Gene Links Nerve Growth, Memory

For the past century, brain scientists have speculated that the act of learning changes connections between brain cells. Now researchers have more direct evidence: A gene that helps nerves hook up also improves a mouse's ability to remember.

Neurons communicate with each other across connections called synapses. The ability to store and recall information appears to require the proliferation of these synapses, which send signals via chemical messengers called neurotransmitters. In an earlier study, neurobiologist Aryeh Routtenberg of Northwestern University and his colleagues found that when mice learn a new trick, the amount of a protein called GAP-43 in their brains increases. Other researchers showed that this protein causes synapses to grow and increases neurotransmitter release.

To test whether GAP-43 is a maker of memories, Routtenberg's team worked with mice that had been genetically engineered to produce extra GAP-43. Compared to normal mice, those souped up on GAP-43 made half as many wrong turns when learning to find food in a maze, the researchers report in the 20 June issue of the Proceedings of the National Academy of Sciences. The mice with extra GAP-43 showed their prowess even more dramatically when they had to wait 20 minutes between bouts of maze running, suggesting they formed memories that lasted longer than those of regular mice.

Routtenberg says that GAP-43 "occupies a pivotal position" in the formation of memories and could be a target of drugs aimed at improving memory. Neurobiologist Charles Stevens of the Salk Institute in La Jolla, California, thinks the research is an exciting starting point, but says that he'd like to see direct evidence that mice with extra GAP-43 also have different synapses, although he says there's no way to track changes in given synapses with today's technology.

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