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LONG-LASTING NEUROSTRUCTURAL CONSEQUENCES IN THE RAT HIPPOCAMPUS BY DEVELOPMENTAL EXPOSURE TO A MIXTURE OF POLYCHLORINATED BIPHENYLS (PCBS).
Citation:
Mervis, R. F., A. D. Bachstetter, G. J. Harry, H A. Tilson, AND P. Kodavanti. LONG-LASTING NEUROSTRUCTURAL CONSEQUENCES IN THE RAT HIPPOCAMPUS BY DEVELOPMENTAL EXPOSURE TO A MIXTURE OF POLYCHLORINATED BIPHENYLS (PCBS). Presented at Society of Toxicology, Nashville, TN, March 17-21, 2002.
Description:
The objective of the study was to assess the effects of developmental exposure to a commercial mixture of PCBs (Aroclor 1254) on neuronal dendritic morphology of hippocampal CA1 pyramidal neurons in postnatal day (PND) 22 and PND 60 male Long-Evans rats. Rat pups were born to mothers who were exposed to Aroclor 1254 (AccuStandard Inc., Lot # 124-191; 0 and 6 mg/kg/day) from gestational day 6 through PND 21. Thus, pups were exposed to PCBs in utero and through weaning. Male rats (N = 5-6 per group) were sacrificed on PND 22 and PND 60. Brains were formalin-fixed for Rapid Golgi staining of tissue blocks; coded slides of hippocampus were prepared. For branching and spine analysis, 6 CA1 pyramids were randomly selected from each brain. Camera lucida drawings of the basilar dendritic tree were analyzed using the Sholl method of concentric circles. For spine analysis, counts were made along internal and terminal tip segments of 6-7 neurons from each brain. Results of the branching analysis for the PND 22 PCB-exposed rats showed that, compared to controls, there was significantly less dendritic branching in the outer 2/3rds of the dendritic tree (p = 0.002, Wilcoxon test). Spine analysis also showed a reduction in spines on the terminal tips segments of 22 day old PCB-exposed rats (p=0.005, T-test). These results suggest that perinatal exposure to Aroclor 1254 resulted in morphometric changes in hippocampus. By PND 60, spine density on terminal tip segments had returned to normal levels. However, branching analysis now showed that compared to controls there was an excessive amount of dendritic material in the distal 2/3rds of the tree (p=0.001, Wilcoxon test). This suggested a possible structural ?hyperplasticity? in neurons damaged by PCB exposure during the developmental period with a residual long-term dysmorphic impact on hippocampal circuitry. (This abstract does not necessarily reflect USEPA policy).