Drainage of interstitial fluid from different regions of rat brain

TLDR

The authors compared interstitial fluid drainage from the caudate nucleus, internal capsule, and midbrain in anesthetized rats by microinjecting radioiodinated albumin and tracing its efflux through the subarachnoid space, lymphatic routes, and olfactory nerve sheaths. Drainage rates were 0.18, 0.19, and 0.29 × 10⁻⁶ g brain⁻¹ min⁻¹, with 60–75 % of midbrain efflux entering bulk CSF versus only 10–15 % from caudate nucleus or internal capsule, and radioiodinated albumin accumulated in subarachnoid sleeves around pericerebral arteries.

Abstract

Studies were carried out in anesthetized rats comparing dynamics and pathways of interstitial fluid (ISF) drainage from different regions of brain. Rates of drainage from brain and flow into cerebrospinal fluid (CSF) were estimated from the efflux from brain and influx into CSF of radioiodinated albumin (RISA) following microinjection into caudate nucleus, internal capsule, or midbrain: pathways of flow through the subarachnoid space and into lymph were traced from the distribution of horseradish peroxidase and/or Evans blue-labeled albumin after injection into brain. ISF drainage rates (mul X g brain-1 X min-1) estimated for the three injection sites were 0.18, 0.19, and 0.29, respectively. Flow of ISF into bulk CSF sampled from the cisterna magna accounted for 60-75% of efflux from midbrain but only 10-15% of efflux from caudate nucleus or internal capsule. RISA was concentrated in the subarachnoid space, relative to bulk CSF, in sleeves of adventitial tissue surrounding pericerebral arteries, possibly accounting for the low recovery of isotope from bulk CSF. From the subarachnoid space, some fluid drained via olfactory nerve sheaths to retropharyngeal lymph nodes.