Tuberous sclerosis complex (TSC) is an autosomal dominant disorder occurring in 1/6,000 individuals with mutations in TSC1 or TSC2 leading to increased mTOR activity. About 80- 90% of the TSC individuals will experience seizures of different types. Most types of seizures are refractory to treatment and require invasive surgical resection leading to manageable seizures in only 50% of the cases. There is thus a serious need to improve epilepsy treatment in TSC. To develop such treatment, we need to better understand the mechanisms of seizure generation. It is known that focal cortical malformations, called cortical tubers in TSC are associated with epilepsy, but understanding how tubers generate seizures is limited because of the lack of an experimental model of focal cortical malformation-associated epilepsy. Here, we have generated a novel model of focal tuber-associated seizures, and we propose to further characterize it and address some of the possible mechanisms of epileptogenesis/seizures. As in humans, we found that experimental cortical tubers are characterized by loss of cortical lamination, the presence of ectopic, cytomegalic neurons with hypertrophic dendrites, and gliosis. Our overarching hypothesis is preventing one of the alterations may be sufficient to prevent seizure generation. Here, due to the exploratory nature and the short duration of a R21, we focused on two specific alterations, neuronal misplacement which is associated with circuit disorganization, and mTORC1-induced changes in biophysical properties (i.e., abnormal acquisition of pacemaker channel). Our more specific hypothesis is that preventing neuronal misplacement or specific alterations in biophysical properties prevents seizures. To address this hypothesis, we have two aims, one focused on neuronal misplacement and the other one on the biophysical properties of tuber neurons. We will use a combination of approaches including in utero electroporation to increase mTOR activity in developing cortical neurons followed by patch clamp recordings in slices and electroencephalogram (EEG)/behavior recordings to monitor epileptiform discharges in vivo. In addition, we will use conditional approaches as well as engineered receptors to silence neurons in vivo. This combination of approaches is innovative and we are in a unique position to accomplish the proposed work. Finally, TSC is an exemplary disorder of mTOR-dependent focal cortical malformation-associated epilepsy. The other disorder is focal cortical dysplasia (FCD) type II, which share similar molecular and cellular alterations. Our model is thus applicable to FCD type II. Both disorders are the leading cause of focal malformation-associated refractory epilepsy.s

Public Health Relevance

This proposal aims at generating a reliable and efficient model of brain malformation- associated epilepsy seen in individuals with tuberous sclerosis complex (TSC) and focal cortical dysplasia (FCD), and to gain insights into the mechanisms of seizure generation. TSC and FCD patients have developmental malformations associated with seizures and worsening of cognitive and psychiatric deficits. Most types of seizures in TSC and FCD are refractory to treatment and require invasive surgical resection with <50% success underscoring the need for understanding how seizures are generated and developing novel treatments.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Exploratory/Developmental Grants (R21)
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Acute Neural Injury and Epilepsy Study Section (ANIE)
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Mamounas, Laura
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Yale University
Schools of Medicine
New Haven
United States
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Feng, Li; Motelow, Joshua E; Ma, Chanthia et al. (2017) Seizures and Sleep in the Thalamus: Focal Limbic Seizures Show Divergent Activity Patterns in Different Thalamic Nuclei. J Neurosci 37:11441-11454
Hsieh, Lawrence S; Wen, John H; Claycomb, Kumiko et al. (2016) Convulsive seizures from experimental focal cortical dysplasia occur independently of cell misplacement. Nat Commun 7:11753