Project summary Grand mal (great malady) seizures, now called generalized tonic clonic seizures (GTCS), are the most feared seizures because they can cause death and injury. Repeated GTCSs are the leading risk factor for sudden unexpected death in epilepsy (SUDEP), which is a leading cause of death in persons with epilepsy. GTCS also leads to fractures and soft tissue injuries. It is long known that the motor cortex generates these seizures and seizures modify the motor cortex. However, the cellular and molecular mechanisms of seizure-induced reorganization of the motor cortex have not been studied. Furthermore, it is not known whether a GTCS makes subsequent seizures more severe. We propose that GTCS enhance the excitability of a subset of motor cortex pyramidal neurons by enhancing AMPA receptor mediated excitation. We found that GluA1 subunit of the AMPA receptor was essential for expressing kindling-induced (grade 5) GTCS. We kindled mice lacking the GluA1 subunit of AMPA receptors and their wild-type (WT) littermates using traditional kindling methods. Whereas WT animals progressed to sustained convulsive GTCS (grade 4 & 5), but knockout animals neither attained nor sustained GTCS, despite repeated stimulation. Furthermore, two (WT) animals died following GTCS, while none of the KO animals died. In Aim 1, we propose to characterize the role of the GluA1 subunit of AMPA receptors in sustaining repeated GTCSs using a combination of conditional knockout mice and biochemical techniques in intrahippocampal kainate (IHK) and kindling models of TLE. Behavioral seizures also become more intense when fully kindled animals were stimulated. Much larger volume of the cortex was active during the 8th GTCS compared to the neocortical activation observed after the 3rd GTCS. Motor cortex cell counts revealed that many more neurons in the motor cortex expressed c-fos in response to the fifth GTCS compared to the first GTCS. In Aim 2 experiments, we propose to confirm and expand these findings. we will compare cortical circuit activity maps and behavioral seizures in response to the first or fifth GTCS in kindling and IHK TLE models. We compared the electrophysiological properties of motor cortex pyramidal neurons that expressed c-fos in response to GTCSs with those of surrounding neurons that did not express c-fos and found surprising differences. Motor cortex pyramidal neurons expressing c-fos were more excitable and demonstrated enhanced AMPA receptor-mediated excitatory post synaptic currents. In Aim 3, we propose to compare the excitability and excitatory transmission of layer 2/3 and layer 4/5 pyramidal neurons expressing c- fos in response to a grade 5 kindled seizure using patch clamp recordings. These studies open a novel area of epilepsy research, focusing on the effects of GTCS on the neocortex using a combination combine novel, state-of-the-art techniques.