Abstract
We introduce a novel all-optical assay for functional studies of biological neural networks in vitro. We created a novel optogenetic construct named OptoCaMP which is a combination of a channelrhodopsin variant (CheRiff) and a red genetically encoded calcium indicator (GECI) (jRCaMP1b). It enables simultaneous optical stimulation and recording from large population of neurons with single-cell readout. Additionally, we have developed a spatio-temporal all-optical assay to simultaneously stimulate a sub-section of a neural network and record evoked calcium activity, in both stimulated and non-stimulated neurons, thus allowing the investigation of the spread of excitation through an interconnected network. Finally, we demonstrate the sensitivity of this assay to the change of neural network connectivity.
Highlights
Functional studies of biological neural networks are fundamental to understand brain activity, to investigate how these networks are altered in brain disorders, and to help develop new treatments (Alivisatos et al, 2012)
CheRiff, a channelrhodopsin variant, is activated under blue illumination at 470 nm and demonstrates rapid kinetics (Hochbaum et al, 2014). We combined it with the mRuby-based genetically encoded calcium indicator (GECI) jRCaMP1b which has a larger dynamic range compared to other red-GECIs
We have presented an all optical strategy for quantifying the connectivity of a neural network, using temporal stimuli protocols and OptoCaMP, a combination of a lightactivated ion channel, CheRiff and a GECI, jRCaMP1b
Summary
Functional studies of biological neural networks are fundamental to understand brain activity, to investigate how these networks are altered in brain disorders, and to help develop new treatments (Alivisatos et al, 2012). To explore heterogeneous neural networks, it is often critical to understand the activity of multiple neurons and how they communicate with each other. The traditional electrophysiology tools typically used are technically demanding and time consuming. They exhibit severe limitations in terms of the number of studied cells, duration of the experiment and cellular viability (Scanziani and Hausser, 2009). Multi-electrode arrays offer the possibility to stimulate and record neuronal electrical activity from multiple neurons simultaneously (Gross et al, 1995); due to their design, they have a relatively low spatial resolution and do not guarantee single-cell resolution for either recording and/or stimulation
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