The interface of oxytocin-labeled cells and serotonin transporter-containing fibers in the primate hypothalamus: a substrate for SSRIs therapeutic effects?

Schizophrenia and alcohol dependence: diverse clinical effects of oxytocin and their evolutionary origins

Beginning in 1979 with the first report that central administration of oxytocin stimulates maternal behavior in virgin rats, decades of animal research and more recent human studies have demonstrated that oxytocin has many pro-social effects. These many findings suggest that oxytocin may be an effective treatment for social deficits that are hallmark features of disorders such as autism and schizophrenia. Effects in preclinical animal models also imply that oxytocin may be an efficacious pharmacotherapy in a wide range of psychiatric disorders including psychoses and addictions. To date, 3 small clinical trials found that daily intranasal oxytocin treatment for 2-8 weeks significantly reduced psychotic symptoms in schizophrenia. Two of these trials also found improvement in social cognition or neurocognition, areas in which patients have significant deficiencies that do not respond to conventional antipsychotic treatment and contribute to disability. In another small trial, intranasal oxytocin potently blocked alcohol withdrawal. After reviewing the rationale for these trials, they are described in more detail. Questions are then asked followed by discussions of the large gaps in our knowledge about brain oxytocin systems in humans. The hope is to highlight important directions for future investigations of the role of oxytocin in the pathophysiology of psychotic disorders and addictions and to extend clinical research in these areas. Heretofore unrecognized roles for which oxytocin may have been selected during the evolution of placental mammalian maternal-infant and other social attachments are considered as possible origins of oxytocin antipsychotic and antiaddiction effects.This article is part of a Special Issue entitled Oxytocin and Social Behav.

Plasma oxytocin changes and anti-obsessive response during serotonin reuptake inhibitor treatment: a placebo controlled study

BACKGROUND

The drug treatments of choice for obsessive-compulsive disorder (OCD) are serotonin reuptake inhibitors (SRIs). However, a correlation between the neuropeptide oxytocin in cerebrospinal fluid and the severity of OCD has previously been shown, and oxytocin and serotonin are interconnected within the brain. Few studies have investigated whether SRIs have any effect on oxytocin; thus, our aim was to explore the possibility that oxytocinergic mechanisms contribute to the anti-obsessive effect of SRIs.

METHOD

In a randomized, double-blind trial, comparing SRIs (clomipramine and paroxetine) with placebo in 36 adults with OCD (characterized for subtypes), plasma oxytocin was measured with radioimmunoassay after plasma extraction, at baseline, after 1 week, and after 4 weeks of treatment, and related to baseline severity and clinical response after 12 weeks, as measured by the Yale-Brown Obsessive Compulsive Scale (Y-BOCS).

RESULTS

Baseline oxytocin levels correlated positively with baseline Y-BOCS ratings, but only among the future SRI responders. Patients with early onset of OCD had higher baseline oxytocin. During treatment, plasma oxytocin did not differ between SRI and placebo treatment. In SRI responders, plasma oxytocin first decreased and then increased; in non-responders (to SRI as well as to placebo), the reverse was the case. After 4 weeks, treatment responders had attained higher oxytocin levels compared to non-responders. The intra-individual range (i.e., the variability) of plasma oxytocin between measurements was the measure that best differentiated responders from non-responders. This range was higher in responders than non-responders, and lower in patients with autistic traits.

CONCLUSIONS

SRIs have highly variable effects on plasma oxytocin between individuals. The associations between baseline oxytocin and OCD severity and between oxytocin changes and treatment response support the notions that oxytocin is involved in OCD pathophysiology, and that the anti-obsessive effects of SRIs are partly exerted through oxytocinergic mechanisms.

The social brain: neurobiological basis of affiliative behaviours and psychological well-being

The social brain hypothesis proposes that the demands of the social environment provided the evolutionary pressure that led to the expansion of the primate brain. Consistent with this notion, that functioning in the social world is crucial to our survival, while close supportive relationships are known to enhance well-being, a range of social stressors such as abuse, discrimination and dysfunctional relationships can increase the risk of psychiatric disorders. The centrality of the social world to our everyday lives is further exemplified by the fact that abnormality in social behaviour is a salient feature of a range of neurodevelopmental and psychiatric disorders. This paper aims to provide a selective overview of current knowledge of the neurobiological basis of our ability to form and maintain close personal relationships, and of the benefits these relationships confer on our health. Focusing on neurochemical and neuroendocrine interactions within affective and motivational neural circuits, it highlights the specific importance of cutaneous somatosensation in affiliative behaviours and psychological well-being and reviews evidence, in support of the hypothesis, that a class of cutaneous unmyelinated, low threshold mechanosensitive nerves, named c-tactile afferents, have a direct and specific role in processing affiliative tactile stimuli.

