Abstracts

Rationale: On-demand optogenetic stimulation of cerebellar Purkinje cells is highly effective at inhibiting hippocampal seizures in a mouse model of TLE. Intriguingly, both optogenetic excitation and inhibition of cerebellar cortical output neurons, Purkinje cells, attenuated seizures. The mechanisms by which the cerebellum impacts seizures, however, are unknown. Additionally, there are no known monosynaptic connections between the cerebellum and hippocampus. The most immediate downstream area to investigate is the projection targets of midline Purkinje cells in the fastigial deep cerebellar nucleus (DCN). Methods: Using on-demand optogenetics in the mouse unilateral intrahippocampal kainate model of temporal lobe epilepsy, we targeted the fastigial nucleus in order to determine whether increases and/or decreases in fastigial output can underlie seizure cessation. We also utilized viral targeting approaches to determine whether stimulation of specific fastigial outputs could also be effective at attenuating seizures. Results: Though Purkinje cell input to fastigial neurons is inhibitory, we found that direct optogenetic inhibition of the fastigial nucleus had no effect on seizures. Conversely, however, fastigial excitation robustly attenuated hippocampal seizures, with even a single, 50 msec pulse of light capable of stopping seizures. Using a viral approach, we selectively targeted fastigial excitatory neurons, and again found robust seizure inhibition.  Fastigial excitatory neurons have projections to areas including the thalamus, superior colliculus, and reticular formation.  We therefore next tested optogenetically activating fastigial terminals in the central lateral nucleus of the thalamus, in order to determine whether fastigial projections to this area contribute to seizure cessation. Our early preliminary results suggest that on-demand excitation of fastigial terminals in the central lateral nucleus is sufficient to attenuate hippocampal seizures. Conclusions: Together, these results shed new light on the potential mechanisms of cerebellar stimulation on seizure inhibition, and highlight new potential therapeutic targets for intervention in TLE. Funding: This work was supported in part by The Winston and Maxine Wallin Neuroscience Discovery Fund Award, an American Epilepsy Society Postdoctoral Fellowship (MLS), NIH R01-NS104071-01, a University of Minnestoa McKnight Land-Grant Professorship award, and the University of Minnesota’s MnDRIVE (Minnesota’s Discovery, Research and Innovation Economy) initiative.