A family of antibiotics including penicillin may help prevent nerve damage in a variety of neurological diseases, research has found.
Antibiotics may protect against Alzheimer's disease
In lab tests on mice a team from Johns Hopkins University in Baltimore found the drugs turn on protective genes
This may have a beneficial effect on conditions such as dementia, stroke and epilepsy and Lou Gehrig's disease.
However, the Nature study stresses it is too soon to recommend the use of antibiotics for this purpose.
There is concern that the widespread over-use of antibiotics is leading to increased levels of resistance, rendering the drugs of less and less use.
In the brain, a chemical called glutamate normally excites nerves so that electrical signals can travel from one to the next.
But too much of the chemical can over stimulate and kill nerves, leading to disease.
Antibiotics appear to tackle the problem by triggering genes which control production of a protein called GLT1, which can transport excess glutamate away from nerve endings.
Researcher Professor Jeffrey Rothstein said: "It would be extremely premature for patients to ask for or take antibiotics on their own.
"Only a clinical trial can prove whether one of these antibiotics can help and is safe if taken for a long time."
The researchers engineered mice to develop the equivalent of Lou Gehrig's disease, which in people causes progressive weakness and paralysis and ends in death, usually within three to five years of diagnosis.
The animals were given daily injections of an antibiotic called ceftriaxone just as symptoms began to develop.
The drug appeared to delay both nerve damage, and symptoms, and extended survival by 10 days compared to untreated animals.
Professor Rothstein said: "We're very excited by these drugs' abilities.
"They show for the first time that drugs, not just genetic engineering, can increase numbers of specific transporters in brain cells."
"This approach has potential applications in numerous neurologic and psychiatric conditions that arise from abnormal control of glutamate."
The researchers plan a major clinical trial in the spring to investigate further the potential of the drug in treating Lou Gehrig's disease.
Ceftriaxone is currently used to treat bacterial infections in the brain.
In tests penicillin, which comes from the same family, protected nerve cells best in lab dishes, but ceftriaxone produced the best results in mice - possibly because it more easily crosses from the blood to the brain.
However, glutamate damage is only aspect of Lou Gehrig's disease, so the drug treatment could not prevent the animals from eventually dying.
Professor Rothstein said the challenge would be to find drugs that protect against the other causes of cell death.
"The combination might offer a real therapy, much like using drug combinations to treat cancer."
Rebecca Wood, of the Alzheimer's Research Trust, described the study as "potentially exciting".
"This is an original and logical approach. However, as the authors have stated, it is far too early to consider prescribing antibiotics for these human conditions.
"We don't yet know whether they will work in people, and since GLT1 loss is only part of the problem in these human diseases, a combination of various therapies will probably be needed.
"While antibiotics have been used against bacterial infections for 50 years, more research will be needed into the effects of long-term antibiotic use."