INJECTIONS OF D-AMPHETAMINE INTO THE VENTRAL PALLIDUM INCREASE LOCOMOTOR-ACTIVITY AND RESPONDING FOR CONDITIONED REWARD - A COMPARISON WITHINJECTIONS INTO THE NUCLEUS-ACCUMBENS

The nucleus accumbens and ventral pallidum receive dopamine (DA) proje ctions from the mesencephalon. Although DA inputs to the nucleus accum bens are implicated in both locomotion and reward processes, little is known of the behavioural significance of DA in the ventral pallidum. These studies examined the effects of D-amphetamine injected into the nucleus accumbens or ventral pallidum on locomotor activity and respon ding for a conditioned reward (CR). In the nucleus accumbens D-ampheta mine dose dependently (1, 3 and 10 mu g) increased locomotion within 5 -10 min of injection. Intra-ventral pallidum microinjections of D-amph etamine also increased activity in this dose range, but the effect occ urred with a longer latency (5-20 min). The magnitude of the response evoked by ventral pallidum injections was lower than that evoked by nu cleus accumbens injections. The GABA(A) antagonist picrotoxin (0.1 mu g) stimulated activity when injected into the ventral pallidum but not the nucleus accumbens, providing a pharmacological dissociation betwe en the two injection sites. In the CR studies, D-amphetamine injected into both sites potentiated responding for a CR previously paired with food delivery, without altering responding on an inactive lever. Picr otoxin injected into the ventral pallidum reduced responding and aboli shed the selectivity of responding for CR. The results show that DA re lease in the ventral pallidum enhances locomotion and responding for a CR, providing evidence that DA in the ventral pallidum plays a signif icant role in the mediation of the effects of D-amphetamine. The failu re of picrotoxin to elevate responding for CR despite increasing locom otor activity indicates that pharmacologically-induced blockade of GAB A(A) receptors in the ventral pallidum disrupts goal-directed respondi ng. (C) 1998 Elsevier Science B.V. All rights reserved.