Vomeronasal Epithelium Research Articles

Prosaposin/Saposin Expression in the Developing Rat Olfactory and Vomeronasal Epithelia

Prosaposin is a glycoprotein widely conserved in vertebrates, and it acts as a precursor for saposins that accelerate hydrolysis in lysosomes or acts as a neurotrophic factor without being processed into saposins. Neurogenesis in the olfactory neuroepithelia, including the olfactory epithelium (OE) and the vomeronasal epithelium (VNE), is known to occur throughout an animal’s life, and mature olfactory neurons (ORNs) and vomeronasal receptor neurons (VRNs) have recently been revealed to express prosaposin in the adult olfactory organ. In this study, the expression of prosaposin in the rat olfactory organ during postnatal development was examined. In the OE, prosaposin immunoreactivity was observed in mature ORNs labeled using olfactory marker protein (OMP) from postnatal day (P) 0. Immature ORNs showed no prosaposin immunoreactivity throughout the examined period. In the VNE, OMP-positive VRNs were mainly observed in the basal region of the VNE on P10 and showed an adult-like distribution from P20. On the other hand, prosaposin immunoreactivity was observed in VRNs from P0, suggesting that not only mature VRNs but also immature VRNs express prosaposin. This study raises the possibility that prosaposin is required for the normal development of the olfactory organ and has different roles in the OE and the VNE.

First Immunohistochemical Demonstration of the Expression of a Type-2 Vomeronasal Receptor, V2R2, in Wild Canids.

The mammalian vomeronasal system enables the perception of chemical signals crucial for social communication via the receptor families V1R and V2R. These receptors are linked with the G-protein subunits, Gαi2 and Gαo, respectively. Exploring the evolutionary pathways of V1Rs and V2Rs across mammalian species remains a significant challenge, particularly when comparing genomic data with emerging immunohistochemical evidence. Recent studies have revealed the expression of Gαo in the vomeronasal neuroepithelium of wild canids, including wolves and foxes, contradicting predictions based on current genomic annotations. Our study provides detailed immunohistochemical evidence, mapping the expression of V2R receptors in the vomeronasal sensory epithelium, focusing particularly on wild canids, specifically wolves and foxes. An additional objective involves contrasting these findings with those from domestic species like dogs to highlight the evolutionary impacts of domestication on sensory systems. The employment of a specific antibody raised against the mouse V2R2, a member of the C-family of vomeronasal receptors, V2Rs, has confirmed the presence of V2R2-immunoreactivity (V2R2-ir) in the fox and wolf, but it has revealed the lack of expression in the dog. This may reflect the impact of domestication on the regression of the VNS in this species, in contrast to their wild counterparts, and it underscores the effects of artificial selection on sensory functions. Thus, these findings suggest a more refined chemical detection capability in wild species.

Following the p63/Keratin5 basal cells in the sensory and non-sensory epithelia of the vomeronasal organ.

The vomeronasal organ (VNO) is a part of the accessory olfactory system, which detects pheromones and chemical factors that trigger a spectrum of sexual and social behaviors. The vomeronasal epithelium (VNE) shares several features with the epithelium of the main olfactory epithelium (MOE). However, it is a distinct neuroepithelium populated by chemosensory neurons that differ from the olfactory sensory neurons in cellular structure, receptor expression, and connectivity. The vomeronasal organ of rodents comprises a sensory epithelium (SE) and a thin non-sensory epithelium (NSE) that morphologically resembles the respiratory epithelium. Sox2-positive cells have been previously identified as the stem cell population that gives rise to neuronal progenitors in MOE and VNE. In addition, the MOE also comprises p63 positive horizontal basal cells, a second pool of quiescent stem cells that become active in response to injury. Immunolabeling against the transcription factor p63, Keratin-5 (Krt5), Krt14, NrCAM, and Krt5Cre tracing experiments highlighted the existence of horizontal basal cells distributed along the basal lamina of SE of the VNO. Single cell sequencing and genetic lineage tracing suggest that the vomeronasal horizontal basal cells arise from basal progenitors at the boundary between the SE and NSE proximal to the marginal zones. Moreover, our experiments revealed that the NSE of rodents is, like the respiratory epithelium, a stratified epithelium where the p63/Krt5+ basal progenitor cells self-replicate and give rise to the apical columnar cells facing the lumen of the VNO.

