Plasma oxytocin and vasopressin do not predict neuropeptide concentrations in human cerebrospinal fluid

Appetite- and Weight-Regulating Neuroendocrine Circuitry in Hypothalamic Obesity

Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques have allowed us to elucidate various components of the intricate neurocircuitry governing appetite and weight regulation connecting the hypothalamus, pituitary gland, brainstem, adipose tissue, pancreas, and gastrointestinal tract. On a background of an increasing prevalence of population-level common obesity, the number of survivors of congenital (eg, septo-optic dysplasia, Prader-Willi syndrome) and acquired (eg, central nervous system tumors) hypothalamic disorders is increasing, thanks to earlier diagnosis and management as well as better oncological therapies. Although to date the discovery of several appetite-regulating peptides has led to the development of a range of targeted molecular therapies for monogenic obesity syndromes, outside of these disorders these discoveries have not translated into the development of efficacious treatments for other forms of HyOb. This review aims to summarize our current understanding of the neuroendocrine physiology of appetite and weight regulation, and explore our current understanding of the pathophysiology of HyOb.

Early life adversity in primates: Behavioral, endocrine, and neural effects

BACKGROUND

Evidence suggests that early life adversity is associated with maladaptive behaviors and is commonly an antecedent of stress-related psychopathology. This is particularly relevant to rearing in primate species as infant primates depend on prolonged, nurturant rearing by caregivers for normal development. To further understand the consequences of early life rearing adversity, and the relation among alterations in behavior, physiology and brain function, we assessed young monkeys that had experienced maternal separation followed by peer rearing with behavioral, endocrine and multimodal neuroimaging measures.

METHODS

50 young rhesus monkeys were studied, half of which were rejected by their mothers and peer reared, and the other half were reared by their mothers. Assessments were performed at approximately 1.8 years of age and included: threat related behavioral and cortisol responses, cerebrospinal fluid (CSF) measurements of oxytocin and corticotropin releasing hormone (CRH), and multimodal neuroimaging measures (anatomical scans, resting functional connectivity, diffusion tensor imaging, and threat-related regional glucose metabolism).

RESULTS

The results demonstrated alterations across behavioral, endocrine, and neuroimaging measures in young monkeys that were reared without their mothers. At a behavioral level in response to a potential threat, peer reared animals engaged in significantly less freezing behavior (p = 0.022) along with increased self-directed behaviors (p < 0.012). Levels of oxytocin in the CSF, but not plasma, were significantly reduced in the peer reared animals (p = 0.019). No differences in plasma cortisol or CSF CRH were observed. Diffusion tensor imaging revealed significantly decreased white matter density across the brain. Exploratory correlational and permutation analyses suggest that the impact of peer rearing on behavior, endocrine and brain structural alterations are mediated by separate parallel mechanisms.

CONCLUSIONS

Taken together, these results demonstrate in NHPs the importance of maternal rearing on the development of brain, behavior and hormonal systems that are linked to social functioning and adaptive responses. The findings suggest that the effects of maternal deprivation are mediated via multiple independent pathways which may account for the heterogeneity in behavioral and biological alterations observed in individuals that have experienced this early life adversity.

Naturally occurring low sociality in female rhesus monkeys: A tractable model for autism or not?

BACKGROUND

Autism spectrum disorder (ASD) is characterized by persistent social interaction impairments and is male-biased in prevalence. We have established naturally occurring low sociality in male rhesus monkeys as a model for the social features of ASD. Low-social male monkeys exhibit reduced social interactions and increased autistic-like trait burden, with both measures highly correlated and strongly linked to low cerebrospinal fluid (CSF) arginine vasopressin (AVP) concentration. Little is known, however, about the behavioral and neurochemical profiles of female rhesus monkeys, and whether low sociality in females is a tractable model for ASD.

METHODS

Social behavior assessments (ethological observations; a reverse-translated autistic trait measurement scale, the macaque Social Responsiveness Scale-Revised [mSRS-R]) were completed on N = 88 outdoor-housed female rhesus monkeys during the non-breeding season. CSF and blood samples were collected from a subset of N = 16 monkeys across the frequency distribution of non-social behavior, and AVP and oxytocin (OXT) concentrations were quantified. Data were analyzed using general linear models.

RESULTS

Non-social behavior frequency and mSRS-R scores were continuously distributed across the general female monkey population, as previously found for male monkeys. However, dominance rank significantly predicted mSRS-R scores in females, with higher-ranking individuals showing fewer autistic-like traits, a relationship not previously observed in males from this colony. Females differed from males in several other respects: Social behavior frequencies were unrelated to mSRS-R scores, and AVP concentration was unrelated to any social behavior measure. Blood and CSF concentrations of AVP were positively correlated in females; no significant relationship involving any OXT measure was found.

LIMITATIONS

This study sample was small, and did not consider genetic, environmental, or other neurochemical measures that may be related to female mSRS-R scores.

CONCLUSIONS

Dominance rank is the most significant predictor of autistic-like traits in female rhesus monkeys, and CSF neuropeptide concentrations are unrelated to measures of female social functioning (in contrast to prior CSF AVP findings in male rhesus monkeys and male and female autistic children). Although preliminary, this evidence suggests that the strong matrilineal organization of this species may limit the usefulness of low sociality in female rhesus monkeys as a tractable model for ASD.

Characterization of social hierarchy formation and maintenance in same-sex, group-housed male and female C57BL/6 J mice

Social hierarchies are a prevalent feature of all animal groups, and an individual's rank within the group can significantly affect their overall health, typically at the greatest expense of the lowest-ranked individuals, or omegas. These subjects have been shown to exhibit various stress-related phenotypes, such as increased hypothalamic-pituitary axis activity and increased amygdalar corticotropin-releasing factor levels compared to higher-ranked subjects. However, these findings have been primarily characterized in males and in models requiring exhibition of severe aggression. The goals of the current study, therefore, were to characterize the formation and maintenance of social hierarchies using the tube test and palatable liquid competition in same-sex groups of male and female C57BL/6 J mice. We also aimed to examine the effects of tube test-determined social rank on plasma and hypothalamic oxytocin and vasopressin levels, peptides with established roles in social behaviors and the stress response. Lastly, we assessed the effects of environmental enrichment and length of testing on the measures outlined above. Overall, we demonstrated that males and females develop social hierarchies and that these hierarchies can be determined using the tube test. While we were unable to establish a consistent connection between peptide levels and social rank, we observed transient changes in these peptides reflecting complex interactions between social rank, sex, environment, and length of testing. We also found that many male and female omegas began to exhibit passive coping behavior after repeated tube test losses, demonstrating the potential of this assay to serve as a model of chronic, mild psychosocial stress.

How does it feel? An exploration of neurobiological and clinical correlates of alexithymia in trauma-exposed police-officers with and without PTSD

Background: Alexithymia, an inability to recognise one's emotions, has been associated with trauma-exposure and posttraumatic stress disorder (PTSD). Previous research suggests involvement of the oxytocin system, and socio-emotional neural processes. However, the paucity of neurobiological research on alexithymia, particularly in trauma-exposed populations, warrants further investigation.Objective: Explore associations between alexithymia, endogenous oxytocin levels, and socio-emotional brain function and morphometry in a trauma-exposed sample.Method: Dutch trauma-exposed police officers with (n = 38; 18 females) and without PTSD (n = 40; 20 females) were included. Alexithymia was assessed with the Toronto Alexithymia Scale (TAS-20). Endogenous salivary oxytocin was assessed during rest, using radioimmunoassay. Amygdala and insula reactivity to socio-emotional stimuli were assessed with functional MRI, amygdala and insula grey matter volume were derived using Freesurfer.Results: Alexithymia was higher in PTSD patients compared to trauma-exposed controls (F(1,70) = 54.031, p < .001). Within PTSD patients, alexithymia was positively associated with PTSD severity (ρ(36) = 0.497, p = .002). Alexithymia was not associated with childhood trauma exposure (β = 0.076, p = .509), police work-related trauma exposure (β = -0.107, p = .355), oxytocin levels (β = -0.164, p = .161), insula (β = -0.170, p = .158) or amygdala (β = -0.175, p = .135) reactivity, or amygdala volume (β = 0.146, p = .209). Insula volume was positively associated with alexithymia (β = 0.222, p = .016), though not significant after multiple testing corrections. Bayesian analyses supported a lack of associations.Conclusions: No convincing neurobiological correlates of alexithymia were observed with any of the markers included in the current study. Yet, the current study confirmed high levels of alexithymia in PTSD patients, independent of trauma-exposure, substantiating alexithymia's relevance in the clinical phenotype of PTSD.

