Chronic cadmium exposure attenuates conditioned place preference produced by cocaine and other drugs

Adult male rats were exposed ad lib for 40 days to 100 ppm dietary cadmium chloride (group cadmium) or an identical diet with no added cadmium (group control). Conditioned place preference (CPP) was conducted in a two-chamber apparatus in which all drugs were paired with the least-preferred side as determined by a pretest. In Experiment 1, animals received 0, 2.5, or 5 mg/kg cocaine HCl (IP) for 4 days and vehicle only for 4 days. Control animals showed a place preference for the drug side at 2.5 and 5 mg/kg, while the cadmium-exposed animals showed a preference at 5 mg/kg only. In Experiment 2, animals received 0, 5, or 10 mg/kg of the D1/D2 dopamine receptor agonist apomorphine HCl (SC) for 4 days and vehicle only for 4 days. Control animals showed a place preference at 5 and 10 mg/kg, while metal-exposed animals showed a preference at 10 mg/kg only. To determine the possible effects of alterations of learning mechanisms by cadmium, a conditioned place aversion (CPA) procedure was employed for Experiment 3. Animals received 0, 10, or 40 mg/kg lithium chloride (IP) for 4 days or vehicle only for 4 days. Control animals showed a significant place aversion at 40 mg/kg, while cadmium-exposed animals did not. These findings are discussed within a framework of possible metal-induced disturbance of neurochemical function and/or associative processing.