RT Journal Article
SR Electronic
T1 Early Synapse Formation in Developing Interneurons of the Adult Olfactory Bulb
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 15039
OP 15052
DO 10.1523/JNEUROSCI.3034-09.2009
VO 29
IS 48
A1 Patrizia Panzanelli
A1 Cedric Bardy
A1 Antoine Nissant
A1 Marta Pallotto
A1 Marco Sassoè-Pognetto
A1 Pierre-Marie Lledo
A1 Jean-Marc Fritschy
YR 2009
UL http://www.jneurosci.org/content/29/48/15039.abstract
AB New olfactory bulb granule cells (GCs) are GABAergic interneurons continuously arising from neuronal progenitors and integrating into preexisting bulbar circuits. They receive both GABAergic and glutamatergic synaptic inputs from olfactory bulb intrinsic neurons and centrifugal afferents. Here, we investigated the spatiotemporal dynamic of newborn GC synaptogenesis in adult mouse olfactory bulb. First, we established that GABAergic synapses onto mature GC dendrites contain the GABAA receptor α2 subunit along with the postsynaptic scaffolding protein gephyrin. Next, we characterized morphologically and electrophysiologically the development of GABAergic and glutamatergic inputs onto newborn GCs labeled with eGFP (enhanced green fluorescent protein) using lentiviral vectors. Already when reaching the GC layer (GCL), at 3 d post-vector injection (dpi), newborn GCs exhibited tiny voltage-dependent sodium currents and received functional GABAergic and glutamatergic synapses, recognized immunohistochemically by apposition of specific presynaptic and postsynaptic markers. Thereafter, GABAergic and glutamatergic synaptic contacts increased differentially in the GCL, and at 7 dpi, PSD-95 clusters outnumbered gephyrin clusters. Thus, the weight of GABAergic input was predominant at early stages of GC maturation, but not later. Newborn GC dendrites first reached the external plexiform layer at 4 dpi, where they received functional GABAergic contacts at 5 dpi. Reciprocal synapses initially were formed on GC dendritic shafts, where they might contribute to spine formation. Their presence was confirmed ultrastructurally at 7 dpi. Together, our findings unravel rapid synaptic integration of newborn GCs in adult mouse olfactory bulb, with GABAergic and glutamatergic influences being established proximally before formation of output synapses by apical GC dendrites onto mitral/tufted cells.