Abstract
Neurons communicate through electrochemical signalling within a complex network. These signals are composed of spatiotemporal changes in membrane potentials that are traditionally measured by electrical recordings or by using optical probes. Since probes are inevitably invasive and damaging to the cells, label-free imaging approaches are sought for. For many years second harmonic (SH) imaging has been a promise for delivering direct label-free neuronal membrane potential information. However, to date this promise has not been delivered, owing to the intrinsic low sensitivity of the method. Here, we demonstrate an improvement in label-free second harmonic neuroimaging sensitivity by ~3 orders of magnitude using a wide-field medium repetition rate illumination [1–4]. We perform a side-by-side patch-clamp and second harmonic imaging comparison to demonstrate the theoretically predicted linear correlation between whole neuron membrane potential changes and the square root of the second harmonic intensity. We assign the ion induced changes to the SH intensity to changes in the orientation of membrane interfacial, which is used to image spatiotemporal changes in the membrane potential and K+ ion flux. We observe a nonuniform spatial distribution and temporal activity of ion channels in the mouse brain neurons.
© 2019 IEEE
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