Estudo morfológico das glândulas anais de Crotalus durissus terrificus (Viperidae: Crotalinae)

Abstract

Snake anal glands consist of structures opening in the cloaca and secreting an odoriferous fluid. Studies about these glands are very scarce, but their function may be related with sexual behaviour, defence and/or aggregation. Unlike other viperids, such as jararacas, rattlesnakes voluntary release their extremely unpleasant anal gland content when they are disturbed, either by human handling, or by predators. Gland morphology as well as the characteristics of the fluid they produce remains unknown. We aim to study the anal glands in the rattlesnake Crotalus durissus terrificus, trying to elucidate their participation in behaviour and/or reproduction. Adult specimens of both sexes (n=10) were obtained from the animal reception of Butantan Institute. After the animals being euthanized, measured and weighted, the glands were dissected, measured and weighted, fixed in 4% paraformaldehyde in PBS for 24 hours or in Karnovsky fixative for 4 hours, and prepared by routine methods for histology and transmission electron microscopy (TEM). The glands are a pair of elongated sac-like structures symmetrically arranged in the post-cloacal region. Striated muscle covers the whole glandular body. Ducts surrounded by sphincters open laterally in the cloacal aperture, where the secretion is released in the form of jets. Measurements show similarity in length and mass of the glands in both sexes. Histology shows that the glands are formed by a thin holocrine secretory epithelium that surrounds a wide lumen. Histochemical results indicate intense production of lipids. The glandular epithelium is enveloped by connective tissue within which another layer of cells with a strongly positive reaction for lipids is observed. The analysis by TEM shows the process of differentiating of the secretory epithelium: as the epithelial cells approach the glandular lumen, they assume a flattened shape at the same time they acquire a large number of secretory granules. The cytoplasm ultrastructure shows predominance of polyribosomes, smooth endoplasmic reticulum and mitochondria. The morphology and histochemistry of the anal glands in C. durissus points to an intense production of lipids, both in the epithelial secretory cells and in the secretory cells immerse in the surrounding connective tissue. The relationship of the surrounding cells with the glandular secretory epithelium has not yet been determined but may 9 indicate participation of a different type of secretion acting together or parallel to the anal gland content. The similar size of the anal glands in both sexes is more indicative of participation of these structures in defence instead of reproduction. In any case, the nature of the secretion and its strong odour suggest participation in intra- or inter- specific chemical communication, since lipid substances are generally present in pheromones. Further biochemical studies may help to clarify anal glands specific function.