In recent years researchers in the department of NanoBiophotonics at the MPI for Biophysical Chemistryin Göttingen have been able to break the Abbe resolution limit of far-field optical microscopy, as applied to fluorescent imaging, using a technique known as Stimulated Emission Depletion (STED) microscopy.The STED microscope used to obtain data for both publications is able to attain a resolution of 50-70 nm; the original fluorescent spot, roughly 200 nm in diameter, is reduced in surface area within the imaging plane by roughly an order of magnitude using the STED technique.
This resolution was sufficient for researchers from the neurobiology department to visualize, for the firsttime, individual synaptic vesicles - more precisely, to visualize the protein synaptotagmin, which is embedded in the membranes of individual vesicles. Vesicles are membrane 'bubbles' roughly 40 nm indiameter filled with neurotransmitters, which transport chemical messenger molecules to synapses, the contact points between nerve cells, enabling nerve signals to pass between cells. Their contents are released at the synapse when the vesicle membranes fuse with the membrane of the nerve cell. Previously it was unclear whether the proteins sticking in the vesicle membrane (e.g. synaptotagmin) spread out over the cell membrane after the fusion event or they remained together, localized in the membrane patch whichpreviously formed the vesicle. With the aid of STED microscopy the researchers in Göttingen were able to show that the synaptotagmin molecules of a single vesicle remain together after fusion. The membrane ofthe nerve cell thus behaves in an 'economical' fashion: the vesicle proteins released onto the membrane ofthe nerve cell can be collectively reabsorbed to form another vesicle.
Neural vesicles do not fuse with the cell membrane with equal probability at all locations alo
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Source:Max-Planck-Gesellschaft