Oxytocin reduces reward-driven food intake in humans

Oxytocin does not acutely improve glucose tolerance in men with type 2 diabetes

AIM

To assess oxytocin's acute glucoregulatory impact in men with type 2 diabetes in the context of our previous findings that oxytocin improves β-cell responsivity in healthy men.

METHODS

In a double-blind, crossover comparison, intranasal oxytocin (24 IU) and placebo, respectively, were administered to 25 fasted men with non-insulin-treated type 2 diabetes (age ± standard error of the mean, 63.40 ± 1.36 years; body mass index, 27.77 ± 0.66 kg/m2; HbA1c, 6.86% ± 0.08%; Homeostatic Model Assessment of Insulin Resistance (HOMA-IR, 3.44 ± 0.39) 60 minutes before an oral glucose tolerance test (oGTT). Key outcomes were compared with previous results in men with normal weight or obesity.

RESULTS

Oxytocin compared with placebo increased plasma oxytocin concentrations and reduced the heart rate, but did not alter glucose metabolism in the 3 hours after oGTT onset (area under the curve, glucose, 2240 ± 80.5 vs. 2190 ± 69.5 mmol/L × min; insulin, 45 663 ± 4538 vs. 44 343 ± 4269 pmol/L × min; C-peptide, 235 ± 5.1 vs. 231 ± 15.9 nmol/L × min).

CONCLUSIONS

This outcome contrasts with the oxytocin-induced attenuation of early postprandial glucose excursions in normal-weight individuals, but is in line with the absence of respective effects in men with obesity. We conclude that insulin resistance in type 2 diabetes is associated with decreased sensitivity to the acute glucoregulatory effect of oxytocin in male individuals.

Understanding oxytocin in human physiology and pathophysiology: A path towards therapeutics

•Oxytocin is a multifaceted hypothalamic-pituitary hormone involved in energy homeostasis, mental health, and bone metabolism.•Oxytocin deficiency in energy deficit states and in hypopituitarism is associated with worse mental health and bone health.•Oxytocin modulates appetitive neurocircuitry, improves impulse control, and reduces food intake in humans.•Defining the oxytocin system in human physiology and pathophysiology could lead to novel therapeutic strategies.

Hippocampus Oxytocin Signaling Promotes Prosocial Eating in Rats

BACKGROUND

Oxytocin (OT) is a hypothalamic neuropeptide involved in diverse physiological and behavioral functions, including social-based behavior and food intake control. The extent to which OT's role in regulating these 2 fundamental behaviors is interconnected is unknown, which is a critical gap in knowledge given that social factors have a strong influence on eating behavior in mammals. Here, we focus on OT signaling in the dorsal hippocampus (HPCd), a brain region recently linked to eating and social memory, as a candidate system where these functions overlap.

METHODS

HPCd OT signaling gain- and loss-of-function strategies were used in male Sprague Dawley rats that were trained in a novel social eating procedure to consume their first nocturnal meal under conditions that varied with regard to conspecific presence and familiarity. The endogenous role of HPCd OT signaling was also evaluated for olfactory-based social transmission of food preference learning, sociality, and social recognition memory.

RESULTS

HPCd OT administration had no effect on food intake under isolated conditions but significantly increased consumption in the presence of a familiar but not an unfamiliar conspecific. Supporting these results, chronic knockdown of HPCd OT receptor expression eliminated the food intake-promoting effects of a familiar conspecific. HPCd OT receptor knockdown also blocked social transmission of food preference learning and impaired social recognition memory without affecting sociality.

CONCLUSIONS

Collectively, the results of the current study identify endogenous HPCd OT signaling as a novel substrate in which OT synergistically influences eating and social behaviors, including the social facilitation of eating and the social transmission of food preference.

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.

Intranasal Oxytocin for Obesity

BACKGROUND

Accumulating preclinical and preliminary translational evidence shows that the hypothalamic peptide oxytocin reduces food intake, increases energy expenditure, and promotes weight loss. It is currently unknown whether oxytocin administration is effective in treating human obesity.

METHODS

In this randomized, double-blind, placebo-controlled trial, we randomly assigned adults with obesity 1:1 (stratified by sex and obesity class) to receive intranasal oxytocin (24 IU) or placebo four times daily for 8 weeks. The primary end point was change in body weight (kg) from baseline to week 8. Key secondary end points included change in body composition (total fat mass [g], abdominal visceral adipose tissue [cm2], and liver fat fraction [proportion; range, 0 to 1; higher values indicate a higher proportion of fat]), and resting energy expenditure (kcal/day; adjusted for lean mass) from baseline to week 8 and caloric intake (kcal) at an experimental test meal from baseline to week 6.

RESULTS

Sixty-one participants (54% women; mean age ± standard deviation, 33.6 ± 6.2 years; body-mass index [the weight in kilograms divided by the square of the height in meters], 36.9 ± 4.9) were randomly assigned. There was no difference in body weight change from baseline to week 8 between oxytocin and placebo groups (0.20 vs. 0.26 kg; P=0.934). Oxytocin (vs. placebo) was not associated with beneficial effects on body composition or resting energy expenditure from baseline to week 8 (total fat: difference [95% confidence interval], 196.0 g [-1036 to 1428]; visceral fat: 3.1 cm2 [-11.0 to 17.2]; liver fat: -0.01 [-0.03 to 0.01]; resting energy expenditure: -64.0 kcal/day [-129.3 to 1.4]). Oxytocin compared with placebo was associated with reduced caloric intake at the test meal (-31.4 vs. 120.6 kcal; difference [95% confidence interval], -152.0 kcal [-302.3 to -1.7]). There were no serious adverse events. Incidence and severity of adverse events did not differ between groups.

CONCLUSIONS

In this randomized, placebo-controlled trial in adults with obesity, intranasal oxytocin administered four times daily for 8 weeks did not reduce body weight. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases and others; ClinicalTrials.gov number, NCT03043053.).

Traditional Japanese medicine Kamikihito ameliorates sucrose preference, chronic inflammation and obesity induced by a high fat diet in middle-aged mice

The high prevalence of obesity has become a pressing global public health problem and there exists a strong association between increased BMI and mortality at a BMI of 25 kg/m2 or higher. The prevalence of obesity is higher among middle-aged adults than among younger groups and the combination of aging and obesity exacerbate systemic inflammation. Increased inflammatory cytokines such as interleukin 6 and tumor necrosis factor alpha (TNFα) are hallmarks of obesity, and promote the secretion of hepatic C-reactive protein (CRP) which further induces systematic inflammation. The neuropeptide oxytocin has been shown to have anti-obesity and anti-inflammation effects, and also suppress sweet-tasting carbohydrate consumption in mammals. Previously, we have shown that the Japanese herbal medicine Kamikihito (KKT), which is used to treat neuropsychological stress disorders in Japan, functions as an oxytocin receptors agonist. In the present study, we further investigated the effect of KKT on body weight (BW), food intake, inflammation, and sweet preferences in middle-aged obese mice. KKT oral administration for 12 days decreased the expression of pro-inflammatory cytokines in the liver, and the plasma CRP and TNFα levels in obese mice. The effect of KKT administration was found to be different between male and female mice. In the absence of sucrose, KKT administration decreased food intake only in male mice. However, while having access to a 30% sucrose solution, both BW and food intake was decreased by KKT administration in male and female mice; but sucrose intake was decreased in female mice alone. In addition, KKT administration decreased sucrose intake in oxytocin deficient lean mice, but not in the WT lean mice. The present study demonstrates that KKT ameliorates chronic inflammation, which is strongly associated with aging and obesity, and decreases food intake in male mice as well as sucrose intake in female mice; in an oxytocin receptor dependent manner.

