Glutamate Injury–Induced Epileptogenesis in Hippocampal Neurons

Abstract

Background and Purpose-Stroke is the major cause of acquired epilepsy. The mechanisms of ischemia-induced epileptogenesis are not understood, but glutamate is associated with both ischemia-induced injury and epileptogenesis in several models. The objective of this study was to develop an in vitro model of epileptogenesis induced by glutamate injury in hippocampal neurons as observed during stroke. Methods-Primary hippocampal cultures were exposed to 5 mol/L glutamate for various durations. Whole-cell current clamp electrophysiology was used to monitor the acute effects of glutamate on neurons and chronic alterations in neuronal excitability up to 8 days after glutamate exposure. Results-A single, 30-minute, 5-mol/L glutamate exposure produced a subset of neurons that died and a larger population of injured neurons that survived. Neuronal injury was characterized by prolonged reversible membrane depolarization, loss of synaptic activity, and neuronal swelling. Surviving neurons manifested spontaneous, recurrent, epileptiform discharges in neural networks characterized by paroxysmal depolarizing shifts and high-frequency spike firing that persisted for the life of the culture. Conclusions-This study demonstrates that glutamate injury produced a permanent epileptiform phenotype expressed as spontaneous, recurrent epileptiform discharges for the life of the hippocampal neuronal culture. These results suggest a novel in vitro model of glutamate injury-induced epileptogenesis that may help elucidate some of the mechanisms that underlie stroke-induced epilepsy.

Thrombin Induces Long-Term Potentiation of Reactivity to Afferent Stimulation and Facilitates Epileptic Seizures in Rat Hippocampal Slices: Toward Understanding the Functional Consequences of Cerebrovascular Insults

“…Likewise, 500 M but not 100 M glutamate could produce spontaneous seizure-like activity in the slice (Fig. 2 B) (n ϭ 9 slices) (Sun et al, 2001). However, in presence of thrombin, the lower concentration of K ϩ (4 mM) and glutamate (100 M) did produce seizure-like activity.…”

In vitro status epilepticus but not spontaneous recurrent seizures cause cell death in cultured hippocampal neurons

“…Both control and low Mg 2+ exposed neurons were treated identically. Glutamate was measured by enzymatic fluorometric assay with a CMA 600 Microdialysis Analyzer (Didier et al, 1990;Sun et al, 2001).…”

“…Neuronal death was assessed at various time points after low Mg 2+ exposure using fluorescein diacetate (FDA)-propidium iodide (PI) microfluorometry (Didier et al, 1990;Sun et al, 2001). The two-dye method allows for the identification of viable and non-viable neurons in the same neuronal field.…”

Incidence and Associations of Poststroke Epilepsy

“…[2][3][4][5] Hemorrhagic strokes, cortical lesions, and large lesions are most consistently associated with poststroke seizures, 6 defined as early or late, based on timing and differing pathophysiology. [7][8][9][10] A wide range (2% to 67%) of patients has been reported for the risk of early or late seizures after ischemic stroke, 11 whereas intracerebral and subarachnoid hemorrhages have been associated with a range of between 8% and 15% over varying durations of follow-up. 6 There is insufficient evidence to reliably predict those who will have development of PSE and would benefit from prophylactic antiepileptic treatment.…”