| OBJECTIVE: to observe the dynamic changes of blood-brain barrier ( BBB ) permeability and part of the parameters of the ischemic microenvironment of hippocampus, and explore the correlation between BBB dysfunction and the changes of ischemic microenvironment and provide the pathophysiologic clues for possible mechanism of neuron injury in the context of ischemia insult. METHODS: The cerebral ischemic model was induced by photochemical reaction in Tree Shrews. Using a kind of single-pumped push-pull perfusing system (SPPPPS) which was designed by the author, with the help of artificial cerebrospinal fluid (aCSF) as perfusate, the ipsilateral and contralateral ischemia hippocampus microenvironment was perfused 4h, 24h and 72h after cerebral ischemia. As tracer to detect BBB permeability, fluorescein thiocarbamoyl dextran (molecular weight 70K Dalton, FITC-D-70K) was injected intravenously before perfusion. The perfusate samples were collected by SPPPPS after the ischemia and the plasma samples were collected after perfusion. The ion concentrations and blood gas parameters of the perfusate in the hippocampus microenvironment were determined with analyzers. The concentrations of FITC-D-70K in the perfusates and plasma samples were detected with fluorescent spectrophotometer and then the unit volume clearance rate of FITC-D-70K (Cf) was estimated respectively, which is defined as the BBB permeability coefficient. The concentrations of amino acidic neurotransmitters glutamate acid (Glu) and gamma-aminobutyric acid (GABA) in the perfusates were detected with high performance liquid chromatography(HPLC) method. We also recognized the stroke indexes (SI) and astrocyte activity indexes (AAI) on respective time and spatial points after ischemia. Furthermore, the morphocytological changes in the ipsilateralischemia hippocampus were observed with electronic microscope 24h after cerebral ischemia. RESULTS: Compared with the sham group, BBB permeability of the ischemic ipsilateral hippocampus started to increase at 4h and reached the peak at 24h(0. 526±0.130 ul, P <0. 01). Glu contents in the microenvironment decreased markedly at 4h (1.72+0. 20 umol. L"1, P <0.05) but increased subsequently, especially at 24h (5. 71 ± 0. 39 umol. L'1, P <0. 01). GABA increased at respective time point and hit culmination at 24h (3.810±0.14 umol. L'1, P <0.01) . The concentration of Na+ in microenvironment fell down at 4h (144.38 ± 7.14 mmol.L"1,P<0. 01) and 24h( 148.48+8. 46 mmol. t"1, P <0. 05) while K+content increased at 4h (3.23 + 0. 16 mmol. L*1, P <0. 01) and72h (3.06±0. 23 mmol. L"1, P <0.05) . Like Na+, Ca2+decreased obviously at 4h (1.41±0. 09mmol. L"1, P <0. 01) . PO2 went down at 4h (114.5 + 7.12 mmHg, P <0. 01) and elevated at 24h ,72h. pH decreased at 4h (7.24 + 0.11, P <0.01) and 24h (7.24±0.14, P <0. 05) .SI decreased at 4h (0.58 + 0.13 ) and increased subsequently, especially at 24h (1.49+0.15, P <0. 05 ) . In contrast to SI, AAI increased markedly at 4h (1.79 + 0.43, P <0.05) and decreased subsequently, especially at 24h (0.68± 0. 07, P <0. 05) . Compared with the sham, the ischemia contralateral hippocampus BBB permeability evidently elevated at 24h after ischemia (0.288 + 0. 04 ul, P <0. 05) , so did both Glu and K+ contents ( respectively3.59+0. 36 umol. L'1 and 3.13 + 0.17 mmol.L"1, P <0.05) . CONLUSION: The results suggest: ?The secondary neuron injury in the hippocampus may be followed the microenvironment deterioration resulted from the spreading of the microenvironment in ischemic core; ?Among many factors in ischemic microenvironment, the increases of excitatory neurotransmitters Glu and the decreases of pH value may account for the BBB destruction; ?Activated astrocytes may have neuroprotective effect by improving the neuron microenvironment; ?The outward diffusion of Glu and K+ in the ischemic microenvironment might be the main causes of cortex spreading depression. |
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