“If you only knew what kind of rubbish…” Anna Akhmatova's catchphrase is the best fit to describe oxytocin and its evolution. A hormone that has risen from the regulation of the most basic instincts to an honorable and inspirational role - the molecule of love.
It all started with voles, close relatives of mice. More precisely, from two species of voles - steppe voles (Microtus ochro-gaster) and meadow voles (Microtus pennsylvanicus), very close to each other in everything except one: love. Steppe voles prefer “romantic” love, or, as scientists say, the K-strategy of reproduction. They are monogamous and bond tightly to their partners. Father and mother raise offspring together, spending up to two thirds of their time in the nest. Unlike steppe voles, meadow voles are polygamous, the father does not take part in caring for the young at all, and the mother stays with them only about a third of the time.
Comparing those and others, biologists have found a serious difference in the work of one of the hormones in their brain - oxytocin: in steppe voles, it works much more actively than in meadow voles. Moreover, turning off the production of oxytocin in the experiment practically "turned off" the concern for offspring and the tendency to monogamy in the vole - and the artificial injection of an amazing substance made even careless meadow voles models of conjugal virtue and parental love.
Experiments have shown that oxytocin acts as a kind of hormonal glue for social relationships. It is produced when familiar individuals of the same species meet; in turn, animals with a “knocked out” (turned off) gene responsible for the synthesis of this substance are unable to recognize their fellow tribesmen. And even more so, they are unable to form a stable pair. However, love, caring and communication have not always been the fiefdom of oxytocin. From the point of view of chemistry, oxytocin is a simple oligopeptide containing only nine amino acids, that is, a hundred times less than the average protein. But from the point of view of behavior, oxytocin is a modulator and stimulator of a great variety of reactions of very different levels and nature.
Breathe deeply and relax
Oxytocin is produced by a tiny, but most important gland in the diencephalon - the hypothalamus. Closely connected with other parts of the central nervous system, the hypothalamus regulates heat transfer and sexual behavior, sets the rhythms of wakefulness and sleep, controls the feeling of hunger and thirst.
Together with the pituitary gland, it forms a pair, which plays a central role in the work of the entire endocrine system, coordinating and directing its activity. Oxytocin is no exception: being produced in the hypothalamus, this peptide hormone is transported by neurons to the pituitary gland, which serves as a kind of depot for it. The accumulated reserves of oxytocin are released from here as needed - and create very diverse effects. And the main task of oxytocin is evident from its name, which can be translated as "accelerating labor."
Evolution does not like fundamentally new solutions and, as a rule, modifies existing ones, adapting old proven tools to perform new functions. Oxytocin is no exception: the hormone's original purpose may have been to stimulate the smooth muscles of the uterus. Already in small doses, it is able to increase the frequency and amplitude of its contractions, and in large doses it can even cause titanic, especially intense spasms.
Oxytocin also has a pronounced effect on nursing mothers, increasing milk production.All these processes manifest themselves with mechanical irritation of the cervix and the walls of the vagina and are mediated by the release of oxytocin from the pituitary gland, which in medicine is called the Ferguson reflex. It also enhances maternal behavior, so doctors used its injections to clinically correct parental love anomalies long before biologists studied voles. Oxytocin can also be bought from veterinarians: it makes childbirth easier for women, cats and dogs.
By the way, due to the effect on the muscles of the uterus, experiments on the study of the effects of oxytocin on humans are tried to be carried out strictly with male volunteers: for obvious reasons, they do not have these effects. But this does not mean that there are no other manifestations: experiments have shown that regardless of gender, people who inhaled oxytocin significantly higher rated the attractiveness of potential partners. And in both sexes, romantic love is necessarily a surge of oxytocin. According to data recently voiced by Japanese scientists, domestication of dogs would hardly be possible without oxytocin. The researchers found that any contact of the animal with the owner leads to an increase in the level of this hormone in the urine of both of them. Moreover, inhalation of oxytocin made bitches pay more attention to their owner and males more suspicious of strangers. At the same time, such effects were not observed in wild wolves: scientists believe that the mechanism that arose, first of all, to ensure contact between mother and child, became a product of the joint evolution of humans and dogs, which they almost took into the family.
From orgasm to exam
Man is a species whose evolutionary history is far from complete. It is believed by many experts that one of the changes occurring to our family throughout cultural history is the slow but sure transition from the r-strategy to the K-strategy. This process is accompanied by the increasing involvement of both parents in raising their offspring, the development of the cult of "true love" and the increasing role of oxytocin.
