Lectin histochemical studies on the olfactory epithelium and vomeronasal organ in the Japanese striped snake, Elaphe quadrivirgata

Histological features and Gαolf expression patterns in the nasal cavity of sea turtles

Sea turtles use olfaction to detect volatile and water-soluble substances. The nasal cavity of green turtles (Chelonia mydas) comprises morphologically defined the anterodorsal, anteroventral, and posterodorsal diverticula, as well as a single posteroventral fossa. Here, we detailed the histological features of the nasal cavity of a mature female green turtle. The posterodorsal diverticulum contained spongy-like venous sinuses and a wave-shaped sensory epithelium that favored ventilation. Secretory structures that were significant in sensory and non-sensory epithelia were probably involved in protection against seawater. These findings suggested that green turtles efficiently intake airborne substances and dissolve water-soluble substances in mucous, while suppressing the effects of salts. In addition, positive staining of Gαs/olf that couples with olfactory, but not vomeronasal, receptors was predominant in all three types of sensory epithelium in the nasal cavity. Both of airborne and water-soluble odorants seemed to be detected in cells expressing Gαolf and olfactory receptors.

Nasal Cavity of Green Sea Turtles Contains 3 Independent Sensory Epithelia

The morphological and histological features of the nasal cavity are diverse among animal species, and the nasal cavities of terrestrial and semiaquatic turtles possess 2 regions lined with each different type of sensory epithelium. Sea turtles can inhale both of volatile and water-soluble odorants with high sensitivity, but details of the architectural features and the distribution of the sensory epithelia within the sea turtle nasal cavity remain uncertain. The present study analyzed the nasal cavity of green sea turtles using morphological, computed tomographic, and histological methods. We found that the middle region of the sea turtle nasal cavity is divided into anterodorsal, anteroventral, and posterodorsal diverticula and a posteroventral excavation by connective tissue containing cartilages. The posterodorsal diverticulum was lined with a thin sensory epithelium, and the anterodorsal and anteroventral diverticula were occupied by a single thick sensory epithelium. In addition, a relatively small area on the posteroventral excavation was covered by independent sensory epithelium that differed from other 2 types of epithelia, and a single thin bundle derived from the posteroventral excavation comprised the most medial nerve that joins the anterior end of the olfactory nerve tract. These findings suggested that the posteroventral excavation identified herein transfers stimuli through an independent circuit and plays different roles when odorants arise from other nasal regions.

Lectin histochemical studies on the olfactory gland and two types of gland in vomeronasal organ of the brown bear

Olfaction is mediated by the vomeronasal and main olfactory systems, and the peripheral vomeronasal organ (VNO) processes species-specific chemicals that are associated with various behaviors in mammals. Sensory epithelial surfaces of the olfactory mucosa and VNO are covered by mucosal fluid that contains secretory products derived from associated glands, and glycoconjugates in the mucosal fluid are involved in odorant reception. The VNO of brown bears contains two types of glands; submucosal vomeronasal glands (VNG) and multicellular intraepithelial glands (MIG). The present study determined the labelling profiles of 21 lectins in the olfactory glands (OG), VNG and MIG of young male brown bears. The OG reacted with 12 lectins, and the VNG and MIG were positive for seven and eight lectins, respectively. Six lectins bound only to the OG, while four reacted with both or either of the VNG and MIG, but not the OG. The differences of lectin labelling pattern between the OG and glands in the VNO suggest that glycans in covering mucosal fluids differ between the olfactory mucosa and VNO. In addition, Bandeiraea simplicifolia lectin-I, Sophora japonica agglutinin and Jacalin reacted with the MIG but not the VNG, whereas Datura stramonium lectin and concanavalin A bound to the VNG, but not the MIG. These findings indicate that the properties of secretory substances differ between the two types of glands in the bear VNO, and that the various secretions from these two types of glands may function in the lumen of VNO together.

Testicular regulation of seasonal change in apocrine glands in the back skin of the brown bear (Ursus arctos)

Brown bears communicate with other individuals using marking behavior. Bipedal back rubbing has been identified as a common marking posture. Oily substances are secreted via enlarged sebaceous glands in the back skin of male bears during the breeding season. However, whether apocrine gland secretions are associated with seasonal changes remains unknown. The present study aimed to identify histological and histochemical changes in the secretory status and the glycocomposition of the apocrine glands in the back skin of male bears in response to changes in seasons and/or reproductive status. The apocrine glands of intact males during the breeding season were significantly larger and more active than those of castrated males during the breeding season and those of intact males during the non-breeding season. Lectin histochemical analyses revealed a more intense reaction to Vicia villosa agglutinin (VVA) in the cytoplasm, mainly Golgi zones of apocrine cells during the breeding season among castrated, compared with intact males. Positive staining for VVA was quite intense and weak in intact males during the non-breeding and breeding seasons, respectively. Ultrastructural analysis revealed VVA positivity in the Golgi zone, especially around secretory granules in apocrine cells. Changes in lectin binding might reflect a change in the secretory system in the apocrine cells. The present histological and histochemical findings of changes in the secretory status and glycocomposition of the apocrine glands according to the season and reproductive status suggest that these glands are important for chemical communication.

