Oxytocin: the neuropeptide of love reveals some of its secrets

An investigation on the role of oxytocin in chronic neuropathic pain in a Wistar rat model

Introduction Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side effect with ineffective preventative and curative treatment. Currently, only Duloxetine has been recommended as effective treatment for CIPN, which has shown individual-dependent, short-term analgesic effects, with limiting adverse effects and poor bioavailability. The neuropeptide, oxytocin, may offer significant analgesic and anxiolytic potential, as it exerts central and peripheral attenuating effects on nociception. However, it is unknown whether the intervention administered in a model of CIPN is an effective therapeutic alternative or adjuvant. Materials and Methods The intervention was divided into two phases. Phase 1 aimed to induce CIPN in adult Wistar rats using the chemotherapeutic agent Paclitaxel. Mechanical (electronic von Frey filament) and thermal (acetone evaporation test and Hargreaves test) hypersensitivity testing were used to evaluate changes due to the neuropathic induction. Phase 2 consisted of a 14-day intervention period with saline (o.g.), duloextine (o.g.), or oxytocin (i.n.) administered as treatment. Following the intervention, anxiety-like behaviour was assessed using the elevated plus maze (EPM) and light-dark box protocols. Analysis of peripheral plasma corticosterone, peripheral plasma oxytocin, and hypothalamic oxytocin concentrations were assessed using ELISA assays. Results The findings showed that we were able to successfully establish a model of chemotherapy-induced peripheral neuropathy during Phase 1, determined by the increase in mechanical and thermal nociceptive responses following Paclitaxel administration. Furthermore, the animals treated with oxytocin displayed a significant improvement in mechanical sensitivity over the intervention phase, indicative of an improvement in nociceptive sensitivity in the presence of neuropathic pain. Animals that received Paclitaxel and treated with oxytocin also displayed significantly greater explorative behaviour during the EPM, indicative of a reduced presence of anxiety-like behaviour. Conclusion Our results support the hypothesis that intranasally administered oxytocin may augment the analgesic and anxiolytic effects of duloxetine in a chemotherapy induced peripheral neuropathy model in a Wistar rat. Future studies should consider administering the treatments in combination to observe the potential synergistic effects.

Post-stress Social Interaction and 3-Cyano-N-(1,3-Diphenyl-1H-Pyrazol-5-yl) Benzamide Treatment Attenuate Depressive-like Behavior Induced by Repeated Social Defeat Stress

Persistent stress increases the probability for developing depression significantly thereafter. Repeated social defeat stress is a widely used model to investigate depressive-like behavior in preclinical models. Hence, the repeated social defeat stress model provided an ideal animal model, through which the hypotheses of prevention and treatment can be investigated. We have successfully induced depressive-like behavior for male C57BL/6J mice with this model. Here, we reported that certain level of during-stress social interactions with single female or multiple male peer(s) exerted a positive role in preventing the development of depressive-like behavior induced by repeated social defeat stress. Our data suggested that the stress-susceptible mice may benefit from positive social interaction, which reduces the chance for depressive-like behavior development. Since numerous studies indicate that the metabotropic glutamate receptor 5 (mGluR5) plays an important role in various cognitive functions, we further investigate the treatment effect of 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl) benzamide (CDPPB) on the depressive-like behavior induced by repeated social defeat stress. Most importantly, robust anti-depressant effects have been achieved through modulating the mGluR5 function. We found that single oral dose administration of CDPPB (20 mg/kg), to some extent, alleviated the social avoidance behaviors for the stress-susceptible mice. Our data implies that the CDPPB, a positive allosteric modulator of mGluR5, is a promising anti-depressant candidate with limited side effect.

