In vivo and in vitro exposure to PCB 153 reduces long-term potentiation

We examined the effects of gestational and lactational exposure to polychlo rinated biphenyl (DCB) 153 (2,4,5,2',4',5'-hexaCB) on the magnitude of long -term potentiation (LTP) observed in the CA1 region of hippocampal brain sl ices prepared from rats at 30 days of age. We compared these actions to tho se observed when PCB 153 is dissolved in normal Krebs-Ringer solution and p erfused on slices from control rats of the same age. In vivo exposure was a t three dose levels (1.25, 5, and 20 mg/kg/day) from gestational day 3 thro ugh weaning at postnatal day 21. Although responses to low-frequency stimul ation of the Schaffer collateral pathway in exposed animals were not differ ent from controls, significantly reduced LTP was induced after tetanic stim ulation, even at the lowest dose studied. We observed a comparable depressi on of LTD when control slices were perfused with Krebs-Ringer that had been equilibrated with PCB 153 in a generator column. Neither in vivo nor in vi tro exposure significantly altered the input-output curves obtained before tetanic stimulation, but both suppressed the increase in response observed in controls after tetanic stimulation. Because LTP is thought to be correla ted with learning ability, these observations may provide at least a partia l mechanism to explain the reduction of intelligence quotient observed in h umans exposed to PCBs early in development.