Reduced growth of intra- and infra-pyramidal mossy fibers is produced by continuous exposure to polychlorinated...

Exposure to polychlorinated biphenyl (PCB) has been shown to produce cognitive deficits in both humans and laboratory animals. However, no study to date has identified long-term brain changes which could account for these problems. This study employed Timm's silver sulfide staining to visualize the hippocampal mossy fibers in Sprague-Dawley rats continuously exposed to either 125 ppm Aroclor 1254 or untreated control food beginning in utero. Reduced growth of hippocampal intra-and infra-pyramidal (II-P) mossy fibers were found in PCB treated rats compared to controls. Other measured hippocampal subdivisions remained relatively unaffected by PCB treatment, as did cortical thickness. The changes observed in hippocampal morphology in response to PCB exposure are the first to provide a potential explanation for at least part of the long-term PCB-induced cognitive deficits.