Oxytocin as a natural antipsychotic: a study using oxytocin knockout mice

Chronic intranasal oxytocin alleviates cognitive impairment and reverses oxytocin signaling upregulation in MK801-induced mice

OBJECTIVE

Cognitive impairment, especially impaired social cognition, is largely responsible for the deterioration of the social life of patients with schizophrenia (SZ). Oxytocin (OT) is a neuropeptide that offers promising therapy for SZ. This study aimed to explore whether OT could affect dizocilpine (MK801)-induced cognitive impairment and to investigate the effect of exogenous OT on the endogenous OT system in the hippocampus.

METHODS

The SZ mouse model was established by repeated administration of dizocilpine [MK801, 0.6 mg/kg, intraperitoneal (i.p.)], and then OT (6-60 μg/kg, intranasal) or risperidone (0.3 mg/kg, i.p.) was administered to explore the effect of OT on cognitive impairment.

RESULTS

OT at a dose of 6 μg/kg alleviated MK801-induced hyperactivity, sociability impairment, and spatial memory impairment. OT at a dose of 20 or 60 μg/kg attenuated the hyperactivity and social novelty impairment. In MK801-injected mice, the compensatory upregulation of OT mRNA in the hippocampus was reversed by three OT doses, whereas 60 μg/kg OT reversed the compensatory upregulation of CD38 protein expression.

CONCLUSION

OT alleviated cognitive impairment in the SZ mouse model to varying degrees, reversing the compensatory upregulation of OT signaling in the hippocampus.

Using global remote camera data of a solitary species complex to evaluate the drivers of group formation

The social system of animals involves a complex interplay between physiology, natural history, and the environment. Long relied upon discrete categorizations of "social" and "solitary" inhibit our capacity to understand species and their interactions with the world around them. Here, we use a globally distributed camera trapping dataset to test the drivers of aggregating into groups in a species complex (martens and relatives, family Mustelidae, Order Carnivora) assumed to be obligately solitary. We use a simple quantification, the probability of being detected in a group, that was applied across our globally derived camera trap dataset. Using a series of binomial generalized mixed-effects models applied to a dataset of 16,483 independent detections across 17 countries on four continents we test explicit hypotheses about potential drivers of group formation. We observe a wide range of probabilities of being detected in groups within the solitary model system, with the probability of aggregating in groups varying by more than an order of magnitude. We demonstrate that a species' context-dependent proclivity toward aggregating in groups is underpinned by a range of resource-related factors, primarily the distribution of resources, with increasing patchiness of resources facilitating group formation, as well as interactions between environmental conditions (resource constancy/winter severity) and physiology (energy storage capabilities). The wide variation in propensities to aggregate with conspecifics observed here highlights how continued failure to recognize complexities in the social behaviors of apparently solitary species limits our understanding not only of the individual species but also the causes and consequences of group formation.

Modulation of Neuron and Astrocyte Dopamine Receptors via Receptor-Receptor Interactions

Dopamine neurotransmission plays critical roles in regulating complex cognitive and behavioral processes including reward, motivation, reinforcement learning, and movement. Dopamine receptors are classified into five subtypes, widely distributed across the brain, including regions responsible for motor functions and specific areas related to cognitive and emotional functions. Dopamine also acts on astrocytes, which express dopamine receptors as well. The discovery of direct receptor-receptor interactions, leading to the formation of multimeric receptor complexes at the cell membrane and providing the cell decoding apparatus with flexible dynamics in terms of recognition and signal transduction, has expanded the knowledge of the G-protein-coupled receptor-mediated signaling processes. The purpose of this review article is to provide an overview of currently identified receptor complexes containing dopamine receptors and of their modulatory action on dopamine-mediated signaling between neurons and between neurons and astrocytes. Pharmacological possibilities offered by targeting receptor complexes in terms of addressing neuropsychiatric disorders associated with altered dopamine signaling will also be briefly discussed.

Exploring a Possible Interplay between Schizophrenia, Oxytocin, and Estrogens: A Narrative Review

Schizophrenia is characterized by symptoms of psychosis and sociocognitive deficits. Considering oxytocin’s antipsychotic and prosocial properties, numerous clinical, and preclinical studies have explored the neuropeptide’s therapeutic efficacy. Sex differences in the clinical course of schizophrenia, as well as in oxytocin-mediated behaviors, indicate the involvement of gonadal steroid hormones. The current narrative review aimed to explore empirical evidence on the interplay between schizophrenia psychopathology and oxytocin’s therapeutic potential in consideration of female gonadal steroid interactions, with a focus on estrogens. The review was conducted using the PubMed and PsychINFO databases and conforms to the Scale for the Assessment of Narrative Review Articles (SANRA) guidelines. The results suggest a potential synergistic effect of the combined antipsychotic effect of oxytocin and neuroprotective effect of estrogen on schizophrenia. Consideration of typical menstrual cycle-related hormonal changes is warranted and further research is needed to confirm this assumption.

Assessment of expression of oxytocin-related lncRNAs in schizophrenia

BACKGROUND

Schizophrenia is a neuropsychiatric disorder characterized by a variety of clinical manifestations. This disorder has a complex inheritance. Oxytocinegic system has been shown to be implicated in the pathophysiology of schizophrenia. This system can alter social cognition through direct interaction with dopaminergic signaling, facilitating brain-stimulation reward, reduction of defense mechanism and stress reactivity, and modulation of social information processing through enhancing the greatness of social incentives. Long non-coding RNAs (lncRNAs) can affect activity of oxytocinegic system, thus contributing in the etiology of this disorder.

