Oxytocin and pain: a systematic review and synthesis of findings. Clin J Pain. 2014;30:453-462. [PMID: 23887343 DOI: 10.1097/ajp.0b013e31829f57df]

Oxytocin/Oxytocin Receptor Signalling in the Gastrointestinal System: Mechanisms and Therapeutic Potential

The neuropeptide hormone oxytocin (OT) is involved in various physiological and pathological processes via the oxytocin receptor (OTR). While OT is most widely known as a reproductive system hormone and a nervous system neurotransmitter, the OT/OTR system has gradually gained much attention for its role in the gastrointestinal (GI) system, such as the GI motility, secretion, and bowel inflammatory reactions. Its importance in GI cancers has also been reported in the past few decades. The promising clinical observations have revealed OT's anti-nociceptive effect, protective effect over gut injury, and the potential of using microbiota to naturally increase endogenous OT levels, which shed a light on the management of GI disorders with lower side effects. However, no current comprehensive review is available on the actions of OT/OTR in the GI tract. This review aims to present the lesser-known role of the OT/OTR system in the GI tract, and the most recent findings are discussed regarding the distribution and functional role of OTR signalling in regulating (patho)physiological functions of the GI tract. Special emphasis is placed on its therapeutic potential for clinical management of GI disorders, such as GI pain, inflammatory bowel disease (IBD), and irritable bowel syndrome (IBS). The recent characterisation of the OTR's crystal structure has advanced research for designing and identifying new OTR-specific molecules. Future in-depth basic and clinical research is needed to further elucidate the involvement and detailed mechanism of OT/OTR in GI disorders, and the development of OTR-specific ligands.

Subcutaneous Oxytocin Injection Reduces Heat Pain: A Randomized-Controlled Trial

Oxytocin (OT) is a neuropeptide broadly implicated in social relationships and behavior. OT also exerts antinociceptive and pain-reducing effects in both humans and rodents. Recent research in rodents demonstrates that these effects can be peripheral and local. In human studies, intravenous OT has reduced visceral pain, and subcutaneous injection of OT has reduced postsurgical pain. However, the local effects of subcutaneous OT on experimental pain have not been studied. We conducted a 2-session crossover study during which healthy adults received a subcutaneous injection of synthetic OT (4 mcg/2 mL) or saline placebo (isotonic saline 2 mL), in a randomized and double-blinded manner. Eighteen participants completed full study procedures. We hypothesized that 10 minutes after injection, OT would reduce measures of acute mechanical pain, pressure pain, and heat pain perception. Subcutaneous OT significantly reduced ratings of heat pain intensity and unpleasantness (both P < .01), but did not alter mechanical pain, pressure pain, or heat pain threshold (all P > .05). Changes in heat pain were observed only on the injected arm and not on the contralateral arm, confirming a localized mechanism. These findings confirm the ability of OT in or near the skin to modulate nociceptive processes in cutaneous tissues in human adults, opening exciting avenues for further mechanistic research as well as potential clinical applications for acute pain. PERSPECTIVE: This randomized-controlled trial showed that a subcutaneous injection of OT could reduce perception of heat pain tested with a thermode. OT did not alter mechanical or pressure pain or thresholds for perceiving heat pain. These findings are relevant to scientists and clinicians seeking nonaddictive local drug treatments for pain.

Arginine vasopressin deficiency: diagnosis, management and the relevance of oxytocin deficiency

Polyuria-polydipsia syndrome can be caused by central diabetes insipidus, nephrogenic diabetes insipidus or primary polydipsia. To avoid confusion with diabetes mellitus, the name 'central diabetes insipidus' was changed in 2022 to arginine vasopressin (AVP) deficiency and 'nephrogenic diabetes insipidus' was renamed as AVP resistance. To differentiate the three entities, various osmotic and non-osmotic copeptin-based stimulation tests have been introduced in the past decade. The hypertonic saline test plus plasma copeptin measurement emerged as the test with highest diagnostic accuracy, replacing the water deprivation test as the gold standard in differential diagnosis of the polyuria-polydipsia syndrome. The mainstay of treatment for AVP deficiency is AVP replacement with desmopressin, a synthetic analogue of AVP specific for AVP receptor 2 (AVPR2), which usually leads to rapid improvements in polyuria and polydipsia. The main adverse effect of desmopressin is dilutional hyponatraemia, which can be reduced by regularly performing the so-called desmopressin escape method. Evidence from the past few years suggests an additional oxytocin deficiency in patients with AVP deficiency. This potential deficiency should be further evaluated in future studies, including feasible provocation tests for clinical practice and interventional trials with oxytocin substitution.

Behavioral and physiological pain structures of PIPP-R and parental stress: structural equation modeling approach

BACKGROUND

Although most non-acute pain assessment tools are multi-dimensional (behavioral and physiological measures) in their approach, the outputs of such tools are considered unidimensional. This study aimed to explore and determine the behavioral and physiological pain structures of Premature Infant Pain Profile-Revised (PIPP-R) for neonates and its association with parental stress.

METHODS

This cross-sectional study was conducted in 2022-2023 in Isfahan, Iran. We recruited 400 pre-term infants, i.e. with gestational age (GA) of less than 37weeks who were admitted to the NICU of educational hospitals. PIPP-R and Parental Stressor Scale: Neonatal Intensive Care Unit (PSS: NICU) were used for data gathering. The latent structures of pain and its association with parental stress were explored using latent variable modeling approach.

RESULTS

A two-factor model, i.e. behavioral and physiological pain factors, was extracted, explaining 65% of the total variance. The results of confirmatory factor analysis showed that the identified structures in the exploratory factor analysis could be nearly replicated (CFI = 0.99، TLI = 0.98, RMSEA = 0.001). Behavioral pain structure, independent from gestational age had a significant direct association with parental stress score (β = 0.005, SE = 0.002, p = 0.026).

CONCLUSIONS

The PIPP-R assesses both behavioral and physiological pain factors. We also found that behavioral pain factor was associated with parental stress.

IMPACT

These results may provide a potential clue for physicians, nurses, and parents to manage the pain in preterm infant. The PIPP-R scores in preterm infants consist of "Behavioral and Physiological" pain factors. Single dependence on behavioral indicators (such as facial expression) has some limitations. Multidimensional tools may be the optimal method in detecting pain in preterm infants. Parental stress can affect behavioral pain structure in preterm infants. Intensive care nurses play an effective role in reducing the parental stress and pain severity of these preterm infants by including the help of mothers in procedures and providing them with psychological support.

The psychophysiology of music-based interventions and the experience of pain

In modern times there is increasing acceptance that music-based interventions are useful aids in the clinical treatment of a range of neurological and psychiatric conditions, including helping to reduce the perception of pain. Indeed, the belief that music, whether listening or performing, can alter human pain experiences has a long history, dating back to the ancient Greeks, and its potential healing properties have long been appreciated by indigenous cultures around the world. The subjective experience of acute or chronic pain is complex, influenced by many intersecting physiological and psychological factors, and it is therefore to be expected that the impact of music therapy on the pain experience may vary from one situation to another, and from one person to another. Where pain persists and becomes chronic, aberrant central processing is a key feature associated with the ongoing pain experience. Nonetheless, beneficial effects of exposure to music on pain relief have been reported across a wide range of acute and chronic conditions, and it has been shown to be effective in neonates, children and adults. In this comprehensive review we examine the various neurochemical, physiological and psychological factors that underpin the impact of music on the pain experience, factors that potentially operate at many levels - the periphery, spinal cord, brainstem, limbic system and multiple areas of cerebral cortex. We discuss the extent to which these factors, individually or in combination, influence how music affects both the quality and intensity of pain, noting that there remains controversy about the respective roles that diverse central and peripheral processes play in this experience. Better understanding of the mechanisms that underlie music's impact on pain perception together with insights into central processing of pain should aid in developing more effective synergistic approaches when music therapy is combined with clinical treatments. The ubiquitous nature of music also facilitates application from the therapeutic environment into daily life, for ongoing individual and social benefit.

