Do delivery routes of intranasally administered oxytocin account for observed effects on social cognition and behavior? A two-level model

Accumulating evidence demonstrates the important role of oxytocin (OT) in the modulation of social cognition and behavior. This has led many to suggest that the intranasal administration of OT may benefit psychiatric disorders characterized by social dysfunction, such as autism spectrum disorders and schizophrenia. Here, we review nasal anatomy and OT pathways to central and peripheral destinations, along with the impact of OT delivery to these destinations on social behavior and cognition. The primary goal of this review is to describe how these identified pathways may contribute to mechanisms of OT action on social cognition and behavior (that is, modulation of social information processing, anxiolytic effects, increases in approach-behaviors). We propose a two-level model involving three pathways to account for responses observed in both social cognition and behavior after intranasal OT administration and suggest avenues for future research to advance this research field.     

Species,sex and individual differences in the vasotocin/vasopressin system: Relationship to neurochemical signaling in the social behavior neural network

Arginine-vasotocin (AVT)/arginine vasopressin (AVP) are members of the AVP/oxytocin (OT) superfamily of peptides that are involved in the regulation of social behavior, social cognition and emotion. Comparative studies have revealed that AVT/AVP and their receptors are found throughout the “social behavior neural network (SBNN)” and display the properties expected from a signaling system that controls social behavior (i.e., species, sex and individual differences and modulation by gonadal hormones and social factors). Neurochemical signaling within the SBNN likely involves a complex combination of synaptic mechanisms that co-release multiple chemical signals (e.g., classical neurotransmitters and AVT/AVP as well as other peptides) and non-synaptic mechanisms (i.e., volume transmission). Crosstalk between AVP/OT peptides and receptors within the SBNN is likely. A better understanding of the functional properties of neurochemical signaling in the SBNN will allow for a more refined examination of the relationships between this peptide system and species, sex and individual differences in sociality.     

Quantitative mapping reveals age and sex differences in vasopressin,but not oxytocin,immunoreactivity in the rat social behavior neural network

The neuropeptides vasopressin (AVP) and oxytocin (OT) have been implicated in the regulation of numerous social behaviors in adult and juvenile animals. AVP and OT signaling predominantly occur within a circuit of interconnected brain regions known collectively as the “social behavior neural network” (SBNN). Importantly, AVP and OT signaling within the SBNN has been shown to differentially regulate diverse social behaviors, depending on the age and/or sex of the animal. We hypothesized that variation in the display of these behaviors is due in part to age and sex differences in AVP and OT synthesis within the SBNN. However, a thorough characterization of AVP and OT‐immunoreactive (ir) fibers and cell bodies across age and sex within the SBNN has been lacking in rats. We therefore quantified AVP‐ and OT‐ir fibers and cell bodies in 22 subregions of the forebrain SBNN in juvenile and adult, male and female rats. We found numerous age (16 subregions) and sex (10 subregions) differences in AVP‐ir fiber fractional areas, and AVP‐ir cell body numbers, which were mainly observed in the medial amygdala/bed nucleus of the stria terminalis to lateral septum circuit. In contrast to AVP, we observed no age or sex differences in OT‐ir fiber fractional areas or cell bodies in any of the 22 subregions of the forebrain SBNN. Thus, unlike the static pattern observed for OT, AVP innervation of the forebrain SBNN appears to undergo developmental changes, and is highly sexually dimorphic, which likely has significant functional consequences for the regulation of social behavior.     

Neuropeptide diversity and the regulation of social behavior in New World primates

Oxytocin (OT) and vasopressin (AVP) are important hypothalamic neuropeptides that regulate peripheral physiology, and have emerged as important modulators of brain function, particularly in the social realm. OT structure and the genes that ultimately determine structure are highly conserved among diverse eutherian mammals, but recent discoveries have identified surprising variability in OT and peptide structure in New World monkeys (NWM), with five new OT variants identified to date. This review explores these new findings in light of comparative OT/AVP ligand evolution, documents coevolutionary changes in the oxytocin and vasopressin receptors (OTR and V1aR), and highlights the distribution of neuropeptidergic neurons and receptors in the primate brain. Finally, the behavioral consequences of OT and AVP in regulating NWM sociality are summarized, demonstrating important neuromodulatory effects of these compounds and OT ligand-specific influences in certain social domains.     

