Abstracts

Rationale: Pharmacological or optogenetic activation of the Deep and Intermediate Layers of the Superior Colliculus (DLSC) display multi-potent anti-seizure effects in a wide array of preclinical epilepsy models. However, prior studies examining this region have focused on evoked (e.g., electroshock or chemoconvulsant) models rather than models with spontaneous seizures. Because epileptogenic processes may disrupt endogenous anti-seizure circuits, it remains unknown if activation of the DLSC would be effective against spontaneous seizures. To test this, we examined the impact of optogenetic activation of the DLSC in the Wistar Albino Glaxo from Rijswijk (WAG/Rij) model of genetic absence epilepsy.

Methods: Female and male WAG/Rij adult rats (4 months old) were employed as study subjects. All procedures were approved by Georgetown Institutional Care and Use Committee. All animals were subjected to a stereotactic surgery for virus injection, fiber optic implantation and cortical EEG electrode placement. Animals were injected with virus coding for either channelrhodopsin-2 (excitatory opsin; rAAV5-hSyn-hChR(H134R)-mCherry) or a control vector (rAAV8-CAG-GFP). We compared the efficacy of open-loop (i.e., continuous neuromodulation) to that of closed-loop (i.e., on-demand neuromodulation) stimulation paradigms on a within-subject basis. For on-demand stimulation, we detected seizures in real time based on the EEG power within the characteristic frequency band of SWDs. Half of detected seizures triggered light delivery, the other half did not. We compared three stimulation frequencies, also on a within-subject basis (5, 20, 100 Hz). In all cases, EEG recordings were collected from tethered animals. WAG/Rij rats display repetitive spike-and-wave discharges (SWDs), which model the SWDs observed in absence epilepsy in humans. We quantified the number and duration of each spike wave discharge (SWD) during each two-hour-long observation period. Following completion of the experiment, virus expression and fiber optic placement were confirmed.

Results: In the open-loop (continuous) stimulation paradigm, optogenetic activation of the DLSC was without effect on the number or duration of SWDs at any of the frequencies examined. By contrast, on-demand neuromodulation was effective in both females and males. We observed the greatest reduction in seizure duration with 100 Hz light delivery. As expected, male and female animals injected with a control (opsin-negative) vector did not show a reduction in seizures in response to light delivery.

Conclusions: These data demonstrate that activation of the SC displays anti-seizure effects in a model of spontaneous seizures. While consistent with prior studies in acute models, the striking difference between open and closed-loop neuromodulation approaches underscores the importance of stimulation paradigm in determining therapeutic effect.

Funding: Please list any funding that was received in support of this abstract.: 5R01NS09776204.