Optically guided neuronal growth at near-infrared wavelengths

Recent work has indicated the potential of light to guide the growth cones of neuronal cells using a Ti: Sapphire laser at 800 nm (Ehrlicher et al, PNAS, 2002). We have developed an optical set-up that has allowed, for the first time, the direct comparison of this process at near infrared wavelengths. A high number of growth cones were studied in order to provide a detailed statistical analysis. Actively extending growth cones of the neuroblastoma cell-line, NG108, can be guided at not only 780 nm, but also at 1064 nm. These wavelengths are an appropriate choice for guidance experiments, as wavelengths in the visible spectrum and UV are highly absorbing by cells and lead to death by phototoxicity and thermal stress. At 780 nm, 47% of actively extending growth cones were found to turn towards the focused incident light by at least 30° (n=32 growth cones). At 1064 nm, 61% of cells were successfully guided (n=31 growth cones). This suggests that the light detection mechanism within the cell is not due a single protein with a defined activity wavelength as occurs for example with the photoreceptor family of opsin proteins in the mammalian eye. We present two novel mechanisms of light induced neuronal guidance which are not related to temperature increases, or optical tweezing of the growth cone. We are also now identifying the signaling pathways that mediate this phenomenon.