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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cerebellar Purkinje cells are selectively vulnerable to ischemia, although the reasons for this are unknown. In cultured embryonic rat cerebellar neurons, the steady state responses to the desensitizing agonist AMPA relative to responses to the nondesensitizing agonist kainate were greater in Purkinje cells compared to other cells, as measured by whole cell voltage clamp studies. Fluorimetric [Ca2+]i imaging experiments similarly found greater responses to AMPA relative to kainate in Purkinje cells than in other cerebellar neurons. In toxicity experiments measuring cell survival 24 hr following agonist exposure, AMPA and glutamate produced Ca(2+)-dependent toxicity which was selective for the Purkinje cell fraction of the neurons, whereas kainate produced nonselective toxicity, and NMDA selectively spared the mature Purkinje cells. Cyclothiazide, which inhibits AMPA receptor desensitization, enhanced steady state current responses to AMPA and increased the toxicity of AMPA. We conclude that the vulnerability of cerebellar neurons in culture to glutamate agonist-induced toxicity parallels the magnitude of the steady state currents produced, and that Purkinje cells may be selectively vulnerable because they express AMPA receptors which undergo less complete desensitization.
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PMID:AMPA receptor desensitization predicts the selective vulnerability of cerebellar Purkinje cells to excitotoxicity. 754 Jun 78

In order to characterize the regional and cellular distribution patterns of individual ionotropic excitatory amino acid receptor subunits in the human hippocampus we performed an immunohistochemical analysis using the monoclonal antibody 3A11 to the AMPA GluR2(4) subunit. The study was based on paraffin embedded hippocampal specimens of five human brains obtained at autopsy. GluR2(4) immunoreactivity was consistently higher in hippocampus as compared to the adjacent areas of the mesial temporal lobe. Virtually all neurons showed intracytoplasmic staining of the perikarya and dendritic profiles with well defined laminar patterns. The most intense GluR2(4) immunoreactivity was observed in the target structures of mossy fibers, thus indicating that GluR2(4) AMPA subunits may be involved in NMDA-independent synaptic transmission pathways and long-term potentiation. Glial cells were not immunoreactive. These findings may provide basic information for studies of the GluR2(4) subunit in human hippocampus during various neuropathological conditions, such as temporal lobe epilepsy, ischemia and Alzheimer's disease.
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PMID:Regional distribution of the AMPA glutamate receptor subunits GluR2(4) in human hippocampus. 755 21

Thalamic reticular (RT) neurons are selectively vulnerable to degeneration following global ischemia. The degenerative mechanism is thought to involve an excitotoxic component, mediated in part by sustained post-ischemic activation of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) type excitatory amino acid (EAA) receptors. In order to test this hypothesis, the selective competitive AMPA type EAA antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F) quinoxalinedione) was administered at 30 mg/kg to rats 1, 3, and 6 h after resuscitation from 10 min cardiac arrest. NBQX treatment resulted in a 2-fold increase of spared RT neurons, from a mean density of 3.6 +/- 0.8 x 10(3) neurons/mm3 in cardiac arrest cases to 7.4 +/- 1.1 x 10(3) neurons/mm3 in the NBQX treated group, which represents sparing of 41.7% of the normal population of RT neurons, and protection of 26.9% of vulnerable RT neurons. Neurons within the central core of the RT manifest both a higher degree of vulnerability to ischemic degeneration, > 92% loss, and a higher sensitivity to sparing following NBQX administration, 460% increased sparing, than neuronal sub-populations in the medial or lateral 1/3 of the RT. Protection by post-arrest administration of NBQX suggests that sustained post-arrest stimulation of AMPA receptors is an important component in the process of ischemic degeneration of RT neurons.
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PMID:The AMPA antagonist NBQX protects thalamic reticular neurons from degeneration following cardiac arrest in rats. 755 36

