Behavioral effects of maternal exposure to an ortho-chlorinated or a coplanar PCB congener in rats.

Polychlorinated biphenyls (PCBs) are still of environmental concern. Neurotoxic effects were described after developmental exposure to PCB mixtures and single congeners. The purpose of the present experiment was to compare the behavioral effects of the coplanar congener 3,4,3',4'-tetrachlorobiphenyl with the ortho-chlorinated 2,4,2',4'-tetrachlorobiphenyl. Female Wistar rats were exposed with a subtoxic dose of 1 mg/kg b.w. of 3,4,3',4'-tetrachlorobiphenyl, 2,4,2',4'-tetrachlorobiphenyl or the vehicle during gestation from day 7 to 18. There were significant lower concentrations of 3,4,3',4'-TCB than of 2,4,2',4'-TCB in dams and offspring at gestational day 19. Decreases from gestational day 19 (F 19) to postnatal day 21 (PND 21) were only observed in the adipose from dams exposed to 2,4,2',4'-TCB. The following behavioral tests were conducted in the offspring: locomotor activity in the open field, spatial learning in the radial arm maze, catalepsy induced by the dopamine receptor blocker haloperidol, and passive avoidance learning at PND 25, PND 95, PND 180, and PND 220, respectively. Significant differences to the control group were detected in the 3,4,3',4'-tetrachlorobiphenyl exposed offspring. There were increases in descent latencies in the catalepsy test and impairments of passive avoidance behavior. These behavioral effects were observed in the adult rats long after the termination of exposure when internal PCB levels were indistinguishable from those of controls. A mediation of the reported effects by alterations of dopaminergic processes or thyroid hormone levels is discussed.