Calcium-dependent epileptogenesis in an in vitro model of stroke-induced "epilepsy".
OBJECTIVE
Stroke is the most common cause of acquired epilepsy. The purpose of this investigation was to characterize the role of calcium in the in vitro, glutamate injury-induced epileptogenesis model of stoke-induced epilepsy.


METHODS
Fura-2 calcium imaging and whole-cell current clamp electrophysiology techniques were used to measure short-term changes in neuronal free intracellular calcium concentration and long-term alterations in neuronal excitability in response to epileptogenic glutamate injury (20 microM, 10 min) under various extracellular calcium conditions and in the presence of different glutamate-receptor antagonists.


RESULTS
Glutamate injury-induced epileptogenesis was associated with prolonged, reversible elevations of free intracellular calcium concentration during and immediately after injury and chronic hyperexcitability manifested as spontaneous recurrent epileptiform discharges for the remaining life of the cultures. Epileptogenic glutamate exposure performed in solutions containing low extracellular calcium, barium substituted for calcium, or N-methyl-d-aspartate (NMDA)-receptor antagonists reduced the duration of intracellular calcium elevation and inhibited epileptogenesis. Antagonism of non-NMDA-receptor subtypes had no effect on glutamate injury-induced calcium changes or the induction epileptogenesis. The duration of the calcium elevation and the total calcium load statistically correlated with the development of epileptogenesis. Comparable elevations in neuronal calcium induced by non-glutamate receptor-mediated pathways did not cause epileptogenesis.


CONCLUSIONS
This investigation indicates that the glutamate injury-induced epileptogenesis model of stroke-induced epilepsy is calcium dependent and requires NMDA-receptor activation. Further, these experiments suggest that prolonged, reversible elevations in neuronal free intracellular calcium initiate the long-term plasticity changes that underlie the development of injury-induced epilepsy.
Sun
David A
DA
Departments of Pharmacology and Toxicology, and the Graduate Program in Neuroscience, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Sombati
Sompong
S
Blair
Robert E
RE
DeLorenzo
Robert J
RJ
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004827:Epilepsy / Q000139:chemically induced / Q000209:etiology* / Q000473:pathology / Q000517:prevention & control; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects; D007425:Intracellular Membranes / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000187:drug effects; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D020521:Stroke / Q000150:complications*; D013997:Time Factors
D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D002118:Calcium