Early formation of GABAergic synapses governs the development of adult-born neurons in the olfactory bulb

• Published in: The Journal of neuroscience 2012-06, Vol.32 (26), p.9103-9115
• Main Authors: Pallotto, Marta, Nissant, Antoine, Fritschy, Jean-Marc, Rudolph, Uwe, Sassoè-Pognetto, Marco, Panzanelli, Patrizia, Lledo, Pierre-Marie
• Format: Article
• Language: English
• Subjects: Adult Stem Cells - physiology; Analysis of Variance; Animals; Animals, Newborn; Area Under Curve; Carrier Proteins - metabolism; Dendrites - physiology; Electric Stimulation; Excitatory Amino Acid Transporter 1 - genetics; Frontal Lobe - cytology; Frontal Lobe - physiology; GABAergic Neurons - physiology; Gene Expression Regulation - genetics; Green Fluorescent Proteins - genetics; Herbicides - toxicity; In Vitro Techniques; Inhibitory Postsynaptic Potentials - genetics; Integrases - genetics; Integrases - metabolism; Lentivirus; Life Sciences; Membrane Proteins - metabolism; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microscopy, Confocal; Microscopy, Immunoelectron; Nerve Tissue Proteins; Neurobiology; Neurons - cytology; Neurons - physiology; Neurons - ultrastructure; Neurons and Cognition; Nitriles - toxicity; Odorants; Olfactory Bulb - cytology; Olfactory Bulb - drug effects; Olfactory Bulb - injuries; Patch-Clamp Techniques; Receptors, GABA - metabolism; Receptors, GABA-A - genetics; Sensory Deprivation - physiology; Synapses - genetics; Synapses - physiology; Synapses - ultrastructure; Tamoxifen - pharmacology
• ISSN: 0270-6474; 1529-2401; 1529-2401
• DOI: 10.1523/jneurosci.0214-12.2012

In mammals, olfactory bulb granule cells (GCs) are generated throughout life in the subventricular zone. GABAergic inputs onto newborn neurons likely regulate their maturation, but the details of this process remain still elusive. Here, we investigated the differentiation, synaptic integration, and survival of adult-born GCs when their afferent GABAergic inputs are challenged by conditional gene targeting. Migrating GC precursors were targeted with Cre-eGFP-expressing lentiviral vectors in mice with a floxed gene encoding the GABA(A) receptor α2-subunit (i.e., Gabra2). Ablation of the α2-subunit did not affect GC survival but dramatically delayed their maturation. We found a reduction in postsynaptic α2-subunit and gephyrin clusters accompanied by a decrease in the frequency and amplitude of GABAergic postsynaptic currents beginning ∼14 d post-injection (dpi). In addition, mutant cells exhibited altered dendritic branching and spine density. Spine loss appeared with mislocation of glutamatergic synapses on dendritic shafts and a reduction of spontaneous glutamatergic postsynaptic currents, underscoring the relevance of afferent GABAergic transmission for a proper synaptic integration of newborn GCs. To test the role of GABAergic signaling during much early stages of GC maturation, we used a genetic strategy to selectively inactivate Gabra2 in precursor cells of the subventricular zone. In these mice, labeling of newborn GCs with eGFP lentiviruses revealed similar morphological alterations as seen on delayed Gabra2 inactivation in migrating neuroblasts, with reduced dendritic branching and spine density at 7 dpi. Collectively, these results emphasize the critical role of GABAergic synaptic signaling for structural maturation of adult-born GCs and formation of glutamatergic synapses.