Assessing the potential neurotoxic effects of soluble factors produced by <i>Batrachochytrium dendrobatidis</i> on locomotor function in <i>Xenopus laevis</i>.csv

Chytridiomycosis, an infectious disease caused by the skin fungus, Batrachochytrium dendrobatidis (Bd), is recognized as a major contributor to declining amphibian populations since it was first described and identified about thirty years ago. The fungus disrupts the ion exchange within the frog epithelium leading to decreased locomotor performance, righting reflexes, and reduced body mass. However, the physiological mechanisms directly impacting performance are unknown. Given the negative effects on locomotor function and movement in infected individuals, it has been suggested that the fungus produces a neurotoxin during development. The objective of this study was to investigate the presence of a possible neurotoxin secreted by Bd to better understand the relationship between infected amphibians and locomotor performance. Frogs, Xenopus laevis, were injected with Bd supernatant at a high- or low-dose concentration or a saline control. After four hours, frogs were filmed with high-speed cameras performing a swimming escape response. Swimming performance for each frog was measured again at twenty-four hours and 1 week post injection. We found that the swimming velocity was initially lower four hours post injection with improvement twenty-four hours and one week post injection. However, lower values were also exhibited in frogs injected with saline. It is likely that the lower performance four hours post injection is due to a stress response and not the neurotoxic secretions present in the fungal supernatant. Given that the injection mimics high fungal burden and was standardized by mass, it is likely that there was no production of a neurotoxin, or the concentrations tested were not sufficient to alter neural functions. Future studies should continue to explore the potential neurotoxicity of the fungal products under other experimental conditions.