Histological features of the vomeronasal organ in the giraffe, Giraffa camelopardalis

Immunohistological study of the unexplored vomeronasal organ of an endangered mammal, the dama gazelle (Nanger dama)

Dama gazelle is a threatened and rarely studied species found primarily in northern Africa. Human pressure has depleted the dama gazelle population from tens of thousands to a few hundred individuals. Since 1970, a founder population consisting of the last 17 surviving individuals in Western Sahara has been maintained in captivity, reproducing naturally. In preparation for the future implementation of assisted reproductive technology, certain aspects of dama gazelle reproductive biology have been established. However, the role played by semiochemical-mediated communications in the sexual behavior of dama gazelle remains unknown due partially to a lack of a neuroanatomical or morphofunctional characterization of the dama gazelle vomeronasal organ (VNO), which is the sensory organ responsible for pheromone processing. The present study characterized the dama gazelle VNO, which appears fully equipped to perform neurosensory functions, contributing to current understanding of interspecies VNO variability among ruminants. By employing histological, lectin-histochemical, and immunohistochemical techniques, we conducted a detailed morphofunctional evaluation of the dama gazelle VNO along its entire longitudinal axis. Our findings of significant structural and neurochemical transformation along the entire VNO suggest that future studies of the VNO should take a similar approach. The present study contributes to current understanding of dama gazelle VNO, providing a basis for future studies of semiochemical-mediated communications and reproductive management in this species. RESEARCH HIGHLIGHTS: This exhaustive immunohistological study of the vomeronasal organ (VNO) of the dama gazelle provides the first evidence of notable differences in the expression of neuronal markers along the rostrocaudal axis of the VNO. This provides a morphological basis for the implementation of pheromones in captive populations of dama gazelle.

Vomeronasal Receptors Associated with Circulating Estrogen Processing Chemosensory Cues in Semi-Aquatic Mammals

In numerous animals, one essential chemosensory organ that detects chemical signals is the vomeronasal organ (VNO), which is involved in species-specific behaviors, including social and sexual behaviors. The purpose of this study is to investigate the mechanism underlying the processing of chemosensory cues in semi-aquatic mammals using muskrats as the animal model. Muskrat (Ondatra zibethicus) has a sensitive VNO system that activates seasonal breeding behaviors through receiving specific substances, including pheromones and hormones. Vomeronasal organ receptor type 1 (V1R) and type 2 (V2R) and estrogen receptor α and β (ERα and ERβ) were found in sensory epithelial cells, non-sensory epithelial cells and lamina propria cells of the female muskrats' VNO. V2R and ERα mRNA levels in the VNO during the breeding period declined sharply, in comparison to those during the non-breeding period, while V1R and ERβ mRNA levels were detected reversely. Additionally, transcriptomic study in the VNO identified that differently expressed genes might be related to estrogen signal and metabolic pathways. These findings suggested that the seasonal structural and functional changes in the VNO of female muskrats with different reproductive status and estrogen was regulated through binding to ERα and ERβ in the female muskrats' VNO.

Flehmen, Osteophagia, and Other Behaviors of Giraffes (Giraffa giraffa angolensis): Vomeronasal Organ Adaptation

The size of adult male giraffes (Giraffa giraffa angolensis) far exceeds the size of the females. At the Namutoni waterholes in Etosha National Park, bulls were seen many times each day screening adult females for their pending sexual receptivity by provoking them to urinate; this mainly involved sniffing their genitalia. If the female accedes to the male's invitation, she widens her hindleg stance, braces her body, and then urinates, usually for at least five seconds. The male places his muzzle and tongue in the urine stream, and then performs flehmen, often raising his head high in the air. Males never investigated urine on the ground. The bilateral papillae on the giraffe's hard palate connect with the nasopalatine ducts, which enter the bilateral vomeronasal organ (VNO). Unlike many mammals, the giraffe's VNO lacks a prominent connection to the nasal cavity and its connections to the oral cavity are primarily via the incisive papillae. Most days, some giraffes were observed searching for bones for extended periods, chewing them, and sometimes being troubled by a bone stuck in their mouth. A giraffe killed by lions was frequented for several days by a procession of giraffes investigating the carcass. A very dark-colored bull giraffe emitted loud pulsed growls that drove off most of the surrounding giraffes.

