ASSESSMENT OF CEREBRAL HEMISPHERIC SYMMETRY IN HATCHLING CHICKENS EXPOSED IN OVO TO POLYCHLORINATED BIPHENYL CONGENERS

Previous investigators have reported that exposure to a mixture of env ironmental contaminants, including polychlorinated biphenyls, results in morphologic asymmetry of the cerebral hemispheres in hatchling grea t blue herons (Ardea herodias) and have suggested that this asymmetry may be a useful biomarker for contamination. This study was made to de termine whether exposure to PCB congeners 3,3',4,4'-tetrachlorobipheny l (IUPAC #77) and 3,3',4,4',5-pentachlorobiphenyl (IUPAC #126) causes similar asymmetry in hatchling domestic chickens (Gallus domesticus). Eggs were injected at day 0 of incubation with either a high dose, low dose, or combination of each congener. At hatching, the chicks were p erfused with 10% formalin-saline. The brains were removed, sectioned a nd stained with cresyl violet. Width and height measurements of each h emisphere were taken at eight locations, caudal to rostral, 400 mu m a part starting at the level of the anterior commissure (CA) and ending at the lobus paraolfactorius (LPO). The absolute differences between m easurements of the left and right sides were used to run a univariate split plot analysis of variance to determine if the amount of asymmetr y present was associated with specific congeners or doses. Significant differences in asymmetry were found between noninjected control group s and vehicle-injected control groups (p less than or equal to 0.05), but not between noninjected controls and treatment groups. A first deg ree orthogonal polynomial contrast analysis illustrated a linear trend with asymmetry increasing from the most caudal section at the CA to t he most rostral section at the LPO for both non-injected control and t reatment groups (p less than or equal to 0.05). These data indicate th at asymmetry may be normal in avian brains resulting from both intrins ic structural asymmetry and extrinsic molding forces acting on the hea d during development. Both of these factors should be taken into consi deration when assessing the usefulness of cerebral asymmetry as a biom arker.