Zebrafish, like a number of lower animals, are far better at regenerating lost tissue than mammals. In recent years, researchers have been investigating the mechanisms by which this superior regeneration works. It is possible that mammals such as we humans still have the necessary machinery, but it is turned off - or if we have lost it, that there is a way to recapture some of that loss through genetic engineering or other advanced medicine. But first, far more must be learned of the way in which regeneration proceeds in species like the zebrafish:
The secret to zebrafish's remarkable capacity for repairing their brains is inflammation ... Neural stem cells in the fish's brains express a receptor for inflammatory signaling molecules, which prompt the cells to multiply and develop into new neurons.
Zebrafish, like many other vertebrates, are able to regenerate a variety of body tissues, including their brains. In fact [mammals] are the ones that seem to have lost this ability - they are kind of the odd ones out. [Given] the therapeutic potential of neuron regeneration for patients with brain or spinal injuries, [we'd] like to figure out if we can somehow reactivate this potential in humans.
Last year, [researchers] discovered that radial glial stem cells are responsible for producing new neurons during brain regeneration in zebrafish. But they didn't know what prompted these cells to spring into action. Inflammation seemed a good candidate, [as] it arises as an immediate response to injury.
[Researchers] introduced Zymosan A - an immunogenic factor derived from yeast - into the brains of zebrafish to induce inflammation in the absence of injury. They found that, just like brain injury, Zymosan A induced significant glial cell proliferation and new neuronal growth. In fish with suppressed immune responses, however, brain injury did not induce regeneration, further suggesting a role for inflammation.