View source for Vomeronasal organ

{{Short description|Smell sense organ above the roof of the mouth}}
{{Infobox anatomy
| Name        = Vomeronasal organ
| Latin       = organum vomeronasale
| Image       = Gray51.png
| Caption     = Frontal section of nasal cavities of a human embryo 28 mm long (vomeronasal organ labeled at right)
| Width       =
| Image2      =
| Caption2    =
| Precursor   = [[Nasal placode]]
| System      =
| Artery      =
| Vein        =
| Nerve       =
| Lymph       = Node
}}

The '''vomeronasal organ''' ('''VNO'''), or '''Jacobson's organ''', is the paired auxiliary [[olfactory]] (smell) [[sense organ]] located in the [[soft tissue]] of the [[nasal septum]], in the [[nasal cavity]] just above the roof of the mouth (the [[hard palate]]) in various [[tetrapods]].<ref>Nakamuta S, Nakamuta N, Taniguchi K, Taniguchi K. Histological and ultrastructural characteristics of the primordial vomeronasal organ in lungfish. Anat Rec (Hoboken). 2012 Mar;295(3):481-91. doi: 10.1002/ar.22415. Epub 23 January 2012 PMID 22271496.</ref> The name is derived from the fact that it lies adjacent to the unpaired [[vomer]] bone (from Latin {{wikt-lang|la|vomer}} {{gloss|plowshare}}, for its shape) in the nasal septum. It is present and functional in all [[snake]]s and [[lizard]]s, and in many [[mammal]]s, including [[cat]]s, [[dog]]s, [[cattle]], [[pig]]s, and some [[primate]]s. [[Human]]s may have physical remnants of a VNO, but it is [[vestigial]] and non-functional.<ref>{{cite journal | pmc=4843235 | date=2016 | last1=Vasuki | first1=A. K. | last2=Fenn | first2=T. K. | last3=Devi | first3=M. N. | last4=Hebzibah | first4=T. D. | last5=Jamuna | first5=M. | last6=Sundaram | first6=K. K. | title=Fate and Development of Human Vomeronasal Organ – A Microscopic Fetal Study | journal=Journal of Clinical and Diagnostic Research | volume=10 | issue=3 | pages=AC08–AC11 | doi=10.7860/JCDR/2016/15930.7373 | pmid=27134849 }}</ref>

The VNO contains the [[cell bodies]] of [[sensory neuron]]s which have receptors that detect specific [[Volatility (chemistry)|non-volatile]] (liquid) [[organic compound]]s which are conveyed to them from the environment. These compounds emanate from [[prey]], [[predator]]s, and the compounds called [[sex pheromone]]s from potential [[Mating|mates]]. Activation of the VNO triggers an appropriate behavioral response to the presence of one of these three.

VNO neurons are activated by the binding of certain chemicals to their [[G protein-coupled receptor]]s: they express receptors from three families, called V1R,<ref name="pmid7585937">{{cite journal | vauthors = Dulac C, Axel R | title = A novel family of genes encoding putative pheromone receptors in mammals | journal = Cell | volume = 83 | issue = 2 | pages = 195–206 | date = October 1995 | pmid = 7585937 | doi = 10.1016/0092-8674(95)90161-2 | s2cid = 18784638 | doi-access = free }}</ref><ref name="pmid9288756">{{cite journal | vauthors = Matsunami H, Buck LB | title = A multigene family encoding a diverse array of putative pheromone receptors in mammals | journal = Cell | volume = 90 | issue = 4 | pages = 775–784 | date = August 1997 | pmid = 9288756 | doi = 10.1016/s0092-8674(00)80537-1 | s2cid = 14898961 | doi-access = free }}</ref><ref name="pmid9292726">{{cite journal | vauthors = Ryba NJ, Tirindelli R | title = A new multigene family of putative pheromone receptors | journal = Neuron | volume = 19 | issue = 2 | pages = 371–379 | date = August 1997 | pmid = 9292726 | doi = 10.1016/S0896-6273(00)80946-0 | hdl-access = free | s2cid = 18615918 | hdl = 11381/2435950 }}</ref> V2R, and FPR.<ref name="Rivière_2009" /><ref name="pmid19497865">{{cite journal | vauthors = Liberles SD, Horowitz LF, Kuang D, Contos JJ, Wilson KL, Siltberg-Liberles J, Liberles DA, Buck LB | display-authors = 6 | title = Formyl peptide receptors are candidate chemosensory receptors in the vomeronasal organ | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106 | issue = 24 | pages = 9842–9847 | date = June 2009 | pmid = 19497865 | pmc = 2690606 | doi = 10.1073/pnas.0904464106 | doi-access = free | bibcode = 2009PNAS..106.9842L }}</ref> The [[axon]]s from these neurons, called [[cranial nerve zero]] (CN 0), project to the [[Olfactory bulb#Accessory olfactory bulb|accessory olfactory bulb]], which targets the [[amygdala]] and [[bed nucleus of the stria terminalis]], which in turn project to the [[anterior hypothalamus]]. These structures constitute the [[accessory olfactory system]].

