Resolution of sensory and mucoid glycoconjugates with terminal alpha-galactose residues in the mucomicrovillar complex of the vomeronasal sensory epithelium by dual confocal laser scanning microscopy

Do fossorial water voles have a functional vomeronasal organ? A histological and immunohistochemical study

The fossorial water vole, Arvicola scherman, is an herbivorous rodent that causes significant agricultural damages. The application of cairomones and alarm pheromones emerges as a promising sustainable method to improve its integrated management. These chemical signals would induce stress responses that could interfere with the species regular reproductive cycles and induce aversive reactions, steering them away from farmlands and meadows. However, there is a paucity of information regarding the water vole vomeronasal system, both in its morphological foundations and its functionality, making it imperative to understand the same for the application of chemical communication in pest control. This study fills the existing gaps in knowledge through a morphological and immunohistochemical analysis of the fossorial water vole vomeronasal organ. The study is primarily microscopic, employing two approaches: histological, using serial sections stained with various dyes (hematoxylin-eosin, Periodic acid-Schiff, Alcian blue, Nissl), and immunohistochemical, applying various markers that provide morphofunctional and structural information. These procedures have confirmed the presence of a functional vomeronasal system in fossorial water voles, characterized by a high degree of differentiation and a significant expression of cellular markers indicative of active chemical communication in this species.

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.

Lectin histochemistry of the olfactory mucosa of Korean native cattle, Bos taurus coreanae

BACKGROUND

The olfactory mucosa (OM) is crucial for odorant perception in the main olfactory system. The terminal carbohydrates of glycoconjugates influence chemoreception in the olfactory epithelium (OE).

OBJECTIVES

The histological characteristics and glycoconjugate composition of the OM of Korean native cattle (Hanwoo, Bos taurus coreae) were examined to characterize their morphology and possible functions during postnatal development.

METHODS

The OM of neonate and adult Korean native cattle was evaluated using histological, immunohistochemical, and lectin histochemical methods.

RESULTS

Histologically, the OM in both neonates and adults consists of the olfactory epithelium and the lamina propria. Additionally, using periodic acid Schiff and Alcian blue (pH 2.5), the mucus specificity of the Bowman's gland duct and acini in the lamina propria was determined. Immunohistochemistry demonstrated that mature and immature olfactory sensory neurons of OEs express the olfactory marker protein and growth associated protein-43, respectively. Lectin histochemistry indicated that numerous glycoconjugates, including as N-acetylglucosamine, mannose, galactose, N-acetylgalactosamine, complex type N-glycan, and fucose groups, were expressed at varied levels in the different cell types in the OMs of neonates and adults at varying levels. According to our observations, the cattle possessed a well-developed olfactory system, and the expression patterns of glycoconjugates in neonatal and adult OMs varied considerably.

CONCLUSIONS

This is the first study to describe the morphological assessment of the OM of Korean native cattle with a focus on lectin histochemistry. The findings suggest that glycoconjugates may play a role in olfactory chemoreception, and that their labeling properties may be closely related to OM development and maturity.

The vomeronasal system of the newborn capybara: a morphological and immunohistochemical study

The vomeronasal system (VNS) is responsible for the perception mainly of pheromones and kairomones. Primarily studied in laboratory rodents, it plays a crucial role in their socio-sexual behaviour. As a wild rodent, the capybara offers a more objective and representative perspective to understand the significance of the system in the Rodentia, avoiding the risk of extrapolating from laboratory rodent strains, exposed to high levels of artificial selection pressure. We have studied the main morphological and immunohistochemical features of the capybara vomeronasal organ (VNO) and accessory olfactory bulb (AOB). The study was done in newborn individuals to investigate the maturity of the system at this early stage. We used techniques such as histological stains, lectins-labelling and immunohistochemical characterization of a range of proteins, including G proteins (Gαi2, Gαo) and olfactory marking protein. As a result, we conclude that the VNS of the capybara at birth is capable of establishing the same function as that of the adult, and that it presents unique features as the high degree of differentiation of the AOB and the active cellular migration in the vomeronasal epithelium. All together makes the capybara a promising model for the study of chemical communication in the first days of life.

