Network properties revealed during multi-scale calcium imaging of seizure activity in zebrafish

Abstract

Seizures are characterized by hypersynchronization of neuronal networks. Understanding these networks could provide a critical window for therapeutic control of recurrent seizure activity i.e., epilepsy. However, imaging seizure networks has largely been limited to microcircuits in vitro or small “windows” in vivo. Here we combine fast confocal imaging of GCaMP-expressing larval zebrafish with local field potential (LFP) recordings to study epileptiform events at whole-brain and single-neuron levels in vivo. Using an acute seizure model (pentylenetetrazole, PTZ), we reliably observed recurrent electrographic ictal-like events associated with generalized activation of all major brain regions and uncovered a well-preserved anterior-to-posterior seizure propagation pattern. We also examined brain-wide network synchronization and spatiotemporal patterns of neuronal activity in the optic tectum microcircuit. Brain-wide and single-neuronal level analysis of PTZ- and 4-aminopyridine (4-AP)-exposed zebrafish revealed distinct network dynamics associated with seizure and non-seizure hyperexcitable states, respectively. Neuronal ensembles, comprised of coactive neurons, were also uncovered during interictal-like periods. Taken together, these results demonstrate that macro- and micro-network calcium motifs in zebrafish may provide a greater understanding of epilepsy.

Significance Statement Monitoring the dynamic activities in large-scale neuronal networks is critical to understanding seizure initiation and propagation. Here, we utilized well-established larval zebrafish seizure protocols and fast confocal imaging of GCaMP-expressing fish to investigate the epileptic network properties at brain-wide and single-cell levels. We revealed the rapid propagation of seizure activity from anterior-to-posterior brain regions in zebrafish central nervous system. We also showed that micro-ensembles of neuronal subpopulations are active during interictal-like periods in a manner similar to that seen in human electrophysiology data sets. Our findings demonstrate that these non-invasive optical imaging approaches will advance our understanding of the network basis underlying seizures and facilitate the development of methods to suppress these events.