Early changes to the extracellular space in the hippocampus under simulated microgravity conditions

• DOI: 10.1007/s11427-021-1932-3
• Publication Date: 2021-06-29T11:02:44Z
• Authors: Yajuan Gao; Hongbin Han; Jichen Du; Qingyuan He; Yanxing Jia; Junhao Yan; Hui Dai; Bin Cui; Jing Yang; Xunbin Wei; Liu Yang; Rui Wang; Ren Long; Qiushi Ren; Xing Yang; Jiabin Lu
• Keywords: Male; Rats, Sprague-Dawley; 0303 health sciences; 03 medical and health sciences; Animals; Extracellular Fluid; Extracellular Space; Hippocampus; Magnetic Resonance Imaging; Weightlessness Simulation; Rats

The smooth transportation of substances through the brain extracellular space (ECS) is crucial to maintaining brain function; however, the way this occurs under simulated microgravity remains unclear. In this study, tracer-based magnetic resonance imaging (MRI) and DECS-mapping techniques were used to image the drainage of brain interstitial fluid (ISF) from the ECS of the hippocampus in a tail-suspended hindlimb-unloading rat model at day 3 (HU-3) and 7 (HU-7). The results indicated that drainage of the ISF was accelerated in the HU-3 group but slowed markedly in the HU-7 group. The tortuosity of the ECS decreased in the HU-3 group but increased in the HU-7 group, while the volume fraction of the ECS increased in both groups. The diffusion rate within the ECS increased in the HU-3 group and decreased in the HU-7 group. The alterations to ISF drainage and diffusion in the ECS were recoverable in the HU-3 group, but neither parameter was restored in the HU-7 group. Our findings suggest that early changes to the hippocampal ECS and ISF drainage under simulated microgravity can be detected by tracer-based MRI, providing a new perspective for studying microgravity-induced nano-scale structure abnormities and developing neuroprotective approaches involving the brain ECS.