Morphological study on the olfactory systems of the snapping turtle, Chelydra serpentina

In this study, the olfactory system of a semi-aquatic turtle, the snapping turtle, has been morphologically investigated by electron microscopy, immunohistochemistry, and lectin histochemistry. The nasal cavity of snapping turtle was divided into the upper and lower chambers, lined by the sensory epithelium containing ciliated and non-ciliated olfactory receptor neurons, respectively. Each neuron expressed both Gαolf, the α-subunit of G-proteins coupling to the odorant receptors, and Gαo, the α-subunit of G-proteins coupling to the type 2 vomeronasal receptors. The axons originating from the upper chamber epithelium projected to the ventral part of the olfactory bulb, while those from the lower chamber epithelium to the dorsal part of the olfactory bulb. Despite the identical expression of G-protein α-subunits in the olfactory receptor neurons, these two projections were clearly distinguished from each other by the differential expression of glycoconjugates. In conclusion, these data indicate the presence of two types of olfactory systems in the snapping turtle. Topographic arrangement of the upper and lower chambers and lack of the associated glands in the lower chamber epithelium suggest their possible involvement in the detection of odorants: upper chamber epithelium in the air and the lower chamber epithelium in the water.

Molecular clock regulates daily α1-2-fucosylation of the neural cell adhesion molecule (NCAM) within mouse secondary olfactory neurons

The circadian clock regulates various behavioral and physiological rhythms in mammals. Circadian changes in olfactory functions such as neuronal firing in the olfactory bulb (OB) and olfactory sensitivity have recently been identified, although the underlying molecular mechanisms remain unknown. We analyzed the temporal profiles of glycan structures in the mouse OB using a high-density microarray that includes 96 lectins, because glycoconjugates play important roles in the nervous system such as neurite outgrowth and synaptogenesis. Sixteen lectin signals significantly fluctuated in the OB, and the intensity of all three that had high affinity for α1-2-fucose (α1-2Fuc) glycan in the microarray was higher during the nighttime. Histochemical analysis revealed that α1-2Fuc glycan is located in a diurnal manner in the lateral olfactory tract that comprises axon bundles of secondary olfactory neurons. The amount of α1-2Fuc glycan associated with the major target glycoprotein neural cell adhesion molecule (NCAM) varied in a diurnal fashion, although the mRNA and protein expression of Ncam1 did not. The mRNA and protein expression of Fut1, a α1-2-specific fucosyltransferase gene, was diurnal in the OB. Daily fluctuation of the α1-2Fuc glycan was obviously damped in homozygous Clock mutant mice with disrupted diurnal Fut1 expression, suggesting that the molecular clock governs rhythmic α1-2-fucosylation in secondary olfactory neurons. These findings suggest the possibility that the molecular clock is involved in the diurnal regulation of olfaction via α1-2-fucosylation in the olfactory system.

Phylogenic studies on the olfactory system in vertebrates

The olfactory receptor organs and their primary centers are classified into several types. The receptor organs are divided into fish-type olfactory epithelium (OE), mammal-type OE, middle chamber epithelium (MCE), lower chamber epithelium (LCE), recess epithelium, septal olfactory organ of Masera (SO), mammal-type vomeronasal organ (VNO) and snake-type VNO. The fish-type OE is observed in flatfish and lungfish, while the mammal-type OE is observed in amphibians, reptiles, birds and mammals. The MCE and LCE are unique to Xenopus and turtles, respectively. The recess epithelium is unique to lungfish. The SO is observed only in mammals. The mammal-type VNO is widely observed in amphibians, lizards and mammals, while the snake-type VNO is unique to snakes. The VNO itself is absent in turtles and birds. The mammal-type OE, MCE, LCE and recess epithelium seem to be descendants of the fish-type OE that is derived from the putative primitive OE. The VNO may be derived from the recess epithelium or fish-type OE and differentiate into the mammal-type VNO and snake-type VNO. The primary olfactory centers are divided into mammal-type main olfactory bulbs (MOB), fish-type MOB and mammal-type accessory olfactory bulbs (AOB). The mammal-type MOB first appears in amphibians and succeeds to reptiles, birds and mammals. The fish-type MOB, which is unique to fish, may be the ancestor of the mammal-type MOB. The mammal-type AOB is observed in amphibians, lizards, snakes and mammals and may be the remnant of the fish-type MOB.

