Insights into Nerve Regeneration in Worms

Utilizing a precisely targeted laser, investigators have cut apart a single neuron in the roundworm Caenorhabdtis elegans--an accomplishment that opens up new approaches for researching nerve regeneration in this genetically modifiable organism. Certainly, these early studies have shown that the severed nerves of worms are able to regenerate and regain full function.

Researching nerve regeneration in the worm, according to the investigators, could provide answers to elusive questions not currently accessible by studying more complicated animals, including zebra fish and mice.

"This new capability of cutting individual nerves offers the opportunity to use the well-characterized genetics of C elegans to study the basic mechanisms of nerve regeneration,” state Dr. Yishi Jin, a researcher at the University of California, Santa Cruz (UCSC). "Until now, there has been little study of nerve regeneration using genetic methodology because most studies have been done on higher vertebrate organisms, where following the consequences of genetic manipulation is not yet readily accessible.” These studies, according to Dr. Jin, would involve producing gene mutations thought to be involved in nerve regeneration and evaluating the effects on regeneration following laser cutting of the nerves.

The study, published in the December 16, 2004, issue of the journal Nature, incorporated using a laser that produces energy pulses of 200-quadrillionths of a second in a beam focused to less than one-hundredth the diameter of a human hair. The laser can vaporize tissue accurately without causing extensive heat or damage that would compromise the viability of the targeted cell or surrounding tissue, according to Dr. Jinn.

The investigators first introduced a gene that generated a green fluorescent protein in the target nerve, in this instance, one that controls a specific muscle movement in the worm. When they focused the laser at the cable-like axon that slid sway from the nerve-cell body, they discovered that they could precisely cut the axon. They noted that both ends of the severed nerve axon immediately retracted, but that in approximately 50% of the cases, the nerve regrew in about one day. By conducting dye-uptake studies, the investigators could see that the laser had cut the axons, and had not merely bleached the area struck by the beam.

The investigators also observed a fascinating and possibly significant finding: the worms that had been operated on demonstrated evidence that the nerves had regrown and also regained the ability to move the muscle served by the neuron. This finding indicated that the nerve regrowth caused functional alterations.

"We see that the proximal end, nearest the cell body, appears to begin regrowth, and the distal end seems to hang around for a while. Depending on how fast the proximal end regrows, it might attach to the distal end. Otherwise, the distal end seems to deteriorate, and the nerve regeneration will proceed from the proximal end. However, we will need to do more detailed studies to determine whether regeneration is of the two cut axons, or due to a complete regrowth,” said Dr. Jin.

The laser the scientists used had a custom-built device that provided a precise laser focus on biologic samples, but the laser itself is available commercially. Therefore, the method can be readily used by other laboratories, according to Dr. Jin. And with its established ability to sever individual nerves, she foresees the laser being utilized for other applications, such as selective ablation of subcellular structures, to research their role in nerve regeneration.


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