Guerrero, G., Rieff, D.F., Agarwal, G., Ball, R.W., Borst, A., Goodman, C.S., Isacoff, E.Y. (2005). Heterogeneity in synaptic transmission along a Drosophila larval motor axon. Nat. Neurosci. 8(9): 1188--1196.
FlyBase ID
FBrf0188161
Publication Type
Research paper
Abstract
At the Drosophila melanogaster larval neuromuscular junction (NMJ), a motor neuron releases glutamate from 30-100 boutons onto the muscle it innervates. How transmission strength is distributed among the boutons of the NMJ is unknown. To address this, we created synapcam, a version of the Ca2+ reporter Cameleon. Synapcam localizes to the postsynaptic terminal and selectively reports Ca2+ influx through glutamate receptors (GluRs) with single-impulse and single-bouton resolution. GluR-based Ca2+ signals were uniform within a given connection (that is, a given bouton/postsynaptic terminal pair) but differed considerably among connections of an NMJ. A steep gradient of transmission strength was observed along axonal branches, from weak proximal connections to strong distal ones. Presynaptic imaging showed a matching axonal gradient, with higher Ca2+ influx and exocytosis at distal boutons. The results suggest that transmission strength is mainly determined presynaptically at the level of individual boutons, possibly by one or more factors existing in a gradient.
