Stimulated Raman scattering microscopy reveals a unique and steady nature of brain water dynamics

The biological activities of substances in the brain are shaped by their spatiotemporal dynamics in brain tissues, all of which are regulated by water dynamics. In contrast to solute dynamics, water dynamics have been poorly characterized, owing to the lack of appropriate analytical tools. To overcome this limitation, we apply stimulated Raman scattering multimodal multiphoton microscopy to live brain tissues. The micro-scopy system allows for the visualization of deuterated water, fluorescence-labeled solutes, and cellular structures at high spatiotemporal resolution, revealing that water moves faster than fluorescent molecules in brain tissues. Detailed analyses demonstrate that water, unlike solutes, diffuses homogeneously in brain tissues without differences between the intra-and the extracellular routes. Furthermore, we find that the water dynamics are steady during development and ischemia, when diffusions of solutes are severely affected. Thus, our approach reveals routes and uniquely robust properties of water diffusion in brain tissues.

Automated summary

The spatiotemporal dynamics of substances in the brain are influenced by the water dynamics, which have been poorly understood due to the lack of suitable analytical tools. In this study, we used stimulated Raman scattering multimodal multiphoton microscopy to visualize deuterated water, fluorescence-labeled solutes, and cellular structures in live brain tissues, revealing that water diffuses more quickly than fluorescent molecules. Unlike solutes, water diffuses homogeneously in brain tissues without differences between intra- and extracellular routes. Our findings also show that water dynamics remain steady during development and ischemia, despite the severe effects on solute diffusion. Therefore, our approach provides insights into the routes and robust properties of water diffusion in brain tissues.