Transportation in the Brain Extracellular Space of the Rat Brain Can Be Regulated by Neuronal Activity

Substances transportation in the brain extracellular space (ECS) is crucial to maintain brain homeostasis, however its link to neuronal activity remains unclear. Here, we report a marked reduction in substances transportation in the ECS after neuronal excitation. Using a tracer-based method, water molecules in the interstitial fluid (ISF) could be specifically visualized by magnetic resonance imaging (MRI). We first observed the ISF flow in the thalamus and caudate nucleus of rats. The ISF flow was then modulated using a painful stimulation model. We demonstrated that the ISF flow slowed significantly following neuronal activity in the thalamus. This reduction in ISF flow continued for hours and was not accompanied by slow diffusion in the ECS. This observation suggests that the substances transportation in the ECS can be regulated by a selective external stimulation.