Conditioned Incentive Paradigm with Lever Pressing
behavioralratNot specified
Objective: To assess whether amphetamine sensitization enhances cue-triggered reward pursuit by measuring lever pressing behavior in response to Pavlovian auditory cues associated with sucrose reward
Materials & Equipment Checklist
9 items
Gather these items before starting the experiment. Check off items as you prepare.
Equipment3
Not specified • Not specified • Not specified • Not specified
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Protocol Steps
View Abstract
We reported previously that an amphetamine microinjection into the nucleus accumbens enables Pavlovian reward cues in a conditioned incentive paradigm to trigger excessive instrumental pursuit. Here we show that sensitization caused by previous amphetamine administration also causes reward cues to trigger excessive pursuit of their associated reward, even when sensitized rats are tested in a drug-free state. Rats learned to lever press for sucrose pellets, and they separately learned to associate sucrose pellets with Pavlovian cues (30 sec auditory cues). Amphetamine sensitization was induced by six daily injections of amphetamine (3 mg/kg, i.p.; controls received saline). Rats were tested for lever pressing under extinction conditions 10 d later, after a bilateral microinjection of intra-accumbens vehicle or amphetamine (5 microg/0.5 microl per side). Cue-triggered pursuit of sucrose reward was assessed by increases in pressing on the sucrose-associated lever during intermittent presentations of a free conditioned stimulus (CS+) sucrose cue. Sensitized rats pressed at normal levels during baseline and during the CS-, but the CS+ triggered 100% greater increases in pressing from sensitized rats than from control rats after vehicle microinjection. Sensitization therefore enhanced the incentive salience attributed to the CS+ even when rats were tested while drug-free. For control rats, a microinjection of intra-accumbens amphetamine was needed to produce the same enhancement of cue-triggered reward "wanting." The amphetamine microinjection also interacted synergistically in sensitized rats to produce intrusive cue-triggered pursuit behaviors (e.g., investigatory sniffing) that interfered with goal-directed lever pressing. These results support the incentive-sensitization theory postulate that sensitization causes excessive cue-triggered "wanting" for an associated reward.
1
Amphetamine sensitization induction
Rats received six daily intraperitoneal injections of amphetamine to induce sensitization. Control rats received saline injections instead.
Six daily injectionsNot specified
Note: Sensitization protocol completed before behavioral testing
View evidence from paper
“Amphetamine sensitization was induced by six daily injections of amphetamine (3 mg/kg, i.p.; controls received saline)”
2
Lever pressing training
Rats learned to press a lever to obtain sucrose pellets as reward
Not specifiedNot specified
Note: Instrumental conditioning phase
View evidence from paper
“Rats learned to lever press for sucrose pellets”
3
Pavlovian cue-reward association
Rats separately learned to associate sucrose pellets with 30 second auditory Pavlovian cues
30 sec auditory cuesNot specified
Note: Classical conditioning phase pairing auditory stimulus with sucrose
View evidence from paper
“they separately learned to associate sucrose pellets with Pavlovian cues (30 sec auditory cues)”
4
Waiting period after sensitization
Rats waited 10 days after the final amphetamine injection before behavioral testing
10 daysNot specified
Note: Testing occurred in drug-free state
View evidence from paper
“Rats were tested for lever pressing under extinction conditions 10 d later”
5
Nucleus accumbens microinjection
Bilateral microinjection of either vehicle or amphetamine into nucleus accumbens immediately before behavioral testing
Not specifiedNot specified
Note: 5 μg/0.5 μl per side injected
View evidence from paper
“after a bilateral microinjection of intra-accumbens vehicle or amphetamine (5 μg/0.5 μl per side)”
6
Extinction lever pressing test with cue presentation
Rats tested for lever pressing under extinction conditions with intermittent presentations of the conditioned stimulus (CS+) sucrose cue. Cue-triggered pursuit measured by increases in pressing on sucrose-associated lever during CS+ presentations.
Not specifiedNot specified
Note: Testing assessed both baseline pressing and pressing during CS+ and CS- presentations
View evidence from paper
“Rats were tested for lever pressing under extinction conditions 10 d later. Cue-triggered pursuit of sucrose reward was assessed by increases in pressing on the sucrose-associated lever during intermittent presentations of a free conditioned stimulus (CS+) sucrose cue”
Subjects / Specimens
Species
rat
Strain
Not specified
Age
Not specified
Sex
unknown
Weight
Not specified
Rats were divided into sensitized and control groups