Behavioral assessments of learning and attention in rats exposed perinatally to 3,3 ',4,4 ',5-pentachlorobiphenyl (PCB 126)

Evidence from humans suggests that cognitive dysfunction may result from pe rinatal exposure to polychlorinated biphenyls (PCBs), and the results of so me animal research with PCBs have been interpreted in terms of possible imp airment of attention. Long-Evens rats were fed 3,3',4,4',5-pentachlorobiphe nyl (PCB 126), a coplanar congener, at doses of 0.25 or 1 mg/kg/day through out gestation and nursing. Male offspring of these rats were trained as adu lts to perform 2 tests of attention for food reward. First, a cued target-d etection task, modeled after Posner's covert orienting method for humans, w as used to assess visuospatial attention. In this task, a visual target sti mulus was presented in 1 visual hemifield on each trial, preceded either by a valid cue, an invalid cue, or no cue. A valid cue appeared in the same h emifield as the target, and an invalid cue appeared in the opposite hemifie ld. As expected, valid cues increased accuracy and speed of target detectio n and invalid cues decreased accuracy and speed; moreover, these effects we re systematically related to changes in cue intensity and target duration. However, perinatal exposure to PCB 126 did not affect acquisition or perfor mance of this task. The second task assessed sustained attention by means o f a signal detection method in which a brief, spatially-constant but tempor ally unpredictable, Visual signal indicated which of 2 responses would yiel d food. Varying the intensity of the signal greatly affected the probabilit y of correctly reporting the signal. Perinatal exposure to PCB 126 did not affect acquisition of the response rule or performance of the task. Finally , all rats were challenged with chlordiazepoxide (CDP) at doses of 0, 3, 5, 8, or 12 mg/kg SC, 20 min before testing in the sustained attention task. In control rats, low doses (3, 5, and 8 mg/kg) of CDP reduced accuracy at l ow signal intensities only, suggesting an increase in visual threshold. The high dose of CDP reduced accuracy at all signal intensities and increased the false-alarm rate as well, suggesting an impairment of attention. The ra ts exposed perinatally to PCB 126 at 0.25 mg/kg were unaffected by CDP, and those exposed to PCB 126 at 1 mg/kg showed a smaller decrement in performa nce after CDP than did the controls. Taken together, these data provide lit tle support for the possibility that perinatal exposure to PCB 126 causes d eficits in attention, but suggest that PCB 126 may alter GABA-mediated path ways in the CNS during development. Published by Elsevier Science Inc.