Resilience by design: How nature, nurture, environment, and microbiome mitigate stress and allostatic load

Resilience to psychological stress is defined as adaption to challenging life experiences and not the absence of adverse life events. Determinants of resilience include personality traits, genetic/epigenetic modifications of genes involved in the stress response, cognitive and behavioral flexibility, secure attachment with a caregiver, social and community support systems, nutrition and exercise, and alignment of circadian rhythm to the natural light/dark cycle. Therefore, resilience is a dynamic and flexible process that continually evolves by the intersection of different domains in human’s life; biological, social, and psychological. The objective of this minireview is to summarize the existing knowledge about the multitude factors and molecular alterations that result from resilience to stress response. Given the multiple contributing factors in building resilience, we set out a goal to identify which factors were most supportive of a causal role by the current literature. We focused on resilience-related molecular alterations resulting from mind-body homeostasis in connection with psychosocial and environmental factors. We conclude that there is no one causal factor that differentiates a resilient person from a vulnerable one. Instead, building resilience requires an intricate network of positive experiences and a healthy lifestyle that contribute to a balanced mind-body connection. Therefore, a holistic approach must be adopted in future research on stress response to address the multiple elements that promote resilience and prevent illnesses and psychopathology related to stress allostatic load.

Oxytocin: A Multi-Functional Biomolecule with Potential Actions in Dysfunctional Conditions; From Animal Studies and Beyond

Oxytocin is a hormone secreted from definite neuroendocrine neurons located in specific nuclei in the hypothalamus (mainly from paraventricular and supraoptic nuclei), and its main known function is the contraction of uterine and/or mammary gland cells responsible for parturition and breastfeeding. Among the actions of the peripherally secreted oxytocin is the prevention of different degenerative disorders. These actions have been proven in cell culture and in animal models or have been tested in humans based on hypotheses from previous studies. This review presents the knowledge gained from the previous studies, displays the results from oxytocin intervention and/or treatment and proposes that the well described actions of oxytocin might be connected to other numerous, diverse actions of the biomolecule.

Relationship between Oxytocin and Osteoarthritis: Hope or Despair?

Oxytocin (OT) is involved in breastfeeding and childbirth and appears to play a role in regulating the bone matrix. OT is synthesized in the supraoptic and paraventricular nuclei of the hypothalamus and is released in response to numerous stimuli. It also appears to be produced by osteoblasts in the bone marrow, acting as a paracrine–autocrine regulator of bone formation. Osteoarthritis (OA) is a disease of the whole joint. Different tissues involved in OA express OT receptors (OTRs), such as chondrocytes and osteoblasts. This hormone, which levels are reduced in patients with OA, appears to have a stimulatory effect on chondrogenesis. OT involvement in bone biology could occur at both the osteoblast and chondrocyte levels. The relationships between metabolic syndrome, body weight, and OA are well documented, and the possible effects of OT on different parameters of metabolic syndrome, such as diabetes and body weight, are important. In addition, the effects of OT on adipokines and inflammation are also discussed, especially since recent data have shown that low-grade inflammation is also associated with OA. Furthermore, OT also appears to mediate endogenous analgesia in animal and human studies. These observations provide support for the possible interest of OT in OA and its potential therapeutic treatment.

Structurally related peptide impurity identification and accurate quantification for synthetic oxytocin by liquid chromatography-high-resolution mass spectrometry

Oxytocin (OXT) is an important peptide that is mainly used as a therapeutic drug to induce labor or strengthen uterine contractions, or to control bleeding after childbirth. OXT has also been reported as a biomarker linked to emotion, and as a potential biomarker for cancer diagnosis. The accurate purity characterization of OXT calibrators is critical for quality control of pharmaceuticals and the development of reference measurement systems for this analyte in laboratory medicine. OXT possesses the particular analytical measurement challenge of a disulfide bond. Accurate value assignment of the purity of oxytocin calibrators can be carried out by applying the mass balance approach or alternative approaches such as amino acid analysis, quantitative nuclear magnetic resonance spectrometry, and nitrogen determination. In order to avoid biases, all these approaches require a correction for structurally related peptide impurities. Structurally related peptide impurities present in a synthetic OXT material have been identified and quantified by a newly developed and in-house-validated liquid chromatography-high-resolution mass spectrometry (LC-hrMS) method. This method was adopted for the measurement of the study material used for an international comparison evaluating the competencies of laboratories to perform peptide characterization. Eighteen structurally related impurities were identified, confirmed, and accurately quantified in the OXT study material by using LC-hrMS. The study material contained a total mass fraction of 31.1 mg/g structurally related OXT impurities with an associated expanded uncertainty of 1.7 mg/g.

