Abstracts

Rationale: Most zebrafish research is focusing on genetic and pharmacological approaches to study epilepsy. However, the neural mechanisms underlying seizure generation are not fully understood. Here, we present a comprehensive study focusing on this phenomenon. Methods: We first benchmarked the use of two-photon calcium imaging by simultaneously performing high quality electrophysiological recordings as well as behavioral measurements of pharmacologically induced epileptic seizures in zebrafish larvae. Our results suggest that two-photon calcium imaging and local field potential recordings are equally good in studying the temporal aspects of seizure generation. Moreover, our simultaneous calcium imaging and behavioral recordings suggest that only half of the locomotor behavioral events are correlated with epileptic brain activity. Next, we performed in depth analysis of neural activity from thousands of individual neurons across the zebrafish brain. Our data includes altogether more than 40 fish (7 fish for electrophysiology, 12 for behavioral measurements, and more than 20 for two-photon imaging). The results were statistically significant when using common tests like Wilcoxon RANK sum test and Kolmogorov-Smirnov test. Results: Our findings suggest, that while the number of active neurons increases during epileptogenesis, the activity levels of active neurons remain unaffected. This suggests that epileptogenesis is due to changes in the properties of the network as a whole, rather than in individual neurons. Moreover, our data suggest that the synchrony of the brain network increases drastically during the period preceding the generalized seizures. Finally, we found that the transition from a pre-seizure to a generalized seizure state, cannot be explained by the gradual changes of the network connectivity and synchrony. Instead, we observed an explosion of network activity, which does not follow neuronal connectivity rules based on synaptic communication across neurons. Our results suggest that this transition from a local oscillatory state to a generalized seizure state involves the recruitment of neuro-glia interactions. Conclusions: We propose that changes in neuro-glia interactions can be a common mechanism for the manifestation of generalized seizures. Funding: This research is funded by The Liaison Committee for Education, Research and Innovation in Central Norway, ‘Samarbeidsorganet’ Grant (SMS, NJY, EY), Flanders Science Foundation Grant (CDV,EY), and ERC Starting Grant (RP,EY). We declare no competing financial interest.