Effects of postnatal exposure of monkeys to a PCB mixture on spatial discrimination reversal and DRL performance

Behavioral impairment as a consequence of PCB exposure beginning in utero has been reported in both humans and animals. The present study assessed the behavioral consequences of postnatal exposure to PCBs. Male monkeys (Macaca fascicularis) were dosed from birth to 20 weeks of age with 7.5 microg/kg/ day of a PCB mixture representative of the PCBs typically found in human breast milk (eight monkeys) or vehicle (four monkeys). Blood PCB levels at 20 weeks of age were 0.30-0.37 ppb for control and 1.84-2.84 ppb for treated monkeys, and fat levels were 50-198 and 1694-3560 ppb for the two groups, respectively. At about 4.5-5.0 years of age, monkeys performed on a series of three spatial discrimination reversal tasks, followed by a differential reinforcement of low rate (DRL) 30-s schedule of reinforcement. There were no differences between groups for the number of errors across reversals for any of the discrimination reversal tasks, whereas the PCB-treated group tended to have shorter median response latencies than the control group. On the DRL schedule, there were robust differences in performance between the treated and control groups. Treated monkeys displayed shorter mean and median interresponse times (IRTs), obtained fewer reinforcements, and emitted more nonreinforced responses. The treated groups also had more short IRTs (< or =10 s) than control monkeys. Performance of the treated group did not improve to control levels over the 51 sessions of the DRL 30-s schedule; their performance remained much less efficient than that of controls. The results of this study extend previous research in this cohort of monkeys, and provide further evidence that PCB exposure limited to the early postnatal period and resulting in environmentally relevant body burdens produces long-term behavioral effects.