Abstracts

Rationale: There are at least 30 human syndromes that disrupt the normal cytoarchitecktonic organization of the cortical architecture, leading to focal cortical dysplasia (FCD) and related malformations of cortical development (MCDs). FCD and MCDs represent an increasingly recognized cause of medically intractable epilepsy. Animal models encompass several advantages for these studies and for developing novel therapies to treat FCD and MCD related epilepsy. However, in commonly used animal models of FCD such as the rat and mouse neonatal freeze lesion, neither clinical nor EEG seizures have been observed despite a highly reliable evoked epileptiform activity in vitro. Our goal is to conduct long-term EEG recording over the entire life span to examine if animals developed spontaneous chronic epilepsy in a mouse model of FCD. Methods: Unilateral single freeze lesions was made in P0?"1 mice pups to induce neocortical microgyria in the right S1 area (SFLS1R). Within a litter, 3 pups will be treated and the remaining 3 pups will be sham treated (i.e. identical surgical procedures minus the freeze lesion). The entire litter will be kept in the vivarium that is maintained at 22 C?"23 C and has a 12:12 h light-dark cycle. Food and water are available ad libitum. Intracranial EEG recordings. 2 month old mice will be anesthetized under isoflurane anesthesia (2%), mixed with medical oxygen and secured in a stereotaxic frame. Polyimide-insulated stainless steel wires and connecting pins will be implanted into the malformed S1, ipsilateral M1, VPM or left S1. Mice shall be returned to the vivarium after EEG implantation. EEG recordings will be performed in a 24 hour cycle with simultaneous video behavior monitoring and automated infrared (IR)-activity tracking at a frequency of twice per month to minimize disturbances. Animals will be able to move freely in a recording chamber supplied with water gel. EEG signals will be amplified via a differential AC amplifier (Model 1700, A-M system), digitized using Power 1401, and analyzed using the Spike-2 program (Cambridge Electronic Design). Offline analysis will be conducted using custom programs developed using Matlab?(R). Results: 89% (40/45) of SFLS1R and 0% (0/12) of control, age matched mice developed chronic spontaneous ictal-spikes. 61% (27/45) SFLS1R mice with IS activities exhibited highly frequent, persistent and repeatable spontaneous electrographic seizures that occurred predominantly during the NREM sleep. The epileptic discharge pattern closely resembled the pattern of continuous spike-waves during slow-wave sleep (CSWS) of the human epileptic syndrome described as an electrical status epilepticus during slow wave sleep (ESES). CSWS were more prevalent in female (18/23) vs. male (9/22, p < 0.01). Electrographic seizures were strongest in the right S1 region though generalized to contralateral cortex, hippocampus and thalamus, and were associated with significant cognitive and behavioral deficits. Seizures were temporarily alleviated by ethosuximide treatment or optogenetic activation of cortical S1 GABAergic neurons. Using optogenetics and coherence analysis we found that the theta band activities centered around 5Hz play a key role in the generalization of the CSWS. EEG seizure alone contributes to additional cognitive and behavior deficits in FCD animals. Conclusions: This is the first report of a FCD model displaying chronic CSWS/ESES type EEG seizures in mice. Further characterization of the abnormal corticocortical and corticothalamic oscillations in this mouse model may lead to a better understanding of the mechanisms and treatment of CSWS and FCD in human. Funding: The research is support by grants from NINDS (No. 5R01NS094550 and 5R21NS084182.