Incentive sensitization by previous XXXX exposure: increased cue-triggered "wanting" for @entity969 reward.

@entity35 @entity4944 @entity969
We reported previously that an @entity4944 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 @entity4944 administration also causes reward cues to trigger excessive pursuit of their associated reward, even when sensitized @entity35 are tested in a drug-free state. @entity35 learned to lever press for @entity969 pellets, and they separately learned to associate @entity969 pellets with Pavlovian cues (30 sec auditory cues). @entity4944 sensitization was induced by six daily injections of @entity4944 (3 mg/kg, i.p.; controls received saline). @entity35 were tested for lever pressing under extinction conditions 10 d later, after a bilateral microinjection of intra-accumbens vehicle or @entity4944 (5 microg/0.5 microl per side). Cue-triggered pursuit of @entity969 reward was assessed by increases in pressing on the @entity969 -associated lever during intermittent presentations of a free conditioned stimulus (CS+) @entity969 cue. Sensitized @entity35 pressed at normal levels during baseline and during the CS-, but the CS+ triggered 100% greater increases in pressing from sensitized @entity35 than from control @entity35 after vehicle microinjection. Sensitization therefore enhanced the incentive salience attributed to the CS+ even when @entity35 were tested while drug-free. For control @entity35 , a microinjection of intra-accumbens @entity4944 was needed to produce the same enhancement of cue-triggered reward "wanting." The @entity4944 microinjection also interacted synergistically in sensitized @entity35 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.
