Despite many advances made in understanding the pathophysiology of epileptic disorders, seizures remain poorly controlled in approximately one third of mesial temporal lobe epilepsy patients. Here, we established the efficacy of cell type-specific low-frequency stimulation (LFS) in controlling ictogenesis in the mouse entorhinal cortex (EC) in an in vitro brain slice preparation. Specifically, we used 1 Hz optogenetic stimulation of Ca2+/calmodulin-dependent protein kinase II-positive principal cells as well as of parvalbumin- or somatostatin-positive interneurons to study the effects of such repetitive activation on epileptiform discharges induced by 4-aminopyridine. We found that 1 Hz stimulation of any of these cell types reduced the frequency and duration of ictal discharges in some trials, while completely blocking them in others. The field responses evoked by the stimulation of each cell type revealed that their duration and amplitude were higher when principal cells were targeted. Furthermore, following a short period of silence ranging from 67 to 135 s, ictal discharges were re-established with similar duration and frequency as before stimulation; however, this period of silence was longer following principal cell stimulation compared to parvalbumin- or somatostatin-positive interneuron stimulation. Our results show that LFS of either excitatory or inhibitory cell networks in EC are effective in controlling ictogenesis. Although optogenetic stimulation of either cell type significantly reduced the occurrence of ictal discharges, principal cell stimulation resulted in a more prolonged suppression of ictogenesis and thus, it may constitute a better approach for controlling seizures.
Epilepsy is a neurological disorder characterized by an imbalance between excitation and inhibition leading to seizures. Many epileptic patients do not achieve adequate seizure control using antiepileptic drugs. Low-frequency stimulation (LFS) is an alternative tool for controlling epileptiform activity in these patients. However, despite the temporal and spatial control offered by LFS, such procedure lacks cell-specificity, which may limit its efficacy. Using an optogenetic approach, we report here that LFS of two interneuron subtypes and even more so, of principal cells can reliably shorten or abolish seizures in vitro. Our work suggests that targeted LFS may constitute a reliable means for controlling seizures in patients presenting with focal seizures.
The authors declare no competing financial interests.
This study was supported by the Canadian Institutes of Health Research (CIHR grants 74609 to MA, and MOP119340 to SW); Z. Shiri received a student scholarship from the Savoy Foundation for Epilepsy.