The use of intranasal oxytocin in the treatment of eating disorders

Oxytocin (OXT) is a hypothalamic peptide that plays a number of roles in the body, being involved in labor and lactation, as well as cognitive-emotional processes and social behavior. In recent years, knowledge of the physiology of OXT has been repeatedly used to explore its potential role in the treatment of numerous diseases, identifying a significant role for OXT in appetite regulation, eating behavior, weight regulation, and food-related beliefs. In this review we provide an overview of publications on this topic, but due to the wealth of research, we have limited our focus to studies based on the use of intranasal OXT in psychiatric diseases, with a particular focus on the role of oxytocin in eating disorders and obesity. Accumulating evidence that OXT intranasal supplementation may provide some therapeutic benefit seems promising. In individuals with autistic spectrum disorders (ASD) and schizophrenia, OXT may affect core deficits, improving social cognition and reducing symptom severity in schizophrenia. Dysregulation of serum and CSF OXT levels, as well as polymorphisms of its genes, may affect emotion perception in patients with eating disorders and correlate with co-occurring depressive and anxiety disorders. Nevertheless, there are still many critical questions regarding the pharmacokinetics and pharmacodynamics of intranasal OXT that can only be answered in larger randomized controlled trials.

Effect of intranasal oxytocin on palatable food consumption and c-Fos immunoreactivity in relevant brain areas in rats

Peripheral and central injections of oxytocin (OT) in laboratory animals decrease eating for energy and palatability, but the hypophagic response is dependent on the administration route. Human studies rely on intranasal (IN) administration of the peptide, the route underutilized in OT animal feeding studies thus far. Therefore, we examined the effect of IN OT on various aspects of food consumption in rats: (a) overnight deprivation-induced standard chow intake, (b) episodic (2-h) consumption of calorie-dense and palatable high-fat high-sugar (HFHS) chow, (c) 2-h episodic intake of palatable and calorie-dilute sucrose and Intralipid solutions, and (d) 2-h sucrose solution intake in rats habituated to ingesting this solution daily for several weeks. Finally, we assessed c-Fos changes in response to the acute IN OT administration in rats habituated to daily sugar consumption. We found that IN 20μg OT decreased deprivation-induced intake of standard chow and HFHS chow in nondeprived rats without affecting water consumption. IN OT also reduced 2-hour episodic fluid consumption of sucrose, but not Intralipid. In the habitual sugar consumption paradigm, acute IN OT diminished sucrose solution intake in animals accustomed to the 2-hour/day sucrose meal regimen. In rats habitually consuming sucrose, IN OT altered c-Fos immunoreactivity in brain areas related to energy homeostasis and reward, including the central nucleus of the amygdala, the hypothalamic paraventricular and the arcuate nuclei. We conclude that IN OT is an effective appetite suppressant for carbohydrate/sugar diets in rats and its effects involve feeding-related brain circuits.

Microbes, oxytocin and stress: Converging players regulating eating behavior

Oxytocin is a peptide-hormone extensively studied for its multifaceted biological functions and has recently gained attention for its role in eating behavior, through its action as an anorexigenic neuropeptide. Moreover, the gut microbiota is involved in oxytocinergic signaling through the brain-gut axis, specifically in the regulation of social behavior. The gut microbiota is also implicated in appetite regulation and is postulated to play a role in central regulation of hedonic eating. In this review, we provide an overview on oxytocin and its individual links with the microbiome, the homeostatic and non-homeostatic regulation of eating behavior as well as social behavior and stress.

Intranasal oxytocin as a treatment for obesity: safety and efficacy

INTRODUCTION

Known for its effect on labor and lactation and on emotional and social functions, oxytocin has recently emerged as a key modulator of feeding behavior and indeed suggested as a potential treatment for obesity. The potential positive effect of oxytocin on both metabolic and psychological-behavioral complications of hypothalamic lesions makes it a promising tool in the management of these conditions.

AREAS COVERED

The aim of the present review article is to provide an overview of the mechanism of action and clinical experience of the use of oxytocin in different forms of obesity.

EXPERT OPINION

Current evidence suggests a potential role of oxytocin in the treatment of obesity with different causes. Several challenges remain: an improved understanding of the physiological regulation, mechanisms of action of oxytocin, and interplay with other endocrine axes is fundamental to clarify its role. Further clinical trials are needed to determine the safety and efficacy of oxytocin for the treatment of different forms of obesity. Understanding the mechanism(s) of action of oxytocin on body weight regulation might also improve our understanding of obesity and reveal possible new therapeutic targets - as well as promoting advances in other fields in which oxytocin might be used.

Impact of virtual adjunctive cognitive remediation therapy on cognitive flexibility and treatment outcomes in comorbid anorexia nervosa and exercise dependence as quantified using novel biomarkers: A stage 1 registered report

OBJECTIVE

Anorexia nervosa (AN) is associated with significant individual mental and physical suffering and public health burden and fewer than half of patients recover fully with current treatments. Comorbid exercise dependence (ExD) is common in AN and associated with significantly worse symptom severity and treatment outcomes. Research points to cognitive inflexibility as a prominent executive function inefficiency and transdiagnostic etiologic and maintaining mechanism linking AN and ExD. This study will evaluate the initial efficacy of adjunctive Cognitive Remediation Therapy (CRT), which has been shown to produce cognitive improvements in adults with AN, in targeting cognitive inflexibility in individuals with comorbid AN and ExD. As an exploratory aim, this study also addresses the current lack of quick and cost-effective assessments of cognitive flexibility by establishing the utility of two proposed biomarkers, heart rate variability and salivary oxytocin.

METHOD

We will conduct a single-group, within-subjects trial of an established CRT protocol delivered remotely as an adjunct to inpatient or intensive outpatient treatment as usual (TAU) to adult patients (n = 42) with comorbid AN and ExD. Assessments, including self-report, neuropsychological, and biomarker measurements, will occur at three time points.

RESULTS

We expect CRT to increase cognitive flexibility transdiagnostically and consequently, along with TAU, positively impact AN and ExD compulsivity and symptom severity, including weight gain.

DISCUSSION

Findings will inform the development of more effective integrative interventions for AN and ExD targeting shared mechanisms and facilitate the routine assessment of cognitive flexibility as a transdiagnostic risk and maintaining factor across psychopathologies in clinical and research settings.

PUBLIC SIGNIFICANCE

Patients with anorexia nervosa often engage in excessive exercise, leading to harmful outcomes, including increased suicidal behavior. This study examines the preliminary efficacy of an intervention that fosters flexible and holistic thinking in patients with problematic eating and exercise to, along with routine treatment, decrease harmful exercise symptoms. This study also examines new biological markers of the inflexible thinking style thought to be characteristic of anorexia nervosa and exercise dependence.

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.

Modulation of the thermosensory system by oxytocin

Oxytocin (OT) is a neurohormone involved early in neurodevelopment and is implicated in multiple functions, including sensory modulation. Evidence of such modulation has been observed for different sensory modalities in both healthy and pathological conditions. This review summarizes the pleiotropic modulation that OT can exercise on an often overlooked sensory system: thermosensation. This system allows us to sense temperature variations and compensate for the variation to maintain a stable core body temperature. Oxytocin modulates autonomic and behavioral mechanisms underlying thermoregulation at both central and peripheral levels. Hyposensitivity or hypersensitivity for different sensory modalities, including thermosensitivity, is a common feature in autism spectrum disorder (ASD), recapitulated in several ASD mouse models. These sensory dysregulations occur early in post-natal development and are correlated with dysregulation of the oxytocinergic system. In this study, we discussed the potential link between thermosensory atypia and the dysregulation of the oxytocinergic system in ASD.

