A Procedure to Study the Effect of Prolonged Food Restriction on Heroin Seeking in Abstinent Rats

Summary

A procedure that allows a demonstration of robust augmentation of drug seeking in food-restricted rats is described. Following heroin self-administration training, rats go through an abstinence period, in a drug-free environment, during which they are mildly food restricted. Drug seeking is then tested in the drug-associated environment.

Abstract

In human drug addicts, exposure to drug-associated cues or environments that were previously associated with drug taking can trigger relapse during abstinence. Moreover, various environmental challenges can exacerbate this effect, as well as increase ongoing drug intake.

The procedure we describe here highlights the impact of a common environmental challenge, food restriction, on drug craving that is expressed as an augmentation of drug seeking in abstinent rats.

Rats are implanted with chronic intravenous i.v. catheters, and then trained to press a lever for i.v. heroin over a period of 10-12 days. Following the heroin self-administration phase the rats are removed from the operant conditioning chambers and housed in the animal care facility for a period of at least 14 days. While one group is maintained under unrestricted access to food (sated group), a second group (FDR group) is exposed to a mild food restriction regimen that results in their body weights maintained at 90% of their nonrestricted body weight. On day 14 of food restriction the rats are transferred back to the drug-training environment, and a drug-seeking test is run under extinction conditions (i.e. lever presses do not result in heroin delivery).

The procedure presented here results in a highly robust augmentation of heroin seeking on test day in the food restricted rats. In addition, compared to the acute food deprivation manipulations we have used before, the current procedure is a more clinically relevant model for the impact of caloric restriction on drug seeking. Moreover, it might be closer to the human condition as the rats are not required to go through an extinction-training phase before the drug-seeking test, which is an integral component of the popular reinstatement procedure.

Introduction

One of the major difficulties in the treatment of drug addiction is the high rate of relapse, even after prolonged periods of abstinence^1,2. Studies in human addicts have identified a critical contribution of environmental challenges, such as the exposure to drug-associated discrete cues or environments³ and stressful life events⁴, to relapse. A common environmental challenge that was found to have an effect on drug taking and craving is chronic food restriction. For example, it has been reported that chronic caloric restriction is associated with increased cigarette smoking⁵. Furthermore, dieting severi....

Protocol

1. Animals

All rats are treated in accordance with the guidelines of the Canadian Council on Animal Care and approval for all the experimental procedures was granted by the Concordia University Animal Research Ethics Committee.

1. Obtain rats at 275-300 g (males) or 225-250 g (females). House rats in pairs until surgery in standard plastic cages containing corncob bedding and shredded paper.
2. Maintain rats on a reversed light-dark cycle (light off at 9:30 AM).
3. Make sure food and water are available ad libitum, except during the abstinence period. We use a regular rat chow (20.9% protein, 67.2% carbohydra....

Results

Body weights over time: Typical results demonstrate that body weights remain stable throughout heroin self-administration training. During abstinence, rats with unrestricted access to chow increase their body weight, while those that are food restricted decrease their body weight to approximately 90% of their own original body weight or 75-80% of the sated rats' body weight (Figure 2).

Infusions, active and inactive lever responses over training: Infusions and ac.......

Discussion

The procedure described here has strong face validity because 1) it allows for voluntary drug intake and control over drug administration, 2) it uses a route of administration that is common in human addicts, 3) it reflects (relatively) prolonged periods of drug exposure and abstinence, and 4) it avoids the extinction training before the drug-seeking test that is integral to the reinstatement procedure but is rarely observed in human addicts¹⁴. In addition, the procedure models a prolonged food restriction con.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Name	Company	Catalogue Number
Ketamine (Vetalar, 100 mg/ml)	Bioniche Animal Health	Obtained through local distributer
Xylazine (Rompun, 100 mg/ml)	Bayer	Obtained through local distributer
Heroin HCl	National Institute for Drug Abuse, Research Triangle Park, NC, USA
Anafen injection 1 mg/ml Vial/20 ml	CDMV, Canada	12868
Equipment
Name	Company	Catalogue Number
Silastic tubing (ID 0.02, OD 0.037)	Fisher Scientific	1118915A
GE marine silicon	GE	SE-1134
Tygon tubing (ID 0.02, OD 0.060)	VWR	63018-044
Cannulae (22 G, 5-up)	Plastics One	C313G-5up
Liquid swivels, plastic, 22 G	Lomir Biomedical, Inc.	RSP1
Fixed speed infusion pump (3.3 rpm)	Coulbourn Instruments	A73-01-3.3
Rat test cage	Coulbourn Instruments	H10-11R-TC
Stainless steal grid floor	Coulbourn Instruments	H10-11R-TC-SF
House light-rat	Coulbourn Instruments	H11-01R
Single high-bright cue-rat	Coulbourn Instruments	H11-03R
Tone module 2.9 kHz	Coulbourn Instruments	H12-02R-2.9
Retractable lever-rat	Coulbourn Instruments	H23-17RA
Balance arm	Coulbourn Instruments	H29-01
Sound attenuation boxes	Concordia University	Home made
System controller 2	Coulbourn Instruments	SYS CTRL 2
System power base	Coulbourn Instruments	H01-01
Habitest Universal Linc	Coulbourn Instruments	H02-08
Environment connection board & Linc cable	Coulbourn Instruments	H03-04
Graphic State Notation 3	Coulbourn Instruments	GS3