Silent synapses in developing rat nucleus tractus solitarii have AMPA receptors.
NMDA-only synapses, called silent synapses, are thought to be the initial step in synapse formation in several systems. However, the underlying mechanism and the role in circuit construction are still a matter of dispute. Using combined morphological and electrophysiological approaches, we searched for silent synapses at the level of the nucleus tractus solitarii (NTS), a brainstem structure that is a gateway for many visceral sensory afferent fibers. Silent synapses were detected at birth by using electrophysiological recordings and minimal stimulation protocols. However, anatomical experiments indicated that nearly all, if not all, NTS synapses had AMPA receptors. Based on EPSC fluctuation measurements and differential blockade by low-affinity competitive and noncompetitive glutamate antagonists, we then demonstrated that NTS silent synapses were better explained by glutamate spillover from neighboring fibers and/or slow dynamic of fusion pore opening. Glutamate spillover at immature NTS synapses may favor crosstalk between active synapses during development when glutamate transporters are weakly expressed and contribute to synaptic processing as well as autonomic circuit formation.
Balland
Bénédicte
B
Centre National de la Recherche Scientifique, Unité Mixte de Recherche 6231, Université Paul Cézanne, Université de la Méditerranée, Faculté de Médecine, 13916 Marseille cedex 20, France.
Lachamp
Philippe
P
Kessler
Jean-Pierre
JP
Tell
Fabien
F
D000818:Animals; D000831:Animals, Newborn; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005260:Female; D008297:Male; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000378:metabolism*; D017552:Solitary Nucleus / Q000166:cytology* / Q000254:growth & development*; D013569:Synapses / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D050496:Vesicular Glutamate Transport Proteins / Q000378:metabolism
C113688:Bsn protein, rat; D018691:Excitatory Amino Acid Antagonists; D009419:Nerve Tissue Proteins; D018091:Receptors, AMPA; D050496:Vesicular Glutamate Transport Proteins