Mutagenic and histopathological effects of hexavalent chromium in tadpoles of Lithobates catesbeianus (Shaw, 1802) (Anura, Ranidae).

The potential mutagenic and histopathological effects of the hexavalent chromium were investigated in Lithobates catesbeianus tadpoles. These larvae (GS 25-31) were exposed to three nominal concentrations of potassium dichromate (4, 12, and 36 mg L-1) and 5 mg L-1 of Cyclophosphamide as a positive control (PC), for 24 h. A negative control (NC) was also added to the experiment. Our results showed that, in general, the micronuclei (MN) were less frequent than the erythrocyte nuclear abnormalities (ENA); there was a significant difference in the frequency of MN between the NC and all treated groups (p < 0.05) in a concentration-dependent curve, in addition the PC did not differ from the chromium treatments. Also, only PC and the group treated with potassium dichromate at 36 mg L-1 showed significantly higher frequencies of ENA than NC (p < 0.05). Chromium treatments promoted cell retention in the Sub-G1 phase and a decrease of cells in the S and G2/M phases indicating inhibition of the cell cycle. All treatments with chromium led to liver and kidney histopathological lesions, especially with 36 mg L-1 (greater number of lesions). In conclusion, hexavalent chromium was mutagenic to L. catesbeianus tadpoles and its toxic effects also resulted in anti-mitotic activity, besides inducing histopathological alterations in liver and kidney. Amphibians have been proven to be useful bioindicators, and we suggest that tadpoles of different species can be used to represent the environmental impacts in aquatic ecosystems.

Natural modulation of redox status throughout the ontogeny of Amazon frog Physalaemus ephippifer (Anura, Leptodactylidae).

During their development, amphibians undergo various physiological processes that may affect their susceptibility to environmental pollutants. Naturally occurring fluctuations caused by developmental events are often overlooked in ecotoxicological studies. Our aim is to investigate how biomarkers of oxidative stress are modulated at different stages of larval development in the Amazonian amphibian species, Physalaemus ephippifer. The premetamorphosis, prometamorphosis and metamorphic climax stages were used to analyze total antioxidant capacity (ACAP), glutathione S-transferase (GST) activity, lipid peroxidation (LPO) levels and the expression of genes nrf2, gst, gsr (glutathione reductase) and gclc (glycine-cysteine ligase, catalytic subunit). Although there was no difference in ACAP and the genes expression among the studied stages, individuals from the premetamorphosis and prometamorphosis showed higher GST activity than ones under the climax. LPO levels were highest in individuals from the metamorphic climax. The present study suggests that the oxidative status changes during ontogeny of P. ephippifer tadpoles, especially during the metamorphic climax, the most demanding developmental phase. Variations in the redox balance at different developmental stages may lead to a divergent response to pollution. Therefore, we recommend that studies using anuran larvae as biomonitors consider possible physiological differences during ontogeny in their respective analyses.

Ontogenetic development of the oral apparatus and oropharyngeal cavity in bullfrog tadpoles (Lithobates catesbeianus, Shaw 1802).

OBJECTIVE: The present study aimed to describe the morphology of oral apparatus and oral cavity of bullfrog tadpoles during their development and metamorphosis. DESIGN: The oral apparatus and oropharyngeal cavity of tadpoles from hatching up to metamorphosis stage was dissected for further analysis. These structures were fixed in Karnovsky solution, afterwards in osmium tetroxide and metalized in palladium gold and electron-micrographed using the scanning electron microscope. RESULTS: The development of oral apparatus started with the formation and keratinization of the jaw sheaths and labial teeth followed by the formation of marginal and sub-marginal papillae. Degeneration of oral apparatus and formation of mouth was observed during metamorphosis. From stage-42 (metamorphic climax) to stage-43, the jaw sheath and labial tooth rows were disappeared progressively while the size and number of labial papillae were decreased. At stage-44, mouth formation started with the development of anterior and posterior labium though the labial papillae were still present. At stage-45 and 46, mouth was already formed, being very similar to the adult and characterized by the progressive increase in size. CONCLUSION: The sequence of events that happen during the development of oral apparatus of Lithobates catesbeianus Shaw, 1802 tadpoles follows the same pattern as occur in other anuran species but metamorphic atrophy of the oral apparatus follows the sequence of morphogenesis.

Histologia do rim, fígado e intestino de girinos de rã-touro (Rana catesbeiana) alimentados com dietas contendo própolis / Histology of kidney, liver and intestine of bullfrog tadpoles (Rana catesbeiana) fed with diets containing propolis

Este trabalho teve como objetivo verificar a ocorrência de possíveis alterações no fígado, rim e intestino de girinos de rã-touro no estágio 42, alimentados com dietas contendo diferentes concentrações (0,0; 0,2; 0,5; 1,0; e 1,5 por cento) de extrato hidroalcoólico de própolis. O experimento foi conduzido no laboratório de Nutrição de Organismos Aquáticos do Centro de Aqüicultura da UNESP, onde foram utilizados 1.400 girinos no estágio 26, distribuídos em vinte tanques experimentais. No final do experimento (60 dias), foram sacrificados três girinos de cada repetição e retiradas amostras de rim, fígado e intestino para processamento de lâminas histológicas no Laboratório de Histologia do Departamento de Morfologia e Fisiologia Animal da FCAV - UNESP. As amostras foram fixadas, desidratadas, coradas com HE, analisadas, fotomicrografadas e medida a espessura do epitélio intestinal. Não foram observadas alterações histológicas no intestino, rins e fígado dos girinos. A espessura do epitélio do intestino dos mesmos não foi influenciada (P>0,05) pelas concentrações de própolis.

This research was aimed at verifying the occurrence of possible alterations in liver, kidney and intestine of bullfrog tadpoles in stage 42 fed with diets containing different concentrations (0.0; 0.2; 0.5; 1.0 and 1.5 percent) of propolis hydroalcoholic extract. The experiment was carried out in laboratory of Aquatic Organisms Nutrition from Aquaculture Center of UNESP, where 1,400 tadpoles in stage 26 were used and distributed in twenty experimental aquariums. In the end of experiment (60 days) three tadpoles from each repetition were sacrificed and kidney, liver and intestine samples were collected to processing of histological slices in Histology´s Laboratory pertaining to Department of Morphology and Physiology from FCAV - UNESP. Samples were fixed, dehydrated, stained in HE, analysed, photomicrographed and thickness of intestinal epithelium was measured. Histological disturbances in tadpoles´s intestine, kidneys and liver were not observed. Thickness of intestinal epithelium from the same ones was not influenced (P>0.05) by propolis concentrations.