Chronic lead exposure attenuates sensitization to the locomotor-stimulating effects of cocaine

Adult male rats were exposed to a water supply containing 500 ppm lead acetate (Lead Group), or a comparable concentration of sodium acetate (Control Group), for 30 days prior to commencing testing for behavioral sensitization to cocaine. Locomotor activity (total distance (cm) travelled) was monitored for animals in both exposure conditions across 14 daily 1 h test sessions. Across successive sessions, baseline activity was recorded for a 20-min baseline period, at which time half the animals from each exposure condition received an i.p. injection of saline or 10 mg/kg cocaine HCl. Post-injection locomotor responding was then monitored for 40 min prior to returning the animal to the home cage where the respective watering regimens remained intact. On the day following the completion of sensitization testing (day 15 of testing), animals in all groups received a saline injection, and on day 16 of testing all animals received a 10 mg/kg cocaine challenge. The results showed that repeated experience with cocaine augmented the stimulatory effects of the drug in both control and lead-exposed animals. However, this behavioral sensitization effect was slower to develop and less pronounced in lead-exposed animals. These data are discussed within the context of lead-related changes in sensitivity to cocaine.