Objective: To assess cue-triggered pursuit behavior for sucrose reward in rats with and without amphetamine sensitization, measuring how conditioned stimulus presentations increase lever pressing during extinction conditions
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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Extinction Testing with Conditioned Stimulus — Cindy L. Wyvell | ReplicateScience
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.
Protocol Steps
1
Lever pressing training
Rats learned to lever press for sucrose pellets in operant conditioning chambers
not specifiednot specified
Note: This establishes the instrumental response
View evidence from paper
“Rats learned to lever press for sucrose pellets”
2
Pavlovian cue conditioning
Rats separately learned to associate sucrose pellets with 30 second auditory conditioned stimulus cues
30 seconds per cue presentationnot specified
Note: This establishes the CS+ (sucrose-associated cue)
View evidence from paper
“they separately learned to associate sucrose pellets with Pavlovian cues (30 sec auditory cues)”
3
Amphetamine sensitization induction
Sensitized group received six daily intraperitoneal injections of amphetamine at 3 mg/kg; control group received saline injections
6 days of daily injectionsnot specified
Note: Controls received saline instead of amphetamine
View evidence from paper
“Amphetamine sensitization was induced by six daily injections of amphetamine (3 mg/kg, i.p.; controls received saline)”
4
Waiting period
Rats were allowed to rest for 10 days after sensitization induction before testing
10 daysnot specified
Note: Testing occurred after this delay period
View evidence from paper
“Rats were tested for lever pressing under extinction conditions 10 d later”
5
Intra-accumbens microinjection
Bilateral microinjection of either vehicle or amphetamine (5 μg/0.5 μl per side) into the nucleus accumbens immediately before extinction testing
not specifiednot specified
Note: All rats received microinjection; sensitized rats received either vehicle or amphetamine; control rats received either vehicle or amphetamine
View evidence from paper
“after a bilateral microinjection of intra-accumbens vehicle or amphetamine (5 μg/0.5 μl per side)”
6
Extinction testing with conditioned stimulus presentations
Rats were tested for lever pressing under extinction conditions with intermittent presentations of the free conditioned stimulus (CS+) sucrose cue to measure cue-triggered pursuit behavior
not specifiednot specified
Note: Cue-triggered pursuit assessed by increases in pressing on sucrose-associated lever during CS+ presentations
View evidence from paper
“Rats were tested for lever pressing under extinction conditions...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 based on amphetamine or saline pretreatment