Brain active transmembrane water cycling measured by MR is associated with neuronal activity

Ruiliang Bai, Charles S. Springer, Dietmar Plenz, Peter J. Basser

Research output: Contribution to journalArticle

9 Scopus citations

Abstract

Purpose: fMRI is widely used to study brain activity. Unfortunately, conventional fMRI methods assess neuronal activity only indirectly, through hemodynamic coupling. Here, we show that active, steady-state transmembrane water cycling (AWC) could serve as a basis for a potential fMRI mechanism for direct neuronal activity detection. Methods: AWC and neuronal actitivity in rat organotypic cortical cultures were simultaneously measured with a hybrid MR-fluorescence system. Perfusion with a paramagnetic MRI contrast agent, Gadoteridol, allows NMR determination of the kinetics of transcytolemmal water exchange. Changes in intracellular calcium concentration, [Cai2+] were used as a proxy of neuronal activity and were monitored by fluorescence imaging. Results: When we alter neuronal activity by titrating with extracellular [K+] near the normal value, we see an AWC response resembling Na+-K+-ATPase (NKA) Michaelis-Menten behavior. When we treat with the voltage-gated sodium channel inhibitor, or with an excitatory postsynaptic inhibitor cocktail, we see AWC decrease by up to 71%. AWC was found also to be positively correlated with the basal level of spontaneous activity, which varies in different cultures. Conclusions: These results suggest that AWC is associated with neuronal activity and NKA activity is a major contributor in coupling AWC to neuronal activity. Although AWC comprises steady-state, homeostatic transmembrane water exchange, our analysis also yields a simultaneous measure of the average cell volume, which reports any slower net transmembrane water transport.

Original languageEnglish (US)
Pages (from-to)1280-1295
Number of pages16
JournalMagnetic Resonance in Medicine
Volume81
Issue number2
DOIs
StatePublished - Feb 1 2019

Keywords

  • Na/K ATPase
  • active
  • fMRI
  • functional MRI
  • membrane
  • neuronal activity
  • pump
  • transcytolemmal
  • water exchange

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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