Histological evaluation of the alpaca (Vicugna pacos) vomeronasal organ.

Little is known about the neuronal structure of the vomeronasal organ (VNO), a receptor organ responsible for pheromone perception, in the alpaca (Vicugna pacos). This study was performed to determine the localization of neuronal elements, including protein gene product 9.5 (PGP 9.5), a pan-neuronal marker, olfactory marker protein (OMP), a marker of mature olfactory receptor cells, and phospholipase C beta 2 (PLC-β2), a marker of solitary chemoreceptor cells (SCCs), in the VNO. OMP was identified in receptor cells of the vomeronasal sensory epithelium (VSE), while PGP 9.5 and PLC-β2 were localized in both the VSE and vomeronasal non-sensory epithelium. Collectively, these results suggested that the alpaca VNO possesses SCCs and olfactory receptor cells, which recognize both harmful substances and pheromones.

Long-COVID cognitive impairments and reproductive hormone deficits in men may stem from GnRH neuronal death

We have recently demonstrated a causal link between loss of gonadotropin-releasing hormone (GnRH), the master molecule regulating reproduction, and cognitive deficits during pathological aging, including Down syndrome and Alzheimer's disease. Olfactory and cognitive alterations, which persist in some COVID-19 patients, and long-term hypotestosteronaemia in SARS-CoV-2-infected men are also reminiscent of the consequences of deficient GnRH, suggesting that GnRH system neuroinvasion could underlie certain post-COVID symptoms and thus lead to accelerated or exacerbated cognitive decline. We explored the hormonal profile of COVID-19 patients and targets of SARS-CoV-2 infection in post-mortem patient brains and human fetal tissue. We found that persistent hypotestosteronaemia in some men could indeed be of hypothalamic origin, favouring post-COVID cognitive or neurological symptoms, and that changes in testosterone levels and body weight over time were inversely correlated. Infection of olfactory sensory neurons and multifunctional hypothalamic glia called tanycytes highlighted at least two viable neuroinvasion routes. Furthermore, GnRH neurons themselves were dying in all patient brains studied, dramatically reducing GnRH expression. Human fetal olfactory and vomeronasal epithelia, from which GnRH neurons arise, and fetal GnRH neurons also appeared susceptible to infection. Putative GnRH neuron and tanycyte dysfunction following SARS-CoV-2 neuroinvasion could be responsible for serious reproductive, metabolic, and mental health consequences in long-COVID and lead to an increased risk of neurodevelopmental and neurodegenerative pathologies over time in all age groups. European Research Council (ERC) grant agreements No 810331, No 725149, No 804236, the European Union Horizon 2020 research and innovation program No 847941, the Fondation pour la Recherche Médicale (FRM) and the Agence Nationale de la Recherche en Santé (ANRS) No ECTZ200878 Long Covid 2021 ANRS0167 SIGNAL, Agence Nationale de la recherche (ANR) grant agreements No ANR-19-CE16-0021-02, No ANR-11-LABEX-0009, No. ANR-10-LABEX-0046, No. ANR-16-IDEX-0004, Inserm Cross-Cutting Scientific Program HuDeCA, the CHU Lille Bonus H, the UK Medical Research Council (MRC) and National Institute of Health and care Research (NIHR).

Natural and Pathological Aging Distinctively Impacts the Pheromone Detection System and Social Behavior

Normal aging and many age-related disorders such as Alzheimer’s disease cause deficits in olfaction; however, it is currently unknown how natural and pathological aging impacts the detection of social odors which might contribute to the impoverishment of social behavior at old age further worsening overall health. Analysis of the vomeronasal organ, the main gateway to pheromone-encoded information, indicated that natural and pathological aging distinctively affects the neurogenic ability of the vomeronasal sensory epithelium. Whereas cell proliferation remained majorly preserved in 1-year-old APP/PS1 mice, naturally aged animals exhibited significant deficiencies in the number of mature, proliferative, and progenitor cells. These alterations may support age-related deficits in the recognition of social cues and the display of social behavior. Our findings indicate that aging disrupts the processing of social olfactory cues decreasing social odor exploration, discrimination, and habituation in both wild-type senescent (2-year-old) mice and in 1-year-old double mutant model of Alzheimer’s disease (APP/PS1). Furthermore, social novelty was diminished in 1-year-old APP/PS1 mice, indicating that alterations in the processing of social cues are accelerated during pathological aging. This study reveals fundamental differences in the cellular processes by which natural and pathological aging disrupts the exploration of social information and social behavior.

