Oxytocin—a social peptide? Deconstructing the evidence

The interplay of oxytocin and sex hormones

The neuropeptide oxytocin has historically been associated with reproduction and maternal behavior. However, more recent research has uncovered that oxytocin has a much wider range of roles in physiology and behavior. Despite the excitement surrounding potential therapeutical applications of intranasally administered oxytocin, the results of these intervention studies have been inconsistent. Various reasons for these mixed results have been proposed, which tend to focus on methodological issues, such as study design. While methodological issues are certainly important, emerging evidence suggests that the interaction between oxytocin and sex hormones may also account for these varied findings. To better understand the purpose and function of the interaction of oxytocin with sex hormones, with a focus on estrogens, progesterone, and testosterone, we conducted a comprehensive thematic review via four perspectives: evolutionary, developmental, mechanistic, and survival. Altogether, this synergistic approach highlights the critical function of sex hormone activity for accomplishing the diverse roles of oxytocin via the modulation of oxytocin release and oxytocin receptor activity, which is also likely to contribute to the heterogeneity of outcomes after oxytocin administration.

A career in numbers: A citation network analysis of the work of RP Millar and his contribution to GnRH research

Here, we reflect on the long career in neuroendocrinology of a single, highly productive scientist ('Bob' Millar), by analysing his oeuvre of published papers through the lens of citation metrics. We use citation network analysis in a novel manner to identify the specific topics to which his papers have made a particular contribution, allowing us to compare the citations of his papers with those of contemporary papers on the same topic, rather than on the same broad field as generally used to normalise citations. It appears that citation rates are highest for topics on which Bob has published a relatively large number of papers that have become core to a tightly-knit community of authors that cite each other. This analysis shows that an author's impact depends on the existence of a receptive community that is alert to the potential utility of papers from that author, and which uses, amplifies, extends and qualifies the contents of their papers-activities that entail reciprocal citation between authors. The obvious conclusion is that a scientist's impact depends on the use that his or her contemporaries make of his or her contributions, rather than on the contributions in themselves.

Neuropeptides affecting social behavior in mammals: Oxytocin

Oxytocin (OXT), a neuropeptide consisting of only nine amino acids, is synthesized in the paraventricular and supraoptic nuclei of the hypothalamus. Although OXT is best known for its role in lactation and parturition, recent research has shown that it also has a significant impact on social behaviors in mammals. However, a comprehensive review of this topic is still lacking. In this paper, we systematically reviewed the effects of OXT on social behavior in mammals. These effects of OXT from the perspective of five key behavioral dimensions were summarized: parental behavior, anxiety, aggression, attachment, and empathy. To date, researchers have agreed that OXT plays a positive regulatory role in a wide range of social behaviors, but there have been controversially reported results. In this review, we have provided a detailed panorama of the role of OXT in social behavior and, for the first time, delved into the underlying regulatory mechanisms, which may help better understand the multifaceted role of OXT. Levels of OXT in previous human studies were also summarized to provide insights for diagnosis of mental disorders.

Long-range projections of oxytocin neurons in the marmoset brain

The neurohormone oxytocin (OT) has become a major target for the development of novel therapeutic strategies to treat psychiatric disorders such as autism spectrum disorder because of its integral role in governing many facets of mammalian social behavior. Whereas extensive work in rodents has produced much of our knowledge of OT, we lack basic information about its neurobiology in primates making it difficult to interpret the limited effects that OT manipulations have had in human patients. In fact, previous studies have revealed only limited OT fibers in primate brains. Here, we investigated the OT connectome in marmoset using immunohistochemistry, and mapped OT fibers throughout the brains of adult male and female marmoset monkeys. We found extensive OT projections reaching limbic and cortical areas that are involved in the regulation of social behaviors, such as the amygdala, the medial prefrontal cortex, and the basal ganglia. The pattern of OT fibers observed in marmosets is notably similar to the OT connectomes described in rodents. Our findings here contrast with previous results by demonstrating a broad distribution of OT throughout the marmoset brain. Given the prevalence of this neurohormone in the primate brain, methods developed in rodents to manipulate endogenous OT are likely to be applicable in marmosets.

