Opto non-genetic enhancement of activity inprimary cortical neurons

It has been recently demonstrated that the exposure of naive neuronal cells to light,which is at the basis of optogenetic techniques and calcium imaging measurements, may alterneuronal firing. Indeed, understanding the effect of light on non-genetically modified neurons iscrucial for a correct interpretation of calcium imaging and optogenetic experiments. Here weinvestigated the effect of continuous visible LED light exposure (490 nm,0.18−1.3mW/mm2) onspontaneous activity of primary neuronal networks derived from the early post-natal mouse cortex.We demonstrated, by calcium imaging and patch clamp experiments, that illumination higher than1.0mW/mm2causes an enhancement of network activity in cortical cultures. We investigated onthe possible origin of the phenomena by blocking the TRPV4 channel, demonstrating a complexconnection between this temperature dependent channel and the measured effect. The resultspresented here shed light on an exogenous artifact, potentially present in all calcium imagingexperiments, that should be taken into account in the analysis of fluorescence data.