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WIREs Dev Biol
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Electrophysiological analysis of synaptic transmission in Drosophila

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Synaptic transmission is dynamic, plastic, and highly regulated. Drosophila is an advantageous model system for genetic and molecular studies of presynaptic and postsynaptic mechanisms and plasticity. Electrical recordings of synaptic responses represent a wide‐spread approach to study neuronal signaling and synaptic transmission. We discuss experimental techniques that allow monitoring synaptic transmission in Drosophila neuromuscular and central systems. Recordings of synaptic potentials or currents at the larval neuromuscular junction (NMJ) are most common and provide numerous technical advantages due to robustness of the preparation, large and identifiable muscles, and synaptic boutons which can be readily visualized. In particular, focal macropatch recordings combined with the analysis of neurosecretory quanta enable rigorous quantification of the magnitude and kinetics of transmitter release. Patch‐clamp recordings of synaptic transmission from the embryonic NMJ enable overcoming the problem of lethality in mutant lines. Recordings from the adult NMJ proved instrumental in the studies of temperature‐sensitive paralytic mutants. Genetic studies of behavioral learning in Drosophila compel an investigation of synaptic transmission in the central nervous system (CNS), including primary cultured neurons and an intact brain. Cholinergic and GABAergic synaptic transmission has been recorded from the Drosophila CNS both in vitro and in vivo. In vivo patch‐clamp recordings of synaptic transmission from the neurons in the olfactory pathway is a very powerful approach, which has a potential to elucidate how synaptic transmission is associated with behavioral learning. WIREs Dev Biol 2017, 6:e277. doi: 10.1002/wdev.277

Recording of synaptic activity from cultured KCs. (a) Neurons in culture. Top panels show live cultures imaged with Nomarski optics. Bottom panels show labeled cholinergic and GABAergic neurons. (b) Whole‐cell recordings of cholinergic and GABAergic synaptic currents (Reprinted with permission from Ref . Copyright 2003 Society of Neuroscience).
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A diagram showing an olfactory neuronal pathway in Drosophila.
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Intracellular recordings from DLM in adult Drosophila. (a) A diagram showing the DLM innervation. (b) Recording configuration. (c) Recordings from DLM in wild type and comt flies at different temperature in response to a repeated stimulation (Reprinted with permission from Ref . Copyright 1998 Society of Neuroscience).
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Patch clamp recordings from the embryonic NMJ. (a) Dissected Drosophila embryo (Reprinted with permission from Ref . Copyright 1994 Elsevier). (b) A recording configuration. (c) Synaptic currents recoded at different holding potentials (Reprinted with permission from Ref . Copyright 1995 Society of Neuroscience). (d) The relationship between the EJC amplitude and the holding membrane potential (Reprinted with permission from Ref . Copyright 1995 Society for Neuroscience).
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Focal macropatch recordings in the Drosophila larval NMJ. (a) A macropatch electrode is positioned on the top of a bouton. Neuronal membranes tagged with CD8‐GFP show clearly defined boutons (A.1, arrows), which are also visible in bright‐field with DIC optics (A.2, arrows). An electrode can be positioned on the top of the bouton (A.3), which is confirmed by an overlay of the fluorescent and DIC images (A.4). Scale bar: 10 µm. (b) A current trace showing EJC and mEJC. (c) Recordings of EJCs and mEJCs from complexin null mutant show a quantifiable increase in mEJC frequency and a prolonged EJC decay. (d) Automated analysis of mEJCs employing Quantan software. Quantal peaks (red arrows) and current deviations from the baseline (green) are detected.
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Intracellular recordings. (a) The recording configuration. The axon is pulled in the stimulating suction electrode, and EJPs are recorded from the muscle with a sharp microelectrode. (b) Diagram representing a position of the recording electrode in relation to the NMJ. Scale bar: 10 µm. (c) mEJPs recorded by two sharp electrodes positioned at a distance of 200 µm are similar, showing that the muscle is iso‐potential. (Reprinted with permission from Ref. Copyright 1976 John Wiley and Sons) (d) Recordings of EJPs at different stimulation intensities show two peaks produced by response of two axons. Lower intensities produce a single peak, corresponding to a response of a single axon with a lower stimulation threshold (Reprinted with permission from Ref . Copyright 1976 John Wiley and Sons). (e) Two‐electrode voltage clamp configuration. Two sharp microelectrodes maintain command voltage Vcmd and record synaptic currents. (f) Characterization of dunce (dnc) and rutabaga (rut) mutants employing two‐electrode voltage clamp (Reprinted with permission from Ref . Copyright 1991 The American Association for the Advancement of Science). Traces show EJCs and mEJCs, and Ca2+ dependence of the quantal content is shown on the right.
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Drosophila larval NMJ preparation. (a) Bright‐field image of a dissected larvae. The rectangle marks segment 4. (b) Enlarged segment showing the muscle fibers. (c) The diagram denoting the muscle fibers on the surface of the preparation. (d) Innervation of the muscles 6 and 7 labeled by horseradish peroxidase. The enlarged boxed area is shown in the bottom, 1b and 1s innervation types are labeled. Scale bar: 10 µm. (e) Electron micrograph showing a 1b type bouton. SSR, subsynaptic reticulum; AZ, active zone; SV, synaptic vesicle.
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Paired patch‐clamp recordings from Drosophila CNS in vivo. (a) A diagram showing the recording configuration. (b) Visualized LN (green) and PN (red) neurons. (c) Individual recordings from LN aligned with the presynaptic PN depolarization (Reprinted with permission from Ref . Copyright 2004 The American Association for the Advancement of Science).
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