Relationships among estrogen receptor, oxytocin and vasopressin gene expression and social interaction in male mice

The incidence of social disorders such as autism and schizophrenia is significantly higher in males, and the presentation more severe, than in females. This suggests the possible contribution of sex hormones to the development of these psychiatric disorders. There is also evidence that these disorders are highly heritable. To contribute toward our understanding of the mechanisms underlying social behaviors, particularly social interaction, we assessed the relationship of social interaction with gene expression for two neuropeptides, oxytocin (OT) and arginine vasopressin (AVP), using adult male mice. Social interaction was positively correlated with: oxytocin receptor (OTR) and vasopressin receptor (V1aR) mRNA expression in the medial amygdala; and OT and AVP mRNA expression in the paraventricular nucleus of the hypothalamus (PVN). When mice representing extremes of social interaction were compared, all of these mRNAs were more highly expressed in high social interaction mice than in low social interaction mice. OTR and V1aR mRNAs were highly correlated with estrogen receptor α (ERα) mRNA in the medial amygdala, and OT and AVP mRNAs with estrogen receptor β (ERβ) mRNA in the PVN, indicating that OT and AVP systems are tightly regulated by estrogen receptors. A significant difference in the level of ERα mRNA in the medial amygdala between high and low social interaction mice was also observed. These results support the hypothesis that variations of estrogen receptor levels are associated with differences in social interaction through the OT and AVP systems, by upregulating gene expression for those peptides and their receptors.     

Role of the neurohypophysis in psychological stress

Effects of different psychological stimuli on oxytocin (OT) and vasopressin (AVP) secretion are reviewed in animals and in humans. The secretion of neuropituitary hormones is also discussed in various psychiatric diseases such an anorexia nervosa, bipolar disorder, schizophrenia and obsessive-compulsive disorder. AVP and OT are secreted into the hypophyseal portal circulation by neurons which project from the paraventricular nucleus to the external zone of the median eminence. AVP and OT-containing neurons in the suprachiasmatic and paraventricular nuclei project to limbic areas, including the hippocampus, the subiculum, the ventral nucleus of the amygdala and the nucleus of the diagonal band. Specific AVP receptors which are pharmacologically different from the pressor and antidiuretic AVP receptors have been found in the anterior pituitary. OT receptors have been identified in a variety of forebrain sites. The neurohypophyseal secretion is regulated by the cholinergic muscarinic, histaminergic and beta-adrenergic systems. Stress alters the secretion of one or more of the hypothalamic factors which interact at the pituitary to increase the secretion of ACTH. AVP and OT have been shown to modulate the effect of Corticotropin-Releasing Factor (CRF) on ACTH secretion and appear to play a key role in mediating the ACTH response to stress. Although AVP is a relatively weak secretagogue for ACTH, it markedly potentiates the activity of CRF both in vitro and in vivo. The role of OT is more complex. In vitro, OT stimulates ACTH release at high doses whereas in human it inhibits ACTH secretion at low doses. The type of stressor appear to determine the relative importance of these secretatogues in ACTH response. Several recent studies indicate that psychological stressors display a similar degree of variety of secretagogue release patterns as was found earlier for physical stressors. A bewildering array of technique produces a bewildering array of conclusions. In rats, OT may be an important secretagogue during a novel stimulus, whereas the role for AVP is less clear. Indeed two studies out of ten suggest a stimulating role for AVP. In response to frustration and submission, OT and AVP are secreted. Regarding social isolation, results are difficult to interpret and the role of AVP could be species-dependent. In contrast plasma OT levels do not change. After restraint, ACTH release is primarily mediated by the active increase of OT and AVP does not appear to play a role. When restraint is associated with moderate levels of physical components and during immobilisation, all two secretagogs are involved in the ACTH response. With fear, ACTH response appears to be driven by OT. In humans, one study indicates that high emotionality women increase plasma OT in response to uncontrollable noise. Various neuroendocrine dysregulations have been observed in psychiatric disease. Either an increase or a decrease of the hypothalamic-pituitary-adrenal (HPA) function have been described in several illnesses. Effects of OT appear to be reciprocal to the effects of AVP. OT has been called the "amnestic" neuropeptide due to its capacity to attenuate memory consolidation and retrieval. AVP exhibits a central activating action on mood, memory and selective attention. Underweight patients with anorexia nervosa have abnormally high levels of centrally directed AVP and reduced OT levels. These modifications could enhance the retention of cognitive distortions of aversive consequences of eating. Patients with bipolar disorder show a biphasic secretion of AVP. Depressive episodes are associated with decreased vasopressinergic activity whereas manic episodes involve an increased release. AVP might be responsible for an increased catecholamine activity. In addition, lithium could act as an antagonist to AVP. In schizophrenic patients, studies using the apomorphine stimulation suggest increased oxytoninergic and decreased vasopressinergic functions. These findings are consistent with the beneficial role of AVP on schizophrenic symptoms noted in several trials. The increased OT could be responsible for "positive" symptomatology such as delusions and hallucinations. Obsessive compulsive disorder (OCD) includes a range of cognitive and behavioral disturbances that could be influenced by OT. In animals, several studies have emphasized the role of AVP in promoting repetitive grooming behaviors and maintaining conditioned response to aversive stimuli. In OCD patients, one study have reported that AVP/OT ratio was negatively correlated with symptom severity. However, an independent report found similar AVP concentrations in OC patients without a personal or family history of tic disorder and in normal subjects. Whether these modifications are only a consequence of the central disturbances or whether those peptides could participate in the pathogenesis of these affections remains to be elucidated.     

