Elasticity Maps of Living Neurons Measured by Combined Fluorescence and\n Atomic Force Microscopy

Detailed knowledge of mechanical parameters such as cell elasticity,\nstiffness of the growth substrate, or traction stresses generated during axonal\nextensions is essential for understanding the mechanisms that control neuronal\ngrowth. Here we combine Atomic Force Microscopy based force spectroscopy with\nFluorescence Microscopy to produce systematic, high-resolution elasticity maps\nfor three different types of live neuronal cells: cortical (embryonic rat),\nembryonic chick dorsal root ganglion, and P-19 (mouse embryonic carcinoma stem\ncells) neurons. We measure how the stiffness of neurons changes both during\nneurite outgrowth and upon disruption of microtubules of the cell. We find\nreversible local stiffening of the cell during growth, and show that the\nincrease in local elastic modulus is primarily due to the formation of\nmicrotubules. We also report that cortical and P-19 neurons have similar\nelasticity maps, with elastic moduli in the range 0.1-2 kPa, with typical\naverage values of 0.4 kPa (P-19) and 0.2 kPa (cortical). In contrast, DRG\nneurons are stiffer than P-19 and cortical cells, yielding elastic moduli in\nthe range 0.1-8 kPa, with typical average values of 0.9 kPa. Finally, we report\nno measurable influence of substrate protein coating on cell body elasticity\nfor the three types of neurons.\n