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In development or injury repair, neurons extend axons and dendrites across great distanges to innervate specific targets for nerve signalling. These axonal and dendritic processes, collectively called neurites, are long, thin cell processes which extend from the main cell body. They are guided to their destinations by the neurite's specialized tip, the growth cone, which senses physical and chemical markers that determine its rate and direction of outgrowth.

Studying these outgrowth and pathfinding phenomena is important not only for increasing our general understanding of development, but also as a prerequisite for any type of tissue engineering involving the reconnection of damaged nerves in the future.

To create a well-define experimental study of this process, we observe the behavior of dorsal root ganglia (DRG) explants or dissociated neurons cultured on a surface which has been micropatterned using a laser-driven photoimmobilization process.

If a chick embryonic dorsal root ganglion (DRG) explant is cultured on a unmodified polystyrene surface, one would expect to see fibroblasts and schwann cells spreading outward in all directions. The neurites would then wander in random directions, primarily growing on top of other cells, as shown below in figure 1.

Figure 1

However, in response to the invisible pattern of immobilized IKVAV-containing peptide, neurites can grow preferentially along the pattern. Figure 2 shows an example of the type of directed neurite outgrowth that can result when neurons are cultured on these patterned surfaces. Here, the pattern drawn with the laser is a rectangular grid of lines, spaced 50 µm apart in the horizontal direction and 100 microns apart in the vertical. The peptide is an IKVAV-containing sequence based on laminin. The DRG explant is out of the field of view, to the upper left.

Figure 2

This type of experiment has also been used to study neurite responses to obstacles, such as the end of a line or a choice of several lines. By controlling the peptide density through the laser dosage, this technology also allows for the study of neurite outgrowth onto gradients.

This work was funded by NSF.

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