PERSISTING LEARNING-DEFICITS IN RATS AFTER EXPOSURE TO PFIESTERIA-PISCICIDA

Pfiesteria piscicida and other toxic Pfiesteria-like dinoflagellates h ave been implicated as a cause of fish kill in North Carolina estuarie s and elsewhere. Accidental exposure of humans to P. piscicida has bee n reported to cause a complex syndrome including cognitive impairment. The current project was conducted to experimental assess the possibil ity of cognitive effects of P. piscicida exposure in rats. Samples of water from Aquaria in which P. piscicida zoospores were killing fish f rozen, a procedure that has been found to induce encystment. Thawed sa mples were injected into albino Sprague-Dawley rats. A significant lea rning impairment was documented in rats administered samples P. piscic ida that were recently frozen. Prolonged storage of Pfiesteria samples diminished the effect. No effect was seen in the recall of a previous ly learned task, but when the rats were called upon to learn a new tas k, the Pfiesteria-treated animals showed a significant learning defici t. This effect persisted up to at least 10 weeks after a single inject ion of Pfiesteria. The Pfiesteria-induced learning deficit did not see m associated with any obvious debilitation or health impairment of the exposed rats. Deficits in habitation of arousal and rearing behavior were detected using a functional observational battery. No Pfiesteria- induced effects on blood count and white cell differential or in a sta ndard pathological screening of brain, liver, lung, kidney, and spleen tissue were seen at 2 months after exposure. These studies document a persistent learning impairment in rats after exposure to the dinoflag ellate P. piscicida in otherwise physically well-appearing rats. This effect may partially model the symptoms of cognitive impairments that humans have shown after Pfiesteria exposure.