Responsiveness to kainate in young rats after 2-week zinc deprivation |
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Authors: | Atsushi Takeda Hiromasa Itoh Haruna Tamano Naoto Oku |
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Institution: | (1) Department of Medical Biochemistry, School of Pharmaceutical Sciences, University of Shizuoka, 52- 1 Yada, Shizuoka 422-8526, Japan |
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Abstract: | On the basis of the evidence of the enhanced susceptibility to kainate-induced seizures in young rats fed a zinc-deficient
diet for 4 weeks, the relationship between zinc release from hippocampal neuron terminals and seizure susceptibility was studied
in young rats fed the zinc-deficient diet for 2 weeks. Timm’s stain, with which histochemically reactive zinc in the presynaptic
vesicle is detected, was not attenuated in mossy fibers and other areas in the hippocampus after 2-week zinc deprivation,
whereas the attenuation was observed after 4-week zinc deprivation. Extracellular zinc concentration was not also decreased
after 2-week zinc deprivation, unlike the case after 4-week zinc deprivation. To check the capacity for zinc release from
neuron terminals after 2-week zinc deprivation, the hippocampus was excessively stimulated with 100 mM KCl. The increase in
extracellular zinc concentration of zinc-deficient group was significantly more than that of control group. These results
suggest that zinc release from hippocampal neuron terminals is not affected by 2-week zinc deprivation. On the other hand,
the latency in myoclonic jerks of zinc-deficient group was significantly shorter than in the control group after treatment
with kainate, while the latency in clonic convulsions was not different between the two groups. Intracellular fura-2 signal,
a calcium indicator, was significantly higher in the hippocampal CA3 areas of zinc-deficient group 4 s after delivery of kainate
to dentate granule cells. These results suggest that susceptibility to kainate-induced seizures is altered prior to the decrease
in extracellular zinc concentration and zinc release from neuron terminals in zinc-deficient young rats. The alteration of
calcium signaling seems to be involved in the susceptibility in zinc deficiency. |
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Keywords: | calcium hippocampus kainate seizure zinc |
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