F1‐03‐01: Convective Influx/Glymphatic System: Tracers Injected Into the CSF Enter and Leave the Brain Along Separate Periarterial Basement Membrane Pathways

Abstract

Tracers injected into CSF pass into the brain alongside arteries and out again. This has been recently termed the "glymphatic system" that proposes tracers enter the brain along periarterial "spaces" and leave the brain along the walls of veins. The object of the present study is to test the hypothesis that 1) tracers from the CSF enter the cerebral cortex along pial-glial basement membranes as there are no perivascular "spaces" around cortical arteries, 2) tracers leave the brain along smooth muscle cell basement membranes that form the Intramural Peri-Arterial Drainage (IPAD) pathways for the elimination of interstitial fluid and solutes from the brain. 2μL of 100μM soluble, fluorescent fixable amyloid β (Aβ) were injected into the CSF of the cisterna magna of 6-10 and 24-30 month-old male mice and their brains were examined 5 and 30 mins later. At 5 mins, immunocytochemistry and confocal microscopy revealed Aβ on the outer aspects of cortical arteries colocalized with α-2 laminin in the pial-glial basement membranes. At 30 mins, Aβ was colocalised with collagen IV in smooth muscle cell basement membranes in the walls of cortical arteries corresponding to the IPAD pathways. No evidence for drainage along the walls of veins was found. Measurements of the depth of penetration of tracer were taken from 11 regions of the brain. Maximum depths of penetration of tracer into the brain were achieved in the pons and caudoputamen. Conclusions drawn from the present study are that tracers injected into the CSF enter and leave the brain along separate periarterial basement membrane pathways. The exit route is along IPAD pathways in which Aβ accumulates Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Responses to comments from reviewers for Albargothy et al 05/05/2018 "Convective influx/glymphatic system. Tracers injected into the CSF enter and leave the brain along separate periarterial basement membrane pathways" Dear Professor Paulus, Thank you for offering us the opportunity to respond to the comments from reviewers. Our responses are in italics, under each comment.