Response of mechanically-created neurites to extension

We use micromanipulation techniques and real-time particle tracking to develop an approach to study specific attributes of neuron mechanics. We use a mechanical probe composed of a hollow micropipette with its tip fixed to a functionalized bead to induce the formation of a neurite in a sample of rat hippocampal neurons. We then move the sample relative to the pipette tip, elongating the neurite while simultaneously measuring its tension by optically tracking the deflection of the beaded tip. By calibrating the spring constant of the pipette, we can convert this deflection to a force. We use this technique to obtain uniaxial strain measurements of induced neurites and investigate the dependence of the force-extension relationship on mechanical pull speed. We show that in the range of pull speeds studied (0.05-1.8 μm/s), the variation in the work to extend a neurite 10 μm is consistent across pull speeds. We do not observe statistically significant rate-dependent effects in the force-extension profiles; instead we find the same quadratic behaviour (with parameters drawn from the same distributions) at each pull speed.