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The olfactory organ of tetrapods, with few exceptions, comprises the main and accessory organs: olfactory epithelium (OE) and vomeronasal organ (VNO). Unlike tetrapods, teleost fish lack a VNO. However, lungfish, a type of sarcopterygian fish closely related to tetrapods, possesses a lamellar OE similar to the OE of teleosts and a recess epithelium (RecE) resembling the amphibian VNO. The RecE has been hypothesized as a primordial VNO. Olfactory receptors in tetrapods are distinctively expressed in the OE and VNO. For instance, type 2 vomeronasal receptors (V2Rs) in Xenopus are categorized into those exclusively expressed in the OE and those solely expressed in the VNO. It remains unclear whether V2Rs are differentially expressed between the lamellar OE and RecE in lungfish. This study investigated V2R expression in the lamellar OE and RecE of the African lungfish, Protopterus annectens. P. annectens V2Rs were categorized into three groups: those exclusively expressed in the lamellar OE, those exclusively expressed in the RecE, and those expressed in both the lamellar OE and RecE. V2Rs exclusively expressed in the RecE and those expressed in both the lamellar OE and RecE formed a distinct clade in the phylogenetic tree, whereas others were solely expressed in the lamellar OE. These findings suggest that lungfish V2R expression represents an intermediate stage toward complete segregation between V2Rs expressed in the OE and those expressed in the VNO. [ABSTRACT FROM AUTHOR]

Central arginine vasopressin (AVP) facilitates social recognition and modulates many complex social behaviors in mammals that, in many cases, recognize each other based on olfactory and/or pheromonal signals. AVP neurons are present in the accessory olfactory bulb (AOB), which is the first relay in the vomeronasal system and has been demonstrated to be a critical site for mating-induced mate recognition (olfactory memory) in female mice. The transmission of information from the AOB to higher centers is controlled by the dendrodendritic recurrent inhibition, i.e., inhibitory postsynaptic currents (IPSCs) generated in mitral cells by recurrent dendrodendritic inhibitory inputs from granule cells. These reports suggest that AVP might play an important role in regulating dendrodendritic inhibition in the AOB. To test this hypothesis, we examined the effects of extracellularly applied AVP on synaptic responses measured from mitral and granule cells in slice preparations from 23-–36-day-old Balb/c mice. To evoke dendrodendritic inhibition in a mitral cell, depolarizing voltages of −70 to 0  mV (10  ms duration) were applied to a mitral cell using a conventional wholecell configuration. We found that AVP significantly reduced the IPSCs. The suppressive effects of AVP on the IPSCs was diminished by an antagonist for vasopressin receptor 1a (V1aR) (Manning compound), but not by an antagonist for vasopressin receptor 1b (SSR149415). An agonist for V1aRs [(Phe2 )OVT] mimicked the action of AVP on IPSCs. Additionally, AVP significantly suppressed voltage-activated currents in granule cells without affecting the magnitude of the response of mitral cells to gamma-aminobutyric acid (GABA). The present results suggest that V1aRs play a role in reciprocal transmission between mitral cells and granule cells in the mouse AOB by reducing GABAergic transmission through a presynaptic mechanism in granule cells. [ABSTRACT FROM AUTHOR]

Animals have the innate ability to select optimal defensive behaviors with appropriate intensity within specific contexts. The vomeronasal organ (VNO) serves as a primary sensory channel for detecting predator cues by relaying signals to the medial hypothalamic nuclei, particularly the ventromedial hypothalamus (VMH), which directly controls defensive behavioral outputs. Here, we demonstrate that cat saliva contains predator cues that signal the imminence of predator threat and modulate the intensity of freezing behavior through the VNO in mice. Cat saliva activates VNO neurons expressing the V2R-A4 subfamily of sensory receptors, and the number of VNO neurons activated in response to saliva correlates with both the freshness of saliva and the intensity of freezing behavior. Moreover, the number of VMH neurons activated by fresh, but not old, saliva positively correlates with the intensity of freezing behavior. Detailed analyses of the spatial distribution of activated neurons, as well as their overlap within the same individual mice, revealed that fresh and old saliva predominantly activate distinct neuronal populations within the VMH. Collectively, this study suggests that there is an accessory olfactory circuit in mice that is specifically tuned to time-sensitive components of cat saliva, which optimizes their defensive behavior to maximize their chance of survival according to the imminence of threat. [ABSTRACT FROM AUTHOR]

The production of glucocorticoids by the hypothalamic-pituitary-interrenal axis of amphibians and reptiles allows individuals to respond to acute stressors, but chronic elevation can have negative fitness consequences. Amphibians offer a unique opportunity to study the potential effects of elevated glucocorticoids, such as corticosterone (CORT), as lipid-soluble glucocorticoids readily pass through the skin and into the bloodstream. Interestingly, glucocorticoids are also secreted and excreted by amphibians to such an extent that relative rates of CORT release have been used to assess the relative 'health' of populations. Given that CORT has the potential to be both absorbed and secreted through the skin of amphibians and may have a negative impact on fitness, I attempted to assess the degree to which salamanders could identify 'stressed' conspecifics whose CORT levels were experimentally elevated through the use of a dermal patch. Plethodontid salamanders provide a convenient opportunity to evaluate the discrimination of 'stress' levels in amphibians because they utilize well-developed vomeronasal organs to facilitate a range of behavior, and their plasma CORT levels are readily manipulated via transdermal delivery. I tested the ability of Desmognathus ochrophaeus to detect and avoid substrates sullied by conspecifics with elevated CORT. The test was conducted via a simple choice experiment in which male and female test subjects were exposed to substrates sullied by an individual with baseline levels of CORT or the same individual with experimentally elevated CORT. Overall, I found that females did not differentially respond to substrates sullied by 'high-stress' females or males. Males did not avoid substrates sullied by high-stress males but did spend less time than expected on substrates from high-stress females. The differential response by males toward stimuli from high-stress females was replicated in a second study conducted approximately seven months after the first. These findings suggest that male D. ochrophaeus are capable of discerning among females, but not males, in 'high-stress' and 'low-stress' states. Female salamanders did not respond differently to substrates based on the stress level of stimulus donors. [ABSTRACT FROM AUTHOR]

The stem lineage of Archosauria is populated by a diverse fossil record that remains notably understudied relative to the crown clade. Prominent among these specimens is a beautifully preserved skull of the early mid-Triassic rhynchosaur Mesosuchus browni [Iziko South African Museum (SAM) 6536], whose phylogenetic position has considerable influence on patterns of pan-archosaurian cranial evolution. We used high-resolution, micro-computed tomography to re-examine the anatomy of this specimen, building on previous studies that were either limited to external observations or restricted to the braincase. A digital segmentation of the cranial elements and primary neurovascular canals of SAM-PK-6536 allows for expanded character scoring and constitutes a foundation for future comparative insights. Our data support the phylogenetically oldest instance of a pneumatized maxilla in a pan-archosaur, bringing the record of antorbital pneumatization into closer alignment with that of the neurocranium. The nasal cavity and primary palate of Mesosuchus includes a complex septomaxilla, a novel element anterior to the vomer, and is likely to have supported a well-developed vomeronasal system. The evolution of this system is discussed in terms of both phylogenetic pattern and how the skeletal architecture of Mesosuchus and other fossils could inform the signalling dynamics that pattern the vomeronasal system during development. [ABSTRACT FROM AUTHOR]