The VNO triggers the [[flehmen response]] in some mammals, which helps direct liquid organic chemicals to the organ. The VNO was discovered by [[Frederik Ruysch]] prior to 1732, and later by [[Ludwig Jacobson]] in 1813.<ref name="Jacobson, L. 1813">Jacobson, L. (1813). Anatomisk Beskrivelse over et nyt Organ i Huusdyrenes Næse. Veterinær=Selskapets Skrifter [in Danish] 2,209–246.</ref>

==Structure==
===The organ===
[[File:Jacobson's organ in a reptile.svg|thumbnail|right|Placement of Jacobson's organ in a snake]]
The VNO is found at the base of the [[nasal cavity]]. It is split into two, being divided by the nasal septum, with both sides possessing an elongated C-shaped, or crescent, [[Lumen (anatomy)|lumen]]. It is encompassed inside a bony or cartilaginous capsule which opens into the base of the nasal cavity.<ref>{{Cite web |url=http://www.neuro.fsu.edu/~mmered/vomer/ |title=The Vomeronasal Organ |first=Michael |last=Meredith |work=FSU Program in Neuroscience |publisher=[[Florida State University]] |access-date=2013-05-27 |archive-url=https://web.archive.org/web/20130211023317/http://www.neuro.fsu.edu/~mmered/vomer/ |archive-date=2013-02-11 |url-status=dead }}</ref>

===The system===
The vomeronasal receptor neurons possess [[axon]]s which travel from the VNO to the [[Olfactory bulb#Accessory olfactory bulb|accessory olfactory bulb]] (AOB), also known as the vomeronasal bulb. These sensory receptors are located on the medial concave surface of the crescent lumen. The lateral, convex surface of the lumen is covered with non-sensory ciliated cells, where the basal cells are also found. At the dorsal and ventral aspect of the lumen are vomeronasal glands, which fill the vomeronasal lumen with fluid. Sitting next to the lumen are blood vessels that dilate or constrict, forming a vascular pump that deliver stimuli to the lumen. A thin duct, which opens onto the floor of the nasal cavity inside the [[nostril]], is the only way of access for stimulus chemicals.

During embryological development, the vomeronasal sensory neurons form from the nasal (olfactory) [[placode]], at the anterior edge of the neural plate ([[cranial nerve zero]]).

===Sensory epithelium and receptors===
The VNO is a tubular crescent shape and split into two pairs, separated by the [[nasal septum]]. The medial, concave area of the lumen is lined with a pseudo stratified [[epithelium]] that has three main cell types: receptor cells, supporting cells, and basal cells. The supporting cells are located superficially on the membrane while the basal cells are found on the basement membrane near the non-[[wikt:sensory|sensory]] epithelium. The receptor neurons possess apical [[microvilli]], to which the sensory receptors are localized. These are [[G-protein-coupled receptor]]s, which are often referred to as [[pheromone]] receptors since vomeronasal receptors have been tied to detecting pheromones.

Three G-protein-coupled receptors have been identified in the VNO, each found in distinct regions: the V1Rs, V2Rs, and FPRs. V1Rs, V2Rs and FPRs are seven transmembrane receptors which are not closely related to odorant receptors expressed in the main olfactory neuroepithelium.<ref>{{cite journal | vauthors = Tirindelli R, Dibattista M, Pifferi S, Menini A | title = From pheromones to behavior | journal = Physiological Reviews | volume = 89 | issue = 3 | pages = 921–956 | date = July 2009 | pmid = 19584317 | doi = 10.1152/physrev.00037.2008 | citeseerx = 10.1.1.460.5566 }}</ref>

* V1 receptors, V1Rs, are linked to the G protein, [[Gαi2]]. The benefit of the GPCR is that they signal in more than one direction. V1Rs are located on the apical compartment of the VNO and a relatively short [[NH2-terminal]] and have a great sequence diversity in their [[transmembrane domain]]s. V1R is specifically expressed in the rodent vomeronasal organ (VNO) and is thought to be responsible for [[pheromone]] reception, eliciting a signal transduction.<ref name="pmid18238827">{{cite journal | vauthors = Date-Ito A, Ohara H, Ichikawa M, Mori Y, Hagino-Yamagishi K | title = Xenopus V1R vomeronasal receptor family is expressed in the main olfactory system | journal = Chemical Senses | volume = 33 | issue = 4 | pages = 339–346 | date = April 2008 | pmid = 18238827 | doi = 10.1093/chemse/bjm090 | doi-access = free }}</ref>
* V2 receptors, V2Rs, are linked to the G-protein, [[Gαo]]. These have long extracellular NH2 terminals which are thought to be the binding domain for pheromonal molecules and are located on the basal compartment of the VNO. V2R genes can be grouped into four separate families, labelled A&nbsp;– D. Family C V2Rs are quite distinct from the other families, and they are expressed in most basal neurons of the VNO.

