The Recessus Olfactorius: A Cryptic Olfactory Organ of Anuran Amphibians
The recessus olfactorius is a presumably olfactory structure found on the rostral floor of the main nasal cavity of many anuran amphibians. Nevertheless, it has rarely been investigated or even recognized in the past. The aim of the present study was to broaden the knowledge regarding this enigmatic sensory organ. Therefore, we examined the nasal epithelia of the cane toad Bufo marinus and the fire-bellied toad Bombina orientalis, using histology, scanning electron microscopy and lectin histochemistry.
Histologically, the recessus olfactorius largely resembles a typical pseudostratified olfactory epithelium. However, we found significant differences when comparing the recessus olfactorius with the main olfactory organ and the vomeronasal organ. The surface differentiations of the recessus olfactorius can be assigned to four different cell types: sensory cells covered with either cilia located on protruding knobs or with long microvilli, and supporting cells bearing either short microvilli or cilia without any surface elevation. Additionally, the lectin binding patterns indicate the presence of a unique mucous constitution of the recessus olfactorius.
Taken together our results strongly support the idea, that the recessus olfactorius has a discrete olfactory function. Furthermore, a possible homology between the recessus olfactorius and the middle chamber epithelium of clawed frogs like Xenopus laevis is discussed.
KeywordsSupporting Cell Olfactory Epithelium Sensory Epithelium Cane Toad Olfactory Receptor Neuron
The authors would like to sincerely thank Harald Rühling, Julia Schulze, and Andreas Arendt for their very helpful technical support. Parts of this research were supported by the Zentrale Forschungsförderung (ZFF) of the University of Kassel (grant number 1415, P/249).
- Paterson NF (1951) The nasal cavities of the toad Hemipipa carvalhoi Mir.-Rib. and other Pipidae. Proc Zool Soc Lond 121:381–415Google Scholar
- Reiss JO, Eisthen HL (2008) Chemical senses: comparative anatomy and physiology of chemical senses in amphibians. In: Thewissen JGM, Nummela S (eds) Sensory evolution on the threshold: adaptions in secondarily aquatic vertebrates. University of California Press, California, pp 43–63Google Scholar
- Slabbert GK (1945) Contributions to the cranial morphology of the European anuran Bombina variegata (Linné). Ann Univ Stell 23:67–89Google Scholar
- Trotier T, Døving KB, Rosin JF (1994) Functional properties of frog vomeronasal receptor cells. In: Kurihana K, Suzuki N, Ogawa H (eds) Olfaction and taste XI, Springer. Tokyo, Japan, pp 188–191Google Scholar