Abstracts

Rationale: Rationale: To study how focal seizures arise, we conducted transcriptome analysis of epileptogenic tissue obtained from surgical resection of pediatric focal epilepsy cases. Identification of gene expression changes may define novel pathways and therapeutic targets for common causes of epilepsy. We found reduced levels of the circadian transcription factor, Circadian Locomotor Output Cycles Kaput (Clock), in epileptogenic tissue. Furthermore, we tested Clock expression in a recognized model of temporal lobe epilepsy and found reduction of Clock prior to onset of spontaneous seizures. We modeled the effect of reduced Clock using mice with developmental deletions of the Clock gene in excitatory neurons of the cortex and hippocampus. Results: Results: In epileptogenic tissue, the Clock expression is significantly decreased compared with normal brain tissue. We found decreased Clock in 22 out of 27 patient samples. Cases with decreased Clock included all types of focal cortical dysplasias, tuberous sclerosis complex, Sturge Weber, and Rassmussen's encephalitis. Furthermore, we find that in the pilocarpine-lithium model of temporal lobe epilepsy, a reduction of Clock prior to onset of spontaneous seizures. To determine the functional significance of diminished Clock in epilepsy, we created mice with conditional deletions of Clock in both excitatory and inhibitory neurons in the cortex. In mice, deletion of Clock in excitatory neurons alone results spontaneous seizures and a decreased seizure threshold. Furthermore, we find a loss of spines in the apical dendrite and primary branches, a phenotype also observed in human pyramidal neurons from epileptogenic tissue. We demonstrate that mouse excitatory neurons lacking Clock have an imbalance in excitation vs. inhibition due to a severe defect in spontaneous IPSCs as compared with EPSCs ascertained by whole cell patch-clamp electrophysiology. Conclusions: Conclusions: Circadian genes play a key role in the pathogenesis of focal epilepsy and our study provides a link between seizure threshold and the sleep-wake cycle. Furthermore, these functional analyses suggest that the circadian pathway may be a promising target for therapeutic intervention. Funding: Goldwin Foundation award for pediatric research