The vomeronasal organ's sensory neurons act on a different signaling pathway than that of the main olfactory system's sensory neurons. Activation of the receptors stimulates [[phospholipase C]],<ref>{{cite journal | vauthors = Holy TE, Dulac C, Meister M | title = Responses of vomeronasal neurons to natural stimuli | journal = Science | volume = 289 | issue = 5484 | pages = 1569–1572 | date = September 2000 | pmid = 10968796 | doi = 10.1126/science.289.5484.1569 | citeseerx = 10.1.1.420.6387 | bibcode = 2000Sci...289.1569H }}</ref> which in turn opens the ion channel [[TRPC2]].<ref name="Stowers">{{cite journal | vauthors = Stowers L, Holy TE, Meister M, Dulac C, Koentges G | title = Loss of sex discrimination and male-male aggression in mice deficient for TRP2 | journal = Science | volume = 295 | issue = 5559 | pages = 1493–1500 | date = February 2002 | pmid = 11823606 | doi = 10.1126/science.1069259 | s2cid = 84419443 | bibcode = 2002Sci...295.1493S | doi-access = free }}</ref><ref>{{cite journal | vauthors = Leypold BG, Yu CR, Leinders-Zufall T, Kim MM, Zufall F, Axel R | title = Altered sexual and social behaviors in trp2 mutant mice | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 99 | issue = 9 | pages = 6376–6381 | date = April 2002 | pmid = 11972034 | pmc = 122956 | doi = 10.1073/pnas.082127599 | doi-access = free | bibcode = 2002PNAS...99.6376L }}</ref> Upon stimulation activated by pheromones, [[Inositol trisphosphate|IP3]] production has been shown to increase in VNO membranes in many animals, while adenylyl cyclase and [[cyclic adenosine monophosphate]] (cAMP), the major signaling transduction molecules of the main olfactory system, remain unaltered. This trend has been shown in many animals, such as the [[hamster]], the [[pig]], the [[rat]], and the [[garter snake]] upon introduction of vaginal or seminal secretions into the environment.

V1Rs and V2Rs are activated by distinct ligands or pheromones.
* [[Gi protein]]s are activated upon stimulation with [[lipophilic]] odorants.
* Go proteins are activated by nonvolatile proteins, such as the [[major urinary proteins]] in mice<ref name="BBCreport">{{cite web| title = Aggression protein found in mice | publisher = [[BBC News]] | date =  5 December 2007  | url = http://news.bbc.co.uk/2/hi/science/nature/7129176.stm | access-date = 26 September 2009}}</ref><ref name=Chamero1>{{cite journal | vauthors = Chamero P, Marton TF, Logan DW, Flanagan K, Cruz JR, Saghatelian A, Cravatt BF, Stowers L | display-authors = 6 | title = Identification of protein pheromones that promote aggressive behaviour | journal = Nature | volume = 450 | issue = 7171 | pages = 899–902 | date = December 2007 | pmid = 18064011 | doi = 10.1038/nature05997 | s2cid = 4398766 | bibcode = 2007Natur.450..899C }}</ref> and exocrine gland-secreting peptide 1 (ESP1).<ref name=Kimoto1>{{cite journal | vauthors = Kimoto H, Haga S, Sato K, Touhara K | title = Sex-specific peptides from exocrine glands stimulate mouse vomeronasal sensory neurons | journal = Nature | volume = 437 | issue = 7060 | pages = 898–901 | date = October 2005 | pmid = 16208374 | doi = 10.1038/nature04033 | s2cid = 4388164 | bibcode = 2005Natur.437..898K }}</ref>

Many vomeronasal neurons are activated by chemicals in urine. Some of the active compounds are sulfated [[steroids]].<ref>{{cite journal | vauthors = Nodari F, Hsu FF, Fu X, Holekamp TF, Kao LF, Turk J, Holy TE | title = Sulfated steroids as natural ligands of mouse pheromone-sensing neurons | journal = The Journal of Neuroscience | volume = 28 | issue = 25 | pages = 6407–6418 | date = June 2008 | pmid = 18562612 | pmc = 2726112 | doi = 10.1523/JNEUROSCI.1425-08.2008 }}</ref> Detecting the types and amounts of different sulfated steroids conveys information about the urine donor's physiological state, and may therefore serve as an [[honest signal]].

