Authors :
Presenting Author: Shreya Malhotra, MPH – Stanford University
Barna Dudok, PhD – Baylor College of Medicine
Eliza Schnitzer, _ – Stanford University
Quynh Anh Nguyen, PhD – Vanderbilt University
Jordan Farrell, PhD – Stanford University
Tilo Gschwind, PhD – Stanford University
Ivan Soltesz, PhD – Stanford University
Rationale:
Hippocampal basket cells (BCs) are critical GABAergic interneurons that modulate the spiking output of pyramidal cells (PCs) and thereby shape network activity. BCs are primarily classified based on expression of either parvalbumin (PV) or cholecystokinin (CCK). While PV-Cre mouse lines have enabled in vivo studies of PV BCs, equivalent tools for population-level investigation of CCK BCs have been lacking. Recent single-cell RNA sequencing identified gamma-synuclein (Sncg) as a selective marker for CCK BCs, leading to the development of an Sncg-Flp mouse line. However, the role of CCK BCs in chronic epilepsy and their potential as therapeutic targets remain poorly understood.Methods:
We validated the Sncg-Flp mouse line as a specific genetic tool to label CCK BCs in the intrahippocampal kainate (IHKA) mouse model of chronic temporal lobe epilepsy (TLE). Using in vivo two-photon calcium imaging, we monitored the activity of CCK BCs, PV BCs, and PCs during both interictal periods and seizures. We then implemented closed-loop optogenetics to selectively activate CCK BCs at seizure onset and measured seizure burden. Finally, to examine the impact of endocannabinoid (eCB) signaling, we conditionally knocked out type-1 cannabinoid receptors (CB1Rs) specifically in CCK BCs.Results:
We confirmed that Sncg is a reliable and specific marker for identifying CCK BCs in the epileptic hippocampus. In vivo 2-photon imaging revealed that during seizures, CCK BCs are robustly suppressed, while both PV BCs and PCs exhibit increased activity. Contrary to our hypothesis, closed-loop optogenetic activation of CCK BCs at seizure onset failed to reduce seizure burden. This lack of efficacy is likely due to elevated seizure-induced eCB levels, which may prevent sufficient GABA release from CCK BCs through CB1R activation. Conditional CB1R knockout in CCK BCs enabled further dissection of their functional contribution to seizure dynamics.Conclusions:
Our findings demonstrate that the Sncg-Flp line is a valuable tool for large-scale, cell-type-specific interrogation of CCK BCs in the mouse model of TLE. CCK and PV BCs exhibit opposing dynamics during seizures, suggesting a functional division of inhibitory control. Although CCK BCs appear to have an unused "reserve" of inhibition, their activation does not reduce seizure burden, likely due to eCB signaling. Funding:
National Institute Of Neurological Disorders And Stroke of the National Institutes of Health (NINDS, NIH): R01NS99457 (I.S.), R01NS121106 (I.S.), R00NS117795 (B.D.); American Epilepsy Society Predoctoral Research Fellowship (S.M); and Knight-Hennessy Scholars Program (S.M.).