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Experts claim to have found how stress can lead to memory loss in old age.

Edinburgh University researchers have shown how two receptors in older brains react to the stress hormone cortisol linked to forgetfulness as people age.

The study on older mice found one receptor was activated by low levels of cortisol, which helped memory.

But once levels of the hormone were too high they spilled over on to a second receptor, activating brain processes which contribute to memory loss.

When the receptor linked to poor memory was blocked, the memory recall problem was reversed.

Scientists say the discovery could lead to treatment for conditions such as early Alzheimer's.

Dr Joyce Yau, who led the study at Edinburgh University's centre for cardiovascular science, said: "While we know that stress hormones affect memory, this research explains how the receptors they engage with can switch good memory to poorly functioning memory in old age.

"We now know that lowering the levels of these stress hormones will prevent them from activating a receptor in the brain that is bad for memory.

"Understanding the mechanisms in the brain which affect memory as we age will help us to find ways to combat conditions linked to memory loss."

The scientists said the research helps explain why too much stress over a prolonged period interferes with the normal processes in storing everyday memories, despite the fact that a little bit of stress can help people better remember emotional memories.

Scientists found that high levels of cortisol in aged mice made them less able to remember how to navigate a maze.

The study was published in the Journal of Neuroscience and was funded by the Medical Research Council (MRC).

Professor Chris Kennard, chairman of the MRC's neuroscience and mental health board, said: "This research highlights some interesting, original concepts relating to why memory loss occurs in old age.

"With people living ever longer, the MRC is really focusing on research which allows elderly people not just to survive but also to stay healthy."

The researchers are looking at a new chemical compound which blocks an enzyme, known as 11beta-HSD1, which helps produce stress hormones within cells.

The study is supported by a Seeding Drug Discovery award from the Wellcome Trust charity.

It is hoped this could be used to develop a drug treatment to slow the normal decline in memory associated with ageing, or even improve memory in people who are very old.