Recent studies proved a new family of [[formyl peptide receptor]] like proteins in VNO membranes of mice, which points to a close phylogenetic relation of signaling mechanisms used in olfaction and [[Chemoreceptor|chemosensor]]s.<ref name="Rivière_2009">{{cite journal | vauthors = Rivière S, Challet L, Fluegge D, Spehr M, Rodriguez I | title = Formyl peptide receptor-like proteins are a novel family of vomeronasal chemosensors | journal = Nature | volume = 459 | issue = 7246 | pages = 574–577 | date = May 2009 | pmid = 19387439 | doi = 10.1038/nature08029 | s2cid = 4302009 | bibcode = 2009Natur.459..574R }}</ref>

===Sensory neurons===
Vomeronasal sensory neurons are extremely sensitive and fire action potentials at currents as low as 1 p[[Ampere|A]]. Many patch-clamp recordings have confirmed the sensitivity of the vomeronasal neurons. This sensitivity is tied to the fact that the [[resting potential]] of the vomeronasal neurons is relatively close to that of the firing threshold of these neurons. Vomeronasal sensory neurons also show remarkably slow adaptation and the firing rate increases with increasing current up to 10 pA. The main olfactory sensory neurons fire single burst action potentials and show a much quicker adaptation rate. Activating neurons that have V1 receptors, V1Rs, cause field potentials that have weak, fluctuating responses that are seen the anterior of the accessory olfactory bulb, AOB. Activation of neurons that contain V2 receptors, V2Rs, however, promote distinct oscillations in the posterior of the AOB.<ref>{{cite journal | vauthors = Keverne EB | title = The vomeronasal organ | journal = Science | volume = 286 | issue = 5440 | pages = 716–720 | date = October 1999 | pmid = 10531049 | doi = 10.1126/science.286.5440.716 }}</ref>

==Function==
Sensory neurons of the vomeronasal organ detect non-volatile chemical cues which requires direct physical contact with the source of odor but can also detect volatile compounds. Notably, some scents act as chemical-communication signals ([[pheromone]]s, allomones and kairomones) from other individuals of the same or from other species. Unlike sensory neurons from the main olfactory epithelium which project to the main olfactory bulb that then sends neuronal signals to the olfactory cortex, the VNO sends neuronal signals to the accessory olfactory bulb and then to the [[amygdala]], [[BNST]], and ultimately [[hypothalamus]]. Since the hypothalamus is a major neuroendocrine center (affecting aspects of reproductive physiology and behavior as well as other functions such as body temperature), this may explain how scents influence aggressive and mating behavior. For example, in many vertebrates, nerve signals from the brain pass sensory information to the hypothalamus about seasonal changes and the availability of a mate. In turn, the hypothalamus regulates the release of reproductive hormones required for breeding.<ref>{{Cite web |url=http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Pheromones.html |title=Kimball, J.W. Pheromones. ''Kimball's Biology Pages''. Sep 2008 |access-date=2008-11-01 |archive-date=2018-01-21 |archive-url=https://web.archive.org/web/20180121113903/http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Pheromones.html |url-status=dead }}</ref> Some [[pheromones]] are detected by the main [[olfactory system]].<ref>{{cite journal | vauthors = Keller M, Baum MJ, Brock O, Brennan PA, Bakker J | title = The main and the accessory olfactory systems interact in the control of mate recognition and sexual behavior | journal = Behavioural Brain Research | volume = 200 | issue = 2 | pages = 268–276 | date = June 2009 | pmid = 19374011 | doi = 10.1016/j.bbr.2009.01.020 | hdl = 2268/72698 | s2cid = 3997259 | url = https://orbi.uliege.be/bitstream/2268/72698/1/Keller%20%26%20Brock%20-%202009.pdf }}</ref>