Oxytocin Modulation in Mindfulness-Based Pain Management for Chronic Pain

In the context of chronic pain management, opioid-based treatments have been heavily relied upon, raising concerns related to addiction and misuse. Non-pharmacological approaches, such as Mindfulness-Based Pain Management, offer alternative strategies. We conducted a mechanistic clinical study to investigate the impact of an 8-week Mindfulness-Based Pain Management intervention on chronic pain, the modulation of inflammatory markers, stress physiology, and oxytocin, and their interplay with clinical pain symptoms and perception, in comparison to a patient wait-list active control. A total of 65 participants, including 50 chronic pain patients and 15 healthy controls, underwent salivary assays to assess endocrine markers, oxytocin, interleukin (IL)-1b, IL-6, IL-8, tumor necrosis factor (TNF)-a, and dehydroepiandrosterone sulphate (DHEA-S). Psychological assessments were also conducted to evaluate aspects of pain perception, mindfulness, mood, and well-being. Findings revealed significant differences between chronic pain patients and healthy controls in various clinical metrics, highlighting the psychological distress experienced by patients. Following Mindfulness-Based Pain Management, oxytocin levels significantly increased in chronic pain patients, that was not observed in the patient wait-list control group. In contrast, cytokine and DHEA-S levels decreased (not to statistically significant margins) supporting anti-inflammatory effects of Mindfulness-Based Pain Management. The fact DHEA-S levels, a marker of stress, did attenuate but not to statistically meaningful levels, suggests that pain reduction was not solely related to stress reduction, and that oxytocin pathways may be more salient than previously considered. Psychological assessments demonstrated substantial improvements in pain perception and mood in the intervention group. These results contribute to the growing body of evidence regarding the effectiveness of mindfulness-based interventions in chronic pain management and underscore oxytocin's potential role as a therapeutic target.

How Sex Hormones Affect Migraine: An Interdisciplinary Preclinical Research Panel Review

Sex hormones and migraine are closely interlinked. Women report higher levels of migraine symptoms during periods of sex hormone fluctuation, particularly during puberty, pregnancy, and perimenopause. Ovarian steroids, such as estrogen and progesterone, exert complex effects on the peripheral and central nervous systems, including pain, a variety of special sensory and autonomic functions, and affective processing. A panel of basic scientists, when challenged to explain what was known about how sex hormones affect the nervous system, focused on two hormones: estrogen and oxytocin. Notably, other hormones, such as progesterone, testosterone, and vasopressin, are less well studied but are also highlighted in this review. When discussing what new therapeutic agent might be an alternative to hormone therapy and menopause replacement therapy for migraine treatment, the panel pointed to oxytocin delivered as a nasal spray. Overall, the conclusion was that progress in the preclinical study of hormones on the nervous system has been challenging and slow, that there remain substantial gaps in our understanding of the complex roles sex hormones play in migraine, and that opportunities remain for improved or novel therapeutic agents. Manipulation of sex hormones, perhaps through biochemical modifications where its positive effects are selected for and side effects are minimized, remains a theoretical goal, one that might have an impact on migraine disease and other symptoms of menopause. This review is a call to action for increased interest and funding for preclinical research on sex hormones, their metabolites, and their receptors. Interdisciplinary research, perhaps facilitated by a collaborative communication network or panel, is a possible strategy to achieve this goal.

Persistent Postpartum Pain - A Somatic and Psychologic Perfect Storm

Persistent postpartum pain is common and has a complex etiology. It has both somatic and psychosocial provoking factors and has both functional and psychological ramifications following childbirth. Pain that limits the functional capacity of a person who has the daunting task to take care of all the demands of managing a growing newborn and infant can have debilitating consequences for several people simultaneously. We will review the incidence of persistent postpartum pain, analyze the risk factors, and discuss obstetric, anesthetic, and psychological tools for prevention and management. Based on the current knowledge, early antenatal screening and management is described as the most likely measure to identify patients at risk for persistent postpartum pain. Such antenatal management should be based on the close collaboration between obstetricians, anesthesiologists, and psychologists to tailor peripartum pain management and psychological support-based individual needs.

Peripheral Branch Injury Induces Oxytocin Receptor Expression at the Central Axon Terminals of Primary Sensory Neurons

Considerable evidence suggests that oxytocin, as a regulatory nonapeptide, participates in modulatory mechanisms of nociception. Nonetheless, the role of this hypothalamic hormone and its receptor in the sensory pathway has yet to be fully explored. The present study performed immunohistochemistry, enzyme-linked immunosorbent assay, and RT-qPCR analysis to assess changes in the expression of the neuronal oxytocin receptor in female rats following tight ligation of the sciatic nerve after 1, 3, and 7 days of survival. Oxytocin receptor immunoreactivity was present in both dorsal root ganglia and lumbar spinal cord segments, but not accumulated at the site of the ligation of the peripheral nerve branch. We found a time-dependent change in the expression of oxytocin receptor mRNA in L5 dorsal root ganglion neurons, as well as an increase in the level of the receptor protein in the lumbar segment of the spinal cord. A peak in the expression was observed on day 3, which downturned slightly by day 7 after the nerve ligation. These results show that OTR expression is up-regulated in response to peripheral nerve lesions. We assume that the importance of OTR is to modify spinal presynaptic inputs of the sensory neurons upon injury-induced activation, thus to be targets of the descending oxytocinergic neurons from supraspinal levels. The findings of this study support the concept that oxytocin plays a role in somatosensory transmission.

Intranasal Oxytocin and Pain Reduction: Testing a Social Cognitive Mediation Model

Oxytocin is well known for its role in relationships and social cognition and has more recently been implicated in pain relief and pain perception. Connections between prosocial feelings and pain relief are also well documented; however, the effects of exogenous oxytocin on social cognition and pain have not been explored. The current study tested whether intranasally delivered oxytocin affects pain perception through prosocial behaviors. Additionally, moderation of the effects of oxytocin by life history or genetic polymorphisms is examined. Young adults (n = 43; 65% female) were administered intranasal oxytocin (24 IU) or placebo in a crossover design on two visits separated by a one-week washout period. Pain was delivered via cold pressor. Baseline measures for decision-making and social cognition were collected, as well as pain sensitivity and medication history. Saliva samples were collected for analysis of genetic markers, and urine samples were collected to assess oxytocin saturation. Following oxytocin administration, participants reported increased prosocial cognition and decision-making. Pain perception appeared to be adaptive, with procedural order and expectation affecting perception. Finally, behavioral trust and cooperation responses were significantly predicted by genetic markers. Oxytocin may increase a patient's trust and cooperation and reduce pain sensitivity while having fewer physiological side effects than current pharmaceutical options.

Design, synthesis, conformational analysis, and biological activity of Cα1-to-Cα6 1,4- and 4,1-disubstituted 1H-[1,2,3]triazol-1-yl-bridged oxytocin analogues

Oxytocin (OT) is a neurohypophyseal peptide hormone containing a disulphide-bridged pseudocyclic conformation. The biomedical use of OT peptides is limited amongst others by disadvantageous pharmacokinetic parameters. To increase the stability of OT by replacing the disulphide bridge with the stable and more rigid [1,2,3]triazol-1-yl moiety, we employed the Cu2+-catalysed side chain-to-side chain azide-alkyne 1,3-cycloaddition. Here we report the design, synthesis, conformational analysis, and in vitro pharmacological activity of a homologous series of Cα1-to-Cα6 side chain-to-side chain [1,2,3]triazol-1-yl-containing OT analogues differing in the length of the bridge, location, and orientation of the linking moiety. Exploiting this macrocyclisation approach, it was possible to generate a systematic series of compounds providing interesting insight into the structure-conformation-function relationship of OT. Most analogues were able to adopt similar conformation to endogenous OT in water, namely, a type I β-turn. This approach may in the future generate stabilised pharmacological peptide tools to advance understanding of OT physiology.

