1166 Optogenetic Modulation of Network Activity in Human Hippocampus

INTRODUCTION: Seizures are made up of the coordinated activity of networks of neurons. It follows that control of neurons in the pathologic circuits of epilepsy could allow for control of the disease. In non-human disease models of epilepsy, optogenetics has been effective at stopping seizure-like activity by increasing inhibitory tone or decreasing excitation. However, this has not been shown in human brain tissue. Many of the genetic means for achieving channelrhodopsin expression in non-human models are not possible in humans, and vector-mediated methods are susceptible to species-specific tropism that may affect translational potential. There is currently no platform for testing the effects of these potentially disease-modifying tools on network activity in human brain tissue. METHODS: Human hippocampus resected from patients with refractory epilepsy were collected, cut to 300um and plated at the air-fluid interface on cell-culture inserts. AAV transduction with channelrhodopsins driven by a glutamatergic promoter took place on the day of collection. Slices were plated on high-density micro-electrode arrays. Hyperactivity was promoted via bicuculline, low-magnesium media and kainic acid. Slices were illuminated by LED fiberoptics positioned over the slice using a custom recording chamber. RESULTS: Neuronal transduction ranged from 12 – 54% (median 23%). Illumination of slices expressing the depolarizing channelrhodopsin HcKCR1 caused reduction in network firing rates in 8/8 slices expressing HcKCR1. Reductions in network firing rates were significant in all conditions, physiologic media, GABAaR blockade, low-magnesium media and low-magnesium media with kainic acid. CONCLUSIONS: Here, we demonstrate AAV-mediated, optogenetic reductions in network firing rates of human hippocampal slices recorded on high-density microelectrode arrays under several hyperactivity provoking conditions. This platform can serve to bridge the gap between human and animal studies by exploring genetic interventions on network activity human brain tissue.