METHODS

We designed the current study to appraise dysregulation of nine oxytocin-associated mRNAs and lncRNAs in the venous blood of patients with schizophrenia.

RESULTS

Expression of FOS was up-regulated in total patients compared with total control group (Expression ratio (95% CI)= 13.64 (5.46-34.05), adjusted P value<0.0001) and in female patients compared with female control group (Expression ratio (95% CI)=32.13 (5.81-176), adjusted P value<0.0001). Such pattern was also seen for Lnc-FOXF1 (Expression ratio (95% CI)= 6.41 (2.84-14.3), adjusted P value<0.0001 and Expression ratio (95% CI)= 14.41 (3.2-64.44), adjusted P value<0.0001, respectively). ITPR1 was down-regulated in total patients compared with total controls (Expression ratio (95% CI)= 0.22 (0.076-0.67), adjusted P value=0.0079). ROC curve analyses demonstrated that FOS had the best AUC value among other genes in differentiation between patients and controls (AUC=0.78).

CONCLUSION

The above-mentioned results imply dysregulation of oxytocin-related genes in the circulatory blood of patients with schizophrenia.

Oxytocin Prevents the Development of 3-NP-Induced Anxiety and Depression in Male and Female Rats: Possible Interaction of OXTR and mGluR2

Huntington disease (HD) is a progressive neurological disorder with dominant motor symptoms. It also has psychiatric manifestations, like anxiety and depression, that can emerge themselves before motor symptoms and impose a major burden on patients. Oxytocin (OXT) is a newly emerged treatment for disorders like autism and schizophrenia and recently is using to alleviate depression and anxiety. In the current study, we investigated the behavioral and molecular effects of OXT on the development of anxiety and depression in 3-nitropropionic acid (3-NP)-induced model of HD. Anxiety- and depression-like behaviors as well as the levels of oxytocin receptor (OXTR), metabotropic glutamate receptor (mGluR) 2, mGluR5, and glutathione (GSH) were measured in striatum, hippocampus, prefrontal cortex, and amygdala. Also, we questioned if sex had any modulatory effect. We found that 3-NP increased anxiety and depression compared to controls. It also reduced the levels of OXTR and mGluR2, increased mGluR5, and reduced GSH in studied brain regions. Pretreatment with OXT before the injection of 3-NP ameliorated anxiety and depression. Additionally, it protected the brain from developing low levels of OXTR, mGluR2, and GSH and high levels of mGluR5 in studied regions. The protective effects of OXT were similar between male and female animals. These data suggest that OXTR, mGluR2, mGluR5, and GSH may contribute to psychiatric manifestations of HD. In addition, pretreatment with OXT could prevent the mood changes in male and female rats.

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

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

Impaired prepulse inhibition in mice with IRSp53 deletion in modulatory neurotransmitter neurons including dopamine, acetylcholine, oxytocin, and serotonin

Prepulse inhibition (PPI) is a neurophysiological finding that is decreased in schizophrenia patients and has been used in pathophysiology studies of schizophrenia and the development of antipsychotic drugs. PPI is affected by several drugs including amphetamine, ketamine, and nicotinic agents, and it is reported that several brain regions and modulatory neurotransmitters are involved in PPI. Here we showed that mice with IRSp53 deletion in each dopaminergic, cholinergic, oxytocinergic, and serotoninergic modulatory neurons showed a decrease in PPI. Other than PPI, there were no other behavioral changes among IRSp53 deletion mice. Through this study, we could reconfirm that dysfunction of each modulatory neuron such as dopamine, acetylcholine, oxytocin, and serotonin can result in PPI impairment, and it should be considered that PPI could be broadly affected by changes in one of a certain kind of modulatory neurons.

Oxytocin attenuates schizophrenia-like reduced sensorimotor gating in outbred and inbred rats in line with strain differences in CD38 gene expression

Prepulse inhibition (PPI) of the startle response is a measure of sensorimotor gating that is impaired in many clinical conditions, including schizophrenia. The inbred Roman high-avoidance (RHA) rats, compared to their low-avoidance (RLA) counterparts, show distinct schizophrenia-like phenotypes, such as spontaneous deficits in PPI accompanied by decreased medial prefrontal cortex (mPFC) activity and volume. Schizophrenia-like deficits are usually attenuated by antipsychotic drugs, but these drugs often produce severe side effects. In order to reduce these side effects, the neuropeptide oxytocin has been proposed as an alternative natural antipsychotic for schizophrenia. Here, we examined the effects of peripheral oxytocin administration (saline, 0.04, and 0.2 mg/kg) on PPI in the RHA vs. RLA rats, as well as in the outbred heterogeneous stock (HS) rats. Our results showed that oxytocin increased PPI in the HS rats and attenuated PPI deficits in the RHA rats, but it did not significantly affect PPI in the RLAs. To explore whether these divergent effects were associated with differences in oxytocinergic mechanisms, we analyzed gene expression of the oxytocin receptor (OXTR) and the regulator of oxytocin release (CD38) in the mPFC of the Roman rats. Consistent with the differential oxytocin effects on PPI (RHA > RLA), constitutive CD38 expression was reduced in the RHA rats compared to the RLAs, while oxytocin administration increased OXTR expression in both strains. Overall, the present work reveals that oxytocin administration shows antipsychotic-like effects on PPI in outbred and inbred rats, and it suggests that these effects may be related to basal differences in oxytocin-mediated mechanisms in the mPFC.