Simple Summary: The vomeronasal organ is essential for chemical communication in many species, particularly in pigs, in which the establishment of a social hierarchy in groups is crucial. Alterations to the vomeronasal organ have been shown to be linked to aggressive behaviors in this species. Moreover, it was recently demonstrated in a mouse model that the environmental air composition can impact the condition of the vomeronasal organ. As pigs can be farmed in intensive and free-range farming conditions, the aim of this study was to analyze whether the porcine farming method influences the condition of the vomeronasal organ using a histological approach. The results showed that pigs housed in free-range farming conditions exhibited more alterations in their vomeronasal organs than did those housed in intensive conditions. The vomeronasal organ (VNO) plays a key role in mammals, since it detects pheromones thus enabling social interactions between congeners. VNO inflammatory changes have been shown to severely impact animal life, leading to impaired social interactions in groups, such as in pigs. Environmental air is known to be strongly modified in farms, and it is suspected to be one of the causes of this alteration. This study aimed to compare via histology the VNOs of pigs housed in intensive conditions (n = 38) to those of pigs housed in free-range farming conditions (n = 35). VNO sections were stained in hematoxylin and eosin to assess the presence of nonsensory and sensory epithelium alterations and collagenolysis. The nonsensory epithelium was significantly more inflamed in animals in free-range farming conditions than those in intensive conditions (p < 0.0001) and was more strongly affected by signs of collagenolysis (p < 0.0001). The sensory epithelium seemed to be less altered by the different environmental conditions (p = 0.7267). These results suggest that species-typical pig behaviors, such as digging and rooting for food, could facilitate the presence of microparticles in the oral cavity and their entrance into the vomeronasal canals, leading to changes to the VNO. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Wolves, akin to their fellow canids, extensively employ chemical signals for various aspects of communication, including territory maintenance, reproductive synchronisation and social hierarchy signalling. Pheromone‐mediated chemical communication operates unconsciously among individuals, serving as an innate sensory modality that regulates both their physiology and behaviour. Despite its crucial role in the life of the wolf, there is a lacuna in comprehensive research on the neuroanatomical and physiological underpinnings of chemical communication within this species. This study investigates the vomeronasal system (VNS) of the Iberian wolf, simultaneously probing potential alterations brought about by dog domestication. Our findings demonstrate the presence of a fully functional VNS, vital for pheromone‐mediated communication, in the Iberian wolf. While macroscopic similarities between the VNS of the wolf and the domestic dog are discernible, notable microscopic differences emerge. These distinctions include the presence of neuronal clusters associated with the sensory epithelium of the vomeronasal organ (VNO) and a heightened degree of differentiation of the accessory olfactory bulb (AOB). Immunohistochemical analyses reveal the expression of the two primary families of vomeronasal receptors (V1R and V2R) within the VNO. However, only the V1R family is expressed in the AOB. These findings not only yield profound insights into the VNS of the wolf but also hint at how domestication might have altered neural configurations that underpin species‐specific behaviours. This understanding holds implications for the development of innovative strategies, such as the application of semiochemicals for wolf population management, aligning with contemporary conservation goals. [ABSTRACT FROM AUTHOR]

Background. The objective of this study was to describe the histological and immunohistochemical aspects of vomeronasal organ in two groups of (normal and pathological) embryos and fetuses, with chromosomal morphological abnormalities. Methods. The research was based on a retrospective, descriptive analysis, carried out over a period of 5 years. The study included 46 biopsy fragments taken from aborted embryos and fetuses aged between 9 and 23 weeks. We compared the microscopic structure of the vomeronasal organ using different histologic and immunohistochemical staining procedures. Results. Our results showed that in both groups of embryos and fetuses there are three major stages of histological development of the vomeronasal organ, depending by intrauterine age. We also observed that in the group of abnormal embryos and fetuses, although the morphological and immunohistochemical characteristics of vomeronasal organ were similar to the control group, the specific structures of the vomeronasal organ persisted beyond 22 weeks. In the control group, the vomeronasal organ was no longer visible at this age. The results of the immunohistochemical study indicated that the positive surface for cytokines in the control group decreased with age, and in the group with morphological anomalies, the number of positive cells was low. On the other hand, in fetuses with chromosomal anomalies, the positivity, although a slight downward trend was recorded, it remained high. Conclusions. This study is still ongoing in order to identify the increased frequency of vomeronasal organ in fetuses. Moreover, we anticipate that our study can be a starting point for other researchers in order to identify a relationship between the behavioral pattern of the fetuses with trisomy 21 and the persistence of the VNO.

Pheromones are specialized chemical messengers used for inter-individual communication within the same species, playing crucial roles in modulating behaviors and physiological states. The detection mechanisms of these signals at the peripheral organ and their transduction to the brain have been unclear. However, recent identification of pheromone molecules, their corresponding receptors, and advancements in neuroscientific technology have started to elucidate these processes. In mammals, the detection and interpretation of pheromone signals are primarily attributed to the vomeronasal system, which is a specialized olfactory apparatus predominantly dedicated to decoding socio-chemical cues. In this mini-review, we aim to delineate the vomeronasal signal transduction pathway initiated by specific vomeronasal receptor-ligand interactions in mice. First, we catalog the previously identified pheromone ligands and their corresponding receptor pairs, providing a foundational understanding of the specificity inherent in pheromonal communication. Subsequently, we examine the neural circuits involved in processing each pheromone signal. We focus on the anatomical pathways, the sexually dimorphic and physiological state-dependent aspects of signal transduction, and the neural coding strategies underlying behavioral responses to pheromonal cues. These insights provide further critical questions regarding the development of innate circuit formation and plasticity within these circuits. [ABSTRACT FROM AUTHOR]

In mammals, especially rodents, social behaviours, such as parenting, territoriality or mate attraction, are largely based on olfactory communication through chemosignals. These behaviours are mediated by species-specific chemosignals, including small organic molecules and proteins that are secreted in the urine or in various fluids from exocrine glands. Chemosignal detection is mainly ensured by olfactory neurons in two specific sensory organs, the vomeronasal organ (VNO) and the main olfactory epithelium (MOE). This study aimed to characterise the olfactory communication in the fossorial ecotype of the water voles, Arvicola terrestris. We first measured the olfactory investigation of urine and lateral scent gland secretions from conspecifics. Our results showed that water voles can discriminate the sex of conspecifics based on the smell of urine, and that urinary male odour is attractive for female voles. Then, we demonstrated the ability of the VNO and MOE to detect volatile organic compounds (VOCs) found in water vole secretions using live-cell calcium imaging in dissociated cells. Finally, we evaluated the attractiveness of two mixtures of VOCs from urine or lateral scent glands in the field during a cyclical outbreak of vole populations. [ABSTRACT FROM AUTHOR]