Cocaine use disorder effects on blood oxytocin levels and OXTR DNA methylation

Substance use disorders have been associated with alterations in the oxytocinergic system, but few studies have investigated both the peptide and epigenetic mechanisms potentially implicated in the regulation of oxytocin receptor. In this study, we compared plasma oxytocin and blood DNA methylation in the OXTR gene between people with and without cocaine use disorder (CUD). We measured the oxytocin levels of 51 people with CUD during acute abstinence and of 30 healthy controls using an enzyme immunoassay. The levels of DNA methylation in four CpG sites at exon III of the OXTR gene were evaluated in a subsample using pyrosequencing. The Addiction Severity Index was used to assess clinical characteristics. We found higher oxytocin levels in men with CUD (56.5 pg/mL; 95% CI: 48.2-64.7) than in control men (33.6 pg/mL; 95% CI: 20.7-46.5), while no differences between women with and without CUD were detected. With a moderate effect size, the interaction effect between group and sex remained significant when controlling for height, weight and age data. A positive correlation in the CUD sample was found between oxytocin levels and days of psychological suffering prior to treatment enrollment. No group differences were observed regarding DNA methylation data. This suggests that CUD is associated with higher peripheral oxytocin levels in men during acute abstinence. This finding may be considered in future studies that aim at using exogenous oxytocin as a potential treatment for cocaine addiction.

Development of circadian neurovascular function and its implications

The neurovascular system forms the interface between the tissue of the central nervous system (CNS) and circulating blood. It plays a critical role in regulating movement of ions, small molecules, and cellular regulators into and out of brain tissue and in sustaining brain health. The neurovascular unit (NVU), the cells that form the structural and functional link between cells of the brain and the vasculature, maintains the blood-brain interface (BBI), controls cerebral blood flow, and surveils for injury. The neurovascular system is dynamic; it undergoes tight regulation of biochemical and cellular interactions to balance and support brain function. Development of an intrinsic circadian clock enables the NVU to anticipate rhythmic changes in brain activity and body physiology that occur over the day-night cycle. The development of circadian neurovascular function involves multiple cell types. We address the functional aspects of the circadian clock in the components of the NVU and their effects in regulating neurovascular physiology, including BBI permeability, cerebral blood flow, and inflammation. Disrupting the circadian clock impairs a number of physiological processes associated with the NVU, many of which are correlated with an increased risk of dysfunction and disease. Consequently, understanding the cell biology and physiology of the NVU is critical to diminishing consequences of impaired neurovascular function, including cerebral bleeding and neurodegeneration.

Enhancing precision in human neuroscience

Human neuroscience has always been pushing the boundary of what is measurable. During the last decade, concerns about statistical power and replicability - in science in general, but also specifically in human neuroscience - have fueled an extensive debate. One important insight from this discourse is the need for larger samples, which naturally increases statistical power. An alternative is to increase the precision of measurements, which is the focus of this review. This option is often overlooked, even though statistical power benefits from increasing precision as much as from increasing sample size. Nonetheless, precision has always been at the heart of good scientific practice in human neuroscience, with researchers relying on lab traditions or rules of thumb to ensure sufficient precision for their studies. In this review, we encourage a more systematic approach to precision. We start by introducing measurement precision and its importance for well-powered studies in human neuroscience. Then, determinants for precision in a range of neuroscientific methods (MRI, M/EEG, EDA, Eye-Tracking, and Endocrinology) are elaborated. We end by discussing how a more systematic evaluation of precision and the application of respective insights can lead to an increase in reproducibility in human neuroscience.

Inaccuracies in plasma oxytocin extraction and enzyme immunoassay techniques

Numerous studies have reported extensive associations between plasma oxytocin (OXT) concentrations and various human physiological and neurobehavioral processes. Measurement of OXT is fraught with difficulty due to its low molecular weight and plasma concentrations, with no consensus as to the optimal conditions for pre-analytical sample extraction, standards for immunoassay validation or the ideal protease inhibitors to prevent OXT degradation. Previous attempts at determining the efficacy of various purification techniques such as solid phase extraction (SPE) or ultrafiltration have only utilized human plasma samples, making it difficult to dissect out whether the effect of interference comes from the extraction process itself or cross-reactivity with other proteins. By testing these on pure OXT solutions, we demonstrate poor recovery efficacy and reliability of reversed phase SPE (maximum 58.1%) and ultrafiltration (<1%) techniques, and the potential for the former to introduce interference into enzyme immunoassay (EIA) measurements. The clonality of antibodies used in EIA kits also potentially contributes to the differences in the readings obtained, and we validate an EIA kit which did not require pre-analytical sample extraction with low cross-reactivity and high reliability (intraclass correlation coefficient 0.980 (95% CI 0.896-0.999). Biochemical techniques used for measuring plasma OXT concentrations must therefore be internally validated prior to translation into clinical studies.

Oxytocin measurements in saliva: an analytical perspective

Oxytocin has traditionally been known for its physiological effects on muscle contraction associated with birth and lactation, but in the last years is widely used as a biomarker of "positive experiences" in psychology and behavior. Different types of samples have been used for oxytocin measurements with saliva samples having the particular advantage of an easy and non-stressful collection. However, the low concentration of oxytocin in saliva can represent a limitation for its use. For this reason, sensitive assays and even a previous sample treatment in some cases are required for saliva oxytocin quantification. In addition, the lack of standardized and generally agreed-upon approach to peripheral oxytocin measurement leads to large discrepancies between different laboratories, that use different sample treatment protocols and different assays. The main objectives of this review are to describe the current status of the use of saliva for oxytocin measurement, provide details of the different sample processing techniques that can be applied and inform about the analytical techniques and assays available in different animal species, and also in humans for comparative purposes. It is expected that this information can contribute to an increase in the knowledge about the measurements of oxytocin in saliva and to its wider use in the future.

Sex-specific issues of central and peripheral arginine-vasopressin concentrations in neurocritical care patients

BACKGROUND

Arginine-Vasopressin (AVP) is a nonapeptide that exerts multiple functions within the central nervous system and in the blood circulation that might contribute to outcome in critically ill patients. Sex differences have been found for mental and physical effects of AVP. For example, stress response and response due to hemorrhage differ between males and females, at least in animal studies. Data on humans -especially on AVP within the central nervous system (CNS)-are scarce, as cerebrospinal fluid (CSF) which is said to represent central AVP activity, has to be collected by means of invasive procedures. Here we present data on 30 neurocritical care patients where we simultaneously collected blood, CSF and saliva to analyze concentrations in the central and peripheral compartments.

PATIENTS AND METHODS

30 neurocritical care patients were included (13 male, 13 postmenopausal female, 4 premenopausal female) with a median age of 60 years. CSF, plasma and saliva were obtained simultaneously once in each patient and analyzed for AVP concentrations. Correlations between the central compartment represented by CSF, and the peripheral compartment represented by plasma and saliva, were identified. Relations between AVP concentrations and serum sodium and hematocrit were also determined.

RESULTS

In the whole patient collective, only very weak to weak correlations could be detected between AVP plasma/CSF, plasma/saliva and CSF/saliva as well as between AVP concentrations in each of the compartments and serum sodium/hematocrit. Regarding the subgroup of postmenopausal females, a significant moderate correlation could be detected for AVP in plasma and CSF and AVP CSF and serum sodium.

CONCLUSION

Absolute concentrations of AVP in central and peripheral compartments did not show sex differences. However, correlations between AVP plasma and CSF and AVP CSF and serum sodium in postmenopausal females indicate differences in AVP secretion and AVP response to triggers that deserve further examination.

Infant Stimulation Induced a Rapid Increase in Maternal Salivary Oxytocin

Oxytocin (OT) is a neuropeptide involved in human social behaviors and reproduction. Non-invasive OT levels in saliva have recently roused interest as it does not require a specialized medical setting. Here, we observed one woman’s basal serum and saliva OT from pregnancy to 1 year postpartum to track OT concentration changes over this period. We examined the changes in salivary OT levels over time in response to maternal physiological and behavioral responses. The fluctuation of saliva OT levels is well correlated with serum OT during pregnancy and breastfeeding. However, while salivary OT increased rapidly during direct interaction (social interaction tests) with the infant and/or when the mother was watching her own infant’s video (video tests), no increase was observed in serum. We used social interaction and video tests on a group of mothers (nine mothers for social interaction and six for the video test) to clarify these single-subject results. In both tests, the mothers had increased OT in their saliva but not serum. Our study may suggest that salivary samples reflect not only the physical but also the emotional state and that saliva samples may be useful for monitoring women’s OT levels during pre- and postpartum periods. Further studies with larger sample numbers are necessary to confirm the rapid changes in salivary OT levels in response to maternal physiological and behavioral responses.

