Chemical Audit of a Single Neuron

LOS ANGELES--Scientists have developed an electronic nose, of sorts, that sniffs out dozens of chemicals in an individual nerve cell. The remarkable achievement, described here last week at the annual meeting of the Society for Neuroscience, provides the first snapshot of a single neuron's chemical milieu and could lead to an early warning system for tracking biochemical changes within cells that signal the development of tumors.

To send nerve impulses, animals rely on more than 100 kinds of small messenger molecules called neurotransmitters, which dart between individual neurons. But detecting which neurotransmitters come from which neuron is arduous: Like other cells, neurons are packed with thousands of chemicals. To simplify the task, a team led by chemist Jonathan Sweedler of the University of Illinois, Urbana-Champaign, has been working on marine snails that have particularly large neurons.

The researchers teased out single neurons, ground them up and, dabbed the slurry onto a glass tube no wider than a human hair. A mild electric field separated the neurotransmitters and their byproducts by dragging them down the tube at different rates according to their charge and size. Lighting up the separated compounds using an ultraviolet laser beam, the team was able to distinguish up to 30 different compounds from a single neuron. The device could detect neurotransmitters from a sample of just 1% of the cell.

The technique has the potential to unmask subtle warning signs of disease in single cells, such as specific strings of amino acids and other telltale chemical tracers of cancer, says chemist Andrew Ewing of Pennsylvania State University, University Park. And it may prove a boon to neural biochemistry, he says, by sorting out the roles of individual neurons in memory and learning in the mammalian brain. The technique should soon be sensitive enough to study mammalian neurons, which are 10 times narrower than those of snails, Sweedler says.