Neurotransmitter concentrations and binding at dopamine receptors in rats after maternal exposure to 3,4,3',4'-tetrachlorobiphenyl: the role of reduced thyroid hormone concentrations.
Polychlorinated biphenyls (PCBs) are environmental contaminants, which accumulate in the food chain and are transferred to the offspring during prenatal development through the placenta and postnatally via breast milk. It is reported that PCBs exert effects on thyroid hormone levels and brain neurotransmitter levels. Both actions may alter neuronal development. The aim of the present study was to investigate, if PCB-induced effects on concentrations of catecholamines and serotonin can be attributed to PCB-induced reductions in thyroid hormone concentrations. In addition, binding to dopamine D(1) and D(2) receptors was examined. Time-mated Wistar rats were treated prenatally with 1 mg 3,4,3',4'-tetrachlorobiphenyl (PCB 77)/kg bodyweight or the vehicle. A third group serving as the positive control received perinatally 5 mg propylthiouracil (PTU)/l drinking water. There were no overt toxic signs in dams or offspring. Thyroid hormone measurements demonstrated effects in dams and offspring up to postnatal day 40. In particular, total T(4) in serum and in the thyroid were decreased in PCB- and PTU-treated dams and offspring. Only PTU exposed rats exhibited significantly increased concentrations of TSH in the serum and pituitary. Measurement of neurotransmitters revealed changes in the PCB-exposed offspring at PND 40, while PTU-treatment was without effect. Dopamine and DOPAC were increased in the medial prefrontal cortex. In adulthood, there were no PCB-related effects on thyroid hormones and neurotransmitters. Binding studies of dopamine D1 and D2 receptors demonstrated that PCB and PTU had no influence on receptor concentration and affinity. Comparison of PCB 77 exposed offspring to PTU exposed offspring demonstrated differential effects on TSH and neurotransmitter levels, the latter result indicating that not all PCB-induced effects on the nervous system can be ascribed to decreases in thyroid hormone concentrations.
Roth-Härer
A
A
Department of Biological Psychology, Medical Institute of Environmental Hygiene, Aufm Hennekamp 50, D-40225, Düsseldorf, Germany
Lilienthal
H
H
Bubser
M
M
Kronthaler
U
U
R Mundy
W
W
R Ward
T
T
Schmidt
W
W
Winterhoff
H
H
Winneke
G
G