title: Central cholinergic synaptic vesicle loading obeys the set-point model in Drosophila.
abstract: Experimental evidence shows that neurotransmitter release, from presynaptic terminals, can be regulated by altering transmitter load per synaptic vesicle (SV) and/or through change in the probability of vesicle release. The vesicular acetylcholine transporter (VAChT) loads acetylcholine into SVs at cholinergic synapses. We investigated how the VAChT affects SV content and release frequency at central synapses in Drosophila melanogaster by using an insecticidal compound, 5Cl-CASPP, to block VAChT and by transgenic overexpression of VAChT in cholinergic interneurons. Decreasing VAChT activity produces a decrease in spontaneous SV release with no change to quantal size and no decrease in the number of vesicles at the active zone. This suggests that many vesicles are lacking in neurotransmitter. Overexpression of VAChT leads to increased frequency of SV release, but again with no change in quantal size or vesicle number. This indicates that loading of central cholinergic SVs obeys the "set-point" model, rather than the "steady-state" model that better describes loading at the vertebrate neuromuscular junction. However, we show that expression of a VAChT polymorphism lacking one glutamine residue in a COOH-terminal polyQ domain leads to increased spontaneous SV release and increased quantal size. This effect spotlights the poly-glutamine domain as potentially being important for sensing the level of neurotransmitter in cholinergic SVs.
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom;
authors.forename: Francesca
authors.initials: F
authors.lastname: Cash
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom;
authors.forename: Samuel W
authors.initials: SW
authors.lastname: Vernon
authors.affiliation: School of Biosciences, University of Kent, Kent, United Kingdom; and.
authors.forename: Pauline
authors.initials: P
authors.lastname: Phelan
authors.affiliation: Syngenta Crop Protection Research, Bracknell, Berkshire, United Kingdom.
authors.forename: Jim
authors.initials: J
authors.lastname: Goodchild
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom; Richard.Baines@manchester.ac.uk.
authors.forename: Richard A
authors.identifier: http://orcid.org/0000-0001-8571-4376
authors.initials: RA
authors.lastname: Baines
mesh_terms: D000818:Animals; D059329:Cholinergic Neurons / Q000378:metabolism* / Q000502:physiology; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster; D005089:Exocytosis; D007395:Interneurons / Q000378:metabolism / Q000502:physiology; D055369:Miniature Postsynaptic Potentials; D009154:Mutation; D013569:Synapses / Q000378:metabolism / Q000502:physiology; D013572:Synaptic Vesicles / Q000378:metabolism*; D050494:Vesicular Acetylcholine Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D050494:Vesicular Acetylcholine Transport Proteins
keywords: acetylcholine; central synapse; vesicular transporter