Vasopressin Explained: How Oxytocin’s Partner Shapes Stress, Bonding, and Survival
Last week we talked about the peptide oxytocin (OT). This week we explore the other ancient peptide molecule, vasopressin (VT). Oxytocin and VP are genetic and biochemical siblings. Both originated from a single ancestral gene that produced vasotocin. Vasotocin is found in reptiles and other vertebrates and can be measured in the mammalian fetus. OT and VP, with their receptors, function as an integrated, adaptive system, allowing the mammalian body to survive, maintain homeostasis, and reproduce in an ever-changing world.
Sources of individual differences in OT and VP and the sensitivity of their receptors include gender and basic genetic differences. For example, some species, including humans and other socially monogamous mammals, such as prairie voles and dogs, have high levels of OT and an apparent dependence on OT to allow the expression of high sociality and attention to positive social cues. The OT receptor (OTR) and V1 receptor (V1aR) also can be epigenetically tuned by experience, increasing the capacity of OT and VP to have complex adaptive functions.
Vasopressin
Vasopressin peptides and their receptors are evolved components of an integrated and adaptive system pathway. Following are some of the primary functions they support including individual survival and defensive behaviors:
- Physical and Emotional Adaption
Vasopressin and its receptors may be of critical importance in the capacity for physical and emotional adaption in the presence of stressful experiences. VP is involved, synergizing with the corticotrophin-releasing hormone (CRH) in hypothalamic regulation of the pituitary, supporting the release of glucocorticoids and mobilized defense strategies against various physical and emotional stressors or threats.
- Protective Role
Vasopressin also plays a protective role in the behavioral defense of self and the family. It is associated with physical and emotional mobilization and helps support vigilance and behaviors needed for guarding a partner or territory, as well as other forms of adaptive self-defense. Prairie voles have provided a useful model for examining the importance of peptides in selective aggression. In this species, immediately after mating males became lethally aggressive toward strangers, but not familiar partners or family Members.
- Avoidance of Danger and Survival
The development of memory necessary for the avoidance of danger or survival and psychological processes associated with anxiety and obsessions also may rely on VP. VP, in the context of other centrally active molecules, such as CRH, dopamine, and serotonin, regulates emotional states, including anxiety.
- Aggression, Anxiety, and Cardiovascular Risk
The VP system may also lower thresholds to impulsive forms of aggression, possibly by reducing cortical inhibition. The actions of VP also help to explain the association of anxiety and ruminations with cardiovascular risk. VP plays a central role in circadian rhythms and is likely to be important in sleep disturbances or elevations in blood pressure, which are also common following stress and considered defining features of posttraumatic stress (PTS) disorders. In human males, high blood levels of VP have been correlated with emotional dysregulation and aggression.
Vasopressin Partnership with Oxytocin
Current knowledge concerning OT and VP and their receptors indicate that these are interactive components of an evolved and integrated system (OT–VP pathway). It has long been known that both peptides can bind to both the OT and VP receptors in vitro. When looking at the whole organism, OT and VP tend to affect more than one receptor and several types of behavioral functions. In mammals, receptors for OT and/or VP are typically abundant in areas of the nervous system that regulate social, emotional, and adaptive behaviors and reward.
Complex behavioral functions, including selective sexual behaviors, social bonds, and parenting require combined activities of OT and VP. The behavioral effects of OT and VP vary depending on perceived emotional context and the history of the individual. Paradoxical or contextual actions of OT also may reflect differential interactions with the OTR and V1aR. Adding to the complexity of this pathway is the fact that OT and VP receptors are variable, across species, individuals, and brain region, and these receptors are capable of being epigenetically tuned. This variation may help to explain experience-related individual and sex differences in behaviors that are regulated by these peptides, including the capacity to form social attachments and the emotional consequences of these attachments. The following bullet points provide some of the functions where both OT and VP or their receptors are required:
- Lactation
Lactation is a defining feature of mammals, and contraction of breast tissue and milk ejection requires stimulation of the OTR. Lactation arose in conjunction with the evolution of mammals and is one of the comparatively few reproductive functions that do not continue in the absence of OT or the OTR. Immature mammalian offspring depend for varying periods of time after birth on their mother’s milk. Conservation of fluids is necessary for lactation and effects of VP on the kidney and blood pressure probably support normal milk production, but this is presumably under separate control from milk ejection.