Socio-behavioral dysfunction in disorders of hypothalamic-pituitary involvement: The potential role of disease-induced oxytocin and vasopressin signaling deficits

Disorders involving hypothalamic and pituitary (HPIT) structures-including craniopharyngioma, Langerhans cell histiocytosis, and intracranial germ cell tumors-can disrupt brain and endocrine function. An area of emerging clinical concern in patients with these disorders is the co-occurring socio-behavioral dysfunction that persists after standard hormone replacement therapy. Although the two neuropeptides most implicated in mammalian social functioning (oxytocin and arginine vasopressin) are of hypothalamic origin, little is known about how disease-induced damage to HPIT structures may disrupt neuropeptide signaling and, in turn, impact patients' socio-behavioral functioning. Here we provide a clinical primer on disorders of HPIT involvement and a review of neuropeptide signaling and socio-behavioral functioning in relevant animal models and patient populations. This collective evidence suggests that neuropeptide signaling disruptions contribute to socio-behavioral deficits experienced by patients with disorders of HPIT involvement. A better understanding of the biological underpinnings of patients' socio-behavioral symptoms is now needed to enable the development of the first targeted pharmacological strategies by which to manage patients' socio-behavioral dysfunction.

Evaluating the neuropeptide-social cognition link in ageing: the mediating role of basic cognitive skills

The roles of oxytocin (OT) and arginine-vasopressin (AVP) as crucial modulators of social cognition and related behaviours have been extensively addressed in the literature. The involvement of these neuropeptides in social cognition in ageing, however, and a potential mediating effect of basic cognitive capacities on this link, are not well understood. To fill these research gaps, this study assessed associations of plasma OT and AVP levels with dynamic emotion identification accuracy in generally healthy older men (aged 55-95 years) and probed the underlying roles of crystallized and fluid cognition in these associations. Higher plasma OT levels were associated with lower accuracy in dynamic emotion identification, with this negative relationship fully mediated by cognition. For plasma AVP levels, in contrast, there was no association with dynamic emotion identification accuracy. Integrated within existing theoretical accounts, results from this study advance understanding of the neuropeptide-social cognition link in ageing and support basic cognitive capacities as mediators in this association. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

Approaches to Improve the Quantitation of Oxytocin in Human Serum by Mass Spectrometry

The neuropeptide oxytocin (OT) regulates several peripheral and central functions and is a molecule of interest in psychiatric diseases such as autism spectrum disorder, schizophrenia, anxiety and depression. The study of OT in human serum samples is however hampered by inconsistent sample preparation and analysis as well as low endogenous blood concentration (1-10 pM). This results in varying reports on OT's blood levels and interpretation of OT's role in different (patho)physiological states. Quantitative mass spectrometry (MS) is a highly promising technology to address this problem but still requires large sample volumes to achieve adequate sensitivity and reliability for the quantitation of compounds at low concentrations. We therefore systematically evaluated sample preparation methods for MS to achieve a reliable sample preparation protocol with good peptide recovery, minimal matrix effects and good overall method efficiency in line with FDA guidelines for bioanalytic method development and validation. Additionally, we investigated a strategy to improve the ionization efficiency of OT by adding charged and/or hydrophobic moieties to OT to improve the lower limit of quantitation. Optimized sample preparation in combination with OT modification with a quaternary pyridinium ion improved the sensitivity of OT by ∼40-fold on a tandem triple quadrupole mass spectrometer (API4000 QTRAP), resulting in a lower limit of quantitation of 5 pM in water (linear range 5 pM - 1 mM) and 2 nM in human serum (linear range 2 nM - 1 mM) compared to 200 pM in water and 86 nM in serum with unmodified OT. This approach and protocol provide a solid foundation towards method development for OT quantitation using MS, which should be of high value for fundamental research as well as clinical monitoring of OT upon drug treatments.

Leveraging a translational research approach to drive diagnostic and treatment advances for autism

Autism spectrum disorder (ASD) is a prevalent and poorly understood neurodevelopmental disorder. There are currently no laboratory-based diagnostic tests to detect ASD, nor are there any disease-modifying medications that effectively treat ASD's core behavioral symptoms. Scientific progress has been impeded, in part, by overreliance on model organisms that fundamentally lack the sophisticated social and cognitive abilities essential for modeling ASD. We therefore saw significant value in studying naturally low-social rhesus monkeys to model human social impairment, taking advantage of a large outdoor-housed colony for behavioral screening and biomarker identification. Careful development and validation of our animal model, combined with a strong commitment to evaluating the translational utility of our preclinical findings directly in patients with ASD, yielded a robust neurochemical marker (cerebrospinal fluid vasopressin concentration) of trans-primate social impairment and a first-in-class medication (intranasal vasopressin) shown in a small phase 2a pilot trial to improve social abilities in children with ASD. This translational research approach stands to advance our understanding of ASD in a manner not readily achievable with existing animal models, and can be adapted to investigate a variety of other human brain disorders which currently lack valid preclinical options, thereby streamlining translation and amplifying clinical impact more broadly.

The importance of pro-social processing, and ameliorating dysfunction in schizophrenia. An FMRI study of oxytocin

Schizophrenia is often a severe and debilitating mental illness, frequently associated with impairments in social cognition that hinder individuals' abilities to relate to others and integrate effectively in society. Oxytocin has emerged as a putative therapeutic agent for treating social deficits in schizophrenia, but the mode of action remains unclear. This placebo-controlled crossover study aimed to elucidate the neural underpinnings of oxytocin administration in patients with schizophrenia. 20 patients with schizophrenia were examined using functional magnetic resonance imaging under oxytocin (40 IU) or placebo nasal spray. Participants performed a stochastically rewarded decision-making task that incorporated elements of social valence provided by different facial expressions, i.e. happy, angry and neutral. Oxytocin attenuated the normal bias in selecting the happy face accompanied by reduced activation in a network of brain regions that support mentalising, processing of facial emotion, salience, aversion, uncertainty and ambiguity in social stimuli, including amygdala, temporo-parietal junction, posterior cingulate cortex, precuneus and insula. These pro-social effects may contribute to the facilitation of social engagement and social interactions in patients with schizophrenia and warrant further investigation in future clinical trials for social cognitive impairments in schizophrenia.

Longitudinal tracking of human plasma oxytocin suggests complex responses to moral elevation

Positive social experiences may induce oxytocin release. However, previous studies of moral elevation have generally utilized cross-sectional and simple modeling approaches to establish the relationship between oxytocin and emotional stimuli. Utilizing a cohort of 30 non-lactating women (aged 23.6 ± 5.7 years), we tested whether exposure to a video identified as capable of eliciting moral elevation could change plasma oxytocin levels. Uniquely, we utilized a high-frequency longitudinal sampling approach and multilevel growth curve modeling with landmark registration to test physiological responses. The moral elevation stimulus, versus a control video, elicited significantly greater reports of being “touched/inspired” and “happy/joyful”. However, the measured plasma oxytocin response was found to be markedly heterogeneous. While the moral elevation stimulus elicited increased plasma oxytocin as expected, this increase was only modestly larger than that seen following the control video. This increase was also only present in some individuals. We found no relationship between plasma oxytocin and self-report responses to the stimulus. From these data, we argue that future studies of the relationship between oxytocin and emotion need to anticipate heterogeneous responses and thus incorporate comprehensive individual psychological data; these should include evidence-based variables known to be associated with oxytocin such as a history of trauma, and the individual’s psychological and emotional state at the time of testing. Given the complexity of physiological oxytocin release, such studies also need to incorporate frequent biological sampling to properly examine the dynamics of hormonal release and response.

