Measurement of intravascular Na⁺ during increased CBF using ²³Na NMR with a shift reagent

Sodium ions are intimately involved with neural activity. Thus, it is highly desirable to devise a way of mapping brain activity via sodium imaging. Sodium ions exist in the extravascular and intravascular spaces. To separate the two components, the shift reagent Tm(DOTP)^5- was intravenously introduced into rats. Intravascular sodium changes in the rat brain were measured during increased blood flow induced by hypercapnia using volume-localized ²³Na-NMR. The intravascular sodium changes, equivalent to cerebral blood volume changes, are significant during hypercapnia conditions and correlate well with the increase in arterial pCO₂. This suggests that the intravascular sodium change is dominant in total ²³Na spectroscopy or imaging of the brain during blood flow increase induced by external perturbation.