Abstracts

Rationale: Epileptic seizure is characterized by an excessive synchrony of neurons which causes transient loss of normal brain function. The mechanism of icto-genesis, i.e. how seizure develops in normal neural network, is poorly understood because it is difficult to reproduce and observe seizures using conventional animal models. Recent development of optogenetics enabled us to intervene functions of specific cells via optical control of ion channels. Although this technique facilitated our understanding on mechanism of disease at functional circuit level, applications to epilepsy research are still scarce. Here we developed a novel in vivo model of epileptic seizures using optogenetics as a potential tool for studying icto-genesis. Methods: Repetitive pulse or continuous photo stimuli were delivered to the hippocampus of anesthetized Thy1.2 - Channelrhodopsin 2 - Venus (ChR2V) transgenic rat under simultaneous recording of local field potentials (LFPs). Stimulations with various parameters including pulse frequency and duty ratio were tested to induce epileptic seizures. The experiment was also performed to the hippocampus of wild Wister rats transfected with adeno-associate viral vector carrying ChR2V. The relation of c-fos expression and epileptic seizures were investigated. Results: Epileptic seizures were induced by pulse photo-stimulation of the hippocampus in both transgenic rats and transfected wild Wister rats. The LFP during the icto-genesis was observed with no interference of electrical artifacts. Rhythmic activities emerged during stimulation and became self-sustained afterwards for 39.8 ±1.9 seconds with peak frequency around 10 Hz, reminiscent of epileptic seizures in human. The seizure was most efficiently induced by stimulation with 10 and 20 Hz pulse frequency and smaller duty ratio. No rats were died during and after the experiment. C-Fos expression was increased in all subregions along septo-temporal axis of the hippocampus. Conclusions: This novel hippocampal seizure model is advantageous for its high reproducibility, artifact-less observation and low mortality compared with conventional animal models of seizures. It is promising tool to study the mechanism of icto-genesis.