==In animals==
The vomeronasal organ originated in [[tetrapods]]. The functional vomeronasal system is found in all [[snake]]s and [[lizard]]s,<ref>{{cite journal | vauthors = Baeckens S, Herrel A, Broeckhoven C, Vasilopoulou-Kampitsi M, Huyghe K, Goyens J, Van Damme R | title = Evolutionary morphology of the lizard chemosensory system | journal = Scientific Reports | volume = 7 | issue = 1 | pages = 10141 | date = September 2017 | pmid = 28871144 | pmc = 5583331 | doi = 10.1038/s41598-017-09415-7 | bibcode = 2017NatSR...710141B }}</ref> and many [[mammal]]s.
* [[Mice]] use their vomeronasal organ to interact with peers, detect predators, and identify and avoid sick conspecifics.
* [[Salamander]]s perform a nose-tapping behavior to presumably activate their VNO.<ref>{{cite journal | vauthors = Dawley EM, Bass AH | title = Chemical access to the vomeronasal organs of a plethodontid salamander | journal = Journal of Morphology | volume = 200 | issue = 2 | pages = 163–174 | date = May 1989 | pmid = 29865657 | doi = 10.1002/jmor.1052000206 | s2cid = 46931736 }}</ref>
* The organ is well developed in [[strepsirrhine]] [[primate]]s such as [[lemur]]s and [[loris]]es,<ref name="Lemurs">{{cite book | veditors = Gould L, Sauther ML, Tattersall I | chapter = Chapter 1: Origin of the Malagasy Strepsirhine Primates | title = Lemurs: Ecology and Adaptation | pages = 3–18 | publisher = Springer | year = 2006 | isbn = 978-0-387-34585-7}}</ref> developed to varying degrees in [[New World monkey]]s, and underdeveloped in [[Old World monkey]]s and [[ape]]s.<ref name="PrimateAnatomy9">{{cite book | vauthors = Ankel-Simons F | title= Primate Anatomy | edition = 3rd | chapter = Chapter 9: Sense Organs and Viscera | pages = 392–514 | publisher = Academic Press | year = 2007 | isbn = 978-0-12-372576-9}}</ref><ref>{{Cite journal |last1=Smith |first1=Timothy D. |last2=Garrett |first2=Eva C. |last3=Bhatnagar |first3=Kunwar P. |last4=Bonar |first4=Christopher J. |last5=Bruening |first5=Amanda E. |last6=Dennis |first6=John C. |last7=Kinznger |first7=Jonathan H. |last8=Johnson |first8=Edward W. |last9=Morrison |first9=Edward E. |date=December 2011 |title=The Vomeronasal Organ of New World Monkeys (Platyrrhini) |url=https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.21509 |journal=The Anatomical Record |language=en |volume=294 |issue=12 |pages=2158–2178 |doi=10.1002/ar.21509 |pmid=22042751 |issn=1932-8486}}</ref>
* [[Elephant]]s transfer chemosensory stimuli to the vomeronasal opening in the roof of their mouths using the [[prehensile]] structure, sometimes called a ''finger'', at the tips of their trunks.<ref name="Simon2010">{{cite book |first=Verne A. |last=Simon | name-list-style = vanc |title=Adaptations in the Animal Kingdom |publisher=Xlibris Corp. |year=2010 |page=31 |isbn=978-1450033640 }}{{self-published source|date=December 2017}}</ref>{{self-published inline|certain=yes|date=December 2017}}
* [[Painted turtle]]s use this organ to use their sense of smell underwater.<ref name="Simon2010" />
* [[Snake]]s use this organ to sense prey, sticking their tongue out to gather scents and touching it to the opening of the organ when the tongue is retracted.<ref>{{cite journal | vauthors = Baeckens S, Van Damme R, Cooper WE | title = How phylogeny and foraging ecology drive the level of chemosensory exploration in lizards and snakes | journal = Journal of Evolutionary Biology | volume = 30 | issue = 3 | pages = 627–640 | date = March 2017 | pmid = 28009479 | doi = 10.1111/jeb.13032 | s2cid = 32804222 | hdl = 10067/1396740151162165141 | hdl-access = free }}</ref> [[Garter snake]]s also use the vomeronasal organ in pheromone communication. Odors and vomodors should be distinguished. Odors are chemicals detected by the sensory cells in the nasal epithelium through the process of [[olfaction]]. Vomodors are chemicals detected by the sensory cells from the vomeronasal organ through the process of vomerolfaction.<ref>{{cite journal | vauthors = Cooper WE, Burghardt GM | title = Vomerolfaction and vomodor | journal = Journal of Chemical Ecology | volume = 16 | issue = 1 | pages = 103–105 | date = January 1990 | pmid = 24264899 | doi = 10.1007/BF01021271 | bibcode = 1990JCEco..16..103C | s2cid = 26924795 }}</ref> Entering the lumen, molecules contact the sensory cells attached to the neurosensory epithelium of the vomeronasal organ. The vomeronasal organ is vital to Garter snakes' perception of airborne prey odors; snakes with vomeronasal nerves cut responded to nonprey odors only.<ref>{{cite journal | vauthors = Zuri I, Halpern M | title = Differential effects of lesions of the vomeronasal and olfactory nerves on garter snake (Thamnophis sirtalis) responses to airborne chemical stimuli | journal = Behavioral Neuroscience | volume = 117 | issue = 1 | pages = 169–183 | date = February 2003 | pmid = 12619919 | doi = 10.1037/0735-7044.117.1.169 }}</ref>
* Bats— The vomeronasal organ is non-functional in the whole suborder Yinpterochiroptera.<ref>{{Cite journal |last1=Zhao |first1=Huabin |last2=Xu |first2=Dong |last3=Zhang |first3=Shuyi |last4=Zhang |first4=Jianzhi |date=January 2011 |title=Widespread Losses of Vomeronasal Signal Transduction in Bats |url=https://academic.oup.com/mbe/article-lookup/doi/10.1093/molbev/msq207 |journal=Molecular Biology and Evolution |language=en |volume=28 |issue=1 |pages=7–12 |doi=10.1093/molbev/msq207 |issn=1537-1719 |pmc=3108603 |pmid=20693241}}</ref> In the other suborder of bats, Yangochiroptera, only two families have retained function of the VNO (Phyllostomidae and Miniopteridae).<ref>{{Cite journal |last1=Yohe |first1=Laurel R. |last2=Krell |first2=Nicholas T. |date=November 2023 |title=An updated synthesis of and outstanding questions in the olfactory and vomeronasal systems in bats: Genetics asks questions only anatomy can answer |journal=The Anatomical Record |language=en |volume=306 |issue=11 |pages=2765–2780 |doi=10.1002/ar.25290 |issn=1932-8486|doi-access=free |pmid=37523493 }}</ref>
* Birds— The VNO is absent in all birds<ref>{{Cite journal |last1=Silva |first1=Liliana |last2=Antunes |first2=Agostinho |date=2017-02-08 |title=Vomeronasal Receptors in Vertebrates and the Evolution of Pheromone Detection |url=https://www.annualreviews.org/doi/10.1146/annurev-animal-022516-022801 |journal=Annual Review of Animal Biosciences |language=en |volume=5 |issue=1 |pages=353–370 |doi=10.1146/annurev-animal-022516-022801 |pmid=27912243 |issn=2165-8102|url-access=subscription }}</ref>

