fg-9041 and Ischemic-Attack--Transient

Over-activation of ionotropic glutamate receptors can cause an excessive influx of calcium ions into neurons, which subsequently triggers the degeneration and death of cells in a process known as excitotoxicity. Here, we examined the effects of modulating ionotropic glutamate receptors and L-type voltage-gated calcium channels (L-VGCC) on the expression and activation of c-Jun in hippocampus of SD rats after transient global ischemia. The total protein of c-Jun was altered by ischemia-reperfusion and reached its high levels at 3-6 h of reperfusion. However, the increased expression was prevented by pretreatment of ketamine (a non-competitive N-methyl-D-aspartate (NMDA) receptors antagonist) or nifedipine (a blocker of L-VGCC), but not by 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX), an AMPA/KA receptor antagonist. On the other hand, c-Jun phosphorylation was significantly increased 3 h after reperfusion, which was inhibited by DNQX, but not ketamine or nifedipine. AP-1 binding activity reactions were also performed by electrophoretic mobility shift assay (EMSA), which detected similar results as those in Western blotting. Our results clearly showed that c-Jun expression is NMDA receptor/L-VGCC-dependent and c-Jun activation is AMPA/KA receptor-dependent, which expands our knowledge of the JNK-c-Jun signaling pathway in ischemic brain damage.

Topics: Animals; Calcium Channel Blockers; Calcium Channels, L-Type; Carotid Stenosis; Enzyme Activation; Hippocampus; Ischemic Attack, Transient; JNK Mitogen-Activated Protein Kinases; Ketamine; Male; Nifedipine; Phosphorylation; Protein Binding; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Reperfusion; Transcription Factor AP-1

The mechanism underlying ischemia-induced hearing loss was studied in gerbils with transient hindbrain ischemia. Occlusion of the vertebral arteries caused an increase in the concentration of glutamate in the perilymph and elevated the compound action potential (CAP) threshold to 24.6 dB at 5 minutes. the CAP threshold subsequently recovered on reperfusion, gradually reaching 8.3 dB 120 minutes after reperfusion. Under electron microscopy, afferent dendrites of the cochlear nerve in contact with inner hair cells exhibited abnormal swelling 5 minutes after ischemia/reperfusion. These morphological changes were not observed in cochleas treated with an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate-type glutamate receptor antagonist, 6-7-dinitroquinoxaline-2,3-dione (DNQX), before hindbrain ischemia; an N-methyl-D-aspartate (NMDA)-type receptor antagonist, D-2-amino-5-phosphonopentanoate (D-AP5), was ineffective. Moreover, the histopathological alterations noted 5 minutes after reperfusion were spontaneously ameliorated 120 minutes after ischemia/reperfusion. These findings suggest that the ischemia-induced increase in extracellular glutamate concentration with subsequent activation of AMPA/kainate receptors is responsible for neurite degeneration and hearing loss in the early stages following transient hindbrain ischemia.

Topics: 2-Amino-5-phosphonovalerate; Animals; Audiometry, Evoked Response; Cerebrovascular Circulation; Cochlear Nerve; Deafness; Dendrites; Excitatory Amino Acid Antagonists; Gerbillinae; Glutamic Acid; Ischemic Attack, Transient; Neurons; Perilymph; Quinoxalines; Rhombencephalon

Five minutes of oxygen and glucose deprivation (termed "in vitro ischemia") causes long-term synaptic transmission failure (LTF) in the CA1 region of the rat hippocampal slice. Dependence of LTF on cell calcium was tested by generating graded reductions in cell Ca. There was a strong correlation between the average level of exchangeable cell Ca in CA1 during ischemia, and the extent of LTF. In standard buffer, exchangeable cell Ca in CA1 increased by 35% after 3 min of ischemia and remained elevated for the entire 5 min of ischemia. Unidirectional Ca influx increased by 35% during the first 2.5 min of ischemia and remained at that level for the next 2.5 min. There were no changes in unidirectional Ca efflux during this period. Thus, the accumulation results from increased influx of Ca. Ca influx during the first 2.5 min of ischemia depended entirely on NMDA channels; it was completely blocked by the noncompetitive NMDA receptor antagonist MK-801. However MK-801 had no effect during the second 2.5 min. This inactivation of NMDA-mediated influx during ischemia appears to result from dephosphorylation. Okadaic acid increased Ca influx during the second 2.5 min of ischemia and this increase was blocked by MK-801. The ischemia-induced Ca influx during the second 2.5 min of ischemia was attenuated 25% by nifedipine (50 microM) and an additional 35% by the Na/Ca exchange inhibitor benzamil (100 microM). The AMPA/kainate antagonist DNQX had no effect on the Ca influx. Antagonists were used to relate Ca influx to LTF. Blockade of enhanced Ca entry during ischemia in standard buffer (2.4 mM Ca) had no effect on LTF, consistent with total cell Ca prior to ischemia being adequate to cause complete LTF. However, MK-801 strongly protected against LTF when the buffer contained 1.2 mM Ca, a more physiological level. MK-801 combined with DNQX prevented transmission damage in standard buffer. Thus, AMPA/kainate receptor activation contributes to ischemic damage, although not by enhancing Ca entry.

Topics: Amiloride; Animals; Calcium; Dizocilpine Maleate; Ethers, Cyclic; Guanidines; Hippocampus; In Vitro Techniques; Ischemic Attack, Transient; Kinetics; Male; Microscopy, Electron; Okadaic Acid; Pyramidal Tracts; Quinoxalines; Rats; Rats, Sprague-Dawley; Time Factors

We studied the development of brain atrophy after transient focal ischemia in rats. The animals were subjected to cerebral ischemia induced by embolization of the right middle cerebral artery (MCA) for 60 min. The brains were studied morphologically 7 days, 1 month, 3 months and 9 months after recirculation. In addition, the effects of a new calcium antagonist, KB-2796, and a glutamate receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX); were evaluated in this model 1 month after ischemia. The hemispheric volume of the ipsilateral ischemic side, expressed as a percentage of that on the contralateral non-ischemic side, was 99% in the sham operation group, 94% at 7 days, 87% at 1 month, 68% at 3 months and 65% at 9 months. Atrophy of the striatum and cortex, but not the hippocampus, was observed 1 month after ischemia. Atrophy of the ipsilateral substantia nigra and the thalamus, which are remote from the ischemic region, was observed 7 days and 1 month, respectively, after ischemia. Correlations between the extent of the atrophy in the striatum and that in the substantia nigra and between the extent of the atrophy in the cortex and in the thalamus were statistically significant. Treatment with KB-2796 or DNQX administered intraperitoneally at a dose of 10 mg/kg twice 30 min before ischemia and immediately after ischemia was effective in reducing the extent of atrophy in both the ipsilateral ischemic and non-ischemic regions. These results suggest that brain atrophy on the ipsilateral ischemic side develops time-sequentially after transient focal ischemia and that ischemia affects not only the primary ischemic focus but also remote regions through transsynaptic connections, and that KB-2796 and DNQX have beneficial effects on atrophy in the chronic phase after ischemia.

Topics: Animals; Atrophy; Brain; Calcium Channel Blockers; Cerebral Arteries; Excitatory Amino Acid Antagonists; Ischemic Attack, Transient; Male; Piperazines; Quinoxalines; Rats; Rats, Wistar; Time Factors