A randomized, double-blind, placebo-controlled clinical trial of 8-week intranasal oxytocin administration in adults with obesity: Rationale, study design, and methods

BACKGROUND

Obesity affects more than one-third of adults in the U.S., and effective treatment options are urgently needed. Oxytocin administration induces weight loss in animal models of obesity via effects on caloric intake, energy expenditure, and fat metabolism. We study intranasal oxytocin, an investigational drug shown to reduce caloric intake in humans, as a potential novel treatment for obesity.

METHODS

We report the rationale, design, methods, and biostatistical analysis plan of a randomized, double-blind, placebo-controlled clinical trial of intranasal oxytocin for weight loss (primary endpoint) in adults with obesity. Participants (aged 18-45 years) were randomly allocated (1:1) to oxytocin (four times daily over eight weeks) versus placebo. Randomization was stratified by biological sex and BMI (30 to <35, 35 to <40, ≥40 kg/m2). We investigate the efficacy, safety, and mechanisms of oxytocin administration in reducing body weight. Secondary endpoints include changes in resting energy expenditure, body composition, caloric intake, metabolic profile, and brain activation via functional magnetic resonance imaging in response to food images and during an impulse control task. Safety and tolerability (e.g., review of adverse events, vital signs, electrocardiogram, comprehensive metabolic panel) are assessed throughout the study and six weeks after treatment completion.

RESULTS

Sixty-one male and female participants aged 18-45 years were randomized (mean age 34 years, mean BMI 37 kg/m2). The study sample is diverse with 38% identifying as non-White and 20% Hispanic.

CONCLUSION

Investigating intranasal oxytocin's efficacy, safety, and mechanisms as an anti-obesity medication will advance the search for optimal treatment strategies for obesity and its associated severe sequelae.

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

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

The oxytocin signalling gene pathway contributes to the association between loneliness and cardiometabolic health

Increasing evidence has shown adverse effects of loneliness on cardiometabolic health. The neuromodulator and hormone oxytocin has traditionally been linked with social cognition and behaviour. However, recent implications of the oxytocin system in energy metabolism and the overrepresentation of metabolic issues in psychiatric illness suggests that oxytocin may represent a mechanism bridging mental and somatic traits. To clarify the role of the oxytocin signalling system in the link between cardiometabolic risk factors and loneliness, we calculated the contribution of single nucleotide polymorphisms (SNPs) in the oxytocin signalling pathway gene-set (154 genes) to the polygenic architecture of loneliness and body mass index (BMI). We investigated the associations of these oxytocin signalling pathway polygenic scores with body composition measured using body magnetic resonance imaging (MRI), bone mineral density (BMD), haematological markers, and blood pressure in a sample of just under half a million adults from the UK Biobank (BMD subsample n = 274,457; body MRI subsample n = 9796). Our analysis revealed significant associations of the oxytocin signalling pathway polygenic score for BMI with abdominal subcutaneous fat tissue, HDL cholesterol, lipoprotein(a), triglycerides, and BMD. We also found an association between the oxytocin signalling pathway polygenic score for loneliness and apolipoprotein A1, the major protein component of HDL. Altogether, these results provide additional evidence for the oxytocin signalling pathway's role in energy metabolism, lipid homoeostasis, and bone density, and support oxytocin's complex pleiotropic effects.

Oxytocin as a potential pharmacological tool to combat obesity

The neuropeptide oxytocin (OT) has emerged as an important anorexigen in the regulation of food intake and energy balance. It has been shown that the release of OT and activation of hypothalamic OT neurons coincide with food ingestion. Its effects on feeding have largely been attributed to limiting meal size through interactions in key regulatory brain regions governing the homeostatic control of food intake such as the hypothalamus and hindbrain in addition to key feeding reward areas such as the nucleus accumbens and ventral tegmental area. Furthermore, the magnitude of an anorexigenic response to OT and feeding-related activation of the brain OT circuit are modified by the composition and flavor of a diet, as well as by a social context in which a meal is consumed. OT is particularly effective in reducing consumption of carbohydrates and sweet tastants. Pharmacologic, genetic, and pair-feeding studies indicate that OT-elicited weight loss cannot be fully explained by reductions of food intake and that the overall impact of OT on energy balance is also partly a result of OT-elicited changes in lipolysis, energy expenditure, and glucose regulation. Peripheral administration of OT mimics many of its effects when it is given into the central nervous system, raising the questions of whether and to what extent circulating OT acts through peripheral OT receptors to regulate energy balance. Although OT has been found to elicit weight loss in female mice, recent studies have indicated that sex and estrous cycle may impact oxytocinergic modulation of food intake. Despite the overall promising basic research data, attempts to use OT in the clinical setting to combat obesity and overeating have generated somewhat mixed results. The focus of this mini-review is to briefly summarize the role of OT in feeding and metabolism, address gaps and inconsistencies in our knowledge, and discuss some of the limitations to the potential use of chronic OT that should help guide future research on OT as a tailor-made anti-obesity therapeutic.

OXTR DNA methylation differentiates men on the obesity spectrum with and without binge eating disorder

BACKGROUND

The neuropeptide oxytocin (OXT) plays a role in the regulation of eating behavior and metabolism. OXT functioning is altered in patients with eating and weight disorders, and a variant of the oxytocin receptor gene (OXTR) has been associated with impulsive eating behavior as it is seen in patients with binge eating disorder (BED). Gene × environment interactions could play a role in BED. One mechanism mediating this interaction is the epigenetic alteration of gene expression. We therefore investigated if DNA methylation of the OXTR differs between individuals with obesity depending on a comorbid BED. We analyzed DNA methylation of the OXTR in peripheral blood of 227 individuals on the obesity spectrum (mean age: 40.3 ± 13.1 yrs; mean BMI: 38.6 ± 7.3 kg/m²), 130 of which were diagnosed with BED.

RESULTS

There were no overall differences in OXTR methylation between participants with and those without BED (p > 0.05), while both subgroups were comparable regarding age and body mass index (BMI), but significantly differed in sex distribution (p = 0.035). We found no relationship between mean DNA methylation and BMI or self-reported eating disorder (ED) pathology. Analyzing potential sex differences revealed a significantly lower OXTR DNA methylation in male participants with BED as compared to those without BED (p = 0.017). No such difference was found in the female subsample (p > 0.05).

CONCLUSIONS

Clinically significant binge eating pathology might be associated with lower OXTR DNA methylation exclusively in males. The differential DNA methylation of OXTR in males with BED supports the view that BED represents a phenotype within the obesity spectrum that is characterized by specific vulnerability factors. A better understanding of the epigenetic underpinnings of the OXT system might contribute to the refinement of OXT administration approaches as potential interventions in eating and weight disorders.

Hippocampal oxytocin is involved in spatial memory and synaptic plasticity deficits following acute high-fat diet intake in juvenile rats

The hippocampus undergoes maturation during juvenility, a period of increased vulnerability to environmental challenges. We recently found that acute high-fat diet (HFD) impaired hippocampal long-term potentiation (LTP) and hippocampal-dependent spatial memory. We also recently reported that similar HFD exposure affected prefrontal plasticity and social memory through decreased oxytocin levels in the prefrontal cortex. In the present study, we therefore evaluated whether hippocampal oxytocin levels are also affected by juvenile HFD and could mediate deficits of hippocampal LTP and spatial memory. We found that postweaning HFD decreased oxytocin levels in the CA1 of the dorsal hippocampus. Interestingly, systemic injection of high, but not low, dose of oxytocin rescued HFD-induced LTP impairment in CA1. Moreover, deficits in long-term object location memory (OLM) were prevented by systemic injection of both high and low dose of oxytocin as well as by intra-CA1 infusion of oxytocin receptor agonist. Finally, we found that blocking oxytocin receptors in CA1 impaired long-term OLM in control-fed juvenile rats. These results suggest that acute HFD intake lowers oxytocin levels in the CA1 that lead to CA1 plasticity impairment and spatial memory deficits in juveniles. Further, these results provide the first evidence for the regulatory role of oxytocin in spatial memory.