Oxygen is an essential gasotransmitter directly sensed via protein gasoreceptors

The current restrictive criteria for gasotransmitters exclude oxygen (O2) as a gasotransmitter in vertebrates. In this manuscript, I propose a revision of gasotransmitter criteria to include O2 per se as a signaling molecule and 'essential gasotransmitter' for vertebrates. This revision would enable us to search for protein-based O2-binding sensors (gasoreceptors) in all cells in the brain or other tissues rather than specialized tissues such as the carotid body or gills. If microorganisms have protein-based O2-binding sensors or gasoreceptors such as DosP or FixL or FNR with diverse signaling domains, then eukaryotic cells must also have O2-binding sensors or gasoreceptors. Just as there are protein-based receptor(s) for nitric oxide (GUCY1A, GUCY1B, CLOCK, NR1D2) in cells of diverse tissues, it is reasonable to consider that there are protein-based receptors for O2 in cells of diverse tissues as well. In mammals, O2 must be acting as a gasotransmitter or gaseous signaling molecule via protein-based gasoreceptors such as androglobin that very likely mediate acute sensing of O2. Accepting O2 as an essential gasotransmitter will enable us to search for gasoreceptors not only for O2 but also for other nonessential gasotransmitters such as hydrogen sulfide, ammonia, methane, and ethylene. It will also allow us to investigate the role of environment-derived metal ions in acute gas (or solute) sensing within and between organisms. Finally, accepting O2 per se as a signaling molecule acting via gasoreceptors will open up the field of gasocrinology.

Long range projections of oxytocin neurons in the marmoset brain

The neurohormone oxytocin (OT) has become a major target for the development of novel therapeutic strategies to treat psychiatric disorders such as autism spectrum disorder because of its integral role in governing many facets of mammalian social behavior. Whereas extensive work in rodents has produced much of our knowledge of OT, we lack basic information about its neurobiology in primates making it difficult to interpret the limited effects that OT manipulations have had in human patients. In fact, previous studies have revealed only limited OT fibers in primate brains. Here, we investigated the OT connectome in marmoset using immunohistochemistry, and mapped OT fibers throughout the brains of adult male and female marmoset monkeys. We found extensive OT projections reaching limbic and cortical areas that are involved in the regulation of social behaviors, such as the amygdala, the medial prefrontal cortex and the basal ganglia. The pattern of OT fibers observed in marmosets is notably similar to the OT connectomes described in rodents. Our findings here contrast with previous results by demonstrating a broad distribution of OT throughout the marmoset brain. Given the prevalence of this neurohormone in the primate brain, methods developed in rodents to manipulate endogenous OT are likely to be applicable in marmosets.

Selective oxytocin receptor activation prevents prefrontal circuit dysfunction and social behavioral alterations in response to chronic prefrontal cortex activation in male rats

Introduction

Social behavioral changes are a hallmark of several neurodevelopmental and neuropsychiatric conditions, nevertheless the underlying neural substrates of such dysfunction remain poorly understood. Building evidence points to the prefrontal cortex (PFC) as one of the key brain regions that orchestrates social behavior. We used this concept with the aim to develop a translational rat model of social-circuit dysfunction, the chronic PFC activation model (CPA).

Methods

Chemogenetic designer receptor hM3Dq was used to induce chronic activation of the PFC over 10 days, and the behavioral and electrophysiological signatures of prolonged PFC hyperactivity were evaluated. To test the sensitivity of this model to pharmacological interventions on longer timescales, and validate its translational potential, the rats were treated with our novel highly selective oxytocin receptor (OXTR) agonist RO6958375, which is not activating the related vasopressin V1a receptor.

Results

CPA rats showed reduced sociability in the three-chamber sociability test, and a concomitant decrease in neuronal excitability and synaptic transmission within the PFC as measured by electrophysiological recordings in acute slice preparation. Sub-chronic treatment with a low dose of the novel OXTR agonist following CPA interferes with the emergence of PFC circuit dysfunction, abnormal social behavior and specific transcriptomic changes.

Discussion

These results demonstrate that sustained PFC hyperactivity modifies circuit characteristics and social behaviors in ways that can be modulated by selective OXTR activation and that this model may be used to understand the circuit recruitment of prosocial therapies in drug discovery.

Spatial transcriptomics reveal basal sex differences in supraoptic nucleus gene expression of adult rats related to cell signaling and ribosomal pathways

BACKGROUND

The supraoptic nucleus (SON) of the hypothalamus contains magnocellular neurosecretory cells that secrete the hormones vasopressin and oxytocin. Sex differences in SON gene expression have been relatively unexplored. Our study used spatially resolved transcriptomics to visualize gene expression profiles in the SON of adult male (n = 4) and female (n = 4) Sprague-Dawley rats using Visium Spatial Gene Expression (10x Genomics).

