Persisting learning deficits in rats after exposure to Pfiesteria piscicida

Pfiesteria piscicida and other toxic Pfiesteria-like dinoflagellates have been implicated as a cause of fish kill in North Carolina estuaries and elsewhere. Accidental exposure of humans to P. piscicida has been reported to cause a complex syndrome including cognitive impairment. The current project was conducted to experimental assess the possibility of cognitive effects of P. piscicida exposure in rats. Samples of water from Aquaria in which P. piscicida zoospores were killing fish frozen, a procedure that has been found to induce encystment. Thawed samples were injected into albino Sprague-Dawley rats. A significant learning impairment was documented in rats administered samples P. piscicida that were recently frozen. Prolonged storage of Pfiesteria samples diminished the effect. No effect was seen in the recall of a previously learned task, but when the rats were called upon to learn a new task, the Pfiesteria-treated animals showed a significant learning deficit. This effect persisted up to at least 10 weeks after a single injection of Pfiesteria. The Pfiesteria-induced learning deficit did not seem 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 standard 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 dinoflagellate 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.