How a goldfish keeps its nerve

Research into how animals repair damaged tissue may help spinal injury victims, says Paul Rodgers

Goldfish do it, iguanas do it, so why can't the former Superman actor Christopher Reeve and other spinal injury victims do it too - regenerate their damaged nerve cells? The question, which has long perplexed neurologists, may finally have an answer - and with it a possible new treatment for paralysis.

It is our ability to even ask such questions that is at the heart of the problem. According to Professor Michal Schwartz at the Weizmann Institute of Science in Israel, mammalian nerve cells have traded a talent for regeneration for the ability to learn. In general, the bargain benefits humans; except when injury to the spinal cord - the 45cm, finger-thick bundle of nerves running through 38 vertebrae - leaves us without feeling or the use of our limbs.

Schwartz's theory is based on the earlier discovery that the action of the immune system is suppressed in the brain. She says this is partly because the process of learning involves rewiring the billions of connections between neurons. An automatic repair mechanism that returned this network of nerve cells to its original form would cause something akin to amnesia. "Clearly you don't want interference from outside systems," she said.

This may explain the goldfish's famous short memory - said to last only as long as it takes to swim around a bowl. Its immune system may be wiping its memory as it swims.

But this leads to the idea that the same suppression of the immune system in higher organisms also stops regrowth of the neurons, which occur in the brain, spinal column and optic nerve. Experiments by Schwartz and her team offer evidence that this is the case, and also suggest a way of getting around the problem.

One of the curiosities of spinal injuries is that the damage done to the nerves tends to be greater than would be expected from the initial injury itself. With ordinary organs, such as the skin, the first reaction to damage is the release of chemical messengers which attract macrophages, cells in the immune system that gobble up foreign bodies and the remains of dead cells, to the site of the wound. These release hormones which promote regrowth of the damaged cells. The arrival of the macrophages is visible even to the non-scientific eye, being signalled by swelling.

But when spinal nerves are damaged, the swelling is much less than in other parts of the body. Schwartz found that the nerve cells were giving off a chemical - she dubbed it Immune Privilege Factor - that discouraged macrophages from coming to the site of the injury, and stopped them from doing their work if they did show up.

Without the macrophages to effect a cleaning operation, toxins released from dead cells went on to damage neighbouring healthy ones. The suppressed macrophages also appeared to release highly reactive free radicals, which added to the damage. Without the hormonal doses, the remaining nerve cells made no effort to rebuild connections across the damaged section.

The odd thing is that this does not apply to parts of the nerve cells that extend to the rest of the body. The long tendrils known as axons that connect one nerve cell to another can stretch the length of the spinal column, or to the extremities of the body. If a cut on your finger severs an axon, the immune system reacts normally and the damage is repaired.

In Schwartz's experiments, the neurons of a rat's optical nerve were severed. She took blood samples from the animal, separated the macrophages, and in a test tube exposed a damaged axon from elsewhere in the rat's body to them. The macrophages became activated; when they were then injected into the damaged optic nerve, they began removing the debris of the dead cells and releasing their healing hormones.

Schwartz is cautious about predicting a cure for paralysis, though she does think doctors will eventually use a technique similar to her own. It is theoretically possible to come up with a drug that blocks Immune Privilege Factor. The problem would be to keep it from spreading to other parts of the central nervous system, where it could play havoc with memory and learned responses. Injected macrophages might also spread to some extent, though probably not as far.

Other researchers favour a drug-based approach. Schwartz says her work is based in part on earlier studies by Professor Schwab at the Swiss Institute for Brain Research. He has not only identified two growth inhibitors, but also developed antibodies to block them. Treated with these, axons that would normally sprout for a millimetre and then halt will keep growing for a centimetre.

An effective clinical treatment, however, is years away. Schwartz measured her success by counting the new fibres that had grown across the surgical cut made in her rat's optical nerves. It did not measure how well the new connections were working - something the team is now trying to discover.

Another question is whether the treatment works only when a wound is fresh. If so, it would be of little help to Mr Reeve and others who have been injured in the past. But it could provide a new life for future victims of spinal injury.

Suggested Topics
Start your day with The Independent, sign up for daily news emails
  • Get to the point
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Junior Web Designer - Client Liaison

£6 per hour: Recruitment Genius: This is an exciting opportunity to join a gro...

Recruitment Genius: Service Delivery Manager

Negotiable: Recruitment Genius: A Service Delivery Manager is required to join...

Recruitment Genius: Massage Therapist / Sports Therapist

£12000 - £24000 per annum: Recruitment Genius: A opportunity has arisen for a ...

Ashdown Group: Practice Accountant - Bournemouth - £38,000

£32000 - £38000 per annum: Ashdown Group: A successful accountancy practice in...

Day In a Page

Election 2015: How many of the Government's coalition agreement promises have been kept?

Promises, promises

But how many coalition agreement pledges have been kept?
The Gaza fisherman who built his own reef - and was shot dead there by an Israeli gunboat

The death of a Gaza fisherman

He built his own reef, and was fatally shot there by an Israeli gunboat
Saudi Arabia's airstrikes in Yemen are fuelling the Gulf's fire

Saudi airstrikes are fuelling the Gulf's fire

Arab intervention in Yemen risks entrenching Sunni-Shia divide and handing a victory to Isis, says Patrick Cockburn
Zayn Malik's departure from One Direction shows the perils of fame in the age of social media

The only direction Zayn could go

We wince at the anguish of One Direction's fans, but Malik's departure shows the perils of fame in the age of social media
Young Magician of the Year 2015: Meet the schoolgirl from Newcastle who has her heart set on being the competition's first female winner

Spells like teen spirit

A 16-year-old from Newcastle has set her heart on being the first female to win Young Magician of the Year. Jonathan Owen meets her
Jonathan Anderson: If fashion is a cycle, this young man knows just how to ride it

If fashion is a cycle, this young man knows just how to ride it

British designer Jonathan Anderson is putting his stamp on venerable house Loewe
Number plates scheme could provide a licence to offend in the land of the free

Licence to offend in the land of the free

Cash-strapped states have hit on a way of making money out of drivers that may be in collision with the First Amendment, says Rupert Cornwell
From farm to fork: Meet the Cornish fishermen, vegetable-growers and butchers causing a stir in London's top restaurants

From farm to fork in Cornwall

One man is bringing together Cornwall's most accomplished growers, fishermen and butchers with London's best chefs to put the finest, freshest produce on the plates of some of the country’s best restaurants
Don't believe the stereotype - or should you?

Don't believe the stereotype - or should you?

We exaggerate regional traits and turn them into jokes - and those on the receiving end are in on it too, DJ Taylor
How to make your own Easter egg: Willie Harcourt-Cooze shares his chocolate recipes

How to make your own Easter egg

Willie Harcourt-Cooze talks about his love affair with 'cacao' - and creates an Easter egg especially for The Independent on Sunday
Bill Granger recipes: Our chef declares barbecue season open with his twist on a tradtional Easter Sunday lamb lunch

Bill Granger's twist on Easter Sunday lunch

Next weekend, our chef plans to return to his Aussie roots by firing up the barbecue
Joe Marler: 'It's the way I think the game should be played'

Joe Marler: 'It's the way I think the game should be played'

The England prop relives the highs and lows of last Saturday's remarkable afternoon of Six Nations rugby
Cricket World Cup 2015: Has the success of the tournament spelt the end for Test matches?

Cricket World Cup 2015

Has the success of the tournament spelt the end for Test matches?
The Last Word: Justin Gatlin knows the price of everything, the value of nothing

Michael Calvin's Last Word

Justin Gatlin knows the price of everything, the value of nothing