Activating transcription factor 5 (ATF5) is a transcription factor that belongs to the cAMP-response element-binding protein/ATF family and is essential for the differentiation and survival of sensory neurons in mouse olfactory organs. However, transcriptional target genes for ATF5 have yet to be identified. In the present study, chromatin immunoprecipitation-quantitative polymerase chain reaction (ChIP-qPCR) experiments were performed to verify ATF5 target genes in the main olfactory epithelium and vomeronasal organ in the postnatal pups. ChIP-qPCR was conducted using hemagglutinin (HA)-tagged ATF5 knock-in olfactory organs. The results obtained demonstrated that ATF5-HA fusion proteins bound to the CCAAT/enhancer-binding protein-ATF response element (CARE) site in the enhancer region of nescient helix-loop-helix 1 (Nhlh1), a transcription factor expressed in differentiating olfactory and vomeronasal sensory neurons. Nhlh1 mRNA expression was downregulated in ATF5-deficient (ATF5−/−) olfactory organs. The LIM/homeobox protein transcription factor Lhx2 co-localized with ATF5 in the nuclei of olfactory and vomeronasal sensory neurons and bound to the homeodomain site proximal to the CARE site in the Nhlh1 gene. The CARE region of the Nhlh1 gene was enriched by the active enhancer marker, acetyl-histone H3 (Lys27). The present study identified Nhlh1 as a novel target gene for ATF5 in murine olfactory organs. ATF5 may upregulate Nhlh1 expression in concert with Lhx2, thereby promoting the differentiation of olfactory and vomeronasal sensory neurons. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The present study was undertaken on vomeronasal organ in SVVU T-17 breed of domestic pig at different levels i.e., papilla incisiva, first palatine rugae, third palatine rugae and fifth palatine rugae. The vomeronasal organ consisted of an internal epithelial duct, middle propria submucosa and cartilage. At the level of papilla incisiva, it was lined by stratified squamous non-keratinized epithelium. At the level of first palatine rugae, stratified squamous non-keratinized epithelium to respiratory epithelium was seen. At the level of third palatine rugae, lateral and medial walls were lined by respiratory and olfactory epithelium, respectively. At the level of fifth palatine rugae, both the walls were lined by olfactory epithelium. The propria submucosa had dense connective tissue at the level of papilla incisiva whereas, loose connective tissue was observed at remaining levels with collagen, elastic and reticular fibres. Nerve bundles were observed at the level of third and fifth palatine rugae levels. The cartilage was incomplete dorsolaterally at papilla incisiva and first rugae level whereas, incomplete dorsally at remaining levels. [ABSTRACT FROM AUTHOR]

The vomeronasal organ (VNO) is located in the anteroinferior part of the nose and the accessory olfactory organ in mammals which is responsible of sense of smell. This study aims to compare the macro and microanatomical structure of the VNO between sheep and dogs. In the current study, we used ten adult slaughtered sheep and ten adult synchronized dogs with different sexes ages 1-2 years. The head of both animals were preserved in 10 % formalin for one week. This study shows in both animals, the VNO occupies the same position in the cavity of the vomer bone and the same relationship in the cranial part of the nasal cavity. Furthermore, the VNO is divided into three parts based on shape that are the rostral, central, and caudal part. The results show the VNO in sheep has a (U) shape and is opened dorsolaterally. It has a small and narrow cavity. It is long 6 cm long, and it has different diameters on its course. In comparison, the vomeronasal organ in dogs is very developed and has a (J) shape. It has a large and long cavity and ends at the fourth molar. Its length is about 10 cm, and it has one diameter on its course. The VNO receives the blood supply from the sphenopalatine and caudal palatine arteries. The present study shows main differences between sheep and dogs VNO in which the structure of vomeronasal bone between the sheep and dog is completely different. The finding will illustrate fundamental differences and provide specific structural differences between the two species. [ABSTRACT FROM AUTHOR]

Animals use the vomeronasal organ for interactions, including sexual intercourse, with conspecifics. Whether this orientation exists in humans is not yet fully understood. In this study, we aimed to compare the sexual behavior and libido changes of septorhinoplasty patients who underwent vomeronasal organ dissection according to gender. This is a cross-sectional descriptive study. The study sample included n=63 septorhinoplasty patients with vomeronasal organ dissection (31 females and 32 males). The data were collected using a personal and clinical characteristics form, the Arizona Sexual Experiences Scale (ASES) and the Libido Scoring System (LSS). The homogeneity test conducted for the personal characteristics of female and male septorhinoplasty patients did not reveal statistical significance, indicating homogeneity of the distribution. Both female and male patients had sexual dysfunction. The females had low libido, while the males had high libido, whereby the difference between them was statistically significant (p<0.01). Based on the results of this study, dissection of the vomeronasal organ does not affect the development of sexual dysfunction or decreased libido in septorhinoplasty patients. This study did not compare septorhinoplasty patients with healthy controls. Future studies are recommended to compare septorhinoplasty patients with healthy controls in this field. [ABSTRACT FROM AUTHOR]

In terrestrial vertebrates, the olfactory system is divided into main (MOS) and accessory (AOS) components that process both volatile and nonvolatile cues to generate appropriate behavioral responses. While much is known regarding the molecular diversity of neurons that comprise the MOS, less is known about the AOS. Here, focusing on the vomeronasal organ (VNO), the accessory olfactory bulb (AOB), and the medial amygdala (MeA), we reveal that populations of neurons in the AOS can be molecularly subdivided based on their ongoing or prior expression of the transcription factors Foxp2 or Dbx1, which delineate separate populations of GABAergic output neurons in the MeA. We show that a majority of AOB neurons that project directly to the MeA are of the Foxp2 lineage. Using single‐neuron patch‐clamp electrophysiology, we further reveal that in addition to sex‐specific differences across lineage, the frequency of excitatory input to MeA Dbx1‐ and Foxp2‐lineage neurons differs between sexes. Together, this work uncovers a novel molecular diversity of AOS neurons, and lineage and sex differences in patterns of connectivity. [ABSTRACT FROM AUTHOR]

