The Journal of Neuroscience, August 15, 2000, 20(16):6282-6288
NMDA, But Not Dopamine D2, Receptors in the Rat
Nucleus Accumbens Are Involved in Guidance of Instrumental Behavior by
Stimuli Predicting Reward Magnitude
Wolfgang
Hauber,
Ines
Bohn, and
Christian
Giertler
Abteilung Tierphysiologie, Biologisches Institut, Universität
Stuttgart, Stuttgart, Germany D-70550
Expectancy of future reward is an important factor guiding the
speed of instrumental behavior. The present study sought to explore
whether signals transmitted via the NMDA subtype
of glutamate receptors and via dopamine D2 receptors in the
nucleus accumbens (NAc) are critical for the determination of reaction
times (RTs) of instrumental responses by the expectancy of future
reward. A simple RT task for rats demanding conditioned lever release was used in which the upcoming reward magnitude (5 or 1 pellet) was
signaled in advance by discriminative stimuli. In trained rats, RTs of
conditioned responses with expectancy of a high reward magnitude were
found to be significantly shorter. The shortening of RTs by stimuli
predictive of high reward to be obtained was dose-dependently impaired
by bilateral intra-NAc infusion of the competitive NMDA antagonist
DL-2-amino-5-phosphonovaleric acid (APV) (1, 2, or 10 µg in 0.5 µl/side), but not by infusion of the preferential
dopamine D2 antagonist haloperidol (5 and 12.5 µg in 0.5 µl/side) or by infusion of vehicle (0.5 µl/side). In conclusion,
the data reveal that in well trained animals stimulation of intra-NAc
NMDA, but not of dopamine D2, receptors, is
critically involved in guiding the speed of instrumental responses
according to stimuli predictive of the upcoming reward magnitude.
Key words:
nucleus accumbens; goal-directed behavior; reward; dopamine; glutamate; reaction time; rat
Copyright © 2000 Society for Neuroscience 0270-6474/00/20166282-07$05.00/0