Itt írjon a(z) Oxytocin-ról/ről

Oxytocin release in humans and dogs as a response to petting

Contents

General information

About oxytocin

Oxytocin is a peptide hormone produced in the magnocellular area of the hypothalamus. This area consists of the two parts supraoptic- and paraventricular nucleus. The hormone is transported along the axons to the neurohypophysis (posterior lobe of pituitary gland). During different stimuli oxytocin is released into the systemic circulation where it has a widespread effect, like the classical effect such as contraction of the smooth muscles in the uterus during labor and milk ejection during lactation. Peripheral tissue like placenta, uterus, heart, corpus luteum, testis and amnion can also synthesize this peptide hormone. There is equal amount of oxytocin in neurohypophysis and in the plasma in both female and male, so there are to believe that the hormone has many physiological functions. Most of the studies done with oxytocin are done with rats, so there can be some species differences concerning regulation, location and effects. Oxytocin regulation is closely related to the regulation of sex steroids, especially estrogen and estradiol. Oxytocin prepropeptide is cleaved and is transported down the axon. At the terminal of the axon the peptide hormone and its carrier molecule neurophysin are stored until a type of stimuli elicits their release. Neurophysin is a small, disulfide rich protein which target, pack and store oxytocin in granula before the release to the bloodstream.

Structure of the peptide hormone

Oxytocin was the first peptide hormone to have its structure determined and also the first to be chemically synthesized. The gene structure was discovered in 1984, and the sequence of the receptor was distinguished in 1992. Hormones from the neurohypophysis are nonapeptides, oligopeptides with 9 amino acids. There is a disulfide bridge between cysteine residues 1 and 6 (Gimpl, Gerald and Fahrenholz, Falk, 2001). Receptors areas located in the ventral medial amygdala and hypothalamus are associated with affectionate, sexual and reproductive behavior. This can also explain why we see an increased oxytocin level during positive correlations (Odendaa, J.S.J and Meintjes, R.A, 2003).

Causes of release

There are several factors that will stimulate to oxytocin release in the body, such as suckling, parturition, hemorrhage, stress factors like fever, territorial marking, mating and touch. Physical contact between the dog and a familiar person is an important for elevated oxytocin level, in both the human and dog. The afferent sensory fibers in the skin will send signals so the oxytocin level increases. This will be discussed more detailed later. Parent care, nursing, social interaction, pair bonding as important social behaviors that can lead to love, reduced stress and safety (Gerald, Gimpl and Fahrenholz, Falk, 2001).

At the initial phase of labor, number of oxytocin receptors in the uterus (in the myometrium) increases up to 200 times higher than in a non-pregnant animal. Because of the increase in number of oxytocin receptors in the uterus the female gets very sensitive to the peptide hormone. The reason for the elevated oxytocin level can be related to the gonadal steroids. Near the end of the gestation there is a high concentration of plasma progesterone and a low concentration of plasma estrogen. In the placenta to primates CRH (corticotropin releasing hormone) is synthesized and will stimulate the fetal adrenal gland to produce precursors of placental estrogen, so the estrogen level will increase in the maternal placenta, gap junctions is formed in the myometrium in the uterus, thus increase production of prostaglandins and also more oxytocin receptors are developed (as well as luteolysis happens, so increased oxytocin level increase PGF2-α production). Also during the labor, the fetus pushes on the birth canal so the Ferguson reflex is released, and more oxytocin is released. Oxytocin antagonist may be used for avoid premature births. After the birth the number of oxytocin receptors reduces rapidly. Estrogen and progesterone has apposite effects on the function and expression of the oxytocin. Oxytocin stabilizes the progesterone synthesis before the parturition.

As mentioned, milk ejection is one of the classical pathways for oxytocin. When the offspring starts suckling on the nipple, afferent sensory fibers (tactile) are stimulated and the signals are first sent to the central nervous system and then to the hypothalamus, and the oxytocin is released from the posterior lobe of the pituitary gland, which is released into the bloodstream and enters the lactating glands. The effect is called milk-let down reflex where the oxytocin enters the myoepithelium surrounding the muscles, then the muscles contract and release the milk into the ducts. Other sensory factors like olfactory, visual (see the offspring) and auditory (begging for food) can elicits this reflex as well. In experiments on mice it has been showed that lack of oxytocin lead to absence to nurse, but it has also been recorded that injection with oxytocin can lead to milk production again (Gimpl, Gerald and Farenholz, Falk 2001).

