Study of the release of endogenous amines in Drosophila brain in vivo in response to stimuli linked to aversive olfactory conditioning

Abstract

A highly challenging question in neuroscience is to understand how aminergic neural circuits contribute to the planning and execution of behaviors, including the generation of olfactory memories. In this regard, electrophysiological techniques like Local Field Potential or imaging methods have been used to answer questions relevant to cell and circuit physiology in different animal models, such as the fly Drosophila melanogaster. However, these techniques do not provide information on the neurochemical identity of the circuits of interest. Different approaches including fast scan cyclic voltammetry, allow researchers to identify and quantify in a timely fashion the release of endogenous neuroactive molecules, but have been only used in in vitro Drosophila brain preparations. Here, we report a procedure to record for the first time the release of endogenous amines –dopamine, serotonin and octopamine‐ in adult fly brain in vivo, by fast scan cyclic voltammetry. As a proof of principle, we carried out recordings in the calyx region of the Mushroom Bodies, the brain area mainly associated to the generation of olfactory memories in flies. By using principal component regression in normalized training sets for in vivo recordings, we detect an increase in octopamine and serotonin levels in response to electric shock and olfactory cues respectively. This new approach allows the study of dynamic changes in amine neurotransmission that underlie complex behaviors in Drosophila and shed new light on the contribution of these amines to olfactory processing in this animal model.

Fast‐Scan Cyclic Voltammetry (FSCV) Reveals Behaviorally Evoked Dopamine Release by Sugar Feeding in the Adult Drosophila Mushroom Body

“…[7] Also, behaviorally evoked serotonin responses in the Drosophila MB calyx were delayed from the presentation of an odorant stimulant. [15] The delay could be caused by dopamine being indirectly activated by multiple modulatory pathways. Imaging and genetic studies revealed that octopamine triggers dopamine activity for sugar reward to form appetitive memory by regulating dopaminergic neurons in the MB.…”

“…A similar phenomenon was observed in behavior studies in rats, where phasic dopamine changes were measured a few seconds after an unpredicted food reward (sugar pellet) was delivered [7] . Also, behaviorally evoked serotonin responses in the Drosophila MB calyx were delayed from the presentation of an odorant stimulant [15] . The delay could be caused by dopamine being indirectly activated by multiple modulatory pathways.…”

Fast‐Scan Cyclic Voltammetry (FSCV) Reveals Behaviorally Evoked Dopamine Release by Sugar Feeding in the Adult Drosophila Mushroom Body

“…[7] Also, behaviorally evoked serotonin responses in the Drosophila MB calyx were delayed from the presentation of an odorant stimulant. [15] The delay could be caused by dopamine being indirectly activated by multiple modulatory pathways. Imaging and genetic studies revealed that octopamine triggers dopamine activity for sugar reward to form appetitive memory by regulating dopaminergic neurons in the MB.…”

“…Fast‐scan cyclic voltammetry (FSCV) is an electrochemical technique that measures sub‐second concentration changes and provides fingerprint cyclic voltammograms to identify neurochemicals [12] . FSCV has been previously employed to measure neuromodulators in Drosophila larval ventral nerve cord (VNC) and in the adult central complex and MB [13–15] . Moreover, a similar approach was implemented to measure dopamine in the honey bee [16] .…”

“…[12] FSCV has been previously employed to measure neuromodulators in Drosophila larval ventral nerve cord (VNC) and in the adult central complex and MB. [13][14][15] Moreover, a similar approach was implemented to measure dopamine in the honey bee. [16] However, these studies were performed either in ex vivo preparations or during aversive stimulation.…”