title: Development of connectivity in a motoneuronal network in Drosophila larvae.
abstract: BACKGROUND
  Much of our understanding of how neural networks develop is based on studies of sensory systems, revealing often highly stereotyped patterns of connections, particularly as these diverge from the presynaptic terminals of sensory neurons. We know considerably less about the wiring strategies of motor networks, where connections converge onto the dendrites of motoneurons. Here, we investigated patterns of synaptic connections between identified motoneurons with sensory neurons and interneurons in the motor network of the Drosophila larva and how these change as it develops.
  
  
  RESULTS
  We find that as animals grow, motoneurons increase the number of synapses with existing presynaptic partners. Different motoneurons form characteristic cell-type-specific patterns of connections. At the same time, there is considerable variability in the number of synapses formed on motoneuron dendrites, which contrasts with the stereotypy reported for presynaptic terminals of sensory neurons. Where two motoneurons of the same cell type contact a common interneuron partner, each postsynaptic cell can arrive at a different connectivity outcome. Experimentally changing the positioning of motoneuron dendrites shows that the geography of dendritic arbors in relation to presynaptic partner terminals is an important determinant in shaping patterns of connectivity.
  
  
  CONCLUSIONS
  In the Drosophila larval motor network, the sets of connections that form between identified neurons manifest an unexpected level of variability. Synapse number and the likelihood of forming connections appear to be regulated on a cell-by-cell basis, determined primarily by the postsynaptic dendrites of motoneuron terminals.
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
authors.forename: Louise
authors.initials: L
authors.lastname: Couton
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
authors.forename: Alex S
authors.initials: AS
authors.lastname: Mauss
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
authors.forename: Temur
authors.initials: T
authors.lastname: Yunusov
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
authors.forename: Soeren
authors.initials: S
authors.lastname: Diegelmann
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK; Centre for Organismal Studies, Ruprecht-Karls-Universität, 69120 Heidelberg, Germany. Electronic address: jan-felix.evers@cos.uni-heidelberg.de.
authors.forename: Jan Felix
authors.initials: JF
authors.lastname: Evers
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
authors.forename: Matthias
authors.initials: M
authors.lastname: Landgraf
mesh_terms: D000818:Animals; D063132:Connectome; D004330:Drosophila / Q000254:growth & development*; D007814:Larva / Q000254:growth & development; D018613:Microscopy, Confocal; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology*; D009415:Nerve Net; D011984:Sensory Receptor Cells / Q000502:physiology; D013569:Synapses / Q000502:physiology*