Abstracts

Rationale: Animal models of status epilepticus (SE) have shown a progression of glutamate-mediated neuronal destruction with increasing duration. Depending on the induction model, animals progress through SE with varying time courses, from hours to days. Therefore, duration of SE is not a reliable predictor of the degree of damage. Treiman et al. (Epilepsy Res. 1990; 5: 49-60) described a predictable progression of EEG patterns in SE that varied little across species and across different induction models: stage I - discrete seizures; stage II - merging of seizures; stage III - continuous ictal activity; stage IV -continuous ictal pattern with periods of attenuation; stage V - PLEDs. Our objective was to correlate EEG stage of SE with the degree of necrosis. A supplementary objective was to evaluate what degree of pathology, if any, corresponds with prolonged PLEDs. Methods: 36 Male Sprague Dawley rats were implanted with EEG electrodes. SE was induced with an IP injection of lithium chloride followed by subcutaneous injection of pilocarpine. SE was terminated by IP injection of diazepam and phenobarbital after the animals' progression to their respective stage of SE. Of the 30 rats that survived, 6 were terminated at stage I (discrete seizures), 6 at stage III (continuous ictal pattern), 7 at stage V (PLEDS), and 6 at stage V plus 4 hours. Three pre-treatment controls and two sham controls were analyzed for comparison. Seven days post-SE, animals were sacrificed. The brains were removed, fixed, frozen and sectioned at 40 microns in the coronal plane through the hippocampus. One set of sections was stained with H&E and a second was stained with de Olmos amino cupric silver stain, which stains necrotic neuronal cell bodies, axons, and dendrites black. 23 brain regions were inspected. H&E sections were analyzed at 20x with a Zeiss light microscope. De Olmos stained sections were photographed at 2.5x at 3 levels corresponding to 0.20 mm, 3.30 mm, and 5.60 mm from Bregma. With ImageJ software (NIH), densiometry was used to quantify the degree of necrosis in each of the 23 regions. Treatment groups were compared to one another using appropriate statistical models. Results: pre-treatment controls and stage I rats showed sparse, non-specific degeneration. In stage III, regional damage became apparent, particularly in the hippocampus (CA1 and CA3) as well as the striatum and cortex. Degeneration increased in stage V (PLEDs), particularly in the cortex, striatum, and thalamus. In Stage V plus 4 hours, progression of neuronal degeneration was noted in most brain regions. The quantitative analysis will be discussed further on the poster. Conclusions: EEG stage correlates with the degree of neuronal degradation. Furthermore, additional neuronal degeneration occurred in the 4 hours after rats entered stage V (PLEDs) of SE, providing evidence that PLEDs denote a physiologic process that is not benign. This study will be repeated using different induction models to see if the correlation between EEG stage and extent of necrosis persists, independent of the duration of SE.