Seizure Suppression by High Frequency Optogenetic Stimulation Using In Vitro and In Vivo Animal Models of Epilepsy

Abstract

Background: Electrical high frequency stimulation (HFS) has been shown to suppress seizures. However, the mechanisms of seizure suppression remain unclear and techniques for blocking specific neuronal populations are required. Objective: The goal is to study the optical HFS protocol on seizures as well as the underlying mechanisms relevant to the HFS-mediated seizure suppression by using optogenetic methodology. Methods: Thy1-ChR2 transgenic mice were used in both vivo and in vitro experiments. Optical stimulation with pulse trains at 20 and 50 Hz was applied on the focus to determine its effects on in vivo seizure activity induced by 4-AP and recorded in the bilateral and ipsilateral-temporal hippocampal CA3 regions. In vitro methodology was then used to study the mechanisms of the in vivo suppression. Results: Optical HFS was able to generate 82.4 % seizure suppression at 50 Hz with light power of 6.1 mW and 80.2 % seizure suppression at 20 Hz with light power of 2.0 mW. The suppression percentage increased by increasing the light power and saturated when the power reached above-mentioned values. In vitro experimental results indicate that seizure suppression was mediated by activation of GABA receptors. Seizure suppression effect decreased with continued application but the suppression effect could be restored by intermittent stimulation. Conclusions: This study shows that optical stimulation at high frequency targeting an excitatory opsin has potential therapeutic application for fast control of an epileptic focus. Furthermore, electrophysiological observations of extracellular and intracellular signals reveled that GABAergic neurotransmission activated by optical stimulation was responsible for the suppression.

Seizure reduction through interneuron-mediated entrainment using low frequency optical stimulation

“…The number of YFP positive cells that co-expressed GAD 65–67 and morphologically appeared to be interneurons was comparable at both ages (21701±249 cells/mm3 from P14, and 22669±421 cells/mm3 from P100, P>0.05). A similar pattern of expression was observed in the Thy1-ChR2-YFP line (Chiang et al , 2014). This data show that the pattern of expression of ChR2 in GABA neurons was similar at P14 and P100 suggesting that the activation of the VGAT promoter occurs at very early time during development and is consistently maintained during adulthood.…”

Semaphorin 4D promotes inhibitory synapse formation and suppresses seizures in vivo

“…Together with our previous work on the prosynaptogenic effects of Sema4D in vitro , our results are consistent with a model in which administration of Sema4D promotes the rapid assembly of GABAergic synapses in the hippocampus, suggesting that inhibitory synapse formation can occur quickly in the adult brain. Furthermore, Sema4D application in a discrete hippocampal region ameliorated seizure activity, supporting the hypothesis that spatially restricted modulation of the inhibitory network can limit recurrent excitation in the temporal lobe . Our findings suggest that a novel antiepilepsy therapy could enhance network inhibition by increasing the number of GABAergic synapses through treatment with a synaptogenic molecule such as Sema4D.…”

Seizing Control

“…Optogenetics can shed light on these mechanisms by allowing cell-specific stimulations in animal models, the effects of which can then be compared with those of the global stimulation generated by DBS. For example, in a 4-aminopyridine model of acute seizures, optogenetic stimulation of interneurons, at frequencies standardly used with DBS (Koubeissi and others 2013), was sufficient to recapitulate the seizure suppressive effect observed when all neuronal cells were stimulated (Chiang and others 2014; Ladas and others 2015). Mechanistically, inhibitory cells appeared to initially induce a paradoxical excitatory bursting in pyramidal cells, which caused synchronization, and then ultimately suppression of pyramidal cell activity (Ladas and others 2015).…”