title: Diverse in- and output polarities and high complexity of local synaptic and non-synaptic signaling within a chemically defined class of peptidergic Drosophila neurons.
abstract: Peptidergic neurons are not easily integrated into current connectomics concepts, since their peptide messages can be distributed via non-synaptic paracrine signaling or volume transmission. Moreover, the polarity of peptidergic interneurons in terms of in- and out-put sites can be hard to predict and is very little explored. We describe in detail the morphology and the subcellular distribution of fluorescent vesicle/dendrite markers in CCAP neurons (NCCAP), a well defined set of peptidergic neurons in the Drosophila larva. NCCAP can be divided into five morphologically distinct subsets. In contrast to other subsets, serial homologous interneurons in the ventral ganglion show a mixed localization of in- and output markers along ventral neurites that defy a classification as dendritic or axonal compartments. Ultrastructurally, these neurites contain both pre- and postsynaptic sites preferably at varicosities. A significant portion of the synaptic events are due to reciprocal synapses. Peptides are mostly non-synaptically or parasynaptically released, and dense-core vesicles and synaptic vesicle pools are typically well separated. The responsiveness of the NCCAP to ecdysis-triggering hormone may be at least partly dependent on a tonic synaptic inhibition, and is independent of ecdysteroids. Our results reveal a remarkable variety and complexity of local synaptic circuitry within a chemically defined set of peptidergic neurons. Synaptic transmitter signaling as well as peptidergic paracrine signaling and volume transmission from varicosities can be main signaling modes of peptidergic interneurons depending on the subcellular region. The possibility of region-specific variable signaling modes should be taken into account in connectomic studies that aim to dissect the circuitry underlying insect behavior and physiology, in which peptidergic neurons act as important regulators.
authors.affiliation: Department of Comparative Anatomy and Developmental Biology, Institute of Biology, Faculty of Science, University of Pécs Pécs, Hungary ; Neurobiology and Genetics, Biocenter, Theodor-Boveri-Institute, University of Würzburg Würzburg, Germany.
authors.forename: Gergely
authors.initials: G
authors.lastname: Karsai
authors.forename: Edit
authors.initials: E
authors.lastname: Pollák
authors.forename: Matthias
authors.initials: M
authors.lastname: Wacker
authors.forename: Matthias
authors.initials: M
authors.lastname: Vömel
authors.forename: Mareike
authors.initials: M
authors.lastname: Selcho
authors.forename: Gergely
authors.initials: G
authors.lastname: Berta
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Nachman
authors.forename: R Elwyn
authors.initials: RE
authors.lastname: Isaac
authors.forename: László
authors.initials: L
authors.lastname: Molnár
authors.forename: Christian
authors.initials: C
authors.lastname: Wegener
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D004331:Drosophila melanogaster; D007395:Interneurons / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D008969:Molecular Sequence Data; D009474:Neurons / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D010446:Peptide Fragments / Q000032:analysis / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013569:Synapses / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000502:physiology
chemical_list: D010446:Peptide Fragments
keywords: CCAP; bursicon; ecdysis; myoinhibitory peptide; neuromodulation; paracrine release; synaptic signaling; volume transmission
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