The Human Vomeronasal (Jacobson's) Organ: A Short Review of Current Conceptions, With an English Translation of Potiquet's Original Text.

The vomeronasal organ (VNO) is a structure located in the anteroinferior portion of the nasal septum and is part of the accessory olfactory system. The VNO, together with its associated structures, has been shown to play a role in the formation of social and sexual behavior in animals, thanks to its pheromone receptor cells and the stimulating effect on the secretion of gonadotropin-releasing hormone. The VNO was first described as a structure by the Dutch botanist and anatomist Frederik Ruysch in 1703 while dissecting a young male cadaver. This finding, however, is widely contradicted due to no elaborate descriptions being made by the Ruysch. The description of the VNO is more widely attributed to the Danish surgeon Ludwig Jacobson, with whom the VNO has been synonymized, as in 1803 he described the structure in a variety of mammals. Whilst Jacobson extensively studied prior reports of the VNO, he publicly denied its existence in humans. Following these discoveries and some contradictory statements in 1891, M. Potiquet published one of the more influential reviews on the topic. To this day, despite the first report of the organ's existence being made in a human and many articles stating its presence and supporting its function, the presence of a VNO in humans is still widely debated upon.

Introduction and background

In humans, the vomeronasal organ (VNO), also known as (Jacobson’s) organ is an accessory olfactory organ situated on the anteroinferior third of the nasal septum [1]. It consists of a blind sac with a duct opening anteriorly, both supplied with a rich vascular and glandular network. The organ contains specialized olfactory sensory cells or esthesiocytes, which function both as afferent neurons in the reception of pheromones via the terminal cranial nerve and also produces gonadotropin-releasing hormone.

Review

Discovery

The VNO was first recorded by Dutch anatomist Frederick Ruysh, who made a very clear depiction of it in his line diagram of the dissection of a recently deceased two-year-old male cadaver [1]. The diagram depicts a vomeronasal organ; however, Ruysh never made any specific reference to it.

Over the following decades, other anatomists made mention of this same structure [1,2]. However, since the VNO was much larger in domestic and wild animals, research was primarily aimed at the mammalian counterpart.

The vomeronasal organ was formerly known (and often still is) by the eponymous name of the Danish anatomist, Ludwin Jacobson, later translated into anatomical Latin (and then English), by the Swiss anatomist Wilhelm His as Ludwig Jacobson [3]. Much confusion still surrounds Jacobson’s contribution and over the years he has been misquoted by a number of subsequent researchers [4,5]. This could well be due to the fact that Jacobson’s original seminal work, published in 1813 was not very accessible; it was printed in Gothic script and in Danish and remained almost unknown [6]. It was not until 1950 that it was translated into French by Danish scholars, but only 150 copies of that version were made and it too remained mainly unacknowledged. Eventually, it was discovered in the library of the Agricultural University of Copenhagen and translated in 1998 by two Europeans, Trotier and Døving [7].

The title of Jacobson’s paper was “Anatomical Description of a New Organ in the Nose of Domesticated Animals” and there is no dispute about his discovery of the anatomical feature in mammals [6,7]. Where the later confusion arises is when subsequent workers refer to humans. Jacobson neither discovered the human vomeronasal organ nor did he refute its existence in homo sapiens: he mentions it twice in his paper. He says, “in the monkeys, it becomes so small that we are prepared to see it vanish completely in man” and further, that humans, who possess a very well-developed sense of taste, have only a rudiment of the organ.

Human vomeronasal organ

The function (and in some cases the existence) of Jacobson's organ is still the subject of heated controversy [8]. There is little doubt however that the VNO is present in humans (Figures 1-3). Since its discovery, it has been reported using different modalities: direct and endoscopic observation (in vivo and cadaveric); imaging modalities – computed tomography (CT) and magnetic resonance imaging (MRI) (with and without contrast); histological – classical stains and on electron microscopy [9-15].

Figure 1

Endoscopic view of the human vomeronasal organ located on the right side of the nasal septum (arrow)

Figure 3

Histology of the human vomeronasal organ on the nasal septum of a 17th gestational week human fetus with ciliated estheziocytes, supporting cells and ganglion cells

Hematoxilin and Eosin, original magnification 400x

3D reconstruction of the nasal septum from a CT scan of the patient from the previous figure with the vomeronasal organ visible (arrow)

3D: three dimensional; CT: computer tomography

Despite this abundant evidence, this small and insignificant anatomical feature is nonetheless often still overlooked by contemporary otorhinolaryngologists in the clinical examination of the anterior nares.

Although a constant incidence has been found in different adult populations around the world (Bulgaria, Canada, Egypt, France, Mexico, and the United States of America), studies have shown it to be present (at least unilaterally and predominantly on the left side) in around one third of the population [9-11, 15-18]. Reports suggest that it is more commonly found in children [6, 16-18]. Some studies claim that it is present in over two-thirds of young people, with an increased incidence bilaterally, whilst other researchers suggest that it is present on both sides of the septum in almost all newborn babies [14, 18-19].

Function in humans

Human studies using an evoked electrical potential in the nasal mucosa (electrovomeronasogram) have claimed to demonstrate a definite receptor function of the VNO, but there is also genetic evidence to the contrary claiming that genes which code for vomeronasal receptor proteins and the specific ionic channels involved in the transduction process are mutated and nonfunctional in humans [19].

Claims that surgery in the septal area of Jacobson’s pit might cause possible changes in sexual behavior are clearly of great concern to rhinologists [19]. These worries are reinforced by the findings that the neural bodies in the terminal nerve liberate gonadotrophin-releasing hormone in response to stimulation of the VNO.

The connections of the terminal nerve (also known as cranial nerve N) to the VNO is the latest factor in the ongoing controversy surrounding Jacobson’s organ [9]. Although the nerve has received much attention in non-primates (where it is relatively much bigger in size), studies of both its structure and function have been comparatively neglected in humans [20-21].

Another recent interesting finding is the implication that the accessory olfactory system may play a role in the development and treatment of post-traumatic stress disorder.

Yet another intriguing suggestion was made in 1891 in this paper by the French surgeon, Potiquet [22].

After more than three centuries of debate on the topic, the vomeronasal organ continues to incite controversy and argument.

Questions undeniably remain unresolved about its function in humans and its role in the development of sexual and social behavior as a whole. However, there are some indisputable facts. One such is the presence of ectopic esthesioneuroblastoma, a rare type of malignant tumor developing from olfactory neuroepithelial cells. This most often arises in the areas containing olfactory neuroepithelium, (adjacent to lamina cribrosa, the superior aspect of the nasal septum, and the superior nasal concha). However, there have been rare reports of this malignancy developing in the area of Jacobson's duct. Since there are no esthesioblasts normally found at this site, this would definitely suggest that the VNO is an accessory nasal area in humans.

Further possible tenuous evidence comes from the theory of the pneumatization of the vomer. It has been posited that a "pumping" mechanism leads to pneumatization of the vomer and in this case, the formation of the vomeronasal duct.

Conclusions

Although it is a very small and somewhat obscure (and undoubtedly very neglected) anatomical landmark, the vomeronasal organ remains a hot controversial topic for research both to the intimacies of the structure, its functions, and connections to other systems in both humans and animals.