In some other mammals the entire organ contracts or pumps in order to draw in the scents.<ref>{{cite book |editor1-first=J. G. M. |editor1-last=Thewissen |editor2-first=Sirpa |editor2-last=Nummela |title=Sensory Evolution on the Threshold: Adaptations in Secondarily Aquatic Vertebrates |publisher=University of California Press |location=Berkeley |year=2008 |page=45 |isbn=9780520252783 }}</ref>
[[File:Flehmendes Pferd 32 c.jpg|thumb|[[Stallion]] exhibiting the [[flehmen response]]]]

==Flehmen response==
Some mammals, particularly [[felid]]s (cats) and [[ungulates]] (which includes horses, cattle, and pigs among other species), use a distinctive facial movement called the [[flehmen response]] to direct inhaled compounds to the VNO. The animal lifts its head after finding the odorant, wrinkles its nose while lifting its lips, and ceases to breathe momentarily.

Flehmen behavior is associated with "anatomical specialization", and animals that present flehmen behavior have [[incisive papilla]] and ducts, which connect the oral cavity to the VNO, that are found behind their teeth. However, [[horse]]s are the exception: they exhibit flehmen response but do not have an incisive duct communication between the nasal and the oral cavity because they do not breathe through their mouths; instead, the VNOs connect to the nasal passages by the [[Incisive foramen|nasopalatine duct]].<ref name="Briggs smell">{{cite web|last=Briggs|first=Karen|title=Equine Sense of Smell|url=http://www.thehorse.com/articles/10055/equine-sense-of-smell|publisher=The Horse|access-date=2013-12-15|date=2013-12-11}}</ref>

Cats use their vomeronasal organ when [[scent rubbing]]; they are able to discriminate between similar smelling substances using this organ, and then perform the rubbing behaviour.<ref>{{cite journal | vauthors = Griffith CA, Steigerwald ES, Buffington CA | title = Effects of a synthetic facial pheromone on behavior of cats | journal = Journal of the American Veterinary Medical Association | volume = 217 | issue = 8 | pages = 1154–1156 | date = October 2000 | pmid = 11043684 | doi = 10.2460/javma.2000.217.1154 | doi-access = free }}</ref>

