Optical manipulation of cellular functions represents a growing field in biomedical sciences. The possibility to modulate specific targets with high spatial and temporal precision in a contactless manner allows a broad range of applications. Here, we present a study on stimulation of neuronal cells by optical means. As a long-term objective, we seek to improve the performance of current electric neurostimulation, especially in the context of cochlear implants. Firstly, we tested a gold nanoparticle mediated approach to modulate transmembrane conductivity by irradiation using a picosecond pulsed Nd:YAG laser at 532 nm for 40 ms in a neuroblastoma cell line (N2A) and primary murine neurons. The light absorption leads to a rapid temperature increase of the gold nanoparticles, which can induce an increased permeabilisation of the cellular membrane. Calcium transients were recorded as an indicator of neuronal activity. Although calcium signals were reliably detected upon laser irradiation, the temporal behavior did not resemble action potentials. The origin of these signals was investigated by an inhibitor study. These results indicate calcium induced calcium release (CICR) as the major source of the calcium transients. Consecutively, we tested alternative approaches for cell stimulation, such as glutamate release and optogenetics, and evaluated the potential of these methods for the application in a cochlear implant. Compared to the gold nanoparticle approach, both techniques induce less cellular stress and reliably produce action potentials.
Sonja Johannsmeier, Patrick Heeger, Mitsuhiro Terakawa, Alexander Heisterkamp, Tammo Ripken, and Dag Heinemann, "Optical cell stimulation for neuronal excitation (Conference Presentation)," Proc. SPIE 10052, Optogenetics and Optical Manipulation, 100520E (Presented at SPIE BiOS: January 29, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2252017.5371339430001.
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