Oxidative Stress Parameters in Goitrogen-Exposed Crested Newt Larvae (Triturus spp.): Arrested Metamorphosis

Does the anesthetic tricaine methanesulfonate (MS-222) distort oxidative status parameters in tadpoles?

The effect of anesthesia/euthanasia with ethyl 3-aminobenzoate methanesulfonate (MS-222) on the oxidative status of Hyla arborea tadpoles was examined to determine whether the use of the anesthetic can confound the experimental results of the oxidative stress-based investigation. The experiment was conducted on two groups of tadpoles reared at different temperatures to produce differences in antioxidant capacity between the groups. After development at different temperatures (20 °C and 25 °C), the animals were exposed to different concentrations of MS-222 (0, 0.1, 1, and 5 g/L) for 15 min. The higher temperature decreased catalase activity, glutathione and protein carbonyl levels and increased glutathione reductase activity. The glutathione level and glutathione/thiol-related parameters were significantly changed after MS-222 exposure. However, individuals from the different temperature groups responded differently to the tested anesthetic, pointing to the possible influence of the initial levels of antioxidant capacity. The analysis of the interaction between the factors (temperature and MS-222) confirmed that the anesthetic can confound the results regarding the effects of temperature on the oxidative status parameters. The concentration of 0.1 g/L MS-222 had the lowest influence on the alterations in oxidative status and the results of the effect of temperature. A brief review of the current literature on the use of MS-222 in tadpoles made clear the absence of precise information on anesthetic concentration and exposure time. Similar studies should be repeated and extended to other amphibian species and other factors of interest to provide better guidance on tadpole anesthesia/euthanasia for future experiments that consider oxidative status parameters.

Changes in thyroid histomorphology and thyroglobulin immunostaining upon exposure to thiourea in Triturus newts

Amphibians are useful bioindicators for monitoring aquatic health and the influence of xenobiotics such as endocrine disrupting chemicals. Because aquatic ecosystems experience the majority of global pollution, aquatic organisms are most exposed and vulnerable to endocrine disruptors. Furthermore, penetration of endocrine disruptors into aquatic organisms especially in amphibians is even easier because of more permeable skin, resulting in high bioavailability and bioaccumulation of chemicals. One of the most potent endocrine disruptors is thiourea, which chemically blocks the synthesis of thyroid hormones and prevents metamorphosis in amphibians. We investigated the influence of thiourea on histomorphology of the thyroid gland in Triturus newts at the metamorphic stage, when thyroid hormone concentrations should reach their maximum level. Chronic exposure to thiourea induced hypertrophy and hyperplasia of follicular cells as well as a significant reduction of interstitial tissue. The intensity of the thyroglobulin immunostaining signal significantly decreases upon chronic exposure to thiourea. Successful cross-reactivity of human primary antibody in immunochemical detection of thyroglobulin in Urodela confirms potential homology in thyroglobulin structure throughout the vertebrates.

Carry-Over Effects of Desiccation Stress on the Oxidative Status of Fasting Anuran Juveniles

Amphibians are sensitive to deteriorating environmental conditions, especially during transition to a terrestrial environment which is full of uncertainties. Harsh conditions, such as desiccation during earlier stages, affect different larval traits with possible carry-over effects on juvenile and adult life histories. The first consequences of the effects can be seen in juveniles in the challenges to find food and the ability to survive without it in a terrestrial habitat. Body size and the internal energy reserves acquired during the larval phase play an important role in this period. Herein, we tested how different water regimes (low water availability, desiccation and constant high-water availability) during larval development reflect on the oxidative status and ability of yellow belly toad (Bombina variegata) juveniles to endure short-term fasting. The desiccation regime significantly reduced the body size of metamorphs. The same was observed after 2 weeks of fasting, while the feeding treatment reduced differences mostly in the body mass of individuals from different water regimes. This was the result of a greater gain in mass in juveniles pre-exposed to desiccation. Pre-exposure to desiccation also modified the parameters of the antioxidant system (AOS) under feeding conditions, leading to higher values of superoxide dismutase, glutathione reductase and glutathione S-transferase, glutathione and sulfhydryl group concentrations, and lower glutathione peroxidase in comparison to juveniles reared under constant water. The increase in the AOS of juveniles can be considered as a physiological carry-over effect of desiccation, probably as the result of compensatory growth and/or earlier exposure to chronic stress. However, water levels during larval development did not exert significant effects on the oxidative status of juveniles subjected to food unavailability. Fasting juveniles, both control and desiccated, were exposed to oxidative stress, significantly higher lipid peroxide concentrations, lower superoxide dismutase, glutathione peroxidase, glutathione S-transferase, glutathione and sulfhydryl group values in comparison to feeding individuals. The lack of food in juvenile anurans activated the AOS response in the same manner, regardless of body size and stress pre-exposure, suggesting that the generally accepted hypothesis about the influence of metamorphic body size on the fitness of the postmetamorphic stage should be tested further.