==Evidence for existence in humans==
Many studies have tried to determine whether there is a VNO in adult human beings. Trotier ''et al.''<ref>{{cite journal | vauthors = Trotier D, Eloit C, Wassef M, Talmain G, Bensimon JL, Døving KB, Ferrand J | title = The vomeronasal cavity in adult humans | journal = Chemical Senses | volume = 25 | issue = 4 | pages = 369–380 | date = August 2000 | pmid = 10944499 | doi = 10.1093/chemse/25.4.369 | doi-access = free }}</ref> estimated that around 92% of their subjects that had no [[septal]] surgery had at least one intact VNO. Kjaer and Fisher Hansen, on the other hand,<ref>{{cite journal | vauthors = Kjaer I, Fischer Hansen B | title = The human vomeronasal organ: prenatal developmental stages and distribution of luteinizing hormone-releasing hormone | journal = European Journal of Oral Sciences | volume = 104 | issue = 1 | pages = 34–40 | date = February 1996 | pmid = 8653495 | doi = 10.1111/j.1600-0722.1996.tb00043.x }}</ref> stated that the VNO structure disappears during [[fetal development]] as it does for some [[primate]]s.<ref>{{cite journal | vauthors = Smith TD, Siegel MI, Bhatnagar KP | title = Reappraisal of the vomeronasal system of catarrhine primates: ontogeny, morphology, functionality, and persisting questions | journal = The Anatomical Record | volume = 265 | issue = 4 | pages = 176–192 | date = August 2001 | pmid = 11519019 | doi = 10.1002/ar.1152 | s2cid = 24546998 | doi-access = free }}</ref> However, Smith and Bhatnagar (2000)<ref>{{cite journal | vauthors = Smith TD, Bhatnagar KP | title = The human vomeronasal organ. Part II: prenatal development | journal = Journal of Anatomy | volume = 197 | issue = 3 | pages = 421–436 | date = October 2000 | pmid = 11117628 | pmc = 1468143 | doi = 10.1046/j.1469-7580.2000.19730421.x }}</ref> asserted that Kjaer and Fisher Hansen simply missed the structure in older fetuses. Won (2000) found evidence of a VNO in 13 of his 22 cadavers (59.1%) and 22 of his 78 living patients (28.2%).<ref>{{cite journal | vauthors = Won J, Mair EA, Bolger WE, Conran RM | title = The vomeronasal organ: an objective anatomic analysis of its prevalence | journal = Ear, Nose, & Throat Journal | volume = 79 | issue = 8 | pages = 600–605 | date = August 2000 | pmid = 10969469 | doi = 10.1177/014556130007900814 | doi-access = free }}</ref> In a study using retrospective analysis of nearly one thousand outpatient nasal endoscopies, Stoyanov et al. (2016) found the organ to be present in 26.83% of the Bulgarian population.<ref>{{cite journal | vauthors = Stoyanov G, Moneva K, Sapundzhiev N, Tonchev AB | title = The vomeronasal organ - incidence in a Bulgarian population | journal = The Journal of Laryngology and Otology | volume = 130 | issue = 4 | pages = 344–347 | date = April 2016 | pmid = 26831012 | doi = 10.1017/S0022215116000189 | s2cid = 1696242 }}</ref>

Given these findings, some scientists have argued that there is a VNO in adult human beings.<ref>{{cite journal | vauthors = Johnson A, Josephson R, Hawke M | title = Clinical and histological evidence for the presence of the vomeronasal (Jacobson's) organ in adult humans | journal = The Journal of Otolaryngology | volume = 14 | issue = 2 | pages = 71–79 | date = April 1985 | pmid = 4068105 }}</ref><ref>{{cite journal | vauthors = Foltán R, Sedý J | title = Behavioral changes of patients after orthognathic surgery develop on the basis of the loss of vomeronasal organ: a hypothesis | journal = Head & Face Medicine | volume = 5 | pages = 5 | date = January 2009 | pmid = 19161592 | pmc = 2653472 | doi = 10.1186/1746-160X-5-5 | doi-access = free }}</ref> However, most investigators have sought to identify the opening of the VNO in humans, rather than identify the tubular [[epithelial]] structure itself.<ref name=":0">{{cite journal | vauthors = Bhatnagar KP, Smith TD | title = The human vomeronasal organ. III. Postnatal development from infancy to the ninth decade | journal = Journal of Anatomy | volume = 199 | issue = Pt 3 | pages = 289–302 | date = September 2001 | pmid = 11554506 | pmc = 1468331 | doi = 10.1046/j.1469-7580.2001.19930289.x }}</ref> Thus it has been argued that such studies, employing macroscopic observational methods, have sometimes misidentified or even missed the vomeronasal organ.<ref name=":0" />

