Enhancing burst activation and propagation in cultured neuronal networks by photo-stimulation

Spontaneous bursting activity in cultured neuronal networks is initiated by leader neurons, which constitute a small subset of first-to-fire neurons forming a sub-network that recruits follower neurons into the burst. While the existence and stability of leader neurons is well established, the influence of stimulation on the leader-follower dynamics is not sufficiently understood. By combining multi-electrode array recordings with whole field optical stimulation of cultured Channelrhodopsin-2 transduced hippocampal neurons, we show that fade-in photo-stimulation induces a significant shortening of intra-burst firing rate peak delay of follower electrodes after offset of the stimulation compared to unperturbed spontaneous activity. Our study shows that optogenetic stimulation can be used to change the dynamical fine structure of self-organized network bursts. Introduction – Synchronized bursting is a major constituent of spontaneous activity that has been observed in cultured hippocampal and cortical neurons [1, 2]. There are numerous quantitative studies that investigated the ignition and spread of collective spontaneous bursting activity [3,4,5,6,7] showing that the order of activation within a synchronized burst is a stereotypical hierarchical process [4] and that multiple ignition sites, termed as initiation zones [6,7], privileged neurons [4]or leader neurons [5], create network bursts by recruiting follower neurons. Leader neurons are relatively robust and they carry information about the identity of the burst. They are supposed to be part of an underlying sub-network that is excited first [5], which then recruits the follower neurons into the orchestrated activation of neuronal cell assemblies. Functionally, leader-follower neuron temporal relationships reflect the dynamical state of the network and can be used to assess network topology [3]. Despite numerous reports on the existence of leader and follower neurons, the effect of stimulation modifying the leader – follower dynamics have not been sufficiently studied. The modification of leader – follower relationships may provide insights on how the internal structure of synchronized bursting activity can be regulated by activity dependent network-level potentiation. This will contribute to our understanding of the relationship between network level plasticity and neuronal recruitment into synchronized bursting activity. Therefore, we investigated the leaderfollower dynamics using a combination of multielectrode array recording and optical stimulation of channelrhodopsin-2 transduced hippocampal cultures. This approach offers a non-invasive technique for recording and stimulating cultured neuronal networks. Electrodes are divided into two subsets of 1) leader electrodes, which are a small subset of neurons initiating the bursts and 2) follower electrodes, which register other neurons being recruited by the leaders into an emerging synchronized activity burst. We found that a fade-in photo-stimulation paradigm consisting of slowly not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/027177 doi: bioRxiv preprint first posted online Sep. 18, 2015;