Frequency and localization of the putative vomeronasal organ in humans in relation to age and gender

The clinical significance of the human vomeronasal organ

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.

Evidence for accessory chemosensory cells in the adult human nasal cavity

The existence of functionally relevant accessory olfactory organs in humans is still a matter of controversy. A vomeronasal organ (VNO) with sensory and non-sensory epithelia exists only in macrosmatic mammals. A similar structure is regularly observed in humans during fetal development. The postnatal persistence of a VNO like epithelial duct has been described in about 10 %. Here we studied tissue samples of nasal mucosa from adults. In all individuals we found epithelial cells in the lower part of the nasal septum which exhibited morphological features of sensory neurons and which showed immunostaining for olfactory marker protein OMP. These cells were interposed by ciliated cells, goblet cells and small intraepithelial capillaries. Only occasionally we found such cells within a morphologically defined epithelial duct. A clear separation of sensory and non-sensory epithelia could not be observed. In most cases we found OMP positive groups of cells either in epithelial cavities or just embedded in respiratory epithelium. With RT-PCR we could confirm the presence of OMP encoding mRNA thus supporting the idea of intrinsic expression of this protein in the nasal mucosa. We conclude that accessory chemosensory structures are regularly conserved in adult humans in the approximate anatomical location of the VNO of microsmatic animals. Their functional importance is yet to be determined.

Anatomy of the olfactory mucosa

The classic notion that humans are microsmatic animals was born from comparative anatomy studies showing the reduction in the size of both the olfactory bulbs and the limbic brain relative to the whole brain. However, the human olfactory system contains a number of neurons comparable to that of most other mammals, and humans have exquisite olfactory abilities. Major advances in molecular and genetic research have resulted in the identification of extremely large gene families that express receptors for sensing odors. Such advances have led to a renaissance of studies focused on both human and nonhuman aspects of olfactory physiology and function. Evidence that olfactory dysfunction is among the earliest signs of a number of neurodegenerative and neuropsychiatric disorders has led to considerable interest in the use of olfactory epithelial biopsies for potentially identifying such disorders. Moreover, the unique features of the olfactory ensheathing cells have made the olfactory mucosa a promising and unexpected source of cells for treating spinal cord injuries and other neural injuries in which cell guidance is critical. The olfactory system of humans and other primates differs in many ways from that of other species. In this chapter we provide an overview of the anatomy of not only the human olfactory mucosa but of mucosae from a range of mammals from which more detailed information is available. Basic information regarding the general organization of the olfactory mucosa, including its receptor cells and the large number of other cell types critical for their maintenance and function, is provided. Cross-species comparisons are made when appropriate. The polemic issue of the human vomeronasal organ in both the adult and fetus is discussed, along with recent findings regarding olfactory subsystems within the nose of a number of mammals (e.g., the septal organ and Grüneberg ganglion).

The Human Vomeronasal Organ: Part IV. Incidence, Topography, Endoscopy, and Ultrastructure of the Nasopalatine Recess, Nasopalatine Fossa, and Vomeronasal Organ

Background

Previous reports on the human vomeronasal organ (VNO) have been inconsistent. Observations of fossae on the nasal septum have been reported as the VNO.

Methods

Adult human subjects (210) and cadavers (31) were examined using rigid nasal endoscopy, serial histology, and biopsy ultrastructure (5).

Results

The nasopalatine fossa (NPF) and the nasopalatine recess (NPR) are discrete, but variable, structures located adjacent to the VNO region. The NPF is not a vomeronasal pit. A septal mucosal pit could hide the vomeronasal duct opening. The VNO is a submucosal structure located 2–8 mm superior to the NPR and cannot be positively identified either macroscopically or endoscopically.

Conclusion

The VNO has long been mistaken for the NPF and septal mucosal pits. We show that serial histology is the correct method for identifying the VNO.

Human Body Scents: Do they Influence our Behavior?

Pheromonal communication in the animal world has been of great research interest for a long time. While extraordinary discoveries in this field have been made, the importance of the human sense of smell was of far lower interest. Humans are seen as poor smellers and therefore research about human olfaction remains quite sparse compared with other animals. Nevertheless amazing achievements have been made during the past 15 years. This is a collection of available data on this topic and a controversial discussion on the role of putative human pheromones in our modern way of living. While the focus was definitely put on behavioral changes evoked by putative human pheromones this article also includes other important aspects such as the possible existence of a human vomeronasal organ. If pheromones do have an influence on human behavior there has to be a receptor organ. How are human body scents secreted and turned into odorous substances? And how can con-specifics detect those very odors and transmit them to the brain? Apart from that the most likely candidates for human pheromones are taken on account and their impact on human behavior is shown in various detail.