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A moral elevation stimulus elicits positive emotional responses

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The human oxytocin responses to a morel elevation stimulus are more heterogenous than previously reported

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Future studies need to utilize longitudinal hormone measurements and comprehensive psychological assessments

Sequential Social Exclusion in a Novel Cyberball Paradigm Leads to Reduced Behavioral Repair and Plasma Oxytocin in Borderline Personality Disorder

Patients with borderline personality disorder (BPD) show interpersonal deficits, and altered emotional and oxytocin (OT) responses to social exclusion (Cyberball). In order to extend previous findings, this study applies a novel Cyberball variant. Nineteen BPD patients and 56 healthy controls (HC) played Cyberball for 2 minutes of inclusion, 5 minutes of partial exclusion by one of two co-players, and 2 minutes total exclusion by both. Plasma OT levels at baseline and after 7, 9, 15, and 40 minutes were measured with radioimmunoassay. BPD patients showed a greater aversive reaction and a trend for greater OT reduction after social exclusion than HC. BPD patients also tended to play less frequently with the excluder. Though limited by our sample size, we partially replicate previous findings. Our preliminary behavioral data support the notion of an altered OT regulation and reduced capacity for social cooperation in BPD.

Salivary oxytocin in autistic patients and in patients with intellectual disability

BACKGROUND

Assessing the role of oxytocin (OT) in the regulation of social interaction is a promising area that opens up new opportunities for studying the mechanisms of developing autism spectrum disorders (ASD).

AIM

To assess the correlation between the salivary OT level and age-related and psychopathological symptoms of children with intellectual disability (ID) and ASD.

METHODS

We used the clinical and psychopathological method to assess the signs of ASD based on International Classification of Diseases (ICD-10), the severity of ASD was specified by the selected Russian type version "Childhood Autism Rating Scale" (CARS). Patients of both groups had an IQ score below 70 points.

RESULTS

The median and interquartile range of salivary OT levels in patients with ID and ASD were 23.897 [14.260-59.643] pg/mL, and in the group ID without ASD - Me = 50.896 [33.502-83.774] pg/mL (p = 0.001). The severity of ASD on the CARS scale Me = 51.5 [40.75-56.0] score in the group ID with ASD, and in the group ID without ASD-at the level of Me = 32 [27.0-38.0] points (p < 0.001). According to the results of correlation-regression analysis in the main group, a direct correlation was established between salivary OT level and a high degree of severity of ASD Rho = 0.435 (p = 0.005). There was no correlation between the salivary OT level and intellectual development in the group ID with ASD, Rho = 0.013 (p = 0.941) and we have found a relationship between oxytocin and intellectual development in the group ID without ASD, Rho = 0.297 (p = 0.005). There was no correlation between salivary OT and age, ASD and age.

CONCLUSION

The results of this study indicate that patients in the group ID with ASD demonstrated a lower level of salivary OT concentration and a direct relationship between the maximum values of this indicator and the severity of autistic disorders, in contrast to patients in the group ID without ASD.

Role of Oxytocin in Different Neuropsychiatric, Neurodegenerative, and Neurodevelopmental Disorders

Oxytocin has recently gained significant attention because of its role in the pathophysiology and management of dominant neuropsychiatric disorders. Oxytocin, a peptide hormone synthesized in the hypothalamus, is released into different brain regions, acting as a neurotransmitter. Receptors for oxytocin are present in many areas of the brain, including the hypothalamus, amygdala, and nucleus accumbens, which have been involved in the pathophysiology of depression, anxiety, schizophrenia, autism, Alzheimer's disease, Parkinson's disease, and attention deficit hyperactivity disorder. Animal studies have spotlighted the role of oxytocin in social, behavioral, pair bonding, and mother-infant bonding. Furthermore, oxytocin protects fetal neurons against injury during childbirth and affects various behaviors, assuming its possible neuroprotective characteristics. In this review, we discuss some of the concepts and mechanisms related to the role of oxytocin in the pathophysiology and management of some neuropsychiatric, neurodegenerative, and neurodevelopmental disorders.

Low oxytocin levels are broadly associated with more pronounced psychopathology in anorexia nervosa with primarily restricting but not binge/purge eating behavior

OBJECTIVE

Anorexia nervosa (AN) is commonly associated with depression, anxiety, and deficits in socioemotional functioning. Basal levels of oxytocin, a neurohormone with antidepressant, anxiolytic, and prosocial properties, are low in women with AN. However, the relationship between oxytocin and psychopathology of AN/atypical AN has not been examined in individuals with primarily food restriction (AN/AtypAN-R) or those with restriction plus binge/purge behaviors (AN/AtypAN-BP) alone, which is important to further elucidate the neurobiology of different AN presentations. We investigated whether oxytocin levels are related to eating, affective, and socioemotional psychopathology in women with AN/AtypAN-R and separately AN/AtypAN-BP.

METHODS

In a cross-sectional study of 53 women with low-weight AN or atypical AN based on DSM-5 (AN/AtypAN-R: n=21, AN/AtypAN-BP: n=32), we obtained fasting serum oxytocin levels and self-report measures of psychopathology, including the Eating Disorder Examination-Questionnaire (EDE-Q), Beck Depression Inventory-IA (BDI), State-Trait Anxiety Inventory (STAI), and Toronto Alexithymia Scale (TAS-20).

RESULTS

In individuals with AN/AtypAN-R, oxytocin levels were negatively associated with eating psychopathology (EDE-Q Global Score: r=-0.49, p=0.024), depressive and anxiety symptoms (BDI Total Score: r=-0.55, p=0.009; STAI Trait Score: r=-0.63, p=0.002), and socioemotional symptoms (TAS-20 Difficulty Identifying Feelings Score: r=-0.49, p=0.023). In contrast, in those with AN/AtypAN-BP oxytocin levels were negatively associated with depressive symptoms only (BDI Total Score: r=-0.52, p=0.049).

CONCLUSIONS

These findings support the notion that AN/AtypAN-R and AN/AtypAN-BP might have divergent underlying neurobiology. Understanding these differences is crucial to develop targeted treatments for a population with high levels of chronicity, for which no specific pharmacological treatments are currently available.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov, identifier: NCT01121211.

An improved sample extraction method reveals that plasma receptor for advanced glycation end-products (RAGE) modulates circulating free oxytocin in mice

The receptor for advanced glycation end-products (RAGE) binds oxytocin (OT) and transports it from the blood to the brain. As RAGE's OT-binding capacity was lost in RAGE knockout (KO) mice, we predicted that circulating concentrations of unbound (free) OT should be elevated compared to wild-type (WT) mice. However, this hypothesis has not yet been investigated. Unfortunately, the evaluation of the dynamics of circulating free and bound plasma OT is unclear in immunoassays, in part because of interference from plasma proteins. A radioimmunoassay (RIA) is considered the gold standard method for overcoming this issue, but is more challenging to implement; thus, commercially available enzyme-linked immunosorbent assays (ELISAs) are more commonly used. Here, we developed a pre-treatment method to remove the interference-causing components from plasma before performing ELISA. The acetonitrile protein precipitation (PPT) approach was reliable, with fewer steps needed to measure free OT concentrations than by solid-phase extraction of plasma samples. PPT-extracted plasma samples yielded higher concentrations of OT in RAGE KO mice than in WT mice using ELISA. After peripheral OT injection, free OT plasma levels spiked immediately then rapidly declined in WT mice, but remained high in KO mice. These results suggest that plasma samples with PPT pre-treatment appear to be superior and that circulating soluble RAGE can most likely serve as a buffer for plasma OT, which indicates a novel physiological function of RAGE.

Discussions and perspectives regarding oxytocin as a biomarker in human investigations

This article introduces a review of research that has implemented oxytocin measurements in different fluids such as plasma, cerebrospinal fluid, urine and, mainly, saliva. The main purpose is to evaluate the level of evidence supporting the measurement of this biomarker implicated in a variety of psychological and social processes. First, a review of the technical developments that allowed the characterization, function establishing, and central and peripheral levels of this hormone is proposed. Then, the article approaches the current discussions regarding the level of reliability of the laboratory techniques that enable the measurement of oxytocin, focusing mainly on the determination of its concentration in saliva through Enzyme-Linked Immunosorbent Assay (ELISA). Finally, research results, which have established the major physiological correlates of this hormone in fields such as social neuroscience and neuropsychology, are collected and discussed in terms of the hormone measurement methods that different authors have used. In this way, the article is expected to contribute to the panorama of debates and current perspectives regarding investigation involving this important biomarker.

