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Effects of intraaccumbens administration of SCH‐23390 on cocaine‐induced locomotion and conditioned place preference

The effects of systemic (0–1.0 mg/kg) or intraaccumbens (0–1.0 μg/side) administration of SCH‐23390 on cocaine‐induced (0 or 4.2 mg/kg, IV) locomotion, sniffing, and conditioned place preference (CPP) were investigated in rats. After behavioral testing was completed, animals were injected with their respective dose of SCH‐23390 into the nucleus accumbens (NAc), followed by a systemic injection of the irreversible antagonist N‐ethoxycarbonyl‐2‐ethoxy‐1,2‐dihydroquinoline (EEDQ). Receptors occupied by intraaccumbens SCH‐23390, and therefore protected from EEDQ‐induced inactivation, were then quantified from autoradiograms of sections labeled with 3H‐SCH‐23390. Systemic administration of 0.5 and 1.0 mg/kg SCH‐23390 reversed cocaine‐induced locomotion, sniffing, and CPP, suggesting that stimulation of D1‐like receptors is necessary for these behavioral changes. Intraaccumbens administration of 1.0 μg/side SCH‐23390 reversed cocaine‐CPP, and this dose occupied D1‐like receptors primarily in the rostral pole of the NAc. Intraaccumbens administration of 0.5 μg/side SCH‐23390 reversed cocaine‐induced locomotion. However, this dose occupied a similar number of D1‐like receptors in the NAc as a lower and behaviorally ineffective dose of 0.1 μg/side, but occupied more receptors in the caudate‐putamen relative to both the 0.1 and 1.0 μg/side doses. These findings suggest that stimulation of D1‐like receptors in the NAc is necessary for cocaine‐CPP, but not for cocaine‐induced locomotion. Synapse 30:181–193, 1998. © 1998 Wiley‐Liss, Inc.