Specification of oxytocinergic and vasopressinergic circuits in the developing mouse brain

Oxytocin (OXT) and arginine vasopressin (AVP) support a broad range of behaviors and homeostatic functions including sex-specific and context-appropriate social behaviors. Although the alterations of these systems have been linked with social-related disorders such as autism spectrum disorder, their formation and developmental dynamics remain largely unknown. Using novel brain clearing techniques and 3D imaging, we have reconstructed the specification of oxytocinergic and vasopressinergic circuits in the developing mouse brain with unprecedented cellular resolution. A systematic quantification indicates that OXT and AVP neurons in the hypothalamus display distinctive developmental dynamics and high cellular plasticity from embryonic to early postnatal stages. Our findings reveal new insights into the specification and consolidation of neuropeptidergic systems in the developing CNS.

Oxytocin in Schizophrenia: Pathophysiology and Implications for Future Treatment

Schizophrenia is a form of mental disorder that is behaviorally characterized by abnormal behavior, such as social function deficits or other behaviors that are disconnected from reality. Dysregulation of oxytocin may play a role in regulating the expression of schizophrenia. Given oxytocin’s role in social cognition and behavior, a variety of studies have examined the potential clinical benefits of oxytocin in improving the psychopathology of patients with schizophrenia. In this review, we highlight the evidence for the role of endogenous oxytocin in schizophrenia, from animal models to human studies. We further discuss the potential of oxytocin as a therapeutic agent for schizophrenia and its implication in future treatment.

Oxytocin increases eye gaze in schizophrenia

Abnormal eye gaze is common in schizophrenia and linked to functional impairment. The hypothalamic neuropeptide oxytocin modulates visual attention to social stimuli, but its effects on eye gaze in schizophrenia are unknown. We examined visual scanning of faces in men with schizophrenia and neurotypical controls to quantify oxytocin effects on eye gaze. In a randomized, double-blind, crossover study, 33 men with schizophrenia and 39 matched controls received one dose of intranasal oxytocin (40 IU) and placebo on separate testing days. Participants viewed 20 color photographs of faces while their gaze patterns were recorded. We tested for differences in fixation time on the eyes between patients and controls as well as oxytocin effects using linear mixed-effects models. We also tested whether attachment style, symptom severity, and anti-dopaminergic medication dosage moderated oxytocin effects. In the placebo condition, patients showed reduced fixation time on the eyes compared to controls. Oxytocin was associated with an increase in fixation time among patients, but a decrease among controls. Higher attachment anxiety and greater symptom severity predicted increased fixation time on the eyes on oxytocin versus placebo. Anti-dopaminergic medication dosage and attachment avoidance did not impact response to oxytocin. Consistent with findings that oxytocin optimizes processing of social stimuli, intranasal oxytocin enhanced eye gaze in men with schizophrenia. Further work is needed to determine whether changes in eye gaze impact social cognition and functional outcomes. Both attachment anxiety and symptom severity predicted oxytocin response, highlighting the importance of examining potential moderators of oxytocin effects in future studies.

Neurochemical effects of oxytocin in people at clinical high risk for psychosis

Alterations in neurochemical metabolites are thought to play a role in the pathophysiology of psychosis onset. Oxytocin, a neuropeptide with prosocial and anxiolytic properties, modulates glutamate neurotransmission in preclinical models but its neurochemical effects in people at high risk for psychosis are unknown. We used proton magnetic resonance spectroscopy (¹H-MRS) to examine the effects of intranasal oxytocin on glutamate and other metabolites in people at Clinical High Risk for Psychosis (CHR-P) in a double-blind, placebo-controlled, crossover design. 30 CHR-P males were studied on two occasions, once after 40IU intranasal oxytocin and once after placebo. The effects of oxytocin on the concentration of glutamate, glutamate+glutamine and other metabolites (choline, N-acetylaspartate, myo-inositol) scaled to creatine were examined in the left thalamus, anterior cingulate cortex (ACC) and left hippocampus, starting approximately 75, 84 and 93 min post-dosing, respectively. Relative to placebo, administration of oxytocin was associated with an increase in choline levels in the ACC (p=.008, Cohen's d = 0.54). There were no other significant effects on metabolite concentrations (all p>.05). Our findings suggest that, at ∼75-99 min post-dosing, a single dose of intranasal oxytocin does not alter levels of neurochemical metabolites in the thalamus, ACC, or hippocampus in those at CHR-P, aside from potential effects on choline in the ACC.

Oxytocin improves probabilistic reversal learning but not effortful motivation in Brown Norway rats

Deficits in cognition and motivation are common and debilitating aspects of psychiatric disorders, yet still go largely untreated. The neuropeptide oxytocin (OT) is a potential novel therapeutic for deficits in social cognition and motivation in psychiatric patients. However, the effects of OT on clinically relevant domains of non-social cognition and motivation remain under studied. The present study investigated the effects of acute and chronic (21-day) administration of subcutaneous OT (0.04, 0.2, and 1 mg/kg) in cross-species translatable operant paradigms of reward learning and effortful motivation in male and female Brown Norway (BN) rats (n = 8-10/group). Reward learning was assessed using the probabilistic reversal learning task (PRLT) and effortful motivation was measured using the progressive ratio breakpoint task (PRBT). As predicted, BN rats exhibited baseline deficits in the detection of reversals of reward contingency in the PRLT relative to Long Evans (LE) rats. The two strains performed equally in the PRBT. Thirty minutes after a single OT injection (1 mg/kg), measures of both initial probabilistic learning (trials to first criterion) and subsequent reversal learning (contingency switches) were significantly improved to levels comparable with LE rats. The OT effect on switches persisted in male, but not female, BN rats 30 min, 24 h, and 6 days after long-term OT administration, suggesting the induction of neuroplastic changes. OT did not affect effortful motivation at any time-point. The beneficial effects of OT on reward learning in the absence of increased effortful motivation support the development of OT as a novel therapeutic to improve cognitive functioning.

