Guided neuronal growth using optical line traps

SUPA, School of Physics & Astronomy, University of St Andrews, St Andrews, KY16 9SS, Scotland, UK.
Optics Express (Impact Factor: 3.49). 08/2008; 16(14):10507-17. DOI: 10.1364/OE.16.010507
Source: PubMed


Optically guided neuron growth is a relatively new field where the exact mechanisms that initiate growth are not well understood. Both Gaussian light beams and optical line traps have been purported to initiate neuronal growth. Here we present a detailed study using optical line traps with symmetric and asymmetric intensity profiles which have been previously reported to bias the direction of neuronal growth. In contrast to these previous studies, we show similar levels of growth regardless of the direction of the intensity variation along the line trap. Furthermore, our experimental observations confirm previous suggestions that the filopodia produced from neuronal growth cones can be affected by laser light. We experimentally observe alignment of filopodia with the laser field and present a theoretical model describing the optical torques experienced by filopodia to explain this effect.

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    • "Clearly, optical neuronal guidance has been demonstrated across a broad range of laser wavelengths, spot sizes, spot intensities , beam shapes and beam modulations. Moreover, for the low laser-power in the optical guidance experiments, the magnitude of optical forces is minute (Ehrlicher et al., 2002), and although it has been hypothesized that the very low optical gradient forces played a role in steering the neuronal growth cones with optical line traps (Mohanty et al., 2005), this has later been disproven (Carnegie et al., 2008). This makes an explanation of the underlying mechanism based on optical gradient forces unlikely. "
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    ABSTRACT: Recently, it has been shown that it is possible to control the growth direction of neuronal growth cones by stimulation with weak laser light; an effect dubbed optical neuronal guidance. The effect exists for a broad range of laser wavelengths, spot sizes, spot intensities, optical intensity profiles and beam modulations, but it is unknown which biophysical mechanisms govern it. Based on thermodynamic modeling and simulation using published experimental parameters as input, we argue that the guidance is linked to heating. Until now, temperature effects due to laser-induced heating of the guided neuron have been neglected in the optical neuronal guidance literature. The results of our finite-element-method simulations show the relevance of the temperature field in optical guidance experiments and are consistent with published experimental results and modeling in the field of optical traps. Furthermore, we propose two experiments designed to test this hypotheses experimentally. For one of these experiments, we have designed a microfluidic platform, to be made using standard microfabrication techniques, for incubation of neurons in temperature gradients on micrometer lengthscales.
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    • "Neurons functionally reshape their interconnectivity not only in response to incoming activity from other cells, but also to external stimuli and changes of environmental conditions (Muotri and Gage 2006). Thus, studying cell physiology, cell motility and interconnectivity by interacting with cells or their organelles (Carnegie et al. 2008; Kress et al. 2009; Mejean et al. 2009) and controlling the intercellular organization and environment (Macdonald et al. 2002; Steubing et al. 1991) may lead to a better understanding of cell growth and differentiation during the formation of a specific tissue architecture . For instance, during differentiation, cell processes such as lamellipodia and filopodia explore the extracellular matrix by random motion (Goodman 1996) biased by chemical and physical constraints (Allioux-Guerin et al. 2008), which Address correspondence to F. Difato, Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, via Morego 30, 16163, Genoa, Italy. "
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