Glymphatic flow in rat brains: A comparative study with mice

The glymphatic system clears wastes from the brain by circulating water-like fluids around and through its tissue, especially along the perivascular spaces (PVSs) that surround arteries. While extensive research has been conducted on glymphatic flow in mice, no in vivo studies have been performed in rats, a species with a lower average heart rate and larger arteries that is otherwise physiologically similar to mice. Using two-photon microscopy to collect in vivo videos of fluid motion, we analyzed fluid speeds, artery wall motion, and PVS shapes using the techniques developed for mice. Our initial results indicate that mean flow speeds and artery wall velocities are similar, but the fluid is more pulsatile in rats compared with mice. Additionally, the rat PVSs tend to have a hydraulic resistance comparable to the low range of the resistances found in mice. Understanding the similarities and differences between the glymphatic systems of two similar species can offer insight into how fluid flows vary across species, and whether results gathered in mouse models can be applied appropriately to humans.