METHODS

Briefly, 10-μm coronal sections (~ 4 × 4 mm) containing the SON were collected from each rat and processed using Visium slides and recommended protocols. Data were analyzed using 10x Genomics' Space Ranger and Loupe Browser applications and other bioinformatic tools. Two unique differential expression (DE) analysis methods, Loupe Browser and DESeq2, were used.

RESULTS

Loupe Browser DE analysis of the SON identified 116 significant differentially expressed genes (DEGs) common to both sexes (e.g., Avp and Oxt), 31 significant DEGs unique to the males, and 73 significant DEGs unique to the females. DESeq2 analysis revealed 183 significant DEGs between the two groups. Gene Ontology (GO) enrichment and pathway analyses using significant genes identified via Loupe Browser revealed GO terms and pathways related to (1) neurohypophyseal hormone activity, regulation of peptide hormone secretion, and regulation of ion transport for the significant genes common to both males and females, (2) Gi signaling/G-protein mediated events for the significant genes unique to males, and (3) potassium ion transport/voltage-gated potassium channels for the significant genes unique to females, as some examples. GO/pathway analyses using significant genes identified via DESeq2 comparing female vs. male groups revealed GO terms/pathways related to ribosomal structure/function. Ingenuity Pathway Analysis (IPA) identified additional sex differences in canonical pathways (e.g., 'Mitochondrial Dysfunction', 'Oxidative Phosphorylation') and upstream regulators (e.g., CSF3, NFKB complex, TNF, GRIN3A).

CONCLUSION

There was little overlap in the IPA results for the two different DE methods. These results suggest sex differences in SON gene expression that are associated with cell signaling and ribosomal pathways.

Oxytocin levels and self-reported anxiety during interactions between humans and cows

Introduction

Positive social interactions with farm animals may have therapeutic benefits on humans by increasing brain oxytocin secretion, as inferred from circulating oxytocin levels. The aim of this observational study was to investigate acute changes in human plasma oxytocin levels and state anxiety associated with interactions with dairy cows.

Methods

Data were collected from 18 healthy female nursing students who performed stroking and brushing of an unfamiliar cow for 15 min. Blood samples were drawn before entering the cowshed (T1, baseline), and after 5 (T2) and 15 (T3) min of interaction with a cow. At T1 and T3, the students filled out the Norwegian version of the Spielberger State-Trait Anxiety Inventory-State Subscale (STAI-SS).

Results

Across participants, no significant changes in average plasma oxytocin concentration were detected between time points (p>0.05). There was, however, a modest decline in the STAI-SS scores between T1 and T3 (p=0.015) and a positive correlation between the change in individual level of state anxiety between T1 and T3 and the change in OT concentration of the same individual between T2 and T3 (p = 0.045).

Discussion

The results suggest that friendly social interactions with cows are beneficial in lowering state anxiety, but any relationship with release of OT into the circulation was complex and variable across individuals. The acute reduction in state anxiety lends support to the value of interacting with farm animals in the context of Green Care for people with mental health challenges.

Neuroimaging of social motivation during winning and losing: Associations with social anhedonia across the psychosis spectrum

BACKGROUND

Individuals with psychosis spectrum disorders (PSD) have difficulty developing social relationships. This difficulty may reflect reduced response to social feedback involving functional alterations in brain regions that support the social motivation system: ventral striatum, orbital frontal cortex, insula, dorsal anterior cingulate cortex, and amygdala. Whether these alterations span PSD is unknown.

METHODS

71 individuals with PSD, 27 unaffected siblings, and 37 control participants completed a team-based fMRI task. After each trial, participants received performance feedback paired with the expressive face of a teammate or opponent. A 2 × 2 (win versus loss outcome x teammate versus opponent) repeated measures ANOVA by group was performed on activation in the five key regions of interest during receipt of feedback.

RESULTS

Across groups, three social motivation regions, ventral striatum, orbital frontal cortex, and amygdala, showed sensitivity to feedback (significant main effect of outcome), with greater activation during win versus loss trials, regardless of whether the feedback was from a teammate or opponent. In PSD, ventral striatum and orbital frontal cortex activation to win feedback was negatively correlated with social anhedonia scores.

CONCLUSIONS

Patterns of neural activation during social feedback were similar in PSD, their unaffected siblings, and healthy controls. Across the psychosis spectrum, activity in key social motivation regions during social feedback was associated with individual differences in social anhedonia.

