GABA puts the brake on stem cells.

This article focuses on a new study according to which newborn neuroblasts release the transmitter GABA, which reduces the proliferation of stem cells and thereby neurogenesis, by a nonsynaptic mechanism. Tight regulation of neurogenesis in the adult brain is therefore essential. Neurons destined for the olfactory bulb are produced in the subventricular zone (SVZ) and added continuously through adulthood. GABA affects embryonic neurogenesis at ages after GABAergic neurons are produced, but before the development of synaptic GABA transmission. The new report is consistent with these studies of embryonic neurogenesis, showing a GABA-mediated feedback regulation of adult neurogenesis controlled by nonsynaptic GABA release. Surgical removal of the olfactory bulb results in the accumulation of neuroblasts in the rostral migratory stream (RMS) and SVZ9. Despite the buildup of neuroblasts, proliferation is maintained for weeks, resulting in a dramatic increase in the size of the RMS and SVZ9.