Abstracts

Rationale: Focal cortical dysplasia (FCD) is the most common cause of intractable epilepsy in children. Despite the increase in available antiepileptic drugs and epilepsy surgery, seizure freedom cannot be achieved in many patients with FCD. Given our growing understanding of contributions of immunity and brain inflammation to epilepsy progression, we aim to characterize inflammatory changes in an animal model of FCD established in 2004 by Scantlebury et al. (Epilepsia) to identify new targets for intervention. Methods: We induced cortical malformations by subjecting male and female Sprague Dawley rats at P0-1 to freeze lesions, wherein a 2 mm diameter copper probe frozen in liquid nitrogen was held to the skull over the parietal lobe for 10 seconds. Sham rats had a room temperature probe held to the skull. At P10, lesioned (n=11) and sham (n=8) rats were exposed to febrile seizures (lipopolysaccharide (LPS) (200 ug/kg, i.p,) + 30 minute of hyperthermia under a heat lamp). Behavioral seizures and rectal temperature were recorded every two minutes. Seizure onset temperature and seizure progression were assessed. Two and half hours after febrile seizures, blood was collected for cytokine assay with ELISA and brain tissue was harvested and processed for cresyl violet stain, and GFAP and anti-Iba1 immunohistochemistry. Results: During febrile seizure induction, all rats showed behavioral seizures (19/19). All but one experienced generalized tonic clonic (GTC) convulsions with lesioned rats tending to show GTC at a lower mean threshold than shams (40.4 C 0.586 vs. 41.7 C 0.531, p = 0.13). Serum ELISA for circulating levels of cytokine IL-6 suggested that lesioned rats had greater levels of IL-6 than shams. (33.0 vs. 31.7 ng/ml). Lesions were evident on the brain surface and a convoluted fold in the cortex, reminiscent of a microgyrus, was noted in cresyl violet stained brain sections. GFAP-positive astrocytes and Iba1 labeled microglia clustered proximally to the cortical lesion at the base of the microgyrus, extending down to the hippocampus in some rats. Microglia staining tended to be darker throughout the cortex ipsilateral to the lesion compared with contralateral cortex. Conclusions: The trends of decreased seizure threshold and increased circulating proinflammatory cytokine IL-6 suggest that the immune response to seizures is heightened in lesioned rats after febrile seizures at P10, prior to the presumed onset of spontaneous seizures and evolution of epilepsy. Reactive gliosis evident near the microgyrus and the hippocampus demonstrate neuroinflammation near the malformation. Whether microglia or other immune cells contribute to or are present as a consequence of lesion development, and their relation to a previously reported hyperexcitable zone near the microgyrus, remain to be determined. Funding: NIH/NINDS R01 NS073768