Vomeronasal organ
Encyclopedia
The vomeronasal organ or Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animal
s. It was discovered by Frederik Ruysch
and later by Ludwig Jacobson in 1813.
During embryological development, it forms from the nasal (olfactory) placode
, at the anterior edge of the neural plate (cranial nerve zero
). It is a chemoreceptor organ which is completely separated from the nasal cavity some of the time, being enclosed in a separate bony or cartilaginous capsule which opens into the base of the nasal cavity. It is a tubular crescent shape and split into two pairs, separated by the nasal septum. It is the first processing stage of the accessory olfactory system, after which chemical stimuli go to the accessory olfactory bulb, then to targets in the amygdala
and bed nucleus of the stria terminalis, which in turn project to the hypothalamus
.
The vomeronasal organ is mainly used to detect pheromone
s, chemical messengers that carry information between individuals of the same species. As with other olfactory systems, chemical messages are detected by their binding to G protein-coupled receptors. The neurons in the VNO express receptors from 3 families, called V1R, V2R, and FPR. The receptors are distinct from each other and from the large family of receptors in the main olfactory system. Evidence shows that the VNO responds to nonvolatile cues which stimulate the receptor neurons.
Its presence in many animals has been widely studied and the importance of the vomeronasal system to the role of reproduction and social behavior (through influence on anterior hypothalamus) has been shown in many studies. Its presence and functionality in humans was controversial, though most studies agree the organ regresses during fetal development. Many genes essential for VNO function in animals (such as TRPC2
) are non-functional in humans. Chemical communication does appear to occur among humans but this may not mean a human vomeronasal organ is functional.
. It is split into two, being divided by the nasal septum, with both sides possessing an elongated c-shaped, or crescent, lumen
. It is encompassed inside a bony or cartilaginous capsule which opens into the base of the nasal cavity. The vomeronasal receptor neurons possess axon
s which travel from the VNO to the accessory olfactory bulb (AOB) or, as its also known, 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 to pump the lumen.
s, the sensory neurons of the vomeronasal organ detect non-volatile chemical cues, which requires direct physical contact with the source of odor. Notably, some scents act as chemical-communication signals (pheromone
s) from other individuals of the same species. Unlike the main olfactory bulb that 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. It should be noted that some pheromones are detected by the main olfactory system
.
. The crescent lumen
is lined with receptor neuron
s on the medial concave side and is filled with fluid from the VN glands. There VN neurons are isolated from the nasal cavity
and therefore isolated from the air stream that passes during normal respiration. This means that a stimulus requires arousal of the vascular pump which is lateral to the lumen. 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 sensory
epithelium. The vomeronasal sensory cells form in the olfactory placode along with other sensory olfaction neurons. They are located in a sensory epithelium and are separated from olfactory epithelium, lining an elongated cavity (lumen) inside the bone capsule which encloses the organ. A thin duct, which opens onto the floor of the nasal cavity inside the nostril
, is the only way of access for stimulus chemicals. The vomeronasal sensory neurons communicate with the hypothalamus to change neuroendocrine function. These sensory receptors are G-protein-coupled receptors, and are often referred to as pheromone
receptors since vomeronasal receptors have been tied to detecting pheromones.
The receptor neurons possess apical microvilli whose axons merge together to form VN nerves which move from the paired olfactory bulb
s to the main olfactory bulb, entering the posterior dorsal aspect through the AOB. There have been three different G-protein-coupled receptors identified in the VNO, each found in distinct regions. These are V1Rs and 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.
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 stimlates phospholipase C
, which in turns opens the ion channel TRPC2
. Upon stimulation activated by pheromones, 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 suggested to be activated by distinct ligands or pheromones. The evidence that Gi and Go proteins are activated upon stimulation via different pheromones supports this.
Many vomeronasal neurons are activated by chemicals in urine. Some of the active compounds are sulfated steroids. 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 chemotaxis
.
. 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.
s, including all snake
s, and lizards, plus many mammals, such as mice
, rat
s, elephant
s, cattle
, dog
s, cats, goat
s, and pig
s.
In some other mammals, the entire organ contracts or pumps in order to draw in the scents.
Some mammals, particularly felids and ungulates, use a distinctive facial movement called the flehmen response
to direct inhaled compounds to this organ. The animal will lift its head after finding the odorant, wrinkle its nose while lifting its lips, and cease 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, horses are the exception, they exhibit Flehmen response but do not have an incisive duct communication between the nasal and the oral cavity.
Another study conducted by Beauchamp et al. investigated the role of the VNO in male guinea pigs social behavior. Half of the guinea pigs vomeronasal systems were removed, while the other half were put under fake surgeries with their vomeronasal systems left intact. The findings suggested that the VNO in the male domestic guinea pig is necessary for the maintenance of normal responsiveness to sex odors. However, “in its absence, other sensory systems are capable of maintaining normal sexual behavior under conditions of laboratory testing.”
