Abstracts

Rationale: Transgenic mice offer tools to obtain insights into molecular mechanisms underlying pathophysiological processes. However, the pilocarpine model of status epilepticus(SE), which is commonly used in mice, is associated with high mortality. We have developed another model of SE in mice using continuous hippocampal stimulation (CHS).   Methods: Adult male and female C57Bl/6 mice were implanted with bipolar insulated stainless steel electrode in the left hippocampus, bilateral supra-dural cortical electrodes and a reference cerebellar electrode. A 0.75 msec biphasic square wave pulse at 50 Hz was applied for 10 s to determine after discharge threshold (ADT). The stimulation intensity was set to twice ADT and cycles of 10 sec stimulation followed by a 5 sec off period were applied for 60 min. Animals were monitored by continuous video-EEG recordings during and after the stimulation. Animals were classified to be in SE when the electrographic seizure activity lasted for 15 min or longer after the end of stimulation. End of SE was marked by irregular spikes at less than 1 Hz frequency. Neurodegeneration was assessed using fluorojade-C labeling 3 days following SE. Starting 2 weeks after SE, the animals were monitored for recurrent spontaneous seizures.  Results: The mean ADT in 37 animals, 21 males and 16 females, was 75 ± 6 mA. Thirty five animals survived 60 min of stimulation at twice ADT. SE was induced in 30 animals (86%) and 21 animals (70%) survived SE which lasted for 214 ± 25 min (n=21). The power of EEG in the delta, theta, and alpha frequencies was high at the onset of SE and it reduced towards the end of SE. During 60 min of CHS the animals experienced behavioral seizures ranging between stages 1 to 2 on a modified Racine scale, whresa during the first half of SE duration, the behavioral seizures ranged between stages 3 to 5. Five animals were assessed for neurodegeneration. Bilateral flurojade labeling was observed in all the animals; a number of CA1 and CA3 pyramidal neurons were labeled in addition to sparse labeling of hilar interneurons. Spontaneous seizures were recorded in 7 out of 17 (41%) animals with an average latency of 28 ± 4 days. Conclusions: We have developed and characterized a CHS model of self-sustained limbic SE in mice. This model is associated with high survival without diazepam treatment during SE and shows hallmarks of SE including neurodegeneration and epileptogenesis.  Funding: NIH grants RO1 NS 040337 and RO1 NS 044370