Expression patterns of prosaposin and its receptors, G protein-coupled receptor (GPR) 37 and GPR37L1, in the mouse olfactory organ

Prosaposin is a glycoprotein conserved widely in vertebrates, because it is a precursor for saposins that are required for normal lysosomal function and thus for autophagy, and acts as a neurotrophic factor. Most tetrapods possess two kinds of olfactory neuroepithelia, namely, the olfactory epithelium (OE) and the vomeronasal epithelium (VNE). This study examined the expression patterns of prosaposin and its candidate receptors, G protein-coupled receptor (GPR) 37 and GPR37L1, in mouse OE and VNE by immunofluorescence and in situ hybridization. Prosaposin immunoreactivity was observed in the olfactory receptor neurons, vomeronasal receptor neurons, Bowman’s gland (BG), and Jacobson’s gland (JG). Prosaposin expression was mainly observed in mature neurons. Prosaposin mRNA expression was observed not only in these cells but also in the apical region of the VNE. GPR37 and GPR37L1 immunoreactivities were found only in the BG and/or the JG. Prosaposin was suggested to secrete and facilitate the autophagic activities of the neurons and modulate the mucus secretion in mouse olfactory organ.

Glycoconjugate-Specific Developmental Changes in the Horse Vomeronasal Organ

The vomeronasal organ (VNO) is a tubular pheromone-sensing organ in which the lumen is covered with sensory and non-sensory epithelia. This study used immunohistochemistry and lectin histochemistry techniques to evaluate developmental changes, specifically of the glycoconjugate profile, in the horse VNO epithelium. Immunostaining analysis revealed PGP9.5 expression in some vomeronasal non-sensory epithelium (VNSE) cells and in the vomeronasal receptor cells of the vomeronasal sensory epithelium (VSE) in fetuses, young foals, and adult horses. Olfactory marker protein expression was exclusively localized in receptor cells of the VSE in fetuses, young foals, and adult horses and absent in VNSE. To identify the glycoconjugate type, lectin histochemistry was performed using 21 lectins. Semi-quantitative analysis revealed that the intensities of glycoconjugates labeled with WGA, DSL, LEL, and RCA₁₂₀ were significantly higher in adult horse VSE than those in foal VSE, whereas the intensities of glycoconjugates labeled with LCA and PSA were significantly lower in adult horse VSE. The intensities of glycoconjugates labeled with s-WGA, WGA, BSL-II, DSL, LEL, STL, ConA, LCA, PSA, DBA, SBA, SJA, RCA₁₂₀, jacalin, and ECL were significantly higher in adult horse VNSE than those in foal VNSE, whereas the intensity of glycoconjugates labeled with UEA-I was lower in adult horse VNSE. Histochemical analysis of each lectin revealed that various glycoconjugates in the VSE were present in the receptor, supporting, and basal cells of foals and adult horses. A similar pattern of lectin histochemistry was also observed in the VNSE of foals and adult horses. In conclusion, these results suggest that there is an increase in the level of N-acetylglucosamine (labeled by WGA, DSL, LEL) and galactose (labeled by RCA₁₂₀) in horse VSE during postnatal development, implying that they may influence the function of VNO in adult horses.

Inflammation interferes with chemoreception in pigs by altering the neuronal layout of the vomeronasal sensory epithelium.