Histological and lectin histochemical studies on the olfactory and respiratory mucosae of the sheep

The olfactory and respiratory mucosae of the Corriedale sheep were examined using lectin histochemistry in order to clarify the histochemical and glycohistochemical differences between these two tissues. The olfactory epithelium was stained with 13 lectins out of 21 lectins examined, while the respiratory epithelium was positive to 16 lectins. The free border of both of the olfactory and respiratory epithelia was stained with 12 lectins: Wheat germ agglutinin (WGA), succinylated-wheat germ agglutinin (s-WGA), Lycopersicon esculentum lectin (LEL), Solanum tuberosum lectin (STL), Datura stramonium lectin (DSL), Soybean agglutinin (SBA), Bandeiraea simplicifolia lectin-I (BSL-I), Ricinus communis agglutinin-I (RCA-120), Erythrina cristagalli lectin (ECL), Concanavalin A (Con A), Phaseolus vulgaris agglutinin-E (PHA-E) and Phaseolus vulgaris agglutinin-L (PHA-L). The associated glands of the olfactory mucosa, Bowman’s glands, were stained with 13 lectins. While both the goblet cells and mucous nasal glands were stained with 8 lectins; five of them (WGA, s-WGA, STL, Vicia villosa agglutinin (VVA) and ECL) were mutually positive among the Bowman’s glands, mucous nasal glands and the goblet cells. These findings indicate that the glycohistochemical characteristics of the free borders of both olfactory and respiratory epithelia are similar to each other, suggesting that secretions from the Bowman’s glands and those of the goblet cells and mucous nasal glands are partially exchanged between the surface of two epithelia to contribute the functions of the respiratory epithelium and the olfactory receptor cells, respectively.

Lectin histochemical studies on the vomeronasal organ of the sheep

The vomeronasal organ of sheep was examined using lectin histochemistry in order to compare the types and amounts of the glycoconjugates among various components of the vomeronasal sensory and non-sensory epithelia. In the vomeronasal sensory epithelium, Dolichos biflorus agglutinin (DBA) stained particular cells, located at the same level as the vomeronasal receptor cells, while the distribution, shape and number of the stained cells did not correspond to those of the vomeronasal receptor cells. Datura stramonium lectin (DSL), Concanavalin A (Con A), Phaseolus vulgaris agglutinin-E (PHA-E) and Phaseolus vulgaris agglutinin-L (PHA-L) labeled the basal cells of both vomeronasal sensory and non-sensory epithelia. While, Wheat germ agglutinin (WGA), Succinylated-wheat germ agglutinin (s-WGA), Lycopersicon esculentum lectin (LEL), Solanum tuberosum lectin (STL) and Ricinus communis agglutinin-I (RCA-120) labeled the basal cells of the sensory epithelium, and Bandeiraea simplicifolia lectin-I (BSL-I) stained the basal cells of the non-sensory epithelium, respectively. Seventeen lectins labeled the free border of both vomeronasal sensory and non-sensory epithelia, while Sophora japonica agglutinin (SJA), Jacalin and Pisum sativum agglutinin (PSA) labeled neither free border of the sensory nor that of non-sensory epithelia. The expression pattern of glycoconjugate was similar, but not identical, in the free border between the sensory and non-sensory epithelia. These results indicate that there are dissimilar features in the type and amount of glycoconjugates between the vomeronasal sensory and non-sensory epithelia, and at the same time, among the various cell types either in the vomeronasal sensory or non-sensory epithelium.

Analysis of glycoproteins produced by the associated gland in the olfactory organ of lungfish

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.

Histological and lectin histochemical studies on the main and accessory olfactory bulbs in the Japanese striped snake, Elaphe quadrivirgata

The main and accessory olfactory bulbs were examined by histological methods and lectin histochemistry in the Japanese striped snake. As the results, the histological properties are similar between the main olfactory bulb and the accessory olfactory bulb. In lectin histochemistry, 21 lectins used in this study showed similar binding patterns in the main olfactory bulb and the accessory olfactory bulb. In detail, 15 lectins stained these olfactory bulbs with similar manner, and 6 lectins did not stain them at all. Two lectins, Lycopersicon esculentum lectin (LEL) and Solanum tuberosum lectin (STL), stained the nerve and glomerular layers and did not stain any other layers in both olfactory bulbs. Four lectins, Soybean agglutinin (SBA), Vicia villosa agglutinin (VVA), Peanut agglutinin (PNA) and Phaseolus vulgaris agglutinin-L (PHA-L) stained the nerve and glomerular layers more intensely than other layers in both olfactory bulbs. In addition, VVA showed the dot-like stainings in the glomeruli of both olfactory bulbs. These findings suggest that the degree of development and the properties of glycoconjugates are similar between the main olfactory bulb and the accessory olfactory bulb in the Japanese striped snake.