Maternal outcomes related to Genetic and epigenetic Variation in the oxytocin system: A scoping review

Purpose

In this scoping review, we synthesize the literature on oxytocin and oxytocin receptor genetic and epigenetic variation in relationship to breastfeeding, maternal caregiving behavior, and maternal mental health.

Methods

A literature search was conducted in early 2022, and updated in 2023, utilizing the PRISMA scoping review reporting method, using the following MeSH headings and key terms: oxytocin, oxytocin receptor, genetics, epigenetics, methylation, pregnancy, postnatal, breastfeeding, lactation, mother-infant relations and perinatal outcomes. The search was conducted using PubMed, EMBASE, CINAHL, Google Scholar, SCOPUS, and the Cochrane Library. Inclusion criteria included: human literature which was peer reviewed and found in primary sources, printed in the English language. In addition, the study must have reported genetic/epigenetic data in either the oxytocin or oxytocin receptor gene (maternal or infant up to 12 months after birth) in relation to a breastfeeding, maternal caregiving behavior or a maternal mental health outcome. There was no date limitation. Four authors reviewed studies for eligibility. Data was extracted using a structured data extraction form.

Results

A total of 23 studies met inclusion criteria for this review (breastfeeding n = 4, maternal caregiving behavior n = 7, and maternal mental health n = 16). Seventeen papers reported on oxytocin or oxytocin receptor genotype and nine reported epigenetic associations (namely DNA methylation). These totals are greater than 23, as studies reported on multiple outcomes. One paper assessed the interaction between genotype and methylation. While a number of genotype variations were reported, the single nucleotide polymorphism rs53576 on the oxytocin receptor gene was the most studied. Overall, variation in this polymorphism was related to postnatal depression symptoms. Among numerous epigenetic markers, site -934 was the most studied methylation site, and methylation status was associated with maternal depression and maternal caregiving behavior outcomes. Results suggest that early life experiences impact adult maternal caregiving behaviors and mental health outcomes, and vary based on genetic vulnerability. Breastfeeding outcomes were minimally studied.

Conclusion

This scoping review found that genetic and epigenetic variation at the oxytocin and oxytocin receptor genes were associated with maternal caregiving behavior and mental health, likely through complex gene and environment interactions. The findings suggest that maternal early life experiences and stress impact later caregiving behaviors and mental health in the postnatal period. The findings highlight potential pathways by which environment, experiences, and genes interact to impact maternal caregiving behavior and maternal mental health.

Paraventricular nucleus-central amygdala oxytocinergic projection modulates pain-related anxiety-like behaviors in mice

AIMS

Anxiety disorders associated with pain are a common health problem. However, the underlying mechanisms remain poorly understood. We aimed to investigate the role of paraventricular nucleus (PVN)-central nucleus of the amygdala (CeA) oxytocinergic projections in anxiety-like behaviors induced by inflammatory pain.

METHODS

After inflammatory pain induction by complete Freund's adjuvant (CFA), mice underwent elevated plus maze, light-dark transition test, and marble burying test to examine the anxiety-like behaviors. Chemogenetic, optogenetic, and fiber photometry recordings were used to modulate and record the activity of the oxytocinergic projections of the PVN-CeA.

RESULTS

The key results are as follows: inflammatory pain-induced anxiety-like behaviors in mice accompanied by decreased activity of PVN oxytocin neurons. Chemogenetic activation of PVN oxytocin neurons prevented pain-related anxiety-like behaviors, whereas inhibition of PVN oxytocin neurons induced anxiety-like behaviors in naïve mice. PVN oxytocin neurons projected directly to the CeA, and microinjection of oxytocin into the CeA blocked anxiety-like behaviors. Inflammatory pain also decreased the activity of CeA neurons, and optogenetic activation of PVNoxytocin -CeA circuit prevented anxiety-like behavior in response to inflammatory pain.

CONCLUSION

The results of our study suggest that oxytocin has anti-anxiety effects and provide novel insights into the role of PVNoxytocin -CeA projections in the regulation of anxiety-like behaviors induced by inflammatory pain.

Oxytocin increases itch sensitivity of mice in late pregnancy and its peripheral receptor mechanism of itch-promoting effect

Oxytocin (OXT) is secreted in a large amount during the middle and late pregnancy. Except for the regulation of functions related to childbirth, OXT is involved in the regulation of cognition, social behavior, addiction, pain and so on. Our aim is to confirm the increase of OXT content in mice in late pregnancy is the main cause of itch during pregnancy and observe whether exogenously administered OXT can induce or increase itch sensitivity. The research shows that itch sensitivity of mice increased significantly in late pregnancy and basically returned to normal one day after delivery. The number of OXT-positive neurons in paraventricular nucleus (PVN) and the content of OXT in serum of the late pregnant mice increased significantly, and decreased sharply after delivery. Intradermal injection of low concentration of OXT (0.2 nmol/L) could not induce scratching behavior in mice, but high concentration of OXT (5 nmol/L, 10 nmol/L) could do this in a dose-dependent manner. Low concentration of OXT significantly increased the itch sensitivity to histamine. Intradermal injection of oxytocin receptor (OXTR) or arginine vasopressin-1a receptor (AVPR1A) antagonist did not affect histamine-induced scratching behavior, but both reversed the increase of itch sensitivity in late pregnant mice or the facilitated itch sensitivity by OXT. Study suggests that both endogenous and exogenous increases in OXT can increase the body's sensitivity to itch, and even induce itch directly. Pruritus during pregnancy is closely related to the increase of OXT content in vivo. In the periphery, the itch-promoting effect of OXT is mediated by OXTR and AVPR1A.

The relationship between oxytocin and empathy for others' pain: Testing the mediating effect of first-hand pain sensitivity

Although previous studies have shown that oxytocin attenuates first-hand pain sensitivity, studies of its effects on empathic reactions to the observation of others' pain have yielded inconsistent and controversial results. Given the link between first-hand pain and empathy for others' pain, we hypothesized that oxytocin affects empathy for others' pain by modulating first-hand pain sensitivity. Using a double-blind, placebo-controlled, between-participant experimental design, healthy participants (n = 112) were randomly assigned to either an intranasal oxytocin or placebo group. Pain sensitivity was evaluated by pressure pain threshold, and empathic responses were assessed by ratings in response to viewing video clips depicting others in physically painful scenarios. Results showed that pressure pain thresholds decreased over time in both groups, indicating increased sensitivity to first-hand pain after repeated measurements. However, this decrease was smaller for participants who received intranasal oxytocin, indicative of oxytocin-induced attenuation of first-hand pain sensitivity. In addition, although empathic ratings were comparable between oxytocin and placebo groups, first-hand pain sensitivity fully mediated the impact of oxytocin on pain empathetic ratings. Thus, intranasal oxytocin can indirectly affect pain empathic ratings by reducing first-hand pain sensitivity. These findings expand our understanding of the relationship among oxytocin, pain, and empathy.

Evaluating the efficacy of oxytocin for pain management: An updated systematic review and meta-analysis of randomized clinical trials and observational studies

Background

There is a need for novel analgesics with favorable risk to benefit profiles. Oxytocin has recently gained attention for its potential analgesic properties.

Aim

The aim of this study was to perform an updated systematic review and meta-analysis evaluating the effect of oxytocin for pain management.

Method

Ovid MEDLINE, Embase, PsycINFO, CINAHL, and Clinicaltrials.gov were searched for articles reporting on associations between oxytocin and chronic pain management from January 2012 to February 2022. Studies published before 2012 that were identified in our previous systematic review were also eligible. Risk of bias of included studies was assessed. Synthesis of results was performed using meta-analysis and narrative synthesis.

Results

Searches returned 2087 unique citations. In total, 14 articles were included that reported on 1504 people living with pain. Results from meta-analysis and narrative review were mixed. Meta-analysis of three studies indicated that exogenous oxytocin administration did not result in a significant reduction in pain intensity relative to placebo (N = 3; n = 95; g = 0.31; 95% confidence interval [CI] -0.10, 0.73). Narrative review provided encouraging evidence that exogenous oxytocin administration reduced pain sensitivity among individuals with back pain, abdominal pain, and migraines. Results suggested that individual difference factors (e.g., sex and chronic pain condition) may influence oxytocin-induced nociception, but the heterogeneity and limited number of studies identified precluded further investigation.