Oxytocin: An Old Hormone, A Novel Psychotropic Drug And Possible Use In Treating Psychiatric Disorders

BACKGROUND

Oxytocin is a nonapeptide synthesized in the paraventricular and supraoptic nuclei of the hypothalamus. Historically, this molecule has been involved as a key factor in the formation of infant attachment, maternal behavior and pair bonding and, more generally, in linking social signals with cognition, behaviors and reward. In the last decades, the whole oxytocin system has gained a growing interest as it was proposed to be implicated in etiopathogenesis of several neurodevelopmental and neuropsychiatric disorders.

METHODS

With the main goal of an in-depth understanding of the oxytocin role in the regulation of different functions and complex behaviors as well as its intriguing implications in different neuropsychiatric disorders, we performed a critical review of the current state of art. We carried out this work through PubMed database up to June 2021 with the search terms: 1) "oxytocin and neuropsychiatric disorders"; 2) "oxytocin and neurodevelopmental disorders"; 3) "oxytocin and anorexia"; 4) "oxytocin and eating disorders"; 5) "oxytocin and obsessive-compulsive disorder"; 6) "oxytocin and schizophrenia"; 7) "oxytocin and depression"; 8) "oxytocin and bipolar disorder"; 9) "oxytocin and psychosis"; 10) "oxytocin and anxiety"; 11) "oxytocin and personality disorder"; 12) "oxytocin and PTSD".

RESULTS

Biological, genetic, and epigenetic studies highlighted quality and quantity modifications in the expression of oxytocin peptide or in oxytocin receptor isoforms. These alterations would seem to be correlated with a higher risk of presenting several neuropsychiatric disorders belonging to different psychopathological spectra. Collaterally, the exogenous oxytocin administration has shown to ameliorate many neuropsychiatric clinical conditions.

CONCLUSION

Finally, we briefly analyzed the potential pharmacological use of oxytocin in patient with severe symptomatic SARS-CoV-2 infection due to its anti-inflammatory, anti-oxidative and immunoregulatory properties.

Crosstalk between Schizophrenia and Metabolic Syndrome: The Role of Oxytocinergic Dysfunction

The high prevalence of metabolic syndrome in persons with schizophrenia has spurred investigational efforts to study the mechanism beneath its pathophysiology. Early psychosis dysfunction is present across multiple organ systems. On this account, schizophrenia may be a multisystem disorder in which one organ system is predominantly affected and where other organ systems are also concurrently involved. Growing evidence of the overlapping neurobiological profiles of metabolic risk factors and psychiatric symptoms, such as an association with cognitive dysfunction, altered autonomic nervous system regulation, desynchrony in the resting-state default mode network, and shared genetic liability, suggest that metabolic syndrome and schizophrenia are connected via common pathways that are central to schizophrenia pathogenesis, which may be underpinned by oxytocin system dysfunction. Oxytocin, a hormone that involves in the mechanisms of food intake and metabolic homeostasis, may partly explain this piece of the puzzle in the mechanism underlying this association. Given its prosocial and anorexigenic properties, oxytocin has been administered intranasally to investigate its therapeutic potential in schizophrenia and obesity. Although the pathophysiology and mechanisms of oxytocinergic dysfunction in metabolic syndrome and schizophrenia are both complex and it is still too early to draw a conclusion upon, oxytocinergic dysfunction may yield a new mechanistic insight into schizophrenia pathogenesis and treatment.

Age and sex influence the response in lipid metabolism of dehydrated Wistar rats

Aging is associated a decrease in thirst sensation, which makes old people more susceptible to dehydration. Dehydration produces energy metabolism alterations. Our objective was to determinate the effect of water deprivation (WD) in the lipid metabolism of old male and female rats. Here we show that in the state of WD, aging and sex alters retroperitoneal white adipose tissue (R-WAT) weight of rats, WD old female rats had more lipolysis products than old male rats, a sexual dimorphism in the hormonal response related with metabolism of the adipose tissue of old rats during WD, the expression of P-para mRNA in R-WAT did not present any alteration in animals submitted to WD, the expression of Aqp7 mRNA in R-WAT is altered by WD, age, and sex. Also, WD stimulated an increase in the plasma concentration of oxytocin and the expression of mRNA of the oxytocin receptors in R-WAT.

Transactivation of TrkB Receptors by Oxytocin and Its G Protein-Coupled Receptor

Brain-derived Neurotrophic Factor (BDNF) binds to the TrkB tyrosine kinase receptor, which dictates the sensitivity of neurons to BDNF. A unique feature of TrkB is the ability to be activated by small molecules in a process called transactivation. Here we report that the brain neuropeptide oxytocin increases BDNF TrkB activity in primary cortical neurons and in the mammalian neocortex during postnatal development. Oxytocin produces its effects through a G protein-coupled receptor (GPCR), however, the receptor signaling events that account for its actions have not been fully defined. We find oxytocin rapidly transactivates TrkB receptors in bath application of acute brain slices of 2-week-old mice and in primary cortical culture by increasing TrkB receptor tyrosine phosphorylation. The effects of oxytocin signaling could be distinguished from the related vasopressin receptor. The transactivation of TrkB receptors by oxytocin enhances the clustering of gephyrin, a scaffold protein responsible to coordinate inhibitory responses. Because oxytocin displays pro-social functions in maternal care, cognition, and social attachment, it is currently a focus of therapeutic strategies in autism spectrum disorders. Interestingly, oxytocin and BDNF are both implicated in the pathophysiology of depression, schizophrenia, anxiety, and cognition. These results imply that oxytocin may rely upon crosstalk with BDNF signaling to facilitate its actions through receptor transactivation.

Birth with synthetic oxytocin and the risk of being overweight or obese during childhood

BACKGROUND

Despite the importance of oxytocinergic signalling for satiety regulation and energy balance, the impact of exposure to synthetic oxytocin during childbirth on obesity during childhood remains unknown.

OBJECTIVES

To examine the association between oxytocin exposure during labour and the risk of being overweight or obese during childhood.

METHODS

Synthetic oxytocin exposure data of mothers from the Danish Medical Birth Registry were linked with self-reported anthropometric data of their children from the Danish National Birth Cohort (5 months-11 years of age). Multinomial logistic regression and latent class growth analyses were performed to determine the association between oxytocin exposure and obesity during childhood.

RESULTS

With the exception of the normal weight-to-overweight group between ages 5 and 12 months, none of the other analyses revealed a significant association between synthetic oxytocin use and the risk of being overweight until the age of 11 years. Furthermore, latent class growth analysis did not reveal an association between oxytocin exposure at birth and the risk of being overweight or obese during childhood.

CONCLUSIONS

Our analysis of a large cohort of children who varied in their synthetic oxytocin exposure status at childbirth did not reveal an association between oxytocin exposure and the risk of childhood overweight/obesity.

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

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

Heterodimer of A2A and Oxytocin Receptors Regulating Glutamate Release in Adult Striatal Astrocytes

BACKGROUND

Roles of astrocytes in the modulatory effects of oxytocin (OT) in central nervous system are increasingly considered. Nevertheless, OT effects on gliotransmitter release have been neglected.

METHODS

In purified astrocyte processes from adult rat striatum, we assessed OT receptor (OTR) and adenosine A2A receptor expression by confocal analysis. The effects of receptors activation on glutamate release from the processes were evaluated; A2A-OTR heteromerization was assessed by co-immunoprecipitation and PLA. Structure of the possible heterodimer of A2A and OT receptors was estimated by a bioinformatic approach.