Oxytocin is also found in the male, because it has a role in the reproduction and sexual control. In the male it can be found among other, in the testis. There are species differences where the oxytocin is located, in the testis, prostate gland or epididymis. Oxytocin is found in the Leyding´s cell in the rats. Leydig cells are responsible and the main source for production of testosterone in the male. But it is has been revealed that the testosterone itself has no impact on the secretion of oxytocin. Two roles are found for the oxytocin here, where one is the regulation of the smooth muscle contraction around the seminiferous tubules, where the sperm goes from there to the lumen of epididymis. The other is the modulation of steroidogenesis (formation of steroids from adrenal gland, testis or ovaries). Oxytocin is associated with ejaculation, which could happen when stimulating the smooth muscles of the reproductive organs in the male (Gimpl, Gerald and Farenholz, Falk, 2001).

Effects

Stress

Oxytocin can reduce the stress by decreasing the blood pressure and the corticosterone/cortisol, and increase the insulin and CCK (cholecystokinin) level. Oxytocin is able to decrease the mean arterial pressure and reduce the heart rate. During lactation: increased level of oxytocin leads to reduced stress. If the mother is stressed it can have a negative impact on the milk ejection and maternal caretaking. Because oxytocin has shown some anti-stress effects, it is also to assume that oxytocin is important for bonding between persons/animals, and social behavior.

Sexual behavior

Oxytocin is important in the regulation of the reproductive organs. During stimulation of the genitals and breasts oxytocin will be released into the blood circulation where it has a many effects. In female induced lordosis (willingness for copulation) and in male erection can be mentioned. Most of the animals, like the dog, breed only during certain time of year when the concentration of steroid hormones in the body is right.

Maternal behavior

Some signs can be seen before the actual delivery of the fetus, like nest building. Many studies has proven that increased oxytocin level in the blood will switch on the maternal instinct, but it is important to point out that is does not maintain the maternal behavior itself.

Why studies are relevant

Dogs have been living among humans for several millennia, and during this domestication dogs have developed many human-like social skills, e.g. attachment towards the owner. They have adapted the special socio-cognitive skills needed to make them excellent human companions. Studies measuring hormonal and physiological responses in humans and dogs during interaction indicate a similar “neuro-physiological” response to connect and interact with each other (Kis, Anna et al. 2014). This is important for understanding the mechanisms behind the social part of interspecies cohabitation and can also explain the mechanisms behind the psychosocial advantages behind human-animal interaction in treatment of both psychological and physical diseases, which can provide several advantages in both human and veterinary medicine.

Presentation of the studies

Behavioral and endocrine studies show that Human-dog interactions have a significant impact on the endocrine oxytocin level in the dog. Various studies address oxytocin release in the domestic dogs during social interaction with humans. All the research we addressed included a dog and human being; the measurement of oxytocin was a urine sample, saliva sample or blood sampling where the blood and saliva sample gave the best result.

Many studies show how oxytocin acts as a key hormone in pair-bonding between two dogs and maternal bonding mother and puppy. In this essay we have looked at several different studies that have investigated how oxytocin is released and how it affect the social behavior of the dog brain.

In this first study (Rhen Therese et al. 2014) they researched how physical interaction and non-physical interaction, vocal and eye contact with the domestic dog and ignorance of the dog affected release of oxytocin in the brain. The result shows a significant release of oxytocin, which has a great affect in the social bonding between the dog and owner. The study also showed that physical contact has a stronger effect on the release, than non-physical contact.

Non-physical contact will affect the oxytocin release especially when the dog was being reunited with a familiar person. How the studies is executed is that it is divided into three parts, one where the owner is physical and vocal towards the dog, second when the owner used only vocal communication and third when the owner ignores the dog. It is performed a series of sequences involving separation, approaching, reappearance, reunion and relaxation between the dog and its owner.