Background. The objective of this study was to describe the histological and immunohistochemical aspects of vomeronasal organ in two groups of (normal and pathological) embryos and fetuses, with chromosomal morphological abnormalities. Methods. The research was based on a retrospective, descriptive analysis, carried out over a period of 5 years. The study included 46 biopsy fragments taken from aborted embryos and fetuses aged between 9 and 23 weeks. We compared the microscopic structure of the vomeronasal organ using different histologic and immunohistochemical staining procedures. Results. Our results showed that in both groups of embryos and fetuses there are three major stages of histological development of the vomeronasal organ, depending by intrauterine age. We also observed that in the group of abnormal embryos and fetuses, although the morphological and immunohistochemical characteristics of vomeronasal organ were similar to the control group, the specific structures of the vomeronasal organ persisted beyond 22 weeks. In the control group, the vomeronasal organ was no longer visible at this age. The results of the immunohistochemical study indicated that the positive surface for cytokines in the control group decreased with age, and in the group with morphological anomalies, the number of positive cells was low. On the other hand, in fetuses with chromosomal anomalies, the positivity, although a slight downward trend was recorded, it remained high. Conclusions. This study is still ongoing in order to identify the increased frequency of vomeronasal organ in fetuses. Moreover, we anticipate that our study can be a starting point for other researchers in order to identify a relationship between the behavioral pattern of the fetuses with trisomy 21 and the persistence of the VNO. [ABSTRACT FROM AUTHOR]

Many organisms communicate using signals in different sensory modalities (multicomponent or multimodal). When one signal or component is lost over evolutionary time, it may be indicative of changes in other characteristics of the signalling system, including the sensory organs used to perceive and process signals. Sceloporus lizards predominantly use chemical and visual signals to communicate, yet some species have lost the ancestral ventral colour patch used in male–male agonistic interactions and exhibit increased chemosensory behaviour. Here, we asked whether evolutionary loss of this sexual signal is associated with larger vomeronasal organ (VNO) volumes (an organ that detects chemical scents) compared with species that have retained the colour patch. We measured VNO coronal section areas of 7–8 adult males from each of 11 Sceloporus species (4 that lost and 7 that retained the colour patch), estimated sensory and total epithelium volume, and compared volumes using phylogenetic analysis of covariance, controlling for body size. Contrary to expectations, we found that species retaining the ventral patch had similar relative VNO volumes as did species that had lost the ancestral patch, and that body size explains VNO epithelium volume. Visual signal loss may be sufficiently compensated for by increased chemosensory behaviour, and the allometric pattern may indicate sensory system trade-offs for large-bodied species. [ABSTRACT FROM AUTHOR]

In most mammals, conspecific chemosensory communication relies on semiochemical release within complex bodily secretions and subsequent stimulus detection by the vomeronasal organ (VNO). Urine, a rich source of ethologically relevant chemosignals, conveys detailed information about sex, social hierarchy, health, and reproductive state, which becomes accessible to a conspecific via vomeronasal sampling. So far, however, numerous aspects of social chemosignaling along the vomeronasal pathway remain unclear. Moreover, since virtually all research on vomeronasal physiology is based on secretions derived from inbred laboratory mice, it remains uncertain whether such stimuli provide a true representation of potentially more relevant cues found in the wild. Here, we combine a robust low-noise VNO activity assay with comparative molecular profiling of sex- and strain-specific mouse urine samples from two inbred laboratory strains as well as from wild mice. With comprehensive molecular portraits of these secretions, VNO activity analysis now enables us to (i) assess whether and, if so, how much sex/strain-selective ‘raw’ chemical information in urine is accessible via vomeronasal sampling; (ii) identify which chemicals exhibit sufficient discriminatory power to signal an animal’s sex, strain, or both; (iii) determine the extent to which wild mouse secretions are unique; and (iv) analyze whether vomeronasal response profiles differ between strains. We report both sex- and, in particular, strain-selective VNO representations of chemical information. Within the urinary ‘secretome’, both volatile compounds and proteins exhibit sufficient discriminative power to provide sex- and strain-specific molecular fingerprints. While total protein amount is substantially enriched in male urine, females secrete a larger variety at overall comparatively low concentrations. Surprisingly, the molecular spectrum of wild mouse urine does not dramatically exceed that of inbred strains. Finally, vomeronasal response profiles differ between C57BL/6 and BALB/c animals, with particularly disparate representations of female semiochemicals.

This review addresses the role of chemical communication in mammals, giving special attention to the vomeronasal system in pheromone-mediated interactions. The vomeronasal system influences many social and sexual behaviors, from reproduction to species recognition. Interestingly, this system shows greater evolutionary variability compared to the olfactory system, emphasizing its complex nature and the need for thorough research. The discussion starts with foundational concepts of chemocommunication, progressing to a detailed exploration of olfactory systems. The neuroanatomy of the vomeronasal system stands in contrast with that of the olfactory system. Further, the sensory part of the vomeronasal system, known as the vomeronasal organ, and the integration center of this information, called the accessory olfactory bulb, receive comprehensive coverage. Secondary projections of both the olfactory and vomeronasal systems receive attention, especially in relation to the dual olfactory hypothesis. The review concludes by examining the organization of the vomeronasal system in four distinct mammalian groups: rodents, marsupials, herpestids, and bovids. The aim is to highlight the unique morphofunctional differences resulting from the adaptive changes each group experienced.

The vomeronasal organ (VNO) plays a key role in mammals, since it detects pheromones thus enabling social interactions between congeners. VNO inflammatory changes have been shown to severely impact animal life, leading to impaired social interactions in groups, such as in pigs. Environmental air is known to be strongly modified in farms, and it is suspected to be one of the causes of this alteration. This study aimed to compare via histology the VNOs of pigs housed in intensive conditions (n = 38) to those of pigs housed in free-range farming conditions (n = 35). VNO sections were stained in hematoxylin and eosin to assess the presence of nonsensory and sensory epithelium alterations and collagenolysis. The nonsensory epithelium was significantly more inflamed in animals in free-range farming conditions than those in intensive conditions (p < 0.0001) and was more strongly affected by signs of collagenolysis (p < 0.0001). The sensory epithelium seemed to be less altered by the different environmental conditions (p = 0.7267). These results suggest that species-typical pig behaviors, such as digging and rooting for food, could facilitate the presence of microparticles in the oral cavity and their entrance into the vomeronasal canals, leading to changes to the VNO.

Abstract Background Rodents utilize chemical cues to recognize and avoid other conspecifics infected with pathogens. Infection with pathogens and acute inflammation alter the repertoire and signature of olfactory stimuli emitted by a sick individual. These cues are recognized by healthy conspecifics via the vomeronasal or accessory olfactory system, triggering an innate form of avoidance behavior. However, the molecular identity of the sensory neurons and the higher neural circuits involved in the detection of sick conspecifics remain poorly understood. Results We employed mice that are in an acute state of inflammation induced by systemic administration of lipopolysaccharide (LPS). Through conditional knockout of the G-protein Gαi2 and deletion of other key sensory transduction molecules (Trpc2 and a cluster of 16 vomeronasal type 1 receptors), in combination with behavioral testing, subcellular Ca2+ imaging, and pS6 and c-Fos neuronal activity mapping in freely behaving mice, we show that the Gαi2+ vomeronasal subsystem is required for the detection and avoidance of LPS-treated mice. The active components underlying this avoidance are contained in urine whereas feces extract and two selected bile acids, although detected in a Gαi2-dependent manner, failed to evoke avoidance behavior. Our analyses of dendritic Ca2+ responses in vomeronasal sensory neurons provide insight into the discrimination capabilities of these neurons for urine fractions from LPS-treated mice, and how this discrimination depends on Gαi2. We observed Gαi2-dependent stimulation of multiple brain areas including medial amygdala, ventromedial hypothalamus, and periaqueductal grey. We also identified the lateral habenula, a brain region implicated in negative reward prediction in aversive learning, as a previously unknown target involved in these tasks. Conclusions Our physiological and behavioral analyses indicate that the sensing and avoidance of LPS-treated sick conspecifics depend on the Gαi2 vomeronasal subsystem. Our observations point to a central role of brain circuits downstream of the olfactory periphery and in the lateral habenula in the detection and avoidance of sick conspecifics, providing new insights into the neural substrates and circuit logic of the sensing of inflammation in mice.

