A atividade secretória cutânea em pererecas: uma abordagem morfológica

Abstract

The skin in amphibians is an organ involved in several functions, such as breathing and chemical defense against predators and microorganisms. These functions are related to different skin components, such as cutaneous glands of two basic types, the mucous glands and the poison glands. Among anurans, in special in tree frogs, calls attention the fact that, in stressful situations, while some species can release large amounts of secretion, usually thick and sticky, others do not modify their secretory mode, making use of behavioral strategies to escape of danger. These differences, at first sight, may be related to greater or lesser capacity to control myoepithelial cells that involve the skin glands, isolated or together with other cutaneous morphological characteristics. This work aims at the morphological and morphometric study of the skin of different tree frogs capable of release abundant secretion, Trachycephalus mesophaeus and Corythomantis greeningi, in comparison with a little secretory tree frog, Itapotihyla langsdorffii. We tried to focus on the main characteristics of the cutaneous glands, mainly with regard to the myoepithelial cells, but we also analyzed other specific characteristics, such as the thickness of the calcified dermal layer and the number of pillar cells scattered in the dermis. Samples of dorsal skin of adults (n = 3) from T. mesophaeus, I. langsdorffii and C. greeningi obtained from animals previously fixed in buffered paraformaldehyde solution, were processed for histology in historesin. The sections (2 µm) were stained with toluidine blue-fuchsin. The images were analyzed in an Olympus BX51 light microscope, equipped with a digital camera and the Olympus Cellsens 1.17 software. The measurements were performed in triplicate and the media was calculated. A statistical analysis was performed using unidirectional ANOVA and the differences were significant when P ≤ 0.05. The results showed that in all analyzed species, in some cases, both the poison and the mucous glands, did not show differences in thickness, contrarily of what was expected. In relation to the other structural characteristics, called attention the number of pillar cells that were apparently more numerous in I. langsdorffii and in C. greeningi, fact that was not initially expected, in addition to the thicker calcified layer in T. mesophaeus and C. greeningi. Our results demonstrate that the cutaneous morphological structures do not seem to perform a predominant individual role in any of the analyzed species. All structures seem to participate of a more complex system of skin secretion release, together with other factors of phylogenetic, physiological and behavioral origin.