Vasopressin but Not Oxytocin Responds to Birth Stress in Infants

Context

Birth triggers a large fetal neuroendocrine response, which is more pronounced in infants born vaginally than in those born by elective cesarean section (ECS). The two related peptides arginine vasopressin (AVP) and oxytocin (OT) play an essential role in peripheral and central stress adaptation and have a shared receptor mediating their function. Elevated cord blood levels of AVP and its surrogate marker copeptin, the C-terminal part of AVP prohormone, have been found after vaginal delivery (VD) as compared to ECS, while release of OT in response to birth is controversial. Moreover, AVP, copeptin and OT have not yet been measured simultaneously at birth.

Objective

To test the hypothesis that AVP but not OT levels are increased in infants arterial umbilical cord blood in response to birth stress and to characterize AVP secretion in direct comparison with plasma copeptin.

Methods

In a prospective single-center cross-sectional study, we recruited healthy women with a singleton pregnancy and more than 36 completed weeks of gestation delivering via VD or ECS (cesarean without prior uterine contractions or rupture of membranes). Arterial umbilical cord blood samples were collected directly after birth, centrifuged immediately and plasma samples were frozen. Concentrations of AVP and OT were determined by radioimmunoassay and that of copeptin by ultrasensitive immunofluorescence assay.

Results

A total of 53 arterial umbilical cord blood samples were collected, n = 29 from VD and n = 24 from ECS. Ten venous blood samples from pregnant women without stress were collected as controls. AVP and copeptin concentrations were significantly higher in the VD group than in the ECS group (both p < 0.001), median (range) AVP 4.78 (2.38–8.66) vs. 2.38 (1.79–3.88) (pmol/L), copeptin 1692 (72.1–4094) vs. 5.78 (3.14–17.97), respectively, (pmol/L). In contrast, there was no difference in OT concentrations (pmol/L) between VD and ECS, 6.00 (2.71–7.69) vs. 6.14 (4.26–9.93), respectively. AVP and copeptin concentrations were closely related (Rs = 0.700, p < 0.001) while OT did not show any correlation to either AVP or copeptin. In linear regression models, vaginal delivery and biochemical stress indicators, base deficit and pH, were independent predictors for both AVP and copeptin. OT was not linked to base deficit or pH.

Conclusion

Vaginal birth causes a profound secretion of AVP and copeptin in infants. Whereas AVP indicates acute stress events, copeptin provides information on cumulative stress events over a longer period. In contrast, fetal OT is unaffected by birth stress. Thus, AVP signaling but not OT mediates birth stress response in infants. This unique hormonal activation in early life may impact neurobehavioral development in whole life.

The Effects of Oxytocin on Appetite Regulation, Food Intake and Metabolism in Humans

The hypothalamic peptide oxytocin and its receptor are involved in a range of physiological processes, including parturition, lactation, cell growth, wound healing, and social behavior. More recently, increasing evidence has established the effects of oxytocin on food intake, energy expenditure, and peripheral metabolism. In this review, we provide a comprehensive description of the central oxytocinergic system in which oxytocin acts to shape eating behavior and metabolism. Next, we discuss the peripheral beneficial effects oxytocin exerts on key metabolic organs, including suppression of visceral adipose tissue inflammation, skeletal muscle regeneration, and bone tissue mineralization. A brief summary of oxytocin actions learned from animal models is presented, showing that weight loss induced by chronic oxytocin treatment is related not only to its anorexigenic effects, but also to the resulting increase in energy expenditure and lipolysis. Following an in-depth discussion on the technical challenges related to endogenous oxytocin measurements in humans, we synthesize data related to the association between endogenous oxytocin levels, weight status, metabolic syndrome, and bone health. We then review clinical trials showing that in humans, acute oxytocin administration reduces food intake, attenuates fMRI activation of food motivation brain areas, and increases activation of self-control brain regions. Further strengthening the role of oxytocin in appetite regulation, we review conditions of hypothalamic insult and certain genetic pathologies associated with oxytocin depletion that present with hyperphagia, extreme weight gain, and poor metabolic profile. Intranasal oxytocin is currently being evaluated in human clinical trials to learn whether oxytocin-based therapeutics can be used to treat obesity and its associated sequela. At the end of this review, we address the fundamental challenges that remain in translating this line of research to clinical care.

Territorial blueprint in the hippocampal system

As we skillfully navigate through familiar places, neural computations of distances and coordinates escape our attention. However, we perceive clearly the division of space into socially meaningful territories. 'My space' versus 'your space' is a distinction familiar to all of us. Spatial frontiers are social in nature since they regulate individuals' access to utilities in space depending on hierarchy and affiliation. How does the brain integrate spatial geometry with social territory? We propose that the action of oxytocin (OT) in the entorhinal-hippocampal regions supports this process. Grounded on the functional role of the hypothalamic neuropeptide in the hippocampal system, we show how OT-induced plasticity may bias the geometrical coding of place and grid cells to represent social territories.

Oxytocin and social anxiety: Interactions with sex hormones

Oxytocin has been associated with anxiolytic and stress reducing effects in a number of studies. Less is known about the associations of endogenous oxytocin concentrations and their interaction with other hormones such as sex hormones in relation to self-reported anxiety levels. In this study, endogenous oxytocin and sex hormone levels were analyzed in 99 high (51 women) and 100 low (50 women) socially anxious individuals. Regression analyses showed that women with high oxytocin and estradiol levels reported a lower total Liebowitz Social Anxiety Score (LSAS) as well as a lower score on the subscale LSAS Fear. This association of hormonal interaction with social anxiety scores was significant in the subsample of high socially anxious women. In men there were no significant associations for endogenous hormones with LSAS scores. These findings suggest that in women the link between oxytocin and anxiety might be dependent on basal anxiety levels as well as on individual sex hormone levels.

Increased oxytocin release precedes hyponatremia after pituitary surgery

PURPOSE

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a well-known complication of transsphenoidal pituitary surgery, related to inappropriate secretion of arginine vasopressin (AVP). Its diagnosis is based on hyponatremia, with a peak of occurrence around day 7 after surgery and, to date, no early marker has been reported. In particular, copeptin levels are not predictive of hyponatremia in this case. Oxytocin (OXT) is secreted into the peripheral blood by axon terminals adjacent to those of AVP neurons in the posterior pituitary. Besides its role in childbirth and lactation, recent evidences suggested a role for OXT in sodium balance. The contribution of this hormone in the dysnatremias observed after pituitary surgery has however never been investigated.

METHODS

We analyzed the urinary output of OXT in patients subjected to transsphenoidal pituitary surgery.

RESULTS

While OXT excretion remained stable in patients who presented a normonatremic postoperative course, patients who were later diagnosed with SIADH-related hyponatremia presented with a significantly increased urinary secretion of OXT 4 days after surgery.

CONCLUSION

Taken together, these results show for the first time that urinary OXT output remains normally stable after transsphenoidal pituitary surgery. OXT excretion however becomes abnormally high on or around 4 days after surgery in patients later developing hyponatremia, suggesting that this abnormal dynamics of OXT secretion might serve as an early marker for transsphenoidal surgery-related hyponatremia attributed to SIADH.

Eye-Tracking Reveals a Role of Oxytocin in Attention Allocation Towards Familiar Faces

Visual attention directed towards the eye-region of a face emerges rapidly, even before conscious awareness, and regulates social interactions in terms of approach versus avoidance. Current perspectives on the neuroendocrine substrates of this behavioral regulation highlight a role of the peptide hormone oxytocin (OXT), but it remains unclear whether the facilitating effects of OXT vary as a function of facial familiarity. Here, a total of 73 healthy participants was enrolled in an eye-tracking experiment specifically designed to test whether intranasal OXT (24 IU) augments gaze duration toward the eye-region across four different face categories: the participants' own face, the face of their romantic partner, the face of a familiar person (close friend) or an unfamiliar person (a stranger). We found that OXT treatment induced a tendency to spend more time looking into the eyes of familiar persons (partner and close friend) as compared to placebo. This effect was not evident in the self and unfamiliar conditions. Independent of treatment, volunteers scoring high on autistic-like traits (AQ-high) spent less time looking at the eyes of all faces except their partner. Collectively, our results show that the OXT system is involved in facilitating an attentional bias towards the eye region of familiar faces, which convey safety and support, especially in anxious contexts. In contrast, autistic-like traits were associated with reduced attention to the eye region of a face regardless of familiarity and OXT-treatment.