Vomeronasal sensory neurons (VSNs) recognize pheromonal and kairomonal semiochemicals in the lumen of the vomeronasal organ. VSNs send their axons along the vomeronasal nerve (VN) into multiple glomeruli of the accessory olfactory bulb (AOB) and form glutamatergic synapses with apical dendrites of mitral cells, the projection neurons of the AOB. Juxtaglomerular interneurons release the inhibitory neurotransmitter γ-aminobutyric acid (GABA). Besides ionotropic GABA receptors, the metabotropic GABAB receptor has been shown to modulate synaptic transmission in the main olfactory system. Here we show that GABAB receptors are expressed in the AOB and are primarily located at VN terminals. Electrical stimulation of the VN provokes calcium elevations in VSN nerve terminals, and activation of GABAB receptors by the agonist baclofen abolishes calcium influx in AOB slice preparations. Patch clamp recordings reveal that synaptic transmission from the VN to mitral cells can be completely suppressed by activation of GABAB receptors. A potent GABAB receptor antagonist, CGP 52432, reversed the baclofen-induced effects. These results indicate that modulation of VSNs via activation of GABAB receptors affects calcium influx and glutamate release at presynaptic terminals and likely balances synaptic transmission at the first synapse of the accessory olfactory system. [ABSTRACT FROM AUTHOR]

This review addresses the role of chemical communication in mammals, giving special attention to the vomeronasal system in pheromone-mediated interactions. The vomeronasal system influences many social and sexual behaviors, from reproduction to species recognition. Interestingly, this system shows greater evolutionary variability compared to the olfactory system, emphasizing its complex nature and the need for thorough research. The discussion starts with foundational concepts of chemocommunication, progressing to a detailed exploration of olfactory systems. The neuroanatomy of the vomeronasal system stands in contrast with that of the olfactory system. Further, the sensory part of the vomeronasal system, known as the vomeronasal organ, and the integration center of this information, called the accessory olfactory bulb, receive comprehensive coverage. Secondary projections of both the olfactory and vomeronasal systems receive attention, especially in relation to the dual olfactory hypothesis. The review concludes by examining the organization of the vomeronasal system in four distinct mammalian groups: rodents, marsupials, herpestids, and bovids. The aim is to highlight the unique morphofunctional differences resulting from the adaptive changes each group experienced. [ABSTRACT FROM AUTHOR]

While we understand how the five main sensory organs enable and facilitate stimulus detection, little is known about how the vomeronasal organ enables pheromone sensation. A new study finds specialized muscles poised to coordinate stimulus delivery, dynamics, and arousal. [ABSTRACT FROM AUTHOR]

Background: Rodents utilize chemical cues to recognize and avoid other conspecifics infected with pathogens. Infection with pathogens and acute inflammation alter the repertoire and signature of olfactory stimuli emitted by a sick individual. These cues are recognized by healthy conspecifics via the vomeronasal or accessory olfactory system, triggering an innate form of avoidance behavior. However, the molecular identity of the sensory neurons and the higher neural circuits involved in the detection of sick conspecifics remain poorly understood. Results: We employed mice that are in an acute state of inflammation induced by systemic administration of lipopolysaccharide (LPS). Through conditional knockout of the G-protein Gαi2 and deletion of other key sensory transduction molecules (Trpc2 and a cluster of 16 vomeronasal type 1 receptors), in combination with behavioral testing, subcellular Ca2+ imaging, and pS6 and c-Fos neuronal activity mapping in freely behaving mice, we show that the Gαi2+ vomeronasal subsystem is required for the detection and avoidance of LPS-treated mice. The active components underlying this avoidance are contained in urine whereas feces extract and two selected bile acids, although detected in a Gαi2-dependent manner, failed to evoke avoidance behavior. Our analyses of dendritic Ca2+ responses in vomeronasal sensory neurons provide insight into the discrimination capabilities of these neurons for urine fractions from LPS-treated mice, and how this discrimination depends on Gαi2. We observed Gαi2-dependent stimulation of multiple brain areas including medial amygdala, ventromedial hypothalamus, and periaqueductal grey. We also identified the lateral habenula, a brain region implicated in negative reward prediction in aversive learning, as a previously unknown target involved in these tasks. Conclusions: Our physiological and behavioral analyses indicate that the sensing and avoidance of LPS-treated sick conspecifics depend on the Gαi2 vomeronasal subsystem. Our observations point to a central role of brain circuits downstream of the olfactory periphery and in the lateral habenula in the detection and avoidance of sick conspecifics, providing new insights into the neural substrates and circuit logic of the sensing of inflammation in mice. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Organisms may retain nonfunctional anatomical features as a consequence of evolutionary natural selection. Resultant atavistic and vestigial anatomical structures have long been a source of perplexity. Atavism is when an ancestral trait reappears after loss through an evolutionary change in previous generations, whereas vestigial structures are remnants that are largely or entirely functionless relative to their original roles. While physicians are cognizant of their existence, atavistic and vestigial structures are rarely emphasized in anatomical curricula and can, therefore, be puzzling when discovered incidentally. In addition, the literature is replete with examples of the terms atavistic and vestigial being used interchangeably without careful distinction between them. We provide an overview of important atavistic and vestigial structures in the head, neck, and spine that can serve as a reference for anatomists and clinical neuroscientists. We review the literature on atavistic and vestigial anatomical structures of the head, neck, and spine that may be encountered in clinical practice. We define atavistic and vestigial structures and employ these definitions consistently when classifying anatomical structures. Pertinent anatomical structures are numerous and include human tails, plica semilunaris, the vomeronasal organ, levator claviculae, and external ear muscles, to name a few. Atavistic and vestigial structures are found throughout the head, neck, and spine. Some, such as human tails and branchial cysts may be clinically symptomatic. Literature reports indicate that their prevalence varies across populations. Knowledge of atavistic and vestigial anatomical structures can inform diagnoses, prevent misrecognition of variation for pathology, and guide clinical interventions. [ABSTRACT FROM AUTHOR]

Ethologically relevant chemical senses and behavioral habits are likely to coadapt in response to selection. As olfaction is involved in intrinsically motivated behaviors in mice, we hypothesized that selective breeding for a voluntary behavior would enable us to identify novel roles of the chemosensory system. Voluntary wheel running (VWR) is an intrinsically motivated and naturally rewarding behavior, and even wild mice run on a wheel placed in nature. We have established 4 independent, artificially evolved mouse lines by selectively breeding individuals showing high VWR activity (High Runners; HRs), together with 4 non-selected Control lines, over 88 generations. We found that several sensory receptors in specific receptor clusters were differentially expressed between the vomeronasal organ (VNO) of HRs and Controls. Moreover, one of those clusters contains multiple single-nucleotide polymorphism loci for which the allele frequencies were significantly divergent between the HR and Control lines, i.e., loci that were affected by the selective breeding protocol. These results indicate that the VNO has become genetically differentiated between HR and Control lines during the selective breeding process. Although the role of the vomeronasal chemosensory receptors in VWR activity remains to be determined, the current results suggest that these vomeronasal chemosensory receptors are important quantitative trait loci for voluntary exercise in mice. We propose that olfaction may play an important role in motivation for voluntary exercise in mammals.

