Old drug pentylenetetrazole may improve learning and memory in Down syndrome victims

Feb 26 2007

Researchers in the United States have discovered that an old drug once used to study epilepsy substantially improved learning and memory in mice with Down syndrome symptoms.

They believe the drug pentylenetetrazole, or PTZ, may improve learning in children and adults with Down syndrome.

Furthermore the beneficial effects of PTZ, continued for two weeks after treatment and the researchers say this suggests the drug can make long-term changes in the brain as some psychiatric drugs do.

Dr. Craig Garner, a professor of psychiatry and a director of the Down Syndrome Research Center at California's Stanford University, says the treatment has remarkable potential and may help scientists understand what causes the mental retardation seen in Down syndrome patients.

The researchers are now considering a clinical trial to test whether the compound has a similar effect in humans with Down syndrome.

More than 300,000 people in the U.S. have Down syndrome, which is caused by an extra copy of chromosome 21.

It is the most frequent genetic cause of mental retardation and occurs in about one in every 800 births; it is also associated with childhood heart disease, leukemia and early onset Alzheimer's disease.

As many as 5,000 children are born each year in the United States with Down syndrome.

The majority of people have two copies of each chromosome and the additional activity of the genes on the third copy of chromosome 21 is thought to cause the symptoms of Down syndrome.

Symptoms range from moderate mental retardation to very mild disability but many of those with Down syndrome also have health problems, in particular heart trouble.

Fabian Fernandez, a graduate student in Garner's laboratory had been working on the theory that the brains of Down's patients are too strongly affected by a chemical called GABA, a neurotransmitter, or message-carrying chemical, that stops brain cells from becoming too excited.

The researchers used a mouse model of Down syndrome for their study in which about 150 genes are triplicated.

The mice used exhibited many of the cognitive problems that afflict human Down syndrome patients.

Fernandez found that after being fed 17 daily doses of milk containing a compound called pentylenetetrazole, or PTZ, the affected mice were significantly better able to identify novel objects and navigate a maze.

The treated mice performed as well as their wild-type counterparts for up to two months after drug treatment was discontinued.

The researchers say normally a precise ratio between neuronal excitation and inhibition is maintained that allows efficient learning to take place.

It is thought that Down syndrome patients have too much GABA-related inhibition, making it difficult to process information.

The researchers discovered two interesting things when testing the mice: daily doses were required for several days before any effect was detected, and once established, the effect lasted for up to two months after the drug was withdrawn.

PTZ apparently causes more GABA to be available in the brain, however too high doses cause seizures.

PTZ was once used to study epilepsy but the FDA withdrew approval for use in people when it appeared to show no benefit.

Garner and Fernandez both strongly caution individuals against experimenting with the compound or others like it on their own as they say appropriate doses and schedules have not yet been determined for humans, and the purity and safety of similar over-the-counter concoctions are questionable.

They also emphasise that PTZ treatment did not improve the learning capabilities of normal mice.

The center was created by researchers at Stanford and Packard Children’s in 2003 to rapidly translate research discoveries into useful treatments for people with Down syndrome.

The research is published in the journal Nature Neuroscience.