Synapses Shout for Long Distance

How do you make yourself heard while standing far from the fray? Neuroscientists have wondered the same thing about synapses, the connection points between neurons that send signals to the center of a nerve cell. The answer, just in, is that distant synapses shout.

Neurons communicate via long tendrils, called dendrites, that branch out from the neuronal cell body and are studded with synapses. The cells listen for signals picked up at the synapses, where other neurons make contact. A neuron will pass along its own message only when it has something to say; that decision is reached once it receives enough messages from its dendrites. In certain neurons in the brain region called the hippocampus, dendrites can stretch as far as a millimeter from the cell body--far enough to fade a synapse's signal. These hinterland synapses do seem to relay useful signals to the neuron, but no one knew quite how they managed.

Suspecting that distant synapses might speak with louder voices, two neuroscientists--Jeffrey Magee of Louisiana State University Medical Center in New Orleans and Erik Cook of Baylor College of Medicine in Houston, Texas--listened closely as they stimulated synapses. The researchers found that the more distant the synapses, the stronger the signal. By the time the signal reached the cell body, those that traveled long distances sounded about as loud as those that originated nearby, they report in the September issue of Nature Neuroscience.

The researchers aren't sure yet what mechanism pumps up the volume on distant synapses. The finding "will open up a whole new field," says Daniel Johnston of Baylor College of Medicine, as neuroscientists try to figure it out.

Related sites
Synapse Web, featuring images and models of synapses