Basal forebrain cholinergic dysfunction in sleep-related epilepsy

PROJECT SUMMARY/ABSTRACT The relationship between sleep and epilepsy has long been recognized. In particular, the timing of seizure occurrence is largely correlated with sleep-wake cycles. For instance, seizures in patients with mesial temporal lobe epilepsy (MTLE) occur more frequently during wakefulness, while patients with frontal lobe epilepsy (NFLE) almost exclusively have seizures during NREM sleep. While hippocampal dysfunction has been proposed and studied in MTLE, the neuropathology of NFLE remains elusive. In this proposal, we utilize a genetic mouse model of NFLE to investigate how sleep and sleep circuits regulate seizures. Specifically, we make use of optogenetics, fiber photometry, electrophysiology, and mouse genetics to study the role of basal forebrain cholinergic circuitry in sleep-related epilepsy. At a fundamental level, the work proposed in this research proposal will provide novel therapeutic targets for epilepsy treatments. Human genetic studies have identified several genes associated with ADNFLE (autosomal dominant NFLE), including CHRNA4, CHRNB2, CHRNA2, KCNT1, DEPDC5, and CRH. Several mouse models of ADNFLE are available, notably mutations of CHRNA4 and CHRNB2. These models display abnormal excitability and are generally accompanied by disturbed sleep. However, circuit dysfunctions have not been examined. Recently, our co-investigator Wayne Frankel at Columbia has developed an epilepsy mouse model with a missense mutation in KCNT1. They determined that homozygous Kcnt1 mutant mice exhibit spontaneous tonic seizures and generalized tonic-clonic seizures. In our preliminary work to examine the relationship between sleep and epilepsy, we observed that seizures in Kcnt1 mutants predominantly occur during NREM sleep, recapitulating the sleep correlation in the human disease. Considering the roles of the cholinergic system in ADNFLE and sleep regulation, we hypothesize that dysfunction of the basal forebrain (BF) cholinergic circuitry causally contribute to sleep-related epilepsy. In Aim1, we will examine cell type specific neural activity of basal forebrain circuits in Kcnt1 mutant animals. To genetically target different cell types, we will cross Kcnt1 mutants with three Cre lines (Chat-Cre, Vglut2-Cre, Sst-Cre). Then, we will combine fiber photometry and EEG/EMG recording to compare the activity between mutant and control animals in different brain states (i.e. wake, NREM sleep, REM sleep). Next, using axon- targeted AAV to express GCaMP6 in Kcnt1 mutant mice we will record neural activity in the axonal terminals of BF cholinergic neurons in the hippocampus. In Aim2, we will use closed-loop optogenetics to manipulate neural activity of different BF cell types in Kcnt1 mutant animals to examine the causal effect of BF cholinergic dysfunctions on sleep-related epilepsy. Specifically, we will optogenetically inhibit ChAT+ neurons or activate SOM+ GABAergic neurons in sleep or seizures and examine whether compensating for abnormal neural activity can terminate or reduce spontaneous seizures in Kcnt1 mutant animals.