Three-dimensional visualization and analysis of dendritic spines in human brain tissue.

We developed a simple yet powerful technique to visualize neuronal morphology in human brain tissues. By ballistically shooting DiI (1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate)-coated tungsten particles to randomly label neurons, then clearing tissues with OPTIClear, we demonstrated the tracing of branched dendritic trees and spines in three dimensions. High-resolution imaging revealed dendrites up to 300 μm long and spine necks down to 200 nm across. Quantitative analyses of 1304 dendritic spines showed no decrease in spine density with imaging depth, indicating excellent clearing and tracing. Segmentation and modeling of dendritic spines enabled morphological characterization. This technique enables assumption-free, high-resolution and cost-efficient visualization of neuronal morphology in human tissues. Combined with immunohistochemistry and electron microscopy, it could provide new perspectives for studying human neuroanatomy and pathology.