The vomeronasal organ of wild canids: the fox (Vulpes vulpes) as a model

The vomeronasal system (VNS) has been extensively studied within specific animal families, such as Rodentia. However, the study of the VNS in other families, such as Canidae, has long been neglected. Among canids, the vomeronasal organ (VNO) has only been studied in detail in the dog, and no studies have examined the morphofunctional or immunohistochemical characteristics of the VNS in wild canids, which is surprising, given the well-known importance of chemical senses for the dog and fox and the likelihood that the VNS plays roles in the socio-reproductive physiology and behaviours of these species. In addition, characterising the fox VNS could contribute to a better understanding of the domestication process that occurred in the dog, as the fox would represent the first wild canid to be studied in depth. Therefore, the aim of this study was to analyze the morphological and immunohistochemical characteristics of the fox VNO. Tissue dissection and microdissection techniques were employed, followed by general and specific histological staining techniques, including with immunohistochemical and lectin-histochemical labelling strategies, using antibodies against olfactory marker protein (OMP), growth-associated protein 43 (GAP-43), calbindin (CB), calretinin (CR), α-tubulin, Gαo, and Gαi2 proteins, to highlight the specific features of the VNO in the fox. This study found significant differences in the VNS between the fox and the dog, particularly concerning the expression of Gαi2 and Gαo proteins, which were associated with the expression of the type 1 vomeronasal receptors (V1R) and type 2 vomeronasal receptors (V2R), respectively, in the vomeronasal epithelium. Both are immunopositive in foxes, as opposed to the dog, which only expresses Gαi2. This finding suggests that the fox possesses a well-developed VNO and supports the hypothesis that a profound transformation in the VNS is associated with domestication in the canid family. Furthermore, the unique features identified in the fox VNO confirm the necessity of studying the VNS system in different species to better comprehend specific phylogenetic aspects of the VNS.

Glycan changes in the olfactory mucosa of rats with experimental autoimmune encephalomyelitis

Glycans are components of glycoconjugates and function in odorant recognition and cell signaling in the olfactory mucosa. However, little is known about glycan expression in the olfactory mucosa in the presence of neuroinflammatory disorders, which can influence olfaction. We evaluated the changes in glycan in the olfactory mucosa of rats with experimental autoimmune encephalomyelitis (EAE) by histochemical analyses of 21 lectins. In the olfactory mucosa of normal control rats, 16 lectins bound to olfactory sensory neurons, supporting cells, basal cells, nerve and Bowman's glands, and their expression did not significantly change during the course of EAE. In rats with paralytic-stage EAE, five lectins showed different reactivities with the olfactory mucosa compared to those of normal control rats. Of them, Bandeiraea simplicifolia lectin (BSL)-II and BSL-I showed transiently downregulated binding to olfactory sensory neurons and supporting cells in rats with EAE. The reactivities of Lens culinaris agglutinin for the basement membrane, Vicia villosa agglutinin for Bowman's glands and Dolichos biflorus agglutinin for all nuclei were upregulated in the olfactory mucosa of EAE rats. These results suggest that BSL-II-binding N-acetyl-glucosamine and BSL-I-binding N-acetyl-galactose are involved in transient olfactory dysfunction in EAE, which may hamper odor perception and/or signal processing in olfactory sensory neurons.

Functionally important glycosyltransferase gain and loss during catarrhine primate emergence

A glycosyltransferase, alpha1,3galactosyltransferase, catalyzes the terminal step in biosynthesis of Galalpha1,3Galbeta1-4GlcNAc-R (alphaGal), an oligosaccharide cell surface epitope. This epitope or antigenically similar epitopes are widely distributed among the different forms of life. Although abundant in most mammals, alphaGal is not normally found in catarrhine primates (Old World monkeys and apes, including humans), all of which produce anti-alphaGal antibodies from infancy onward. Natural selection favoring enhanced resistance to alphaGal-positive pathogens has been the primary reason offered to account for the loss of alphaGal in catarrhines. Here, we question the primacy of this immune defense hypothesis with results that elucidate the evolutionary history of GGTA1 gene and pseudogene loci. One such locus, GGTA1P, a processed (intronless) pseudogene (PPG), is present in platyrrhines, i.e., New World monkeys, and catarrhines but not in prosimians. PPG arose in an early ancestor of anthropoids (catarrhines and platyrrhines), and GGTA1 itself became an unprocessed pseudogene in the late catarrhine stem lineage. Strong purifying selection, denoted by low nonsynonymous substitutions per nonsynonymous site/synonymous substitutions per synonymous site values, preserved GGTA1 in noncatarrhine mammals, indicating that the functional gene product is subjected to considerable physiological constraint. Thus, we propose that a pattern of alternative and/or more beneficial glycosyltransferase activity had to first evolve in the stem catarrhines before GGTA1 inactivation could occur. Enhanced defense against alphaGal-positive pathogens could then have accelerated the replacement of alphaGal-positive catarrhines by alphaGal-negative catarrhines. However, we emphasize that positively selected regulatory changes in sugar chain metabolism might well have contributed in a major way to catarrhine origins.

