Abstract
From an early postnatal period and throughout life there is a continuous production of olfactory bulb (OB) interneurons originating from neuronal precursors in the subventricular zone. To reach the OB circuits, immature neuroblasts migrate along the rostral migratory stream (RMS). In the present study, we employed cultured postnatal mouse forebrain slices and used lentiviral vectors to label neuronal precursors with GFP and to manipulate the expression levels of the Na-K-2Cl cotransporter NKCC1. We investigated the role of this Cl- transporter in different stages of postnatal neurogenesis, including neuroblast migration and integration in the OB networks once they have reached the granule cell layer (GCL). We report that NKCC1 activity is necessary for maintaining normal migratory speed. Both pharmacological and genetic manipulations revealed that NKCC1 maintains high [Cl-]i and regulates the resting membrane potential of migratory neuroblasts whilst its functional expression is strongly reduced at the time cells reach the GCL. As in other developing systems, NKCC1 shapes GABAA-dependent signaling in the RMS neuroblasts. Also, we show that NKCC1 controls the migration of neuroblasts in the RMS. The present study indeed indicates that the latter effect results from a novel action of NKCC1 on the resting membrane potential, which is independent of GABAA-dependent signaling. All in all, our findings show that early stages of the postnatal recruitment of OB interneurons rely on precise, orchestrated mechanisms that depend on multiple actions of NKCC1.
Highlights
The subventricular zone (SVZ) and the rostral migratory stream (RMS) contain neural progenitors that proliferate and migrate to the olfactory bulb (OB) throughout life [1]
Immunohistochemical staining performed at 6 div with antibodies directed against a neuronal precursor marker (doublecortin (DCX); n = 3 slices; Additional file 1) and more mature neuronal markers (NeuN, tyrosine hydroxylase (TH) and gamma-aminobutyric acid (GABA); n = 3 slices for each; Additional files 1 and 2) were in agreement with the expected distribution patterns observed at similar postnatal ages, as visually compared to the Allen Institute for Brain Science atlas for P14 animals for TH and DCX
We found that NKCC1 activity is important for the neuroblasts to maintain a normal migratory speed since two independent manipulations employed to impair NKCC1 function, pharmacological blockade with bumetanide and transduction with shNKCC1, produced a diminution of the migration speed (Figure 3A)
Summary
The subventricular zone (SVZ) and the rostral migratory stream (RMS) contain neural progenitors that proliferate and migrate to the olfactory bulb (OB) throughout life [1]. Migration in the SVZ-OB system is sensitive to the action of neurotransmitters [10,11], providing a basis for neural activity-dependent regulation of NKCC1 is frequently expressed in developing central nervous system regions and its activity has been associated with depolarizing actions of GABA [19,20,21,22,23]. It is presently unknown if NKCC1 regulates the [Cl-]i in the RMS. This is an important issue since, in several regions, depolarizing GABA signaling appears early in development and can modulate neuronal excitability to promote neuronal maturation [21,24,25,26,27]
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