Fig. 1

Two major routes of neuronal migration and the volume-sensitive outwardly rectifying (VSOR) channel hypothesis in the developing cerebral cortex. a Schematic of the routes of radial migration of glutamatergic neurons (black arrows) originating from the ventricular zone (VZ) and tangential migration of gamma-aminobutyric acid (GABA) ergic interneurons (gray arrows) from the lateral and medial ganglionic eminences (LGE and MGE, respectively). A half of a coronal section of the forebrain at about embryonic days 15–17 (E15–17) in mice is depicted. The dashed box indicates the region discussed in b. b “VSOR channel hypothesis” during the radial migration. Taurine is released through VSOR anion channels from the cells, particularly those located in the marginal zone (MZ) and the subplate (SP) [16]. Most of newly born glutamatergic neurons in the VZ at this embryonic stage migrate along the vertical fibers of the radial glial cells (leftmost column). When the leading edges of migrating neurons reach the taurine-rich SP zone (middle column) and MZ (rightmost column), taurine binds to and activates GABA_A receptors (GABA _A R) in the migrating neurons [16], and this increases the frequency of oscillatory rises in the intracellular calcium ion concentration ([Ca ²⁺] _i ). It may be hypothesized that these rises in [Ca²⁺]_i would trigger VSOR channel activation and the net efflux of chloride ions (Cl ⁻), potassium ions (K ⁺) and water (H ₂ O) across the cell membrane, thereby slowing down the migration and shrinking the leading edges. CP Cortical plate, IZ intermediate zone, SVZ subventricular zone