For a comprehensive review, see:
Berg, D.A., Belnoue, L.,Song,H., Simon A. (2013) Neurotransmitter-mediated control of neurogenesis in the adult vertebrate brain. Development, 140(12), 2548-2561. [DOI].
active adult neurogenesis is confined to two distinct
locations: the subventricular zone (SVZ) of the lateral ventricles in
the forebrain; and the subgranular zone (SGZ) of the dentate gyrus
(DG) in the hippocampus
These areas contain radial glial-like cells, which act as neural stem cells, and the growth of which is modulated by the respective neurotransmitters. For example, cells which are GABAnergic will be modulated (enhanced in the SVZ and inhibited in the DG) via GABA that has diffused out of the synapses of neighboring cells
GABA is released from parvalbumin-expressing interneurons in the adult dentate gyrus
(DG) and inhibits the activation of quiescent RGLs through activation of the γ 2-subunit-containing GABA A
In the SVZ, GABA also signals to and depolarizes neural
progenitor cells, but the mechanism of release is different from that
in the DG (Wang et al., 2003; Liu et al., 2005). Migrating
neuroblasts release GABA in a non-synaptic, non-vesicular fashion,
which tonically activates signaling in progenitor cells.
There are mechanisms through which the progenitor cells are stimulated that rely on neurotransmitters, but are not specific to cell subtype:
Neurotransmitters control neurogenesis without subtype specificity. If NSCs have restricted potential, transmitters could act on both NSCs and/or amplifying populations.
It's still a complicated story, but the long and short of it is, in specific regions of the brain, adult neurogenesis is known to be possible and some of the neurotransmitter-based growth factors are now being elucidated.