Reduced Levels of Vasopressin and Reduced Behavioral Modulation of Oxytocin in Psychotic Disorders

Oxytocin (OT) and arginine vasopressin (AVP) exert robust influence on social affiliation and specific cognitive processes in healthy individuals. Abnormalities in these neuroendocrine systems have been observed in psychotic disorders, but their relation to impairments in behavioral domains that these endocrines modulate is not well understood. We compared abnormalities of OT and AVP serum concentrations in probands with schizophrenia (n = 57), schizoaffective disorder (n = 34), and psychotic bipolar disorder (n = 75); their first-degree relatives without a history of psychosis (n = 61, 43, 91, respectively); and healthy controls (n = 66) and examined their association with emotion processing and cognition. AVP levels were lower in schizophrenia (P = .002) and bipolar probands (P = .03) and in relatives of schizophrenia probands (P = .002) compared with controls. OT levels did not differ between groups. Familiality estimates were robust for OT (h ² = 0.79, P = 3.97e−15) and AVP (h ² = 0.78, P = 3.93e−11). Higher levels of OT were associated with better emotion recognition (β = 0.40, P < .001) and general neuropsychological function (β = 0.26, P = .04) in healthy controls as expected but not in any proband or relative group. In schizophrenia, higher OT levels were related to greater positive symptom severity. The dissociation of OT levels and behavioral function in all proband and relative groups suggests that risk and illness factors associated with psychotic disorders are not related to reduced OT levels but to a disruption in the ability of physiological levels of OT to modulate social cognition and neuropsychological function. Decreased AVP levels may be a marker of biological vulnerability in schizophrenia because alterations were seen in probands and relatives, and familiality was high.Key words: oxytocin, vasopressin, schizophrenia, bipolar disorder, emotion recognition     

Salivary Oxytocin and Vasopressin Levels in Police Officers With and Without Post‐Traumatic Stress Disorder

Post‐traumatic stress disorder (PTSD) is characterised by symptoms associated with maladaptive fear and stress responses, as well as with social detachment. The neuropeptides oxytocin (OT) and arginine vasopressin (AVP) have been associated with both regulating fear and neuroendocrine stress responsiveness and social behaviour. However, there is only limited evidence for dysregulated peripheral OT and AVP levels in PTSD patients. The present study aimed to investigate basal salivary OT and AVP levels in trauma‐exposed male and female police officers with and without PTSD. Saliva samples were collected during rest and OT and AVP levels were determined using a radioimmunoassay. Men and women were analysed separately, having adjusted for differences in trauma history, and for hormonal contraception use in women. The results showed that male PTSD patients had lower basal salivary OT levels, and did not differ in AVP levels compared to male trauma‐exposed healthy controls after adjusting for childhood emotional abuse. There were no significant differences in basal salivary OT and AVP levels in women. Our findings indicate potential dysfunctioning of the OT system in male PTSD patients. Future studies are needed to replicate these findings and to further unravel the relationship between the OT and AVP systems, sex, trauma history and PTSD.     

