Spatial Learning Deficits in Adult Rats Exposed to ortho-Substituted PCB Congeners during Gestation and Lactation

Spatial learning and memory was assessed in rats following gestationaland lactational exposure to specific ortho-substituted PCBs.Time-mated Sprague-Dawley rats were exposed to PCB 28 (2,4,4'-trichlorobiphenyl),8 or 32 mg/kg/day, PCB 118 (2,3',4,4',5-pentachlorobiphenyl),4 or 16 mg/kg/day, PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl),16 or 64 mg/kg/day, or corn oil vehicle via gavage on GestationDays 10–16. Litters were culled to eight on Day 2 andweaned on Day 21. Beginning on Day 90, one male and one femalefrom each litter were tested on a working/reference memory taskon an eight-arm maze. For each rat, the same four arms werebaited throughout training. Animals were tested Monday-Friday,for seven consecutive weeks. No differences in working or referencememory errors were observed. The same animals were later testedon a T-maze delayed spatial alternation task. On each trial,the reinforcer was placed in the arm opposite that chosen bythe rat on the previous trial. Intertrial delays of 15, 25,or 40 sec appeared in counterbalanced order. Rats were testedMonday-Friday for three consecutive weeks. The higher dosesof all three congeners resulted in slower acquisition by femalerats. Males were not affected. PCB-exposed females were impairedat all delays and were not differentially more impaired at longerdelays, suggesting a learning or attentional deficit, ratherthan a mnemonic deficit. These findings demonstrate that perinatalexposure to ortho-substituted PCBs can result in long-lastingdeficits in learning and suggest that the effects of PCBs onlearning may be sex specific.