NKCC1 Knockdown Decreases Neuron Production through GABAA-Regulated Neural Progenitor Proliferation and Delays Dendrite Development

Signaling through GABA A receptors controls neural progenitor cell (NPC) development in vitro and is altered in schizophrenic and autistic individuals. However, the in vivo function of GABA A signaling on neural stem cell proliferation, and ultimately neurogenesis, remains unknown. To examine GABA A function in vivo , we electroporated plasmids encoding short-hairpin (sh) RNA against the Na-K-2Cl cotransporter NKCC1 (shNKCC1) in NPCs of the neonatal subventricular zone in mice to reduce GABA A -induced depolarization. Reduced GABA A depolarization identified by a loss of GABA A -induced calcium responses in most electroporated NPCs led to a 70% decrease in the number of proliferative Ki67 + NPCs and a 60% reduction in newborn neuron density. Premature loss of GABA A depolarization in newborn neurons resulted in truncated dendritic arborization at the time of synaptic integration. However, by 6 weeks the dendritic tree had partially recovered and displayed a small, albeit significant, decrease in dendritic complexity but not total dendritic length. To further examine GABA A function on NPCs, we treated animals with a GABA A allosteric agonist, pentobarbital. Enhancement of GABA A activity in NPCs increased the number of proliferative NPCs by 60%. Combining shNKCC1 and pentobarbital prevented the shNKCC1 and the pentobarbital effects on NPC proliferation, suggesting that these manipulations affected NPCs through GABA A receptors. Thus, dysregulation in GABA A depolarizing activity delayed dendritic development and reduced NPC proliferation resulting in decreased neuronal density.