The social deficits of the oxytocin knockout mouse

Numerous studies have implicated oxytocin (OT) and oxytocin receptors in the central mediation of social cognition and social behavior. Much of our understanding of OT's central effects depends on pharmacological studies with OT agonists and antagonists. Recently, our knowledge of OT's effects has been extended by the development of oxytocin knockout (OTKO) mice. Mice with a null mutation of the OT gene manifest several interesting cognitive and behavioral changes, only some of which were predicted by pharmacological studies. Contrary to studies in rats, mice do not appear to require OT for normal sexual or maternal behavior, though OT is necessary for the milk ejection reflex during lactation. OTKO pups thrive if raised by a lactating female, but OTKO pups emit fewer ultrasonic vocalizations with maternal separation and OTKO adults are more aggressive than WT mice. Remarkably, OTKO mice fail to recognize familiar conspecifics after repeated social encounters, though olfactory and non-social memory functions appear to be intact. Central OT administration into the amygdala restores social recognition. The development of transgenic mice with specific deficits in social memory represents a promising approach to examine the cellular and neural systems of social cognition. These studies may provide valuable new perspectives on diseases characterized by social deficits, such as autism or reactive attachment disorder.     

Effects of intranasal oxytocin and vasopressin on cooperative behavior and associated brain activity in men

The neural mechanisms supporting social bonds between adult men remain uncertain. In this double-blind, placebo-controlled study, we investigate the impact of intranasally administered oxytocin (OT) and vasopressin (AVP) on behavior and brain activity among men in the context of an iterated Prisoner's Dilemma game, which models a real-life social situation. fMRI results show that, relative to both AVP and placebo, OT increases the caudate nucleus response to reciprocated cooperation, which may augment the reward of reciprocated cooperation and/or facilitate learning that another person can be trusted. OT also enhances left amygdala activation in response to reciprocated cooperation. Behaviorally, OT was associated with increased rates of cooperation following unreciprocated cooperation in the previous round compared with AVP. AVP strongly increased cooperation in response to a cooperative gesture by the partner compared with both placebo and OT. In response to reciprocated cooperation, AVP increased activation in a region spanning known vasopressin circuitry implicated in affiliative behaviors in other species. Finally, both OT and AVP increase amygdala functional connectivity with the anterior insula relative to placebo, which may increase the amygdala's ability to elicit visceral somatic markers that guide decision making. These findings extend our knowledge of the neural and behavioral effects of OT and AVP to the context of genuine social interactions.     

Neuroendocrinology of social information processing in rats and mice

We reviewed oxytocin (OT), arginine–vasopressin (AVP) and gonadal hormone involvement in various modes of social information processing in mice and rats. Gonadal hormones regulate OT and AVP mediation of social recognition and social learning. Estrogens foster OT-mediated social recognition and the recognition and avoidance of parasitized conspecifics via estrogen receptor (ER) alpha (ERα) and ERβ. Testosterone and its metabolites, including estrogens, regulate social recognition in males predominantly via the AVP V1a receptor. Both OT and AVP are involved in the social transmission of food preferences and ERα has inhibitory, while ERβ has enhancing, roles. OT also enhances mate copying by females. ERα mediates the sexual, and ERβ the recognition, aspects of the risk-taking enhancing effects of females on males. Thus, androgens and estrogens control social information processing by regulating OT and AVP. This control is finely tuned for different forms of social information processing.     