[Oxytocin in schizophrenia : Evidence for an etiological and therapeutic relevance of the social neuromodulator]

Neurobiological results from animal models as well as biochemical and genetic findings in patients indicate that the oxytocin (OT) system may be dysfunctional in schizophrenia. On this pathogenetic basis transnasally administered OT (tnOT) could be an innovative treatment option for schizophrenia. Experimental data from animal studies are also suggestive of a particular effectiveness in treatment-resistant schizophrenia. To date, clinical data on tnOT treatment of schizophrenia patients does not unequivocally support a general therapeutic effect on the psychopathology but suggests positive effects on higher integrated social cognitive performance, such as empathy and mentalization. In particular, tnOT augmentation of a social cognitive skills training resulted in a marked and lasting treatment effect; however, numerous person- and context-dependent variables can potentially moderate individual effects of OT and may even reverse effects in certain constellations. Most clinical studies so far have not systematically accounted and controlled for these factors with the probable result of larger variance of recorded treatment effects and lower likelihood of ascertaining positive effectiveness. Furthermore, there is still a gap of knowledge on dose response relations and central nervous system (CNS) permeation in man following tnOT administration. This review aims to give a concise overview on the evidence for the etiological relevance of the neurohormone OT and its treatment potential in schizophrenia.

Oxytocin attenuates phencyclidine hyperactivity and increases social interaction and nucleus accumben dopamine release in rats

The pituitary neuropeptide oxytocin promotes social behavior, and is a potential adjunct therapy for social deficits in schizophrenia and autism. Oxytocin may mediate pro-social effects by modulating monoamine release in limbic and cortical areas, which was investigated herein using in vivo microdialysis, after establishing a dose that did not produce accompanying sedative or thermoregulatory effects that could concomitantly influence behavior. The effects of oxytocin (0.03-0.3 mg/kg subcutaneous) on locomotor activity, core body temperature, and social behavior (social interaction and ultrasonic vocalizations) were examined in adult male Lister-hooded rats, using selective antagonists to determine the role of oxytocin and vasopressin V_1a receptors. Dopamine and serotonin efflux in the prefrontal cortex and nucleus accumbens of conscious rats were assessed using microdialysis. 0.3 mg/kg oxytocin modestly reduced activity and caused hypothermia but only the latter was attenuated by the V_1a receptor antagonist, SR49059 (1 mg/kg intraperitoneal). Oxytocin at 0.1 mg/kg, which did not alter activity and had little effect on temperature, significantly attenuated phencyclidine-induced hyperactivity and increased social interaction between unfamiliar rats without altering the number or pattern of ultrasonic vocalizations. In the same rats, oxytocin (0.1 mg/kg) selectively elevated dopamine overflow in the nucleus accumbens, but not prefrontal cortex, without influencing serotonin efflux. Systemic oxytocin administration attenuated phencyclidine-induced hyperactivity and increased pro-social behavior without decreasing core body temperature and selectively enhanced nucleus accumbens dopamine release, consistent with activation of mesocorticolimbic circuits regulating associative/reward behavior being involved. This highlights the therapeutic potential of oxytocin to treat social behavioral deficits seen in psychiatric disorders such as schizophrenia.

The role of oxytocin in the pathogenesis and treatment of schizophrenia

Introduction: Until recently, oxytocin was mainly associated with the pathophysiology of childbirth and sexual functions, but lately this hormone has become the object of interest to psychiatry and psychology due to the significant influence of oxytocin on human behavior in the field of social and emotional functioning. Current scientific research focuses on the participation of oxytocin in the pathogenesis and therapy of mental disorders.

Aim: The aim of the paper is to present, on the basis of available literature, the significance of oxytocin for various psychological functions, with particular emphasis on the influence of oxytocin on the course and clinical picture of schizophrenia.

Method: Available articles from the Medline / PubMed database were analyzed, which were searched using keywords: oxytocin, schizophrenia, therapeutic use of oxytocin, social cognition, positive symptoms, negative symptoms and time descriptors: 2013-2017. There are included articles published in Polish and English.

Results:The research results carried out so far suggest that oxytocin plays a significant role in modulating complex socio-emotional behaviors in schizophrenic patients. The existing research results also indicate a relationship between the dysregulation of the oxytocinergic system and the pathophysiology of schizophrenia. Many of the studies prove that there is a relationship between the level of oxytocin in the patients' blood plasma and the severity of the disease symptoms. Recent genetic studies indicate a possible relationship between polymorphism of oxytocin genesand polymorphism of oxytocin receptor genes and the risk of developing schizophrenia.

Conclusions: Contemporary research on the therapeutic potential of oxytocin and its influence on the functioning of schizophrenia patients seem to be very promising and may contribute to increasing the effectiveness of treatment of schizophrenia and possibly other mental disorders, which in turn will improve the quality of life of patients in cognitive, social and emotional functioning.