This study examines the relationship between the concentration of extracellular glutamate released during 30 min of forebrain ischemia, and the subsequent development of ischemic neural necrosis, in the presence of three agents which act at distinct sites on the glutamatergic synapse: a presynaptic inhibitor of glutamate release (5-(2,3,5-trichlorophenyl)-2,4-diamino-pyramidine ethane sulphonate (BW1003C87)); a competitive NMDA receptor antagonist (cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS19755)); and a competitive AMPA receptor antagonist (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX)). Pretreatment with either BW1003C87 or NBQX markedly attenuated the peak concentration of extracellular glutamate and offered protection from post-ischemic neuronal necrosis in the CA1 hippocampus. In contrast, pretreatment with CGS19755 had no effect on extracellular glutamate release and did not protect CA1 hippocampal neurons from ischemic injury.
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PMID:BW1003C87 and NBQX but not CGS19755 reduce glutamate release and cerebral ischemic necrosis. 781 84

Severe forebrain ischemia induces a large increase in expression of NMDA receptor subunits in rat brain. One week after ischemia, levels of NMDA-R1 mRNAs in the CA1 pyramidal cells of hippocampus are 7 times higher than those observed in control rats. At 7 days postischemia, an enhanced immunostaining of the NMDA-R1 subunit was observed in all hippocampal structures indicating that changes in mRNA levels are accompanied by changes in receptor protein level. Riluzole, a potent inhibitor of glutamate release and CNQX, a selective AMPA/kainate antagonist, drastically reduced the ischemia-induced expression of mRNAs for the three NMDA receptor subunits while D-AP5, a selective NMDA antagonist, had essentially no effect. Therefore ischemia-induced expression of NMDA receptor subunits is associated with glutamate release and proceeds via an AMPA/kainate pathway. These results together with those of other groups concerning ischemia effects on AMPA and GABAA receptor levels, suggest an important role of the induced expression of NMDA receptor subunits in the deleterious effects of ischemia.
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PMID:Glutamate-induced overexpression of NMDA receptor messenger RNAs and protein triggered by activation of AMPA/kainate receptors in rat hippocampus following forebrain ischemia. 782 Jun 82

Protein synthesis was measured in hippocampal slices which were exposed to glutamate (1 mM or 10 mM) or which were deprived of glucose and oxygen ('in vitro ischemia') for 15 min. Glutamate at 1 mM, a concentration estimated to occur during in vivo ischemia did not affect protein synthesis. Ten mM glutamate inhibited protein synthesis immediately after exposure (50% of control values) and reduced ATP levels to about 30% of the control. After two hours, slices fully recovered their protein synthesis and energy metabolism. The effect of 10 mM glutamate was not receptor-mediated, as NMDA, AMPA, or metabotropic receptor antagonists failed to block the glutamate effect. Immediately after ischemia, protein synthesis was reduced to 30% of control values, and 2 hours later it was still depressed to one-half of control values. Energy charge, however, recovered completely. Ischemic inhibition of protein synthesis was not reversed by glutamate receptor antagonists. The data indicate that inhibition of protein synthesis in hippocampal slices during ischemia is not glutamate-dependent.
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PMID:Protein synthesis in the hippocampal slice: transient inhibition by glutamate and lasting inhibition by ischemia. 783 66

In a model of perinatal hypoxic-ischemic brain damage, we examined the neuroprotective efficacy of posttreatment with the NMDA receptor antagonist MK-801 and the AMPA receptor antagonist NBQX. Unilateral brain damage developed in 95% of rat pups subjected to hypoxia-ischemia with a 27.8 +/- 1.2% weight deficit of the damaged hemisphere. MK-801 in doses of 0.3 and 0.5 mg/kg i.p. reduced the brain damage by 61% (p < 0.001) and 43% (p < 0.001), respectively. A higher dose of MK-801 (0.75 mg/kg) did not offer neuroprotection. Treatment with NBQX (40 mg/kg) reduced the hemispheric lesion by 28% (p < 0.05). In conclusion, posttreatment with both NBQX and low doses of MK-801 reduced perinatal brain damage. The NMDA receptor antagonist offered stronger neuroprotection which is in agreement with a proposed NMDA receptor hyperactivity around postnatal day 7 in rats.
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PMID:Hypoxia-ischemia in the neonatal rat brain: histopathology after post-treatment with NMDA and non-NMDA receptor antagonists. 786 35