Discussion

There is equipoise for the benefit of oxytocin for pain management. Future studies are imperative and should undertake more precise exploration of potential confounds and mechanisms of analgesic action to clarify inconsistency in the literature.

Evaluation of aglepristone and oxytocin on induction of parturition in guinea pig

BACKGROUND

Induction of parturition in guinea pigs appears to be essential because these animals have a higher rate of reproductive problems than rabbits and small rodents.

OBJECTIVES

Since aglepristone (AGL) is a competitive progesterone antagonist acting through binding to progesterone receptors while oxytocin (OT) is a powerful constituent of uterine smooth muscle, the aim of this study was to evaluate the clinical and ultrasonographic impacts of AGL and OT on guinea pig parturition induction.

METHODS

In this study, guinea pigs were allocated into five groups; each included five animals on the 61st day of pregnancy. In the aglepristone group (Agle), AGL was administrated subcutaneously (SC) once daily on 2 consecutive days (Days 61 and 62 post mating). Oxytocin (OT) was administered subcutaneously once and twice at 4-h intervals on Day 62 post mating in oxytocin 1 (Oxy1) and oxytocin 2 (Oxy2) groups, respectively. The animals in the aglepristone-oxytocin group (Agle-Oxy) received AGL subcutaneously once daily on 2 consecutive days (Days 61 and 62 post mating) and OT on Day 62 post mating. The remaining sows received saline solution (0.9% NaCl) in the control group.

RESULTS

According to the results, fetal heart rate, temperature, neonatal and maternal survival rates were not significantly different between the treatment and control groups (p > 0.05). Biparietal diameter of head and body weight of neonates in the Agle, Oxy2 and Agle-Oxy groups showed a significant decline, compared to the control group (p < 0.05). The time interval between injection and delivery and the duration of pregnancy was significantly reduced in Agle, Oxy2, Agl-Oxy groups, compared to the control and Oxy1 groups.

CONCLUSIONS

In conclusion, it seems that treatment Oxy2 can induce parturition in guinea pigs without side effects and lower pain during induction of parturition.

Only empathy-related traits, not being mimicked or endorphin release, influence social closeness and prosocial behavior

Seminal studies suggest that being mimicked increases experienced social closeness and prosocial behavior to a mimicking confederate (i.e., interaction partner). Here we reexamine these results by considering the role of empathy-related traits, an indirect proxy for endorphin uptake, and their combined effects as an explanation for these results. 180 female participants were mimicked or anti-mimicked in an interaction with a confederate. The effects of being mimicked versus anti-mimicked in relation to empathy-related traits and endorphin release (assessed indirectly via pain tolerance) on experienced closeness and prosocial behavior were assessed using Bayesian analyses. Our results suggest that high individual empathy-related traits increase social closeness to the anti-mimicking and mimicking confederate and to one's romantic partner, as compared to mimicry alone. Results furthermore strongly suggest that high individual empathy-related traits increase prosocial behavior (donations and willingness to help) as compared to mimicry alone. These findings extend previous work by highlighting that empathy-related traits are more influential in creating positive effects on social closeness and prosocial behavior than a one-shot mimicking encounter.

Structure-Based Design of Glycosylated Oxytocin Analogues with Improved Selectivity and Antinociceptive Activity

Acute and chronic pain is often treated with opioids despite the negative side effects of constipation, physical dependence, respiratory depression, and overdose. The misuse of opioid analgesics has given rise to the opioid crisis/epidemic, and alternate nonaddictive analgesics are urgently needed. Oxytocin, a pituitary hormone, is an alternative to the small molecule treatments available and has been used as an analgesic as well as for the treatment and prevention of opioid use disorder (OUD). Clinical implementation is limited by its poor pharmacokinetic profile, a result of the labile disulfide bond between two cysteine residues in the native sequence. Stable brain penetrant oxytocin analogues have been synthesized by replacement of the disulfide bond with a stable lactam and glycosidation of the C-terminus. These analogues show exquisite selectivity for the oxytocin receptor and potent in vivo antinociception in mice following peripheral (i.v.) administration, supporting further study of their clinical potential.

Effects of intranasal oxytocin on pain perception among human subjects: A systematic literature review and meta-analysis

INTRODUCTION

Oxytocin (OXT) is a peptide hormone produced in the hypothalamus that plays a neuromodulatory role in emotion, stress, and anxiety. Due to its multidimensional role, OXT is a promising target for therapeutic interventions to treat pain.

OBJECTIVE

Perform a systematic literature review, followed by a meta-analysis to identify the effects of intranasal OXT on the self-perception of clinical and experimental pain among human subjects.

METHOD

A systematic review was conducted in the PubMed, PsycINFO, Scielo, Lilacs, and Web of Science databases, using the keywords Oxytocin, Pain, Analgesia, and Nociception.

RESULTS

Fifteen papers were included in the meta-analysis. None of the outcomes presented statistical significance in terms of the interventions' effect size: pain intensity (SMD = -0.02 (CI 95 %: -0.14 to 0.10; p = 0.76)) and pain unpleasantness (SMD = -0.15 (CI 95 %: -0.34 to 0.04; p = 0.12)). No meta-analysis was performed for pain threshold or tolerance because few papers address these outcomes.

CONCLUSION

There was no statistically significant effect of intranasal OXT administration on pain perception, considering equivalence limits between (-0.2 and 0.2). However, it must be considered that the study designs may not have been sensitive enough to detect minor analgesic effects of OXT, which, being weak, may also not be perceived at a conscious level. Additionally, OXT effects possibly depend on specific characteristics of the painful condition, such as pain complexity, intensity, and duration, contextual variables like the presence of social and affective support, and individual characteristics.

Individual Characteristics and Pain Sensitivity during Pregnancy-A Cross-Sectional Study in Pregnant and Non-Pregnant Women

The aim of the study was to describe the characteristics and factors related to pain perception in pregnant women, such as optimism, personality traits, and fear of developing COVID-19 consequences. Sixty-six pregnant women aged 23 to 42 years participated in the study, and the comparison group consisted of n = 59 non-pregnant female students aged 19 to 23 years. Pressure pain threshold and pain tolerance were measured with an algometer. To assess psychological characteristics, the Life-Orientation Test-Revised was used to assess optimism, the Fear of COVID-19 Scale was used to assess COVID-19 anxiety, and the Ten-Item Personality Inventory was applied to assess personality traits in a five-factor model. The main results of the study showed that pain tolerance was significantly lower in both dominant and non-dominant hand pregnant women than in the comparison group. The studied pregnant women had higher scores for conscientiousness, fear of COVID-19, and optimism compared with the non-pregnant women. Regression analysis showed that the variability in pain perception among pregnant women could not be explained by individual differences in personality traits, optimism, and fear of COVID-19.

Catecholaminergic innervation and D2-like dopamine receptor-mediated modulation of brainstem nucleus incertus neurons in the rat

Nucleus incertus (NI) is a brainstem structure involved in the control of arousal, stress responses and locomotor activity. It was reported recently that NI neurons express the dopamine type 2 (D2) receptor that belongs to the D2-like receptor (D2R) family, and that D2R activation in the NI decreased locomotor activity. In this study, using multiplex in situ hybridization, we observed that GABAergic and glutamatergic NI neurons express D2 receptor mRNA, and that D2 receptor mRNA-positive neurons belong to partially overlapping relaxin-3- and cholecystokinin-positive NI neuronal populations. Our immunohistochemical and viral-based retrograde tract-tracing studies revealed a dense innervation of the NI area by fibers containing the catecholaminergic biosynthesis enzymes, tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH), and indicated the major sources of the catecholaminergic innervation of the NI as the Darkschewitsch, raphe and hypothalamic A13 nuclei. Furthermore, using whole-cell patch clamp recordings, we demonstrated that D2R activation by quinpirole produced excitatory and inhibitory influences on neuronal activity in the NI, and that both effects were postsynaptic in nature. Moreover, the observed effects were cell-type specific, as type I NI neurons were either excited or inhibited, whereas type II NI neurons were mainly excited by D2R activation. Our results reveal that rat NI receives a strong catecholaminergic innervation and suggest that catecholamines acting within the NI are involved in the control of diverse processes, including locomotor activity, social interaction and nociceptive signaling. Our data also strengthen the hypothesis that the NI acts as a hub integrating arousal-related neuronal information.