Up-regulated expression of oxytocin mRNA in peripheral blood lymphocytes from first-episode schizophrenia patients

Schizophrenia (SZ) is a severe neuropsychiatric disorder with significant social cognition impairment. Increasing evidence has suggested that neuropeptides oxytocin (OXT) and arginine vasopressin (AVP) are important mediators of complex social cognition and behavior associates with SZ. In the present study, forty-three first-episode schizophrenia (FES) patients and forty-seven healthy controls (HC) were included. The peripheral mRNA expression of OXT, OXT receptor (OXTR), AVP, AVP 1a receptor (AVPR1a) and CD38 was determined by real-time quantitative polymerase chain reaction (RT-qPCR). The FES patients have a relatively higher mRNA level of OXT and OXTR genes and lower expression of AVP and CD38 genes than HC. No difference was found for AVPR1a between FES patients and HC. As for the sex difference, the mRNA expression of OXT and OXTR showed no difference in both male and female FES patients compared to HC group. The AVP and CD38 genes in female FES patients showed decreased mRNA expression than female HC. Our findings support disrupted OXT and AVP systems in the FES patients.

Oxytocin effects in schizophrenia: Reconciling mixed findings and moving forward

Schizophrenia is a severe mental illness that causes major functional impairment. Current pharmacologic treatments are inadequate, particularly for addressing negative and cognitive symptoms of the disorder. Oxytocin, a neuropeptide known to moderate social behaviors, has been investigated as a potential therapeutic for schizophrenia in recent years. Results have been decidedly mixed, leading to controversy regarding oxytocin's utility. In this review, we outline several considerations for interpreting the extant literature and propose a focused agenda for future work that builds on the most compelling findings regarding oxytocin effects in schizophrenia to date. Specifically, we examine underlying causes of heterogeneity in randomized clinical trials (RCTs) conducted thus far and highlight the complexity of the human oxytocin system. We then review evidence of oxytocin's effects on specific deficits in schizophrenia, arguing for further study using objective, precise outcome measures in order to determine whether oxytocin has the potential to improve functional impairment in schizophrenia.

Understanding the Role of GPCR Heteroreceptor Complexes in Modulating the Brain Networks in Health and Disease

The introduction of allosteric receptor-receptor interactions in G protein-coupled receptor (GPCR) heteroreceptor complexes of the central nervous system (CNS) gave a new dimension to brain integration and neuropsychopharmacology. The molecular basis of learning and memory was proposed to be based on the reorganization of the homo- and heteroreceptor complexes in the postjunctional membrane of synapses. Long-term memory may be created by the transformation of parts of the heteroreceptor complexes into unique transcription factors which can lead to the formation of specific adapter proteins. The observation of the GPCR heterodimer network (GPCR-HetNet) indicated that the allosteric receptor-receptor interactions dramatically increase GPCR diversity and biased recognition and signaling leading to enhanced specificity in signaling. Dysfunction of the GPCR heteroreceptor complexes can lead to brain disease. The findings of serotonin (5-HT) hetero and isoreceptor complexes in the brain over the last decade give new targets for drug development in major depression. Neuromodulation of neuronal networks in depression via 5-HT, galanin peptides and zinc involve a number of GPCR heteroreceptor complexes in the raphe-hippocampal system: GalR1-5-HT1A, GalR1-5-HT1A-GPR39, GalR1-GalR2, and putative GalR1-GalR2-5-HT1A heteroreceptor complexes. The 5-HT1A receptor protomer remains a receptor enhancing antidepressant actions through its participation in hetero- and homoreceptor complexes listed above in balance with each other. In depression, neuromodulation of neuronal networks in the raphe-hippocampal system and the cortical regions via 5-HT and fibroblast growth factor 2 involves either FGFR1-5-HT1A heteroreceptor complexes or the 5-HT isoreceptor complexes such as 5-HT1A-5-HT7 and 5-HT1A-5-HT2A. Neuromodulation of neuronal networks in cocaine use disorder via dopamine (DA) and adenosine signals involve A2AR-D2R and A2AR-D2R-Sigma1R heteroreceptor complexes in the dorsal and ventral striatum. The excitatory modulation by A2AR agonists of the ventral striato-pallidal GABA anti-reward system via targeting the A2AR-D2R and A2AR-D2R-Sigma1R heteroreceptor complex holds high promise as a new way to treat cocaine use disorders. Neuromodulation of neuronal networks in schizophrenia via DA, adenosine, glutamate, 5-HT and neurotensin peptides and oxytocin, involving A2AR-D2R, D2R-NMDAR, A2AR-D2R-mGluR5, D2R-5-HT2A and D2R-oxytocinR heteroreceptor complexes opens up a new world of D2R protomer targets in the listed heterocomplexes for treatment of positive, negative and cognitive symptoms of schizophrenia.

Oxytocin and behavior: Lessons from knockout mice

It is well established that the nonapeptide oxytocin (Oxt) is important for the neural modulation of behaviors in many mammalian species. Since its discovery in 1906 and synthesis in the early 1950s, elegant pharmacological work has helped identify specific neural substrates on which Oxt exerts its effects. More recently, mice with targeted genetic disruptions of the Oxt system-i.e., both the peptide and its receptor (the Oxtr)-have further defined Oxt's actions and laid some important scientific groundwork for studies in other species. In this article, we highlight the scientific contributions that various mouse knockouts of the Oxt system have made to our understanding of Oxt's modulation of behavior. We specifically focus on how the use of these mice has shed light on our understanding of social recognition memory, maternal behavior, aggression, and several nonsocial behaviors. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 190-201, 2017.