Oxytocin and postpartum depression: delivering on what's known and what's not

The role of oxytocin in the treatment of postpartum depression has been a topic of growing interest. This subject carries important implications, given that postpartum depression can have detrimental effects on both the mother and her infant, with lifelong consequences for infant socioemotional and cognitive development. In recent years, oxytocin has received attention for its potential role in many neuropsychiatric conditions beyond its well-described functions in childbirth and lactation. In the present review, we present available data on the clinical characteristics and neuroendocrine foundations of postpartum depression. We outline current treatment modalities and their limitations, and proceed to evaluate the potential role of oxytocin in the treatment of postpartum depression. The aim of the present review is twofold: (a) to bring together evidence from animal and human research concerning the role of oxytocin in postpartum depression, and (b) to highlight areas that deserve further research in order to bring a fuller understanding of oxytocin's therapeutic potential. This article is part of a Special Issue entitled Oxytocin and Social Behav.

Acute responsivity of the serotonergic system to S-citalopram and positive emotionality-the moderating role of the 5-HTTLPR

According to the idea that the central serotonergic system has a modulatory function on behavior and personality in general, we aimed to highlight its association to habitual positive emotionality. In a placebo-controlled double-blind and randomized cross-over neuroendocrine challenge design (n = 72 healthy males) we investigated the association of the central serotonergic responsivity, 5-HTTLPR-genotype as well as their combined effects on positive emotionality. Regression analyses revealed an involvement of the serotonergic system in positive emotionality. There was, however, no direct association between positive emotionality and cortisol responses to S-citalopram; rather 5-HTTLPR-genotype showed an association (p < 0.05). That is, positive emotionality scores increased with the number of s-alleles carried by the individuals. Most notable was the moderating role of 5-HTTLPR-genotype (p < 0.05) on the association between acute serotonergic responsivity and positive emotionality. Indeed, this association was only found in ss-homozygotes, in which the acute responsivity of the serotonergic system additionally seems to contribute to the level of positive emotionality (r = 0.70, p < 0.05). The findings correspond to previous research demonstrating that the 5-HTTLPR is not only involved in the negative-emotional aspects of behavior and temperament, but is associated, moreover, with positive affectivity-supporting the assumption of its valence-neutrality. In addition, our data are in line with the idea of possible influences of the 5-HTTLPR-genotype on early neuronal development. They also indicate the need for further studies in order to clearly elucidate the role of the serotonergic system and its subcomponents in the regulation of positive emotionality.

Effects of selective serotonin reuptake inhibitor treatment on plasma oxytocin and cortisol in major depressive disorder

BACKGROUND

Oxytocin is known for its capacity to facilitate social bonding, reduce anxiety and for its actions on the stress hypothalamopituitary adrenal (HPA) axis. Since oxytocin can physiologically suppress activity of the HPA axis, clinical applications of this neuropeptide have been proposed in conditions where the function of the HPA axis is dysregulated. One such condition is major depressive disorder (MDD). Dysregulation of the HPA system is the most prominent endocrine change seen with MDD, and normalizing the HPA axis is one of the major targets of recent treatments. The potential clinical application of oxytocin in MDD requires improved understanding of its relationship to the symptoms and underlying pathophysiology of MDD. Previous research has investigated potential correlations between oxytocin and symptoms of MDD, including a link between oxytocin and treatment related symptom reduction. The outcomes of studies investigating whether antidepressive treatment (pharmacological and non-pharmacological) influences oxytocin concentrations in MDD, have produced conflicting outcomes. These outcomes suggest the need for an investigation of the influence of a single treatment class on oxytocin concentrations, to determine whether there is a relationship between oxytocin, the HPA axis (e.g., oxytocin and cortisol) and MDD. Our objective was to measure oxytocin and cortisol in patients with MDD before and following treatment with selective serotonin reuptake inhibitors, SSRI.

METHOD

We sampled blood from arterial plasma. Patients with MDD were studied at the same time twice; pre- and post- 12 weeks treatment, in an unblinded sequential design (clinicaltrials.govNCT00168493).