Chemical communication is widely used by animals to exchange information in their environment, through the emission and detection of semiochemicals to maintain social organization and hierarchical rules in groups. The vomeronasal organ (VNO) is one of the main detectors of these messages, and its inflammation has been linked to behavioral changes because it potentially prevents molecule detection and, consequently, the translation of the signal into action. Our previous study highlighted the link between the intensity of vomeronasal sensory epithelium (VNSE) inflammation, probably induced by farm contaminant exposure, and intraspecific aggression in pigs. The aim of this study was to evaluate the cellular and molecular changes that occur during vomeronasalitis in 76 vomeronasal sensorial epithelia from 38 intensive-farmed pigs. Histology was used to evaluate the condition of each VNO and classify inflammation as healthy, weak, moderate, or strong. These data were compared to the thickness of the sensorial epithelium and the number of type 1 vomeronasal receptor cells using anti-Gαi2 protein immunohistochemistry (IHC) and analysis. The presence of odorant-binding proteins (OBPs) in the areas surrounding the VNO was also analyzed by IHC and compared to inflammation intensity since its role as a molecule transporter to sensory neurons has been well-established. Of the 76 samples, 13 (17%) were healthy, 31 (41%) presented with weak inflammation, and 32 (42%) presented with moderate inflammation. No severe inflammation was observed. Epithelial thickness and the number of Gαi2+ cells were inversely correlated with inflammation intensity (Kruskal–Wallis and ANOVA tests, p < 0.0001), while OBP expression in areas around the VNO was increased in inflamed VNO (Kruskal–Wallis test, p = 0.0094), regardless of intensity. This study showed that inflammation was associated with a reduction in the thickness of the sensory epithelium and Gαi2+ cell number, suggesting that this condition can induce different degrees of neuronal loss. This finding could explain how vomeronasalitis may prevent the correct functioning of chemical communication, leading to social conflict with a potential negative impact on welfare, which is one of the most important challenges in pig farming.

Differential Cellular Balance of Olfactory and Vomeronasal Epithelia in a Transgenic BACHD Rat Model of Huntington's Disease.

Background. For neurodegenerative diseases such as Huntington’s disease (HD), early diagnosis is essential to treat patients and delay symptoms. Impaired olfaction, as observed as an early symptom in Parkinson´s disease, may also constitute a key symptom in HD. However, there are few reports on olfactory deficits in HD. Therefore, we aimed to investigate, in a transgenic rat model of HD: (1) whether general olfactory impairment exists and (2) whether there are disease-specific dynamics of olfactory dysfunction when the vomeronasal (VNE) and main olfactory epithelium (MOE) are compared. Methods. We used male rats of transgenic line 22 (TG22) of the bacterial artificial chromosome Huntington disease model (BACHD), aged 3 days or 6 months. Cell proliferation, apoptosis and macrophage activity were examined with immunohistochemistry in the VNE and MOE. Results. No differences were observed in cellular parameters in the VNE between the groups. However, the MOE of the 6-month-old HD animals showed a significantly increased number of mature olfactory receptor neurons. Other cellular parameters were not affected. Conclusions. The results obtained in the TG22 line suggest a relative stability in the VNE, whereas the MOE seems at least temporarily affected.

Notch signaling determines cell-fate specification of the two main types of vomeronasal neurons of rodents.

ABSTRACTThe ability of terrestrial vertebrates to find food and mating partners, and to avoid predators, relies on the detection of chemosensory information. Semiochemicals responsible for social and sexual behaviors are detected by chemosensory neurons of the vomeronasal organ (VNO), which transmits information to the accessory olfactory bulb. The vomeronasal sensory epithelium of most mammalian species contains a uniform vomeronasal system; however, rodents and marsupials have developed a more complex binary vomeronasal system, containing vomeronasal sensory neurons (VSNs) expressing receptors of either the V1R or V2R family. In rodents, V1R/apical and V2R/basal VSNs originate from a common pool of progenitors. Using single cell RNA-sequencing, we identified differential expression of Notch1 receptor and Dll4 ligand between the neuronal precursors at the VSN differentiation dichotomy. Our experiments show that Notch signaling is required for effective differentiation of V2R/basal VSNs. In fact, Notch1 loss of function in neuronal progenitors diverts them to the V1R/apical fate, whereas Notch1 gain of function redirects precursors to V2R/basal. Our results indicate that Notch signaling plays a pivotal role in triggering the binary differentiation dichotomy in the VNO of rodents.

Histological and Immunohistochemical Characterization of Vomeronasal Organ Aging in Mice.

