title: Development of Synaptic Boutons in Layer 4 of the Barrel Field of the Rat Somatosensory Cortex: A Quantitative Analysis.
abstract: Understanding the structural and functional mechanisms underlying the development of individual brain microcircuits is critical for elucidating their computational properties. As synapses are the key structures defining a given microcircuit, it is imperative to investigate their development and precise structural features. Here, synapses in cortical layer 4 were analyzed throughout the first postnatal month using high-end electron microscopy to generate realistic quantitative 3D models. Besides their overall geometry, the size of active zones and the pools of synaptic vesicles were analyzed. At postnatal day 2 only a few shaft synapses were found, but spine synapses steadily increased with ongoing corticogenesis. From postnatal day 2 to 30 synaptic boutons significantly decreased in size whereas that of active zones remained nearly unchanged despite a reshaping. During the first 2 weeks of postnatal development, a rearrangement of synaptic vesicles from a loose distribution toward a densely packed organization close to the presynaptic density was observed, accompanied by the formation of, first a putative readily releasable pool and later a recycling and reserve pool. The quantitative 3D reconstructions of synapses will enable the comparison of structural and functional aspects of signal transduction thus leading to a better understanding of networks in the developing neocortex.
authors.affiliation: Institute of Neuroscience and Medicine INM-2, Research Centre Jülich GmbH, Jülich 52425, Germany.|Institute of Anatomy II, Medical Faculty, Heinrich-Heine University Düsseldorf, Düsseldorf 40225, Germany.
authors.forename: Amandine
authors.initials: A
authors.lastname: Dufour
authors.affiliation: Institute of Neuroscience and Medicine INM-2, Research Centre Jülich GmbH, Jülich 52425, Germany.
authors.forename: Astrid
authors.initials: A
authors.lastname: Rollenhagen
authors.affiliation: School of Biomedical Sciences, University of Ulster, Londonderry BT52 1SA, UK.
authors.forename: Kurt
authors.initials: K
authors.lastname: Sätzler
authors.affiliation: Institute of Neuroscience and Medicine INM-2, Research Centre Jülich GmbH, Jülich 52425, Germany.|Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH/University Hospital Aachen, Aachen 52074, Germany.|JARA Translational Brain Medicine, Aachen 52074, Germany.
authors.forename: Joachim H R
authors.initials: JHR
authors.lastname: Lübke
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D009415:Nerve Net / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D013003:Somatosensory Cortex / Q000166:cytology* / Q000254:growth & development*; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D013572:Synaptic Vesicles / Q000648:ultrastructure
keywords: 3D reconstructions; electron microscopy; pool of synaptic vesicles; synapse geometry; synaptogenesis