Investigating the potential neurotoxic effects of cell-free factors by <i>Batrachochytrium dendrobatidis</i> on locomotion in <i>Xenopus laevis</i>

Chytridiomycosis is a contributor to amphibian population declines. Diseased amphibians show symptoms of lethargy and loss of righting reflexes, likely due to an ion imbalance across the skin. However, it is possible developing zoosporangia release toxins that affect neuromuscular activity. Using Xenopus laevis as a model, we hypothesized that locomotor performance would be affected by injection of Bd supernatant factors. X. laevis were injected and then filmed performing a swimming escape response with high-speed cameras at 4 h, 24 h, and 1-week post-injection. Average maximum swimming velocity and escape latency were digitized using high-speed video. Despite no difference in escape velocity, there was a significant difference in escape latency 24 h post injection at both concentrations tested, 106 and 107 cell equivalents, though only differences at 106 cell equivalents/ml supernatant persisted 1 week post injection. Changes in specific locomotor function suggest that there may be neurotoxins present, though the potential neurotoxins may exhibit neural circuit specificity across escape behavior. This study provides a method to test more purified extracts to determine whether Bd produces neurotoxic factors that could enter the blood stream and alter locomotion during a natural skin infection.