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Lack of postexposure analgesic efficacy of low concentrations of eugenol in zebrafish
Bernardo Baldisserotto1, Thaylise V Parodi1, E Don Stevens2
1Departamento de Fisiologia e Farmacologia, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.
Objective:
To test the postexposure analgesic efficacy of low doses of eugenol in zebrafish.
Study Design:
Prospective experimental study.
Animals:
A total of 76 large adult zebrafish (Danio rerio).
Methods:
Fish swimming behavior (median velocity, freeze time, high-speed swimming and distance moved in the vertical direction) was recorded in a 1.6 L video arena before and after exposure to eugenol (0, 1, 2, 5, 10 and 20 mg L-1). In a second experiment, fish were anesthetized with 2-phenoxy-ethanol and treated with an injection of 5% acetic acid (noxious stimulus), and then exposed to 0, 1, 2 and 5 mg L-1 eugenol. The fish swimming behavior was also recorded.
Results:
The higher doses (10 and 20 mg L-1) reduced the median velocity, high-speed swimming and distance moved in the vertical direction, and increased the freeze time. Zebrafish behavior was not altered by eugenol (1, 2 and 5 mg L-1) after noxious stimulation.
Conclusions And Clinical Relevance:
The change in the behavior of zebrafish associated with a noxious stimulus can be monitored and is a good model for studying analgesia in fish. Eugenol (10 and 20 mg L-1) induced zebrafish sedation. The response after a noxious stimulus was not affected by postexposure to lower doses, and thus we cannot recommend its use as an analgesic.
