Odorous secretions in anurans: morphological and functional assessment of serous glands as a source of volatile compounds in the skin of the treefrog Hypsiboas pulchellus (Amphibia: Anura: Hylidae)

BRUNETTI, A.E.; HERMIDA, G.N.; IURMAN, M.; FAIVOVICH, J.

JOURNAL OF ANATOMY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016 vol. 228 p. 430 - 442

0021-8782

Serous (granular or venom) glands occur in the skin of almost all species of adult amphibians, and arethought to be the source of a great diversity of chemical compounds. Despite recent advances in theirchemistry, odorous volatile substances are compounds that have received less attention, and until now nostudy has attempted to associate histological data with the presence of these molecules in amphibians, or inany other vertebrate. Given the recent identification of 40 different volatile compounds from the skinsecretions of H. pulchellus (a treefrog species that releases a strong odour when handled), we examined thestructure, ultrastructure, histochemistry, and distribution of skin glands of this species. Histological analysisfrom six body regions reveals the presence of two types of glands that differ in their distribution. Mucousglands are homogeneously distributed, whereas serous glands are more numerous in the scapular region.Ultrastructural results indicate that electron-translucent vesicles observed within granules of serous glands aresimilar to those found in volatile-producing glands from insects and also with lipid vesicles from differentorganisms. Association among lipids and volatiles is also evidenced from chemical results, which indicate thatat least some of the volatile components in H. pulchellus probably originate within the metabolism of fattyacids or the mevalonate pathway. As odorous secretions are often considered to be secreted under stresssituations, the release of glandular content was assessed after pharmacological treatments, epinephrineadministrated in vivo and on skin explants, and through surface electrical stimulation. Serous glandsresponded to all treatments, generally through an obvious contraction of myoepithelial cells that surroundtheir secretory portion. No response was observed in mucous glands. Considering these morpho-functionalresults, along with previous identification of volatiles from H. pulchellus and H. riojanus after electricalstimulation, we suggest that the electron-translucent inclusions found within the granules of serous glandslikely are the store sites of volatile compounds and/or their precursors. Histochemical and glandulardistribution analyses in five other species of frogs of the hylid tribe Cophomantini, revealed a high lipidcontent in all the species, whereas a heterogeneous distribution of serous glands is only observed in speciesof the H. pulchellus group. The distribution pattern of serous glands in members of this species group, andthe odorous volatile secretions are probably related to defensive functions.