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By Suzanne Rostler
NEW YORK, Mar 14 (Reuters Health) - In preliminary study results that may pave the way for an eventual cure for memory loss associated with stroke and Alzheimer's disease, US scientists have found that the growth of new nerves in the brain was linked to at least one type of memory in adult rats.
The researchers looked at trace conditioning, a type of memory that involves an area of the brain known as the hippocampus. Blocking the growth of new nerves impaired this type of memory, but cultivating new nerves reversed the damage.
The adult brain continues to develop new nerves or neurons but it has been unclear, until now, whether these nerves are involved in memory.
"These results indicate that newly generated neurons in the adult are not only affected by the formation of a hippocampal-dependent memory, but also participate in it," according to Dr. Tracey J. Shors from Rutgers University in Piscataway, New Jersey, and colleagues.
To investigate, the scientists conditioned the rats to associate a sound with a stimulus to their eyes. The rats learned to blink when they heard the sound, suggesting that they recalled the sensation and had formed a memory.
Once rats were trained, the researchers injected them with a substance that killed nerve cells in the hippocampus. The investigators found that destroying 80% of new nerves affected trace conditioning but not other types of memory that does not involve the hippocampus.
In an accompanying editorial, Dr. Jeffrey D. Macklis of Harvard Medical School in Boston, Massachusetts, said that the study answers some important preliminary questions about whether scientists will be able to one day control the development of immature neurons and stem cells--biologic building blocks that can develop into many different types of cells--to replace cells that have died as a result of disease, stroke and spinal cord injury.
"For such approaches to even be realistically considered, it is crucial to understand whether newly incorporated neurons can actually play a functional role in already existent nervous system circuitry," Macklis explained to Reuters Health.
The current study, he said, "provides evidence that newborn neurons in the adult mammalian brain actually can contribute critically to the complex behavioral function involved in certain forms of memory formation."
Shors said that while research suggests that the hippocampus is associated with memory deficits seen in patients with Alzheimer's disease, it is not clear whether restoring these cells in humans would help.
She told Reuters Health that future research will try to identify more of the details of these cells in the role of memory.
SOURCE: Nature 2001;410:314-315, 372-376.
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