Several reports have indicated that the two glutamate receptor antagonists, dizocilpine (that binds to the phencyclidine recognition site of the NMDA (N-methyl-D-aspartate) receptor) and NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline, that binds to the AMPA (alpha-amino-3-hydroxy-5-methyl-isoxazole) receptor), protect neurons against damage caused by hypoxia, ischemia or excitotoxicity. We, therefore, used a combination of these drugs to achieve enhanced neuroprotection. Primary cultures of rat hippocampal neurons were challenged by glutamate intoxication. Both dizocilpine and NBQX produced dose-dependent increases in the percentage of viable neurons. Combined treatment with both glutamate receptor antagonists had an over-additive neuroprotective effect. Simultaneous administration of dizocilpine and NBQX also had a pronounced neuroprotective effect in vivo in mice subjected to focal cerebral ischemia and rats with global forebrain ischemia. This suggest that such a combination may have therapeutic relevance.
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PMID:Over-additive protective effect of dizocilpine and NBQX against neuronal damage. 791 Oct 83

The synapses between the inner hair cells (IHCs) and the radial auditory dendrites are thought to be glutamatergic. Besides its fast excitatory properties, glutamate is known to be neurotoxic when released in excess or incompletely recycled. In the cochlea, this may occur in two pathological conditions: ischemia and noise trauma. We have further investigated the acute excitotoxicity (i.e. the swelling of type I afferent dendrites) by electron microscopy processing on guinea pig cochleas after an ischemic exposure lasting 5 to 40 min. The radial auditory dendrites reacted to ischemia in a time-dependent manner, with the swelling extending when the duration of ischemia increased. The type and the specificity of swelling were comparable to what acutely occurs after an exposure to glutamate analogs such as kainic acid or AMPA. A protection against this swelling was obtained by perfusing the cochlea with glutamate antagonists prior to ischemia. DNQX, an antagonist at AMPA/kainate receptors, had a powerful protective effect, and almost complete protection was obtained by perfusing both DNQX and D-AP5 (a NMDA antagonist). The latter results indicate that the two classes of glutamate receptors (AMPA/kainate and NMDA), both found to be electrophysiologically active at the IHC-auditory nerve synapse, are also involved in the excitotoxic processes. In addition, we also report data involving dopamine (its D2 agonist piribedil) a putative neurotransmitter at the lateral efferent synapses, in a postsynaptic protection of primary auditory neurons during transient ischemia. Altogether, these findings constitute a promising pharmacological approach of cochlear pathologies such as neural presbycusis.
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PMID:Pathophysiology of the glutamatergic synapses in the cochlea. 810 Jan 8

The autoradiographic distribution of N-methyl-D-aspartate (NMDA) and D,L-a-amino-3-hydroxyl-5-methyl-4-isoxazoleproprionic acid/quisqualate (AMPA/QUIS) receptors was determined in cerebellum obtained at autopsy from 37 human individuals, aged from 24 weeks gestation to 95 years. [3H]MK801 was used to label the NMDA receptor and [3H]CNQX to label the AMPA/QUIS receptor. AMPA/QUIS receptors were concentrated in the cerebellar molecular layer, and NMDA receptors in the granular layer. Significant (3- to 4-fold) increases in binding were seen for both ligands from the fetal to neonatal periods in the molecular layer (CNQX) and in both molecular and granular layers (MK801). MK801 binding in the molecular layer continued to increase with age up to the tenth decade and together with binding in the granular layer, increased 2-fold between 10-40 years. The Purkinje cell layer was negative for MK801 binding until the 6-7th decade when it became positive. [3H]CNQX binding in the molecular layer increased significantly with age between the fetal period and the tenth decade, whereas in the granular layer binding increased from neonate to 40 years, but then decreased significantly from 60 years to the tenth decade. Lamination of the molecular and granular layers was absent during the fetal period and appeared with both ligands during the neonatal period. These marked differences in age-related expression of ligand binding sites in the granular layer during development and aging are of potential significance in relation both to selective vulnerability to ischemia, and synaptic plasticity and remodelling related to neuronal loss in senescence.
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PMID:Autoradiographic comparison of the distribution of [3H]MK801 and [3H]CNQX in the human cerebellum during development and aging. 810 15


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