Figure 8.

D‐ and L‐serine form amino acid compartmentalization between neurons and astroglia. The de novo synthesis of L‐serine occurs in the astroglial glycolytic pathway. L‐serine is transported to neurons, where it is converted to D‐serine by serine racemase (SRR) and acts as a co‐agonist of N‐methyl‐D‐aspartate (NMDA) receptors (red line). ① Na⁺,K⁺‐ATPase. ② Glucose transporter 1 (GLUT1). ③ Glucose transporter 3 (GLUT3). ④ Monocarboxylate transporter 1 (MCT1) and MCT4 (astrocytic form). ⑤ MCT2 (neuronal form). ⑥ Astrocytic Na⁺‐independent asc‐type amino acid transporter‐1 (ASCT‐1). ⑦ ASCT‐2.