia or global cerebral repeated ischemia-reperfusion would injured the brain,damaged the ability of learning and memory;enriched environment could help the resume of brain function which were damaged by cerebral ischemia,and enhanced the learning and memory of sham rats and mice.To clarify the effects of enriched environment on cerebral infarct and apoptosis, measure the cerebral infarct range by TTC(2,3,5-triphenyltetrazolium chloride)and examine the shape change of nerve cell by HE(hematoxylin and eosin)staining. Agarose gel electrophoresis technique,reverse transcription poly-merase chain reaction (RT-PCR)amplification techniques were used to investigate the effect of enriched environment on apoptotic in repeated cerebral ischemia-reperfusion mice induced by fastening bilateral common carotid artery.The result of TTC staining showed that enriched environment reduced the cerebral infarct range.The result of HE staining showed that after transient focal cerebral ischemia,the cells in cortex S1(sensorimotor1)and hippocampus CA1 region appeared to be a series of cell putrescence phenomena,such as sparsity,disorder,smaller volume,irregular-shape and so on.Enriched environment can attenuate the damage of neuronal cells in hippocampus CA1 region.The result of agarose gel electrophoresis showed that,after 2 days of ischemia-reperfusion,the degree of DNA damage in model mice was more serious and some typical DNA ladder bands(DNA Ladder)were appeared.3 days of ischemia-reperfusion DNA electrophoresis only assumed dispersion shape.7 days of ischemia-reperfusion DNA ladder bands were disappeared.The effect of enriched environment was not significantly.The result of RT-PCR showed that After 2 days, 3days and 7 days of ischemia-reperfusion,XIAP mRNA expression in the hippocampus tissue of cerebral ischemia mice dramatically down-regulated compared with sham group(P＜0.01);as the reperfusion time prolong,the XIAP mRNA expression up-regulation,but still significant different with sham mice(P＜0.01).The expression of XIAP mRNA in cortex in mice 7 days of ischemia-reperfusion was significantly higher than ischemia mice maintained in standard environment(P＜0.05).These results suggest that the enriched environment could up-regulate the expression of XIAP gene, restrained the apoptosis,reduced the cell injury and cerebral infarct range.To further investigate the mechanism how did the enriched environment improve the learning-memory of cerebral ischemia and sham rats,the synaptic density and structural of synapse interface in cortex S1 and hippocampus CA1 were observed by transmission electron microscope.The expression of PSD-95(post synaptic density protein 95)mRNA in cortex S1 and hippocampus CA1 were analyzed by RT-PCR.The results as follow:the perforated synapse density in cortex and hippocampus and the synapse density in cortex were significantly reduced by MCAO(P＜0.01). Environmental enrichment enhanced the perforated synapse density and the synapse density in cortex damaged by ischemia(P＜0.01)as well as enhanced the perforated synapse density in both ipsilateral and opposite side of hippocampus.Obverse the structural of synapse interface showed that,the clef of synaptic widened significantly (P＜0.01),the postsynaptic density thinned obviously(P＜0.01),the length of active zone shortened distinctly(P＜0.05,P＜0.01),and the curvature of synapse interface decreased(P＜0.05,P＜0.01)in cortex S1 and hippocampus CA1 after transient focal cerebral ischemia;environmental enrichment reversed the changes of synaptic interface parameters caused by cerebral ischemia in different levers,especially enlarging the thickness of postsynaptic density(P＜0.01)and decrease the synaptic cleft width (P＜0.01)in hippocampus CA1 after transient focal cerebral ischemia,and also enlarging the thickness of postsynaptic density(P＜0.01)in hippocampus CA1 of sham rats.Furthermore,the environmental enrichment significantly up-regulated the expression of PSD-95 mRNA in ipsilateral cortex and hippocampus of MACO rats.Summarily,enriched environment affect the damage induced by cerebral isehemia on different levels.On macrocosm,enriched environment can help the resume of brain function which were damaged by cerebral ischemia,and enhanced the learning and memory of sham rats and mice.On cell level,the enriched environment can up-regulate the expression of XIAP gene,restrain the apoptosis,reduced the cell injury and cerebral infarct range.On sub-cell and molecule level,the environmental enrichment restrained the reduction of the synaptic density caused by cerebral ischemia,reversed the changes of synaptic interface parameters caused by cerebral ischemia in different levels, especially enlarging the thickness of postsynaptic density and decrease the synaptic cleft width,and significantly up-regulated the expression of PSD-95 mRNA which has osculation correlation with structural plasticity.
|
PDF Full Text Request