ABSTRACT
Complete small subunit ribosomal RNA, internal transcribed spacer 1 and 2, 5.8S, and partial large subunit ribosomal RNA gene sequences were generated from multiple isolates of Pfiesteria piscicida. Sequences were derived from isolates that have been shown to be ichthyotoxic as well as isolates that have no history of toxic behavior. All of the sequences generated were identical for the different cultures, and we therefore conclude that differences in toxicity seen between isolates of P. piscicida are linked to factors other than genetic strain variation detectable by ribosomal gene sequence analyses.
Subject(s)
DNA, Protozoan/genetics , Fish Diseases/parasitology , Pfiesteria piscicida/pathogenicity , Protozoan Infections, Animal/parasitology , RNA, Ribosomal/genetics , Animals , Base Sequence , DNA, Protozoan/chemistry , DNA, Ribosomal Spacer/chemistry , DNA, Ribosomal Spacer/genetics , Molecular Sequence Data , Pfiesteria piscicida/genetics , Pfiesteria piscicida/parasitology , Phenotype , Protozoan Infections, Animal/classification , RNA, Ribosomal/chemistry , Sequence AlignmentABSTRACT
Pfiesteria piscicida, an estuarine dinoflagellate, which has been shown to kill fish, has also been associated with neurocognitive deficits in humans. With a rat model, we have demonstrated the cause-and-effect relationship between Pfiesteria exposure and learning impairment. In several studies, we have replicated the finding in Sprague-Dawley rats that exposure to fixed acute doses of Pfiesteria cells or filtrates caused radial-arm maze learning impairment. Recently, this finding of Pfiesteria-induced learning impairment in rats has been independently replicated in another laboratory as well. We have demonstrated significant Pfiesteria-induced learning impairment in both the win-shift and repeated-acquisition tasks in the radial-arm maze and in reversal learning in a visual operant signal detection task. These learning impairments have been seen as long as 10 weeks after a single acute exposure to Pfiesteria. In the current study, we used a hydrophilic toxin isolated from clonal P. piscicida cultures (PfTx) and tested its effect when applied locally to the ventral hippocampus on repeated acquisition of rats in the radial-arm maze. Toxin exposure impaired choice accuracy in the radial-arm maze repeated acquisition procedure. The PfTx-induced impairment was seen at the beginning of the session and the early learning deficit was persistent across 6 weeks of testing after a single administration of the toxin. Eventually, with enough practice, in each session, the PfTx-exposed rats did learn that session's problem as did control rats. This model has demonstrated the cause-and-effect relationship between exposure to a hydrophilic toxin produced by P. piscicida and learning impairment, and specifically that the ventral hippocampus was critically involved.
Subject(s)
Hippocampus/microbiology , Learning Disabilities/etiology , Neurotoxins/toxicity , Pfiesteria piscicida/metabolism , Protozoan Infections, Animal/physiopathology , Animals , Behavior, Animal/drug effects , Female , Hippocampus/drug effects , Maze Learning/drug effects , Rats , Rats, Sprague-Dawley , Reaction Time , Time FactorsABSTRACT
Several dinoflagellate strains of the genus Pfiesteria were isolated by culturing techniques from sediment samples taken in the Oslofjord region of Norway. Pfiesteria piscicida, well known as a fish killer from the Atlantic coast of America, was identified by genetic methods and light microscopy. The related species Pfiesteria shumwayae was attracted from the sediment by the presence of fish, and has proved toxic. This present survey demonstrates the wide distribution of these potentially harmful species, but so far they have not been connected with fish kills in Europe.
