Synapses are highly specialized junctions between neurons that are the basis of our understanding of neuronal signal transmission and how memories are formed in the brain. The structure, molecular organization and plastic properties of synapses have been intensely studied by a variety of methods, to understand how the processes of learning and memory occur at a molecular level. Due to their small size, which is below the resolution limit of a light microscope, direct observation of synapses has required using an electron microscope (EM), which reveals the ultrastructure of individual synapses in exquisite detail, but is not particularly suitable for quantitative molecule identification at a single synapse level. In the past few years, the invention of new “super-resolution” optical techniques, in particular STORM (Stochastic Optical Reconstruction Microscopy) by Xiaowei Zhuang’s group (at the department of Chemistry and Chemical Biology) has enabled observation of sub-cellular structures at close to EM resolution, while retaining several advantages of light microscopy.
Our study, done in a collaboration between the Dulac and Zhuang’s groups and published recently in Neuron, describes a novel application of STORM for imaging synapse structure and molecular organization, directly on brain slices. First, using the 3D, multicolor ability of STORM, we could image and position several synaptic proteins in a reference frame and demonstrate how a molecular architecture of the synapse can be reconstructed using super-resolution microscopy. Secondly, we also demonstrate that the content of neurotransmitter receptors at individual synapses, key determinants of synaptic strength and plasticity, could be quantitatively determined. These approaches have tremendous potential to derive new insights into how specific brain circuits function. For instance we observed that the rodent accessory olfactory bulb, which gets synaptic inputs from neurons of the vomeronasal organ and is important for eliciting innate behaviors, had a synaptic composition that was very different from other olfactory brain regions, and could significantly impact our understanding of how neurons within these brain regions process sensory signals
Read more in Neuron