The vomeronasal organ is not involved in the perception of endogenous odors

Chemosensory-based communication is a vital signaling tool in most species, and evidence has recently emerged in support of the notion that humans also use social chemosignals (so-called pheromones) to communicate. An ongoing controversy does exist, however, concerning the receptor organ through which these chemicals are processed. There is a widespread belief that the vomeronasal organ (VNO) is responsible for processing social chemosignals in humans. Here we demonstrate that functional occlusion of the VNO does not change the percept of, sensitivity toward, or functional neuronal processing of a putative human pheromone. Perithreshold and suprathreshold perception of the endogenous chemical androstadienone (AND) were compared, as were positron emission tomography brain activations evoked by AND when the VNO was either occluded or left open. In addition, we compared sensitivity to AND in subjects with an identifiable VNO to those in whom no VNO could be detected. Thus we could examine the effects of the VNO at several different levels of processing. Occlusion or absence of the VNO did not affect either the perceptual measurements or the functional processing of the putative human pheromone, AND. These results provide strong evidence that the human VNO has no obvious function. Pheromonal communication in humans may be conveyed via the main olfactory system.

Electrical responses to chemosensory stimulation recorded from the vomeronasal duct and the respiratory epithelium in humans

The physiological significance of the human vomeronasal duct (VND) is still unclear. The aim of the present study was to investigate the question whether mucosal responses obtained from the VND are different from those obtained from the respiratory epithelium. There were 15 healthy subjects (8 male, 7 female; age range 19-45 years; 14 normosmic subjects, 1 anosmic subject). All subjects participated in two sessions whereby the first session was used to acquaint them with the experimental conditions. For chemical stimulation, an olfactometer was used which delivered chemical stimulants without altering mechanical or thermal conditions at the stimulated nasal mucosa. For stimulation we used substances previously reported to produce vomeronasal activation ("estra"=estra-1,3,5(10),16-tetraen-3ol and "andro"=androsta-4,16-dien-3-on); in addition, gaseous CO(2) was used as a non-odorous, relatively specific stimulant of the trigeminal nerve. Placement of electrodes either in the VND or on the respiratory epithelium was performed under endoscopical guidance. Subjects rated the overall intensity of the stimuli, the strength of trigeminally mediated sensations, and the hedonic tone of the stimulants. Responses could not be recorded from all subjects. For the remaining 7 subjects, intensity was strongest for CO(2) stimuli (p<0.001), whereas no significant difference was observed between "andro" and "estra" (p=0.33). All three stimulants produced responses at the respiratory epithelium with largest responses obtained after stimulation with CO(2). Similar findings were made for recordings inside the VND. Due to the small sample size sexual dimorphisms could not be addressed. In summary, these results seem to indicate that the presently used stimulants produce similar responses at the respiratory epithelium and in the VND which argues against a specific responsiveness of the VND epithelium to chemosensory stimuli although it has to be kept in mind that the effective sample size was small.

Cladistic analysis of olfactory and vomeronasal systems

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

The risk of extrapolation in neuroanatomy: the case of the Mammalian vomeronasal system

The sense of smell plays a crucial role in mammalian social and sexual behaviour, identification of food, and detection of predators. Nevertheless, mammals vary in their olfactory ability. One reason for this concerns the degree of development of their pars basalis rhinencephali, an anatomical feature that has been considered in classifying this group of animals as macrosmatic, microsmatic or anosmatic. In mammals, different structures are involved in detecting odours: the main olfactory system, the vomeronasal system (VNS), and two subsystems, namely the ganglion of Grüneberg and the septal organ. Here, we review and summarise some aspects of the comparative anatomy of the VNS and its putative relationship to other olfactory structures. Even in the macrosmatic group, morphological diversity is an important characteristic of the VNS, specifically of the vomeronasal organ and the accessory olfactory bulb. We conclude that it is a big mistake to extrapolate anatomical data of the VNS from species to species, even in the case of relatively close evolutionary proximity between them. We propose to study other mammalian VNS than those of rodents in depth as a way to clarify its exact role in olfaction. Our experience in this field leads us to hypothesise that the VNS, considered for all mammalian species, could be a system undergoing involution or regression, and could serve as one more integrated olfactory subsystem.