The association of oxytocin with major depressive disorder: role of confounding effects of antidepressants

Major depressive disorder is a genetic susceptible disease, and a psychiatric syndrome with a high rate of incidence and recurrence. Because of its complexity concerning etiology and pathogenesis, the cure rate of first-line antidepressants is low. In recent years, accumulative evidences revealed that oxytocin act as a physiological or pathological participant in a variety of complex neuropsychological activities, including major depressive disorder. Six electronic databases (Web of Science, PubMed, Scopus, Google Scholar, CNKI, and Wanfang) were employed for researching relevant publications. At last, 226 articles were extracted. The current review addresses the correlation of the oxytocin system and major depressive disorder. Besides, we summarize the mechanisms by which the oxytocin system exerts potential antidepressant effects, including regulating neuronal activity, influencing neuroplasticity and regeneration, altering neurotransmitter release, down regulating hypothalamic-pituitary-adrenal axis, anti-inflammatory, antioxidation, and genetic effects. Increasing evidence shows that oxytocin and its receptor gene may play a potential role in major depressive disorder. Future research should focus on the predictive ability of the oxytocin system as a biomarker, as well as its role in targeted prevention and early intervention of major depressive disorder.

Delivering Clinically on Our Knowledge of Oxytocin and Sensory Stimulation: The Potential of Infant Carrying in Primary Prevention

Oxytocin (OT) is one of the most intensively researched neuropeptides during the three past decades. In benign social contexts, OT exerts a range of desirable socioemotional, stress-reducing, and immunoregulatory effects in mammals and humans and influences mammalian parenting. Consequentially, research in potential pharmacological applications of OT toward human social deficits/disorders and physical illness has increased substantially. Regrettably, the results from the administration of exogenous OT are still relatively inconclusive. Research in rodent maternal developmental programming has demonstrated the susceptibility of offspring endogenous OT systems to maternal somatosensory stimulation, with consequences for behavioral, epigenetic, cognitive, and neurological outcomes. A translation of this animal research into practically feasible human parenting recommendations has yet to happen, despite the significant prevention potential implied by the maternal developmental programming research. Extended physical contact with full-term healthy infants in the months following birth (infant carrying) might constitute the human equivalent of those specific rodent maternal behaviors, found to positively influence emerging OT systems. Findings from both OT and maternal programming research parallel those found for infants exposed to such extended parental physical contact, whether through skin-to-skin contact or infant carrying. Clinical support of parents to engage in extended physical contact represents a feasible intervention to create optimum conditions for the development of infant OT systems, with potential beneficial long-term health effects.

Arginine Vasopressin-Containing Neurons of the Suprachiasmatic Nucleus Project to CSF

While it is well established that there are robust circadian rhythms of arginine vasopressin (AVP) in the cerebrospinal fluid (CSF), the route whereby the peptide reaches the CSF is not clear. A, AVP neurons constitute the largest fraction of the SCN neuronal population. Here, we show that processes of AVP-expressing SCN neurons cross the epithelium of the 3rd ventricular wall to reach the CSF (black arrows). Additionally, we report rostro-caudal differences in AVP neuron size and demonstrate that the localization of cells expressing the clock protein PER2 extend beyond the AVP population, thereby indicating that the size of this nucleus is somewhat larger than previously understood. B, Following lateral ventricle (LV) injection of cholera toxin β subunit (CTβ ; magenta) the retrograde tracer is seen in AVP neurons of the SCN, supporting the anatomical evidence that AVP neuronal processes directly contact the CSF.

Arginine vasopressin (AVP) expressing neurons form the major population in the brain’s circadian clock located in the hypothalamic suprachiasmatic nucleus (SCN). They participate in inter-neuronal coupling and provide an output signal for synchronizing daily rhythms. AVP is present at high concentrations in the cerebrospinal fluid (CSF) and fluctuates on a circadian timescale. While it is assumed that rhythms in CSF AVP are of SCN origin, a route of communication between these compartments has not been delineated. Using immunochemistry (ICC) and cell filling techniques, we determine the morphology and location of AVP neurons in mouse and delineate their axonal and dendritic processes. Cholera toxin β subunit (CTβ) tracer injected into the lateral ventricle tests whether AVP neurons communicate with CSF. Most importantly, the results indicate that AVP neurons lie in close proximity to the third ventricle, and their processes cross the ventricular wall into the CSF. We also report that contrary to widely held assumptions, AVP neurons do not fully delineate the SCN borders as PER2 expression extends beyond the AVP region. Also, AVP neurons form a rostral prong originating in the SCN medial-most and ventral-most aspect. AVP is lacking in the mid-dorsal shell but does occur at the base of the SCN just above the optic tract. Finally, neurons of the rostral SCN are smaller than those lying caudally. These findings extend our understanding of AVP signaling potential, demonstrate the heterogeneity of AVP neurons, and highlight limits in using this peptide to delineate the mouse SCN.

Ventricular volume, white matter alterations and outcome of major depression and their relationship to endocrine parameters - A pilot study

OBJECTIVES

Brain morphology and its relation to endocrine parameters were examined, in order to determine the link of these parameters to treatment outcome to psychopharmacological treatment in depressed patients.

METHODS

We examined the potentially predictive value of Magnetic Resonance Imaging (MRI) parameters related to mineralocorticoid receptor (MR) function on the treatment outcome of depression. 16 inpatients with a major depressive episode (MDE) were studied at baseline and 14 of them approximately six weeks later. Physiological biomarkers and 3-T-structural MRI based volume measures, using FreeSurfer 6.0 software, were determined.

RESULTS

Non-responders (<50% reduction of HAMD-21; n = 6) had a significantly smaller volume of the right anterior cingulate cortex, a significantly larger ventricle to brain ratio (VBR) and third ventricle volume, and smaller volumes of the central and central-anterior corpus callosum (CC) in comparison to responders (n = 7; all p ≤ 0.05). Correlational analysis (Spearman) demonstrated that larger ventricle volume was correlated to a worse treatment outcome, higher body mass index (BMI) and smaller CC segment volume, whereas the total CC volume was negatively correlated to the saliva aldosterone/cortisol concentration ratio (AC-ratio).

CONCLUSION

Large ventricular volume may be a predictive marker for worse treatment response to standard antidepressant treatment, potentially via compression of white matter structures. A mediating role of the previously identified markers BMI and the AC-ratio, is suggested.

Is Oxytocin "Nature's Medicine"?

Oxytocin is a pleiotropic, peptide hormone with broad implications for general health, adaptation, development, reproduction, and social behavior. Endogenous oxytocin and stimulation of the oxytocin receptor support patterns of growth, resilience, and healing. Oxytocin can function as a stress-coping molecule, an anti-inflammatory, and an antioxidant, with protective effects especially in the face of adversity or trauma. Oxytocin influences the autonomic nervous system and the immune system. These properties of oxytocin may help explain the benefits of positive social experiences and have drawn attention to this molecule as a possible therapeutic in a host of disorders. However, as detailed here, the unique chemical properties of oxytocin, including active disulfide bonds, and its capacity to shift chemical forms and bind to other molecules make this molecule difficult to work with and to measure. The effects of oxytocin also are context-dependent, sexually dimorphic, and altered by experience. In part, this is because many of the actions of oxytocin rely on its capacity to interact with the more ancient peptide molecule, vasopressin, and the vasopressin receptors. In addition, oxytocin receptor(s) are epigenetically tuned by experience, especially in early life. Stimulation of G-protein–coupled receptors triggers subcellular cascades allowing these neuropeptides to have multiple functions. The adaptive properties of oxytocin make this ancient molecule of special importance to human evolution as well as modern medicine and health; these same characteristics also present challenges to the use of oxytocin-like molecules as drugs that are only now being recognized.

Oxytocin modulates local topography of human functional connectome in healthy men at rest

Oxytocin has recently received remarkable attention for its role as a modulator of human behaviour. Here, we aimed to expand our knowledge of the neural circuits engaged by oxytocin by investigating the effects of intranasal and intravenous oxytocin on the functional connectome at rest in 16 healthy men. Oxytocin modulates the functional connectome within discrete neural systems, but does not affect the global capacity for information transfer. These local effects encompass key hubs of the oxytocin system (e.g. amygdala) but also regions overlooked in previous hypothesis-driven research (i.e. the visual circuits, temporal lobe and cerebellum). Increases in levels of oxytocin in systemic circulation induce broad effects on the functional connectome, yet we provide indirect evidence supporting the involvement of nose-to-brain pathways in at least some of the observed changes after intranasal oxytocin. Together, our results suggest that oxytocin effects on human behaviour entail modulation of multiple levels of brain processing distributed across different systems.

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.

