Introduction

Since 1910, when Ott and Scott [1] published their discovers about the oxytocin participation in milk ejection, the comprehension about function and role of oxytocin in several physiological functions didn’t stop enlarging and growing. In birth, through his action over uterus contractions, in uterus contractions in women’s orgasm and men’s erection [2,3], for instance. However, this approach always considers its peripheral effects. After this, some oxytocin effects had been reported to have actions over behavioural traits, like we can see in publishings of Pedersen and Prange [4] and Winslow and co-workers [5], reporting the oxytocin actions over, respectively, maternal behaviour and pair bonding. Since then, the increasing data about the oxytocin’s function in behaviour and its central action can’t be ignored. In this short proposal, we’ll consider the opportunity or utility of thinking about oxytocin as a system, instead of a single neurotransmitter.

Neurotransmitter or Hormone: Central and Peripheral Actions of Oxytocin

Once a molecule could have his function defined through the way it acts over the organism, not for his special chemical properties we can think about oxytocin as a hormone or neurotransmitter. If it is released into the bloodstream and have his effects on distant organs, we used to consider a particular molecule a “hormone”. If this release takes place in a close and specific locus, very close to the releasing point and with specific effects, we used to consider this molecule a “neurotransmitter”. So, oxytocin has both functions and its neurotransmitter action has been heavily and abundantly reported in academic publishing since decades ago to more recent studies [6-10].

More recently we found the oxytocin participation in broader traits, as social behaviour [11-13] in a great spectrum of functions and actions, like affiliative and romantic behaviours [14], empathy [15,16] or the oxytocin’s effect in social contact [17,18] and the benefits of oxytocin-releasing over stress [19,20]. This kind of publishing list goes far and far [21].

Special mention to the Porge’s work [22], who assembled great amount of data about a social behaviour system, including a particular theory that gathers these results in a comprehensive whole, presenting the idea that the mammalians have three systems: social engagement system (relax and interact, oxytocin being the main neurotransmitter), mobilization system (to face the challenges, stress-like reactions) and immobilization (feigning death, passive avoidance). In the same direction, we have the Cozolino works [23], who consider the human relationships in a neural point of view, presenting the importance of oxytocin in attachment too. There is a great number of publishing about the importance of oxytocin in social behaviour or even and especially the importance of this molecule to regulate stress reactions in a very beneficial way, in this way our research about oxytocin effects on stress reaction in a model of social stress: the findings were indicative that oxytocin exerts an inhibitory effect on cortisol levels, pointing oxytocin have an inhibitory effect over stress reaction [24].

In a very informative and insightful publishing, Lee and coworkers [25] reviewed the actions of oxytocin and noticed that all these actions can be understood under a single line: interaction, social behaviour, friendship, bonding, reproduction and nurture. In this line of thinking they consider oxytocin “the great facilitator of life” (indeed, the title of his article).

Reasons for an Oxytocinergic System Research

Some consider this kind of proposal simply “philosophical”, or, in other words, purely logical questions with no empirical consequences. We consider it in a very different way. When you think about dopamine like a “rewarding system” we can understand a lot of behaviours better, like addiction or the search for something “better” in human behaviour. Or when we consider the clinical approach of serotonin, we think better when we consider how it can be relevant to the human mood with great consequences for the affective disorders treatment. This progress does not come considering simply or uniquely a molecule effect, isolated from a class or behaviour that we have studying at the moment. When we think of emotions in the context of mammalian survival we can understand its action much better and in an insightful way, like in Panksepp analysis [26,27].

Bringing to the discussion Nicholas Tinbergen's teachings [28], the researchers must always have in mind the different classes of causes. Considering the action of a single molecule the researcher is in the field of “proximate explanations”. And when the researcher considers a “system”, involving a certain class of behaviour, he is able to step forward to “ultimate explanations”, what brings the full picture. So, it is not a simple matter of “philosophical” question, but the very ground of Evolutive Psychology. Not considering this can bring a lot of unfortunate misleading and misinterpretation of the results.

It is so because we are trying to understand an organism, not a single chemical interaction isolated from the context where it happens – the animal itself (despite the fact that without understanding the chemical interaction we can’t understand the whole). Simplifying the complex to achieve a better comprehension of the whole is an approach that has brought to us much of our actual knowledge [29]. So, when we have solid material and information about a molecule and its action through a range of functions and behaviours, and we can see that these actions belong to the same class, is time to consider if we don’t have a “system”.

Which advantage does it bring to us?

The same that we have found in considering a “noradrenergic system” or a “dopaminergic system”. A concept like “oxytocinergic system” makes question formulation easier formulating questions, design experimental essays and the interpretation of the results can be much more accurate [30].

Conclusions

The research about complex behaviour has had a great benefit and improvement when we consider not just a punctual effect of a molecule, but its action in a broader context. Why not think about oxytocin as a system with a particular function and purposes instead of a simple molecule? It is time to change it and subscribe “oxytocin” officially a system of social behaviour with great function against the hazardous chronic stress effects. We say “officially” because it already happens informally. Despite in scientific publishing, one doesn’t find the expression “oxytocinergic system” we think about oxytocin as a system of social behaviour. It seems to us that is a great advance and means a guidance for the future research and discussion of the results of essays and can put the question that drives the research in a more accurate way. Adding to it, this allows the approximation of social issues and psychological questions to the laboratory, what we can see – very richly in stress studies, for instance.

