Abstract
Optical microheating is a powerful non-invasive method for manipulating biological functions such as gene expression, muscle contraction, and cell excitation. Here, we demonstrate its potential usage for regulating neurite outgrowth. We found that optical microheating with a water-absorbable 1,455-nm laser beam triggers directional and explosive neurite outgrowth and branching in rat hippocampal neurons. The focused laser beam under a microscope rapidly increases the local temperature from 36 °C to 41 °C (stabilized within 2 s), resulting in the elongation of neurites by more than 10 μm within 1 min. This high-speed, persistent elongation of neurites was suppressed by inhibitors of both microtubule and actin polymerization, indicating that the thermosensitive dynamics of these cytoskeletons play crucial roles in this heat-induced neurite outgrowth. Furthermore, we showed that microheating induced the regrowth of injured neurites and the interconnection of neurites. These results demonstrate the efficacy of optical microheating methods for the construction of arbitrary neural networks.
Highlights
Exposure of cells to a localized temperature gradient through focusing of the 1,455-nm laser resulted in neurite outgrowth from rat hippocampal neurons [1 day in vitro (DIV)] (Fig. 1c,d), while in the absence of laser-mediated heating, neurites incubated at a starting temperature (T0) of 36 °C exhibited frequent changes in their positions (Supplementary Movie S1)
Our results strongly suggest that the activation of microtubule polymerization and microtubule sliding mediates neurite outgrowth during microscopic heating
It is well documented that temperature increases initiate microtubule polymerization, and our results are consistent with studies demonstrating directional microtubule polymerization in the presence of non-microscopic, steady-state temperature gradients[38]
Summary
We observed that neurites around the heat source elongated during heat treatment, and physical connections between neurites from distinct neurons occurred within 1 min When the laser power was 18 mW, neurons in the observation area (within ~100 μ m from the heat source) exhibited neurite outgrowth (Fig. 2a, Supplementary Movie S6).
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