The Journal of Neurophysiology Vol. 78 No. 6 December 1997, pp. 3465-3467
Copyright ©1997 The American Physiological Society

Imaging of Calcium in Drosophila Larval Motor Nerve Terminals

Shanker Karunanithi, John Georgiou, Milton P. Charlton, and Harold L. Atwood

Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada

Karunanithi, Shanker, John Georgiou, Milton P. Charlton, and Harold L. Atwood. Imaging of calcium in Drosophila larval motor nerve terminals. J. Neurophysiol. 78: 3465-3467, 1997. 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.

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