RESULTS

Both A2A and OT receptors were expressed on the same astrocyte processes. Evidence for A2A-OTR receptor-receptor interaction was obtained by measuring the release of glutamate: OT inhibited the evoked glutamate release, while activation of A2A receptors, per se ineffective, abolished the OT effect. Biochemical and biophysical evidence for A2A-OTR heterodimers on striatal astrocytes was also obtained. The residues in the transmembrane domains 4 and 5 of both receptors are predicted to be mainly involved in the heteromerization.

CONCLUSIONS

When considering effects of OT in striatum, modulation of glutamate release from the astrocyte processes and of glutamatergic synapse functioning, and the interaction with A2A receptors on the astrocyte processes should be taken into consideration.

Intranasal oxytocin reduces attentional bias to food stimuli

Attentional biases to food-related stimuli have been demonstrated in response to hunger as well as during restrained eating. Such biases are often associated with obesity, but healthy-weight individuals who do not self-report hunger have also demonstrated attentional biases to stimuli signalling food using laboratory-based cognitive tasks. Levels of the anorectic neuropeptide oxytocin are elevated by food intake and, when administered intranasally, oxytocin inhibits food intake in the laboratory. To investigate whether oxytocin can affect appetite via an action on attentional processes, 40 adults (29 women; mean age 24.0 years old) self-administered 24 IU of oxytocin or placebo intranasally. Forty minutes after administration, participants ate a small snack to maintain alertness and ameliorate deprivation-induced hunger before starting a computerized dot-probe attentional bias task that presented 180 trials of paired visual stimuli comprising neutral, food, social and/or romantic images (500 ms presentation time). Reaction times to probe stimuli that appeared after the offset of the visual images indicated a significant attentional bias to food pictures after placebo; this effect was significantly attenuated by oxytocin, p < .001. The effect of oxytocin on attentional bias to the food pictures was not altered by the type of stimulus paired with the food image, and was independent of BMI, age, sex, self-rated eating behaviour, and self-reported parental bonding; however, the effect was modulated by self-reported food cravings and trait stress. The findings support and extend previous work which has suggested that oxytocin can counteract attentional biases to food-related stimuli in a sample with anorexia by demonstrating the same effect for the first time in a cohort who do not have an eating disorder.

Acute Hypophagia and Changes in c-Fos Immunoreactivity in Adolescent Rats Treated with Low Doses of Oxytocin and Naltrexone

A recent case report has shown that an adjunctive oxytocin + naltrexone (OT + NTX) treatment promoted more robust hypophagia and body weight reduction than OT alone in an adolescent male with hypothalamic obesity after craniopharyngioma resection. Thus far, there has been no basic research in adolescent laboratory animals that would examine whether the benefit of OT + NTX on appetite extends onto adolescent individuals without surgically induced overeating. Thus, here we examined whether low doses of combined OT + NTX acutely affect post-deprivation intake of energy-dense, standard chow; intake of energy-dense and palatable high-fat high-sugar (HFHS) diet; or calorie-dilute, palaTable 10% sucrose solution without deprivation in adolescent male rats. We assessed whether OT + NTX decreases water intake after water deprivation or produces a conditioned taste aversion (CTA). Finally, by using c-Fos immunoreactivity, we determined changes in activity of feeding-related brain areas after OT + NTX. We found that individual subthreshold doses of OT and NTX decreased feeding induced by energy and by palatability. Significant c-Fos changes were noted in the arcuate and dorsomedial hypothalamic nuclei. The hypophagic doses of OT + NTX did not suppress water intake in thirsty rats and did not cause a CTA, which suggests that feeding reduction is not a secondary effect of gastrointestinal discomfort or changes in thirst processing. We conclude that OT + NTX is an effective drug combination to reduce appetite in adolescent male rats.

Identification of oxytocin receptor activating chemical components from traditional Japanese medicines

Oxytocin (Oxt) is known to regulate social communication, stress and body weight. The activation of Oxt receptors (OTR) has clinical potential to abate stress disorders and metabolic syndrome. Kamikihito (KKT) is a traditional Japanese medicine used to treat psychological stress-related disorders. We investigated the effects of KKT, its ingredients and chemical components on Oxt neurons and OTR. C-Fos expression was examined after oral and peripheral administration of KKT in rats. Electrophysiological change of Oxt neurons and Oxt release upon application of KKT were measured in rat brain slice. The direct effect of KKT, its ingredients and its chemical components were examined by cytosolic Ca²⁺([Ca²⁺]_i) measurement in Oxt neurons and OTR-expressing HEK293 cells. Both intraperitoneal and oral administration of KKT in rats induced c-Fos expression in neurons of the paraventricular nucleus (PVN) including Oxt neurons. Application of KKT induced activation of Oxt neurons and Oxt release. KKT increased [Ca²⁺]_i in OTR-expressing HEK293 cells, and failed to activate with OTR antagonist. KKT-induced PVN Oxt neuron activation was also attenuated by OTR antagonist. Seven chemical components (rutin, ursolic acid, (Z )-butylidenephtalide, p-cymene, senkunolide, [6]-shogaol, [8]-shogaol) of three ingredients (Zizyphi Fructus, Angelicae Acutilobae Radix, Zingiberis Rhizoma) from KKT had potential to activate OTR. KKT can directly activate PVN Oxt neurons by interacting with OTR. The interaction of seven chemical components from KKT may contribute to activate OTR. Effect of KKT on Oxt neurons and OTR may contribute to the treatment of Oxt related disorders.

Oxytocin-pathway polygenic scores for severe mental disorders and metabolic phenotypes in the UK Biobank

Oxytocin is a neuromodulator and hormone that is typically associated with social cognition and behavior. In light of its purported effects on social cognition and behavior, research has investigated its potential as a treatment for psychiatric illnesses characterized by social dysfunction, such as schizophrenia and bipolar disorder. While the results of these trials have been mixed, more recent evidence suggests that the oxytocin system is also linked with cardiometabolic conditions for which individuals with severe mental disorders are at a higher risk for developing. To investigate whether the oxytocin system has a pleiotropic effect on the etiology of severe mental illness and cardiometabolic conditions, we explored oxytocin's role in the shared genetic liability of schizophrenia, bipolar disorder, type-2 diabetes, and several phenotypes linked with cardiovascular disease and type 2 diabetes risk using a polygenic pathway-specific approach. Analysis of a large sample with about 480,000 individuals (UK Biobank) revealed statistically significant associations across the range of phenotypes analyzed. By comparing these effects to those of polygenic scores calculated from 100 random gene sets, we also demonstrated the specificity of many of these significant results. Altogether, our results suggest that the shared effect of oxytocin-system dysfunction could help partially explain the co-occurrence of social and cardiometabolic dysfunction in severe mental illnesses.

Oxytocin as an Anti-obesity Treatment

Obesity is a growing health concern, as it increases risk for heart disease, hypertension, type 2 diabetes, cancer, COVID-19 related hospitalizations and mortality. However, current weight loss therapies are often associated with psychiatric or cardiovascular side effects or poor tolerability that limit their long-term use. The hypothalamic neuropeptide, oxytocin (OT), mediates a wide range of physiologic actions, which include reproductive behavior, formation of prosocial behaviors and control of body weight. We and others have shown that OT circumvents leptin resistance and elicits weight loss in diet-induced obese rodents and non-human primates by reducing both food intake and increasing energy expenditure (EE). Chronic intranasal OT also elicits promising effects on weight loss in obese humans. This review evaluates the potential use of OT as a therapeutic strategy to treat obesity in rodents, non-human primates, and humans, and identifies potential mechanisms that mediate this effect.