Basal phase is the first phase, where the dog is being prepared and the first blood sample is taken to measure the oxytocin level of the blood. Next is the approaching phase when the owner approaches the dog and is reunited, the three different tests were done and blood tests were taken when reuniting at the beginning and after a few minutes. The relaxation phase lasted for a longer period where the owner sat down and read a book, and three blood samples were collected at the beginning, after 30 min. and at the end of the phase.

The result showed the maximum increase during the reunion with the physical and vocal treatment, as well as during the relaxation phase, compared to the samples taken at basal phase. During the vocal treatment there were only an increase in the oxytocin level at the reuniting phase, then the level drops and stabilized when entering relaxation phase. Even when being ignored the oxytocin level increased during reuniting phase and decreased in the relaxation phase, showing similar result as to the vocal treatment.

The study shows us that endocrine response is affected in social interactions with humans. However there was a significant difference between interacting with the dog using both vocal and physical communication, compared to interaction using only vocal communication. They conclude that being present and using physical contact is important for socializing and the welfare of the animal. Where being in contact with the animal has a greater influence of hormone release.

Another study (Romero Teresa et al 2013), address how oxytocin can inflect social behavior and interaction with humans and other dogs, by triggering an increase of the dogs oxytocin level in the blood by spraying it intranasal. There were two test groups and the control group was sprayed with saline solution without oxytocin. A urine sample was taken on all the test dogs before the test and after the test to measure the level of oxytocin. The study looked at how the dog interacted with its owner and how the oxytocin level in the brain affected this interaction.

After given the oxytocin spray, the dog and owner were together in the same room. The owner did not interact much with the dog, it was either ignored or briefly pushed away if the dog were making contact.

The group that were treated with the oxytocin spray showed significant more contact and with the owner while the control group that were sprayed with the saline solution didn’t show any specific changes when interacting. The urine sample had no significant increase in oxytocin, however the oxytocin treatment affected the dog’s social interaction towards the owner, looking back at the owner, licking and standing closer.

A third study (Odendaal J. S. J and Meintjes R. A. 2003) measuring hormonal changes in both species during human-dog interaction. The tests were performed in a neutral space without any outside disturbance The research measures the blood pressure and different hormones levels in the blood in both human and animals. The dogs were used to human contact and got time to adapt to the environment. The interaction between the dog and human consisted of talking with a calm voice, stroking the dog, playing with it and scratching behind its ear. Blood samples were taken when the blood pressure were stable.

The research indicates that the mean arterial blood pressure decreased in both human and dog during positive interaction as well as a significant increase in oxytocin and other hormones (prolactin, beta-endorphins).

The different studies are showing the social interaction between human and dogs, and the increase of oxytocin. The different studies have concluded with, when there is interaction with humans, oxytocin is released. The oxytocin release has a greater effect on how the dog interacts with the owner.

Meaning of the results

Results of studies show that both human and dogs have an increased oxytocin level (in blood plasma), as well as several other hormonal and physiological changes, in response to positive interaction between pets and owners. The hormonal changes and responses are able to cross a species barrier. In some studies the pet didn’t even belong to the human they preformed the experiment with, but the humans possessed feelings of affection towards dogs and the dogs were used to human contact (Odendaal J. S. J. and Meintjes R. A. 2003). Meaning both humans and dogs benefit from positive interaction, and the human-dog interaction promotes a relaxing and bonding affiliation.

The increasing oxytocin is probably the reason why we can observe decreasing blood pressure. Through the mechanisms of oxytocin companion animals are believed to decrease anxiety, loneliness and depression, while increasing a “feeling of safety” and provides contact comfort and companionship. Oxytocin is known to promote intimate bonding, and strongly correlates with joyous, affectionate, sexual and reproductive behavior. Increasing prolactin levels probably inhibits the sexual behavior, as prolactin promotes bonding in association with a more parental behavior (Odendaal J. S. J. and Meintjes R. A. 2003).