The vomeronasal system in semiaquatic beavers

In contrast to the main olfactory system that detects volatile chemicals in the nasal air, the vomeronasal system can detect nonvolatile chemicals as well as volatiles. In the vomeronasal system, chemicals are perceived by the vomeronasal organ (VNO) projecting axons to the accessory olfactory bulb (AOB). Beavers (Castor spp.) are semiaquatic mammals that have developed chemical communication. It is possible that the beaver's anal gland secretions, nonvolatile and insoluble substances, may work as a messenger in the water and that beavers may detect the nonvolatile chemicals floating on the water surface via the VNO. The present study aimed to clarify the specificities of the beaver vomeronasal system by histologically and immunohistochemically analyzing the VNO and AOB of 12 Eurasian beavers (C. fiber). The VNO directly opened to the nasal cavity and was independent of a narrow nasopalatine duct connecting the oral and nasal cavities. The VNO comprised soft tissues including sensory and nonsensory epithelium, glands, a venous sinus, an artery, as well as cartilage inner, and bone outer enclosures. The AOB had distinct six layers, and anti-G protein α-i2 and α-o subunits were, respectively, immunoreactive in rostral and caudal glomeruli layers indicating expressions of V1Rs and V2Rs. According to gene repertories analysis, the beavers had 23 and six intact V1R and V2R genes respectively. These findings suggested that beavers recognize volatile odorants and nonvolatile substances using the vomeronasal system. The beaver VNO was developed as well as in other rodents, and it had two specific morphological features, namely, disadvantaged contact with the oral cavity because of a tiny nasopalatine duct, and a double bone and cartilage envelope. Our results highlight the importance of the vomeronasal system in beaver chemical communication and support the possibility that beavers can detect chemicals floating on the water surface via the VNO.

Morphological and Histological Features of the Vomeronasal Organ in African Pygmy Hedgehog (Atelerix albiventris)

Simple Summary

Hedgehogs have a sensitive olfaction, but little is known about their vomeronasal organ, which detects specific chemicals such as pheromones. This is the first study to reveal the morphological and histological features of the vomeronasal organ in the African pygmy hedgehog. Notably, unlike other mammals, the hedgehog has a large, well-developed serous gland in the vomeronasal organ. This gland seems to allow flushing out odorous substances from the vomeronasal organ and might be favorable for subsequent stimulus reception.

Abstract

The vomeronasal organ (VNO) detects specific chemicals such as pheromones and kairomones. Hedgehogs (Eulipotyphla: Erinaceidae) have a well-developed accessory olfactory bulb that receives projections from the VNO, but little is known about the hedgehog VNO. Here, we studied the histological features of the VNO in five individual African pygmy hedgehogs by hematoxylin-eosin, periodic acid-Schiff, and Alcian blue stains. The hedgehog VNO comprises a hyaline cartilage capsule, soft tissue and epithelial lumen, and it branches from the site just before the incisive duct opening into the nasal cavity. The soft tissues contain several small mucous (or mucoserous) glands and a large serous gland, and many venous sinuses all around the lumen. The VNO lumen is round to oval throughout the hedgehog VNO, and the sensory epithelium lines almost the entire rostral part and medial wall of the middle part. These findings indicate that the VNO is functional and plays an important role in the hedgehog. Notably, the VNO apparently has a characteristic flushing mechanism with serous secretions like those of gustatory glands, which the hedgehog might frequently use to recognize the external environment.