A direct main olfactory bulb projection to the 'vomeronasal' amygdala in female mice selectively responds to volatile pheromones from males

The main olfactory system, like the accessory olfactory system, responds to pheromones involved in social communication. Whereas pheromones detected by the accessory system are transmitted to the hypothalamus via the medial ('vomeronasal') amygdala, the pathway by which pheromones are detected and transmitted by the main system is not well understood. We examined in female mice whether a direct projection from mitral/tufted (M/T) cells in the main olfactory bulb (MOB) to the medial amygdala exists, and whether medial amygdala-projecting M/T cells are activated by volatile urinary odors from conspecifics or a predator (cat). Simultaneous anterograde tracing using Phaseolus vulgaris leucoagglutinin and Fluoro-Ruby placed in the MOB and accessory olfactory bulb (AOB), respectively, revealed that axons of MOB M/T cells projected to superficial laminae of layer Ia in anterior and posterodorsal subdivisions of the medial amygdala, whereas projection neurons from the AOB sent axons to non-overlapping, deeper layer Ia laminae of the same subdivisions. Placement of the retrograde tracer cholera toxin B into the medial amygdala labeled M/T cells that were concentrated in the ventral MOB. Urinary volatiles from male mice, but not from female conspecifics or cat, induced Fos in medial amygdala-projecting MOB M/T cells of female subjects, suggesting that information about male odors is transmitted directly from the MOB to the 'vomeronasal' amygdala. The presence of a direct MOB-to-medial amygdala pathway in mice and other mammals could enable volatile, opposite-sex pheromones to gain privileged access to diencephalic structures that control mate recognition and reproduction.

[The existence vomeronasal organ in adult humans]

The influence of chemical substances (feromones) on human emotional and physical condition has fascinated psychologists, sexuologists and laryngologists since centurie. Literature conveys inconsistent information on vomeronasal organ (VNO) occurrence in humans. This organ is often called Jacobson's, and 2 symmetrical openings leading into it, located on both sides of septum, are called Ruyasch's ducts. The aim of the study was to analyze vomeronasal organ occurrence in humans in relation to age and sex. The study was conducted in a group of 634 patients, aged 18-80 years. All patients underwent routine ENT examination including rhinoscopy, nasal cavity examination with usage of 2.5x magnification lens (surgical glasses) and surgical microscope with 10x magnification. All persons had nasal cavities examined endoscopically. Every time presence of vomeronasal organ openings, along with localization, size and symmetry of these was noted. Subjects, who presented Jacobson's organ, were asked to fill a questionnaire concerning influence of smells on erotic sensations. Vomeronasal organ was fund in 312 persons, that is 49.21%. In 83.65% of cases vomeronasal organ opening size was smaller than 0.2 mm, what restricted its visibility to usage of magnifying lens, microscope, or endoscope. In 16.34% of cases only vomeronasal organ ducts openings were well visible in routine rhinoscopy without magnification. Vomeronasal organ was found more often in men than women. VNO was significantly more rare in patients with nasal septal deviation. In these cases, vomeronasal organ was usually found unilaterally, in all the cases on the concave side of deviated nasal septum.

Vomeronasal versus olfactory epithelium: is there a cellular basis for human vomeronasal perception?

The vomeronasal organ (VNO) constitutes an accessory olfactory organ that receives chemical stimuli, pheromones, which elicit behavioral, reproductive, or neuroendocrine responses among individuals of the same species. In many macrosmatic animals, the morphological substrate constitutes a separate organ system consisting of a vomeronasal duct (ductus vomeronasalis, VND), equipped with chemosensory cells, and a vomeronasal nerve (nervus vomeronasalis, VNN) conducting information into the accessory olfactory bulb (AOB) in the central nervous system (CNS). Recent data require that the long-accepted dual functionality of a main olfactory system and the VNO be reexamined, since all species without a VNO are nevertheless sexually active, and species possessing a VNO also can sense other than "vomeronasal" stimuli via the vomeronasal epithelium (VNE). The human case constitutes a borderline situation, as its embryonic VNO anlage exerts a developmental track common to most macrosmatics, but later typical structures such as the VNN, AOB, and probably most of the chemoreceptor cells within the still existent VND are lost. This review also presents recent information on the VND including immunohistochemical expression of neuronal markers, intermediate filaments, lectins, integrins, caveolin, CD44, and aquaporins. Further, we will address the issue of human pheromone candidates.

