title: Imaging of calcium in Drosophila larval motor nerve terminals.
abstract: Calcium measurements in the presynaptic terminal are essential in the investigation of mechanisms underlying neurotransmitter release. To enhance the genetic analysis of secretory mechanisms, we have developed Ca2+ imaging techniques for Drosophila larval motor nerve terminals. We studied Ca2+ signals in "big" (type Ib) and "small" (type Is) boutons that innervate ventral longitudinal muscles 6 and 7 in each abdominal segment of Canton-S (CS)-strain 3rd instar larvae. The indicator fluo-3 in conjunction with confocal microscopy was used to detect stimulus-dependent changes in [Ca2+]i. The Ca2+ signals were reliable and reproducible, and the resting fluorescence remained constant throughout the experiments. The Ca2+ signals increased with stimulus frequency from 5 to 20 Hz for both bouton types. No significant differences in the Ca2+ signals were seen between the two bouton types at 5 and 20 Hz, but there was a difference at 10 Hz. The decay of the Ca2+ signal was more prolonged after 20-Hz stimulation than after 5 and 10 Hz. At the single-synapse level, the secretory efficacy of Is synapses is greater than that of Ib synapses, but our data show that factors other than differences in Ca2+ entry may govern the strength of synaptic transmission.
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Karunanithi
authors.forename: J
authors.initials: J
authors.lastname: Georgiou
authors.forename: M P
authors.initials: MP
authors.lastname: Charlton
authors.forename: H L
authors.initials: HL
authors.lastname: Atwood
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000378:metabolism*; D004558:Electric Stimulation; D007814:Larva / Q000378:metabolism; D018613:Microscopy, Confocal; D009046:Motor Neurons / Q000378:metabolism*; D009411:Nerve Endings / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology
chemical_list: D002118:Calcium