Abstract Lungfish are the most closely related fish to tetrapods. The olfactory organ of lungfish contains lamellae and abundant recesses at the base of lamellae. Based on the ultrastructural and histochemical characteristics, the lamellar olfactory epithelium (OE), covering the surface of lamellae, and the recess epithelium, contained in the recesses, are thought to correspond to the OE of teleosts and the vomeronasal organ (VNO) of tetrapods. With increasing body size, the recesses increase in number and distribution range in the olfactory organ. In tetrapods, the expression of olfactory receptors is different between the OE and VNO; for instance, the type 1 vomeronasal receptor (V1R) is expressed only in the OE in amphibians and mainly in the VNO in mammals. We recently reported that V1R-expressing cells are contained mainly in the lamellar OE but also rarely in the recess epithelium in the olfactory organ of lungfish of approximately 30 cm body length. However, it is unclear whether the distribution of V1R-expressing cells in the olfactory organ varies during development. In this study, we compared the expression of V1Rs in the olfactory organs between juveniles and adults of the African lungfish Protopterus aethiopicus and South American lungfish, Lepidosiren paradoxa. The density of V1R-expressing cells was higher in the lamellae than in the recesses in all specimens evaluated, and this pattern was more pronounced in juveniles than adults. In addition, the juveniles showed a higher density of V1R-expressing cells in the lamellae compared with the adults. Our results imply that differences in lifestyle between juveniles and adults are related to differences in the density of V1R-expressing cells in the lamellae of lungfish.

• Fos expression in response to two chemicals of rat alarm pheromone was examined. • Each chemical activated the MeApv through separate olfactory systems. • The mixture further activated the MeApv. • The MeApv is suggested to integrate information from the two olfactory systems. In rats, a mixture of hexanal and 4-methylpentanal is a main component of the alarm pheromone. When detected by the main olfactory system (MOS) and the vomeronasal system, respectively, they activate the anterior part of the bed nucleus of the stria terminalis (BNSTa). Therefore, the information from the two olfactory systems is expected to be integrated before being transmitted to the BNSTa. To specify the integration site, we examined Fos expression in 16 brain regions in response to water (n = 10), hexanal (n = 9), 4-methylpentanal (n = 9), the mixture (n = 9), or the alarm pheromone (n = 9) in male rats. The posteroventral part of the medial amygdala showed increased Fos expression to hexanal and 4-methylpentanal. The expression was further increased by the mixture. Therefore, this region is suggested as the integration site. In addition, the BNSTa, paraventricular nucleus of the hypothalamus, and anteroventral, anterodorsal, and posterodorsal parts of the medial amygdala were suggested to be located downstream of the integrated site because only the mixture increased Fos expression. We suggest that the posterolateral part of the cortical amygdala is upstream of the integration site in the MOS because all stimuli increased Fos expression. The posterior part of the bed nucleus of the stria terminalis and posteromedial part of the cortical amygdala were suggested as being located upstream in the vomeronasal system because 4-methylpentanal and the mixture increased Fos expression. These results provide information about the neural pathway underlying the alarm pheromone effects. [ABSTRACT FROM AUTHOR]

Simple Summary: The vomeronasal organ plays an essential role in animal life, ensuring chemical communication and thus maintaining harmony in social groups. Induced and spontaneous alterations of this organ have been linked to the onset of behavioral disorders in animals. To date, the environmental condition has not been investigated as a possible cause of vomeronasal organ inflammation, even though the pollutant gas emitted by litter decomposition on farms has proven to be responsible for respiratory tract inflammation. The aim of this study was to analyze the impact of the farming environment on the vomeronasal organ condition. The results showed that this organ is significantly impacted by the confined environment, providing new reasons to improve farming conditions. Chemical communication in mammals is ensured by exchanging chemical signals through the vomeronasal organ (VNO) and its ability to detect pheromones. The alteration of this organ has been proven to impact animal life, participating in the onset of aggressive behaviors in social groups. To date, few studies have highlighted the possible causes leading to these alterations, and the farming environment has not been investigated, even though irritant substances such as ammonia are known to induce serious damage in the respiratory tract. The goal of this study was to investigate the environmental impact on the VNO structure. Thirty mice were split into three groups, one housed in normal laboratory conditions and the other two in confined environments, with or without the release of litter ammonia. VNOs were analyzed using histology and immunohistochemistry to evaluate the effect of different environments on their condition. Both restricted conditions induced VNO alterations (p = 0.0311), soft-tissue alteration (p = 0.0480), and nonsensory epithelium inflammation (p = 0.0024). There was glycogen accumulation (p < 0.0001), the olfactory marker protein was underexpressed (p < 0.0001), and Gαi2 positivity remained unchanged while Gαo expression was upregulated in confined conditions. VNO conditions seemed to worsen with ammonia, even if not always significantly. These murine model results suggest that the housing environment can strongly impact VNO conditions, providing novel insights for improving indoor farming systems. [ABSTRACT FROM AUTHOR]

A 1.5‐year‐old, entire male mongrel dog with a bifid nose and primary cleft palate showed aggressiveness towards unknown dogs despite having adequate canine socialisation and the absence of previous traumatic experiences; furthermore, he does not exhibit sexual behaviour towards females in heat. He was previously treated for fear‐related aggression towards unknown people and environmental phobia due to poor human socialisation. Pharmacological treatment with fluoxetine and trazodone, together with behaviour modification, was started without success. Therefore, it was decided to repeat medical tests. CT and MRI revealed a rostral middle raphe ossification defect incompatible with the presence of the vomeronasal organ (VNO) and the absence of the septum pellucidum (SP). The dog was presumptively diagnosed with aggressiveness towards unknown dogs due to an organic cause, a congenital anomaly with agenesis of the VNO and SP. This case shows the importance of both structures in the regular intraspecific interactions of dogs. [ABSTRACT FROM AUTHOR]

