Abstract
Intravenously administered nimodipine (an L-type Ca<sup>2+</sup> antagonist) as well as dizocilpine (an N-methyl-D-aspartate – NMDA – antagonist) showed a wide spectrum of anticonvulsant activity in intracerebroventricular mouse models for excessive activation of excitatory amino acid receptors. The duration of Bay k-8644 (L-type Ca<sup>2+</sup> agonist; intracerebroventricular administration) caused seizures was significantly reduced by intravenously administered nimodipine. Intracisternal administration of Bay k-8644 lowered the convulsion threshold of an intracerebroventricular injection of NMDA. Intracisternal administration of ω-conotoxin GVIA (N-type Ca<sup>2+</sup> antagonist) only tended to inhibit the NMDA-induced tonic convulsions. Intracisternal administration of staurosporine (a protein kinase C inhibitor) or calmidazolium (a calmodulin antagonist) was effective in inhibiting the NMDA-induced tonic convulsions. Calmidazolium, unlike staurosporine, produced side effects at a dose showing its anticonvulsant activity. From these results, it is suggested that excessive activation of excitatory amino acid receptors results in tonic convulsions by virtue of a massive increase of Ca<sup>2+</sup> influx mainly through NMDA receptor channels, and at least in part through L-type Ca<sup>2+</sup> channels, and in subsequent activation of protein kinase C and possibly calmodulin.
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