Anesthesia-related brain microstructure modulations detected by diffusion MRI

Brain clearance has been found to be greatly enhanced during sleep and anesthesia. Studies using optical microscopy have attributed this to an anesthesia-related expansion of the brains extra-cellular space. These results, however, have been based on invasive experiments with a limited field of view. Here, we employ diffusion kurtosis magnetic resonance imaging to assess brain microstructure in the awake and anesthetized mouse brain. We find both mean diffusivity and mean kurtosis to be significantly decreased in the anesthetized mouse brain compared to the awake state. This effect is observed in both gray matter and white matter. Our findings are consistent with the reports of brain ECS volume increase in sleep and anesthesia. Based on simple simulations, we discuss how an ECS volume increase (cell shrinkage) during sleep and anesthesia can coexist with other aspects of brain physiology. Our study demonstrates that diffusion kurtosis MRI can be used in the study of the glymphatic system. Importantly, our study shows an overlooked effect of anesthesia on brain microstructure which is relevant to preclinical MRI as a whole.