Quantitative evaluation of serotonin release and clearance in Drosophila

Abstract

Serotonin signaling plays a key role in the regulation of development, mood and behavior. Drosophila is well suited for the study of the basic mechanisms of serotonergic signaling, but the small size of its nervous system has previously precluded the direct measurements of neurotransmitters. This study demonstrates the first real-time measurements of changes in extracellular monoamine concentrations in a single larval Drosophila ventral nerve cord. Channelrhodopsin2-mediated, neuronal type-specific stimulation is used to elicit endogenous serotonin release, which is detected using fast-scan cyclic voltammetry at an implanted microelectrode. Release is decreased when serotonin synthesis or packaging are pharmacologically inhibited, confirming that the detected substance is serotonin. Similar to tetanus-evoked serotonin release in mammals, evoked serotonin concentrations are 280 -640 nM in the fly, depending on the stimulation length. Extracellular serotonin signaling is prolonged after administering cocaine or fluoxetine, showing that transport regulates the clearance of serotonin from the extracellular space. When ChR2 is targeted to dopaminergic neurons, dopamine release is measured demonstrating that this method is broadly applicable to other neurotransmitter systems. This study shows that the dynamics of serotonin release and reuptake in Drosophila are analogous to those in mammals, making this simple organism more useful for the study of the basic physiological mechanisms of serotonergic signaling.

Functional groups modulate the sensitivity and electron transfer kinetics of neurochemicals at carbon nanotube modified microelectrodes

“…To examine the biological usefulness of these microelectrodes, COOH-CNT modified electrodes were used to measure endogenous serotonin changes in the ventral nerve cord (VNC) of the fruit fly, Drosophila melanogaster . The flies were genetically modified to express Channelrhodopsin-2, a blue light sensitive cation channel, in only serotonergic neurons 25 . Serotonin release was stimulated by exposing the nerve cord to blue light for 10 s. Both CONH 2 -CNT and COOH-CNT modified electrodes could be used to measure serotonin in a Drosophila VNC, but COOH-CNTs were chosen for further study because of the faster time response and lower noise.…”

“…Homozygous 3-day-old larvae expressing a Tph-GAL4;UAS-ChR2 genotype were fed all-trans retinal for two days 25,26 . The central nervous system (CNS) of a wandering, 3 rd instar (5-day-old) larvae was dissected and incubated as described previously 27 .…”

Serotonin: a regulator of neuronal morphology and circuitry

“…The fruit fly also offers considerable advantages, as locomotor circuits of the larva are well studied [90, 91] and genetic amenability not only provides access to specific gene function but also allows cell-labeling techniques crucial for circuit observation. Electrochemical techniques such as fast scan cyclic voltammetry have been modified to measurereal-time serotonin release in Drosophila larval CNS [92,93], meaning that serotonergic input and locomotor output [90] could be quantified simultaneously in addition to monitoring morphology of the serotonergic neurons and the locomotor circuit.…”

Presynaptic Dopamine Dynamics in Striatal Brain Slices with Fast-scan Cyclic Voltammetry

“…One of the primary reasons that FSCV has been used in such a variety of species is due to the small diameter of the carbon fiber microelectrodes, typically less than 7 μm in diameter. As a result, these microelectrodes make it possible to sample tissue from very small environments, as in the case of the fruit fly brain (nL), or to discriminate from discrete sub-anatomical regions like the NAc core versus the shell in larger species [12][13][14] .…”