The tongue has a series of functions that can be related to feeding, such as transporting food to the back of the mouth, sensory function and capturing prey. The tongue of the reptiles has great morphological and functional variations between orders. This study aimed to described the morphological characteristics of the tongue of the snake Bothrops jararaca, relating them to the habitat and eating habits of this species. This work used five adult animals which were collected in the municipality of Viçosa, in the Zona da Mata Mineira region. The animals were euthanized, with anesthetic overdose, for the removal of the tongue, which was used for histological processing and scanning electron microscopy. The tongue had stratified epithelium with an extensive degree of keratinization and pigmentation. It was shown to be strongly muscular, innervated and vascularized. Keratinization and pigmentation is an important protection mechanism, due to the protrability of this organ, which is exposed to the environment to capture odors and locate prey. Mucous secretion was present as an important tool for lubrication and protection of the lingual lining. The tongue of the B. jararaca has no papillae and taste buds, being its function strictly olfactory, in association with the vomeronasal organ. [ABSTRACT FROM AUTHOR]

Introduction: The olfactory epithelium (OE) and olfactory bulb (OB) are the major components of the olfactory system and play critical roles in olfactory perception. However, the embryonic development of OE and OB by using the olfactory specific genes has not been comprehensively investigated yet. Most previous studies were limited to a specific embryonic stage, and very little is known, till date, about the development of OE. Methods: The current study aimed to explore the development of mouse olfactory system by spatiotemporal analysis of the histological features by using the olfactory specific genes of olfactory system from the prenatal to postnatal period. Results: We found that OE is divided into endo-turbinate, ecto-turbinate, and vomeronasal organs, and that putative OB with putative main and accessory OB is formed in the early developmental stage. The OE and OB became multilayered in the later developmental stages, accompanied by the differentiation of olfactory neurons. Remarkably, we found the development of layers of olfactory cilia and differentiation of OE to progress dramatically after birth, suggesting that the exposure to air may facilitate the final development of OE. Discussion: Overall, the present study laid the groundwork for a better understanding of the spatial and temporal developmental events of the olfactory system. [ABSTRACT FROM AUTHOR]

Objective: To find out whether the vomeronasal organ (VNO) can be identified in the nose as a mucosal pit in the anterior nasal septum, to elucidate its function in man and to determine whether it is important to preserve the VNO during septal surgery. Methods: Literature review. Results and conclusion: The VNO is histologically present in almost all humans, but a macroscopically visible septal pit does not necessarily correspond with the actual VNO. The human VNO is probably a vestigial organ with a non-operational sensory function. It is not necessary to take particular care not to damage the VNO during septal surgery. [ABSTRACT FROM AUTHOR]

Introduction: Contactin‐6 (CNTN6), also known as NB‐3, is a neural recognition molecule and a member of the contactin subgroup of the immunoglobulin superfamily. Gene encoding CNTN6 is expressed in many regions of the neural system, including the accessory olfactory bulb (AOB) in mice. We aim to determine the effect of CNTN6 deficiency on the function of the accessory olfactory system (AOS). Methods: We examined the effect of CNTN6 deficiency on the reproductive behavior of male mice through behavioral experiments such as urine sniffing and mate preference tests. Staining and electron microscopy were used to observe the gross structure and the circuitry activity of the AOS. Results: Cntn6 is highly expressed in the vomeronasal organ (VNO) and the AOB, and sparsely expressed in the medial amygdala (MeA) and the medial preoptic area (MPOA), which receive direct and/or indirect projections from the AOB. Behavioral tests to examine reproductive function in mice, which is mostly controlled by the AOS, revealed that Cntn6−/− adult male mice showed less interest and reduced mating attempts toward estrous female mice in comparison with their Cntn6+/+ littermates. Although Cntn6−/− adult male mice displayed no obvious changes in the gross structure of the VNO or AOB, we observed the increased activation of granule cells in the AOB and the lower activation of neurons in the MeA and the MPOA as compared with Cntn6+/+ adult male mice. Moreover, there were an increased number of synapses between mitral cells and granule cells in the AOB of Cntn6−/− adult male mice as compared with wild‐type controls. Conclusion: These results indicate that CNTN6 deficiency affects the reproductive behavior of male mice, suggesting that CNTN6 participated in normal function of the AOS and its ablation was involved in synapse formation between mitral and granule cells in the AOB, rather than affecting the gross structure of the AOS. [ABSTRACT FROM AUTHOR]

Cartilaginous fishes are renowned for a keen sense of smell, a reputation based on behavioral observations and supported by the presence of large and morphologically complex olfactory organs. At the molecular level, genes belonging to the four families coding for most olfactory chemosensory receptors in other vertebrates have been identified in a chimera and a shark, but it was unknown whether they actually code for olfactory receptors in these species. Here, we describe the evolutionary dynamics of these gene families in cartilaginous fishes using genomes of a chimera, a skate, a sawfish, and eight sharks. The number of putative OR, TAAR, and V1R/ORA receptors is very low and stable, whereas the number of putative V2R/OlfC receptors is higher and much more dynamic. In the catshark Scyliorhinus canicula , we show that many V2R/OlfC receptors are expressed in the olfactory epithelium in the sparsely distributed pattern characteristic for olfactory receptors. In contrast, the other three vertebrate olfactory receptor families are either not expressed (OR) or only represented with a single receptor (V1R/ORA and TAAR). The complete overlap of markers of microvillous olfactory sensory neurons with pan-neuronal marker HuC in the olfactory organ suggests the same cell-type specificity of V2R/OlfC expression as for bony fishes, that is, in microvillous neurons. The relatively low number of olfactory receptors in cartilaginous fishes compared with bony fishes could be the result of an ancient and constant selection in favor of a high olfactory sensitivity at the expense of a high discrimination capability. [ABSTRACT FROM AUTHOR]

CCL28 is a mucosal chemokine that has been involved in various responses, including IgA production. We have analyzed its production in human tissues using a comprehensive microarray database. Its highest expression is in the salivary gland, indicating that it is an important component of saliva. It is also expressed in the trachea, bronchus, and in the mammary gland upon onset of lactation. We have also characterized a Ccl28-/- mouse that exhibits very low IgA levels in milk, and the IgA levels in feces are also reduced. These observations confirm a role for the CCL28/CCR10 chemokine axis in the recruitment of IgA plasmablasts to the lactating mammary gland. CCL28 is also expressed in the vomeronasal organ. We also detected olfactory defects (anosmia) in a Ccl28-/- mouse suggesting that CCL28 is involved in the function/development of olfaction. Importantly, Ccl28-/- mice are highly susceptible to Salmonella enterica serovar Typhimurium in an acute model of infection, indicating that CCL28 plays a major role in innate immunity against Salmonella in the gut. Finally, microbiome studies revealed modest differences in the gut microbiota between Ccl28-/- mice and their cohoused wild-type littermates. The latter observation suggests that under homeostatic conditions, CCL28 plays a limited role in shaping the gut microbiome.

