Histological and immunohistochemical characterization of the integument and parotoids glands Rhinella bergi (Anura: Bufsonidae): Development and differentiation

Abstract

A detailed description of the tegument and parotoid glands of pre-metamorphic, post-metamorphic, juvenile and adult individuals of Rhinella bergi is presented to provide an exhaustive analysis of the integumentary characteristics of this species. Fragments of the tegument were fixed in Bouin solution and preserved in buffered Formol 10%. Subsequently, scanning electron microscopy (SEM) was performed to characterize the macroscopic structure of these regions. Microscopic observations were made from histological sections stained with Hematoxylin and Eosin, Alcian Blue (pH 2,5), PAS-H, Coomassie Blue, Oil Red, and Bielschowsky Impregnation. There were three types of protuberance: warts, tubers, and thorns. These structures became evident from post-metamorphic stages. The ventral surface shows elevations similar to flat warts; however, tubers and spines are absent. Histologically, each structure consists of a spongy dermis of lax connective tissue and dense and compact dermis, associated with granular glands and a keratinized epidermis. The latter, in the dorsal region, forms projections called thorns. The granular glands accumulate, and their alveoli increase in size progressively. This work provides a morphological and histological description of the integument and the parotoid glands during the larval and post-metamorphic stage of the genus Rhinella, with aspects described for the first time in the genus.