Vasopressin and oxytocin beyond the pituitary in the human brain

Vasopressin and oxytocin are primarily synthesized in the magnocellular supraoptic and paraventricular nuclei of the hypothalamus and transported to the posterior pituitary. In the human, an extensive accessory magnocellular neuroendocrine system is present with contact to the posterior pituitary and blood vessels in the hypothalamus itself. Vasopressin and oxytocin are involved in social and behavioral functions. However, only few neocortical areas are targeted by vasopressinergic and oxytocinergic nerve fibers, which mostly project to limbic areas in the forebrain, where also their receptors are located. Vasopressinergic/oxytocinergic perikarya in the forebrain project to the brain stem and spinal cord targeting nuclei and areas involved in autonomic functions. Parvocellular neurons containing vasopressin are located in the suprachiasmatic nucleus and synchronize the activity of the pacemaker in this nucleus. From the suprachiasmatic nucleus fibers project to the parvocellular part of the paraventricular nucleus, where preautonomic neurons project to the intermediolateral nucleus in the thoracic spinal cord, from where the superior cervical ganglion is reached whose noradrenergic fibers terminate in the pineal gland to stimulate melatonin secretion at night. The pineal gland is also innervated by vasopressin- and oxytocin-containing fibers reaching the gland via the "central innervation" in the pineal stalk, which might be involve in an annual regulation of melatonin secretion.

Oxytocin, eating behavior, and metabolism in humans

The hypothalamic peptide oxytocin has been increasingly recognized as a hormone and neurotransmitter with important effects on energy intake, metabolism, and body weight and is under investigation as a potential novel therapeutic agent for obesity. The main neurons producing oxytocin and expressing the oxytocin receptor are strategically located in brain areas known to be critically involved in homeostatic energy balance as well as hedonic and motivational aspects of eating behavior. In this chapter, we will review the central and peripheral physiology of oxytocin and the interaction of oxytocin with key hormones and neural circuitries that affect food intake and metabolism. Next, we will synthesize the available data on endogenous oxytocin levels related to caloric intake, body weight, and metabolic status. We will then review the effects of exogenous oxytocin administration on eating behavior, body weight, and metabolism in humans, including in healthy individuals as well as specific populations with suspected perturbations involving oxytocin pathways. Finally, we will address the promise and fundamental challenges of translating this line of research to clinical care.

Effect of reduction and alkylation treatment in three different assays used for the measurement of oxytocin in saliva of pigs

Oxytocin is a hormone that is increasingly being used for welfare evaluation in animals. Although several types of samples have been used for oxytocin measurement, saliva can be a suitable option for pigs producing less stress than blood sampling. In this study, 3 different methods for oxytocin measurements, 2 based on alphaLISA technology (one with a monoclonal and other with a polyclonal antibody) and one commercially available kit, were compared in saliva of pigs. These methods were used in saliva samples obtained from female pigs at 3 different days during gestation and lactation, with and without a reduction/alkylation (R/A), which is a procedure for breaking the links between oxytocin and proteins of the sample. The assays showed a different behavior after the R/A procedure, with no significant changes in the oxytocin results in case of the alphaLISA monoclonal method, a significant decrease with the alphaLISA polyclonal method, and a significant increase with the commercial kit. Although all assays showed a similar tendency in detecting the changes in oxytocin during gestation and lactation, they showed changes of different magnitude and statistical signification. This report indicates that different assays can measure different forms of oxytocin present in saliva and can have a different behavior after R/A of the sample and when are used to measure oxytocin in gestation and lactation.

Advances in the field of intranasal oxytocin research: lessons learned and future directions for clinical research

Reports on the modulatory role of the neuropeptide oxytocin on social cognition and behavior have steadily increased over the last two decades, stimulating considerable interest in its psychiatric application. Basic and clinical research in humans primarily employs intranasal application protocols. This approach assumes that intranasal administration increases oxytocin levels in the central nervous system via a direct nose-to-brain route, which in turn acts upon centrally-located oxytocin receptors to exert its behavioral effects. However, debates have emerged on whether intranasally administered oxytocin enters the brain via the nose-to-brain route and whether this route leads to functionally relevant increases in central oxytocin levels. In this review we outline recent advances from human and animal research that provide converging evidence for functionally relevant effects of the intranasal oxytocin administration route, suggesting that direct nose-to-brain delivery underlies the behavioral effects of oxytocin on social cognition and behavior. Moreover, advances in previously debated methodological issues, such as pre-registration, reproducibility, statistical power, interpretation of non-significant results, dosage, and sex differences are discussed and integrated with suggestions for the next steps in translating intranasal oxytocin into psychiatric applications.

Salivary and plasmatic oxytocin are not reliable trait markers of the physiology of the oxytocin system in humans

Single measurements of salivary and plasmatic oxytocin are used as indicators of the physiology of the oxytocin system. However, questions remain about whether they are sufficiently stable to provide valid trait markers of the physiology of the oxytocin system, and whether salivary oxytocin can accurately index its plasmatic concentrations. Using radioimmunoassay, we measured baseline plasmatic and/or salivary oxytocin from two independent datasets. We also administered exogenous oxytocin intravenously and intranasally in a triple dummy, within-subject, placebo-controlled design and compared baseline levels and the effects of routes of administration. Our findings question the use of single measurements of baseline oxytocin concentrations in saliva and plasma as valid trait markers of the physiology of the oxytocin system in humans. Salivary oxytocin is a weak surrogate for plasmatic oxytocin. The increases in salivary oxytocin observed after intranasal oxytocin most likely reflect unabsorbed peptide and should not be used to predict treatment effects.

Decreased oxytocin plasma levels and oxytocin receptor expression in borderline personality disorder

INTRODUCTION

Borderline personality disorder (BPD) is characterized by intense affective reactions with underlying social and interpersonal cognitive deficits. Oxytocin has largely been associated with both stress regulation and social cognition in psychiatric patients and in non-clinical populations in previous studies. Finally, abnormal oxytocin levels have been preliminary reported in BPD patients.

METHODS

53 patients with moderate-severe BPD and 31 healthy control subjects were investigated for plasma levels of oxytocin and protein expression of oxytocin receptor in blood mononuclear cells. Clinical assessments were made for severity, functionality, and comorbidity with axis I and II conditions.

RESULTS

Oxytocin plasma levels were significantly lower in BPD patients compared with controls. In addition, protein expression of oxytocin receptor was significantly reduced in the BPD group. A positive correlation was found between plasma oxytocin levels and the activity index score of the Zuckerman-Kuhlman Personality Questionnaire (ZKPQ). Oxytocin receptor protein expression, on the contrary, had a negative correlation with the ZKPQ sociability index score.

CONCLUSIONS

Results support the evidence of a dysfunction of the oxytocin system in borderline personality disorder, which could be involved in emotional dysregulation and interpersonal disturbances in these patients.

How Can Intranasal Oxytocin Research Be Trusted? A Systematic Review of the Interactive Effects of Intranasal Oxytocin on Psychosocial Outcomes

Over the past two decades, research about the role of oxytocin (OT) in human behavior has grown exponentially. However, a unified theory of OT effects has yet to be developed. Relatedly, growing concerns about the robustness of conclusions drawn in the field have been raised. The current article contributes to this debate by reporting on and discussing key conclusions from a systematic review of published studies addressing the interactive effects of intranasal OT (IN-OT) administration on psychosocial outcomes in a healthy population. The review indicates that (a) tested interactive IN-OT effects were highly heterogeneous; (b) for most published interactions, no replication was attempted; (c) when attempted, replications were largely unsuccessful; (d) significance was unrelated to sample size; (e) statistical power was critically low and unrelated to the rate of significant results; and (f) research practices were characteristic of an exploratory approach. This concerning state of affairs makes it virtually impossible to tease apart true from false interactive IN-OT effects. We provide constructive directions on the basis of this observation and positive predictive value simulations for future research that should help extract true effects from noise and move the IN-OT field forward.

Tri-Phasic Model ofOxytocin (TRIO): A systematic conceptual review of oxytocin-related ERP research

BACKGROUND

The neuropeptide oxytocin (OT) has been shown to play a role in variety of cognitive and social processes and different hypotheses have been put forth to explain OT's effects on brain and behavior in humans. However, these previous explanatory accounts do not provide information about OT-related temporal modulation in the brain.

OBJECTIVES

This paper systematically reviewed intranasal OT administration studies employing event-related potentials (ERPs) and synthesized the existing evidence into a novel conceptual framework.

