What do your aquarium and Edinburgh University's Centre for
Neuroregeneration have in common? They both contain zebrafish. The
popular pets, often sold under the name zebra danio, provide a wealth of
information for researchers.
Because their bodies are transparent, the fish offer scientists a window through which they can observe the central nervous system without invasive testing. Leading a team of researchers, Edinburgh University's Dr. David Lyons recently discovered that myelin—the fatty tissue that insulates nerve cells—has only a short span of time to form in both humans and zebrafish.
The zebrafish shares more than 80 percent of the genes associated with human disease, which is why it provides a great model for the way human diseases develop. However, unlike in humans, when the fish experiences nerve damage, it can not only repair it, but also create entire replacement neurons and synapses, which are crucial for signal conduction in the brain.
Myelin Is Essential
Myelin insulates nerves the way the plastic coating on a lamp cord serves to insulate its wires. Myelin allows signals from the brain to travel within the body quickly. Without that insulation, our nerve impulses short out in much the same way the lamp would. Studying the way the zebrafish heals its damaged nerve coatings may shed light on how that same process could be accomplished in humans suffering from a disease that damages myelin, such as multiple sclerosis.
Multiple sclerosis (MS) is an autoimmune condition that causes a patient’s own immune system to treat this myelin covering in the brain, spinal cord, and optic nerves as a foreign substance and proceed to destroy it. More than 400,000 people in the United States have been diagnosed with MS, and worldwide that number is above 2.1 million.
When myelin is destroyed in MS patients, nerves are left bare. The human body makes an imperfect attempt to repair the damage, but scar tissue forms in place of the myelin. These scars don't transmit electrical impulses as well as the original myelin, resulting in debilitating symptoms. MS symptoms can range from mild tingling and numbness to burning sensations, bowel and bladder problems, memory issues, vertigo, spasticity (painful cramping of the limbs), and even blindness or complete paralysis.
There are many drugs on the market to reduce the number of relapses a patient with MS might suffer. Some of these drugs also slow the progression of the disease, but none of them has been shown to encourage the regrowth of myelin.
Studying the lowly zebra fish is helping researchers better understand the process by which the fish heal their myelin coatings and are able to make a complete recovery from injuries and disease.
Time Is of the Essence
When Lyons' team examined the zebrafish, they found there's only a short window of time—a matter of hours—during which the the brain and spinal cord can make the special cells necessary to regenerate myelin and repair nerve damage.
Although MS patients have plenty of these cells, called oligodendrocytes, they still don't produce enough myelin to effectively repair nerve damage in the short window in which it's possible.
If scientists can find a way to increase the time span for myelin regeneration in zebrafish and apply it to future studies using human volunteers, they might be able to encourage the body’s oligodendrocytes to successfully remyelinate the nerves. Repairing this nerve damage could mean erasing MS symptoms.
"To enhance myelin repair,” Lyons said in an interview with BBC News, “we will need to improve either [the zebrafish's] ability to make myelin during the short time in which they have to do this, or find a way to allow them to produce myelin for a longer period of time."
Zebrafish Are the New Lab Rats
Lyons’ group isn’t the only one at Edinburgh University studying zebrafish. Dr. Catherina G. Becker and her husband are making their own observations as they study human brain chemicals like dopamine in the tiny fish.
The zebrafish makes such an attractive subject, Becker told Healthline, because it has "a number of great features: Zebrafish are vertebrates, like us, and the principles of their early development are very similar to ours. However, embryonic zebrafish develop fast—within 24 hours, you have a little fish with eyes, a central nervous system (CNS), muscles, a beating heart, and they develop outside the mother's body, so you can watch developmental processes as they happen.”
"Adult zebrafish, unlike us, can regenerate their CNS, so we use them to study processes of successful central nervous system repair,” Becker added.
Further studies must be done to help us understand the neuroregeneration process in zebrafish and its implications for human patients. Until then, when you gaze at the tiny creatures in your aquarium and see their spines through their transparent skin, know that the inspiration for a new treatment or even a cure for diseases like MS often comes from the most unlikely sources.