Enlarged vomeronasal organ in a child: imaging findings

The vomeronasal organ is a special sensory organ that exists in both animals and humans. It is located on the sides of nasal septum and although it involutes with age, occasionally it may be seen in humans. We present the imaging findings in a child with an enlarged nasal septum whose features we believe are compatible with a vomeronasal organ.

Basic and clinical aspects of olfaction

Disturbances of olfaction are a common occurrence in many neurological and neurosurgical patients and their correct diagnosis might be helpful in management and enhancement of quality of life. However, olfaction is seldom checked in most neurosurgical units and the "smell bottles" are often either absent or out of date. This chapter reviews systematically recent advances in our understanding of the anatomy, physiology (olfactory coding) and measurement of olfactory function in the human. The causes and symptoms of smell disorders, risk of damage to the olfactory system by various surgical procedures and, finally, the natural history of recovery and treatment of smell disorders, for example after trauma, are discussed.

The existence of the vomeronasal organ in human beings

The frequency, location, and function of the vomeronasal organ, also known as the Jacopson organ, in human beings remains poorly understood. In this study, a search for the frequency of the vomeronasal organ was performed by nasal examinations of 346 adult patients and 21 cadaver heads by anterior rhinoscopy and videotaped rigid 30 degrees endoscopy. The vomeronasal organ was identified in 112 patients (32%) and in 8 cadaver heads (38%). The location, shape, type, and relation to sex of the vomeronasal organ were described. Ten specimens were examined histologically and histochemically for neuron-specific enolase (anti-neuron-specific enolase), high-molecular-weight cytokeratin (anti-high-molecular-weight cytokeratin), and low-molecular-weight cytokeratin (anti-low-molecular-weight cytokeratin). Considering its variability in shape and the lack of immunohistochemical characteristics of nerve tissue, the present results are not suited to argue for functional significance of the vomeronasal organ in human beings.

[The human vomeronasal organ]

Odors influence human behavior. The perception of so-called pheromones is frequently mentioned in the context of a functional vomeronasal organ. Vomeronasal ducts can be detected in approximately half of the population. Its functionality, still a matter of debate, seems to be unlikely, at least after birth. It is easily conceivable that pheromone-induced changes in behavior are mediated through receptors in the human olfactory epithelium.

Assessment of olfactory function and androstenone odor thresholds in humans with or without functional occlusion of the vomeronasal duct

To obtain information on the possible role of the vomeronasal duct (VND) in odor perception and human pheromone detection, the present study investigated different aspects of olfactory function, including thresholds for androstenone in adults with or without detectable VNDs. The study also examined correlations between detection thresholds of androstenone odor and general olfactory function. Subjects' olfaction was assessed with tests for odor identification, odor discrimination, and phenyl ethyl alcohol odor threshold. Measurements were performed on 1 side only, with and without covering the VND. Subjects with or without detectable VNDs did not differ in olfactory sensitivity or androstenone odor thresholds. A small but significant correlation was found between detection thresholds of androstenone and general olfactory function. Finally, covering of the VND did not affect olfactory function or androstenone sensitivity. Results suggest that the human VND does not play a major role in sensitivity toward odorants or the perception of androstenone.

Anatomical position of the vomeronasal organ in postnatal humans

In the last decade or so, there has been a renewed interest in the adult human vomeronasal organ (VNO). Studies have yielded sometimes disparate findings about the microscopic structure of the organ and its supporting tissues. Such varied descriptions may be due to examination of different regions of the VNO, individual variation of VNOs among humans, or the presence of multiple, non-homologous structures that bear false resemblance to the human VNO. A histological description of the spatial relationship of the human VNO to other nasal septal elements is needed to ensure that all investigators are examining the same regions and homologous structures. Histologically sectioned nasal septa from, 22 human cadavers (1 child, 21 adults) were examined grossly and by light microscopy for the VNO. Using histological sections, the position of the VNO relative to other structures was estimated. Sections containing the VNO were retrospectively compared to scaled photographic slides of the unsectioned septa to identify surface landmarks. Human VNOs varied in anteroposterior and superoinferior position relative to the anterior nasal spine and the nasal cavity floor. In the absence of a visible duct opening, the only reliable surface marker, no consistent surface markings were noted for precise location. VNOs were frequently found superior to swellings associated with the paraseptal and/or septal cartilages. Such findings demonstrate that the human VNO is positionally variable, which may have contributed to previous conflicting findings on presence versus absence. Furthermore, our findings support recent suggestions that the VNO may have been misidentified by some investigators, and that its opening can be easily confused with other structures.