In Vitro Model of Epileptiform Electrical Activity in Kainate- Treated Organotypic Hippocampal Slices

Summary: Rationale: Administration of kainate to rodents in vivo produces temporal lobe lesions, followed several weeks later by the development of delayed spontaneous recurrent motor seizures (Cavalheiro et al. Electroencephalogr. Clin. Neurophysiol. 1982;53:581). Cell loss also occurs following kainate administration to hippocampal slices (Best et al., Eur. J. Neurosci. 1996;8:2109). The present study investigated whether kainate applied in vitro produces subsequent chronic spontaneous epileptiform electrical activity. Methods: Hippocampal slices (400 mM thick; P9 neonatal rats) were cultured (Stoppini et al., J. Neurosci. Methods 1991;37:173) for 5–7 weeks. Organotypic slices were exposed to 5 mM kainate for 24 h, 3 weeks post-cutting and extracellular electrophysiological recordings made 2–3 weeks post-kainate treatment. Results: Propidium iodide revealed cell death, particularly in CA3, in response to the kainate. Spontaneous interictal (short spontaneous bursts 96 ± 20A ms duration, n = 7) and/or “ictal” (long spontaneous bursting, ranging from 120 s to continuous, n = 10) electrical activity was detected in CA1 of all kainate-treated slices. Very little or no spontaneous discharges were detected in control slices (n = 12). Both forms of activity were completely inhibited by the Na channel blocker tetrodotoxin (0.1 mM, n = 3). Interictal activity was completely inhibited by the anticonvulsant lamotrigine (IC50= 51 mM, 28–91 mM, 95% confidence limits, n = 3). However, lamotrigine had no effect on the “ictal” activity (up to 300 mM, n = 3). Discussion: Chronic spontaneous interictal and/or “ictal” epileptiform activity was detected 2–3 weeks following kainate-induced cell loss in cultured hippocampal slices. Pharmacological characterization of the electrical discharges and the potential refractoriness of the “ictal” activity are currently under investigation.