Figure 1.

A two-stage uptake mechanism from blood to cerebrospinal fluid (CSF) and from CSF to neuron. Ascorbic acid is transported by an active mechanism from plasma into CSF and from CSF into the neuron through SVCT2, whereas dehydroascorbic acid is transported through GLUT1 and GLUT 3 (glucose receptors). Concentrations of ascorbate range between 100–500 μmol/L within CSF and extracellular space, eventually reaching concentrations as high as 10 mM within neurons. There is an efflux of neuronal ascorbic acid following synaptic activity and secretion of excitatory amino acids. GLUT1, Glucose transporter 1; GLUT3, Glucose transporter 3; SVCT2, Sodium dependent vitamin transporter 2; μmol/L, Micromole per liter; mM, Millimole.