Polychlorinated biphenyls are selectively neurotoxic in the developing Spisula solidissima embryo

Polychlorinated biphenyls (PCBs) are ubiquitous environmental pollutants th at accumulate to toxic levels in the food chain. Using Spisula solidissima ( surf clam) embryos as a developmental model, it was shown that Aroclor 12 54 specifically targets two neuronal structures during embryonic developmen t. Embryos were exposed to 1, 10, or 100 ppm Aroclor 1254 or an acetone veh icle control posthatching for 24, 48, and 72 h. Embryos labeled with a sero tonin antibody or a neural antigen antibody and a rhodamine-conjugated seco ndary antibody were viewed by confocal microscopy. The cerebropleural gangl ion showed a decrease both in serotonin production and in the size of the s erotonin-synthesizing region upon exposure to 10 and 100 ppm Aroclor 1254. These decreases were detectable as early as 48 h postfertilization. When ex posed to 100 ppm Aroclor 1254, the primitive neural plexus, which coordinat es the movements of the mouth and velum, showed a delay in onset and cessat ion of expression of a molluscan-specific neural antigen. Exposure to Arocl or 1254 did not affect the overall growth and morphology of the embryos. In addition, analyses of total protein profiles and heat-shock protein 70 lev els showed that exposure to Aroclor 1254 did not trigger protein degradatio n or cause a stress or shock response. These results show that exposure of Spisula embryos to Aroclor 1254 specifically targets neurogenesis while hav ing no effect on the overall growth of the embryo.