Central vasopressin and oxytocin receptor distributions in two species of singing mice

The neuropeptides arginine vasopressin (AVP) and oxytocin (OT) are key modulators of vertebrate sociality. Although some general behavioral functions of AVP and OT are broadly conserved, the detailed consequences of peptide release seem to be regulated by species‐specific patterns of receptor distribution. We used autoradiography to characterize central vasopressin 1a receptor (V1aR) and OT receptor (OTR) distributions in two species of singing mice, ecologically specialized Central American rodents with a highly developed form of vocal communication. While both species exhibited high V1aR binding in the auditory thalamus (medial geniculate), binding in structures involved in vocal production (periaqueductal gray and anterior hypothalamus) was significantly higher in the more vocal species, Scotinomys teguina. In S. xerampelinus, receptor binding was significantly higher in a suite of interconnected structures implicated in social and spatial memory, including OTR in the hippocampus and medial amygdala, and V1aR in the anterior and laterodorsal thalamus. This pattern is concordant with species differences in population density and social spacing, which should favor enhanced sociospatial memory in S. xerampelinus. We propose that V1aR and OTR distributions in singing mice support an integral role for the AVP/OT system in several aspects of sociality, including vocal communication and sociospatial memory. J. Comp. Neurol. 516:321–333, 2009. © 2009 Wiley‐Liss, Inc.     

Oxytocin facilitates accurate perception of competition in men and kinship in women

Despite the dominant role of the hormone oxytocin (OT) in social behavior, little is known about the role of OT in the perception of social relationships. Furthermore, it is unclear whether there are sex differences in the way that OT affects social perception. Here, we employed a double-blind, placebo-controlled crossover design to investigate the effect of OT on accurate social perception. Following treatment, 62 participants completed the Interpersonal Perception Task, a method of assessing the accuracy of social judgments that requires identification of the relationship between people interacting in real life video clips divided into three categories: kinship, intimacy and competition. The findings suggest that OT had a general effect on improving accurate perception of social interactions. Furthermore, we show that OT also involves sex-specific characteristics. An interaction between treatment, task category and sex indicated that OT had a selective effect on improving kinship recognition in women, but not in men, whereas men''s performance was improved following OT only for competition recognition. It is concluded that the gender-specific findings reported here may point to some biosocial differences in the effect of OT which may be expressed in women''s tendency for communal and familial social behavior as opposed to men''s tendency for competitive social behavior.     

Social functions of individual vasopressin–oxytocin cell groups in vertebrates: What do we really know?

Vasopressin–oxytocin (VP–OT) nonapeptides modulate numerous social and stress-related behaviors, yet these peptides are made in multiple nuclei and brain regions (e.g., >20 in some mammals), and VP–OT cells in these areas often exhibit overlapping axonal projections. Furthermore, the magnocellular cell groups release peptide volumetrically from dendrites and soma, which gives rise to paracrine modulation in distal brain areas. Nonapeptide receptors also tend to be promiscuous. Hence, behavioral effects that are mediated by any given receptor type (e.g., the OT receptor) in a target brain region cannot be conclusively attributed to either VP or OT, nor to a specific cell group. We here review what is actually known about the social behavior functions of nonapeptide cell groups, with a focus on aggression, affiliation, bonding, social stress, and parental behavior, and discuss recent studies that demonstrate a diversity of sex-specific contributions of VP–OT cell groups to gregariousness and pair bonding.     

Oxytocin increases eye-gaze towards novel social and non-social stimuli

ABSTRACT

Research on oxytocin (OT) has revealed a substantial involvement of this neuropeptide in social cognition processes and attachment behavior.

The rationale of the present project was to decipher the differential role of OT in basic social cognition processes towards non-erotic attachment stimuli vs. reproduction-related stimuli in human subjects.

In a randomized double-blind repeated-measures cross-over design, N = 82 participants were investigated twice and received either intranasal OT or placebo at the first assessment followed by placebo or OT at second assessment. Participants were presented with standardized pictures of parent-child dyads, romantic couples engaging in non-erotic or explicit sexual activities, and non-social pictures while we assessed pupil dilation and eye focus on specific pre-defined areas of interest. Multilevel analyses suggest that during the initial presentation, OT increased pupil dilation towards all categories of stimuli and led the eye focus towards the eyes and body regions, followed by a strong decrease in pupil dilation and fixations at the second session.

