P. Bezzi et al., "Astrocytes contain a vesicular compartment that is competent for regulated exocytosis of glutamate," Nat Neurosci, 7:613-20, 2004. (Cited in 86 papers)
The discovery of a clear, synaptic-like microvesicle in the adult hippocampal astrocyte, by Andrea Volterra's group at the University of Lausanne, Switzerland, provided the framework for understanding the structural and functional mechanisms of its uptake, storage, and release of glutamate.
The treatment of the tissue used to enhance structural resolution of the vesicles decreased the immunogold labeling of glutamate transporters, which signal vesicles releasing glutamate. Vidar Gundersen, an electron microscopist at the University of Oslo, provided guidance on the optimal staining levels, says Volterra.
Zhuan Zhou's team at Peking University observed that glutamate is secreted in a "kiss-and-run" fashion, releasing about 5% to 10% of its contents, allowing vesicles to be rapidly recycled. "This may explain why you do not need too many," according to Volterra, as recent calculations show that there are about tenfold fewer vesicles in astrocytes than in nerve terminals.
Follow-up work in astrocytes reports vesicle sizes that range from 30 nm to 810 nm. Zhou says it is unclear whether they all regulate glutamate.
The work ahead:
The next step, says Zhou, is to show to what extent astrocyte secretion contributes to brain function. Philip Haydon's group at the University of Pennsylvania is examining how astrocyte secretion maps onto behaviors that include sleep patterns and learning abilities.