Oxytocin Controls Chondrogenesis and Correlates with Osteoarthritis

This study investigated the relationship of oxytocin (OT) to chondrogenesis and osteoarthritis (OA). Human bone marrow and multipotent adipose-derived stem cells were cultured in vitro in the absence or presence of OT and assayed for mRNA transcript expression along with histological and immunohistochemical analyses. To study the effects of OT in OA in vivo, a rat model and a human cohort of 63 men and 19 women with hand OA and healthy controls, respectively, were used. The baseline circulating OT, interleukin-6, leptin, and oestradiol levels were measured, and hand X-ray examinations were performed for each subject. OT induced increased aggrecan, collagen (Col) X, and cartilage oligomeric matrix protein mRNA transcript levels in vitro, and the immunolabelling experiments revealed a normalization of Sox9 and Col II protein expression levels. No histological differences in lesion severity were observed between rat OA groups. In the clinical study, a multivariate analysis adjusted for age, body mass index, and leptin levels revealed a significant association between OA and lower levels of OT (odds ratio = 0.77; p = 0.012). Serum OT levels are reduced in patients with hand OA, and OT showed a stimulatory effect on chondrogenesis. Thus, OT may contribute to the pathophysiology of OA.

Tracking oxytocin functions in the rodent brain during the last 30 years: From push-pull perfusion to chemogenetic silencing

A short overview is provided of the last 30 years of oxytocin (and vasopressin) research performed in our laboratories, starting with attempts to monitor the release of this nonapeptide in the rodent brain during physiological conditions such as suckling in the lactating animal. Using push-pull perfusion and microdialysis approaches, release patterns in hypothalamic and limbic brain regions could be characterised to occur from intact neuronal structures, to be independent of peripheral secretion into blood, and to respond differentially to various stimuli, particularly those related to reproduction and stress. Parallel efforts focused on the functional impact of central oxytocin release, including neuroendocrine and behavioural effects mediated by nonapeptide receptor interactions and subsequent intraneuronal signalling cascades. The use of a variety of sophisticated behavioural paradigms to manipulate central oxytocin release, along with pharmacological, genetic and pharmacogenetic approaches, revealed multiple consequences on social behaviours, particularly social fear.

The Oxytocin Receptor: From Intracellular Signaling to Behavior

The many facets of the oxytocin (OXT) system of the brain and periphery elicited nearly 25,000 publications since 1930 (see FIGURE 1 , as listed in PubMed), which revealed central roles for OXT and its receptor (OXTR) in reproduction, and social and emotional behaviors in animal and human studies focusing on mental and physical health and disease. In this review, we discuss the mechanisms of OXT expression and release, expression and binding of the OXTR in brain and periphery, OXTR-coupled signaling cascades, and their involvement in behavioral outcomes to assemble a comprehensive picture of the central and peripheral OXT system. Traditionally known for its role in milk let-down and uterine contraction during labor, OXT also has implications in physiological, and also behavioral, aspects of reproduction, such as sexual and maternal behaviors and pair bonding, but also anxiety, trust, sociability, food intake, or even drug abuse. The many facets of OXT are, on a molecular basis, brought about by a single receptor. The OXTR, a 7-transmembrane G protein-coupled receptor capable of binding to either Gαior Gαqproteins, activates a set of signaling cascades, such as the MAPK, PKC, PLC, or CaMK pathways, which converge on transcription factors like CREB or MEF-2. The cellular response to OXT includes regulation of neurite outgrowth, cellular viability, and increased survival. OXTergic projections in the brain represent anxiety and stress-regulating circuits connecting the paraventricular nucleus of the hypothalamus, amygdala, bed nucleus of the stria terminalis, or the medial prefrontal cortex. Which OXT-induced patterns finally alter the behavior of an animal or a human being is still poorly understood, and studying those OXTR-coupled signaling cascades is one initial step toward a better understanding of the molecular background of those behavioral effects.

