Tests on mice show a vaccine can reduce behavioural defects associated with Alzheimer's disease, raising hope among scientists on Wednesday that a treatment for the main cause of dementia in the elderly is a step closer.

Three separate studies featured in Nature magazine used mice genetically engineered to mimic the disease, and for the first time established how immunisation affected the animals' behaviour, as opposed to the chemistry of their brains.

"This is significant," said Paul Chapman of the Cardiff School of Biosciences. "It's the first demonstration that a treatment strategy can prevent cognitive loss."

The research centres around hopes that a vaccine can be used to stimulate the body's immune system to destroy the waxy plaques that build up on the brains of sufferers.

Results released last year of tests on mice showed the vaccine prevented plaque build-up in younger rodents and stopped it accumulating in older animals.

"The vaccination first hit the headlines in the summer of 1999 when it was found to remove plaques," said David Westaway of the University of Toronto, which performed one of the tests.

"But it did not address learning and memory, which is the main clinical feature of Alzheimer's disease. If it does not address that then it is rather irrelevant," he told Reuters.

As well as raising optimism that the vaccine is as effective on behaviour as it is on reducing plaque build-up, the latest trials reinforce the theory that the plaque and dementia are in some way linked. But Westaway urged caution.

"There is a complication still -- the relationship between plaque and learning and memory might not be a straight-line one. But I think this does give us cause for optimism. We could have done this and come away with nothing."

NEW WATER MAZE TEST

The progress reported by two North American research teams was partly thanks to a new technique developed by scientists at the University of Edinburgh in Scotland.

A statement from the university described the elaborate water test where the exit location keeps changing. When mice want to leave the water, they can rely only on their short term memories of the current location of the exit.

"When you keep changing where they have to go, the mice with the elevated beta-amyloid levels get confused."

Deposits of beta-amyloid peptides in the brain are the hallmark of Alzheimer sufferers and of mouse models.

Alzheimer disease affects millions of mainly elderly people worldwide. Symptoms include memory loss and difficulty with speaking and coordination.

It affects over half the 700,000 Britons suffering from dementia and an estimated four million people in the United States. By 2025 the disease is forecast to plague up to 22 million globally if no cure is found.

A leader in the pharmaceutical research is Irish firm Elan Corp, which developed the vaccine used in the trials. It is conducting clinical trials with American Home Products Corp. Drugs already on the market offer only limited relief from symptoms.

The Alzheimer's Society in London welcomed the development.

"This is a very exciting piece of research," it said in a statement. "If the results of this study can be replicated in humans it means the serious possibility of an intervention that could treat or even prevent dementia developing."

(From ChinaDaily)