A Method for Evaluating the Reinforcing Properties of Ethanol in Rats without Water Deprivation, Saccharin Fading or Extended Access Training

Summary

This protocol describes a novel and efficient method to quickly initiate operant responding for ethanol in rats that, contrary to standard methods, does not require water deprivation or saccharin/sucrose fading to initiate responding.

Abstract

Operant oral self-administration methods are commonly used to study the reinforcing properties of ethanol in animals. However, the standard methods require saccharin/sucrose fading, water deprivation and/or extended training to initiate operant responding in rats. This paper describes a novel and efficient method to quickly initiate operant responding for ethanol that is convenient for experimenters and does not require water deprivation or saccharin/sucrose fading, thus eliminating the potential confound of using sweeteners in ethanol operant self-administration studies. With this method, Wistar rats typically acquire and maintain self-administration of a 20% ethanol solution in less than two weeks of training. Furthermore, blood ethanol concentrations and rewards are positively correlated for a 30 min self-administration session. Moreover, naltrexone, an FDA-approved medication for alcohol dependence that has been shown to suppress ethanol self-administration in rodents, dose-dependently decreases alcohol intake and motivation to consume alcohol for rats self-administering 20% ethanol, thus validating the use of this new method to study the reinforcing properties of alcohol in rats.

Introduction

The development of animal models to study the reinforcing effects of drugs has proven an important tool to study human drug addiction. More specifically, operant self-administration is a widely used behavioral model that is one of the most effective means for assessing the positive reinforcing effects of an orally consumed ethanol solution. An early issue with developing such a model was the primary aversive taste of high concentrations of ethanol for most rodents, a phenomenon that is also shared in humans with little or no experience with alcohol¹. A standard protocol to overcome this barrier requires water deprivation and/or saccharin or sucrose fading f....

Protocol

All procedures are conducted in accordance with the NIH Guide for Care and Use of Laboratory Animals.

1. Animal Care and Housing

1. Upon arrival in the colony, house male Wistar rats weighing 200 - 225 g at arrival in pairs in a temperature (21 °C) and humidity-controlled environment with a reversed 12 h light-dark cycle.
   Note: Depending on the rationale of the experiments, rats may be single-housed.
2. Allow the rats to acclimate to the vivarium and the light cycle for at least one week before starting an experiment and handle them daily. Weigh the animals once weekly.
3. Give rats free access to chow and tap water for the duration ....

Results

Figure 1 shows the representative self-administration behavior of operant- and drug-naive Wistar rats (eight different cohorts amounting to a total of 239 rats) trained on a FR1 schedule to self-administer 20% ethanol without water deprivation or saccharin/sucrose fading during 30-minute sessions. With this protocol, rats initiate lever pressing to obtain an ethanol reward very quickly, already obtaining more than 10 rewards during the first sessions (Figure 1A

Discussion

With this protocol, we are presenting a new method to acquire and maintain stable oral self-administration of 20% ethanol in rats that, contrary to classic models of ethanol self-administration, does not require the use of water deprivation, extended access training, or saccharin/sucrose fading¹². Furthermore, naltrexone, a currently FDA-approved medication for alcohol dependence, successfully decreases alcohol self-administration and the motivation to consume alcohol of Wistar rats trained with this protocol........

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Extra Tall MDF Sound Attenuating Cubicle, Interior: 22"W x 22"H x 16"D	Med Associates Inc.	ENV-018MD
Extra Tall Modular Test Chamber with modified Top, Waste Pan and Photobeam	Med Associates Inc.	ENV-007CT-PH
Stainless Steel Grid Floor for Rat or Small Primate	Med Associates Inc.	ENV-005
Retractable Lever	Med Associates Inc.	ENV-112CM	2 by SA chambers
Stimulus Light, 1" White Lens, Mounted on Modular Panel	Med Associates Inc.	ENV-221M	2 by SA chambers
Dual Cup Liquid Receptacle with 18 ga Stainless Steel Pipes	Med Associates Inc.	ENV-200R3AM
Single Speed Syringe Pump, 3.33 rpm	Med Associates Inc.	PHM-100
Liquid Delivery Kit	Med Associates Inc.	PHM-122-18
SmartCtrl 8 Input / 16 Output Package	Med Associates Inc.	DIG-716P2
MED-PC software	Med Associates Inc.	SOF-735
http://www.mednr.com/	Med Associates Inc.		A website that is open-source and has been created to offer researchers a place to exchange MEDState Notation code
Kendall Monoject 20 cc Syringes, Regular Luer Tip	VWR International	MJ8881-520657
Ethanol, Pure, 190 Proof (95%), USP, KOPTEC	Decon Labs	2801
0.9% Sodium Chloride Injection, USP	Hospira	0409-4888-50
Naltrexone hydrochloride	Sigma Aldrich	N3136-1G
23 G BD PrecisionGlide Needles	BD	305145
Minivette POCT 50 µL, K3EDTA	Sarstedt	17.2113.150	For capillary blood collection