Glutamatergic synapse formation is promoted by α7-containing nicotinic acetylcholine receptors.
Glutamate is the primary excitatory transmitter in adult brain, acting through synapses on dendritic spines and shafts. Early in development, however, when glutamatergic synapses are only beginning to form, nicotinic cholinergic excitation is already widespread; it is mediated by acetylcholine activating nicotinic acetylcholine receptors (nAChRs) that generate waves of activity across brain regions. A major class of nAChRs contributing at this time is a species containing α7 subunits (α7-nAChRs). These receptors are highly permeable to calcium, influence a variety of calcium-dependent events, and are diversely distributed throughout the developing CNS. Here we show that α7-nAChRs unexpectedly promote formation of glutamatergic synapses during development. The dependence on α7-nAChRs becomes clear when comparing wild-type (WT) mice with mice constitutively lacking the α7-nAChR gene. Ultrastructural analysis, immunostaining, and patch-clamp recording all reveal synaptic deficits when α7-nAChR input is absent. Similarly, nicotinic activation of α7-nAChRs in WT organotypic culture, as well as cell culture, increases the number of glutamatergic synapses. RNA interference demonstrates that the α7-nAChRs must be expressed in the neuron being innervated for normal innervation to occur. Moreover, the deficits persist throughout the developmental period of major de novo synapse formation and are still fully apparent in the adult. GABAergic synapses, in contrast, are undiminished in number under such conditions. As a result, mice lacking α7-nAChRs have an altered balance in the excitatory/inhibitory input they receive. This ratio represents a fundamental feature of neural networks and shows for the first time that endogenous nicotinic cholinergic signaling plays a key role in network construction.
Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093-0357, USA.
Adrian F
AF
Lozada
Xulong
X
Wang
Natalia V
NV
Gounko
Kerri A
KA
Massey
Jingjing
J
Duan
Zhaoping
Z
Liu
Darwin K
DK
Berg
D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D000076122:Disks Large Homolog 4 Protein; D004558:Electric Stimulation; D004622:Embryo, Mammalian; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D005260:Female; D018756:GABA Antagonists / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D051528:Guanylate Kinases / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D016501:Neurites / Q000378:metabolism / Q000648:ultrastructure; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D011724:Pyridazines / Q000494:pharmacology; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051381:Rats; D018091:Receptors, AMPA / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014161:Transduction, Genetic / Q000379:methods; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism; D014793:Visual Cortex / Q000166:cytology / Q000378:metabolism; D064569:alpha7 Nicotinic Acetylcholine Receptor
D000076122:Disks Large Homolog 4 Protein; D018756:GABA Antagonists; D018698:Glutamic Acid; D049452:Green Fluorescent Proteins; D051528:Guanylate Kinases; D008565:Membrane Proteins; D009538:Nicotine; D018722:Nicotinic Agonists; D011724:Pyridazines; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D034741:RNA, Small Interfering; D018091:Receptors, AMPA; D011978:Receptors, Nicotinic; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; D050598:Vesicular Glutamate Transport Protein 1; D064569:alpha7 Nicotinic Acetylcholine Receptor; C579166:Chrna7 protein, mouse; C579165:Chrna7 protein, rat; C501447:Dlg4 protein, mouse; C092350:FM 4-64; C049853:gabazine