In neurology, it is generally agreed upon that the function of a neuron is correlated with its morphology and, conversely, that neurons of a certain morphology perform a common function. Functional and structural data must therefore be combined to understand the essence of a particular neuron.
Correlative light and electron microscopy (CLEM) is a powerful technique due to its ability to combine functional information, obtained with a fluorescence microscope, with high resolution structural information obtained with the electron microscope. It is exactly this combination that makes correlative microscopy ideally suited for neuroscience research. With CLEM scientists can correlate these two essential types of information on the exact same neuron or structure of interest.
Neurons are large cells that stretch over relatively “long” distances, originating in one part of the brain and perhaps ending in another. A researcher using CLEM can benefit from FM to trace a whole neuron, while employing EM to study more closely its structural properties.
Figure 1: Overlay of fluorescence and electron images. Imaging was performed using the SECOM platform (DELMIC) mounted on a Quanta 250 FEG SEM (FEI).
In neuroscience, the most fascinating challenge is the mapping of the complete connectivity of the brain. Recent years have seen a rapid expansion in the field of connectomics, the study of tracing and understanding this connectivity map. One of the methods of choice for studying connectomics is 3D electron microscopy. The strength of electron microscopy is its high spatial resolution. EM enables the detection of synapses by resolving synaptic vesicles and post-synaptic densities at high resolution.
This, however, introduces great challenges in terms of data management and analysis. As current information technology is not ready to cope with such datasets, these datasets might be unmanageable. The perfect way of limiting the amount of data and making the data more interpretable is by using integrated CLEM. The multicolor capabilities of fluorescence microscopy, together with labelling power over long distances allows automatic detection of specific neuron types, before imaging them at high resolution in 3D with an electron microscope. The combination of the labelling power over large distances of FM and the high resolution structural information provided by EM thus makes correlative microscopy the perfect tool for studying connectivity maps.