Article: article from journal or magazin.
Morphological and molecular heterogeneity in release sites of single neurons
European Journal of Neuroscience
Comparative Study Journal Article Research Support, Non-U.S. Gov't --- Old month value: Apr
We have previously shown that labelling intensities for synaptic proteins vary strongly among synaptic boutons. Here we addressed the questions as to whether there are heterogeneous levels of integral membrane synaptic vesicle proteins at distinct active release sites of single neurons and if these sites possess the ultrastructural features of synapses. By double-immunostaining with specific antibodies against synaptophysin, synaptotagmin I, VAMP1 and VAMP2, we identified different relative levels of these integral membrane proteins of synaptic vesicles in comparison to boutons of the same rat cortical neuron. This heterogeneity could also be observed between the two isoforms VAMP1 and VAMP2. By studying pairs of these proteins implicated in neurotransmitter release, including both VAMP isoforms, we also show that the sites that contained predominantly one protein were nevertheless functional, as they internalized and released FM1-43 upon potassium stimulation. Using electron microscopy, we show that these active sites could have either synaptic specializations, or the features of vesicle-containing varicosities without a postsynaptic target. Different varicosities of the same neuron showed different intensities for synaptic vesicle proteins; some varicosities were capable of internalizing and releasing FM1-43, while others were silent. These results show that integral membrane synaptic vesicle proteins are differentially distributed among functional release sites of the same neuron.
Animals Animals, Newborn *Calcium-Binding Proteins Cell Adhesion Molecules, Neuronal/metabolism Cell Membrane/drug effects/*metabolism/ultrastructure Cells, Cultured Cerebral Cortex/metabolism Immunohistochemistry Membrane Glycoproteins/metabolism Membrane Proteins/metabolism Microscopy, Electron, Scanning Microtubule-Associated Proteins/metabolism Nerve Tissue Proteins/metabolism Neurons/drug effects/metabolism/*physiology/ultrastructure Potassium/pharmacology Pyridinium Compounds/metabolism Quaternary Ammonium Compounds/metabolism R-SNARE Proteins Rats Rats, Sprague-Dawley Synaptic Membranes/metabolism Synaptic Vesicles/metabolism Synaptophysin/metabolism Synaptosomal-Associated Protein 25 Synaptotagmin I Synaptotagmins Time Factors
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