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Ischemic damage in hippocampal CA1 is dependent on glutamate release and intact innervation from CA3
H Benveniste1, M B Jørgensen, M Sandberg
1Institute of Neuropathology, University of Copenhagen, Denmark.
Insights
Glutamate release from CA3 neurons exacerbates hippocampal damage during ischemia. Protecting CA1 pyramidal cells requires blocking this glutamate pathway, highlighting its role in excitotoxicity.
Area of Science:
- Neuroscience
- Neurobiology
- Cellular Neuroscience
Background:
- CA1 pyramidal cells are vulnerable to transient global ischemia.
- Glutamatergic afferents from CA3 to CA1 are implicated in ischemic neuronal damage.
- Previous studies show CA3 destruction protects CA1 cells during ischemia.
Purpose of the Study:
- To investigate the pathogenetic significance of glutamate in CA1 ischemic injury.
- To quantify glutamate release in intact versus CA3-lesioned CA1 hippocampal tissue during ischemia.
- To assess the neurotoxic potential of ischemia-induced glutamate release.
Main Methods:
- Measurement of glutamate release in intact and CA3-lesioned CA1 hippocampal tissue during transient global ischemia.
- Intra-CA1 injection of glutamate at concentrations mimicking ischemia-induced release.
- Assessment of CA1 pyramidal cell survival following glutamate injection under ischemic and non-ischemic conditions.
Main Results:
- Glutamate levels increased sixfold in intact CA1 during ischemia.
- Glutamate levels increased only 1.4-fold in CA3-lesioned CA1 during ischemia.
- Ischemia-induced glutamate concentrations were neurotoxic to CA1 pyramidal cells, especially when injected during ischemia in CA3-lesioned tissue.
Conclusions:
- Ischemia-induced damage to CA1 pyramidal cells is critically dependent on glutamate release.
- Intact glutamatergic innervation from the CA3 region is essential for this excitotoxic damage.
- Targeting CA3-CA1 glutamatergic pathways may offer neuroprotection against ischemic brain injury.
Abstract:
The removal of glutamatergic afferents to CA1 by destruction of the CA3 region is known to protect CA1 pyramidal cells against 10 min of transient global ischemia. To investigate further the pathogenetic significance of glutamate, we measured the release of glutamate in intact and CA3-lesioned CA1 hippocampal tissue. In intact CA1 hippocampal tissue, glutamate increased sixfold during ischemia; in the CA3-lesioned CA1 region, however, glutamate only increased 1.4-fold during ischemia. To assess the neurotoxic potential of the ischemia-induced release of glutamate, we injected the same concentration of glutamate into the CA1 region as is released during ischemia in normal, CA3-lesioned, and ischemic CA1 tissue. We found that this particular concentration of glutamate was sufficient to destroy CA1 pyramids in the vicinity of the injection site in intact and CA3-lesioned CA1 tissue when administered during control (non-ischemic) conditions. In contrast, the same amount injected during ischemia in the CA3-lesioned CA1 region destroyed pyramidal cells in a widely distributed zone around the injection site in the CA1 region. It is concluded that the ischemia-induced damage of pyramidal cells in CA1 is dependent on glutamate release and intact innervation from CA3.