These carry-over effects indicate that hormonal treatment at an initial contact to social stimuli can determine how these stimuli are processed later. These results might have implications for OT as a treatment in interventions with repeated exposure to social material.     

Comparing oxytocin and cortisol regulation in a double-blind,placebo-controlled,hydrocortisone challenge pilot study in children with autism and typical development

Background

Children with autism spectrum disorder (ASD) show marked impairment in social functioning and poor adaptation to new and changing contexts, which may be influenced by underlying regulatory processes. Oxytocin (OT) and cortisol are key neuromodulators of biological and behavioral responses, show a synergistic effect, and have been implicated in the neuropathological profile in ASD. However, they are rarely investigated together. The purpose of the pilot study was to evaluate the relationship between cortisol and OT in children with ASD under baseline and physiological stress (hydrocortisone challenge) conditions. Arginine vasopressin (AVP), structurally similar to OT, was also examined.

Methods

A double-blind, placebo-controlled, randomly assigned, crossover design was employed in 25 children 8-to-12 years with ASD (N?=?14) or typical development (TD, N?=?11). A low dose of hydrocortisone and placebo were administered via liquid suspension. Analysis of variance (ANOVA) was used to examine the within-subject factor “Condition” (hydrocortisone/placebo) and “Time” (pre and post) and the between-subject factor “Group” (ASD vs. TD). Pearson correlations examined the relationship between hormone levels and clinical profile.

Results

There was a significant Time × Condition × Group interaction F (1.23)?=?4.18, p?=?0.05 showing a rise in OT during the experimental condition (hydrocortisone) and a drop during the placebo condition for the TD group but not the ASD group. There were no group differences for AVP. Hormone levels were associated with social profiles.

Conclusions

For the TD group, an inverse relationship was observed. OT increased during physiological challenge suggesting that OT played a stress-buffering role during cortisol administration. In contrast for the ASD group, OT remained unchanged or decreased during both the physiological challenge and the placebo condition, suggesting that OT failed to serve as a stress buffer under conditions of physiological stress.While OT has been tied to the social ability of children with ASD, the diminished moderating effect of OT on cortisol may also play a contributory role in the heightened stress often observed in children with ASD. These results contribute to our understanding of the growing complexity of the effects of OT on social behavior as well as the functional interplay and differential regulation OT may have on stress modulation.

     

The relationship of social cognition to ward behavior in chronic schizophrenia

The relationship between social cognition (i.e., cognition for social stimuli) and ward behavior among individuals with chronic schizophrenia was investigated. Twenty-seven inpatients completed a battery of cognitive and social-cognitive tasks and were rated by staff on various indices of ward behavior. Overall, there was a relationship between the measures of social cognition and behavior on the ward. Social cognition contributed unique variance beyond cognition to maladaptive behavior on the ward (i.e., irritability). Implications for assessemnt and future research are discussed.     

Low-dose oxytocin delivered intranasally with Breath Powered device affects social-cognitive behavior: a randomized four-way crossover trial with nasal cavity dimension assessment

Despite the promise of intranasal oxytocin (OT) for modulating social behavior, recent work has provided mixed results. This may relate to suboptimal drug deposition achieved with conventional nasal sprays, inter-individual differences in nasal physiology and a poor understanding of how intranasal OT is delivered to the brain in humans. Delivering OT using a novel ‘Breath Powered'' nasal device previously shown to enhance deposition in intranasal sites targeted for nose-to-brain transport, we evaluated dose-dependent effects on social cognition, compared response with intravenous (IV) administration of OT, and assessed nasal cavity dimensions using acoustic rhinometry. We adopted a randomized, double-blind, double-dummy, crossover design, with 16 healthy male adults completing four single-dose treatments (intranasal 8 IU (international units) or 24 IU OT, 1 IU OT IV and placebo). The primary outcome was social cognition measured by emotional ratings of facial images. Secondary outcomes included the pharmacokinetics of OT, vasopressin and cortisol in blood and the association between nasal cavity dimensions and emotional ratings. Despite the fact that all the treatments produced similar plasma OT increases compared with placebo, there was a main effect of treatment on anger ratings of emotionally ambiguous faces. Pairwise comparisons revealed decreased ratings after 8 IU OT in comparison to both placebo and 24 IU OT. In addition, there was an inverse relationship between nasal valve dimensions and anger ratings of ambiguous faces after 8-IU OT treatment. These findings provide support for a direct nose-to-brain effect, independent of blood absorption, of low-dose OT delivered from a Breath Powered device.     

