Three-dimensional X-ray visualization of axonal tracts in mouse brain hemisphere

TL;DR

This study demonstrates three-dimensional visualization of mouse brain axonal networks using X-ray microtomography, revealing detailed structures and distributions of axonal tracts with high resolution.

Contribution

The paper introduces a novel application of X-ray micro-CT with freeze-dried tissue to visualize and reconstruct axonal networks in the mouse brain in three dimensions.

Findings

Visualized whole brain hemisphere with clear axonal structures

Identified contrast mechanisms based on water and phospholipid content

Achieved microstructural resolution of 2.7 μm in tissue samples

Abstract

Neurons transmit active potentials through axons, which are essential for the brain to function. In this study, the axonal networks of the murine brain were visualized with X-ray tomographic microscopy, also known as X-ray microtomography or micro-CT. Murine brain samples were freeze-dried to reconstitute the intrinsic contrast of tissue constituents and subjected to X-ray visualization. A whole brain hemisphere visualized by absorption contrast illustrated three-dimensional structures including those of the striatum, corpus callosum, and anterior commissure. Axonal tracts observed in the striatum start from the basal surface of the cerebral cortex and end at various positions in the basal ganglia. The distribution of X-ray attenuation coefficients indicated that differences in water and phospholipid content between the myelin sheath and surrounding tissue constituents account for the observed contrast. A rod-shaped cutout of brain tissue was also analyzed with a phase retrieval method, wherein tissue microstructures could be resolved with up to 2.7 {\mu}m resolution. Structures of axonal networks of the striatum were reconstructed by tracing axonal tracts. Such an analysis should be able to delineate the functional relationships of the brain regions involved in the observed network.