Lungfish are the most closely related fish to tetrapods. The olfactory organ of lungfish contains lamellae and abundant recesses at the base of lamellae. Based on the ultrastructural and histochemical characteristics, the lamellar olfactory epithelium (OE), covering the surface of lamellae, and the recess epithelium, contained in the recesses, are thought to correspond to the OE of teleosts and the vomeronasal organ (VNO) of tetrapods. With increasing body size, the recesses increase in number and distribution range in the olfactory organ. In tetrapods, the expression of olfactory receptors is different between the OE and VNO; for instance, the type 1 vomeronasal receptor (V1R) is expressed only in the OE in amphibians and mainly in the VNO in mammals. We recently reported that V1R-expressing cells are contained mainly in the lamellar OE but also rarely in the recess epithelium in the olfactory organ of lungfish of approximately 30 cm body length. However, it is unclear whether the distribution of V1R-expressing cells in the olfactory organ varies during development. In this study, we compared the expression of V1Rs in the olfactory organs between juveniles and adults of the African lungfish Protopterus aethiopicus and South American lungfish, Lepidosiren paradoxa. The density of V1R-expressing cells was higher in the lamellae than in the recesses in all specimens evaluated, and this pattern was more pronounced in juveniles than adults. In addition, the juveniles showed a higher density of V1R-expressing cells in the lamellae compared with the adults. Our results imply that differences in lifestyle between juveniles and adults are related to differences in the density of V1R-expressing cells in the lamellae of lungfish. [ABSTRACT FROM AUTHOR]

Simple Summary: Adult male giraffes (Giraffa giraffa angolensis) are far larger than the females; they also carry a sizable head and neck. Observations were made at the Namutoni waterholes, Etosha National Park in Namibia, to monitor males testing the females for sexual receptivity. Lacking estrous signals, males provoke females to urinate by sniffing and prodding them. If the female is going to urinate, she first widens her hindleg stance and sets a stable posture, and then urinates. The male gathers the urine in his mouth with his tongue and then frequently performs flehmen to assess her estrous status. The giraffe is unusual in never investigating urine on the ground. Giraffes have papillae on their hard palate that each open to a nasopalatine duct that enters the vomeronasal organ (VNO), which is used for pheromone assessment. Unusually, giraffes were found to lack a prominent nasal connection to the VNO. Many giraffes also spent extensive time periods seeking bones, chewing them, and some got into trouble from having bones lodged in their mouth. A dark giraffe was apparently killed by two lions, after which a steady procession of giraffes arrived for some days to investigate the carcass. A dark giraffe bull emitted loud, pulsed warning calls that resulted in the giraffes fleeing the area. 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. [ABSTRACT FROM AUTHOR]

Introduction: The olfactory system in most mammals is divided into several subsystems based on the anatomical locations of the neuroreceptor cells involved and the receptor families that are expressed. In addition to the main olfactory system and the vomeronasal system, a range of olfactory subsystems converge onto the transition zone located between the main olfactory bulb (MOB) and the accessory olfactory bulb (AOB), which has been termed the olfactory limbus (OL). The OL contains specialized glomeruli that receive noncanonical sensory afferences and which interact with the MOB and AOB. Little is known regarding the olfactory subsystems of mammals other than laboratory rodents. Methods: We have focused on characterizing the OL in the red fox by performing general and specific histological stainings on serial sections, using both single and double immunohistochemical and lectin-histochemical labeling techniques. Results: As a result, we have been able to determine that the OL of the red fox (Vulpes vulpes) displays an uncommonly high degree of development and complexity. Discussion: This makes this species a novel mammalian model, the study of which could improve our understanding of the noncanonical pathways involved in the processing of chemosensory cues. [ABSTRACT FROM AUTHOR]

Lungfish are the fish related most closely to tetrapods. The olfactory organ of lungfish contains two distinct sensory epithelia: the lamellar olfactory epithelium (OE) and the recess epithelium (RecE). Based on their ultrastructural and histological characteristics, the lamellar OE and the RecE are considered to correspond respectively to the teleost OE and a primitive vomeronasal organ (VNO). In tetrapods, the OE and VNO have been shown to express different families of olfactory receptors; for example, in mammals, the OE expresses odorant receptors and trace amine‐associated receptors, while the VNO expresses type 1 (V1Rs) and type 2 (V2Rs) vomeronasal receptors. In the present study, we examined the expression of V1Rs in the olfactory organs of two African lungfish, Protopterus annectens and Protopterus amphibius. RNA sequencing and phylogenetic analyses identified 29 V1R genes in P. annectens and 50 V1R genes in P. amphibius. Most V1Rs identified in these lungfish were classified as the tetrapod‐type V1Rs initially found in tetrapods and distinct from fish‐type V1Rs. In teleost, which all lack a VNO, all olfactory receptors are expressed in the OE, while in Xenopus V1Rs are expressed exclusively in the OE, and not in the VNO. In situ hybridization analysis indicated that lungfish V1Rs were expressed mainly in the lamellar OE and rarely in the RecE. These results imply that V1R expression in lungfish represents an intermediate step toward the complete segregation of V1R expression between the OE and VNO, reflecting the phylogenetic position of lungfish between teleosts and amphibians. [ABSTRACT FROM AUTHOR]

Chemosensory cues are vital for social and sexual behaviours and are primarily detected and processed by the vomeronasal system (VNS), whose plastic capacity has been investigated in mice. However, studying chemosensory plasticity outside of laboratory conditions may give a more realistic picture of how the VNS adapts to a changing environment. Rabbits are a well-described model of chemocommunication since the discovery of the rabbit mammary pheromone and their vomeronasal organ (VNO) transcriptome was recently characterised, a first step to further study plasticity-mediated transcriptional changes. In this study, we assessed the plastic capacity of the rabbit male and female VNO under sex-separation vs. sex-combined scenarios, including adults and juveniles, to determine whether the rabbit VNO is plastic and, if so, whether such plasticity is already established at early stages of life. First, we characterised the number of differentially expressed genes (DEGs) between the VNO of rabbit male and female under sex-separation and compared it to sex-combined individuals, both in adults and juveniles, finding that differences between male and female were larger in a sex-separated scenario. Secondly, we analysed the number of DEGs between sex-separated and sexcombined scenarios, both in males and females. In adults, both sexes showed a high number of DEGs while in juveniles only females showed differences. Additionally, the vomeronasal receptor genes were strikingly downregulated in sex-separated adult females, whereas in juveniles upregulation was shown for the same condition, suggesting a role of VRs in puberty onset. Finally, we described the environment-modulated plastic capacity of genes involved in reproduction, immunity and VNO functional activity, including G-protein coupled receptors. Our results show that sex-separation induces sex- and stage-specific gene expression differences in the VNO of male and female rabbit, both in adults and juveniles. These results bring out for the first time the plastic capacity of the rabbit VNO, supporting its functional adaptation to specifically respond to a continuous changing environment. Finally, speciesspecific differences and individual variability should always be considered in VNO studies and overall chemocommunication research. [ABSTRACT FROM AUTHOR]