Pfiesteria toxin and learning performance

Pfiesteria piscicida is an estuarine dinoflagellate involved with fish kill s along the east coast of the United States. We previously documented a rad ial-arm maze learning deficit in rats exposed to Pfiesteria that may be rel ated to cognitive deficits seen in humans after accidental Pfiesteria expos ure. The current study elucidated important behavioral parameters of this d eficit. There were six dose groups. Forty (10/group) adult female Sprague-D awley rats were injected (SC) with a single dose of Pfiesteria taken from a quarium-cultured Pfiesteria (35,600, 106,800, or 320,400 Pfiesteria cells/k g of rat body weight or a cell-free filtrate of the 106,800 cells/kg dose). One control group (N = 10) was injected with saline and one (N = 10) with aquarium water not containing Pfiesteria. Half of the rats in each group we re tested on an 8-arm radial maze in a standard test room, and the other ha lf were tested on the radial maze in a sound-attenuating chamber. In the st andard maze room, there was a significant effect of Pfiesteria (p < 0.05) i mpairing choice accuracy improvement over the first six sessions of trainin g among rats administered 106,800, 320,400, and the 106,800 cells/kg filter ed sample. In contrast, there was no indication of an effect of Pfiesteria when the rats were tested-on the same configuration radial maze in the soun d-attenuating chamber. After 18 sessions of training in one room, the rats were switched for six sessions of testing in the other room and finally wer e switched back to their original room for three sessions. There was a sign ificant Pfiesteria-induced deficit when the rats were tested in the standar d test room but not when they were tested in the sound-attenuating chamber. When the Pfiesteria-exposed rats were initially switched from the sound-at tenuating chamber to the standard test room they performed significantly wo rse than controls, whereas Pfiesteria-treated rats switched from the standa rd test room to the sound-attenuating chamber did not perform differently f rom controls. These results suggest that the Pfiesteria-induced learning im pairment may result from the negative impact of distracting stimuli. At the time of the learning impairment, no overt Pfiesteria-related effects were seen using a functional observational battery and no overall response laten cy effects were seen, indicating that the Pfiesteria-induced choice accurac y deficit was not due to generalized debilitation. In the initial use of th e figure-8 maze in this line of research, the rats in the same Pfiesteria t reatment groups that showed significant deficits in the radial-arm maze sho wed greater declines in activity rates in a 1-h figure-8 locomotor activity test. Both the 106,800 and 320,400 Pfiesteria cells/kg groups showed signi ficantly greater linear trends of activity decline relative to tank water-t reated controls. This reflected an initial slight hyperactivity in the Pfie steria-treated animals followed by a decrease to control levels, Pfiesteria effects in the figure-8 maze and in early radial-arm maze training may be useful in a rapid screen for identifying the critical toxin(s) of Pfiesteri a in future studies. Published by Elsevier Science Inc.