- Birth and Uterine Contractions
Although OT has been assumed to play a fundamental role in birth, current evidence suggests that OT alone acting on the OTR is NOT capable of inducing normal labor and blocking only the OTR does NOT prevent premature birth. Rather both OT and VP and both the OTR and V1aR regulate uterine contractions. Thus, it is not surprising that female mice made mutant for OT or the OTR remain capable of giving birth. In fact, especially under conditions of stress, VP is likely to have a much greater role in birth than has been acknowledged. VP’s effects on the uterus, although functionally different from OT, may help to explain premature labor and preeclampsia, which are associated with adversity or stress across the life span.
- Parental Behavior
A functional role for VP in maternal behavior cannot be excluded. The role of OT in maternal behavior may depend in part on the capacity of OT to directly or indirectly override the defensive effects of VP and reduce fear in the presence of young animals. VP, in conjunction with OT, also supports the capacity to protect offspring, in the form of postpartum maternal or paternal aggression in rodents. The formation of partner preferences and pair bonds requires access not only to the V1aR but also the oxytocin receptors. Mate guarding and parental aggression offer examples, among several, suggesting the importance of both OT and VP and their receptors in behaviors that are socially selective.
- Threatening Environments and Aggression
Vasopressin and the V1aR may be of critical importance in the capacity for physical and emotional adaption in the presence of stressful experiences. VP is involved, synergizing with CRH, in hypothalamic regulation of the pituitary, supporting the release of glucocorticoids and mobilized defense strategies against various physical and emotional stressors or threats. OT also can be released during stressful experiences and is sometimes considered a “stress-coping” molecule.
- Selective Aggression
Prairie voles have provided a useful model for examining the importance of peptides in selective aggression. In this species, immediately after mating males became lethally aggressive toward strangers, but not familiar partners or family members; this response was blocked by antagonists for the V1aR. The formation of partner preferences and pair bonds requires access not only to the V1aR but also the OTR. Mate guarding and parental aggression offer examples, among several, suggesting the importance of both OT and VP and their receptors in behaviors that are socially selective.
- Non-Selective versus Selective Social Behaviors
Oxytocin’s role in social behaviors has been documented in many species, including humans. Based primarily on work in nonhuman animals, in many, but not all cases, the effects of OT are mediated via VP receptors. This seems to be the case in behaviors that are non-selective, such as a general tendency toward sociality or gregarious behavior. This may include behavioral patterns involving social recognition. Among other examples, in which both OT and VP receptors were examined, are social contact, including lying adjacent to another member of the same species and huddling with conspecifics in the presence of the odor of a predator; these were facilitated by OT but only when the V1aR was accessible.
Prairie voles demonstrated the capacity of OT to increase social contact between adults. However, in studies in which either the OTR or VP were blocked, both OT and VP receptors were necessary for pair bond formation. When both OTR and the V1aR were blocked animals showed very low levels of contact behavior. In pair bond formation, OT and VP interact with motivational and reward systems and may enhance or otherwise amplify the effects of other molecules including dopamine and opioids in specific brain regions, including those that have been implicated in both maternal behavior and social bonding.
Summary
Across the lifespan, the effects of OT and VP dynamically interact to adjust to and influence the perception of fear and safety. VP is the evolutionarily older molecule with presumably the older receptors. VP is implicated in mobilized behaviors including defense of self and the family. Among the patterns of behavior for which both OT and VP may be necessary are sexual behavior, paternal behavior, and pair bonding. OT is of special relevance to adaptations that involve high levels of sociality, a sense of psychological safety within a family or familiar social group, as well as emotional regulation and higher levels of rational cognition. Furthermore, working together OT and VP, and their receptors, create a biological and genetic pathway that regulates attachment and bonding, which in turn may be protective against threats or other forms of challenge.
To us, and the work we do, this information provides hope that through knowledge and focus on these peptides, we can more efficiently support our clients in areas that may be impacted by the inefficient functioning of this complex molecules. Through the use of dietary and mindful practices, we can initiate enhanced support to these important peptides. Hence, potentially improving the roles they play in our lives.
Note: The majority of the information for this blog was taken from the below referenced article. If you want more information and additional supporting pictures don’t hesitate to check it out.
References:
The Oxytocin–Vasopressin Pathway in the Context of Love and Fear, C. Sue Carter, Dec 2017, Frontiers in Endocrinology,
