When memory is lost due to dementia such as Alzheimer's disease, is it gone for good?
Scientists probed that idea in lab tests on mice. The mice were bred to develop a progressive dementia similar to Alzheimer's disease. The researchers were able to create mice with a gene that could be "turned off."
Symptoms of Alzheimer's disease occur when brain nerve cells that process information and memory degenerate and die. Abnormalities such as amyloid plaque accumulate on nerve cells and tangles of proteins -- called tau -- form in nerve cells.
Tau protein is thought to be responsible for nerve cell death and dementia.
When tau protein production was "turned off," the mice's memory didn't just stop getting worse. It improved.
It's too soon to know if the same could be possible for humans. If so, it might be possible to recover mental function in the early stages of diseases such as Alzheimer's, write Karen Ashe, MD, PhD and colleagues in Science.
Since the findings are based on mice, the clinical implications should be viewed "with caution," they write.
"Most Alzheimer's disease treatments focus on slowing the symptoms or preventing the disease from progressing," says Ashe in a news release.
"But our research suggests that in the future, we may be able to reverse the effects of memory loss, even in patients who have lost brain or neural tissue," she continues.
Ashe is a neurology professor at the University of Minnesota.
About the Study
The tests were done on mice bred to develop Alzheimer's-like dementia.
As dementia settled in, the mice did worse when placed in a water maze -- a test used to assess learning and memory. The test can help determine abnormalities in an area of the brain affected by Alzheimer's dementia.
Before dementia, the mice worked to master the maze quickly. They learned to find a hidden platform where they could get out of the water.
With dementia, the mice forgot the route to the platform.
Then, the researchers laced some mice's food with a drug to turn off tau production. Afterward, memory improved in those mice.
"The ability to acquire and retain new spatial memories was restored ... and the improvement was related to the suppression of tau and not [the chemical used to suppress tau]," write the researchers.
The mice's memory recovery was "surprising," write the researchers.
When tau production was curbed, the mice already had "abundant" brain tangles, had lost a significant amount of brain weight, and had lost brain cells, the researchers write.
"Thus, neurofibrillary tangles are not sufficient to cause cognitive decline or neuronal [brain cell] death in this model," write Ashe and colleagues.
SOURCES: SantaCruz, K. Science, July 15, 2005; vol 309: pp 476-481. News release, University of Minnesota. News release, Science.