Preventing PTSD with oxytocin: effects of oxytocin administration on fear neurocircuitry and PTSD symptom development in recently trauma-exposed individuals

Background: Posttraumatic stress disorder (PTSD) is a debilitating psychiatric disorder which develops in approximately 10% of trauma-exposed individuals. Currently, there are few early preventive interventions available for PTSD. Intranasal oxytocin administration early posttrauma may prevent PTSD symptom development, as oxytocin administration was previously found to beneficially impact neurobiological (e.g. amygdala reactivity) and socio-emotional PTSD vulnerability factors. Objective: The overall aim of this dissertation was to investigate the potential of intranasal oxytocin administration as early preventive intervention for PTSD. Methods: We performed a functional magnetic resonance imaging (fMRI) study to assess the acute effects of a single administration of oxytocin on the functional fear neurocircuitry - consisting of the amygdala and (pre)frontal brain regions - in recently trauma-exposed emergency department patients (range n = 37-41). In addition, we performed a multicentre randomized double-blind placebo-controlled clinical trial (RCT) to assess the efficacy of repeated intranasal oxytocin administration early after trauma for preventing PTSD symptom development up to six months posttrauma (n = 107). Results: In our fMRI experiments we observed acutely increased amygdala reactivity to fearful faces and attenuated amygdala-ventromedial and ventrolateral prefrontal cortex functional connectivity after a single oxytocin administration in recently trauma-exposed individuals. However, in our RCT we found that repeated intranasal oxytocin administration early posttrauma reduced subsequent PTSD symptom development in recently trauma-exposed emergency department patients with high acute PTSD symptoms. Conclusions: These findings indicate that repeated intranasal oxytocin is a promising early preventive intervention for PTSD for individuals at increased risk for PTSD due to high acute symptom severity. Administration frequency dependent effects of oxytocin or the effects of oxytocin administration on salience processing may serve as explanatory frameworks for the contrasting oxytocin effects on anxiety-related measures in our clinical and neuroimaging studies.

The molecular basis of memory. Part 3: tagging with "emotive" neurotransmitters

Many neurons of all animals that exhibit memory (snails, worms, flies, vertebrae) present arborized shapes with many varicosities and boutons. These neurons, release neurotransmitters and contain ionotropic receptors that produce and sense electrical signals (ephaptic transmission). The extended shapes maximize neural contact with the surrounding neutrix [defined as: neural extracellular matrix (nECM) + diffusible (neurometals and neurotransmitters)] as well as with other neurons. We propose a tripartite mechanism of animal memory based on the dynamic interactions of splayed neurons with the "neutrix." Their interactions form cognitive units of information (cuinfo), metal-centered complexes within the nECM around the neuron. Emotive content is provided by NTs, which embody molecular links between physiologic (body) responses and psychic feelings. We propose that neurotransmitters form mixed complexes with cuinfo used for tagging emotive memory. Thus, NTs provide encoding option not available to a Turing, binary-based, device. The neurons employ combinatorially diverse options, with >10 NMs and >90 NTs for encoding ("flavoring") cuinfo with emotive tags. The neural network efficiently encodes, decodes and consolidates related (entangled) sets of cuinfo into a coherent pattern, the basis for emotionally imbued memory, critical for determining a behavioral choice aimed at survival. The tripartite mechanism with tagging of NTs permits of a causal connection between physiology and psychology.

Trial of repeated analgesia with Kangaroo Mother Care (TRAKC Trial)

BACKGROUND

Skin-to-skin contact (SSC) between mother and infant, commonly referred to as Kangaroo Mother Care (KMC), is recommended as an intervention for procedural pain. Evidence demonstrates its consistent efficacy in reducing pain for a single painful procedure. The purpose of this study is to examine the sustained efficacy of KMC, provided during all routine painful procedures for the duration of Neonatal Intensive Care Unit (NICU) hospitalization, in diminishing behavioral pain response in preterm neonates. The efficacy of KMC alone will be compared to standard care of 24% oral sucrose, as well as the combination of KMC and 24% oral sucrose.