Studies suggest that the visual stimulation alone can increase oxytocin levels in dogs, even though verbal and physical contact gives a stronger increase (Rehn Therese etc. 2014). This indicates that the need for nurturance, affiliation and attachment is rooted in the biology of the species and these needs can cross the species barrier, as both species responds with similar neurophysiological changes (Odendaal J. S. J. and Meintjes R. A. 2003).

The human-dog relationship is a two-way fulfilling Attentions evens (Attentionis evens: describes the need for attention on a normal, basic emotional level as a prerequisite for successful social interaction). The positive interspecies interactions provide a good working social symbiotic relationship. Which can be very useful in veterinary practice to understand the bond between the patient and client (Odendaal J. S. J. and Meintjes R. A. 2003).

Benefits of future research

It could be beneficial with more studies to further reveal the dynamics of the oxytocin release during human-animal interactions. New studies could further reveal the health promoting effects of interspecies interactions (Handlin, Linda et al. 2011), and a better understanding of benefits provided by therapy- and service dogs. Studies with a larger number of participants, of both genders, different ages, breeds and relation between human and dogs. Measuring hormonal and physiological responses in both species under standardized conditions with control groups (Handlin, Linda et al 2011).

Many of the studies focus mainly on the human benefits of human-animal interaction. From a veterinary perspective it would be interesting with studies focusing more on the responses and benefits of the animals, giving us a better understanding of how the dogs endocrine system can provide health benefits for pets as well.

Oxytocin has a role in several social disorders in humans, such as Alzheimer’s, schizophrenia, OCD, autism etc. further studies may give a better understanding of these disorders. Because dogs have similar responses and similar structure of the oxytocin-molecule they might be a good model species for treatment in behaviour genetic research ( Kis, Anna et al. 2014 and Gimpl, Gerald and Fahrenholz, Falk 2001).

References

• Beetz,Andrea, Uvnäs-Moberg Kerstin, Julius Henri, Kotrschal Kurt (2012) “Physiosocial and psychophysiological Effects on Human-Animal Interactions: The Possible Role of Oxytocin”, Front Physiol 3: 234. Download: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3408111/

• Gimple, Gerlad and Fahrenholz, Falk (2001) ”The oxytocin Receptor System: Structure, Function, and Regulation”, Physiological reviews 81(2): 630-660 http://physrev.physiology.org/content/physrev/81/2/629.full.pdf

• Handlin Linda, Hydbring-Sandberg Eva, Nilsson Anne, Ejdebäck Mikael, Jansson Anna, Uvnäs-Moberg Kerstin (2001) “Short-Term Interaction between Dogs and Their Owners: Effects on Oxytocin, Cortisol, Insulin and Heart Rate—An Exploratory Study”, Anthrozoös 24(3): 301-315

• Kis Anna, Bence Melinda, Lakatos Gabriella, Pergel Eniko, Turcsán Borbála, Pluijmakers Jolanda, Vas Judit, Elek Zsuzsanna, Brúder Ildikó, Földi Levente,Sasvári-Szèkely Mária,Miklósi Adám,Rónai Zsolt,Kubinyi Eniko (2014) ”Oxytocin Receptor Gene Polymorphisms Are Associated with Human Directed Social Behavior in Dogs (Canis familiaris)”, Plose One 9(1): e83993. Download: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3893090/

• Odendaal, J.S.J and Meintjes, R.A (2003) “Neurophysiological Correlates of Affiliative Behaviour between Humans and dogs”, The veterinary journal 165: 296-301
• Rhen Therese, Handlin Linda, Uvnäs-Moberg Kerstin, Keeling Linda J. (2014) “Dogs' endocrine and behavioural responses at reunion are affected by how the human initiates contact”, Elsevier 45-53
• Romeo Teresa, Nagasawa Miho, Mogi Kazutaka, Hasegawa Toshikazu, Kikusui Takefumi (2014) “Oxytocin promotes social bonding in dogs” PNAS 111 (25): 9085-9090

Pictures

• Oxytocin structure http://www.molecular-networks.com/biopath3/biopath/mols/Oxytocin

• Human and dog interaction http://commons.wikimedia.org/wiki/Category:Dachshunds#mediaviewer/File:Always_Ready_To_Greet_(8120636626).jpg