The evolution of social timing

Sociality and timing are tightly interrelated in human interaction as seen in turn-taking or synchronised dance movements. Sociality and timing also show in communicative acts of other species that might be pleasurable, but also necessary for survival. Sociality and timing often co-occur, but their shared phylogenetic trajectory is unknown: How, when, and why did they become so tightly linked? Answering these questions is complicated by several constraints; these include the use of divergent operational definitions across fields and species, the focus on diverse mechanistic explanations (e.g., physiological, neural, or cognitive), and the frequent adoption of anthropocentric theories and methodologies in comparative research. These limitations hinder the development of an integrative framework on the evolutionary trajectory of social timing and make comparative studies not as fruitful as they could be. Here, we outline a theoretical and empirical framework to test contrasting hypotheses on the evolution of social timing with species-appropriate paradigms and consistent definitions. To facilitate future research, we introduce an initial set of representative species and empirical hypotheses. The proposed framework aims at building and contrasting evolutionary trees of social timing toward and beyond the crucial branch represented by our own lineage. Given the integration of cross-species and quantitative approaches, this research line might lead to an integrated empirical-theoretical paradigm and, as a long-term goal, explain why humans are such socially coordinated animals.

A ligand-receptor interactome atlas of the zebrafish

Studies in zebrafish can unravel the functions of cellular communication and thus identify novel bench-to-bedside drugs targeting cellular communication signaling molecules. Due to the incomplete annotation of zebrafish proteome, the knowledge of zebrafish receptors, ligands, and tools to explore their interactome is limited. To address this gap, we de novo predicted the cellular localization of zebrafish reference proteome using deep learning algorithm. We combined the predicted and existing annotations on cellular localization of zebrafish proteins and created repositories of zebrafish ligands, membrane receptome, and interactome as well as associated diseases and targeting drugs. Unlike other tools, our interactome atlas is based on both the physical interaction data of zebrafish proteome and existing human ligand-receptor pair databases. The resources are available as R and Python scripts. DanioTalk provides a novel resource for researchers interested in targeting cellular communication in zebrafish, as we demonstrate in applications studying synapse and axo-glial interactome. DanioTalk methodology can be applied to build and explore the ligand-receptor atlas of other non-mammalian model organisms.

Mentalization, Oxytocin, and Cortisol in the General Population

Although evidence suggests the role of oxytocin and cortisol in social cognition and emotion regulation, it is less known how their peripheral levels are related to social perception (biological motion detection) and mentalization (self-reflection, emotional awareness, and affect regulation) in the general population. We assessed 150 healthy individuals from the general community on a mentalization questionnaire, a scale measuring the intensity of positive and negative emotions, and measured oxytocin and cortisol levels in the saliva. Oxytocin but not cortisol level and biological motion detection predicted mentalization abilities. There was a positive correlation between mentalization and positive emotions and between mentalization and biological motion detection. These results suggest that oxytocin, but not cortisol, plays a role in low-level perceptual and self-reflective aspects of social cognition.

Oxytocin and eating disorders: Knowledge gaps and future directions

Eating disorders continue to be a major public health issue and important cause of morbidity and premature mortality, particularly for young people. Yet in a concerning dialectic, this occurs in the context of an epidemic of obesity which, with its medical complications, constitutes another vexing public health challenge. While it is not an eating disorder per se obesity is often comorbid with eating disorders. Effective treatment for both eating disorders and obesity has proven to be elusive and in the search for novel therapeutic interventions, the prosocial, anxiolytic, brain plasticity and metabolic effects of oxytocin (OT) have been examined from this perspective. The availability of intranasal oxytocin (IN-OT) has led to a number of interventional treatment studies in anorexia nervosa (AN), bulimia nervosa (BN), binge eating disorder (BED), their atypical and subclinical forms and in medical and psychiatric conditions co-occurring or comorbid with these, obesity with BED would be included here. The aim of this mini review is to collate recent findings on OT as a novel therapeutic intervention in eating disorders and obesity and to identify and address some of the knowledge gaps in the use of IN-OT. The wider clinical perspective utilised here might better address some of the gaps and identify future directions of research. Clearly much remains to be done for OT to fulfil its therapeutic promise in eating disorders. OT might yet be of therapeutic promise and will be appreciated where treatment advances have been hard to come by and prevention challenging for these disorders.