Oxytocin and Food Intake Control: Neural, Behavioral, and Signaling Mechanisms

The neuropeptide oxytocin is produced in the paraventricular hypothalamic nucleus and the supraoptic nucleus of the hypothalamus. In addition to its extensively studied influence on social behavior and reproductive function, central oxytocin signaling potently reduces food intake in both humans and animal models and has potential therapeutic use for obesity treatment. In this review, we highlight rodent model research that illuminates various neural, behavioral, and signaling mechanisms through which oxytocin’s anorexigenic effects occur. The research supports a framework through which oxytocin reduces food intake via amplification of within-meal physiological satiation signals rather than by altering between-meal interoceptive hunger and satiety states. We also emphasize the distributed neural sites of action for oxytocin’s effects on food intake and review evidence supporting the notion that central oxytocin is communicated throughout the brain, at least in part, through humoral-like volume transmission. Finally, we highlight mechanisms through which oxytocin interacts with various energy balance-associated neuropeptide and endocrine systems (e.g., agouti-related peptide, melanin-concentrating hormone, leptin), as well as the behavioral mechanisms through which oxytocin inhibits food intake, including effects on nutrient-specific ingestion, meal size control, food reward-motivated responses, and competing motivations.

Effects of intranasal oxytocin in food intake and craving: A meta-analysis of clinical trials

OBJECTIVE

A rise of endogenous oxytocin (OT) is associated with anxiety and meal size reduction, and the effects of intranasal OT (INOT) have been examined in the management of food intake and craving. However, the discrepancy INOT effects in different disease populations are not entirely clear.

RESEARCH DESIGN AND METHODS

Updated systematic review and meta-analysis. By systematically searching the PubMed, Embase and Cochrane Library, we obtained 12 controlled trials. We performed meta-analyses to examine food intake, craving, anxiety or stress reduction on INOT administration, using standard mean difference (SMD) with a 95% confidence interval (CI) and a random-effects model.

RESULTS

This study examined 12 trials with 266 non-psychiatric and 157 psychiatric participants. The pooled results showed that single-dose INOT induced a significant lesser food intake in non-psychiatric subjects (SMD: -0.66 [95% CI: -1.18, -0.14]), but no effects was found in anorexia nervosa (AN) (SMD: 0.17 [95% CI: -0.32, 0.66]), bulimia nervosa (BN) and binge eating disorder (BED) (SMD: -0.41 [95% CI: -0.94, 0.11]), and schizophrenia (SMD: 0.04 [95% CI: -0.94, 1.02] subjects. Further analysis on leisure food also indicated an inhibition of consumption of chocolate biscuits in non-psychiatric subjects. Neither the non-psychiatric (SMD: -0.08 [95% CI: -0.50, 0.33]) nor the BN and BED (SMD: -0.08 [95% CI: -0.72, 0.88]) and schizophrenia subjects (SMD: -0.07 [95% CI: -1.05, 0.91]) demonstrated a difference in food craving or hunger compared with placebo. Anxiety or stress level was not influenced by INOT in any subgroup (non-psychiatric, SMD: 0.19 [95% CI: -0.22, 0.60]; AN, SMD: -0.01 [95% CI: -0.28, 0.88]; BN and BED: SMD: 0.00 [95% CI: -0.80, 0.80]).

CONCLUSIONS

Single-dose INOT significantly reduces food intake in nonpsychiatric subjects, and further studies are necessary to assess the long-term effects and safety in obese patients. Whether INOT could be a treatment option for patients with eating disorders remains to be investigated.

Neural Basis of Dysregulation of Palatability-Driven Appetite in Autism

PURPOSE OF REVIEW

In research on autism spectrum disorder (ASD), cognitive, speech- and anxiety-related impairments have been the focus of the majority of studies. One consistently reported ASD symptom that has rarely attracted attention is disordered appetite. The goal of this paper is to assess whether ASD-related dysregulation of food intake impacts consumption of palatable foods, including sugar.

RECENT FINDINGS

Aberrant neural processing at the reward system level is at least partially responsible for excessive intake of palatable tastants, including sugar. Impaired oxytocin (OT) signaling likely contributes to the magnitude of this overconsumption. Since intake for reward is generally elevated in individuals with ASD, one strategy to curb sugar overconsumption might utilize presentation of alternative palatable food choices that are more nutritionally adequate than sucrose. Furthermore, OT, which is clinically tested to alleviate other ASD symptoms, might be an effective tool to curb overconsumption of sugar, as well as - likely - of other excessively ingested palatable foods, especially those that have sweet taste.

Sensory Circumventricular Organs, Neuroendocrine Control, and Metabolic Regulation

The central nervous system is critical in metabolic regulation, and accumulating evidence points to a distributed network of brain regions involved in energy homeostasis. This is accomplished, in part, by integrating peripheral and central metabolic information and subsequently modulating neuroendocrine outputs through the paraventricular and supraoptic nucleus of the hypothalamus. However, these hypothalamic nuclei are generally protected by a blood-brain-barrier limiting their ability to directly sense circulating metabolic signals—pointing to possible involvement of upstream brain nuclei. In this regard, sensory circumventricular organs (CVOs), brain sites traditionally recognized in thirst/fluid and cardiovascular regulation, are emerging as potential sites through which circulating metabolic substances influence neuroendocrine control. The sensory CVOs, including the subfornical organ, organum vasculosum of the lamina terminalis, and area postrema, are located outside the blood-brain-barrier, possess cellular machinery to sense the metabolic interior milieu, and establish complex neural networks to hypothalamic neuroendocrine nuclei. Here, evidence for a potential role of sensory CVO-hypothalamic neuroendocrine networks in energy homeostasis is presented.

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.

Can intranasal oxytocin reduce craving in automated addictive behaviours? A systematic review

Existing pharmacotherapies for managing craving, a strong predictor of relapse to automated addictive behaviours, are limited in efficacy and characterised by increased health risks associated with their pharmacological profile. Preclinical studies have identified oxytocin as a promising pharmacotherapy with anticraving properties for addictive behaviours. Here, we provide the first systematic review of 17 human studies (n = 722; 30% female) investigating the efficacy of intranasal oxytocin to reduce craving or consumption in addictive behaviours. We identify intranasal oxytocin as a method that warrants further investigation regarding its capacity to decrease cue-induced, acute stress-induced or withdrawal-related craving and relapse related to alcohol, cannabis, opioids, cocaine or nicotine, including a potential role as ad hoc medication following exposure to drug-related cues. Future studies should investigate the role of factors such as treatment regimens and sample characteristics, including the role of the amygdala, which we propose as a distinct mechanism mediating oxytocin's anticraving properties.

Effect of combination of peripheral oxytocin and naltrexone at subthreshold doses on food intake, body weight and feeding-related brain gene expression in male rats

In a recent case report involving a male with hypothalamic obesity, concurrent administration of oxytocin (OT) and an opioid receptor antagonist, naltrexone (NTX), synergistically affected energy balance. Here, by using laboratory rats, we examined whether the reported synergy between OT and NTX in the context of food intake extends beyond that one unique case. We found that intravenous OT+NTX combination, at doses subthreshold for each of the drugs individually, decreased episodic consumption of a 10% sucrose solution in non-deprived animals. Daily administration of OT and NTX just before a scheduled, 2-hour, high-fat high-sugar (HFHS) meal over 24 days, decreased cumulative HFHS diet intake, but without a change in body weight due to compensatory standard chow intake during the remainder of the day. The NTX-OT treatment affected expression of several feeding-related genes in the hypothalamus, brain stem and nucleus accumbens, brain regions essential for the regulation of energy- and reward-driven consumption. We conclude that OT and NTX act synergistically to decrease food consumption in rats and that this transient effect is accompanied by changes in brain processes relevant to feeding.