These behavioral studies show the importance of the vomeronasal system in animals’ social networks and everyday activities. The importance of the vomeronasal system to the role of reproduction and social networking has been shown in many studies.
as it does for some primate
s. However, Smith and Bhatnagar (2000) 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 in 22 of his 78 living patients (28.2%).
Given these findings, some scientists have argued that there is a VNO in adult human beings. However, most investigators have sought to identify the opening of the vomeronasal organ in humans, rather than identify the tubular epithelial structure itself. Thus it has been argued that such studies, employing macroscopic observational methods, have sometimes missed or even misidentified the vomeronasal organ.[21]
Among studies that use microanatomical methods, there is no reported evidence that human beings have active sensory neurons like those in working vomeronasal systems of other animals.[21] 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. Likewise, there is no evidence for any accessory olfactory bulb in adult human beings, and the key genes involved in VNO function in other mammals have pseudogene
ized in human beings. Therefore while the presence of a structure in adult human beings is debated, a review of the scientific literature by Tristram Wyatt concluded, "most in the field... are sceptical about the likelihood of a functional VNO in adult human beings on current evidence."
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s. It was discovered by Frederik Ruysch
Frederik Ruysch
Frederik Ruysch was a Dutch botanist and anatomist, remembered for his developments in anatomical preservation and the creation of dioramas or scenes incorporating human parts...
and later by Ludwig Jacobson in 1813.
During embryological development, it forms from the nasal (olfactory) placode
Placode
A neurogenic placode is an area of thickening in the embryonic epithelial layer where some organ or structure later develops. The term usually refers to cranial placodes, peripheral nervous system structures associated with the special senses and cranial ganglia...
, at the anterior edge of the neural plate (cranial nerve zero
Cranial nerve zero
The terminal nerve, or cranial nerve zero, was discovered by German scientist Gustav Fritsch in 1878 in the brains of sharks. It was first found in humans in 1913, although its presence in humans remains controversial...
). It is a chemoreceptor organ which is completely separated from the nasal cavity some of the time, being enclosed in a separate bony or cartilaginous capsule which opens into the base of the nasal cavity. It is a tubular crescent shape and split into two pairs, separated by the nasal septum. It is the first processing stage of the accessory olfactory system, after which chemical stimuli go to the accessory olfactory bulb, then to targets in the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
and bed nucleus of the stria terminalis, which in turn project to the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
.
The vomeronasal organ is mainly used to detect pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s, chemical messengers that carry information between individuals of the same species. As with other olfactory systems, chemical messages are detected by their binding to G protein-coupled receptors. The neurons in the VNO express receptors from 3 families, called V1R, V2R, and FPR. The receptors are distinct from each other and from the large family of receptors in the main olfactory system. Evidence shows that the VNO responds to nonvolatile cues which stimulate the receptor neurons.
Its presence in many animals has been widely studied and the importance of the vomeronasal system to the role of reproduction and social behavior (through influence on anterior hypothalamus) has been shown in many studies. Its presence and functionality in humans was controversial, though most studies agree the organ regresses during fetal development. Many genes essential for VNO function in animals (such as TRPC2
TRPC2
Transient receptor potential cation channel, subfamily C, member 2, also known as TRPC2, is a protein that in humans is encoded by the TRPC2 pseudogene. This protein is not expressed in humans but is in certain other species such as mouse....
) are non-functional in humans. Chemical communication does appear to occur among humans but this may not mean a human vomeronasal organ is functional.
Structure
The VNO is found at the base of the nasal cavityNasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
. It is split into two, being divided by the nasal septum, with both sides possessing an elongated c-shaped, or crescent, lumen
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
. It is encompassed inside a bony or cartilaginous capsule which opens into the base of the nasal cavity. The vomeronasal receptor neurons possess axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
s which travel from the VNO to the accessory olfactory bulb (AOB) or, as its also known, 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 to pump the lumen.
Function
In mammalMammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, the sensory neurons of the vomeronasal organ detect non-volatile chemical cues, which requires direct physical contact with the source of odor. Notably, some scents act as chemical-communication signals (pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s) from other individuals of the same species. Unlike the main olfactory bulb that sends neuronal signals to the olfactory cortex, the VNO sends neuronal signals to the accessory olfactory bulb and then to the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
, BNST, and ultimately hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
. 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. It should be noted that some pheromones are detected by the main olfactory system
Olfactory system
The olfactory system is the sensory system used for olfaction, or the sense of smell. Most mammals and reptiles have two distinct parts to their olfactory system: a main olfactory system and an accessory olfactory system. The main olfactory system detects volatile, airborne substances, while the...
.
