Abstracts

Rationale: Numerous epilepsies result from variants in widely-expressed genes in the brain, potentially impacting the function of many systems. In these cases, effective targeting of research and therapies would benefit from knowing the affected networks underlying the disease symptoms. Furthermore, identifying how activity in these networks is modified in the disease state will help link molecular effects to network level abnormalities. In this study, we have addressed these issues in a precision genetic model of KCNT1-related epilepsy.

Methods: As previously reported, we have generated a mouse model of human KCNT1-related epilepsy caused by the gain-of-function variant Y796H. Mutant mice have frequent spontaneous seizures and inter-ictal epileptiform discharges (IEDs). In this study, we used widefield calcium imaging of cortical activity to generate and compare maps of seizure and IED occurrence as well interictal abnormalities.

Results: In total, we collected 16.2 hours of imaging data from 4 wild type mice and 26.7 hours from 6 homozygous KCNT1 mutant mice, containing 52 spontaneous seizures and 1700 IEDs. Most IED localized to Secondary motor cortex (M2), and seizures consistently emerged from, and were most intense in, a set of cortical areas including M2, as well as retrosplenial, anterior higher visual and adjacent trunk somatosensory areas are consistently susceptible to seizure. Both seizures and IEDs were related to more subtle forms of abnormal cortical activity in susceptible brain areas. IEDs represent abnormally intense examples of a general increase in mutant M2 activity, and seizures tend to emerge from episodes in which cortical activity becomes progressively concentrated in the impending seizure emergence zone. To test whether such subtle abnormalities were restricted to susceptible areas, we compared interictal activity during awake, quiet restful periods in WT and mutant animals. This activity clustered into 10 types, based on spatial profile. Highly similar events from both genotypes were found in each cluster, suggesting intact spatial organization of activity. However, no event type or cortical area was spared the effects of the mutation. All showed a reduced event duration and about half showed significant differences in event rate. To investigate whether the susceptibility of an area to seizure and IED reflects an intrinsic vulnerability to epileptic pathology we compared KCNT1-related seizures and IEDs to picrotoxin induced seizures and IEDs in WT mice. In support of this hypothesis, we found wild type M2 was susceptible to both picrotoxin seizure and IED and other areas shared susceptibility to KCNT1 seizure and picrotoxin IEDs.

Conclusions: Seizures and IEDs tend to occur in a susceptible subset of cortical areas in the KCNT1 mutant mice we studied. These events are extreme outcomes of widely altered physiology caused by the mutation. These alterations affected the temporal dynamics and magnitude of activity in the cortex, not its spatial organization. Comparison to picrotoxin driven pathology argues some of this susceptibility reflects the intrinsic properties of cortical areas.

Funding: Please list any funding that was received in support of this abstract.: N/A.