Paraventricular Nucleus of the Hypothalamus Oxytocin and Incubation of Heroin Seeking

INTRODUCTION

There are numerous pharmacologic treatments for opioid use disorder (OUD), but none that directly target the underlying addictive effects of opioids. Oxytocin, a peptide hormone produced in the paraventricular nucleus (PVN) of the hypothalamus, has been investigated as a potential therapeutic for OUD. Promising preclinical and clinical results have been reported, but the brain region(s) and mechanism(s) by which oxytocin impacts reward processes remain undetermined.

METHODS

Here, we assess peripherally administered oxytocin's impacts on cued reinstatement of heroin seeking following forced abstinence and its effects on neuronal activation in the PVN and key projection regions. We also examine how designer receptors exclusively activated by designer drug (DREADD)-mediated activation or inhibition of oxytocinergic PVN neurons alters cued heroin seeking and social interaction.

RESULTS

As predicted, peripheral oxytocin administration successfully decreased cued heroin seeking on days 1 and 30 of abstinence. Oxytocin administration also led to increased neuronal activity within the PVN and the central amygdala (CeA). Activation of oxytocinergic PVN neurons with an excitatory (Gq) DREADD did not impact cued reinstatement or social interaction. In contrast, suppression with an inhibitory (Gi) DREADD reduced heroin seeking on abstinence day 30 and decreased time spent interacting with a novel conspecific.

DISCUSSION

These findings reinforce oxytocin's therapeutic potential for OUD, the basis for which may be driven in part by increased PVN-CeA circuit activity. Our results also suggest that oxytocin has distinct signaling and/or other mechanisms of action to produce these effects, as inhibition, but not activation, of oxytocinergic PVN neurons did not recapitulate the suppression in heroin seeking.

A Call for Drug Therapies for the Treatment of Social Behavior Disorders in Dementia: Systematic Review of Evidence and State of the Art

Growing evidence supports the presence of social cognition deficits and social behavior alterations in major and minor neurocognitive disorders (NCDs). Even though the ability to identify socio-emotional changes has significantly improved in recent years, there is still no specific treatment available. Thus, we explored evidence of drug therapies targeting social cognition alterations in NCDs. Papers were selected according to PRISMA guidelines by searching on the PubMed and Scopus databases. Only papers reporting information on pharmacological interventions for the treatment of social cognition and/or social behavioral changes in major and/or minor NCDs were included. Among the 171 articles entered in the paper selection, only 9 papers were eligible for the scope of the review. Trials testing pharmacological treatments for socio-emotional alterations in NCDs are poor and of low-medium quality. A few attempts with neuroprotective, psychoactive, or immunomodulating drugs have been made. Oxytocin is the only drug specifically targeting the social brain that has been tested with promising results in frontotemporal dementia. Its beneficial effects in long-term use have yet to be evaluated. No recommendation can currently be provided. There is a long way to go to identify and test effective targets to treat social cognition changes in NCDs for the ultimate benefit of patients and caregivers.

Effects of intranasal oxytocin on the self-perception and anxiety of singers during a simulated public singing performance: A randomized, placebo-controlled trial

Professional musicians experience intense social exposure and high levels of preoccupation with their performance and potential negative reactions from the audience, which favor anxiety. Considering that oxytocin (OXT) has a potential therapeutic effect on anxiety, cognitive processes, and decreased psychosocial stress, this study's objective was to assess the effects of a single dose of 24 UI of intranasal OXT among professional singers, during a public singing simulation test, on self-rated performance and mood. This crossover, randomized, double-blinded, placebo-controlled trial addressed 54 male singers with different levels of musical performance anxiety (42% high). The participants took part in different phases of a simulated public singing performance and completed instruments rating their performances (Self Statements During Public Performance- State version) and mood (Visual Analogue Mood Scale). Data were analyzed using ANOVA 2 × 2 for crossover trials. The results show that the use of OXT during the performance and immediate post-stress favored more positive (effect size: d > 1.04) and less negative assessments of musical performance (effect size: d > 1.86) than when placebo was used. No treatment effects were found in any VAMS subscales, indicating no direct anxiolytic effects. The conclusion is that OXT can minimizes social stress, especially during performances. This finding is exploratory and, if confirmed in future studies, may have relevance for musicians, especially those who constantly experience and recognize the impact of negative and catastrophic thoughts on performance and professional activities.

Clinical Trial Registration

[https://ensaiosclinicos.gov.br/rg/RBR-5r5sc5], identifier [RBR-5r5sc5].