D₁ and D₂ dopamine receptor mediation of amphetamine-induced acetylcholine release in nucleus accumbens

To assess the interaction of dopamine and acetylcholine systems in the rat nucleus accumbens in response to direct D-amphetamine administration, in vivo microdialysis measures of acetylcholine were used during reverse dialysis of amphetamine alone and in combination with D₁ and D₂ receptor antagonists SCH 23390 and sulpiride, respectively. During a 15-min exposure to amphetamine (50 μM) in the nucleus accumbens, acetylcholine increased to 33% above pre-infusion levels, became maximal at 15 min post-infusion (+41%) and gradually returned to baseline levels by 60 min post-amphetamine. Conversely, amphetamine (1 mM) administration caused a biphasic change in acetylcholine release with a trend toward a decrease (-14%) during exposure followed by a significant increase (+36%) at 30 min post-amphetamine that returned to baseline levels by 60 min after infusion. The increases observed during amphetamine (50 μM) exposure and during recovery from amphetamine (1 mM) were both blocked by co-administration with the D₁ antagonist, SCH 23390 (10 μM), but not with the D₂ antagonist, sulpiride (10 μM). Co-infusion of sulpiride eliminated the trend toward reduced acetylcholine release observed during 1 mM amphetamine whereas co-administration of SCH 23390 potentiated this decrease. A possible tonic D₁ facilitation of nucleus accumbens acetylcholine release was indicated by the consistent reductions in acetylcholine release observed during infusion of SCH 23390. These results suggest that amphetamine administration in the nucleus accumbens induces a bidirectional change in acetylcholine release that is dependent on dose and opposing effects of nucleus accumbens D₁ and D₂ activation. In general, relatively low doses of amphetamine administered into the nucleus accumbens caused an increase in acetylcholine release that was dependent on dopamine D₁ receptors whereas higher doses of amphetamine resulted in a D₂-mediated decrease.