In neuronal cell cultures, the researchers labeled synaptic vesicles with a fluorescent dye and observed how and when the vesicles released neurotransmitters, both when the neurons were at rest and when they were active. From these observations, as well as data gathered from electrophysiological techniques, the researchers found two distinct types of vesicles.
"The functional differences of these two sets of vesicles may be the result of differences in the protein and/or lipid composition of the vesicles," Dr. Kavalali said. "Higher-resolution analysis is needed to test whether the two sets of vesicles are indeed distinct."
Dr. Kavalali said that if the two types of vesicles have different molecular compositions, as their findings suggest, those differences may make it possible to independently regulate spontaneous and activity-dependent neurotransmitter release. Spontaneous release is thought to play a role in the development of the neural circuitry in the brain and body, while activity-dependent release is responsible for functions such as learning and memory.