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Segeroth M, Wachsmuth L, Gagel M, Albers F, Hess A, Faber C. Disentangling the impact of cerebrospinal fluid formation and neuronal activity on solute clearance from the brain. Fluids Barriers CNS 2023; 20:43. [PMID: 37316849 DOI: 10.1186/s12987-023-00443-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 05/18/2023] [Indexed: 06/16/2023] Open
Abstract
BACKGROUND Despite recent attention, pathways and mechanisms of fluid transposition in the brain are still a matter of intense discussion and driving forces underlying waste clearance in the brain remain elusive. Consensus exists that net solute transport is a prerequisite for efficient clearance. The individual impact of neuronal activity and cerebrospinal fluid (CSF) formation, which both vary with brain state and anesthesia, remain unclear. METHODS To separate conditions with high and low neuronal activity and high and low CSF formation, different anesthetic regimens in naive rat were established, using Isoflurane (ISO), Medetomidine (MED), acetazolamide or combinations thereof. With dynamic contrast-enhanced MRI, after application of low molecular weight contrast agent (CA) Gadobutrol to cisterna magna, tracer distribution was monitored as surrogate for solute clearance. Simultaneous fiber-based Ca2+-recordings informed about the state of neuronal activity under different anesthetic regimen. T2-weighted MRI and diffusion-weighted MRI (DWI) provided size of subarachnoidal space and aqueductal flow as surrogates for CSF formation. Finally, a pathway and mechanism-independent two-compartment model was introduced to provide a measure of efficiency for solute clearance from the brain. RESULTS Anatomical imaging, DWI and Ca2+-recordings confirmed that conditions with distinct levels of neuronal activity and CSF formation were achieved. A sleep-resembling condition, with reduced neuronal activity and enhanced CSF formation was achieved using ISO+MED and an awake-like condition with high neuronal activity using MED alone. CA distribution in the brain correlated with the rate of CSF formation. The cortical brain state had major influence on tracer diffusion. Under conditions with low neuronal activity, higher diffusivity suggested enlargement of extracellular space, facilitating a deeper permeation of solutes into brain parenchyma. Under conditions with high neuronal activity, diffusion of solutes into parenchyma was hindered and clearance along paravascular pathways facilitated. Exclusively based on the measured time signal curves, the two-compartment model provided net exchange ratios, which were significantly larger for the sleep-resembling condition than for the awake-like condition. CONCLUSIONS Efficiency of solute clearance in brain changes with alterations in both state of neuronal activity and CSF formation. Our clearance pathway and mechanism agnostic kinetic model informs about net solute transport, solely based on the measured time signal curves. This rather simplifying approach largely accords with preclinical and clinical findings.
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Affiliation(s)
- Martin Segeroth
- Translational Research Imaging Center (TRIC), Clinic of Radiology, University of Münster, Albert-Schweitzer-Campus 1, Gebäude A16, 48149, Münster, Germany
- Department of Radiology, University Hospital Basel, Basel, Switzerland
| | - Lydia Wachsmuth
- Translational Research Imaging Center (TRIC), Clinic of Radiology, University of Münster, Albert-Schweitzer-Campus 1, Gebäude A16, 48149, Münster, Germany
| | - Mathias Gagel
- Translational Research Imaging Center (TRIC), Clinic of Radiology, University of Münster, Albert-Schweitzer-Campus 1, Gebäude A16, 48149, Münster, Germany
| | - Franziska Albers
- Translational Research Imaging Center (TRIC), Clinic of Radiology, University of Münster, Albert-Schweitzer-Campus 1, Gebäude A16, 48149, Münster, Germany
| | - Andreas Hess
- Department of Experimental and Clinical Pharmacology and Toxicology, Friedrich-Alexander-University of Erlangen-Nürnberg, Erlangen, Germany
- Institute of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Erlangen, Germany
- FAU NeW, Research Center for New Bioactive Compounds, Nikolaus-Fiebiger-Str. 10, 91058, Erlangen, Germany
| | - Cornelius Faber
- Translational Research Imaging Center (TRIC), Clinic of Radiology, University of Münster, Albert-Schweitzer-Campus 1, Gebäude A16, 48149, Münster, Germany.
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