title: Quantal size and variation determined by vesicle size in normal and mutant Drosophila glutamatergic synapses.
abstract: Quantal size and variation at chemical synapses could be determined presynaptically by the amount of neurotransmitter released from synaptic vesicles or postsynaptically by the number of receptors available for activation. We investigated these possibilities at Drosophila glutamatergic neuromuscular synapses formed by two separate motor neurons innervating the same muscle cell. At wild-type synapses of the two neurons we found a difference in quantal size corresponding to a difference in mean synaptic vesicle volume. The same finding applied to two mutants (dlg and lap) in which synaptic vesicle size was altered. Quantal variances at wild-type and mutant synapses were similar and could be accounted for by variation in vesicular volume. The linear relationship between quantal size and vesicular volume for several different genotypes indicates that glutamate is regulated homeostatically to the same intravesicular concentration in all cases. Thus functional differences in synaptic strength among glutamatergic neurons of Drosophila result in part from intrinsic differences in vesicle size.
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8. s.karunanithi@utoronto.ca
authors.forename: Shanker
authors.initials: S
authors.lastname: Karunanithi
authors.forename: Leo
authors.initials: L
authors.lastname: Marin
authors.forename: Kar
authors.initials: K
authors.lastname: Wong
authors.forename: Harold L
authors.initials: HL
authors.lastname: Atwood
mesh_terms: D000818:Animals; D004330:Drosophila; D018698:Glutamic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D007814:Larva / Q000378:metabolism; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D009132:Muscles / Q000166:cytology / Q000294:innervation / Q000502:physiology; D009154:Mutation; D009469:Neuromuscular Junction / Q000378:metabolism / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D010641:Phenotype; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure; D013569:Synapses / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D018698:Glutamic Acid