Comparative histological studies on properties of polysaccharides secreted by vomeronasal glands of eight Laurasiatheria species

Most mammalian species have a vomeronasal organ that detects specific chemical substances, such as pheromones. Mucous fluid covering the vomeronasal sensory epithelium is secreted by vomeronasal glands, and the properties of these fluids have been suggested to be involved in chemical detection. Histological studies using periodic acid-Schiff (PAS) and Alcian blue pH 2.5 (AB) stains, which respectively detect natural and acidic polysaccharides, have suggested variations in the nature of the vomeronasal glands among species. Here, we investigated the responsivity of the vomeronasal glands to PAS and AB stains in eight Laurasiatheria species. All species studied herein possessed vomeronasal glands that stained positive for PAS, like other many reported species. The vomeronasal glands of dogs and minks - like rodents, were AB-negative, whereas those of cows, goats, sika deer, musk shrews and two bat species were positive. Considering the present findings and previous reports, the vomeronasal glands in most of Laurasiatheria species appear to be fundamentally abundant in acidic polysaccharides, whereas those in carnivores essentially contains neutral polysaccharides.

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.

Immunolocalization of Receptor and Chemoreceptor Modules in the Sheep Vomeronasal Organ

The vomeronasal organ (VNO) is the peripheral receptor organ of the accessory olfactory system, which is responsible for both sexual and innate behaviors. The degree of neuronal differentiation and maturation of the vomeronasal receptor cells together with the verification of the presence of the solitary chemoreceptor cells (SCCs) in the VNO of Corriedale sheep were assessed using immunofluorescence. A protein gene product 9.5 (PGP 9.5), which is a neuronal marker recognized to be expressed in most neurons of vertebrate species, an olfactory marker protein (OMP) that is precise for mature olfactory receptor cells, and lastly phospholipase C-β2 (PLC-β2), a marker in the signal transduction pathway of SCCs, were all tested. The cell bodies and dendrites of almost all receptor cells in the sensory epithelium were strongly positive for PGP 9.5 and to a lesser extent for OMP. In the nonsensory wall, all cells were negative for both PGP 9.5 and OMP; however, some positive PGP 9.5 immunoreactive fibers were identified. For PLC-β2, only 1 basally situated SCC could be identified in the sensory epithelium. A higher number was demonstrated in the nonsensory wall. Corriedale sheep possess matured, fully differentiated vomeronasal receptor cells in their sensory wall, suggesting an appropriate pheromone perception. Additionally, the VNO in sheep may participate in the usual transduction mechanisms, though it is seemingly not a chemoreceptor organ.

Morphological and histological features of the vomeronasal organ in the brown bear

The vomeronasal organ (VNO) is a peripheral receptor structure that is involved in reproductive behavior and is part of the vomeronasal system. Male bears exhibit flehmen behavior that is regarded as the uptake of pheromones into the VNO to detect estrus in females. However, the morphological and histological features of the VNO in bears have not been comprehensively studied. The present study investigated the properties and degree of development of the VNO of the brown bear by histological, histochemical and ultrastructural methods. The VNO of bears was located at the same position as that of many other mammals, and it opened to the mouth like the VNO of most carnivores. The shape of the vomeronasal cartilages and the histological features of the sensory epithelium in the bear VNO were essentially similar to those of dogs. Receptor cells in the VNO of the bear possessed both cilia and microvilli like those of dogs. The dendritic knobs of receptor cells were positive for anti-G protein alpha-i2 subunit (Gαi2 ) but negative for anti-G protein alpha-o subunit, indicating preferential use of the V1R-Gαi2 pathway in the vomeronasal system of bears, as in other carnivores. The VNO of the bear possessed three types of secretory cells (secretory cells of the vomeronasal gland, multicellular intraepithelial gland cells and goblet cells), and the present findings showed that the secretory granules in these cells also had various properties. The vomeronasal lumen at the middle region of the VNO invaginated toward the ventral region, and this invagination contained tightly packed multicellular intraepithelial gland cells. To our knowledge, this invagination and intraepithelial gland masses in the VNO are unique features of brown bears. The VNO in the brown bear, especially the secretory system, is morphologically well-developed, suggesting that this organ is significant for information transmission in this species.