METHODS

Empirical studies, published until February 2020 and cited in major databases (EBSCOhost, PubMed, and Web of Science), were examined in accordance with PRISMA guidelines. To be included, studies had to: (i) employ intranasal administration of OT, as the chemical modulator; (ii) measure ERPs; (iii) be peer-reviewed journal articles; (iv) be written in English; and (v) examine human participants.

RESULTS

The search criteria yielded 17 empirical studies. The systematic review resulted in conceptualization of the Tri-Phasic Model ofOxytocin (TRIO), which builds on three processing stages: (i) perception, (ii) selection, and (iii) evaluation. While OT increases attention irrespective of stimuli characteristics in the perception stage, in the selection and evaluation stages, OT acts as a filter to guide attention selectively towards social over non-social stimuli and modulates prosociality/approach motivation associated with social stimuli.

CONCLUSIONS

TRIO offers an empirically-derived conceptual framework that can guide the study of OT-related modulation on attentional processes, starting very early in the processing stream. This novel account furthers theoretical understanding and informs empirical investigation into OT modulation on the brain.

Wireless Optogenetic Stimulation of Oxytocin Neurons in a Semi-natural Setup Dynamically Elevates Both Pro-social and Agonistic Behaviors

Complex behavioral phenotyping techniques are becoming more prevalent in the field of behavioral neuroscience, and thus methods for manipulating neuronal activity must be adapted to fit into such paradigms. Here, we present a head-mounted, magnetically activated device for wireless optogenetic manipulation that is compact, simple to construct, and suitable for use in group-living mice in an enriched semi-natural arena over several days. Using this device, we demonstrate that repeated activation of oxytocin neurons in male mice can have different effects on pro-social and agonistic behaviors, depending on the social context. Our findings support the social salience hypothesis of oxytocin and emphasize the importance of the environment in the study of social neuromodulators. Our wireless optogenetic device can be easily adapted for use in a variety of behavioral paradigms, which are normally hindered by tethered light delivery or a limited environment.

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A small, wireless device is used for optogenetic activation in a complex environment

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PVN oxytocin neurons were activated repeatedly over 2 days in a group setting

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Repeated activation in a group setting elicited both pro-social and agonistic behavior

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Findings support the social salience hypothesis of oxytocin neuro-modulation

Oxytocin and elderly MRI-based hippocampus and amygdala volume: a 7-year follow-up study

Oxytocin is deeply involved in human relations. In recent years, it is becoming clear that oxytocin is also involved in social cognition and social behaviour. Oxytocin receptors are also thought to be present in the hippocampus and amygdala, and the relationship between oxytocin and the structure and function of the hippocampus and amygdala has been reported. However, a few studies have investigated oxytocin and its relationship to hippocampus and amygdala volume in elderly people. The aim of this study is to investigate the association between serum oxytocin levels and hippocampus and amygdala volume in elderly people. The survey was conducted twice in Kurokawa-cho, Imari, Saga Prefecture, Japan, among people aged 65 years and older. We collected data from 596 residents. Serum oxytocin level measurements, brain MRI, Mini–Mental State Examination and Clinical Dementia Rating were performed in Time 1 (2009–11). Follow-up brain MRI, Mini–Mental State Examination and Clinical Dementia Rating were performed in Time 2 (2016–17). The interval between Time 1 and Time 2 was about 7 years. Fifty-eight participants (14 men, mean age 72.36 ± 3.41 years, oxytocin 0.042 ± 0.052 ng/ml; 44 women, mean age 73.07 ± 4.38 years, oxytocin 0.123 ± 0.130 ng/ml) completed this study. We analysed the correlation between serum oxytocin levels (Time 1) and brain volume (Time 1, Time 2 and Times 1–2 difference) using voxel-based morphometry implemented with Statistical Parametric Mapping. Analysis at the cluster level (family-wise error; P < 0.05) showed a positive correlation between serum oxytocin levels (Time 1) and brain volume of the region containing the left hippocampus and amygdala (Time 2). This result suggests that oxytocin in people aged 65 years and older may be associated with aging-related changes in hippocampus and amygdala volume.

Early posttraumatic autonomic and endocrine markers to predict posttraumatic stress symptoms after a preventive intervention with oxytocin

BACKGROUND

Efficient prevention of posttraumatic stress disorder (PTSD) needs to target individuals with an increased risk for adverse outcome after trauma. Prognostic or prescriptive biological markers assessed early posttrauma may inform personalized treatment recommendations.

OBJECTIVE

To test prognostic and prescriptive effects of early (posttraumatic) autonomic and endocrine markers on PTSD symptom development.

METHOD

Autonomic and endocrine markers were assessed within 12 days posttrauma and before treatment initiation within a randomized placebo-controlled trial investigating repeated oxytocin administration as preventive intervention for PTSD. Linear mixed effects models were used to test the effects of heart rate (variability), resting cortisol, morning cortisol and cortisol awakening response (CAR), cortisol suppression by dexamethasone and resting oxytocin on PTSD symptoms 1.5, 3 and 6 months posttrauma in men (n = 54), women using hormonal contraception (n = 27) and cycling women (n = 19).

RESULTS

We found significant prognostic effects of resting oxytocin and cortisol suppression. In women using hormonal contraception, higher oxytocin was associated with higher PTSD symptoms across follow-up. Stronger cortisol suppression by dexamethasone, reflecting increased glucocorticoid receptor feedback sensitivity, was associated with lower PTSD symptoms across follow-up in men, but with higher symptoms at 1.5 months in women using hormonal contraception. These effects were independent of treatment condition. No further significant prognostic or prescriptive effects were detected.

CONCLUSION

Our exploratory study indicates that resting oxytocin and glucocorticoid receptor feedback sensitivity early posttrauma are associated with subsequent PTSD symptom severity. Notably, prognostic effects depended on sex and hormonal contraception use, emphasizing the necessity to consider these factors in biomedical PTSD research.

Effects of route of administration on oxytocin-induced changes in regional cerebral blood flow in humans

Could nose-to-brain pathways mediate the effects of peptides such as oxytocin (OT) on brain physiology when delivered intranasally? We address this question by contrasting two methods of intranasal administration (a standard nasal spray, and a nebulizer expected to improve OT deposition in nasal areas putatively involved in direct nose-to-brain transport) to intravenous administration in terms of effects on regional cerebral blood flow during two hours post-dosing. We demonstrate that OT-induced decreases in amygdala perfusion, a key hub of the OT central circuitry, are explained entirely by OT increases in systemic circulation following both intranasal and intravenous OT administration. Yet we also provide robust evidence confirming the validity of the intranasal route to target specific brain regions. Our work has important translational implications and demonstrates the need to carefully consider the method of administration in our efforts to engage specific central oxytocinergic targets for the treatment of neuropsychiatric disorders.

Unextracted plasma oxytocin levels decrease following in-laboratory social exclusion in young adults with a suicide attempt history

Social exclusion is associated with greater suicide risk and more needs to be known about the biological processes contributing to this association. Oxytocin, a neuropeptide that regulates social interactions, may protect against the negative effects of exclusion by motivating social engagement. Oxytocin levels and desire for social engagement increase when non-psychiatric controls experience acute social exclusion. However, among individuals with borderline personality disorder and chronic depression, oxytocin levels decrease following exclusion. Both of these psychiatric illnesses are associated with high rates of suicidal behavior. No research has examined changes in oxytocin following social exclusion among individuals at risk for suicide. This quasi-experimental study examined differences in oxytocin levels and perceptions of social connectedness following an in-laboratory, acute social exclusion task among (a) individuals with no depression or suicide attempt histories, (b) individuals with current depression symptoms, and (c) individuals with current depression symptoms and suicide attempt histories. Young adults (N = 100) completed self-report measures and provided blood samples before and after an acute social exclusion task (Cyberball). Oxytocin was quantified via enzyme-linked immunosorbent assay. Mixed-design ANCOVAs were used to evaluate changes in unextracted and extracted oxytocin levels, desire for emotional support, thwarted belongingness, and perceived burdensomeness. Among suicide attempters, unextracted oxytocin levels decreased and desire for emotional support did not significantly change following exclusion. Among depressed and healthy controls, desire for emotional support increased and unextracted oxytocin levels did not significantly change. No significant changes in extracted oxytocin levels, thwarted belongingness and perceived burdensomeness emerged. Further research is needed to determine if dysregulated oxytocin-related processes biologically predispose individuals with suicide attempt histories to greater social disconnection and suicide risk.