Scientists Find Storehouse for Memory

The discovery may provide new targets for treating cognitive disorders

FRIDAY, Sept. 24, 2004 (HealthDayNews) -- In a finding that could lead to better insights into how memories are formed, neuroscientists say they have identified the compartment within nerve cells that stows special receptors that can be deployed to intensify incoming messages.

These compartments, called recycling endosomes, also carry other molecules and proteins, which may play a role in remodeling nerve cells, or neurons, to strengthen the connections between them.

The findings provide important clues to understanding how the brain makes memories, say the researchers from Duke University Medical Center and Brown University.

"The gist of what we're interested in is how the strength of communication is altered between neurons as the circuitry of the brain adapts, as we learn and store new memories," explained study leader Dr. Michael Ehlers, an associate professor of neurobiology at Duke.

Having a better understanding of the machinery of the brain also will help pave the way for new treatments targeting diseases that affect memory and cognition, such as Alzheimer's, the researchers said.

The study appears in the Sept. 24 issue of Science.

The brain is a vast communications network, where some neurons serve as transmitters, firing off messages to other neurons that act as receivers, or antennae. All of this data exchange occurs across a small gap between neurons, known as a synapse.

Changes in the strength of a neuron's response to those transmissions depend on the number of receptors that are present. More receptors on the information-receiving cell, called the post-synaptic neuron, make for a stronger antenna. This strengthening of connections between neurons, which can last hours or even days, is known as long-term potentiation, believed to be the cellular basis for memory, the researchers said.

Until now, scientists hadn't known the exact source of these synaptic-strengthening receptors, named AMPA receptors for the chemical substance that activates them. "We wanted to see, can we identify a hidden source of receptors within this postsynaptic neuron?" Ehlers explained.

By injecting mutant protein into rat neurons and into brain tissue, the researchers were able to confirm that the recycling endosomes house those receptors. But they were surprised to find the compartments also carried more than just AMPA receptors. In additional experiments, they found that the recycling endosome houses other material that may be used to expand synapses during memory formation.

"These findings indicate that the molecules for memory are close by to all of our synapses," said neuroscientist Dr. Roberto Malinow, whose research lab at Cold Spring Harbor Laboratory in New York investigates learning and memory by studying synaptic transmission in rodent brain slices. "We just need a way to move them into the right synapses."

In practical terms, these discoveries could lead to a better understanding of normal cognitive decline and memory diseases such as Alzheimer's. It may be that such conditions reflect impairments of synaptic plasticity, an inability of the synapses to change their properties, Ehlers suggested.

"It tells us where in the cell to look for molecular targets to improve or reverse synaptic dysfunction," he said.

"Unfortunately," added Malinow, "so little is currently known regarding the basic cause of neurological diseases that any finding significantly advances our knowledge."

More information

Check with the National Institute of Neurological Disorders and Stroke to learn about the life and death of a neuron.

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