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

TL;DR

This study investigates if a fungus called Batrachochytrium dendrobatidis releases toxins that affect the movement of Xenopus laevis frogs.

Contribution

The study introduces a new behavioral assay to test for neurotoxic effects of Bd supernatant on amphibian locomotion.

Findings

Escape latency was significantly affected 24 hours after injection with Bd supernatant.

Changes in escape behavior suggest the presence of neurotoxins with neural circuit specificity.

Effects persisted one week post-injection at lower concentrations of Bd supernatant.

Abstract

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.

Summary: This study developed a behavioral assay to assess the effects of Bd supernatant as a source of potential neurotoxicity on locomotor performance using Xenopus laevis as a model system.

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