Quantifying cerebrospinal fluid flow in pial perivascular spaces of rats

The circulation of cerebrospinal fluid (CSF) through perivascular spaces (PVSs) has been proposed to play a role in clearing waste from the brain. While several studies have quantified such flow in mice, no in vivo studies with high spatial and temporal resolution have been performed on other species. Here, we imaged pial PVSs of rat brains and the CSF flows they carry, using techniques previously employed with mice. Using vessel pulsatility measurement and automated particle tracking, we quantified and analyzed in vivo CSF velocity profiles, artery wall motion, and PVS resistances in rats, comparing our findings to mice. Both species exhibit net CSF flows in the same direction as blood flow, and CSF pulsations are substantially synchronized with the heartbeat. We found that rats have larger, lower-resistance PVSs, resulting in much larger CSF volume flow rates in rats than in mice. We also found that the choice of anesthetic can significantly affect vasomotion and corresponding CSF pulsations in rats, with ketamine-dexmedetomidine producing a more stable response than ketamine-xylazine. Our results can be used in models of flow through rat PVSs, and as experiments are performed on additional species, can aid in projecting results across scales from animal models to human CSF flows.