Fast-Scan Cyclic Voltammetry (FSCV) Detection of Endogenous Octopamine in Drosophila melanogaster Ventral Nerve Cord

Abstract

Octopamine is an endogenous biogenic amine neurotransmitter, neurohormone, and neuromodulator in invertebrates, and has functional analogy with norepinephrine in vertebrates. Fast-scan cyclic voltammetry (FSCV) can detect rapid changes in neurotransmitters, but FSCV has not been optimized for octopamine detection in situ. The goal of this study was to characterize octopamine release in the ventral nerve cord of Drosophila larvae for the first time. An FSCV waveform was optimized so that the potential for octopamine oxidation would not be near the switching potential where interferences can occur. Endogenous octopamine release was stimulated by genetically inserting either the ATP sensitive channel, P2X2, or the red-light sensitive channelrhodopsin, CsChrimson, into cells expressing tyrosine decarboxylase (TDC), an octopamine synthesis enzyme. To ensure that release is due to octopamine and not the precursor tyramine, the octopamine synthesis inhibitor disulfiram was applied, and the signal decreased by 80%. Stimulated release was vesicular and a 2 s continuous light stimulation of CsChrimson evoked 0.22 ± 0.03 μM of octopamine release in the larval VNC. Repeated stimulations were stable with 2 or 5 minutes interstimulation times. With pulsed stimulations, the release was dependent on the frequency of applied light pulse. An octopamine transporter has not been identified, and blockers of the dopamine transporter and serotonin transporter had no significant effect on the clearance time of octopamine, suggesting they do not take up octopamine. This study shows that octopamine can be monitored in Drosophila, facilitating future studies of how octopamine release functions in the insect brain.

Octopamine Drives Endurance Exercise Adaptations in Drosophila

“…(Figure 3H, I). This result is consistent with prior reports in which differences in raw levels of OA were not detected even when octopaminergic neurons were directly stimulated by optogenetics, attributed to rapid cycling of the compound (Pyakurel et al, 2016). Taken together, these results identify OA as a pharmacological exercise mimetic in Drosophila .…”

Microelectrode Biosensors for in vivo Analysis of Brain Interstitial Fluid

“…This method is based on the oxidation of adenosine into an O−O linked dimer . Finally, octopamine, an important neurotransmitter in the insect brain can be oxidized into an electroactive polymer on carbon fibers to detect neurotransmission at single neuronal terminals .…”

Modulation of neuromuscular synapses and contraction inDrosophila3rd instar larvae

“…The time-course of the amperometric currents was consistent with the opening and closing of a nanopore, suggesting 'kiss-and-run' release, and the quantal size was estimated at approximately 23,000 OA molecules per vesicle (Majdi et al, 2015). Pyakurel, Champaloux, and Venton (2016) used fast scan cyclic voltammetry to demonstrate release of OA from neurons in the ventral nerve cord of 3rd instar larvae. They expressed a red light-sensitive channel rhodopsin in neurons expressing tyrosine decarboxylase (TDC), which converts tyrosine to TA, the first step in synthesizing OA.…”