RESULTS

Results did not reveal differences in oxytocin or cortisol concentrations before relative to following SSRI treatment, and there were no significant relationships between oxytocin and cortisol, or these two physiological variables and psychological symptom scores, before or after treatment.

CONCLUSIONS

These outcomes demonstrate that symptoms of MDD were reduced following effective treatment with an SSRI, and further, stress physiology was unlikely to be a key factor in this outcome. Further research is required to discriminate potential differences in underlying stress physiology for individuals with MDD who respond to antidepressant treatment, relative to those who experience treatment resistance.

Imaging of serotonin transporters with [123I]FP-CIT SPECT in the human hypothalamus

BACKGROUND

Serotonergic neurons in the rodent hypothalamus are implicated in key neuroendocrine and metabolic functions, including circadian rhythmicity. However, the assessment of the serotonergic system in the human hypothalamus in vivo is difficult as delineation of the hypothalamus is cumbersome with conventional region-of-interest analysis. In the present study, we aimed to develop a method to visualize serotonin transporters (SERT) in the hypothalamus. Additionally, we tested the hypothesis that hypothalamic SERT binding ratios are different between patients with hypothalamic impairment (HI), pituitary insufficiency (PI), and control subjects (C).

METHODS

SERT availability was determined in 17 subjects (6 HI, 5 PI, and 6 healthy controls), 2 h after injection of 123I-N-ω-fluoropropyl-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane ([123I]FP-CIT), using single-photon emission computed tomography (performed on a brain-dedicated system) fused with individual magnetic resonance imaging (MRI) scans of the brain. The hypothalamus (representing specific SERT binding) and cerebellum (representing nonspecific binding) were manually delineated on each MRI to assess [123I]FP-CIT binding and specific-to-nonspecific binding ratios.

RESULTS

In each healthy subject, [123I]FP-CIT binding was higher in the hypothalamus than in the cerebellum, and the mean hypothalamic binding ratio of SERT was 0.29 ± 0.23. We found no difference in hypothalamic binding ratios between HI, PI, and control subjects (HI 0.16 ± 0.24, PI 0.45 ± 0.39, C 0.29 ± 0.23, p value 0.281).

CONCLUSIONS

We were able to demonstrate SERT binding in the human hypothalamus in vivo. However, we did not find altered hypothalamic SERT binding in patients with hypothalamic impairment.

TRIAL REGISTRATION

Netherlands Trial Register: NTR2520.

Brain region-specific transcriptomic markers of serotonin-1A receptor agonist action mediating sexual rejection and aggression in female marmoset monkeys

INTRODUCTION

In a marmoset model of hypoactive female sexual function, we have shown that repeated administration of the serotonin (5-HT)-1A agonist R-(+)-8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT) inhibits sexual receptivity in female marmoset monkeys and increases aggression toward the male pairmate.

AIM

The aims of this study are to investigate gene expression changes induced by 8-OH-DPAT in laser-microdissected brain areas that regulate female sexual function and to identify genes, functional gene classes, and pathways associated with 8-OH-DPAT-mediated inhibition of female sexual receptivity.

METHODS

Gene expression was measured in the medial prefrontal cortex (mPFC), medial preoptic area (mPOA), cornu ammonis-1 (CA1) area of the hippocampus (CA1), and dorsal raphé nucleus (DRN) of four 8-OH-DPAT-treated (0.1 mg/kg; daily administration for 16 weeks) and four vehicle-treated female marmosets using a marmoset-specific microarray (European Marmoset Microarray [EUMAMA]) and validated by real-time quantitative polymerase chain reaction (RTqPCR). Enriched functional gene classes were determined. In a parallel candidate gene approach, the expression of serotonergic candidate genes, i.e., the 5-HT1A, 5-HT2A, and 5-HT7 receptors and the 5-HT transporter (5-HTT), was measured by RTqPCR.

MAIN OUTCOME MEASURES

The main outcome is the differential expression of genes between 8-OH-DPAT- and vehicle-treated marmosets.

RESULTS

8-OH-DPAT affected the gene classes important to neural development (mPFC, mPOA, and DRN), neurotransmission (mPOA), energy production (mPFC and mPOA), learning and memory (CA1), and intracellular signal transduction (DRN). Oxytocin (OXT) in the mPOA and 5-HTT in the DRN were strongly increased by 8-OH-DPAT. 5-HT1A tended to increase in the mPFC, while 5-HT7 was decreased in the CA1.

