Behavioural effects in female rats of postnatal exposure to sub-toxic doses of polychlorinated biphenyl congener 153.

Polychlorinated biphenyls (PCBs) are widespread environmental contaminants that are also present in human tissues and breast milk. Behavioural disturbances have been reported in both children and animals exposed perinatally to PCBs. The present study assessed the behavioural consequences in female rats of postnatal exposure to the di-ortho-substituted 2,2',4,4',5,5'-hexachlorobiphenyl (IUPAC no. 153), which is one of the PCB congeners most frequently detected in human milk. The different groups of mothers were dosed via gavage with 5 mg/kg bodyweight of PCB 153 in corn oil or 5 ml/kg bodyweight corn oil vehicle every second day from day 3 to day 13 after delivery. The exposure did not affect the bodyweight of the dams nor the physical development of the pups. Operant behavioural testing of the female offspring by two different schedules of reinforcement was performed. First, the animals were tested by a multiple schedule with two components: fixed interval (FI) and extinction (EXT), which has proved sensitive in revealing changes in activity level. There were no statistically significant differences in frequency or interresponse times of lever pressing between the PCB-exposed female rats and the controls. These results were in contrast to a previous, analogous study where PCB 153 produced an increased frequency of lever presses during the FI in male rats, indicating a sex-specific behavioural effect of PCB 153. The female offspring was also tested by a conjunctive schedule with two components: variable interval (VI) and differential reinforcement of low rate (DRL). This schedule revealed slower acquisition of time discrimination in the PCB 153-exposed females as compared with the controls. The VI-DRL results showed that PCB 153 may also produce long-lasting behavioural effects in female rats following postnatal exposure through the mother's milk.