A control mechanism for intramural periarterial drainage via astrocytes: How neuronal activity could improve waste clearance from the brain

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Abstract
The mechanisms behind waste clearance from deep within the parenchyma of the brain remain unclear to this date. Experimental evidence has shown that one pathway for waste clearance, termed intramural periarterial drainage (IPAD), is the rapid drainage of interstitial fluid (ISF) via basement membranes (BM) of the smooth muscle cells (SMC) of cerebral arteries and its failure is closely associated with the pathology of Alzheimer's disease (AD). We have previously shown that arterial pulsations from the heart beat are not strong enough to drive waste clearance. Here we demonstrate computational evidence for a mechanism for cerebral waste clearance that is driven by functional hyperaemia, that is, the dilation of cerebral arteries as a consequence of increased neuronal demand. This mechanism is based on our model for fluid flow through the vascular basement membrane. It accounts for waste clearance rates observed in mouse experiments and aligns with pathological observations as well as recommendations to lower the individual risk of AD, such as keeping mentally and physically active.

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