Oxytocin in young children with Prader-Willi syndrome: Results of a randomized, double-blind, placebo-controlled, crossover trial investigating 3 months of oxytocin

CONTEXT

Prader-Willi syndrome (PWS) is characterized by hypothalamic dysfunction, hyperphagia and a typical behavioural phenotype, with characteristics of autism spectrum disorder (ASD) like stubbornness, temper tantrums and compulsivity. It has been suggested that the oxytocin system in patients with PWS is dysfunctional. In ASD, intranasal oxytocin treatment has favourable effects on behaviour.

OBJECTIVE

To evaluate the effects of 3 months of twice daily intranasal oxytocin (dose range 16-40 IU/day), compared to placebo, on behaviour and hyperphagia in children with PWS.

DESIGN

Randomized, double-blind, placebo-controlled, crossover study in the Dutch PWS Reference Center.

PATIENTS

Twenty-six children with PWS aged 3-11 years.

MAIN OUTCOME MEASURES

(Change in) behaviour and hyperphagia measured by Oxytocin Questionnaire and Dykens hyperphagia questionnaire.

RESULTS

In the total group, no significant effects of oxytocin on social behaviour or hyperphagia were found. However, in boys, the Oxytocin Questionnaire scores improved significantly during oxytocin treatment, compared to a deterioration during placebo (4.5 (-0.8 to 15.3) vs. -4.0 (-11.3 to 0.8), P = .025). The Dykens hyperphagia questionnaire scores remained similar during oxytocin treatment, while there was a deterioration during placebo (0.0 (-0.8 to 4.3) vs. -3.5 (-6.0 to 0.0), P = .046). Patients with a deletion had significant improvements in both questionnaire scores during oxytocin treatment, but deteriorations during placebo. Oxytocin treatment was well tolerated, and there were no serious adverse events.

CONCLUSIONS

Intranasal oxytocin treatment has positive effects on social and eating behaviour in 3-11 years aged boys with PWS and in children with a deletion without safety concerns. Intranasal oxytocin in children with PWS might be considered, but individual effects should be carefully evaluated and treatment discontinued if no effects are found.

Exiguous premeal saccharide intake reduces subsequent food intake in men

Purpose

Satiety is a crucial factor in the attempt to reduce food intake for long-term body weight loss. Since there is evidence for a negative correlation between cerebral energy levels and food intake, the provision of the primary energy substrate glucose to the brain through oral ingestion of carbohydrates could trigger feelings of satiety. Therefore, we hypothesized that a low-calorie saccharide preload would increase satiety, reduce subsequent food intake, and thereby decrease overall calorie consumption.

Methods

In a randomized single-blind crossover study, 17 healthy young normal-weight men received saccharide (26 kcal in total) or placebo capsules 30 min before a standardized breakfast buffet. We analysed food intake from the test buffet as well as plasma glucose and serum insulin levels.

Results

The saccharide preload reduced food intake from the buffet by 168 (± 34) kcal (p < 0.001) compared to control. This corresponds to a net reduction in total calorie consumption by 142 (± 34) kcal (p < 0.001) or 9.3% due to saccharide capsules.

Conclusion

A very low-calorie saccharide preload considerably reduces subsequent food intake leading to decreased overall calorie consumption. A saccharide preload before meals could, therefore, be a promising support for reducing caloric intake.

German Clinical Trials Register

DRKS00010281 (date of registration: 11.04.2016)

Oxytocin: A Potential Therapeutic for Obesity

Oxytocin is a neuropeptide involved in the homeostasis of food consumption and energy; it affects hedonic eating. Studies in obese or binge-eating patients reported the hypophagic effect of oxytocin, which reduced caloric intake after administration. Several studies have demonstrated the effect of oxytocin’s increasing energy intake, decreasing food consumption, and contributing to weight loss. Oxytocin’s effects on food intake and metabolism suggest its therapeutic potential for treating obesity and binge eating.

The Independent Role of Body Mass Index (BMI) and Severity of Depressive Symptoms on Biological Changes of Women Affected by Overweight/Obesity

Background: Both obesity and depression are medical conditions associated with severe disability and biological abnormalities. Our aim was to study associations between Body Mass Index (BMI), depression and biological changes in women affected by overweight or obesity. Methods: Depressive symptoms were evaluated by the Beck Depression Inventory II (BDI-II) questionnaire in 200 women affected by overweight/obesity (mean age of the sample 52.7 ± 12.9 years, BMI 33.8 ± 5.5 kg/m²). A blood sample was obtained for evaluation of biochemical (oxytocin and vitamin D), inflammatory and epigenetic (methylation of clock genes) parameters. Multivariable linear regression models were used to study the association between BMI or severity of depressive symptoms (BDI-II scores) with different biomarkers. Results: BMI was found to be associated with severity of depressive symptoms (p = 0.050). Severity of obesity resulted to be associated with lower plasma levels of oxytocin (p = 0.053), vitamin D deficiency (p = 0.006) and higher plasma levels of IFN-γ (p = 0.004), IL-6 (p = 0.013), IL-7 (p = 0.013), TNF-alpha (p = 0.036) and chemokine ligand 3 (CCL3) (p = 0.013, R² = 0.03). Severity of depression was significantly associated with more methylation of clock genes CRY1 (p = 0.034, R² = 0.16) and CRY2 (p = 0.019, R² = 0.47). More severe depression together with higher levels of IL-8 strongly predicted lower methylation of CLOCK gene (p = 0.009); Conclusions: Different biological abnormalities have been found to be independently associated with BMI and severity of depressive symptoms in women affected by overweight/obesity. The complex interplay between overweight, depression and biological changes will have to be better clarified by future studies.

Assessing effects of oxytocin on alcohol consumption in socially housed prairie voles using radio frequency tracking

Alcohol use disorder affects millions of people each year. Currently approved pharmacotherapies have limited success in treating this disorder. Evidence suggests that this lack of success is partly due to how these pharmacotherapies are tested in preclinical settings. The vast majority of preclinical studies assessing the effects of pharmacotherapies on alcohol or drug self-administration are done in individually housed animals. However, it is known that alcohol and drug intake are heavily influenced by social settings. Here, we adapted radio frequency tracking technology to determine the effects of oxytocin, a potential therapy for alcohol use disorder, on alcohol consumption in socially housed male and female prairie voles. Voluntary alcohol consumption in these animals resulted in high daily alcohol intakes, blood ethanol concentrations that are considered intoxicating, and central changes in FosB immunoreactivity, indicative of changes in neural activity. Prairie voles that received oxytocin temporarily reduced alcohol consumption but not alcohol preference, compared with control prairie voles regardless whether their cagemates received a similar treatment or not. Our results demonstrate that oxytocin can decrease consummatory behaviors in the presence of peers that are not receiving this treatment, and therefore, its potential use in clinical trials is warranted. Moreover, effectiveness of other pharmacotherapies in preclinical studies can be tested in mixed-treatment socially housed animals similarly to clinical studies in humans.

Effects of peripheral oxytocin administration on body weight, food intake, adipocytes, and biochemical parameters in peri- and postmenopausal female rats

Recent studies have revealed that the administration of oxytocin has beneficial effects on the regulation of body weight, food intake, and metabolic functions, especially in obese individuals. Obesity is common in women after the menopause and drives many components of metabolic syndrome. Weight gain in menopausal women has been frequently reported. Although obesity and associated metabolic disorders are frequently observed in peri- and postmenopausal women, there are few medical interventions for these conditions. In this study, we evaluated the effects of chronic oxytocin administration on appetite, body weight, and fat mass in peri- and postmenopausal female rats. Sixteen naturally premenopausal or menopausal rats were intraperitoneally injected with oxytocin (1,000 μg/day) for 12 days. The daily changes in their body weight and food intake were measured at the same time as the oxytocin and vehicle injections. Intraperitoneally administering oxytocin for 12 days significantly reduced food intake, body weight, and visceral adipocyte size. In addition, oxytocin administration caused reductions in serum triglyceride and low-density lipoprotein-cholesterol levels, while it did not disturb hepatic or renal functions or locomotor activity. This is the first study to show the effects of oxytocin on the metabolic and feeding functions of peri- and postmenopausal female rats. Oxytocin might be a useful treatment for metabolic disorders caused by the menopause or aging.

