Abstract 212: Effects of Therapeutic Hypothermia on Glymphatic Clearance

Abstract

Objectives: Therapeutic hypothermia is the most potent protective therapy for cerebral ischemia in pre-clinical models, however clinical trials have failed to show a significant benefit in patient outcomes. We sought to reconcile this discrepancy by investigating whether hypothermia impaired glymphatic system mediated waste clearance from brain parenchyma in a rat model. Methods: Sprague -Dawley rats were divided into normothermia and hypothermia groups. Hypothermia was achieved using a perivascular closed-loop cooling circuit implanted one week before the experiments in both the groups. Animals in the normothermia group were kept at 37C while the hypothermia animals were cooled to 33C. Once the targeted temperature was reached, two fluorescent tracers, small molecular weight (Texas Red-Dextran 3KdA) and large molecular weight (FITC -Dextran 2MdA) were injected intracisternally in each animal. Animals in both the groups were monitored for blood pressure and blood gases. Thirty minutes after injection, animals were perfused with 4% paraformaldehyde and 50 micron sections were cut using Leica vibratome. Brain sections were mounted on slides and cover slipped using antifade Fluro gold. Sections were imaged on Carl-Zeiss apotome microscope. For each animal 12 sections were imaged, data was analyzed using NIH Image J software. Results and Discussion: Cerebrospinal fluid tracer efflux in brain was significantly reduced in the hypothermia group compared to the normothermia group. This experiment helps provide insight as to a potential reason clinical trials have failed to show benefit in stroke patients, as hypothermia may have an untoward effect of hindering the brain’s natural clearance system from clearing inflammatory molecules and other waste from brain parenchyma.