Optically guided neuronal growth at near infrared wavelengths

Recent work has indicated the potential of light to modify the growth of neuronal cells. The two reported studies however, were performed on two independent optical set-ups and on differing cell-types at different temperatures and at different wavelengths. Therefore, it is unknown whether there is a bias for this effect to a particular wavelength which would have implications for the mechanisms for this phenomenon. Localized changes in heat have been suggested as a possible mechanism for this process, but as yet there is no direct experimental evidence to support or discount this hypothesis. In this paper, we report the first direct comparison on one cell type, of this process at two near infra-red wavelengths: 780 nm and 1064 nm using exactly the same beam shape. We show that light at both wavelengths is equally effective in initiating this process. We also directly measure the temperature rise caused by each wavelength in water and its absorption in the cellular medium. The recorded temperature rises are insufficient to change the rate of actin polymerization.