CONCLUSIONS

Brain region-specific alterations of gene expression regulating neural circuitries, energy demands, and learning processes are associated with 8-OH-DPAT-induced decrease in female sexual receptivity and increase in pairmate aggression. The role of OXT in the serotonergic regulation of female sexual behavior and partner interactions warrants attention in future studies.

Novel oxytocin gene expression in the hindbrain is induced by alcohol exposure: transgenic zebrafish enable visualization of sensitive neurons

BACKGROUND

Fetal Alcohol Spectrum Disorders (FASD) are a collection of disorders resulting from fetal ethanol exposure, which causes a wide range of physical, neurological and behavioral deficits including heightened susceptibility for alcoholism and addictive disorders. While a number of mechanisms have been proposed for how ethanol exposure disrupts brain development, with selective groups of neurons undergoing reduced proliferation, dysfunction and death, the induction of a new neurotransmitter phenotype by ethanol exposure has not yet been reported.

PRINCIPAL FINDINGS

The effects of embryonic and larval ethanol exposure on brain development were visually monitored using transgenic zebrafish expressing cell-specific green fluorescent protein (GFP) marker genes. Specific subsets of GFP-expressing neurons were highly sensitive to ethanol exposure, but only during defined developmental windows. In the med12 mutant, which affects the Mediator co-activator complex component Med12, exposure to lower concentrations of ethanol was sufficient to reduce GFP expression in transgenic embryos. In transgenic embryos and larva containing GFP driven by an oxytocin-like (oxtl) promoter, ethanol exposure dramatically up-regulated GFP expression in a small group of hindbrain neurons, while having no effect on expression in the neuroendocrine preoptic area.

CONCLUSIONS

Alcohol exposure during limited embryonic periods impedes the development of specific, identifiable groups of neurons, and the med12 mutation sensitizes these neurons to the deleterious effects of ethanol. In contrast, ethanol exposure induces oxtl expression in the hindbrain, a finding with profound implications for understanding alcoholism and other addictive disorders.

Balance of brain oxytocin and vasopressin: implications for anxiety, depression, and social behaviors

Oxytocin and vasopressin are regulators of anxiety, stress-coping, and sociality. They are released within hypothalamic and limbic areas from dendrites, axons, and perikarya independently of, or coordinated with, secretion from neurohypophysial terminals. Central oxytocin exerts anxiolytic and antidepressive effects, whereas vasopressin tends to show anxiogenic and depressive actions. Evidence from pharmacological and genetic association studies confirms their involvement in individual variation of emotional traits extending to psychopathology. Based on their opposing effects on emotional behaviors, we propose that a balanced activity of both brain neuropeptide systems is important for appropriate emotional behaviors. Shifting the balance between the neuropeptide systems towards oxytocin, by positive social stimuli and/or psychopharmacotherapy, may help to improve emotional behaviors and reinstate mental health.

A link between oxytocin and serotonin in humans: supporting evidence from peripheral markers

Pharmacological studies indicate a functional interaction between the serotonergic and oxytocinergic systems. In particular, some selective serotonin (5-HT) reuptake inhibitors, such as citalopram and fluvoxamine, seem to exert part of their antidepressant effects through oxytocin (OT) release. Further, the administration of fenfluramine, a serotonergic agonist, to healthy subjects increases plasma OT levels. Interestingly, immunocytochemical and double-immunofluorescent techniques revealed a high degree of overlap between 5-HT transporter (SERT)-labeled fibers and OT-containing cells in the paraventricular and supraoptic nuclei of primate hypothalamus. These findings suggest that the influence of 5-HT on OT system might be mediated by SERT. In this study, we explored the possible existence of a link between OT and SERT in human subjects, by means of two peripheral markers, the platelet SERT, as measured by [³H]-paroxetine ([³H]-Par) binding, and plasma OT levels. As far as [³H]-Par binding parameters are concerned, the Bmax (mean ± SD, fmol/mg protein) was 1155 + 130 and the Kd (mean ± SD, nM) was 1.31 ± 0.61. The OT plasma levels (mean ± SD, pg/ml) were 1.14 ± 1.07. A significant and positive correlation was found between plasma OT levels and Kd values (correlation coefficient: r: 0.466, p = .038). This result represents the first evidence of an interaction between OT and SERT, as measured by [³H]-Par binding, at peripheral levels in humans. Given the several activities mediated by both OT and 5-HT, such a relationship might provide new perspectives and insights into psychiatric disorders and/or social relationship disturbances, as well as novel treatment strategies overcoming and/or integrating the serotonergic paradigm.