Simple SummaryChemical communication has been intensely studied and the importance of its role in animal life has been ascertained. Located in the nasal cavity, the vomeronasal organ is one of the main actors in charge of chemical reception. Alterations of this organ have proven to modify behavioral responses to semiochemical expositions. For all the other organs, a well-known origin of alteration is aging. The objective of this study was to analyze this effect on the vomeronasal organ condition and to determine the nature of these potential changes. This study demonstrates that this organ is significantly impacted by aging. In particular, old mice present strong signs of neuronal degeneration compared to adults.The vomeronasal organ (VNO) plays a crucial role in animal behavior since it is responsible for semiochemical detection and, thus, for intra- and interspecific chemical communication, through the vomeronasal sensory epithelium (VNSE), composed of bipolar sensory neurons. This study aimed to explore a well-recognized cause of neuronal degeneration, only rarely explored in this organ: aging. Murine VNOs were evaluated according to 3 age groups (3, 10, and 24 months) by histology to assess VNSE changes such as cellular degeneration or glycogen accumulation and by immunohistochemistry to explore nervous configuration, proliferation capability, and apoptosis with the expression of olfactory marker protein (OMP), Gαi2, Gαo, Ki-67, and cleaved caspase-3 proteins. These markers were quantified as percentages of positive signal in the VNSE and statistical analyses were performed. Cellular degeneration increased with age (p < 0.0001) as well as glycogen accumulation (p < 0.0001), Gαo expression (p < 0.0001), and the number of cleaved-caspase3 positive cells (p = 0.0425), while OMP and Gαi2 expressions decreased with age (p = 0.0436 and p < 0.0001, respectively). Ki67-positive cells were reduced, even if this difference was not statistically significant (p = 0.9105). Due to the crucial role of VNO in animal life, this study opens the door to interesting perspectives about chemical communication efficiency in aging animals.

Structural and ultrastructural studies on the developing vomeronasal sensory epithelium in the grass snake Natrix natrix (Squamata: Colubroidea).

The sensory olfactory epithelium and the vomeronasal sensory epithelium (VSE) are characterized by continuous turnover of the receptor cells during postnatal life and are capable of regeneration after injury. The VSE, like the entire vomeronasal organ, is generally well developed in squamates and is crucial for detection of pheromones and prey odors. Despite the numerous studies on embryonic development of the VSE in squamates, especially in snakes, an ultrastructural analysis, as far as we know, has never been performed. Therefore, we investigated the embryology of the VSE of the grass snake (Natrix natrix) using electron microscopy (SEM and TEM) and light microscopy. As was shown for adult snakes, the hypertrophied ophidian VSE may provide great resolution of changes in neuron morphology located at various epithelial levels. The results of this study suggest that different populations of stem/progenitor cells occur at the base of the ophidian VSE during embryonic development. One of them may be radial glia-like cells, described previously in mouse. The various structure and ultrastructure of neurons located at different parts of the VSE provide evidence for neuronal maturation and aging. Based on these results, a few nonmutually exclusive hypotheses explaining the formation of the peculiar columnar organization of the VSE in snakes were proposed.

Peripheral oxytocin injection modulates vomeronasal sensory activity and reduces pup-directed aggression in male mice

Behaviors are shaped by hormones, which may act either by changing brain circuits or by modifying sensory detection of relevant cues. Pup-directed behaviors have been previously shown to change via action of hormones at the brain level. Here, we investigated hormonal control of pup-induced activity in the vomeronasal organ, an olfactory sensory structure involved in the detection of non-volatile chemosignals. Vomeronasal activity decreases as males switch from a pup-aggressive state to a non-aggressive parenting state, after they socially contact a female. RNA sequencing, qPCR, and in situ hybridization were used to identify expression, in the vomeronasal sensory epithelium, of candidate GPCR hormone receptors chosen by in silico analyses and educated guesses. After identifying that oxytocin and vasopressin receptors are expressed in the vomeronasal organ, we injected the corresponding hormones in mice and showed that oxytocin administration reduced both pup-induced vomeronasal activity and aggressive behavior. Conversely, injection of an oxytocin receptor antagonist in female-primed male animals, which normally exhibit reduced vomeronasal activity, significantly increased the number of active vomeronasal neurons. These data link oxytocin to the modulation of olfactory sensory activity, providing a possible mechanism for changes in male behavior after social experience with females.

Macro- and micromorphological remodeling of olfactory organs throughout the ontogeny of the fire salamander Salamandra salamandra (Linnaeus, 1758).

