| Budget Amount *help |
¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1998: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
Intracellular and single-electrode voltage-clamp recordings were made to investigate the process of membrane dysfunction induced by superfusion with oxygen and glucose-deprived (isehemia-simulating) medium in hippocampal CAl pyramidal neurons of rat tissue slices. To assess correlation between potential change and membrane dysfunction, the recorded neurons were intracellularly stained with biocytin. A rapid depolarization was produced approximately 6 min after starting superfusion with ischemia-simulating medium. When oxygen and glucose were reintroduced immediately after generating the rapid depolarization, the membrane did not repolarize ; the potential reached 0 mV approximately 5 min after the reintroduction. In single-electrode voltage-clamp recording, supeffusion with ischemia-simulating medium for 4 min depressed the glutamate-mediated fast EPSCs, and abolished the GABA-mediated fast and slow IPSCs. Contrary, both exogenous glutamate- and GABA-induced inward current were augment
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ed, but muscimol-and baclofen-induced outward currents were suppressed. These results suggest that the site of the depression of the fast EPSC or the fast IPSC is presynaptic while the site of the suppression of the slow IPSC is pre-and post-synaptic. The morphological aspects of biocytin-stained neurons during ischemic exposure were not significantly different from control neurons before the rapid depolarization. On the other hand, small blebs were observed on the surface of the neuron within 0.5 min of generating the rapid depolarization and blebs increased in size after i min. After 3 min, neurons became larger and swollen. When Ca^<2+>-free (0 mM) with Co^<2+> (2.5 mM)-containing medium including oxygen and glucose was applied within 1 min after the rapid depolarization, the membrane potential was completely restored to the preexposure level. In these neurons, the long axis was lengthened without any blebs being apparent on the membrane surface. These results suggest that the membrane dysfunction induced by in vitro ischemia may be due to a Ca^<2+>-dependent process which commences around 1.5 min after, and is completed 3 min after the onset of the rapid depolarization. From all the results, it is concluded that the transformation from small to large blebs may result in the observed irreversible membrane dysfunction. Less
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