Ultrastructural analysis of the brain endothelium by electron tomography
Transmission electron microscopy (TEM) is a powerful imaging technique, yielding ultrastructural investigation of organic and non-organic samples. Despite its ability to reach nanoscale resolutions, conventional TEM presents a major disadvantage by only acquiring two-dimensional snapshots, thus hindering our volumetric understanding of samples. Electron tomography (ET) overcomes this limitation by offering detailed views of a thin specimen in 3 dimensions (3D). This technique is widely used in biology and has expanded our understanding of mitochondrial structure or synaptic organization. Proper brain functioning is highly reliable on a constant nutritional support through its microvasculature lined by endothelial cells. These unique cells form a selective and protective barrier, known as the blood-brain barrier (BBB), which limits the entrance of blood-borne molecules into the brain. In pathological conditions, the BBB is disrupted, resulting in neuronal damage. Understanding the fine changes underlying BBB disruption requires advanced imaging tools such as ET, to detect the finest changes in endothelial ultrastructure. This manuscript briefly explains how TEM and ET function, and then provides a detailed, didactic method for sample preparation, tomogram generation and 3D segmentation of brain endothelial cells using ET.