Effects of Exposure to 3,3′,4,4′,5-Pentachlorobiphenyl (PCB 126) Throughout Gestation and Lactation on Behavior (Concurrent Random Interval–Random Interval and Progressive Ratio Performance) in Rats

There is evidence that polychlorinated biphenyl (PCB) congeners have differential effects on endpoints of neurotoxicity depending on their chemical structure: specifically, that ortho-substituted congeners are neurotoxic while coplanar (dioxin-like) congeners are relatively inactive in producing neurotoxic effects. This study extends research on the effects of developmental exposure to the coplanar congener 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126) in Long-Evans rats. Dams were dosed with 0, 0.25, or 1 μg/kg/day Monday to Friday beginning 5 weeks before and continuing through gestation and lactation. The first 2-week breeding period produced 10, 7, and 13 litters in the three dose groups, respectively, used in behavioral assessment. Breeding females from the control and low-dose group that did not conceive were rebred after 76 days of dosing, producing six and six litters used in behavioral testing. This regimen of PCB exposure produced reduced weight gain between birth and weaning in cohort 1, and decreased thyroxine levels and changes in hematology and serum biochemistry parameters in both cohorts. One female and male from each litter were tested under a series of three concurrent random interval–random interval (RI-RI) schedules of reinforcement beginning at about 400 days of age, followed immediately by assessment under a progressive ratio (PR) schedule. The concurrent RI-RI allows assessment of performance during steady state and during behavior in transition (learning). The PR schedule provides the opportunity to assess the strength of the reinforcing event independent of response rate. During the first RI-RI schedule, the high-dose group apportioned responses less accurately than controls with respect to the scheduled relative reinforcement density on the two levers. There was also some evidence for differences in performance between treated and control groups on the third RI-RI schedule of reinforcement. There was no evidence for differences in the relative strength of the reinforcing event as assessed by PR performance. These same rats failed to exhibit PCB-induced impairment on a spatial delayed alternation task or under multiple fixed interval–fixed ratio or DRL schedules of reinforcement, performed prior to the current experiments. These data extend previous findings concerning the pattern of behavioral effects as a consequence of gestational and lactational exposure to a dioxin-like PCB congener.