Researchers at Brigham and Women's Hospital today reported finding a pathway in the brain that allowed them to use an experimental drug to slow the progression of Lou Gehrig's disease in mice.

The treatment, which blocks an enzyme critical to the death of brain cells involved in the disease, may also prove helpful to a variety of other more common illnesses of the brain and nervous system, including Alzheimer's, Parkinson's and Huntington's diseases.

``The finding represents potential with a capital P,'' said Leon J. Charash, chairman of the medical advisory committee of the Muscular Dystrophy Association, which funded the study.

The treatment extended the lives of the mice who received it by the equivalent of 14 human months. The mice had been genetically engineered to contract the human version of Gehrig's disease, also known as amyotrophic lateral sclerosis (ALS).

Dr. Robert M. Friedlander, lead author of the study in today's issue of Science, said the finding is an important, but not final, step in finding a good treatment for these illnesses.

``We don't know the trigger yet, but we at least know the bullet,'' he said. ``Now, we can at least work against the bullet.''

Friedlander and his colleagues identified the process of cell death leading to ALS in the spinal cords of the mice and then treated them with an experimental drug.

The drug, known as a caspase inhibitor, is designed to block caspases, enzymes that signal a damaged or worn-out cell to commit suicide.

Scientists now believe that in a variety of brain diseases caspases that should be lying dormant inside fairly healthy neurons are somehow activated to kill them instead.

If doctors could block caspases' action, they might be able to save important nerve cells.

In this case, the drug proved effective in halting the process of cell death, with the disease progressing more slowly in the treated mice.

``It suggests a new therapy avenue for ALS and other neurodegenerative diseases and adds weight to the idea of a drug cocktail approach to treat these disorders,'' said Charash of the MDA.

In the research, the doctors manipulated the biochemical pathways by which cells in ALS undergo a programmed death.

They used a drug known as zVAD-fmk, which blocks the proteins known to cause programmed cell death. They implanted miniature pumps in the mice's brains to bathe neurons with the drug.

While the drug used in the study on mice is considered too toxic for use in humans, the researchers said the idea is to find less toxic compounds that can do the same thing.

At least a half dozen drug companies are now trying to create caspase inhibitors that are safe for use in humans.

ALS, which affects about 30,000 Americans, is a devastating adult-onset neurodegenerative disease that destroys specific nerve cells in the brain and spinal cord called motor neurons. The result is paralysis and death, usually within five years.

While drug companies might not jump at the opportunity to find a treatment for a disease that affects so few people, Friedlander said one of the most exciting aspects to today's finding is that it may also be of use in the treatment of such other brain diseases as Alzheimer's, Parkinson's and Huntington's.

The Associated Press contributed to this report.