The influence of postsynaptic structure on missing quanta at the Drosophila neuromuscular junction.

Christine T. Nguyen,Bryan A. Stewart

doi:10.1186/s12868-016-0290-7

Abstract

BackgroundSynaptic transmission requires both pre- and post-synaptic elements for neural communication. The postsynaptic structure contributes to the ability of synaptic currents to induce voltage changes in postsynaptic cells. At the Drosophila neuromuscular junction (NMJ), the postsynaptic structure, known as the subsynaptic reticulum (SSR), consists of elaborate membrane folds that link the synaptic contacts to the muscle, but its role in synaptic physiology is poorly understood.ResultsIn this study, we investigate the role of the SSR with simultaneous intra- and extra-cellular recordings that allow us to identify the origin of spontaneously occurring synaptic events. We compare data from Type 1b and 1s synaptic boutons, which have naturally occurring variations of the SSR, as well as from genetic mutants that up or down-regulate SSR complexity. We observed that some synaptic currents do not result in postsynaptic voltage changes, events we called ‘missing quanta’. The frequency of missing quanta is positively correlated with SSR complexity in both natural and genetically-induced variants. Rise-time and amplitude data suggest that passive membrane properties contribute to the observed differences in synaptic effectiveness.ConclusionWe conclude that electrotonic decay within the postsynaptic structure contributes to the phenomenon of missing quanta. Further studies directed at understanding the role of the SSR in synaptic transmission and the potential for regulating ‘missing quanta’ will yield important information about synaptic transmission at the Drosophila NMJ.

Highlights

Synaptic transmission requires both pre- and post-synaptic elements for neural communication
Missing quanta The primary observation of this report is that, in our model synaptic system, not all synaptic currents result in a change in membrane voltage
Because the genetic background of these strains is essentially wildtype, without genetic perturbations to induce changes in subsynaptic reticulum (SSR) complexity and the two bouton types occur on the same postsynaptic target, we conclude that missing quanta are part of the natural physiology of this synapse

Summary

Introduction

Synaptic transmission requires both pre- and post-synaptic elements for neural communication. At the Drosophila neuromuscular junction (NMJ), the postsynaptic structure, known as the subsynaptic reticulum (SSR), consists of elaborate membrane folds that link the synaptic contacts to the muscle, but its role in synaptic physiology is poorly understood. Synaptic transmission is the process used by neurons to communicate with other cells Key to this process is the synapse, which is the very close apposition of cellular membranes of the presynaptic and postsynaptic cells. NMJ are dense postsynaptic muscle membrane folds called the subsynaptic reticulum (SSR) [3, 12, 28]. From ultrastructural analysis of the Drosophila NMJ, the SSR appears to be densely packed convoluted postsynaptic “leaflets” of muscle membrane, forming compartments that underlie and surround the bulbous endings of the presynaptic nerve terminal [3, 19]

Methods

Results

Discussion

Conclusion