Extracellular K+ and Ca2+ changes during epileptiform discharges in the immature rat neocortex.
Picrotoxin-induced epileptiform activity was examined in neocortical slices prepared from 8- to 15-day-old rats. This activity consisted of spontaneous bursts of 3-5 discharges that resembled interictal spikes and were interspersed with ictal-like paroxysms lasting 10-30 s. Measurements of extracellular potassium ([K+]o) and calcium ([Ca2+]o) were made during these spontaneous epileptiform events, using ion-sensitive electrodes. Individual interictal spikes were associated with [Ca2+]o decreases of 0.1-0.2 mM, whereas sustained ictal-like discharges were accompanied by decreases of 0.3-0.4 mM. Measurement of [K+]o showed that individual interictal spikes were associated with increases in [K+]o up to 12 mM, whereas increases to more than 20 mM accompanied long-lasting ictal-like discharges. Maximum increases in [K+]o were observed ca. 600 microns below the pial surface. [K+]o increases were followed by undershoots of the resting [K+]o level. The unusually high [K+]o levels associated with epileptiform discharges in the immature neocortex suggest that disturbances in [K+]o regulation may contribute to the generation of the picrotoxin-induced, spontaneous, prolonged ictal-like discharges observed in the 8- to 15-day age group.
Department of Neurology, Baylor College of Medicine, Houston, Texas 77030.
J J
JJ
Hablitz
U
U
Heinemann
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D004827:Epilepsy / Q000139:chemically induced / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008839:Microelectrodes; D010852:Picrotoxin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D051381:Rats
D002118:Calcium; D010852:Picrotoxin; D011188:Potassium