Abstract
Juxtaglomerular neurons (JGNs) of the mammalian olfactory bulb are generated throughout life. Their integration into the preexisting neural network, their differentiation and survival therein depend on sensory activity, but when and how these adult-born cells acquire responsiveness to sensory stimuli remains unknown. In vivo two-photon imaging of retrovirally labelled adult-born JGNs reveals that ~90% of the cells arrive at the glomerular layer after day post injection (DPI) 7. After arrival, adult-born JGNs are still migrating, but at DPI 9, 52% of them have odour-evoked Ca(2+) signals. Their odourant sensitivity closely resembles that of the parent glomerulus and surrounding JGNs, and their spontaneous and odour-evoked spiking is similar to that of their resident neighbours. Our data reveal a remarkably rapid functional integration of adult-born cells into the preexisting neural network. The mature pattern of odour-evoked responses of these cells strongly contrasts with their molecular phenotype, which is typical of immature, migrating neuroblasts.
Highlights
Juxtaglomerular neurons (JGNs) of the mammalian olfactory bulb are generated throughout life
Their progenitors are generated in the subependymal zone lining the walls of the lateral ventricles and in the rostral migratory stream (RMS), the route used by progenitors for migration towards the olfactory bulb (OB)
The majority of them differentiate into granule cells (GCs) but some 5%–10% enter the glomerular layer of the bulb to become juxtaglomerular neurons (JGNs)[2]
Summary
Juxtaglomerular neurons (JGNs) of the mammalian olfactory bulb are generated throughout life Their integration into the preexisting neural network, their differentiation and survival therein depend on sensory activity, but when and how these adult-born cells acquire responsiveness to sensory stimuli remains unknown. Most of their dendro-dendritic output synapses develop only during the fourth week after birth These data together with the ability to fire action potentials (APs), developing B4 weeks after virus injection in the subependymal zone[10], suggest that adult-born GCs have to listen to the neural network they integrate into for several weeks before they can send any output signals and influence the ongoing neuronal activity[11,12]. Mature glutamatergic synapses (that is, synapses with high AMPA (a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)/NMDA (N-methyl-D-aspartate) ratio) were detected only from DPI 45 onwards[16]
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