Examining autism spectrum disorders by biomarkers: example from the oxytocin and serotonin systems

OBJECTIVE

Autism spectrum disorder (ASD) is a heritable but highly heterogeneous neuropsychiatric syndrome, which poses challenges for research relying solely on behavioral symptoms or diagnosis. Examining biomarkers may give us ways to identify individuals who demonstrate specific developmental trajectories and etiological factors related to ASD. Plasma oxytocin (OT) and whole-blood serotonin (5-HT) levels are consistently altered in some individuals with ASD. Reciprocal relationships have been described between brain oxytocin and serotonin systems during development. We therefore investigated the relationship between these peripheral biomarkers as well as their relationships with age.

METHOD

In our first study, we analyzed correlations between these two biomarkers in 31 children and adolescents who were diagnosed with autism and were not on medications. In our second study, we explored whether whole-blood 5-HT levels are altered in mice lacking the oxytocin receptor gene Oxtr.

RESULTS

In humans, OT and 5-HT were negatively correlated with each other (p < .05) and this relationship was most prominent in children less than 11 years old. Paralleling human findings, mice lacking Oxtr showed increased whole-blood 5-HT levels (p = .05), with this effect driven exclusively by mice less than 4 months old (p < .01).

CONCLUSIONS

Identifying relationships between identified ASD biomarkers may be a useful approach to connect otherwise disparate findings that span multiple systems in this heterogeneous disorder. Using neurochemical biomarkers to perform parallel studies in animal and human populations within a developmental context is a plausible approach to probe the root causes of ASD and to identify potential interventions.

Oxytocin in schizophrenia: a review of evidence for its therapeutic effects

BACKGROUND

The suggestion that the neurohormone oxytocin may have clinical application in the treatment of schizophrenia was first published in 1972. Since then, a considerable body of research on a variety of fronts--including several recent double-blind treatment trials-has buttressed these early reports, providing support for the assertion that the oxytocin system is a promising and novel therapeutic target for this devastating malady. Herein, we review the diverse, convergent lines of evidence supporting the therapeutic potential of oxytocin in psychotic illness.

METHODS

We performed a systematic review of preclinical and clinical literature pertaining to oxytocin's role in schizophrenia.

RESULTS

Multiple lines of evidence converge to support the antipsychotic potential of oxytocin. These include several animal models of schizophrenia, pharmacological studies examining the impact of antipsychotics on the oxytocin system, human trials in patients examining aspects of the oxytocin system, and several double-blind, placebo-controlled clinical treatment trials.

CONCLUSIONS

There exists considerable, convergent evidence that oxytocin has potential as a novel antipsychotic with a unique mechanism of action. Auspiciously, based on the few chronic trials to date, its safety profile and tolerability appear very good. That said, several critical clinical questions await investigation before widespread use is clinically warranted.

Breaking the loop: oxytocin as a potential treatment for drug addiction

Drug use typically occurs within a social context, and social factors play an important role in the initiation, maintenance and recovery from addictions. There is now accumulating evidence of an interaction between the neural substrates of affiliative behavior and those of drug reward, with a role for brain oxytocin systems in modulating acute and long-term drug effects. Early research in this field indicated that exogenous oxytocin administration can prevent development of tolerance to ethanol and opiates, the induction of stereotyped, hyperactive behavior by stimulants, and the withdrawal symptoms associated with sudden abstinence from drugs and alcohol. Additionally, stimulation of endogenous oxytocin systems is a key neurochemical substrate underlying the prosocial and empathogenic effects of party drugs such as MDMA (Ecstasy) and GHB (Fantasy). Brain oxytocin systems exhibit profound neuroplasticity and undergo major neuroadaptations as a result of drug exposure. Many drugs, including cocaine, opiates, alcohol, cannabis, MDMA and GHB cause long-term changes in markers of oxytocin function and this may be linked to enduring deficits in social behavior that are commonly observed in laboratory animals repeatedly exposed to these drugs. Very recent preclinical studies have illustrated a remarkable ability of exogenously delivered oxytocin to inhibit stimulant and alcohol self-administration, to alter associated drug-induced changes in dopamine, glutamate and Fos expression in cortical and basal ganglia sites, and to prevent stress and priming-induced relapse to drug seeking. Oxytocin therefore has fascinating potential to reverse the corrosive effects of long-term drugs abuse on social behavior and to perhaps inoculate against future vulnerability to addictive disorders. The results of clinical studies examining intranasal oxytocin effects in humans with drug use disorders are eagerly awaited. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Differential serotonin transport is linked to the rh5-HTTLPR in peripheral blood cells

