Tracking Activity At Single Synapses

With the aid of a new fluorescent compound, scientists for the first time can observe release and uptake of neurotransmitters at individual synapses in brain tissue (Science, DOI: 10.1126/science.1172278).

Dalibor Sames and David Sulzer of Columbia University dubbed the optical tracer "fluorescent false neurotransmitter 511" (FFN511). The compound behaves like the neurotransmitter dopamine but doesn't interfere with dopamine's normal activity.

The researchers bathed a brain slice in a solution containing FFN511. Using a fluorescent microscope, they observed the tracer—and by extension, dopamine itself—as it accumulated in synaptic vesicles in the presynaptic terminals of neurons in the brain tissue. They then stimulated the neurons and tracked the release of the tracer from the presynaptic terminals.

The scientists deduced from the behavior of the tracer that the amount of dopamine released varies greatly among individual synapses and depends on stimulation frequency. Sulzer says this observation suggests a mechanism underlying learning and decision-making.

Jonathan V. Sweedler, who studies analytical neurochemistry at the University of Illinois, Urbana-Champaign, says the Columbia work provides a new approach for studying chemical communication in the brain. "The ability to have a fluorescent compound taken up and packaged within synaptic vesicles, and to follow the position and release of those vesicles, is fantastic."