Social isolation modulates appetite and avoidance behavior via a common oxytocinergic circuit in larval zebrafish

Animal brains have evolved to encode social stimuli and transform these representations into advantageous behavioral responses. The commonalities and differences of these representations across species are not well-understood. Here, we show that social isolation activates an oxytocinergic (OXT), nociceptive circuit in the larval zebrafish hypothalamus and that chemical cues released from conspecific animals are potent modulators of this circuit's activity. We delineate an olfactory to subpallial pathway that transmits chemical social cues to OXT circuitry, where they are transformed into diverse outputs simultaneously regulating avoidance and feeding behaviors. Our data allow us to propose a model through which social stimuli are integrated within a fundamental neural circuit to mediate diverse adaptive behaviours.

Bridging skin, brain, and behavior to understand pleasurable social touch

Social touch-the affiliative skin-to-skin contact between individuals-can rapidly evoke emotions of comfort, pleasure, or calm, and is essential for mental and physical well-being. Physical isolation from social support can be devastating. During the COVID-19 pandemic, we observed a global increase in suicidal ideation, anxiety, domestic violence, and worsening of pre-existing physical conditions, alerting society to our need to understand the neurobiology of social touch and how it promotes normal health. Gaining a mechanistic understanding of how sensory neuron stimulation induces pleasure, calm, and analgesia may reveal untapped therapeutic targets in the periphery for treatment of anxiety and depression, as well as social disorders and traumas in which social touch becomes aversive. Bridging the gap between stimulation in the skin and positive affect in the brain-especially during naturally occurring social touch behaviors-remains a challenge to the field. However, with advances in mouse genetics, behavioral quantification, and brain imaging approaches to measure neuronal firing and neurochemical release, completing this mechanistic picture may be on the horizon. Here, we summarize some exciting new findings about social touch in mammals, emphasizing both the peripheral and central nervous systems, with attempts to bridge the gap between external stimulation and internal representations in the brain.

The pandemic should catalyze research on social pain: Examining oxytocin administration studies

For decades, researchers have tried to identify drugs that can decrease the painful feelings associated with social loss, rejection, or isolation. One effort has been to investigate whether the neuropeptide oxytocin reduces social pain. In this commentary, I examine intranasal oxytocin's effects on experimentally induced social exclusion. Future recommendations are presented with the goal of spurring new research efforts to elucidate the neurobiological mechanisms underlying the experience of social pain.

Towards better hypothesis tests in oxytocin research: Evaluating the validity of auxiliary assumptions

Various factors have been attributed to the inconsistent reproducibility of human oxytocin research in the cognitive and behavioral sciences. These factors include small sample sizes, a lack of pre-registered studies, and the absence of overarching theoretical frameworks that can account for oxytocin's effects over a broad range of contexts. While there have been efforts to remedy these issues, there has been very little systematic scrutiny of the role of auxiliary assumptions, which are claims that are not central for testing a hypothesis but nonetheless critical for testing theories. For instance, the hypothesis that oxytocin increases the salience of social cues is predicated on the assumption that intranasally administered oxytocin increases oxytocin levels in the brain. Without robust auxiliary assumptions, it is unclear whether a hypothesis testing failure is due to an incorrect hypothesis or poorly supported auxiliary assumptions. Consequently, poorly supported auxiliary assumptions can be blamed for hypothesis failure, thereby safeguarding theories from falsification. In this article, I will evaluate the body of evidence for key auxiliary assumptions in human behavioral oxytocin research in terms of theory, experimental design, and statistical inference, and highlight assumptions that require stronger evidence. Strong auxiliary assumptions will leave hypotheses vulnerable for falsification, which will improve hypothesis testing and consequently advance our understanding of oxytocin's role in cognition and behavior.

Roles of Oxytocin in Stress Responses, Allostasis and Resilience

Oxytocin has been revealed to work for anxiety suppression and anti-stress as well as for psychosocial behavior and reproductive functions. Oxytocin neurons are activated by various stressful stimuli. The oxytocin receptor is widely distributed within the brain, and oxytocin that is released or diffused affects behavioral and neuroendocrine stress responses. On the other hand, there has been an increasing number of reports on the role of oxytocin in allostasis and resilience. It has been shown that oxytocin maintains homeostasis, shifts the set point for adaptation to a changing environment (allostasis) and contributes to recovery from the shifted set point by inducing active coping responses to stressful stimuli (resilience). Recent studies have suggested that oxytocin is also involved in stress-related disorders, and it has been shown in clinical trials that oxytocin provides therapeutic benefits for patients diagnosed with stress-related disorders. This review includes the latest information on the role of oxytocin in stress responses and adaptation.

Non-Opioid Peptides Targeting Opioid Effects

Opioids are the most potent widely used analgesics, primarily, but not exclusively, in palliative care. However, they are associated with numerous side effects, such as tolerance, addiction, respiratory depression, and cardiovascular events. This, in turn, can result in their overuse in cases of addiction, the need for dose escalation in cases of developing tolerance, and the emergence of dose-related opioid toxicity, resulting in respiratory depression or cardiovascular problems that can even lead to unintentional death. Therefore, a very important challenge for researchers is to look for ways to counteract the side effects of opioids. The use of peptides and their related compounds, which have been shown to modulate the effects of opioids, may provide such an opportunity. This short review is a compendium of knowledge about the most important and recent findings regarding selected peptides and their modulatory effects on various opioid actions, including cardiovascular and respiratory responses. In addition to the peptides more commonly reported in the literature in the context of their pro- and/or anti-opioid activity-such as neuropeptide FF (NPFF), cholecystokinin (CCK), and melanocyte inhibiting factor (MIF)-we also included in the review nociceptin/orphanin (N/OFQ), ghrelin, oxytocin, endothelin, and venom peptides.

The multiple faces of the oxytocin and vasopressin systems in the brain

Classically, hypothalamic neuroendocrine cells that synthesise oxytocin and vasopressin were categorised in two major cell types: the magnocellular and parvocellular neurones. It was assumed that magnocellular neurones project exclusively to the pituitary gland where they release oxytocin and vasopressin into the systemic circulation. The parvocellular neurones, on the other hand, project within the brain to regulate discrete brain circuitries and behaviours. Within the last few years, it has become evident that the classical view of these projections is outdated. It is now clear that oxytocin and vasopressin in the brain are released extrasynaptically from dendrites and from varicosities in distant axons. The peptides act principally to modulate information transfer through conventional synapses (such as glutamate synapses) by actions at respective receptors that may be preferentially localised to synaptic regions (on either side of the synapse) to alter the 'gain' of conventional synapses.

The influence of oxytocin-based interventions on sleep-wake and sleep-related behaviour and neurobiology: A systematic review of preclinical and clinical studies

The oxytocin (OXT) system has garnered considerable interest due to its influence on diverse behaviours. However, scant research has considered the influence of oxytocin on sleep-wake and sleep-related behaviour and neurobiology. Consequently, the objective of this systematic review was to assess the extant preclinical and clinical evidence for the influence of oxytocin-based interventions on sleep-wake outcomes. The primary search was conducted on 22/7/2020 using six electronic databases; 30 studies (19 preclinical, 11 clinical) were included based on inclusion criteria. Studies were evaluated for risk of bias using the SYRCLE tool and the Cochrane risk of bias tools for preclinical and clinical studies, respectively. Results indicated manipulation of the OXT system can influence sleep-wake outcomes. Preclinical evidence suggests a wake-promoting influence of OXT system activation whereas the clinical evidence suggests little or no sleep-promoting influence of OXT. OXT dose was identified as a likely modulatory factor of OXT-induced effects on sleep-wake behaviour. Future studies are necessary to validate and strengthen these tentative conclusions about the influence of OXT on sleep-wake behaviour.

