A rapid and reliable behavioral test for the analysis of olfactory function in tadpoles. Our experience with an olfactoy epithelium-specific xenobiotic agent

YOVANOVICH, C.; HEER, T.; JUNGBLUT, L.; POZZI, AG; PAZ, D.A.

Manaos, Brasil

Congreso; 6th World Congress of Herpetology; 2008

Society for the Study of Amphibians and Reptiles

Amphibian larvae represent an excellent experimental model to study the extraordinary ability of the olfactory epithelium to regenerate its neuronal population continuously throughout life, in both physiological and pathological conditions. We have developed an experimental design in which we were able to demonstrate that immersion of Rhinella arenarum larvae in zinc sulphate (ZnSO4) in sublethal concentrations provokes a massive degeneration of the olfactory tissue. The data we obtained also indicates that the normal architecture of the olfactory epithelium is restored by the third day after ZnSO4 treatment. However, the functionality of this recovered epithelium remained to be analyzed. We decided to study this topic at its most complex level of expression, namely, the behavioral level. Thus, in the present work we try to design and perform a simple and reliable method to test larvae behavior that may help to answer the crucial question: ‘Do the “recovered” tadpoles smell or not?’ The method we propose here consists in analyzing the responsiveness of larvae to an olfactory stimulus that indicates the presence of food. We tested different experimental settings to eliminate the influence of cues arising from visual and lateral line sensory systems. We also tested different experimental conditions, such as food deprivation before the test and number of individuals used for the test, in order to improve the sensitivity of the method. The test was performed in ZnSO4 treated animals right after the end of the immersion and at several times post-treatment, as well as in control animals. We observed that shortly after treatment there is no response to the olfactory stimulus, whereas since the second day and thereafter the responsiveness is restored and exhibits the same timing that the response registered for control animals. These results are in accordance with the previous histological observations and suggest that the sensorial ability of the olfactory epithelium recovered after injury is as efficacious as that achieved during the normal physiological turnover of the olfactory neurons. On the other hand, these observations argue in favor of both the utility of behavioral tests to assess the functionality of the olfactory system and the possibility of using them in “non traditional” species, such as amphibians.