This article studies the morphological remodeling of olfactory organs in the fire salamander (Salamandridae, Caudata), from the larval stages of ontogeny to the adult and throughout the course of the annual cycle. The fire salamander exhibits adaptations to the aquatic environment during premetamorphic life and terrestrial adaptations after metamorphosis. During adulthood, the annual activity of this species is divided into three seasonal periods: a breeding period, a nonbreeding period, and hibernation. We observed significant differences in morphology of olfactory organs between developmental stages as well as between each period within the annual cycle. For the first time in caudates, we examined the morphology of olfactory organs during the winter period (wintering larvae, hibernating adults). The results show that the remodeling of olfactory organs during the life of the fire salamander occurs both on macro- and micromorphological levels. Macromorphological ontogenetic variability includes the shape of the main olfactory chamber (MOC) and the distribution of olfactory epithelium (OE) in the MOC and in the vomeronasal organ (VNO). In larvae, the vomeronasal epithelium (VNE) is in a separate cavity, while in the post-metamorphic stages of ontogeny, the VNE occurs in the diverticulum of the MOC. In adult fire salamanders, both olfactory organs are most developed during the breeding season and reduced during hibernation. The VNE and OE in the MOC are also reduced during hibernation. Micro-morphological changes included different types/subtypes of olfactory receptor neurons (ORNs) in the OE in particular stages of ontogeny and periods within the annual cycle, for example, ciliate ORNs are present in the VNE only in the larval stages and giant ORNs occur only in nonbreeding adults. Also, there was a variable set of types of olfactory supporting cells in the VNO of the fire salamander during pre- and postmetamorphic life stages.

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.

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.

Two Preputial Gland-Secreted Pheromones Evoke Sexually Dimorphic Neural Pathways in the Mouse Vomeronasal System.

Hexadecanol (16OH) and hexadecyl acetate (16Ac) are two pheromones secreted in a large quantity by mouse preputial glands and act on male and female mice differentially. Yet the underlying molecular and cellular mechanisms remain to be elucidated. In this study, we examined the activation of vomeronasal sensory neurons (VSNs) by these two pheromones and mapped the downstream neural circuits that process and relay their chemosignals. Using the calcium imaging method and immunohistochemistry, we found that a small number of VSNs were activated by 16OH, 16AC, or both in the male and female mice, most of which were located apically in the vomeronasal epithelium, and their numbers did not increase when the concentrations of 16OH and 16Ac were raised by 10,000-fold except that of female VSNs in response to 16OH. In the accessory olfactory bulb (AOB), the two pheromones evoked more c-Fos+ neurons in the anterior AOB (aAOB) than in the posterior AOB (pAOB); and the increases in the number of c-Fos+ neurons in both aAOB and pAOB were dose-dependent; and between sexes, the female AOB responded more strongly to 16OH than to 16Ac whereas the male AOB had the opposite response pattern. This sexual dimorphism was largely retained in the downstream brain regions, including the bed nucleus of the stria terminalis (BNST), the medial amygdaloid nucleus (MeA), the posteromedial cortical amygdaloid nucleus (PMCo), the medial preoptic area (MPA), and the ventromedial hypothalamic nucleus (VmH). Taken together, out data indicate that there is one V1r receptor each for 16OH, 16Ac, or both, and that activation of these receptors evokes sexually dimorphic neural circuits, directing different behavioral outputs and possibly modulating other pheromone-induced responses.

A Subset of Olfactory Sensory Neurons Express Forkhead Box J1-Driven eGFP.

Forkhead box protein J1 (FOXJ1), a member of the forkhead family transcription factors, is a transcriptional regulator of motile ciliogenesis. The nasal respiratory epithelium, but not olfactory epithelium, is lined with FOXJ1-expressing multiciliated epithelial cells with motile cilia. In a transgenic mouse where an enhanced green fluorescent protein (eGFP) transgene is driven by the human FOXJ1 promoter, robust eGFP expression is observed not only in the multiciliated cells of the respiratory epithelium but in a distinctive small subset of olfactory sensory neurons in the olfactory epithelium. These eGFP-positive cells lie at the extreme apical part of the neuronal layer and are most numerous in dorsal-medial regions of olfactory epithelium. Interestingly, we observed a corresponding small number of glomeruli in the olfactory bulb wherein eGFP-labeled axons terminate, suggesting that the population of eGFP+ receptor cells expresses a limited number of olfactory receptors. Similarly, a subset of vomeronasal sensory neurons expresses eGFP and is distributed throughout the full height of the vomeronasal sensory epithelium. In keeping with this broad distribution of labeled vomeronasal receptor cells, eGFP-labeled axons terminate in many glomeruli in both anterior and posterior portions of the accessory olfactory bulb. These findings suggest that Foxj1-driven eGFP marks a specific population of olfactory and vomeronasal sensory neurons, although neither receptor cell population possess motile cilia.