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 and shares some of its structural features but doesn't interfere with dopamine's normal activity. The researchers bathed a brain slice in a solution containing FFN511. Using a fluorescence 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 FFN511 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.