Individual variation in plasma oxytocin and vasopressin levels in relation to the development of combat-related PTSD in a large military cohort

In an attempt to decrease the risk of developing mental health problems after military deployment, it is important to find biological markers to identify those at risk. Oxytocin (OT) and arginine vasopressin (AVP) are potential biomarkers for the development of posttraumatic stress disorder (PTSD) because they are involved in the regulation of stress and anxiety. Therefore, the aim was to examine whether plasma OT (pOT) and AVP (pAVP) levels before and after deployment are biomarkers for the development of posttraumatic stress symptoms over time in addition to other known risk factors. This study is part of a large prospective cohort study on candidate markers for stress-related mental health symptoms and resiliency after deployment to a combat zone; Prospective Research in Stress-related Military Operations (PRISMO; N = 907). Data was collected prior to deployment and follow-ups were performed at 1 and 6 months, and 1, 2, and 5 years post-deployment. Blood samples were collected in the first three assessments. The levels of pOT and pAVP were not significantly related to the development of PTSD symptoms over time. The results confirm that age, the experience of early life trauma, combat-related stressors and the presence of depressive symptoms are predictive for the development of PTSD symptoms over time. These findings showed that peripherally measured OT and AVP currently do not qualify as useful susceptibility biomarkers for the development of PTSD symptoms over time in military men after combat.     

Binding affinities of oxytocin,vasopressin and Manning compound at oxytocin and V1a receptors in male Syrian hamster brains

Oxytocin (OT) and arginine vasopressin (AVP), as well as synthetic ligands targeting their receptors (OTR, V1aR), are used in a wide variety of research contexts, although their pharmacological properties are determined in only a few species. Syrian hamsters (Mesocricetus auratus) have a long history of use as a behavioural and biomedical model for the study of OT and AVP and, more recently, hamsters have been used to investigate behavioural consequences of OT‐mediated activation of V1aR. We aimed to determine the binding affinities of OT, AVP and the selective V1aR antagonist, Manning compound, for OTR and V1aR in hamster brains. We performed saturation binding assays to determine the Kd values for the selective OTR and V1aR radioligands, [¹²⁵I]ornithine vasotocin analogue and [¹²⁵I]linear vasopressin antagonist. We then performed competition binding assays to determine K_i values for OT, AVP and Manning compound at both the OTR and V1aR. We found that OT and AVP each had the highest affinity for their canonical receptors (OT‐OTR Ki = 4.28 [95% confidence interval (CI) = 2.9‐6.3] nmol L^?1; AVP‐V1ar Ki = 4.70 [95% CI = 1.5‐14.1] nmol L^?1) and had the lowest affinity for their non‐canonical ligands (OT‐V1aR = 495.2 [95% CI = 198.5‐1276] nmol L^?1; AVP‐OTR Ki = 36.1 [95% CI = 12.4‐97.0] nmol L^?1). Manning compound had the highest affinity for the V1aR (MC‐V1aR Ki = 6.87 [95% CI = 4.0‐11.9] nmol L^?1; MC‐OTR Ki = 213.8 [95% CI = 117.3‐392.7] nmol L^?1), although Manning compound was not as selective for the V1aR in hamsters as has been reported for the receptor in rats. When comparing these data with previously published work, we found that the promiscuity of the V1aR in hamsters with respect to OT and AVP binding is more similar to the promiscuity of the human V1aR than to the rat V1aR receptor. Moreover, the selectivity of OT at hamster receptors is more similar to the selectivity of OT at human receptors than the selectivity of OT at rat receptors. These data highlight the importance of determining the pharmacological properties of behaviourally relevant compounds in diverse model species.