Page last updated at 02:10 GMT, Friday, 27 February 2009

Alzheimer's plaques 'big impact'

Alzheimer's cell
Sticky clumps in the brain kill key nerve cells

The sticky amyloid plaques linked to Alzheimer's disease may have a more widespread impact on the brain than thought, American research suggests.

The deposits are known to damage neurons - cells that transmit signals throughout the nervous system.

But now they have also been shown to impact on astrocyte cells, which play a key support role in the brain.

The work, featured in Science, suggests the full effect of plaques on the brain is much more complex than suspected.

Our work suggests that amyloid plaques might have a more complex role in altering brain function than we had thought
Dr Kishore Kuchibhotla
MassGeneral Institute for Neurodegenerative Disease
It also raises the possibility of a new target for drugs to treat Alzheimer's.

Astrocytes are abundant throughout the brain, making up about half of its total volume.

Until recently they had been thought to play a passive support role to neurons, but are now thought to send their own chemical signals, which can travel long distances across the brain.

The researchers, from the MassGeneral Institute for Neurodegenerative Disease, found that the plaques seemed to make astoctyes more active - and not just those cells in their immediate vicinity.

Previously it had been thought that plaques only impacted on neurons - and then only on those that were close by.

But the latest finding suggests individual plaques are able to spread their malign influence much further afield through the tissue of the brain.

Scratching the surface

Lead researcher Dr Kishore Kuchibhotla said: "Our work suggests that amyloid plaques might have a more complex role in altering brain function than we had thought.

"We've only begun to scratch the surface of how plaque deposition impacts astrocyte function.

"One key question will be how increased astrocyte signaling impacts neuronal function, and another will be whether astrocyte activity limits or intensifies plaque deposition."

The researchers labelled astrocytes with a dye that lights up when the cell is active, and shuts off when it is not.

They were surprised to see astrocytes flicker on and off at much higher rates in mice bred to be riddled with plaques.

The astrocyte activity appeared to be synchronized and passed to distant areas of the brain in a wave-like fashion.

Blocking neuron activity had no impact on reducing astrocyte activity, suggesting the effect on the cells was independent.

Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "This development may prove to be a breakthrough in our understanding of the disease, and the hunt for new Alzheimer's drugs.

"It's a new and exciting area of research for Alzheimer's, so these findings mark the beginning of the journey for the scientists involved, but it is a path that may someday lead to the treatment we desperately need."

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