Evaluating the efficacy of intranasal oxytocin on pain and function among individuals who experience chronic pain: a protocol for a multisite, placebo-controlled, blinded, sequential, within-subjects crossover trial

INTRODUCTION

Current treatments for chronic pain (eg, opioids) can have adverse side effects and rarely result in resolution of pain. As such, there is a need for adjuvant analgesics that are non-addictive, have few adverse side effects and are effective for pain management across several chronic pain conditions. Oxytocin is a naturally occurring hormone that has gained attention for its potential analgesic properties. The objective of this trial is to evaluate the efficacy of intranasal oxytocin on pain and function among adults with chronic pain.

METHODS AND ANALYSIS

This is a placebo-controlled, triple-blind, sequential, within-subject crossover trial. Adults with chronic neuropathic, pelvic and musculoskeletal pain will be recruited from three Canadian provinces (British Columbia, Alberta and Newfoundland and Labrador, respectively). Enrolled patients will provide one saliva sample pretreatment to evaluate basal oxytocin levels and polymorphisms of the oxytocin receptor gene before being randomised to one of two trial arms. Patients will self-administer three different oxytocin nasal sprays twice daily for a period of 2 weeks (ie, 24 IU, 48 IU and placebo). Patients will complete daily diaries, including standardised measures on day 1, day 7 and day 14. Primary outcomes include pain and pain-related interference. Secondary outcomes include emotional function, sleep disturbance and global impression of change. Intention-to-treat analyses will be performed to evaluate whether improvement in pain and physical function will be observed posttreatment.

ETHICS AND DISSEMINATION

Trial protocols were approved by the Newfoundland and Labrador Health Research Ethics Board (HREB #20227), University of British Columbia Clinical Research Ethics Board (CREB #H20-00729), University of Calgary Conjoint Health Research Ethics Board (REB20 #0359) and Health Canada (Control # 252780). Results will be disseminated through publication in peer-reviewed journals and presentations at scientific conferences.

TRIAL REGISTRATION NUMBER

NCT04903002; Pre-results.

Safety and tolerability of chronic intranasal oxytocin in older men: results from a randomized controlled trial

RATIONALE

Most studies evaluating the safety and tolerability of intranasal oxytocin (OT) have not reported consistent adverse events (AEs), but they have largely focused on young men and single-dose administration. Thus, it is unclear whether these findings translate to older individuals and with longer administration periods.

OBJECTIVE

Extending previous work, this study investigated the safety and tolerability of chronic intranasal OT in generally healthy older men.

METHODS

Data were from a randomized, placebo (P)-controlled, double-blind clinical trial evaluating the effects of 4 weeks of self-administered intranasal OT (24 IU twice daily) in older adults with no major physical or cognitive impairments. Heart rate, blood pressure, urine osmolality, and serum metabolic biomarkers were obtained before and at the end of the intervention. AEs were collected during the first 3 weeks and 1 week after cessation of treatment.

RESULTS

Of 103 participants recruited, 95 were randomized and received the intervention (OT = 49, P = 46). OT had no significant impact on cardiovascular, urine, or serum measures. The AEs reported for both treatments were generally mild and few in number, though one participant assigned to OT and two assigned to P dropped out due to AEs. Relative to P, OT did not significantly increase the likelihood of reporting AEs, nor the number or severity of AEs reported.

CONCLUSION

Chronic intranasal OT appears safe and well-tolerated in generally healthy older men. These findings provide support for continued human research on potential benefits of chronic OT in older adult populations.

Maternal speech decreases pain scores and increases oxytocin levels in preterm infants during painful procedures

Preterm infants undergo early separation from parents and are exposed to frequent painful clinical procedures, with resultant short- and long-term effects on their neurodevelopment. We aimed to establish whether the mother's voice could provide an effective and safe analgesia for preterm infants and whether endogenous oxytocin (OXT) could be linked to pain modulation. Twenty preterm infants were exposed to three conditions-mother's live voice (speaking or singing) and standard care-in random order during a painful procedure. OXT levels (pg/mL) in saliva and plasma cortisol levels were quantified, and the Premature Infant Pain Profile (PIPP) was blindly coded by trained psychologists. During the mother's live voice, PIPP scores significantly decreased, with a concomitant increase in OXT levels over baseline. The effect on pain perception was marginally significant for singing. No effects on cortisol levels were found. The mother's live voice modulated preterm infants' pain indicators. Endogenous OXT released during vocal contact is a promising protective mechanism during early painful interventions in at-risk populations.

Oxytocin: at birth and beyond. A systematic review of the long-term effects of peripartum oxytocin

Oxytocin is one of the most commonly used medications during labour and delivery. Recent insights from basic neuroscience research suggest that the uterotonic effects of oxytocin may arguably be trivial when compared with its profound effects on higher-order human behaviour. The purpose of this review is to highlight the potential consequences of manipulating oxytocinergic signalling during the peripartum period and its long-term impact on the maternal-infant dyad. We identified four domains where modulation of oxytocinergic signalling might be consequential: postpartum depression; breastfeeding; neurodevelopment; and chronic pain, and performed a literature search to address the impact of peripartum oxytocin administration. We have shown modest, but inconsistent, evidence linking peripartum oxytocin administration with postpartum depression. Breastfeeding success appeared to be negatively correlated with peripartum oxytocin exposure, perhaps secondary to impaired primitive neonatal reflexes and maternal-infant bonding. The association between perinatal oxytocin exposure and subsequent development of neurodevelopmental disorders such as autism in the offspring was weak, but these studies were limited by the lack of information on the cumulative dose. Finally, we identified substantial evidence for analgesic and anti-hypersensitivity effects of oxytocin which might partly explain the low incidence of chronic pain after caesarean birth. Although most data presented here are observational, our review points to a compelling need for robust clinical studies to better dissect the impact of peripartum oxytocin administration, and as stewards of its use, increase the precision with which we administer oxytocin to prevent overuse of the drug.

Nasal oxytocin for the treatment of psychiatric disorders and pain: achieving meaningful brain concentrations

There is evidence of the therapeutic potential of intranasal oxytocin for the treatment of pain and various psychiatric disorders, however, there is scant evidence that oxytocin reaches the brain. We quantified the concentration and distribution pattern of [¹²⁵I]-radiolabeled oxytocin in the brains and peripheral tissues of rats after intranasal delivery using gamma counting and autoradiography, respectively. Radiolabel was detected in high concentrations in the trigeminal and olfactory nerves as well as in brain regions along their trajectories. Considerable concentrations were observed in the blood, however, relatively low levels of radiolabel were measured in peripheral tissues. The addition of a mucoadhesive did not enhance brain concentrations. These results provide support for intranasal OT reaching the brain via the olfactory and trigeminal neural pathways. These findings will inform the design and interpretation of clinical studies with intranasal oxytocin.

Anti-nociceptive effects of oxytocin receptor modulation in healthy volunteers-A randomized, double-blinded, placebo-controlled study

BACKGROUND

There is increasing evidence for oxytocin as a neurotransmitter in spinal nociceptive processes. Hypothalamic oxytocinergic neurons project to the spinal dorsal horn, where they activate GABA-ergic inhibitory interneurons. The present study tested whether the long-acting oxytocin-analogue carbetocin has anti-nociceptive effects in multi-modal experimental pain in humans.

METHODS

Twenty-five male volunteers received carbetocin 100 mcg and placebo (0.9% NaCl) on two different sessions in a randomized, double-blinded, cross-over design. Multi-modal quantitative sensory testing (QST) including a model of capsaicin-induced hyperalgesia and allodynia were performed at baseline and at 10, 60 and 120 min after drug administration. QST data were analysed using mixed linear and logistic regression models. Carbetocin plasma concentrations and oxytocin receptor genotypes were quantified and assessed in an exploratory fashion.

