Old slow monkeys give ageing clue

By STEVE CONNOR

Some of the oldest monkeys in the world have helped scientists solve one of the greatest puzzles of ageing - why do oldies slow down?

Like people, monkeys suffer from a gradual and irreversible loss in the ability to handle sensory information from the eyes, ears and other sense organs.

Now scientists have established that, as well as the sense organs themselves deteriorating, the information-processing centre of the brain which handles incoming sensory data also loses efficiency.

A team led by Audie Leventhal of the University of Utah School of Medicine in Salt Lake City discovered an explanation for this mental decline by studying very old Macaque monkeys in a captive colony set up in China by scientists in the 1950s.

Some of the monkeys are 32 years old - equivalent to a human age of 96 - which makes them twice the age of the oldest macaques found in the wild.

The study, reported in the Science journal, investigated a particular region of the cerebral cortex - the brain's "higher" information-processing centre - involved in handling visual information.

It found very old monkeys' nerves in this region had lost their ability to discriminate between one signal and another and that this loss was directly related to the reduced presence of a neurotransmitter chemical called gamma-aminobutyric acid (Gaba).

Dr Leventhal said the loss of Gaba seemed to be responsible for the indiscriminate "firing" of electrical impulses by old nerves, which suggests that drugs aimed at restoring Gaba could also revive mental agility.

"The good news is that there are a lot of drugs that can facilitate Gaba function and maybe some of them will help," he said.

"If it's going on in the visual cortex, it's probably going on in other parts of the cortex."

The experiment involved showing images to old and young monkeys and observing the electrical reactions of the visual cortex nerves.

As expected, many of the nerve cells of the older animals reacted indiscriminately by responding to a wide range of orientations while a smaller proportion of the nerves belonging to young animals showed such a lack of discrimination.

When the scientists added Gaba or Gaba-like drugs to the older nerves, they behaved like younger ones, doubling or tripling of their discriminatory powers.

Being able to boost sensory discrimination within the information-processing centre of the brain could make it possible for older people to react as quickly as young people to fast-moving changes.

"Many sensory problems suffered by the elderly stem not from deterioration of the eyes and ears, but from declines in the brain regions that process sensory information," the Science article said.

"[Gaba] could be bigger than Viagra and drug companies are drooling - a treatment that turns back time on the ageing brain and makes old neurons act young again."

Dr Leventhal said it was remarkable that his was the only lab studying higher brain functions in ageing monkeys.

"Old monkeys are rare, but the world is full of old human primates," he said. Monkeys aged just like people, he added. "They really do look like grandpa."

Why we slow with age

Older people's brains gradually lose a chemical known as Gaba, which enables us to understand what we see, hear and touch.

Research shows Gaba-boosting drugs help old monkeys to see almost as well as younger ones.

Scientists hope the drug will work the same way for humans.

- INDEPENDENT