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

Abstract

Summary Signaling through GABAA receptors controls neural progenitor cell (NPC) development in vitro and is altered in schizophrenic and autistic individuals. However, the in vivo function of GABAA signaling on neural stem cell proliferation, and ultimately neurogenesis, remains unknown. To examine GABAA function in vivo, we electroporated plasmids encoding short-hairpin RNA against the Na-K-2Cl co-transporter NKCC1 in NPCs of the neonatal subventricular zone (SVZ) in mice to reduce GABAA-induced depolarization. Reduced GABAA depolarization identified by a loss of GABAA-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 GABAA 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 GABAA function on NPCs, we treated animals with a GABAA allosteric agonist, pentobarbital. Enhancement of GABAA 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 GABAA receptors. Thus, dysregulation in GABAA depolarizing activity delayed dendritic development and reduced NPC proliferation resulting in decreased neuronal density.

An Evolutionarily Conserved Switch in Response to GABA Affects Development and Behavior of the Locomotor Circuit of Caenorhabditis elegans

“…We note that previous studies (Jin et al 1999) as well as our data not shown also show that complete lack of GABA signaling (in mutants for the UNC-25 GABA biosynthetic enzyme) are able to rewire the GABAergic DD neurons correctly. In contrast, disruption of Cl 2 gradients in vertebrate nervous systems causes severe developmental defects in the nervous system, not just delays in developmental timing that ultimately result in normal adult structures and normal circuit function (Chudotvorova et al 2005;Akerman and Cline 2006;Ge et al 2006;Cancedda et al 2007;Young et al 2012).…”

“…GABA signaling in the vertebrate brain generally develops prior to glutamate signaling and, if excitatory, potentially provides the initial activity in developing circuits (Saint-Amant and Drapeau 2000; Gao and Van Den Pol 2001;Hennou et al 2002;Gozlan and Ben-Ari 2003;Johnson et al 2003). Genetically manipulating Cl 2 transporters to eliminate early depolarizing effects of GABA leads to defects in dendrite and synapse development (Chudotvorova et al 2005;Akerman and Cline 2006;Ge et al 2006;Cancedda et al 2007;Young et al 2012). However, elucidating the precise linkage between the role of early GABA signaling in specific neurons and a manifested behavior has been difficult due to the complexity of the vertebrate brain.…”

The multifaceted subventricular zone astrocyte: From a metabolic and pro-neurogenic role to acting as a neural stem cell

“…However, GABA can also come from an external source. It was shown that striatal GABAergic neurons located at the border of the V-SVZ could regulate intracellular Ca2+ dynamics in V-SVZ astrocytes through GABA A receptors activation and depolarization of L- and T-type voltage-gated calcium channels (Young et al 2010, Young et al 2012). …”

GABA depolarizes immature neurons and inhibits network activity in the neonatal neocortex in vivo

“…By facilitating the generation of action potentials, GABA was further found to promote the generation of patterned network activity 3,[11][12][13][14][15] . These data led to the suggestion that GABA, whose synapses assemble before the ones for glutamate 16 , acts as one of the major excitatory neurotransmitters of the developing brain, underlying the activity-dependent growth and differentiation of neurons as well as the assembly of synaptic circuits [17][18][19] . Owing to an increase in membrane conductance, depolarizing GABAergic inputs may modulate neuronal output in a complex and bidirectional manner.…”