Regular exercise could halt Parkinson's disease, US researchers believe.
Exercise has many beneficial effects
In a study on rats, exercise prevented degeneration of nerve cells that are normally destroyed by the disease.
The University of Pittsburgh researchers are now recruiting patients to see if regular exercise has the same effect in humans.
They told a meeting of the Society of Neuroscience how exercise might stimulate key proteins vital for nerve cell survival.
In Parkinson's disease, cells in the brain that contain a messenger called dopamine progressively die out.
This means messages don't get through in the normal way, which causes the tell-tale signs of the disease such as uncontrollable tremors, slow movements and rigid limbs.
There is some disagreement within the Parkinson's research community as to the benefits of intense exercise for people with PD.
While none have reported harm caused by physical activity, some studies have shown no statistical positive influence of exercise.
Dr Michael Zigmond and colleagues examined the brains of rats that had exercised for seven days before receiving a toxin that is known to induce a disease resembling Parkinson's in rodents.
They compared these animals to rats that had not been exercised before receiving the toxin.
Exercise appeared to protect the brain against Parkinson's-type damage.
Fewer dopamine-containing nerve cells, or neurons, died in the exercised rats compared to the sedentary rats.
The researchers believe exercise stimulates the production of proteins that are important for the survival of neurons.
These proteins are called neurotrophic factors. One particular neurotrophic factor, GDNF, was increased by 40% in the rats that had exercised.
Dr Zigmond said: "We are certainly encouraged that in our experimental models we can demonstrate that this sort of forced exercise improves motor function and protects the neurons affected by the disease."
He said they were so encouraged by their findings that they were now beginning a study whereby patients with Parkinson's disease will be enrolled in a 60-minute exercise programme that will meet three times a week.
A spokeswoman from the Parkinson's Disease Society said: "These are interesting results.
"For people with Parkinson's, exercise can improve general wellbeing and help with strategies to perform specific movements and tasks, guided by a professional such as a physiotherapist.
"Exercise and physiotherapy can also help with other difficulties through, for example, improving posture, falls prevention and benefiting circulatory problems."
But she said: "There is, as yet, no evidence to suggest that exercise can have a neuroprotective effect in people with Parkinson's disease."