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Establishing Light- and Activity-Dependent Tools for Neural Network Assessment

Liubov Sokhranyaeva1, Martin Schwarz2

1 Functional Neuroconnectomics, Institute for Experimental Epilepsy and Cognition Research (IEECR); Life&Brain Center, University of Bonn Medical Faculty
2 Functional Neuroconnectomics, Institute for Experimental Epilepsy and Cognition Research (IEECR); Life&Brain Center, University of Bonn Medical Faculty

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Optical tools have proven to be indispensable for neural network studies in modern neuroscientific research. Recently two novel systems were introduced: Cal-Light and FLARE. Both enable targeted expression of a fluorescent reporter protein or a modulatory element, such as eNpHR or ChrimsonR only in active neurons upon blue light illumination. In this study we systematically tested both systems in parallel in vitro and in vivo to assess their applicability for neural circuit labelling and manipulation.

Therefore, we tested the Cal-Light and Flare systems in mouse primary neuron cultures and subsequently in mouse olfactory bulbs upon stereotaxic injection utilizing recombinant adeno associated viruses (rAAVs). We firstly confirmed the light dependency of both systems, and secondly show successful identification of active neurons. With regard to identification of active neuronal ensembles the FLARE system appears to be more selective, although this might be due to lower expression levels, compared to Cal-Light.

In conclusion, our results show that both systems can be utilized to label active neuronal populations in response to blue light illumination. However, each labeling endeavor will likely need tailored adjustments for a successful implementation of both systems in vivo.

Additionally, we will discuss the possible modulatory prospects of both systems to actively interfere with the activity of labelled neuronal ensembles. Moreover, we give a prospect of how these systems can be used in the field of regenerative medicine to assess functional integration of grafted neurons into a pre-existing circuitry.