The human serotonin transporter (SERT) gene possesses a 43-base pair (bp) insertion-deletion promoter polymorphism, the h5-HTTLPR. Genotype at this locus correlates with variation in anxiety-related personality traits and risk for major depressive disorder in many studies. Yet, the complex effects of the h5-HTTLPR, in combination with closely associated single-nucleotide polymorphisms (SNPs), continue to be debated. Moreover, although SERT is of high clinical significance, transporter function in vivo remains difficult to assess. Rhesus express a promoter polymorphism related to the h5-HTTLPR. The rh5-HTTLPR has been linked to differences in stress-related behavior and cognitive flexibility, although allelic variations in serotonin uptake have not been investigated. We studied the serotonin system as it relates to the 5-HTTLPR in rhesus peripheral blood cells. Sequencing of the rh5-HTTLPR revealed a 23-bp insertion, which is somewhat longer than originally reported. Consistent with previous reports, no SNPs in the rh5-HTTLPR and surrounding genomic regions were detected in the individuals studied. Reductions in serotonin uptake rates, cell surface SERT binding, and 5-hydroxyindoleacetic acid/serotonin ratios, but not SERT mRNA levels, were associated with the rh5-HTTLPR short allele. Thus, serotonin uptake rates are differentiable with respect to the 5-HTTLPR in an easily accessible native peripheral tissue. In light of these findings, we foresee that primary blood cells, in combination with high sensitivity functional measurements enabled by chronoamperometry, will be important for investigating alterations in serotonin uptake associated with genetic variability and antidepressant responsiveness in humans.

MDMA-induced c-Fos expression in oxytocin-containing neurons is blocked by pretreatment with the 5-HT-1A receptor antagonist WAY 100635

The popular party drug MDMA (3,4-methylenedioxymethamphetamine, "Ecstasy") increases sociability in both humans and laboratory animals. Recent research suggests that these prosocial effects may involve serotonin (5-HT)-stimulated hypothalamic release of the neuropeptide oxytocin. WAY 100635, a 5-HT(1A) receptor antagonist, prevents MDMA-induced increases in plasma oxytocin and also reduces MDMA-mediated increases in social interaction in rats. The present study used c-Fos immunohistochemistry to determine the possible role of 5-HT(1A) receptors in MDMA-mediated activation of oxytocin synthesizing neurons. Male Wistar rats (n=8/group) were administered MDMA (10 mg/kg, i.p.) with or without WAY 100635 (1 mg/kg, i.p.) pre-treatment and c-Fos expression was then assessed throughout the brain. MDMA significantly increased locomotor activity and this effect was partly prevented by WAY 100635, in agreement with previous studies. WAY 100635 significantly reduced MDMA-induced c-Fos expression in a subset of brain regions examined. A particularly prominent reduction was seen in the oxytocin-positive neurons of the supraoptic nucleus and paraventricular hypothalamus, with more modest reductions in the Islands of Calleja, median preoptic nucleus, somatosensory cortex and nucleus of the solitary tract. WAY 100635 did not alter MDMA-induced c-Fos expression in the striatum, thalamus, or central amygdala. These results indicate that MDMA's action on oxytocin producing cells in the hypothalamus is mediated through 5-HT(1A) receptors and that certain specific cortical, limbic and brainstem sites are also activated by MDMA via these receptors.

Interaction of 5-HTTLPR and a variation on the oxytocin receptor gene influences negative emotionality

BACKGROUND

Pharmacological studies indicate a functional interaction between the serotonergic and oxytocinergic system.

METHODS

This study tested for an interaction of the prominent serotonin transporter polymorphism (SLC6A4) and an oxytocin receptor gene variation on individual differences in negative emotionality in healthy Caucasians (n = 750).

RESULTS

Participants carrying both the homozygous LL-variant of the serotonin transporter polymorphism and the TT variant of the single nucleotide polymorphism rs2268498 on the oxytocin receptor gene showed lowest scores on the personality dimensions Fear and Sadness of the Affective Neuroscience Personality Scales, as well as on an underlying factor Negative Emotionality.

