Abstracts

Rationale: Several publications have reported spontaneous recurrent seizures in animal models of acquired epilepsy based on brain insults proposed to be more realistic than previous models. These studies have reported brief periods of oscillatory, spike-and-wave discharges (SWDs) with blank-stare behaviors, which have been considered to represent the non-convulsive seizures of acquired epilepsy. A critical problem, however, is that similar events are also seen in normal animals (i.e., non-injured controls). The present studies aim to compare these normal electrographic events with non-convulsive and convulsive seizures recorded in several diverse animal models of acquired epilepsy. Methods: In addition to pilocarpine- and kainate-induced status epilepticus, animal models (rats) included unilateral carotid occlusion with hypoxia at postnatal day 7, controlled cortical impact in adults, and a model of penetrating brain injury in adults. Several chronic-recording techniques were used across the different laboratories and animal models. Results: SWD-like events in normal rats were much shorter in duration than the non-convulsive and convulsive seizures in the models of acquired epilepsy (see Methods, above). Normal SWD events were typically <5-10 sec, but could be longer; in contrast, the convulsive/non-convulsive seizures in diverse models of acquired epilepsy were routinely 20-40 sec, but could also be longer (e.g., 2-3 min). The SWD-like events typically started abruptly with little or no "build-up", whereas the non-convulsive/convulsive seizures in the brain-injured rats typically began with a progressive increase in amplitude and/or frequency. The inter-spike intervals were relatively homogeneous during normal SWD, while the frequency of EEG spikes in the non-convulsive and convulsive seizures was typically more variable with distinct shifts in pattern. The non-convulsive/convulsive seizures often had post-ictal depression, which was not seen with the SWDs or other rhythmic events in normal rats. Conclusions: Readily observable and quantifiable electrographic properties of SWD in normal rats (and after postnatal hypoxia or fluid percussion injury, see abstract by Barth, Dudek and Rodgers) could be readily distinguished from the seizures characteristic of acquired epilepsy. The non-convulsive and convulsive seizures in these diverse models of brain injury (see Methods, above) were much more similar to each other than they were to the normal SWDs. Research support: NIH and DoD