Reduced oxytocin receptor gene expression and binding sites in different brain regions in schizophrenia: A post-mortem study

Schizophrenia is a severe neuropsychiatric disorder with impairments in social cognition. Several brain regions have been implicated in social cognition, including the nucleus caudatus, prefrontal and temporal cortex, and cerebellum. Oxytocin is a critical modulator of social cognition and the formation and maintenance of social relationships and was shown to improve symptoms and social cognition in schizophrenia patients. However, it is unknown whether the oxytocin receptor is altered in the brain. Therefore, we used qRT-PCR and Ornithine Vasotocin Analog ([¹²⁵I]OVTA)-based receptor autoradiography to investigate oxytocin receptor expression at both the mRNA and protein level in the left prefrontal and middle temporal cortex, left nucleus caudatus, and right posterior superior vermis in 10 schizophrenia patients and 6 healthy controls. Furthermore, to investigate confounding effects of long-term antipsychotic medication we treated rats with clozapine or haloperidol for 12weeks and assessed expression of the oxytocin receptor in cortical and subcortical brain regions. In schizophrenia patients, we found a downregulation of oxytocin receptor mRNA in the temporal cortex and a decrease in receptor binding in the vermis. In the other regions, the results showed trends in the same direction, without reaching statistical significance. We found no differences between antipsychotic-treated rats and controls. Downregulated expression and binding of the oxytocin receptor in brain regions involved in social cognition may lead to a dysfunction of oxytocin signaling. Our results support a dysfunction of the oxytocin receptor in schizophrenia, which may contribute to deficits of social cognition.

Potential of Oxytocin in the Treatment of Schizophrenia

Schizophrenia is a heterogeneous, debilitating disorder characterized by three distinct sets of clinical features: positive symptoms, negative symptoms, and cognitive deficits. Extant antipsychotic drugs have been most successful at treating the positive symptoms of patients with schizophrenia but have minimal therapeutic effects on negative symptoms and cognitive deficits, which are the symptoms that best predict the poor prognosis of these patients. Therefore, there has been a major effort towards identifying compounds that alleviate these symptoms. Oxytocin (OT) is a nonapeptide that regulates peripheral reproductive-relevant functions, and also acts as a neurotransmitter in the brain. Converging evidence from both preclinical and clinical research suggests that OT may have therapeutic efficacy for the positive symptoms, negative symptoms, and cognitive deficits of schizophrenia. In the majority of the small, randomized, placebo-controlled clinical trials conducted to date, OT has shown particular promise in its potential to treat the intractable negative symptoms and social cognitive deficits exhibited by most of the patients with this debilitating disorder. In this leading article, we summarize the clinical evidence relevant to (1) endogenous OT and schizophrenia, and (2) the putative therapeutic effects of OT on each of the three clinical domains.

A Review of Oxytocin's Effects on the Positive, Negative, and Cognitive Domains of Schizophrenia

Schizophrenia is a disabling, heterogeneous disorder with clinical features that can be parsed into three domains: positive symptoms, negative symptoms, and cognitive deficits. Current antipsychotic drugs produce fairly robust clinical benefit against positive symptoms but typically have minimal therapeutic effects on negative symptoms and cognitive deficits. Oxytocin (OT) is a nonapeptide that, in addition to its role as a hormone regulating peripheral reproductive-relevant functions, acts as a neurotransmitter in the brain. Several lines of preclinical and clinical research suggest that the OT system may play a role in regulating the expression of schizophrenia spectrum disorders and that targeting the central OT system may yield novel treatments to address these symptoms. In this review, we summarize the extant preclinical and clinical evidence relevant to the role of OT in schizophrenia with particular emphasis on its putative therapeutic effects on each of the three above-mentioned clinical domains.

Oxytocin and Vasopressin Receptor Gene Polymorphisms: Role in Social and Psychiatric Traits

Oxytocin (OXT) and arginine-vasopressin (AVP) are two phylogenetically conserved neuropeptides that have been implicated in a wide range of social behaviors. Although a large body of research, ranging from rodents to humans, has reported on the effects of OXT and AVP administration on affiliative and trust behaviors, and has highlighted the genetic contributions of OXT and AVP receptor polymorphisms to both social behaviors and to diseases related to social deficits, the consequences of peptide administration on psychiatric symptoms, and the impact of receptor polymorphisms on receptor function, are still unclear. Despite the exciting advances that these reports have brought to social neuroscience, they remain preliminary and suffer from the problems that are inherent to monogenetic linkage and association studies. As an alternative, some studies are using polygenic approaches, and consider the contributions of other genes and pathways, including those involving DA, 5-HT, and reelin, in addition to OXT and AVP; a handful of report are also using genome-wide association studies. This review summarizes findings on the associations between OXT and AVP receptor polymorphism, social behavior, and psychiatric diseases. In addition, we discuss reports on the interactions of OXT and AVP receptor genes and genes involved in other pathways (such as those of dopamine, serotonin, and reelin), as well as research that has shed some light on the impact of gene polymorphisms on the volume, connectivity, and activation of specific neural structures, differential receptor expression, and plasma levels of the OXT and AVP peptides. We hope that this effort will be helpful for understanding the studies performed so far, and for encouraging the inclusion of other candidate genes not explored to date.