Identification of G protein α subunits in the main olfactory system and vomeronasal system of the Japanese Striped snake, Elaphe quadrivirgata

In the olfactory system, G proteins couple to the olfactory receptors, and G proteins expressed in the main olfactory system and vomeronasal system vary according to animal species. In this study, G protein α subunits expressed in the main olfactory system and vomeronasal system of the snake were identified by immunohistochemistry. In the olfactory epithelium, only anti-Gαolf/s antibody labeled the cilia of the receptor cells. In the vomeronasal epithelium, only anti-Gαo antibody labeled the microvilli of the receptor cells. In the accessory olfactory bulb, anti-Gαo antibody stained the whole glomerular layer. These results suggest that the main olfactory system and the vomeronasal system of the snake express Gαolf and Gαo as G proteins coupling to the olfactory receptors, respectively.

Seasonal changes in the histochemical properties of the olfactory epithelium and vomeronasal organ in the Japanese striped snake, Elaphe quadrivirgata

Seasonal changes in the histochemical properties of the vomeronasal and olfactory epithelia of the Japanese striped snake were examined in four seasons, viz. the reproductive, pre-hibernating, hibernating and post-hibernating seasons. In the vomeronasal and olfactory supporting cells, secretory granules were much more abundant in the hibernating season than in the other seasons. In the vomeronasal and olfactory receptor cells, the lipofuscin granules were much fewer in the post-hibernating season than in the other seasons. In histochemical studies with 21 lectins, several lectins stained the vomeronasal and olfactory epithelia (receptor cells, supporting cells and free border) more weakly in the hibernating season than in the reproductive season. However, all lectins stained both epithelia in the hibernating season after sialic acid removal in a similar manner as in the reproductive season after sialic acid removal. These lectin histochemical studies indicate that sialic acid residues in the vomeronasal and olfactory epithelia are more numerous in the hibernating season than in the reproductive season. The results suggest that during hibernation, the vomeronasal and olfactory receptor cells possibly undergo rapid cell turnover, and that during this time, the vomeronasal and olfactory epithelia are securely protected from pathogens by an innate immune defence system.

Cladistic analysis of olfactory and vomeronasal systems

Most tetrapods possess two nasal organs for detecting chemicals in their environment, which are the sensory detectors of the olfactory and vomeronasal systems. The seventies’ view that the olfactory system was only devoted to sense volatiles, whereas the vomeronasal system was exclusively specialized for pheromone detection was challenged by accumulating data showing deep anatomical and functional interrelationships between both systems. In addition, the assumption that the vomeronasal system appeared as an adaptation to terrestrial life is being questioned as well. The aim of the present work is to use a comparative strategy to gain insight in our understanding of the evolution of chemical “cortex.” We have analyzed the organization of the olfactory and vomeronasal cortices of reptiles, marsupials, and placental mammals and we have compared our findings with data from other taxa in order to better understand the evolutionary history of the nasal sensory systems in vertebrates. The olfactory and vomeronsasal cortices have been re-investigated in garter snakes (Thamnophis sirtalis), short-tailed opossums (Monodelphis domestica), and rats (Rattus norvegicus) by tracing the efferents of the main and accessory olfactory bulbs using injections of neuroanatomical anterograde tracers (dextran-amines). In snakes, the medial olfactory tract is quite evident, whereas the main vomeronasal-recipient structure, the nucleus sphaericus is a folded cortical-like structure, located at the caudal edge of the amygdala. In marsupials, which are acallosal mammals, the rhinal fissure is relatively dorsal and the olfactory and vomeronasal cortices relatively expanded. Placental mammals, like marsupials, show partially overlapping olfactory and vomeronasal projections in the rostral basal telencephalon. These data raise the interesting question of how the telencephalon has been re-organized in different groups according to the biological relevance of chemical senses.

Phylogenic outline of the olfactory system in vertebrates

Phylogenic outline of the vertebrate olfactory system is summarized in the present review. In the fish and the birds, the olfactory system consists only of the olfactory epithelium (OE) and the olfactory bulb (B). In the amphibians, reptiles and mammals, the olfactory system is subdivided into the main olfactory and the vomeronasal olfactory systems, and the former consists of the OE and the main olfactory bulb (MOB), while the latter the vomeronasal organ (VNO) and the accessory olfactory bulb (AOB). The subdivision of the olfactory system into the main and the vomeronasal olfactory systems may partly be induced by the difference between paraphyletic groups and monophyletic groups in the phylogeny of vertebrates.