METHODS/DESIGN

Infants admitted to the NICU who are less than 36 6/7 weeks gestational age (according to early ultrasound), that are stable enough to be held in KMC, will be considered eligible (N = 258). Using a single-blinded randomized parallel group design, participants will be assigned to one of three possible interventions: 1) KMC, 2) combined KMC and sucrose, and 3) sucrose alone, when they undergo any routine painful procedure (heel lance, venipuncture, intravenous, oro/nasogastric insertion). The primary outcome is infant's pain intensity, which will be assessed using the Premature Infant Pain Profile (PIPP). The secondary outcome will be maturity of neurobehavioral functioning, as measured by the Neurobehavioral Assessment of the Preterm Infant (NAPI). Gestational age, cumulative exposure to KMC provided during non-pain contexts, and maternal cortisol levels will be considered in the analysis. Clinical feasibility will be accounted for from nurse and maternal questionnaires.

DISCUSSION

This will be the first study to examine the repeated use of KMC for managing procedural pain in preterm neonates. It is also the first to compare KMC to sucrose, or the interventions in combination, across time. Based on the theoretical framework of the brain opioid theory of attachment, it is expected that KMC will be a preferred standard of care. However, current pain management guidelines are based on minimal data on repeated use of either intervention. Therefore, regardless of the outcomes of this study, results will have important implications for guidelines and practices related to management of procedural pain in preterm infants.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01561547.

The role of oxytocin in mating and pregnancy

The hormone oxytocin (OT) is released both centrally and peripherally during and after mating. Although research in humans suggests a central role in sexuality, the most reliable findings to date involve peripheral activation. This review will discuss these results and will particularly focus on understanding the most recent findings from fMRI data and the effects of exogenous peripheral OT administration. We will then consider hypotheses of the roles played by central and systemic OT release as well as their control and modulation in the female, summarizing recent findings from animal research. Finally, we will discuss the contribution of OT to the initiation of pregnancy in rodents. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Pain in neonates is different

Pain processing and management in neonates, especially preterm neonates, differs from older populations. In this review, a brief background on pain processing in neonatal life, pain exposure in Neonatal Intensive Care Units (NICU), the consequences of untreated pain, and the difficulties in treating procedural pain pharmacologically will be presented. A more detailed review of non-pharmacological interventions for procedural pain in neonates will include sensory stimulation approaches, oral sweet solutions, and maternal interventions. Some possible mechanisms for the effectiveness of non-pharmacological interventions are offered. Finally, avenues of research into similar interventions as adjuvant therapies or drug-sparing effects in older populations are suggested.

CD38/cyclic ADP-ribose system: a new player for oxytocin secretion and regulation of social behaviour

Oxytocin is important for regulating a number of physiological processes. Disruption of the secretion, metabolism or action of oxytocin results in an impairment of reproductive function, social and sexual behaviours, and stress responses. This review discusses current views on the regulation and autoregulation of oxytocin release in the hypothalamic-neurohypophysial system, with special focus on the activity of the CD38/cADP-ribose system as a new component in this regulation. Data from our laboratories indicate that an impairment of this system results in alterations of oxytocin secretion and abnormal social behaviour, thus suggesting new clues that help in our understanding of the pathogenesis of neurodevelopmental disorders.

CD38 regulates oxytocin secretion and complex social behavior

The peptide hormone oxytocin plays a critical role in regulating affiliative behaviors including mating, pair-bond formation, maternal/parenting behavior, social recognition, separation distress and other aspects of attachment. Jin and colleagues recently reported intriguing findings that CD38, a transmembrane receptor with ADP-ribosyl cyclase activity, plays a critical role in maternal nurturing behavior and social recognition by regulating oxytocin secretion. This research may have implications for understanding disorders marked by deficits in social cognition and social functioning, including autism, social anxiety disorder, borderline personality disorder and schizophrenia.