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The Journal of Neuroscience, 2000, 20:RC79:1-5
RAPID COMMUNICATION
Accumulation of Zinc in Degenerating Hippocampal Neurons of
ZnT3-Null Mice after Seizures: Evidence against Synaptic Vesicle
Origin
Joo-Yong
Lee1,
Toby B.
Cole2,
Richard D.
Palmiter2, and
Jae-Young
Koh1
1 National Creative Research Initiative Center for the
Study of CNS Zinc, University of Ulsan College of Medicine, Seoul
138-736, Korea, and 2 Howard Hughes Medical Institute,
Department of Biochemistry, University of Washington, Seattle,
Washington 98195
In several brain injury models, zinc accumulates in degenerating
neuronal somata. Suggesting that such zinc accumulation may play a
causal role in neurodegeneration, zinc chelation attenuates neuronal
death. Because histochemically reactive zinc is present in and released
from synaptic vesicles of glutamatergic neurons in the forebrain, it
was proposed that zinc translocation from presynaptic terminals to
postsynaptic neurons may be the mechanism of toxic zinc accumulation.
To test this hypothesis, kainate seizure-induced neuronal death was
examined in zinc transporter 3 gene (ZnT3)-null mice, a
strain that completely lacks histochemically reactive zinc in synaptic
vesicles. Intraperitoneal injection of kainate induced seizures to a
similar degree in wild type and ZnT3-null mice. Staining
of hippocampal sections with a zinc-specific fluorescent dye,
N-(6-methoxy-8-quinolyl)-p-carboxybenzoylsulfonamide,
revealed that zinc accumulated in degenerating CA1 and CA3 neurons
in both groups, indicating that zinc originated from sources other than synaptic vesicles. Injection of CaEDTA into the cerebral ventricle almost completely blocked zinc accumulation in ZnT3-null
mice, suggesting that increases in extracellular zinc concentrations may be a critical event for zinc accumulation. Arguing against the
possibility that zinc accumulation results from nonspecific breakdown
of zinc-containing proteins, injection of kainate into the cerebellum
did not induce zinc accumulation in degenerating granule neurons. Taken
together, these results support the existing idea that zinc is released
into extracellular space and then enters neurons to exert a cytotoxic
effect. However, the origin of zinc is not likely to be synaptic
vesicles, because zinc accumulation robustly occurs in
ZnT3-null mice lacking synaptic vesicle zinc.
Key words:
TFL-Zn; neuronal degeneration; zinc transporter; kainate; cerebellum: CaEDTA
Copyright © 2000 Society for Neuroscience 0270-6474/00/$05.00/0
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