RESULTS

An anti-nociceptive effect of carbetocin was observed on intramuscular electrical temporal summation (estimated difference: 1.26 mA, 95% CI 1.01 to 1.56 mA, p = .04) and single-stimulus electrical pain thresholds (estimated difference: 1.21 mA, 95% CI 1.0 to 1.47 mA, p = .05). Furthermore, the area of capsaicin-induced allodynia was reduced after carbetocin compared to placebo (estimated difference: -6.5 cm² , 95% CI -9.8 to -3.2 cm² , p < .001).

CONCLUSIONS

This study provides evidence of an anti-nociceptive effect of carbetocin on experimental pain in humans.

SIGNIFICANCE

This study provides evidence of the anti-nociceptive effect of intravenous administration of the oxytocin agonist carbetocin in healthy male volunteers.

Oxytocin and positive couple interaction affect the perception of wound pain in everyday life

A large body of animal and human laboratory research has linked social interaction and support to pain perception, with a possible role for the neuropeptide oxytocin as a neuroendocrine mediator. However so far, it has been unclear whether these effects translate to ecologically valid everyday life behavior and pain perception. In a randomized placebo-controlled study, a standard suction blister skin wound was induced to N = 80 romantic couples (N = 160 individuals). Couples then received intranasal oxytocin or placebo twice daily and were either instructed to perform a positive social interaction (partner appraisal task, PAT) once in the laboratory and two times during the following five days, or not. During these days, all participants reported their subjective pain levels multiple times a day using ecologically momentary assessment. Results from hierarchical linear modeling suggest that pain levels within the couples were inter-related. In men, but not in women, oxytocin reduced pain levels. Women reported lower pain levels in the group of positive social interaction, while this effect did not show in men. These results suggest that intranasal oxytocin might have sex-specific effects with pain reducing effects in men but the opposite effects in women. In contrast, especially women benefit from positive interaction in terms of dampened pain levels after positive interaction. The results add to the evidence for health-beneficial effects of positive couple interaction and point to underlying neuroendocrine mechanisms in everyday life pain specifically. The sex-specific effects, in particular, may have implications for psychopharmacological treatment of pain in men and women.

Oxytocin receptor expression in the midbrain dorsal raphe is dynamic across female reproduction in rats

Central oxytocin receptor (OTR) expression is extremely sensitive to circulating steroid hormones and OTRs influence many of the neurobehavioural adaptations associated with female reproduction (e.g., postpartum caregiving, aggression, cognition, affective responses). Changes in central OTR expression across female reproduction have often been studied, but almost all of such research has focused on the forebrain, ignoring hormone-sensitive midbrain sites such as the serotonergic dorsal raphe (DR) that are also critical for postpartum behaviours. To investigate the effects of female reproductive state on OTRs in the DR, we first used autoradiography to examine OTR binding across four female reproductive states in laboratory rats: dioestrous virgin, pregnancy day 10, the day of parturition and postpartum day 7. OTR binding in the rostral DR (but not other DR subregions) was approximately 250% higher in parturient rats compared to dioestrous virgins and dropped back down to virgin levels by postpartum day 7. Given the chemical heterogeneity of the DR, we then examined OTR expression in the three most abundant neuronal phenotypes of the DR (i.e., serotonin, GABA and dopamine) in dioestrous virgins and recently parturient females. Using dual-label immunohistochemistry and in situ hybridisation, we found that twice as many dopaminergic cells in the parturient rostral DR contained OTR immunoreactivity compared to that found in virgins. On the other hand, mothers had fewer rostral DR GABAergic cells expressing OTRs than did virgins. OTR expression in serotonin cells did not differ between the two groups. Overall, these results suggest that the rostral subregion of the midbrain DR is uniquely sensitive to oxytocin around the time of parturition, with subpopulations of cells that become more sensitive (i.e., dopamine), less sensitive (i.e., GABA) and show no change (i.e., serotonin) to this neuropeptide. This dynamic OTR signalling in the female DR may help drive the numerous behavioural changes across female reproduction that are necessary for successful motherhood.

Central and peripheral release of oxytocin: Relevance of neuroendocrine and neurotransmitter actions for physiology and behavior

The hypothalamic neuropeptide oxytocin (OT) is critically involved in the modulation of socio-emotional behavior, sexual competence, and pain perception and anticipation. While intracellular signaling of OT and its receptor (OTR), as well as the functional connectivity of hypothalamic and extra-hypothalamic OT projections, have been recently explored, it remains elusive how one single molecule has pleotropic effects from cell proliferation all the way to modulation of complex cognitive processes. Moreover, there are astonishing species-dependent differences in the way OT regulates various sensory modalities such as touch, olfaction, and vision, which can be explained by differences in OTR expression in brain regions processing sensory information. Recent research highlights a small subpopulation of OT-synthesizing cells, namely, parvocellular cells, which merely constitute 1% of the total number of OT cells but act as "master cells' that regulate the activity of the entire OT system. In this chapter, we summarize the latest advances in the field of OT research with a particular focus on differences between rodents, monkeys and humans and highlight the main differences between OT and its "sister" peptide arginine-vasopressin, which often exerts opposite effects on physiology and behavior.

Oxytocin Pathway Gene (CD38, OXTR) Variants Are Not Related to Psychosocial Characteristics Defined by Strengths and Difficulties Questionnaire in Adolescents: A Field School-Based Study

Background: CD38 is a transmembrane glycoprotein that regulates oxytocin (OT) production and influences social interactions. The oxytocin receptor (OXTR) has been studied intensively regarding its association with human psychosocial functions. Many studies have demonstrated a link between CD38 rs3796863 and OXTR rs53576 polymorphic regions and psychosocial characteristics as well as various psychiatric disorders in adolescents. Some studies, however, have reported null findings. Methods: The Strengths and Difficulties Questionnaire (SDQ) is a brief psychopathologic screening tool recommended for detecting psychosocial problems and psychiatric disorders in adolescents. The current field school-based study, conducted among urban Siberian adolescents (n = 298 aged 12-18), explored the SDQ scales in relation to polymorphisms of the CD38 and the OXTR genes (rs3796863 and rs53576, respectively). Results: None of the studied genotypes were associated with the SDQ results for the complete sample with presumed statistical power as 0.80 to detect a medium-size effect (Cramer's V = 0.3) at α = 0.0083. Post-hoc analysis in subgroups showed that OT pathway high activity may cause some negative consequences, such as emotional instability in older (aged 15-18) adolescent boys who are carriers of the rs53576 GG variant. Conclusion: Variations at the CD38 rs3796863 and OXTR rs53576 loci were not associated with psychosocial characteristics of adolescents assessed with the SDQ. In studies with a similar design, we recommend replication with larger samples and greater power to detect small effects, especially in age-sex subgroups of adolescents.

Intranasal oxytocin and the stress-buffering effects of social support during experimentally induced pain: The role of attachment security

BACKGROUND

This study examined whether intranasal oxytocin enhances the stress-buffering effects of social support during experimentally induced pain, taking into account the role of individual differences in attachment security.

METHODS

Female participants (N = 193) were randomly assigned to oxytocin (24 IU intranasal) or placebo and to receive support or no support from a friend (2 × 2 factorial design with repeated measures)). Participants underwent the Cold Pressor Task (CPT) and were monitored for heart rate variability (HRV: RMSSD) and heart rate and reported pain levels. The Experiences in Close Relationships Questionnaire was used to measure attachment.

RESULTS

Oxytocin reduced RMSSD (p = 0.003, partial ɳ² = 0.03) and increased heart rate (p = 0.039, partial ɳ² = 0.03) in individuals who received support, possibly reflecting an enhanced attentional state. Oxytocin did not enhance beneficial effects of social support on perceived pain, but increased pain intensity in avoidantly attached individuals who were supported by a friend (p = 0.009, partial ɳ² = 0.06).

