Immunohistochemical, morphological and histometrical analyses of follicular development in Astyanax bimaculatus (Teleostei: Characidae) exposed to an organochlorine insecticide

Abstract

Thiodan® is an organochlorine insecticide used in agriculture that can reach aquatic ecosystems where it can affect fish reproduction. This research aimed to evaluate follicular development and the expression of integrin β1, collagen type IV and caspase 3 by morphological, histometrical and immunohistochemical analyses of Astyanax bimaculatus exposed to Thiodan®. Treatments included three sublethal concentrations of Thiodan® (1.15, 2.30, and 5.60 μg L−1) for 96 h and a control without the insecticide. Mature females with ovaries in advanced follicular development were chosen for study (average weight: 11.52 ± 2.0 g; average total length: 9.12 ± 0.64 cm). The follicles of A. bimaculatus exhibited normal morphology, while the diameters of secondary follicles showed an increase (P< 0.05) in all concentrations when compared to the control group; a characteristic of follicles undergoing the initial stages of intoxication. Immunohistochemical analysis revealed secondary follicles with greater expression of integrin β1 and collagen type IV in cytoplasm of follicular cells than in the primary follicles in all treatments and in the control. Immunolocalization of caspase 3 was detected in follicular cells during secondary development in all tested concentrations of Thiodan® and the control. These analyses demonstrate positive immunolocalization throughout the course of follicular development, even in fish exposed to varying concentrations of Thiodan® for 96 h, demonstrating that follicular cells retain their physiological integrity.