CONCLUSIONS

The observed interaction effect provides converging evidence from human molecular genetics that serotonergic and oxytocinergic neurotransmission are entwined and play a crucial role for human personality with implications for affective disorders.

No association between oxytocin or prolactin gene variants and childhood-onset mood disorders

BACKGROUND

Oxytocin (OXT) and prolactin (PRL) are neuropeptide hormones that interact with the serotonin system and are involved in the stress response and social affiliation. In human studies, serum OXT and PRL levels have been associated with depression and related phenotypes. Our purpose was to determine if single nucleotide polymorphisms (SNPs) at the loci for OXT, PRL and their receptors, OXTR and PRLR, were associated with childhood-onset mood disorders (COMD).

METHODS

Using 678 families in a family-based association design, we genotyped 16 SNPs at OXT, PRL, OXTR and PRLR to test for association with COMD.

RESULTS

No significant associations were found for SNPs in the OXTR, PRL, or PRLR genes. Two of three SNPs 3' of the OXT gene were associated with COMD (p≤0.02), significant after spectral decomposition, but were not significant after additionally correcting for the number of genes tested. Supplementary analyses of parent-of-origin and proband sex effects for OXT SNPs by Fisher's Exact test were not significant after Bonferroni correction.

CONCLUSIONS

We have examined 16 OXT and PRL system gene variants, with no evidence of statistically significant association after correction for multiple tests.

Oxytocin and Major Depressive Disorder: Experimental and Clinical Evidence for Links to Aetiology and Possible Treatment

Affective disorders represent the most common psychiatric diseases, with substantial co-morbidity existing between major depressive disorders (MDD) and anxiety disorders. The lack of truly novel acting compounds has led to non-monoaminergic based research and hypotheses in recent years. The large number of brain neuropeptides, characterized by discrete synthesis sites and multiple receptors, represent likely research candidates for novel therapeutic targets. The present review summarises the available preclinical and human evidence regarding the neuropeptide, oxytocin, and its implications in the aetiology and treatment of MDD. While the evidence is not conclusive at present additional studies are warranted to determine whether OXT may be of therapeutic benefit in subsets of MDD patients such as those with comorbid anxiety symptoms and low levels of social attachment.

Serum oxytocin levels in patients with depression and the effects of gender and antidepressant treatment

Abnormalities in the neurohypophyseal system have been reported in depression. This study aimed to investigate serum oxytocin levels in patients with depression and the effects of gender and antidepressant treatment on these levels. Serum oxytocin levels were measured before and after treatment with antidepressant drugs or electroconvulsive therapy (ECT) in 40 inpatients (30 women, 10 men) who met the DSM-IV criteria for major depressive disorder (n=29) or bipolar affective disorder depressive episode (n=11), and in 32 healthy controls (20 women, 12 men). Serum oxytocin levels were decreased both pre-treatment and post-treatment in the patients compared with those in the controls. Serum oxytocin levels were not affected by antidepressant drug treatment or ECT. The female patients had significantly lower oxytocin levels than the control females, whereas no difference was found between the male patients and the male controls. We found no difference in serum levels of oxytocin between the unipolar and bipolar depressive patients. Our result shows reduced oxytocin in depression and a gender difference in oxytocin levels. Furthermore, antidepressant treatments appear to have no effect on serum oxytocin levels.

Oxytocin enhances processing of positive versus negative emotional information in healthy male volunteers

Animal studies have shown the role of oxytocin in affiliation and attachment, and recent evidence suggests that oxytocin is also involved in human models of approach behaviour, possibly by modulating the processing of emotionally valenced stimuli. Although oxytocin administration has been reported to decrease neural responses to facial emotional information, the effects on a wider range of behavioural measures of emotional processing shown to be sensitive to antidepressant manipulation have not been examined. The aim of this study was to investigate whether intranasally administered oxytocin affects the processing of positive and negative affective information in healthy male volunteers across tasks measuring attention, perception and memory. Twenty-nine male healthy volunteers were randomly allocated to receive a single dose of oxytocin nasal spray (24 UI) or placebo. 50 min later, participants completed a battery of psychological tests measuring emotional processing. A single dose of intranasally administered oxytocin slowed reaction time to correctly identify fearful facial expressions and reduced the misclassification of positive emotions as negative ones. These effects occurred in the absence of significant differences in subjective ratings of mood and anxiety. These results suggest that oxytocin modulates emotion processing in healthy male volunteers. This action may contribute to the emerging role of the neuropeptide in promoting affiliative and approach behaviours by reducing the salience of potentially ambiguous and threatening social stimuli.

