GABAergic excitation promotes neuronal differentiation in adult hippocampal progenitor cells

Hippocampal activity influences neurogenesis in the adult dentate gyrus; however, little is known about the involvement of the hippocampal circuitry in this process. In the subgranular zone of the adult dentate gyrus, neurogenesis involves a series of differentiation steps from radial glia-like stem/progenitor (type-1) cells, to transiently amplifying neuronal progenitor (type-2) cells, to postmitotic neurons. In this study, we conducted GFP-targeted recordings of progenitor cells in fresh hippocampal slices from nestin-GFP mice and found that neuronal progenitor (type-2) cells receive active direct neural inputs from the hippocampal circuitry. This input was GABAergic but not glutamatergic. The GABAergic inputs depolarized type-2 cells because of their elevated [Cl ^-]_i. This excitation initiated an increase of [Ca ²⁺]_i and the expression of NeuroD. A BrdU-pulse labeling study with GABA_A-R agonists demonstrated the promotion of neuronal differentiation via this GABAergic excitation. Thus, it appears that GABAergic inputs to hippocampal progenitor cells promote activity-dependent neuronal differentiation.