LIMITATIONS

Only female participants were examined. Future studies are needed to determine sex differences in how oxytocin shapes stress-buffering effects of support.

CONCLUSIONS

Oxytocin may enhance the salience of social proximity and may be a mechanism underlying previously reported social influences on cardiovascular and mental health. However, oxytocin effects depend on interpersonal insecurities and may trigger discomfort in avoidantly attached individuals. Caution about oxytocin's therapeutic promise is warranted.

Advances in the interventional management of neuropathic pain

The management of neuropathic pain, defined as pain as a result of a lesion or disease in the somatosensory nervous system, continues to be researched and explored. As conventional methods demonstrate limited long-term efficacy, there is a significant need to discover therapies that offer both longitudinal and sustained management of this highly prevalent disease, which can be offered through interventional therapies. Tricyclic antidepressants (TCAs), gabapentinoids, lidocaine, serotonin norepinephrine reuptake inhibitors (SNRIs), and capsaicin have been shown to be the most efficacious pharmacologic agents for neuropathic pain relief. With respect to infusion therapies, the use of intravenous (IV) ketamine could be useful for complex regional pain syndrome, fibromyalgia, and traumatic spinal cord injury. Interventional approaches such as lumbar epidurals are a reasonable treatment choice for up to 3 months of pain relief for patients who failed to respond to conservative treatment, with a “B” strength of recommendation and moderate certainty. Neuroablative procedures like pulsed radiofrequency ablation work by delivering electrical field and heat bursts to targeted nerves or tissues without permanently damaging these structures, and have been recently explored for neuropathic pain relief. Alternatively, neuromodulation therapy is now recommended as the fourth line treatment of neuropathic pain after failed pharmacological therapy but prior to low dose opioids. Finally, the intrathecal delivery of various pharmacologic agents, such as quinoxaline-based kappa-opioid receptor agonists, can be utilized for neuropathic pain relief. In this review article, we aim to highlight advances and novel methods of interventional management of neuropathic pain.

Intranasal oxytocin as a treatment for chronic pelvic pain: A randomized controlled feasibility study

OBJECTIVE

To investigate the effect of intranasal oxytocin on chronic pelvic pain in a randomized, double-blind, within-subject crossover trial. Aims included: (1) determine intranasal oxytocin's effect on pain intensity and pain interference relative to placebo; (2) assess feasibility and acceptability.

METHODS

Women with chronic pelvic pain were recruited from chronic pain and gynecology clinics between September 2017 and December 2018. Pain was recorded at pre-trial screening, and while administering intranasal oxytocin and placebo. Pain and pain-related interference were measured using the Brief Pain Inventory - Short Form. Feasibility and acceptability were measured using validated measures and interviews.

RESULTS

Twenty-one women were randomized with sufficient data available from 12 to permit analyses. Relative to placebo, a 2-week course of oxytocin administration resulted in improvement in pain severity with no effect on pain-related interference. This effect was driven by four women who demonstrated a minimal clinically significant improvement in pain following intranasal oxytocin (no women met this threshold for placebo). Adherence to dosing was excellent and occurrence of adverse effects did not differ between oxytocin and placebo.

CONCLUSION

Intranasal oxytocin may represent an adjuvant analgesic that could result in a minimal clinically significant improvement in pain among one in three women with chronic pelvic pain. Registration: ClinicalTrials.gov (Registration# NCT02888574).

Perception of integrative care in paediatric oncology-perspectives of parents and patients

PURPOSE

For some years now, a programme for the use of integrative care in paediatric oncology has been established in a German university hospital and offers patients and parents complementary treatment options. According to their medical condition and wishes. A variety of external applications such as medical wraps, warm oil compresses and rhythmic embrocations are offered. This article analyses how patients and parents perceived and experienced the integrative care program.

METHODS

In this qualitative study, data consists of field notes conducted through participant observation, informal conversations and interviews with parents (n = 25) during the implementation phase of the program. Data was analysed on basis of thematic analysis and organized with the analysis software MAXQDA.

RESULTS

Parents and families intuitively developed strategies for dealing with crisis situations such as childhood cancer. In addition, many of the families brought with them a wealth of experience in complementary medicine. Parents perceived the integrative care treatments as soothing, relaxing and pain-relieving for their child. Patients could relax and side effects of chemotherapy were alleviated. However, children, who undergoing chemotherapy were not always open for physical touch and thus sometimes also rejected the treatments sometimes.

CONCLUSION

The analysed integrative care programme is perceived as a strong patient and family-centred approach of support during the oncological paediatric treatment. From a salutogenetic viewpoint, this program aims to strengthen the dimension of manageability within the concept of sense of coherence. Parents are given supportive means to manage side effects and ease their child's suffering, through touch and attention that can be very beneficial.

Preclinical Considerations about Affective Disorders and Pain: A Broadly Intertwined, yet Often Under-Explored, Relationship Having Major Clinical Implications

Background: Pain, a distinctive undesirable experience, encompasses several different and fluctuating presentations across varying mood disorders. Therefore, the present narrative review aimed to shed further light on the matter, accounting for both experimental animal models and clinical observations about major depressive disorder (MDD) pathology. Method: Major databases were inquired from inception until April 2016 for records about MDD and pain. Results: Pain and MDD are tightly associated with each other in a bi-directional fashion. Several cross-sectional and retrospective studies indicated a high presence of pain in the context of mood disorders, including MDD (up to 65%), but also increased prevalence rates in the case of mood disorders documented among people with a primary diagnosis of either psychological or somatic pain (prevalence rates exceeding 45%). The clinical implications of these observations suggest the need to account for mood and pain manifestations as a whole rather than distinct entities in order to deliver more effective interventions. Limitations: Narrative review, lack of systematic control groups (e.g., people with the primary diagnosis at review, but not the associated comorbidity as a study) to allow reliable comparisons. Prevalence rates and clinical features associated with pain varied across different studies as corresponding operational definitions did. Conclusions: Pain may have a detrimental effect on the course of mood disorders-the opposite holds. Promoting a timely recognition and management of such an often neglected comorbidity would therefore represent a primary goal toward the delivery of effective, multi-disciplinary care.

The neurohypophysial oxytocin and arginine vasopressin system is activated in a knee osteoarthritis rat model

Osteoarthritis (OA) causes chronic joint pain and significantly impacts daily activities. Hence, developing novel treatment options for OA has become an increasingly important area of research. Recently, studies have reported that exogenous, as well as endogenous, hypothalamic-neurohypophysial hormones, oxytocin (OXT) and arginine-vasopressin (AVP), significantly contribute to nociception modulation. Moreover, the parvocellular OXT neurone (parvOXT) extends its projection to the superficial spinal dorsal horn, where it controls the transmission of nociceptive signals. Meanwhile, AVP produced in the magnocellular AVP neurone (magnAVP) is released into the systemic circulation where it contributes to pain management at peripheral sites. The parvocellular AVP neurone (parvAVP), as well as corticotrophin-releasing hormone (CRH), suppresses inflammation via activation of the hypothalamic-pituitary adrenal (HPA) axis. Previously, we confirmed that the OXT/AVP system is activated in rat models of pain. However, the roles of endogenous hypothalamic-neurohypophysial hormones in OA have not yet been characterised. In the present study, we investigated whether the OXT/AVP system is activated in a knee OA rat model. Our results show that putative parvOXT is activated and the amount of OXT-monomeric red fluorescent protein 1 positive granules in the ipsilateral superficial spinal dorsal horn increases in the knee OA rat. Furthermore, both magnAVP and parvAVP are activated, concurrent with HPA axis activation, predominantly modulated by AVP, and not CRH. The OXT/AVP system in OA rats was similar to that in systemic inflammation models, including adjuvant arthritis; however, magnocellular OXT neurones (magnOXT) were not activated in OA. Hence, localised chronic pain conditions, such as knee OA, activate the OXT/AVP system without impacting magnOXT.