Temporal analysis of individual ethanol consumption in socially housed mice and the effects of oxytocin

RATIONALE

The majority of preclinical studies assessing treatments for alcohol use disorder use singly housed animals. Because social factors affect ethanol intake, studies investigating such treatments in group-housed animals are needed.

OBJECTIVES

We investigated the effects of repeated oxytocin treatment on ethanol intake in socially housed male and female C57BL/6J mice.

METHODS

We used the novel "Herdsman" system implementing radiotracking technology to measure individual ethanol intake in group-housed animals. Mice were housed in same-sex groups of 4 per cage and exposed to 3 and 6% ethanol solutions. After baseline drinking was established, half of the animals in each cage received repeated intraperitoneal injections of 3 mg/kg oxytocin.

RESULTS

During baseline, females consumed more ethanol than males partly due to greater number of ethanol drinks taken by females. We also observed a gradual development of two peaks of ethanol consumption during the dark phase of the circadian cycle. The effects of oxytocin treatment were short-acting and varied across treatment days. Oxytocin significantly decreased ethanol intake on three out the four treatment days. On the fourth treatment day, oxytocin decreased ethanol intake and water intake.

CONCLUSION

The greater intake of ethanol in female mice is associated with the number of drinks taken. Oxytocin treatments not only cause an acute decrease in ethanol consumption, but can also change in efficacy over time. While the oxytocin system remains a promising therapeutic target for alcoholism, studies investigating longer periods of repeated oxytocin treatment and those using additional oxytocin receptor agonists are warranted.

The infundibular peptidergic neurons and glia cells in overeating, obesity, and diabetes

Dysfunctional regulation of energy homeostasis results in increased bodyweight and obesity, eventually leading to type 2 diabetes mellitus. The infundibular nucleus (IFN) of the hypothalamus is the main regulator of energy homeostasis. The peptidergic neurons and glia cells of the IFN receive metabolic cues concerning energy state of the body from the circulation. The IFN can monitor hormones like insulin and leptin and nutrients like glucose and fatty acids. All these metabolic cues are integrated into an output signal regulating energy homeostasis through the release of neuropeptides. These neuropeptides are released in several inter- and extrahypothalamic brain regions involved in regulation of energy homeostasis. This review will give an overview of the peripheral signals involved in the regulation of energy homeostasis, the peptidergic neurons and glial cells of the IFN, and will highlight the main intra-hypothalamic projection sites of the IFN.

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.

Oxytocin Administration Increases Proactive Control in Men with Overweight or Obesity: A Randomized, Double-Blind, Placebo-Controlled Crossover Study

OBJECTIVE

Preclinical and clinical evidence suggests that oxytocin administration decreases food intake and weight. The mechanisms underlying the anorexigenic effects of oxytocin in humans are unknown but critical to study to consider oxytocin as a neurohormonal weight loss treatment. Complementing ongoing research into metabolic and food motivation mechanisms of oxytocin, this study hypothesized that in humans, oxytocin improves cognitive control over behavior.

METHODS

In a randomized, double-blind, placebo-controlled crossover study of 24-IU single-dose intranasal oxytocin, 10 men with overweight or obesity completed a stop-signal task assessing ability and strategy to suppress behavioral impulses, in which they performed a choice-reaction task (go task) but had to withhold their response when prompted (stop task). It was hypothesized that oxytocin would improve suppression of behavioral impulses.

RESULTS

After receiving oxytocin, compared with placebo, participants showed increased reaction times in the go task (mean [M] = 936 milliseconds vs. 833 millseconds; P = 0.012; 95% CI: 29 to 178) and displayed fewer stop errors (M = 36.41% vs. 41.15%; P = 0.049; 95% CI: -9.43% to -0.03%).

CONCLUSIONS

Oxytocin triggers increased proactive control over behavior. Future studies need to further characterize the impact of oxytocin on cognitive control and investigate its potential role in the anorexigenic effects of oxytocin in human obesity.

Intranasal oxytocin has sympathoexcitatory effects on vascular tone in healthy males

Oxytocin appears to be involved in the neuroendocrine regulation of sympathetic blood pressure (BP) homeostasis. In animals, intracerebral administration of oxytocin induces BP-relevant sympathetic activation. In humans, central nervous effects of oxytocin on BP regulation remain unclear. Intranasal administration supposedly delivers oligopeptides such as oxytocin directly to the brain. We investigated the effects of intranasal oxytocin on sympathetic vascular baroreflex function in humans using microneurographic techniques. In a balanced, double-blind crossover design, oxytocin or placebo was administered intranasally to 12 lean, healthy males (age 25 ± 4 yr). Muscle sympathetic nerve activity (MSNA) was assessed microneurographically before (presubstance), 30-45 min (postsubstance I), and 105-120 min (postsubstance II) after oxytocin administration. Baroreflex was challenged via graded infusions of vasoactive drugs, and correlation of BP with MSNA and heart rate (HR) defined baroreflex function. Experiments were conducted in the afternoon after a 5-h fasting period. After oxytocin, resting MSNA (burst rate and total activity) showed significant net increases from pre to postsubstance II compared with placebo [Δincrease = +4.3 ± 1.2 (oxytocin) vs. +2.2 ± 1.4 bursts/min (placebo), ANOVA; P < 0.05; total activity = 184 ± 11.5% (oxytocin) vs. 121 ± 14.3% (placebo), ANOVA; P = 0.01). This was combined with a small but significant net increase in resting diastolic BP, whereas systolic and mean arterial BP or HR as well as baroreflex sensitivity at vasoactive drug challenge were not altered. Intranasally administered oxytocin induced vasoconstrictory sympathoactivation in healthy male humans. The concomitant increase of diastolic BP was most likely attributable to increased vascular tone. This suggests oxytocin-mediated upward resetting of the vascular baroreflex set point at centers superordinate to the mere baroreflex-feedback loop.

Unchanged food approach-avoidance behaviour of healthy men after oxytocin administration

The oxytocinergic system has been assumed to contribute to food intake, possibly via interactions with dopamine. However, so far, it is unknown whether oxytocin influences the underlying motivational behaviour towards food. In the present study, we used a food-based approach-avoidance task (AAT) in a randomised, placebo-controlled, double-blind, cross-over design to compare intranasal oxytocin with a placebo. In the AAT, participants pushed or pulled a joystick when images of foods with a high or low craving rating were presented, where differences in response times typically reflect approach and avoidance motivational biases towards positively and negatively valence stimuli, respectively. Thirty-three healthy male participants (age = 25.12 ± 3.51 years; body mass index = 24.25 ± 2.48 kg/m² ) completed the two-session study, one with placebo and the other with oxytocin. We used mixed-effects models to investigate effects of treatment (oxytocin, placebo), response type (approach, avoid) and stimulus (high, low craving). The results showed that both approach and avoid responses tended to be faster for foods higher in craving compared to foods lower in craving. Most importantly, we did not observe any significant effects of oxytocin compared to placebo in motivational behaviour towards food. Our study demonstrates a general response bias towards foods with different craving values, which could have implications for future studies investigating food-related behaviour. We discuss possible explanations for the null effects of oxytocin and suggest further investigation of the relationship between oxytocin, dopamine and food-reward processing.