A Simple Way to Measure Alterations in Reward-seeking Behavior Using Drosophila melanogaster

Summary

We describe a protocol for inducing rewarding and nonrewarding experiences in fruit flies (Drosophila melanogaster) using voluntary ethanol consumption as a measure for changes in reward states.

Abstract

We describe a protocol for measuring ethanol self-administration in fruit flies (Drosophila melanogaster) as a proxy for changes in reward states. We demonstrate a simple way to tap into the fly reward system, modify experiences related to natural reward, and use voluntary ethanol consumption as a measure for changes in reward states. The approach serves as a relevant tool to study the neurons and genes that play a role in experience-mediated changes of internal state. The protocol is composed of two discrete parts: exposing the flies to rewarding and nonrewarding experiences, and assaying voluntary ethanol consumption as a measure of the motivation to obtain a drug reward. The two parts can be used independently to induce the modulation of experience as an initial step for further downstream assays or as an independent two-choice feeding assay, respectively. The protocol does not require a complicated setup and can therefore be applied in any laboratory with basic fly culture tools.

Introduction

Modification of behavior in response to experience allows animals to adjust their behavior to changes in their environment¹. During this process, animals integrate their internal physiological state with the changing conditions of the external environment and subsequently choose one action over another to increase their chances of survival and reproduction. Reward systems evolved to motivate behaviors that are required for the survival of individuals and species by reinforcing behaviors that enhance immediate survival, such as eating or drinking, or those that ensure long-term survival, such as sexual behavior or caring for offspring². Artificial....

Protocol

Note: General overview of the experimental design: The experimental design includes an adapted protocol for courtship suppression^7-9 in which male flies are exposed to rewarding and nonrewarding experiences in 3 consecutive training sessions over the course of 4 d. At the end of the experience phase, the flies are tested in a two-choice voluntary ethanol consumption assay for 3 - 4 d. The protocol herein includes several preparatory steps, some of which can be done in advance to be used in more than one experiment, while others should take place in a timely manner before the beginning of the experiment (Table 1).

1. Preparatory Steps

Results

FPreviously, Devineni et al. showed that when fruit flies are given the choice to consume ethanol-containing food, they display a strong preference for ethanol-containing food over nonethanol containing food⁶. Shown here are some representative results we obtained when assaying the innate ethanol preference of naïve male flies that did not undergo the training protocol.

Naïve Canton S male flies were collecte.......

Discussion

Here, we illustrate the details of an integrated approach to measure alterations in reward-seeking behavior, based on previous work described by Devineni et al.⁶ and Shohat-Ophir et al⁵. The first section of the protocol uses different types of sexual interactions as the experience input, and the second section uses a two-choice feeding assay to assess the effect of experience on the preference to consume ethanol.

As shown by Devineni et al.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Polystyrene 25 x 95 mm Vials	FlyStuff	32-109
narrow plastic vials flugs	FlyStuff	42-102
Disposable Sterile Needle 18 G and 27 G	can be acquired by any company		1.20 X 38 mm (18 G x 1 1/2") , 0.40 X 13 mm (27 G x 1/2")
10 x 75 mm Borosilicate Glass Disposable Culture Tubes	kimble chase	73500-1075
calibrated pipets 5 μL	VWR	53432-706	color coded white to contain 5 μL
Mineral Oil	Sigma-Aldrich	M5904
Sucrose, Molecular Biology Grade	CALBIOCHEM	573113
Yeast extract Powder for microbiology	can be acquired by any company
Ethanol	Sigma-Aldrich	32221
standard pipette Tips (micro-pipetts)	ThermScientific	T114R-Q	volume: 0.1 - 20 μL (ultramicro)
IDENTI-PLUGS (Foam Tube Plugs)	Jaece	L800-A	fits opening 6 - 13 mm
IDENTI-PLUGS (Foam Tube Plugs)	Jaece	L800-D	fits opening 35 - 45 mm
virginator fly stock	bloomington drosophila stock center	#24638
Narrow Vials, Tray Pack (PS)	Genesee Scientific Corporation	# 32-109BR
Drosophila Media Recipes and Methods	Bloomington Drosophila Stock Center	http://flystocks.bio.indiana.edu/Fly_Work/media-recipes/molassesfood.htm
propionic acid	Sigma-Aldrich	P5561
phosphoric acid	Sigma-Aldrich	W290017
Methl 4-Hydroxybenzoate	Sigma-Aldrich	H3647
Agar Agar	can be acquired by any company
corn meal	can be acquired by any company
Grandma's molasses	B&G Foods, Inc	not indicated
instant dry yeast	can be acquired by any company