Sensory epithelium and receptors
The VNO is a tubular crescent shape and split into two pairs, separated by the nasal septumNasal septum
The nasal septum separates the left and right airways in the nose, dividing the two nostrils.It is depressed by the Depressor septi nasi muscle.-Composition:The fleshy external end of the nasal septum is sometimes also called columella....
. The crescent lumen
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
is lined with receptor neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s on the medial concave side and is filled with fluid from the VN glands. There VN neurons are isolated from the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
and therefore isolated from the air stream that passes during normal respiration. This means that a stimulus requires arousal of the vascular pump which is lateral to the lumen. The medial, concave area of the lumen is lined with a pseudo stratified epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
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 sensory
Sensory
Sensory may refer to:relating to senses or smellIn biology:* Sensory preference* Sensory system, part of the nervous system of organisms* Sensory neuron, nerve cell responsible for transmitting information about external stimuli...
epithelium. The vomeronasal sensory cells form in the olfactory placode along with other sensory olfaction neurons. They are located in a sensory epithelium and are separated from olfactory epithelium, lining an elongated cavity (lumen) inside the bone capsule which encloses the organ. A thin duct, which opens onto the floor of the nasal cavity inside the nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
, is the only way of access for stimulus chemicals. The vomeronasal sensory neurons communicate with the hypothalamus to change neuroendocrine function. These sensory receptors are G-protein-coupled receptors, and are often referred to as pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
receptors since vomeronasal receptors have been tied to detecting pheromones.
The receptor neurons possess apical microvilli whose axons merge together to form VN nerves which move from the paired olfactory bulb
Olfactory bulb
The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...
s to the main olfactory bulb, entering the posterior dorsal aspect through the AOB. There have been three different G-protein-coupled receptors identified in the VNO, each found in distinct regions. These are V1Rs and 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.
- V1 receptors, V1Rs, are linked to the G protein, Gαi2. They are located on the apical compartment of the VNO and a relatively short NH2 terminal and have a great sequence diversity in their transmembrane domains.
- 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 in to four separate families, labelled A - 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 stimlates phospholipase C
Phospholipase C
Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in...
, which in turns opens the ion channel TRPC2
TRPC2
Transient receptor potential cation channel, subfamily C, member 2, also known as TRPC2, is a protein that in humans is encoded by the TRPC2 pseudogene. This protein is not expressed in humans but is in certain other species such as mouse....
. Upon stimulation activated by pheromones, IP3 production has been shown to increase in VNO membranes in many animals, while adenylyl cyclase and cyclic adenosine monophosphate
Cyclic adenosine monophosphate
Cyclic adenosine monophosphate is a second messenger important in many biological processes...
(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
Hamster
Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
, the pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
, the rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
, and the garter snake
Garter snake
The Garter snake is a Colubrid snake genus common across North America, ranging from Alaska and Canada to Central America. It is the single most widely distributed genus of reptile in North America. The garter snake is also the Massachusettsstate reptile.There is no real consensus on the...
upon introduction of vaginal or seminal secretions into the environment.
V1Rs and V2Rs are suggested to be activated by distinct ligands or pheromones. The evidence that Gi and Go proteins are activated upon stimulation via different pheromones supports this.
- Gi proteins are activated upon stimulation with lipophilicLipophilicLipophilicity, , refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true...
odorants. - Go proteins on the other hand is activated by nonvolatile proteins, such as the major urinary proteinsMajor urinary proteinsMajor urinary proteins , also known as α2u-globulins, are a subfamily of proteins found in abundance in the urine and other secretions of many animals. Mups provide a small range of identifying information about the donor animal, when detected by the vomeronasal organ of the receiving animal. They...
of mice.
Many vomeronasal neurons are activated by chemicals in urine. Some of the active compounds are sulfated steroids. 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
Formyl peptide receptor
The formyl peptide receptors are a members of a class of G protein-coupled receptors involved in chemotaxis. These receptors where originally identified by their ability to bind N-formyl peptides such as N-formylmethionine produced by the degradation of either bacterial or host cells...
like proteins in VNO membranes of mice, which points to a close phylogenetic relation of signaling mechanisms used in olfaction and chemotaxis
Chemotaxis
Chemotaxis is the phenomenon in which somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food by swimming towards the highest concentration of food molecules,...
.
Sensory neurons
Vomeronasal sensory neurons are extremely sensitive and fire action potentials at currents as low as 1 pAAmpere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
. 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.
Animals
The functional vomeronasal system is found in many animalAnimal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, including all snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s, and lizards, plus many mammals, such as mice
Mouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
, rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s, elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s, cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
, dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
s, cats, goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
s, and pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
s.
- SalamanderSalamanderSalamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s perform a nose tapping behavior to supposedly activate their VNO. - SnakeSnakeSnakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
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. - The organ is well developed in strepsirrhine primatePrimateA primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s such as lemurLemurLemurs are a clade of strepsirrhine primates endemic to the island of Madagascar. They are named after the lemures of Roman mythology due to the ghostly vocalizations, reflective eyes, and the nocturnal habits of some species...
s and lorisLorisLoris is the common name for the strepsirrhine primates of the subfamily Lorisinae in family Lorisidae. Loris is one genus in this subfamily and includes the slender lorises, while Nycticebus is the genus for the slow lorises....
es, developed to varying degrees in New World monkeyNew World monkeyNew World monkeys are the five families of primates that are found in Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Platyrrhini parvorder and the Ceboidea superfamily, which are essentially synonymous since...
s, and underdeveloped in Old World MonkeyOld World monkeyThe Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous...
s and apeApeApes are Old World anthropoid mammals, more specifically a clade of tailless catarrhine primates, belonging to the biological superfamily Hominoidea. The apes are native to Africa and South-east Asia, although in relatively recent times humans have spread all over the world...
s. - ElephantElephantElephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
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. - Painted TurtlePainted TurtleThe painted turtle is the most widespread native turtle of North America. It lives in slow-moving fresh waters, from southern Canada to Louisiana and northern Mexico, and from the Atlantic to the Pacific. The turtle is the only species of the genus Chrysemys, which is part of the pond turtle...
s use this organ to use their sense of smell underwater.
In some other mammals, the entire organ contracts or pumps in order to draw in the scents.
Some mammals, particularly felids and ungulates, use a distinctive facial movement called the flehmen response
Flehmen response
The flehmen response , also called the flehmen position, flehmen reaction, flehming, or flehmening , is a particular type of curling of the upper lip in ungulates, felids, and many other mammals, which facilitates the transfer of pheromones and other scents into the vomeronasal organ, also called the...
to direct inhaled compounds to this organ. The animal will lift its head after finding the odorant, wrinkle its nose while lifting its lips, and cease to breathe momentarily. Flehmen behavior is associated with “anatomical specialization”, and animals that present flehmen behavior have incisive papilla
Incisive papilla
The incisive papilla is a projection on the palate near the incisors.It marks one border of the palatine raphe.-External links:* *...
and ducts, which connect the oral cavity to the VNO, that are found behind their teeth. However, horses are the exception, they exhibit Flehmen response but do not have an incisive duct communication between the nasal and the oral cavity.
- House catCatThe cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
s often may be seen making this grimace when examining a scent that interests them.
Behavioral studies
Kudjakova et al. performed exploratory behavioral studies on non purebred rats by extirpating the VNO. The study showed that the exploratory behavior of the rats with extirpated VNO’s were significantly different from both control groups of rats. These results suggest that removal of the VNO removed the experimental rats from important social information. This is seen in the reduced exploratory activity in the experimental animal and the lower number of species-specific reactions.Another study conducted by Beauchamp et al. investigated the role of the VNO in male guinea pigs social behavior. Half of the guinea pigs vomeronasal systems were removed, while the other half were put under fake surgeries with their vomeronasal systems left intact. The findings suggested that the VNO in the male domestic guinea pig is necessary for the maintenance of normal responsiveness to sex odors. However, “in its absence, other sensory systems are capable of maintaining normal sexual behavior under conditions of laboratory testing.”
These behavioral studies show the importance of the vomeronasal system in animals’ social networks and everyday activities. The importance of the vomeronasal system to the role of reproduction and social networking has been shown in many studies.
Humans
Many studies have been performed to determine whether there is an actual presence of a VNO in adult human beings. Trotier et al. 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, stated that VNO structure disappeared during fetal developmentFetal development
Prenatal or antenatal development is the process in which a human embryo or fetus gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense.After fertilization the embryogenesis starts...
as it does for some primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s. However, Smith and Bhatnagar (2000) 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 in 22 of his 78 living patients (28.2%).
Given these findings, some scientists have argued that there is a VNO in adult human beings. However, most investigators have sought to identify the opening of the vomeronasal organ in humans, rather than identify the tubular epithelial structure itself. Thus it has been argued that such studies, employing macroscopic observational methods, have sometimes missed or even misidentified the vomeronasal organ.[21]
Among studies that use microanatomical methods, there is no reported evidence that human beings have active sensory neurons like those in working vomeronasal systems of other animals.[21] 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. Likewise, there is no evidence for any accessory olfactory bulb in adult human beings, and the key genes involved in VNO function in other mammals have pseudogene
Pseudogene
Pseudogenes are dysfunctional relatives of known genes that have lost their protein-coding ability or are otherwise no longer expressed in the cell...
ized in human beings. Therefore while the presence of a structure in adult human beings is debated, a review of the scientific literature by Tristram Wyatt concluded, "most in the field... are sceptical about the likelihood of a functional VNO in adult human beings on current evidence."