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.