Pavlovian Conditioned Approach Training in Rats

Summary

Here, we present a protocol to elicit Pavlovian conditioned approach behavior in rats. This procedure can be used to measure individual differences in the tendency to approach and attribute incentive salience to reward-related cues and investigate addiction vulnerability.

Abstract

Cues that are contingently paired with unconditioned, rewarding stimuli can acquire rewarding properties themselves through a process known as the attribution of incentive salience, or the transformation of neutral stimuli into attractive, "wanted' stimuli capable of motivating behavior. Pavlovian conditioned approach (PCA) develops after the response-independent presentation of a conditioned stimulus (CS; e.g., a lever) that predicts the delivery of an unconditioned stimulus (US; e.g., a food pellet) and can be used to measure incentive salience. During training, three patterns of conditioned responses (CRs) can develop: sign-tracking behavior (CS-directed CR), goal-tracking behavior (US-directed CR), and an intermediate response (both CRs). Sign-trackers attribute incentive salience to reward-related cues and are more vulnerable to cue-induced reinstatement of drug-seeking as well as other addiction-related behaviors, making PCA a potentially valuable procedure for studying addiction vulnerability. Here, we describe materials and methods used to elicit PCA behavior from rats as well as analyze and interpret PCA behavior in individual experiments.

Introduction

The transition of drug use to addiction involves complex interactions between Pavlovian and instrumental learning^1,2. During drug-taking and drug-seeking behaviors, actions and outcomes are learned through instrumental processes; however, relationships between stimuli (e.g., drug-related cues) and rewards are also learned through Pavlovian processes. Pavlovian cues acquire predictive value, but they can also acquire incentive motivational value³, whereby they become attractive, desirable, and capable of promoting and maintaining reward-seeking behavior⁴.

Many procedures investigating reward learning....

Protocol

All procedures have been approved by the University Committee on the Use and Care of Animals (UCUCA; University of Michigan, Ann Arbor, MI).

1. Equipment and Software

1. Obtain commercial operant chambers and devices. See Materials Table.
2. Conduct training in rat operant conditioning chambers (24.1 cm width × 20.5 cm depth x 29.2 cm height), situated in sound-attenuating cabinets with ventilation fans to provide ambient noise.
3. Equip each chamber with a pellet magazine (receptacle), located centrally in the 21.6 cm wide front wall of the operant chamber 3 cm above the stainless steel grid floor. ....

Results

We have found that 5-7 daily sessions of PCA training is sufficient to phenotype rats as STs, GTs, and intermediate responders (IRs), although rats can be trained further based on the needs of a particular laboratory or experiment. Phenotyping is based on PCA index scores, which are calculated by averaging the response bias, latency score, and probability difference of individual sessions as previously described in the protocol. Phenotypes are determined by averaging the PCA index scores .......

Discussion

PCA training can be used to determine individual variation in the tendency to attribute incentive salience to conditioned cues, which has been argued to be an important component of addiction vulnerability. For example, it has previously been demonstrated that STs attribute incentive salience to both food and drug cues⁶, and both food- and drug-related cues activate similar brain regions within an amygdalo-striatal-thalamic circuit in STs⁷. Moreover, STs are more impulsive⁸, vulnerable to.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Standard Modular Operant Test Chamber with Modified Top for Rat	Med Associates, Inc.	ENV-008CT	Top has access slot for drug delivery leashes or other harness systems; comes with ENV-008CTC (Cover Insert) for access slot
Expanded PVC Sound Attenuating Cubicle	Med Associates, Inc.	ENV-022V
PCI Operating Package for up to Sixteen Chambers	Med Associates, Inc.	MED-SYST-16	Based on the number of operant chambers, MED-SYST-8 (PCI Operating Package for up to Eight Chambers) is also available
SmartCtrl	Med Associates, Inc.	DIG-716P2
Universal Cable, 25′ (7.6 m)	Med Associates, Inc.	SG-210CB	Based on individual needs, SG-210CB-50 (Universal Cable, 50′ [15.2 m]) is also available
18″ (45.7 cm) 3-Pin Mini-Molex	Med Associates, Inc.	SG-216A	Based on individual needs, SG-216A-2 (2′ [61.0 cm] 3-Pin Mini-Molex) is also available
Power Cable, 25′ (7.6 m)	Med Associates, Inc.	SG-210CP-25
Stainless Steel Grid Floor for Rat	Med Associates, Inc.	ENV-005	Based on preference, ENV-005A (Stainless Steel Grid Floor for Mouse) is also available
Reusable Waste Pan	Med Associates, Inc.	ENV-007-P3
Filler Panel Package for Standard Modular Test Chamber	Med Associates, Inc.	ENV-008-FP
Modular Pellet Dispenser for Rat, 45 mg	Med Associates, Inc.	ENV-203M-45
Pellet Receptacle, Trough Type	Med Associates, Inc.	ENV-200R2M	Based on preference, ENV-200R1M (Pellet Receptable, Cup Type) is also available
Retractable Lever	Med Associates, Inc.	ENV-112CM	Calibrated to 25 g; needs to be adjusted to 10 g before Pavlovian conditioned approach training
Retractable Lever Cue Light	Med Associates, Inc.	ENV-112CML
House Light for Rat	Med Associates, Inc.	ENV-215M
100 mA Replacement Bulbs, Pack of 10	Med Associates, Inc.	SG-800R	Red-colored; for use with ENV-215M (House Light for Rat)
Pellets, 45 mg, Primate Purified Diet, Banana Flavor	Bio-Serv	F0059	50,000/box