We also consider it could be a great progress for the teaching and training of students in the field, presenting the subject in a more organized way allowing a deeper understanding of the architecture of behaviour, linking it with the purposes of life and the general lines of the biological way of thinking.

After all, the understanding of the particular effect of a molecule only gets this true meaning when we consider the broader effect in a singular class of behaviour that have this purpose in the pursuit of living well. And in its lays the ultimate porpoise of the scientific labour: the understanding and improvement of the well-being with significance.

References

1. Ott I, Scott JC (1910) The action of infundibulum upon mammary secretion. Proc Soc Exp Biol 8: 48-49.
2. Andersson KE (2011) Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction. Pharmacol Rev 63: 811-859.
3. Carter S (1992) Oxytocin and sexual behavior. Neurosci Biobehav Res Rev 16: 131-144.
4. Pedersen CA, Prange AJ (1979) Induction of maternal behaviour in virgin rats after intracerebroventricular administration of oxytocin. Proc Natl Acad Sci USA 76: 6661-6665.
5. Winslow JT, Hastings N, Carter CS, Harbaugh CR, Insel TR (1993) A Role for Central Vasopressin in pair bonding in monogamous prairie voles. Nature 365: 545-548.
6. Swanson LW, Hökfelt T, Björklund A (1987) Handbook of chemical neuroanatomy, Vol. 5, Integrated Systems of the CNS, part I, Elsevier Science Publishers.
7. Sofroniew MV (1980) Projections from vasopressin, oxytocin, and neurophysin neurons to neural targets in the rat and human. J Histochem Cytochem 28: 475-478.
8. Onaka T (2014) Neural pathways controlling central and peripheral oxytocin release during stress. J Neuroendocrinol 16: 308-312.
9. Herbert J (1994) Peptides in the limbic system: Neurochemical codes for co-ordinated adaptive responses to behavioural and physiological demand. Great Britain: Pergamon Prma Ltd.
10. Sawchenko PE, Swanson LW (1982) Immunohistochemical identification of neurons in the paraventricular nucleus of the hypothalamus that project to the medulla or to the spinal cord in the rat. J Comp Neurol 205: 260-272.
11. Donaldson ZR, Young LJ (2008) Oxytocin, vasopressin, and the neurogenetics of sociality. Science 322: 900-904.
12. Goodson JL, Thompson RR (2010) Nonapeptide mechanisms of social cognition, behavior, and species-specific social systems. Curr Opin Neurobiol 20: 784-794.
13. Heinrichs M, Von Dawans B, Domes G (2009) Oxytocin, vasopressin, and human social behavior. Front Neuroendocrinol 30: 548-557.
14. De’Biec J (2007) From affiliative behaviours to romantic feelings: A role of nanopeptides. FEBS Letters 581: 2580-2586.
15. Wu N, Li Z, Su Y (2012) The association between oxytocin receptor gene polymorphism (OXTR) and trait empathy. J Affect Disord 138: 468-472.
16. Abu-Akel A, Palgi S, Klein E, Decety J, Shamay-Tsoory S (2015) Oxytocin increases empathy to pain when adopting the other- but not the self-perspective. Soc Neurosci 10: 7-15.
17. Uvnäs-Moberg K, Petersson M (2005) Oxytocin, a mediator of anti-stress, well-being, social interaction, growth and healing. Zeitsch Psychosom Med Psychother 51: 57-80.
18. Uvnäs-Moberg K (1997) Physiological and endocrine effects of social contact. Ann N Y Acad Sci 807: 146-163.
19. Uvnäs-Moberg K (1999) Oxytocin may mediate the benefits of positive social interaction and emotions. Psychoneuroendocrinology 23: 819-835.
20. Onaka T, Takayanagi Y, Yoshida M (2012) Roles of Oxytocin Neurones in the Control of Stress, Energy Metabolism, and Social Behaviour. J Neuroendocrinol 24: 587-598.
21. Olff M, Frijling JL, Kubzansky LD, Bradley B, Ellenbogen MA (2013) The role of oxytocin in social bonding, stress regulation and mental health: an update on the moderating effects of context and interindividual differences. Psychoneuroendocrinology 38: 1883-1894.
22. Porges SW (2011) The Polyvagal Theory: neurophysiological foundations of emotions, attachment, communication and self-regulation. New York, WW Norton & Company.
23. Cozolino L (2014) The Neuroscience of Human Relationships: attachment and the development of social brain. 2^nd ed., London: WW Norton & Co.
24. LIMA JPC (2015) Effects of an oxytocin nasal spray over autonomic parameters and cortisol level in a model of social stress. Doctoral thesis, Mentor Prof. Dr Avelino Luiz Rodrigues, Institut of Psychology, University of São Paulo, São Paulo.
25. Lee HJ, Macbeth AH, Pagani JH, Young WS 3^rd (2009) Oxytocin: the great facilitator of life. Prog Neurobiol 88: 127-151.
26. Panksepp J (1998) Affective Neuroscience: the foundations of human and animal emotions. New York: Oxford Press University.
27. Lima JPC, Rodrigues AL (2017) Praise Be to Jaak Panksepp. Acta Psychopathol 3: 3.
28. Tinbergen N (1963) On aims and methods of ethology. Zeitschrift für Tierpsychologie 20: 410-433.
29. Kandel ER (2016) Reductionism in Art and Brain Science. New York, Columbia University Press.
30. Churchland PS, Winkielman P (2012) Modulating social behaviour with oxytocin: How does it work? What does it mean? Oxytocin, vasopressin and social behaviour. Horm Behav 61: 392-399.