ABSTRACT. The olfactory organ of African lungfish, Protopterus annectens, contains two distinct sensory epithelia: the lamellar olfactory epithelium and the recess epithelium. These epithelia correspond to the olfactory epithelium and the vomeronasal organ of tetrapods, respectively. In contrast to the lamellar olfactory epithelium, which has no associated gland, the recess epithelium is equipped with associated glands. Although the glandular cells and/or the supporting cells are generally presumed to secrete proteins involved in the function of olfactory sensory epithelia, the properties of these proteins in lungfish have not been evaluated to date. In this study, we investigated the associated glands in the olfactory organ of lungfish by transmission electron microscopy and found that the glandular cells contain numerous secretory granules and secrete them from the apical membrane. In addition, we analyzed the olfactory organ by lectin histochemistry using 16 biotinylated lectins. All lectins labeled the secretory granules in the glandular cells with different staining patterns from those of the supporting cells in the lamellar olfactory epithelium or in the recess epithelium. Furthermore, lectin blotting analysis showed that multiple bands were detected by the lectins which specifically labeled the glandular epithelium of the olfactory organ. These results indicate that the secretory products of the associated glands in the recess epithelium have different properties from those of the supporting cells in the olfactory sensory epithelia and contain multiple glycoproteins with different carbohydrate moieties. KEY WORDS: electron microscopy, fish, glycoprotein, vomeronasal organ.doi: 10.1292/jvms.12-0547; J. Vet. Med. Sci. 75 (7): [887][888][889][890][891][892][893] 2013 Many vertebrates have two distinct olfactory organs, the olfactory epithelium (OE) and the vomeronasal organ (VNO) for detecting chemical substances in the environment. Unlike the OE found in all vertebrates, it has been suggested that the VNO is not present in fish, but is present only in terrestrial vertebrates [4]. However, the lungfish, phylogenetically the closest fish to tetrapods, have epithelial crypts that express VNO markers of tetrapods [10]. Recently, we have examined the olfactory organ of African lungfish, Protopterus annectens, and revealed the histological and ultrastructural characteristics of the lamellar OE and the recess epithelium, corresponding to the OE of ordinary fish and the VNO of tetrapods, respectively [19]. These two sensory epithelia are separately distributed in the olfactory organ of lungfish: the lamellar OE is located on the surface of olfactory lamellae and the recess epithelium in recesses at the base of lamellae [19].In all vertebrates, olfactory receptors detect chemical substances dissolved in the mucous fluid covering the sensory epithelium [8,20]. The OE and the VNO of terrestrial vertebrates are equipped with the associated glands: the Bowman's glands in the OE and the Jacobson's glands in the VNO [3...