ABSTRACT
We describe an optical technique for label-free detection of the action potential in cultured mammalian neurons. Induced morphological changes due to action potential propagation in neurons are optically interrogated with a phase sensitive interferometric technique. Optical recordings composed of signal pulses mirror the electrical spike train activity of individual neurons in a network. The optical pulses are transient nanoscale oscillatory changes in the optical path length of varying peak magnitude and temporal width. Exogenous application of glutamate to cortical neuronal cultures produced coincident increase in the electrical and optical activity; both were blocked by application of a Na-channel blocker, Tetrodotoxin. The observed transient change in optical path length in a single optical pulse is primarily due to physical fluctuations of the neuronal cell membrane mediated by a yet unknown electromechanical transduction phenomenon. Our analysis suggests a traveling surface wave in the neuronal cell membrane is responsible for the measured optical signal pulses.
ABSTRACT
Optical stimulation of cells expressing light-sensitive proteins (opsins) has allowed targeted activation with cellular specificity. However, since narrow-band light has been used for excitation of these optogenetic probes, only active stimulation strategies are being attempted for clinical applications such as restoration of vision. Here, we report use of broad spectral excitation (white light) for optogenetic stimulation of opsin-sensitized cells. We found that ReaChR is optimally excited with white light offering significantly higher photocurrents compared to spectrally filtered narrow-band light stimulation. Our findings open up the possibility of passive stimulation strategy by use of natural sunlight for retinal stimulation, which could have benefits for ambient light stimulated vision restoration.
