Methylmercury (MeHg) is an environmental pollutant known to induce neurotoxicity in several animal species, including humans. However, studies focusing the effects of MeHg poisoning in chicks were based on phenomenological approaches and did not delve into the molecular mechanisms. The purpose of this study was to evaluate the postnatal consequences of the in ovo exposure to MeHg on behavioral, morphological and biochemical parameters in chicks. At the fifth embryonic day (E5), Gallus domesticus eggs were submitted to a single injection of 0.1 microg MeHg/0.05 ml saline. After treatment, the eggs returned to the incubator until hatching (E21). From first to fifth postnatal days (PN 1-PN 5), the MeHg-treated chicks showed lower frequency of exploratory movements and a significantly higher frequency of wing and anomalous movements. Cerebellar glutathione (GSH) levels and the activities of the GSH-related enzymes GSH reductase and GSH peroxidase were significantly higher (70, 72, and 80%, respectively) in MeHg exposed chicks in comparison to controls. Mercury impregnation was densest in the granular layer, followed by the Purkinje and molecular layers of treated chicks. A significant reduction of the number of Purkinje cells, as well as a greater distance between these cells were observed in chicks of MeHg group. Our results disclose that the prehatching exposure to MeHg induced motor impairments, which were correlated to histological damage and alterations on the cerebellar GSH system's development from PN 1 to PN 5.
Lead intoxication affects the central nervous system and produces structural disorders and behavioral deficits in several animal species. Although lead neurotoxicity is a well-reported phenomenon, studies on the developmental neurotoxicity induced by this metal in avian are scarce. The aim of this study was to evaluate how a single dose of 28 mug lead acetate administered into the yolk sac on the fifth incubation day of Gallus domesticus can affect the behavior and the brain tissue in the first postnatal week. Several behavioral tests, mainly those related to the motor and exploratory functions were evaluated at fifth and sixth postnatal days (PN). The lead deposition into mesencephalon and cerebellum was investigated by autometallography (AMG) method. Congenital anomalies, as failure on closure of body's ventral midline and leg dysfunction, were observed in treated chicks. During the first postnatal week, inactivity and anomalous movements were significantly high in lead treated chicks in comparison to control animals. Lead impregnation was observed in both mesencephalon and cerebellum and the cerebellar molecular layer presented higher lead deposition in comparison to granular layer and Purkinje cells. Our results indicate that the in ovo exposure to lead induces important deficits on motor behavior of chicks during the first postnatal week and such phenomena are related to lead deposition in the cerebellar tissue during embryonic development. The proposed exposure schedule represents an interesting experimental approach for studding behavioral and cellular mechanisms related to lead-induced developmental neurotoxicity.
A contaminação causada pelo chumbo tem sua origem principalmente nas emissões atmosféricas, sendo o ar considerado uma das principais vias de transporte e distribuição deste metal pesado no ambiente. A toxicidade do chumbo em embriões e indivíduos jovens é bastante expressiva, podendo comprometer o padrão estrutural e funcional das espécies. Estudos têm demonstrado que em embriões de galinha somente uma exposição ao chumbo, dependendo da dose ingerida, pode resultar em malformações de face e membros, hidrocefalia e redução da taxa de eclosão. O objetivo deste trabalho foi analisar embriões de Gallus domesticus expostos ao acetato de chumbo para verificar o comprometimento do padrão embrionário, bem como a ação teratogênica deste metal. Foram realizados estudos no Laboratório de Reprodução e Desenvolvimento Animal/UFSC, onde 143 embriões de Gallus domesticus foram expostos ao acetato de chumbo nas seguintes doses: 150 !g, 250 !g, 350 !g e 450 !g. O grupo controle (n = 47) recebeu 0,1 ml de solução salina nos mesmos dias. Os embriões foram tratados no 3º ou no 5º dia e monitorados durante 6 dias, quando foi avaliada a integridade das estruturas embrionárias. Do total de indivíduos tratados com acetato de chumbo, 27 apresentaram o padrão normal, 34 morreram e 82 apresentaram alteração no padrão de desenvolvimento (retardo de desenvolvimento (3), malformações (14), alterações hemorrágicas (65)). Nossos estudos mostram que nas doses utilizadas o acetato de chumbo modifica o processo de morfogênese, causando alterações morfológicas características, assim, deve haver controle de seu uso e liberação no ambiente.
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