Remember what effect this hormone has on the vole? In humans, its effect is no less pronounced: oxytocin clearly enhances attachment to "friends". In experiments using trust games, it was shown that a pair of injections of oxytocin in both nostrils are sufficient to significantly increase the players' confidence in each other. Injections significantly increase goodwill towards strangers. But a particularly powerful release of oxytocin occurs during orgasm, which, apparently, is designed to turn lovers into true lovers.
The ability to forget all bad things and calm down, which is associated with an increase in oxytocin, provides a significant role for the hormone in reducing the body's response to stress. However, at the same time, it reduces anxiety and weakens memory - which means that it is not always useful. Students with elevated levels of oxytocin usually have poor exam results. Perhaps that is why strict and experienced teachers advise to think less about love - and more about learning?
The "love" value of oxytocin is considered secondary, but this role, apparently, has no less ancient history than participation in childbirth. An analogue of this hormone is involved in the regulation of sexual behavior even in roundworms. Rats, "intoxicated" with oxytocin, better maintain contact with relatives, but poorly retain memories of negative experiences - even if it was an electric shock. Perhaps it is the release of oxytocin that allows mothers to forget about all the horrors associated with childbirth - and love their baby, despite all the torment he caused them.
In general, the set of hormones associated with love for a sexual partner is quite close to the set of "love for children." For example, prolactin, which stimulates breast milk production, is also released during orgasm.However, the simplest way to get the pituitary gland to share its accumulated reserves of oxytocin is not even sex, but just a friendly, benevolent hug. Recent experiments in mice have shown that virgin females, inhaled with oxytocin, show almost the same zeal in caring for their offspring as experienced mothers. Forgetting about their usual indifferent behavior, they begin to actively respond to calls for help. This observation allowed scientists to discover some previously unknown details of how oxytocin works. For example, it turned out that especially numerous receptors for this hormone are found in the auditory cortex in the left hemisphere of the brain of rodents, stimulating the susceptibility of neurons located here. Perhaps this is what makes it easier for young female mice to hear and distinguish the voices of babies - and fixes them in memory.
This is not a man's business
Strictly speaking, the effect of oxytocin is not necessarily so positive. We already know that it weakens memory and anxiety, reduces cognitive functions (is it not for nothing that lovers become so stupid?) - all these phenomena are not so joyful. And he does not work on men unambiguously.
For example, young fathers who tend to mess around and play with their babies for longer have relatively high levels of oxytocin - although it is still not clear what comes first: whether the hormone stimulates care, or care causes its release into the blood.
At the same time, it turned out to be more difficult to approach the beautiful stranger “under oxytocin” than when taking a placebo. And in general, single men did not observe serious effects of the hormone, which once again demonstrates an important feature of its action: by itself, oxytocin does not cause the manifestation of this or that behavior, from care to love - it only modulates and consolidates existing inclinations and behavioral tendencies.
Thus, it has been shown that if a man maintains a close relationship with his mother, inhalation of oxytocin makes him speak of her with special warmth and affection. If the connection with the mother is lost or the relationship goes wrong, oxytocin only makes it especially painful to experience it. Interestingly, in addition to attachment to neighbors, oxytocin, apparently, enhances the willingness to protect them, and therefore - to act aggressively towards the “distant”.
However, the closest relative and antipode of oxytocin, vasopressin, is much more effective in this. Almost the exact opposite of oxytocin is another hypothalamic hormone, vasopressin. Its effect is characterized by increased memory and learning, increased anxiety. High activity of vasopressinergic systems and low oxytocinergic systems are observed in anorexia nervosa, and vice versa in schizophrenia. However, on behavior in general, vasopressin acts similarly to oxytocin, although if the latter increases the craving for "friends", then vasopressin is associated with increased hostility to "outsiders". But in general, the main task of vasopressin is the regulation of water-salt metabolism.
Only business - nothing personal
Despite all the odes that we had to lavish on oxytocin, it is worth warning those who, upon hearing an advertisement for a hormone-containing drug, rush to the pharmacy. Apart from medical use to help women in labor or cases of use by experienced doctors for the treatment of autism, some neuroses and dysphoria, pharmacological agents with oxytocin are rather dubious.
Their effects remain unconfirmed, licenses for use as medicines are not issued, and their circulation is not regulated. Strictly speaking, the effect of such drugs, which is sometimes so loudly announced by advertising, is not even proven. There are no known side effects - although, for example, the use of Pitocin, a synthetic analogue of oxytocin, to facilitate labor can be accompanied by vomiting and painful cramps.More research will be required before a "love molecule" grows into something like a "love potion". The official description of the drug oxytocin, which can be bought at the pharmacy, says: it has a stimulating effect on the smooth muscles of the uterus, contributes to the reduction of secretory cells surrounding the alveoli of the mammary glands (which facilitates the movement of milk into the large ducts and milk sinuses), reduces urination. Note, nothing is said about love.