For the first time, transplanted genetically altered cells can prevent brain cell death in laboratory animals suffering from neurological damage similar to Alzheimer's disease in humans, scientists reported this week.

Researchers at University of California-San Diego and Harvard University said their findings showed that grafts of genetically engineered cells may eventually "provide an effective treatment for some disorders of the central nervous system."In a study published in the journal Science, the research team said it altered cultures of connective tissue cells, called fibroblasts, so they contained the gene for nerve growth factor or NGF, a protein that promotes growth of certain cells.

The NGF-secreting cells then were grafted into laboratory rats whose brains had been surgically severed to impair cholinergic neurons - cells that produce a chemical vital for learning and memory. A control group of brain-damaged rats received grafts that did not contain the NGF gene.

"In Alzheimer's, one of the cardinal deficits is the vulnerability of the cholinergic neurons. The evidence is strong that cholinergic loss in Alzheimer's is somehow related to memory loss," said Fred Gage, the study's senior author and a neurosciences professor at the San Diego university's medical school.

Alzheimer's disease - a gradual, irreversible erosion of brain cells that control thought and memory - affects an estimated 1.2 million to 4 million older Americans.

Gage emphasized that cholinergic loss "certainly isn't the whole cause of the disease (Alzheimer's) and replacing those neurons would not cure the patient. The idea would be more of treating certain symptoms of the disease."

Two weeks after the rats received grafts in their brains, the scientists killed the animals and examined their brain cells.

In the eight rats that received NGF-secreting implants, about 90 percent of the cholinergic cells affected by the brain-damaging surgery survived. That compares to a cell survival rate of about 50 percent for the eight rats whose grafts lacked the NGF gene and for other brain-damaged rats that received no implants at all.