Among studies that use [[Microanatomy|microanatomical]] methods, there is no reported evidence that human beings have active sensory neurons like those in working vomeronasal systems of other animals.<ref>{{cite book | vauthors = Witt M, Hummel T | title = Vomeronasal Versus Olfactory Epithelium: Is There a Cellular Basis for Human Vomeronasal Perception? | volume = 248 | pages = 209–59 | year = 2006 | pmid = 16487792 | doi = 10.1016/S0074-7696(06)48004-9 | isbn = 9780123646521 | series = International Review of Cytology }}</ref> Furthermore, there is no evidence to date that suggests there are nerve and axon connections between any existing sensory receptor cells that may be in the adult human VNO and the brain.<ref>{{cite journal | vauthors = Wysocki CJ, Preti G | title = Facts, fallacies, fears, and frustrations with human pheromones | journal = The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology | volume = 281 | issue = 1 | pages = 1201–1211 | date = November 2004 | pmid = 15470677 | doi = 10.1002/ar.a.20125 | doi-access = free }}</ref> Likewise, there is no evidence for any accessory olfactory bulb in adult human beings,<ref>{{cite journal | vauthors = Bhatnagar KP, Kennedy RC, Baron G, Greenberg RA | title = Number of mitral cells and the bulb volume in the aging human olfactory bulb: a quantitative morphological study | journal = The Anatomical Record | volume = 218 | issue = 1 | pages = 73–87 | date = May 1987 | pmid = 3605663 | doi = 10.1002/ar.1092180112 | s2cid = 25630359 }}</ref> and the key genes involved in VNO function in other mammals have [[pseudogene|pseudogenized]] in human beings. Therefore, while many debate the structure's presence in adult human beings, a review of the scientific literature by Tristram Wyatt concluded that on current evidence, "most in the field... are skeptical about the likelihood of a functional VNO in adult human beings."<ref name="wy">Wyatt, Tristram D. (2003). ''Pheromones and Animal Behaviour: Communication by Smell and Taste.'' Cambridge: Cambridge University Press. {{ISBN|0-521-48526-6}}. p295</ref>

==History==
The VNO was discovered by [[Frederik Ruysch]] prior to 1732, and later by [[Ludwig Jacobson]] in 1813.<ref name="Jacobson, L. 1813"/>

==References==
{{Reflist}}

==Further reading==
{{refbegin|32em}}
* {{cite journal | vauthors = Døving KB, Trotier D | title = Structure and function of the vomeronasal organ | journal = The Journal of Experimental Biology | volume = 201 | issue = Pt 21 | pages = 2913–2925 | date = November 1998 | pmid = 9866877 | doi = 10.1242/jeb.201.21.2913 | bibcode = 1998JExpB.201.2913D }}
* {{cite journal | vauthors = Silvotti L, Moiani A, Gatti R, Tirindelli R | title = Combinatorial co-expression of pheromone receptors, V2Rs | journal = Journal of Neurochemistry | volume = 103 | issue = 5 | pages = 1753–1763 | date = December 2007 | pmid = 17854397 | doi = 10.1111/j.1471-4159.2007.04877.x | s2cid = 11198963 | doi-access = free }}
* {{cite journal | vauthors = Keverne EB | title = The vomeronasal organ | journal = Science | volume = 286 | issue = 5440 | pages = 716–720 | date = October 1999 | pmid = 10531049 | doi = 10.1126/science.286.5440.716 }}
* {{cite journal | vauthors = Meredith M | title = Human vomeronasal organ function: a critical review of best and worst cases | journal = Chemical Senses | volume = 26 | issue = 4 | pages = 433–445 | date = May 2001 | pmid = 11369678 | doi = 10.1093/chemse/26.4.433 | s2cid = 17248981 | doi-access = free }}
* {{cite journal | vauthors = Evans CS | title = Accessory chemosignaling mechanisms in primates | journal = American Journal of Primatology | volume = 68 | issue = 6 | pages = 525–544 | date = June 2006 | pmid = 16715503 | doi = 10.1002/ajp.20250 | s2cid = 25874777 }}
* {{cite journal | vauthors = Wekesa KS, Anholt RR | title = Pheromone regulated production of inositol-(1, 4, 5)-trisphosphate in the mammalian vomeronasal organ | journal = Endocrinology | volume = 138 | issue = 8 | pages = 3497–3504 | date = August 1997 | pmid = 9231804 | doi = 10.1210/endo.138.8.5338 | doi-access = free }}
* {{cite journal | vauthors = Monti-Bloch L, Jennings-White C, Berliner DL | title = The human vomeronasal system. A review | journal = Annals of the New York Academy of Sciences | volume = 855 | issue = 1 | pages = 373–389 | date = November 1998 | pmid = 9929629 | doi = 10.1111/j.1749-6632.1998.tb10595.x | s2cid = 38973467 | bibcode = 1998NYASA.855..373M }}
{{refend}}

{{Nose anatomy}}
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{{DEFAULTSORT:Vomeronasal Organ}}
[[Category:Olfactory system]]
[[Category:Vertebrate anatomy]]
[[Category:Pheromones]]
[[Category:Vestigial organs]]