Development and Control of Epileptiform Bursting in Dissociated Cortical Cultures

Citation

Wagenaar, Daniel Alexander (2006) Development and Control of Epileptiform Bursting in Dissociated Cortical Cultures. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1AX7-QT10. https://resolver.caltech.edu/CaltechETD:etd-07032005-170918

Abstract

Cortical cells in dissociated culture form densely interconnected networks. Within days after plating, neurons become electrically active, and soon after start to synchronize their activity into culture-wide bursts. By growing cultures on multi-electrode arrays (Petri dishes with a grid of substrate-embedded electrodes), their electrical activity can be recorded non-invasively.

I developed software, MEABench, for online visualization and analysis of multi-electrode data, and used it to follow the development of cultures obtained from (E18) embryonic rats. Globally synchronized bursting was observed in all but the most sparsely plated cultures. A remarkable range of bursting behaviors was observed, even in cultures with identical plating parameters. Activity patterns varied widely in terms of the frequency, intensity, duration, and degree of temporal clustering of bursts. During the 2nd week in vitro, bursts in many dense cultures clustered into well-defined trains, separated by long periods without bursts. The number of bursts within these 'superbursts' and their spatiotemporal structure were found to be stable for hours or days.

Cortical cultures on multi-electrode arrays are ideal for studying two-way communication between biological systems and computers. I designed and built hardware to deliver electrical stimuli in arbitrary patterns, developed software to remove stimulation artifacts from recordings, and studied the efficacy of several voltage-defined and current-defined stimulus waveforms. MEABench can control the stimulator in real-time. Thus, stimuli can be made dependent on a culture's activity with only 15 ms lag-time.

We hypothesized that synchronized bursting can dominate activity patterns, because lack of external input puts cultures in a hypersensitive state. Indeed, by feeding cultures a steady stream of stimuli, distributed over many electrodes, bursting could be prevented completely. The number of electrodes required for successful burst control could be reduced by fine-tuning the stimuli with real-time feedback, to make each stimulus evoke the same number of spikes. Burst control could not be achieved with single electrode stimulation.

For the final chapter, I tested various protocols for inducing plasticity by tetanic stimulation. In contrast to earlier published reports, I found that none of them induced changes in burst patterns or responses to test pulses that exceeded spontaneously occurring changes.

Thesis Files