A Conflict Model of Reward-seeking Behavior in Male Rats

Summary

This conflict model is used to measure the impairment of inhibitory control after exposure to addictive drugs, or other factors that may influence inhibitory control. A sexual stimulus and an aversive obstacle are concurrently presented, thus male rats have to conquer the obstacle to approach the sexual reward.

Abstract

The present protocol describes a novel conflict task as a model of inhibitory control in rats. In this model, a natural rewarding stimulus (sexual stimulus) that represents a high-value reward, and the aversive stimuli (pins), are concurrently presented. The male rats have to climb or jump over the obstacle full of pins to approach and investigate the sexual partner. If the animal persists in their approaching behavior regardless of the aversive stimuli, it is considered as a maladaptive or risky reward-seeking behavior. The conflict task permits the evaluation of deficit in inhibitory control resulting from exposure to abused drug, such as morphine, or a stressful event.

The main advantage of this model is that it provides a simple and quick way to discover the deficit in inhibitory control after exposure to opiate drugs or other stressful events. In addition to opiates, this behavioral model would also be useful for quickly discovering the inhibitory control deficits induced by other addictive drugs. However, the limitation is that the male rats' performance may be subject to exercising effects with repeated testing under this conflict task. In the future, one can hope that the individuals with the compulsive phenotype of reward-seeking behavior after exposure to opiates will be identified based on modifying this conflict model.

Introduction

Drug addiction is a chronic brain disease which is characterized by impulsive and compulsive drug seeking and taking¹. These key features of addiction have both been hypothesized to result from the impaired ability of inhibitory control^2,3, i.e., failing in inhibiting the immediate pursuit of rewarding stimuli and thus developing maladaptive patterns of behavior⁴.

The go/no-go task and stop-signal task are the prototypical tasks used to measure the ability of response inhibition^2,5

Protocol

This study is approved by the International Review Board (IRB) of the Institute of Psychology, Chinese Academy of Sciences, and all experiments are conducted in accordance with the National Institutes of Health (U.S.A) Guide for Care and Use of Laboratory Animals (2011).

1. Materials and Setup for the Conflict Model

1. House four rats per cage (50 cm long x 22.5 cm wide x 30 cm high) in colony rooms with controlled temperature (22–25 °C) and a reversed 12 h/12 h light/dark cycle (lights on at 21:00) for at least 10 days.
   NOTE: Male and female Sprague-Dawley rats weighing 330–400 and 230̵....

Results

To explore whether this conflict model can reveal maladaptive/risky reward-seeking behavior induced by opiates, the reward-seeking behaviors displayed by the saline- and morphine-pretreated groups were compared by t-tests after short-term (Wd7) and long-term (Wd17) withdrawal from morphine respectively (Figure 2). The results show that on both day 7 and day 17 of withdrawal, the morphine-pretreated rats showed significantly more approaching behaviors than the.......

Discussion

The inhibitory control deficits caused by drug abuse¹⁸ play a key role in promoting compulsive drug seeking/taking behaviors and relapse^19,20. The conflict model presented here provides a new approach to explore the changes in inhibitory control of the individuals exposed to addictive drugs.

There are several critical steps in the protocol. First of all, the subjects (male rats) must acquire sexual experience be.......

Materials

Name	Company	Catalog Number	Comments
Acetic acid	Beijing Tongguangjingxi Chemical company	CN No.81601	CH3COOH
Benzypenicillin sodium for Injection	Huabei Pharmaceutical	F7072109	C16H17N2NaO4S
Cotton swabs	Wan Xin, Shandong, China	8 cm
β-estradiol benzoate	SIGMA-ALDRICH	E8515-200MG	estradiol benzoate
Gauze	Wan Xin, Shandong, China	21s × 21s 110×100
Hemostatic forceps	Beijing Zhong Sheng Wanda Biotechnology Co.,Ltd.
Morphine hydrochloride	Qinghai Pharmaceutical Co. Ltd	20100105	Morphine hydrochloride
Ophthalmic scissors	Beijing Zhong Sheng Wanda Biotechnology Co.,Ltd.
Pentobarbital Sodium	Sigma		C11H17O3N2Na
Precision animal shocker	Coulbourn
Progesterone	SIGMA-ALDRICH	V900699-5G	progesterone
Sesama oil	Fengyi trading company ltd.		Sesama oil
Sodium chloride injection	HuaLu Pharmaceutical	H17092107	NaCl
Scalpels	Gillette	96797241
Surgical blades	Shanghai Pudong Jinhuan Medical Products Co.,Ltd
Suture needles	Han Qin, Shanghai, China	Δ1/2 6×14
Silk sutures	Shanghai Pudong Jinhuan Medical Products Co.,Ltd
Sprague-Dawley rats	Vital River Animal Center, Beijing, China	Sprague-Dawley	animal strain
Syringe	WeiGao Group Medical Polymer Co.Ltd	1ml, 2ml
Tweezers	Beijing Zhong Sheng Wanda Biotechnology Co.,Ltd.