(A and B) Serial sagittal MRI revealing the temporal evolution of H₂¹⁷O tracer for vehicle-treated rats (upper panel, n = 6) (A) and rats treated with AQP4 inhibitor (lower panel, TGN 020, n = 6) (B). Pseudocolor scaling illustrates the distribution of H₂¹⁷O throughout the brain over 80 minutes of recording, with AQP4 inhibition resulting in substantially reduced H₂¹⁷O transport compared with the vehicle. (C) Summary data showing the percent signal change as a function of time for the vehicle (blue circles) and AQP4 inhibitor–treated (red circles) groups in the frontal cortex, cerebellum, and cisterna magna. Artificial CSF (aCSF; i.e., without ¹⁷O-enriched H₂¹⁷O) was used as a negative control. Blue shading on graphs indicates period of contrast agent infusion. (D) Representative images of H₂¹⁷O transport at different time points. The red rectangle has been magnified to better show the actual penetration of H₂¹⁷O, with the top of the red rectangle position on the cerebral cortex. The theoretically calculated displacements of H₂¹⁷O due to diffusion only are 0.53 mm, 0.75 mm, and 0.91 mm at times 231, 459, and 665 seconds, respectively. It is clear that the rapid H₂¹⁷O penetration of the parenchyma cannot be explained by diffusion alone, indicating the presence of convective ISF flow. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Data are presented as mean ± SEM.