The Effect of Oxytocin on Social and Non-Social Behaviour and Striatal Protein Expression in C57BL/6N Mice

Oxytocin has been suggested as a promising new treatment for neurodevelopmental disorders. However, important gaps remain in our understanding of its mode of action, in particular, to what extent oxytocin modulates social and non-social behaviours and whether its effects are generalizable across both sexes. Here we investigated the effects of a range of oxytocin doses on social and non-social behaviours in C57BL/6N mice of both sexes. As the striatum modulates social and non-social behaviours, and is implicated in neurodevelopmental disorders, we also conducted a pilot exploration of changes in striatal protein expression elicited by oxytocin. Oxytocin increased prepulse inhibition of startle but attenuated the recognition memory in male C57BL/6N mice. It increased social interaction time and suppressed the amphetamine locomotor response in both sexes. The striatum proteome following oxytocin exposure could be clearly discriminated from saline controls. With the caveat that these results are preliminary, oxytocin appeared to alter individual protein expression in directions similar to conventional anti-psychotics. The proteins affected by oxytocin could be broadly categorized as those that modulate glutamatergic, GABAergic or dopaminergic signalling and those that mediate cytoskeleton dynamics. Our results here encourage further research into the clinical application of this peptide hormone, which may potentially extend treatment options across a spectrum of neurodevelopmental conditions.

Effects of oxytocin and genetic variants on brain and behaviour: Implications for treatment in schizophrenia

Impairments in social cognition and poor social functioning are core features of schizophrenia-spectrum disorders. In recent years, there has been a move towards developing new treatment strategies that specifically target social cognitive and social behavioural deficits. Oxytocin (OXT) is one such strategy that has gained increasing attention. There is a strong rationale for studying OXT in psychosis, from both an evolutionary perspective and neurodevelopmental-cognitive model of schizophrenia. Thus, the aim of this review was to critique and examine the observational and clinical oxytocin trial literature in schizophrenia-spectrum disorders. A handful of clinical trials suggest that OXT treatment may be beneficial for remediating social cognitive impairments, psychiatric symptoms, and improving social outcomes. However, inconsistencies exist in this literature, which may be explained by individual differences in the underlying neural response to OXT treatment and/or variation in the oxytocin and oxytocin receptor genes. Therefore, we additionally reviewed the evidence for structural and functional neural intermediate phenotypes in humans that link genetic variants to social behaviour/thinking, and discuss the implications of such interactions in the context of dysfunctional brain networks in schizophrenia. Factors that pose challenges for future OXT clinical research include the impact of age, sex, and ancestry, task-specific effects, bioavailability and pharmacokinetics, as well as neurotransmitter and drug interactions. While initial findings from OXT single dose/clinical trial studies are promising, more interdisciplinary research in both healthy and psychiatric populations is needed before determining whether OXT is a viable treatment option/adjunct for addressing poor illness outcomes in psychotic disorders.

Effects of Oxytocin on Neural Response to Facial Expressions in Patients with Schizophrenia

Impaired facial emotion recognition is a core deficit in schizophrenia. Oxytocin has been shown to improve social perception in patients with schizophrenia; however, the effect of oxytocin on the neural activity underlying facial emotion recognition has not been investigated. This study was aimed to assess the effect of a single dose of intranasal oxytocin on brain activity in patients with schizophrenia using an implicit facial emotion-recognition paradigm. Sixteen male patients with schizophrenia and 16 age-matched healthy male control subjects participated in a randomized, double-blind, placebo-controlled crossover trial at Seoul National University Hospital. Delivery of a single dose of 40 IU intranasal oxytocin and the placebo was separated by 1 week. Drug conditions were compared by performing a region of interest (ROI) analysis of the bilateral amygdala on responses to the emotion recognition test. It was found that nasal spray decreased amygdala activity for fearful emotion and increased activity for happy faces. Further, oxytocin elicited differential effects between the patient and control groups. Intranasal oxytocin attenuated amygdala activity for emotional faces in patients with schizophrenia, whereas intranasal oxytocin significantly increased amygdala activity in healthy controls. Oxytocin-induced BOLD signal changes in amygdala in response to happy faces was related to attachment style in the control group. Our result provides new evidence of a modulatory effect of oxytocin on neural response to emotional faces for patients with schizophrenia. Future studies are needed to investigate the effectiveness of long-term treatment with intranasal oxytocin on neural activity in patients with schizophrenia.

Oxytocin: recent developments

Oxytocin is a neurohypophyseal hormone that is produced centrally by neurons in the paraventricular nucleus and supraoptic nucleus of the hypothalamus. It is released directly into higher brain centres and into the peripheral circulation where it produces a multitude of effects. Classically, oxytocin is known for inducing uterine contractions at parturition and milk ejection during suckling. Oxytocin also acts in a species and gender specific manner as an important neuromodulator. It can affect behaviours associated with stress and anxiety, as well social behaviours including sexual and relationship behaviours, and maternal care. Additionally, oxytocin has been shown to have a variety of physiological roles in peripheral tissues, many of which appear to be modulated largely by locally produced oxytocin, dispelling the notion that oxytocin is a purely neurohypophyseal hormone. Oxytocin levels are altered in several diseases and the use of oxytocin or its antagonists have been identified as a possible clinical intervention in the treatment of mood disorders and pain conditions, some cancers, benign prostatic disease and osteoporosis. Indeed, oxytocin has already been successful in clinical trials to treat autism and schizophrenia. This review will report briefly on the known functions of oxytocin, it will discuss in depth the data from recent clinical trials and highlight future targets for oxytocinergic modulation.