Ultrastructural localization of alpha-galactose-containing glycoconjugates in the rat vomeronasal organ

Binding sites of Griffonia simplicifolia I-B4 isolectin (GS-I-B4), which recognizes terminal alpha-galactose residues of glycoconjugates, were examined in the juxtaluminal region of the rat vomeronasal sensory epithelium and its associated glands of the vomeronasal organ, using a lectin cytochemical technique. Lowicryl K4M-embedded ultra-thin sections, which were treated successively with biotinylated GS-I-B4 and streptavidin-conjugated 10 nm colloidal gold particles, were observed under a transmission electron microscope. Colloidal gold particles, which reflect the presence of terminal alpha-galactose-containing glycoconjugates, were present in vomeronasal receptor neurons in the sensory epithelium and secretory granules of acinar cells of associated glands of the epithelium. Quantitative analysis demonstrated that the density of colloidal gold particles associated with sensory cell microvilli that projected from dendritic endings of vomeronasal neurons was considerably higher than that of microvilli that projected from neighboring sustentacular cells. The same was true for the apical cytoplasms of these cells just below the microvilli. These results suggest that of the sensory microvilli and dendritic endings contained a much larger amount of the alpha-galactose-containing glycoconjugates, compared with those in sustentacular microvilli. Further, biochemical analyses demonstrated several vomeronasal organ-specific glycoproteins with terminal alpha-galactose.

Ontogenetic observations on the vomeronasal organ in two species of tamarins using neuron-specific beta-tubulin III

Callitrichid primates (tamarins, marmosets) have extreme variation in the vomeronasal organ (VNO), including ontogenetic differences in the neuroepithelium and vomeronasal duct (VND) patency at birth. Such differences render the timing and extent of VNO maturation debatable in callitrichids, but no studies have used neuron-specific immunohistochemical markers to address this question. The present study compared the number of VNO epithelial cells that express immunoreactivity to neuron-specific beta-tubulin III (BT), VNO length, and VNO cross-sectional area between two species of tamarins (Leontopithecus rosalia and Saguinus geoffroyi) that differed in perinatal VND patency. Neonatal lemurs and adult marmosets and bushbabies were also examined for a comparison to species previously shown to have a relatively large amount of VNO neuroepithelium and patent VNDs. The head of each specimen was serially sectioned in the coronal plane. Based on known rostrocaudal start/stop points of the VNO, selected unstained sections were used for BT protocols and area measurement at three percentiles (25th, 50th, 75th) in each specimen. Each section was photographed and enlarged for cell counts and measurement of cross-sectional epithelial area. In each specimen, the number of BT(+) cells in the VNO was counted at each percentile and expressed as a number per mm(2). Results indicated that lemur VNOs had a dense population of BT(+) cells at birth, but the VNO was more varied in the tamarin species. S. geoffroyi had few or no BT(+) cells in VNOs of neonates, which had fused VNDs, but had an increased BT(+) population by 1 and 2 months postnatal age, when the VND was patent. Of the species with patent VNDs at birth, neonatal L. rosalia had a denser population of BT(+) cells compared to S. geoffroyi, though not to the degree seen in neonatal lemurs or adult marmosets and bushbabies. These findings show that BT immunohistochemistry is a useful comparative method for the study of VNOs in subadult primates. Since the quantity of nonsensory VNO epithelium varies substantially between species, epithelial area measurements may be misleading, and BT(+) cell counts appeared to be the best quantitative method for comparing receptor neuron numbers among primates. It is suggested that the greater BT(+) cell population in L. rosalia at all subadult stages examined reveals an earlier maturation of the neuroepithelium compared to S. geoffroyi. Further investigation should consider whether this may relate to a comparatively brief subadult ontogeny and early onset of adult behaviors in L. rosalia compared to other tamarins studied to date.