Evidence that oxytocin exerts anxiolytic effects via oxytocin receptor expressed in serotonergic neurons in mice

The oxytocin receptor has been implicated in the regulation of reproductive physiology as well as social and emotional behaviors. The neurochemical mechanisms by which oxytocin receptor modulates social and emotional behavior remains elusive, in part because of a lack of sensitive and selective antibodies for cellular localization. To more precisely characterize oxytocin receptor-expressing neurons within the brain, we generated an oxytocin receptor-reporter mouse in which part of the oxytocin receptor gene was replaced with Venus cDNA (a variant of yellow fluorescent protein). Examination of the Venus expression revealed that, in the raphe nuclei, about one-half of tryptophan hydroxylase-immunoreactive neurons were positive for Venus, suggesting a potential role for oxytocin in the modulation of serotonin release. Oxytocin infusion facilitated serotonin release within the median raphe nucleus and reduced anxiety-related behavior. Infusion of a 5-HT(2A/2C) receptor antagonist blocked the anxiolytic effect of oxytocin, suggesting that oxytocin receptor activation in serotonergic neurons mediates the anxiolytic effects of oxytocin. This is the first demonstration that oxytocin may regulate serotonin release and exert anxiolytic effects via direct activation of oxytocin receptor expressed in serotonergic neurons of the raphe nuclei. These results also have important implications for psychiatric disorders such as autism and depression in which both the oxytocin and serotonin systems have been implicated.

From ultrasocial to antisocial: a role for oxytocin in the acute reinforcing effects and long-term adverse consequences of drug use?

Addictive drugs can profoundly affect social behaviour both acutely and in the long-term. Effects range from the artificial sociability imbued by various intoxicating agents to the depressed and socially withdrawn state frequently observed in chronic drug users. Understanding such effects is of great potential significance in addiction neurobiology. In this review we focus on the 'social neuropeptide' oxytocin and its possible role in acute and long-term effects of commonly used drugs. Oxytocin regulates social affiliation and social recognition in many species and modulates anxiety, mood and aggression. Recent evidence suggests that popular party drugs such as MDMA and gamma-hydroxybutyrate (GHB) may preferentially activate brain oxytocin systems to produce their characteristic prosocial and prosexual effects. Oxytocin interacts with the mesolimbic dopamine system to facilitate sexual and social behaviour, and this oxytocin-dopamine interaction may also influence the acquisition and expression of drug-seeking behaviour. An increasing body of evidence from animal models suggests that even brief exposure to drugs such as MDMA, cannabinoids, methamphetamine and phencyclidine can cause long lasting deficits in social behaviour. We discuss preliminary evidence that these adverse effects may reflect long-term neuroadaptations in brain oxytocin systems. Laboratory studies and preliminary clinical studies also indicate that raising brain oxytocin levels may ameliorate acute drug withdrawal symptoms. It is concluded that oxytocin may play an important, yet largely unexplored, role in drug addiction. Greater understanding of this role may ultimately lead to novel therapeutics for addiction that can improve mood and facilitate the recovery of persons with drug use disorders.

Oxytocin receptor (OXTR) and serotonin transporter (5-HTT) genes associated with observed parenting

Both oxytocin and serotonin modulate affiliative responses to partners and offspring. Animal studies suggest a crucial role of oxytocin in mammalian parturition and lactation but also in parenting and social interactions with offspring. The serotonergic system may also be important through its influence on mood and the release of oxytocin. We examined the role of serotonin transporter (5-HTT) and oxytocin receptor (OXTR) genes in explaining differences in sensitive parenting in a community sample of 159 Caucasian, middle-class mothers with their 2-year-old toddlers at risk for externalizing behavior problems, taking into account maternal educational level, maternal depression and the quality of the marital relationship. Independent genetic effects of 5-HTTLPR SCL6A4 and OXTR rs53576 on observed maternal sensitivity were found. Controlling for differences in maternal education, depression and marital discord, parents with the possibly less efficient variants of the serotonergic (5-HTT ss) and oxytonergic (AA/AG) system genes showed lower levels of sensitive responsiveness to their toddlers. Two-way and three-way interactions with marital discord or depression were not significant. This first study on the role of both OXTR and 5-HTT genes in human parenting points to molecular genetic differences that may be implicated in the production of oxytocin explaining differences in sensitive parenting.