Intra-Accumbens Amphetamine Increases the Conditioned Incentive Salience of Sucrose Reward: Enhancement of Reward “Wanting” without Enhanced “Liking” or Response Reinforcement

TLDR

Rats were trained to lever‑press for sucrose, conditioned to a 30‑s light cue paired with free sucrose, and then received bilateral intra‑accumbens microinjections of vehicle or amphetamine (0–20 µg) while lever‑pressing was tested without reinforcement and the cue was presented intermittently. Amphetamine microinjection selectively increased cue‑elicited lever‑pressing (incentive motivation) without enhancing sucrose hedonic reactions or reinforcing responding, indicating that nucleus accumbens dopamine mediates reward “wanting” independently of “liking.”.

Abstract

Amphetamine microinjection into the nucleus accumbens shell enhanced the ability of a Pavlovian reward cue to trigger increased instrumental performance for sucrose reward in a pure conditioned incentive paradigm. Rats were first trained to press one of two levers to obtain sucrose pellets. They were separately conditioned to associate a Pavlovian cue (30 sec light) with free sucrose pellets. On test days, the rats received bilateral microinjection of intra-accumbens vehicle or amphetamine (0.0, 2.0, 10.0, or 20.0 μg/0.5 μl), and lever pressing was tested in the absence of any reinforcement contingency, while the Pavlovian cue alone was freely presented at intervals throughout the session. Amphetamine microinjection selectively potentiated the cue-elicited increase in sucrose-associated lever pressing, although instrumental responding was not reinforced by either sucrose or the cue during the test. Intra-accumbens amphetamine can therefore potentiate cue-triggered incentive motivation for reward in the absence of primary or secondary reinforcement. Using the taste reactivity measure of hedonic impact, it was shown that intra-accumbens amphetamine failed to increase positive hedonic reaction patterns elicited by sucrose (i.e., sucrose “liking”) at doses that effectively increase sucrose “wanting.” We conclude that nucleus accumbens dopamine specifically mediates the ability of reward cues to trigger “wanting” (incentive salience) for their associated rewards, independent of both hedonic impact and response reinforcement.