Abstracts

Despite a large amount of electrophysiological data obtained from human slices resected from patients with intractable epilepsy, few consistent differences have been observed between epileptogenic and juxta-epileptogenic tissue. The purpose of this study is to determine whether differences observed using electrocorticography (EcoG) could be related to cellular function in an [italic]in vitro [/italic]preparation.
Human neocortical tissue was removed from patients with medically intractable epilepsy using a protocol approved by the IRB at the University of Chicago. EcoG, source localization and clinical relevance determined the sites selected for the slice studies. In this study, slices for electrophysiological recordings were selected only when clear differences between the epileptic foci and surrounding areas were observed on intracranial EEG monitoring. Upon resection, the tissue was placed into artificial CSF (aCSF in mM: 118 NaCl, 3 KCl, 1.5 CaCl[sub]2[/sub], 1 Mg Cl[sub]2[/sub], 25 NaHCO[sub]3[/sub], 1 NaH[sub]2[/sub]PO[sub]4[/sub] and 30 D-glucose, pH of 7.4) bubbled with carbogen (95% O[sub]2[/sub] and 5 % CO[sub]2[/sub]). Slices (500 [mu]m) were sectioned perpendicular to the gyri such that the 6-layered cortex could be identified. The slices were immediately transferred to aCSF bubbled with carbogen at room temperature. Experiments were conducted in a recording chamber at 29[deg] C. After 30 minutes the [K⁺][sub]o[/sub] concentration of the aCSF was raised from 3 to 5 mM. Population recordings were obtained with suction electrodes positioned onto the surface of the cortical layers. Intra- and extracellular recordings were simultaneously obtained from human cortical slices.
In 3 patients, differences at the cellular level were observed between slices taken from the epileptic foci compared to juxta-epileptogenic tissue. Application of 5-15 [mu]M NMDA and/or 20 [mu]M bicuculline resulted in conversion of the regular spiking (RS) pattern into a paroxysmal depolarization shift (PDS) in neurons of the focus (5 of 7 neurons), while those of the least abnormal areas did not demonstrate a PDS pattern with the exception of a single neuron (1 of 7). Application of lamotrigine (160 [mu]M) resulted in conversion of the PDS into a more RS-like pattern (n=2).
The present study demonstrates that under certain circumstances electrophysiological differences between the most and least abnormal areas can be observed. PDS, a hallmark of epilepsy, was observed primarily from neurons obtained from the focus. The identification of electrically significant differences between the two tissue types will allow for more directed analysis at the molecular biology level.
[Supported by: NIH HL60120 (JMR)
PEW Fellowship (FP)
PACE (CJM)
Falk Foundation (CJM, WvD, KEH)
NIH F32HL67659 (AKT)]