Epilepsy affects 1-2% of the population, and approximately 30% of epilepsy patients continue to suffer from seizures despite treatment with antiepileptic medications. Stress is the most common seizure precipitating factor reported by epilepsy patients, suggesting that the physiological stress response has the potential to be a new therapeutic target for the treatment of epilepsy. The majority of studies investigating the relationship between stress and epilepsy have used wildtype rodents with normal brain and stress system development. However, little is currently known about how a genetic predisposition to epilepsy interacts with the stress response to influence seizure outcome. Much is now being learned about genetic predispositions to epilepsy, and genetic factors are estimated to contribute to at least 40% of epilepsy cases. Patients with one epilepsy disorder in particular, genetic (generalized) epilepsy with febrile seizures plus (GEFS+), exhibit a wide range of seizure types and severities even within families sharing the same mutation. This clinical heterogeneity suggests that other environmental and/or genetic factors are playing a role in shaping seizure phenotype in GEFS+ patients. Our lab has developed a mouse model of GEFS+ created by knocking in a human SCN1A- GEFS+ mutation (R1648H) into the orthologous mouse gene (Scn1a). Heterozygous R1648H mice have a normal life span, exhibit infrequent spontaneous seizures, have a lower seizure threshold than their wildtype littermates, and have reduced excitability of cortical GABAergic inhibitory interneurons. This proposal will test the hypothesis that R1648H mutant mice will have altered basal stress system function, and that acute stress will increase seizure susceptibility, frequency, and severity of seizures in these mice.
Aim 1 will examine the basal activity of the hypothalamic-pituitary-adrenal (HPA) axis in the R1648H mutant mice by measuring plasma levels of corticosterone, a major stress hormone, in both the morning and evening. Corticosterone receptor expression and distribution within the brain will also be examined, particularly in areas that play a role in both the stress response and seizure generation. Adrenal and thymus gland weights will allow us to determine if the R1648H mutants have chronically altered systemic levels of corticosterone.
Aim 2 will examine the response of these mice to an acute stressor. We will measure the corticosterone response to an acute stressor and determine the amount of time for levels to return to normal. We will use EEG analysis to determine if exposure to an acute stressor is sufficient to increase the frequency of spontaneous seizures. We will also test the effect on seizure threshold and seizure severity by using chemiconvulsants to induce seizures following acute stress exposure. The results from this study will provide new insight into the relationship between sodium channel function, stress, and epilepsy. The long-term objective of this project is to elucidate the mechanisms by which stress works to affect seizure outcome in a genetically predisposed model of epilepsy with the goal of identifying potential new targets for seizure control in epilepsy patients.
Epilepsy affects 1-2% of the general population, and approximately 30% of epilepsy patients do not respond to current treatments. Stress is the number one trigger for seizures reported by epilepsy patients. This proposal aims to investigate the relationship between a genetic predisposition to epilepsy and the stress response, with the goal of identifying new therapeutic targets for the treatment of epilepsy.
|Sawyer, N T; Helvig, A W; Makinson, C D et al. (2016) Scn1a dysfunction alters behavior but not the effect of stress on seizure response. Genes Brain Behav 15:335-47|
|Sawyer, Nikki T; Papale, Ligia A; Eliason, Jessica et al. (2014) Scn8a voltage-gated sodium channel mutation alters seizure and anxiety responses to acute stress. Psychoneuroendocrinology 39:225-36|