A double-blind randomized controlled trial of oxytocin nasal spray and social cognition training for young people with early psychosis

Social-cognitive deficits contribute to poor functional outcomes in early psychosis; however, no effective pharmacological treatments exist for these problems. This study was the first to investigate the efficacy of an extended treatment of oxytocin nasal spray combined with social cognition training (SCT) to improve social cognition, clinical symptoms, and social functioning in early psychosis. In a double-blind, randomized, placebo-controlled, between-subjects trial, 52 individuals (aged 16-35 years) diagnosed with an early psychosis schizophrenia-spectrum illness were recruited. Participants received oxytocin (24 International Units) or placebo nasal spray twice-daily for 6 weeks, combined with group SCT (2 × 1 hour weekly sessions for 6 weeks). An additional dose of oxytocin was administered before each weekly session. Assessments were conducted at baseline, post-treatment, and at 3-month follow-up. Primary outcomes included the Reading the Mind in the Eyes Test, the Scale for the Assessment of Positive and Negative Symptoms, and the Social Functioning Scale. Secondary outcomes included self-report and behavioral assessments of social cognition, symptom severity, and social functioning. Results showed that on all primary and secondary outcomes, there was no benefit of oxytocin nasal spray treatment in comparison to placebo. Exploratory post hoc analysis suggested that increased use of nasal spray was, however, associated with reductions in negative symptoms in the oxytocin condition only. This study represents the first evaluation of oxytocin treatment for early psychosis. Although results suggest no benefit of oxytocin treatment, results also highlight an urgent need to consider nasal spray delivery and dose-related variables for future clinical trials.

A Role for Oxytocin in the Etiology and Treatment of Schizophrenia

Schizophrenia is a chronic debilitating neuropsychiatric disorder estimated to affect 51 million people worldwide. Several symptom domains characterize schizophrenia, including negative symptoms, such as social withdrawal and anhedonia, cognitive impairments, such as disorganized thinking and impaired memory, and positive symptoms, such as hallucinations and delusions. While schizophrenia is a complex neuropsychiatric disorder with no single "cause," there is evidence that the oxytocin (Oxt) system may be dysregulated in some individuals. Further, treatment with intranasal Oxt reduces some of the heterogeneous symptoms associated with schizophrenia. Since Oxt is known for its modulatory effects on a variety of social and non-social behaviors, it is perhaps not surprising that it may contribute to some aspects of schizophrenia and could also be a useful therapeutic agent. In this review, we highlight what is known about Oxt's contributions to schizophrenia and schizophrenia-related behaviors and discuss its potential as a therapeutic agent.

Oxytocin and vasopressin levels are decreased in the plasma of male schizophrenia patients

OBJECTIVE

Impaired social functioning and autistic symptoms are characteristics of schizophrenia. The social hormones oxytocin (OT) and arginine-vasopressin (AVP) both modulate social interaction and therefore may be involved in the pathogenesis of schizophrenia. We investigated whether men with schizophrenia show altered OT and AVP levels compared with healthy controls (HC) and whether autism symptoms are associated with OT levels.

METHODS

Forty-one men with non-acute schizophrenia and 45 matched HC were enrolled. Schizophrenia was assessed with the Positive and Negative Syndrome Scale (PANSS). Blood samples were collected on 2 days, and plasma OT and AVP levels were measured by ELISA immunoassay.

RESULTS

The schizophrenia patients had significantly lower plasma OT levels than the HC; a similar trend was found for AVP. Plasma OT levels were associated with severe life events, fewer important attached persons, and a higher score on the PANSS negative scale; the most dominant PANSS items were 'preoccupation', 'emotional withdrawal', and 'passive/apathetic social withdrawal'.

CONCLUSION

These findings support an association between the social hormones OT and AVP and schizophrenia. We suggest that OT metabolism may be altered in schizophrenia, but other possible causes for decreased plasma OT levels in schizophrenia patients include decreased OT synthesis, mRNA expression, and translation. Especially the 'autistic' symptoms of schizophrenia seem to be closely linked to an altered metabolism of OT, the 'attachment' hormone.

The role of oxytocin in empathy to the pain of conflictual out-group members among patients with schizophrenia

BACKGROUND

Oxytocin (OT) is associated with our ability to empathize and has been shown to play a major role in mediating social behaviors within the context of intergroup dynamics. Schizophrenia is associated with impaired empathy, and with a dysfunctional oxytocinergic system. The effect of OT on the empathic responses of patients with schizophrenia within the context of intergroup relationships has not been studied. The present study examined the effect of OT on the patients' empathic responses to pain experienced by in-group, conflictual out-group and neutral out-group members.

METHOD

In a double-blind, placebo-controlled, within-subject cross-over design, the responses on the Pain Evaluation Task of 28 male patients with schizophrenia were compared to 27 healthy male controls. All participants received a single intranasal dose of 24 IU OT or placebo, 1 week apart.

RESULTS

OT induced an empathy bias in the healthy controls towards the conflictual out-group members. Although this effect was absent in the patient group, OT seems to heighten an empathic bias in the patient group towards the in-group members when rating non-painful stimuli.

CONCLUSIONS

The study demonstrates that the administration of OT can result in empathic bias towards adversary out-group members in healthy controls but not in patients with schizophrenia. However, the OT-induced bias in both the patients (in the no-pain condition towards the in-group members) and the healthy controls (in the no-pain and pain conditions towards the adversary out-group) suggests that OT enhances the distinction between conflictual in-group and out-group members.

Peripherally administered oxytocin modulates latent inhibition in a manner consistent with antipsychotic drugs

BACKGROUND

Peripherally administered oxytocin (OT) has produced antipsychotic drug (APD)-like effects in animal tests that are predictive of APD efficacy. However, these effects have mainly been demonstrated using animal models of schizophrenia-like deficits in prepulse inhibition (PPI) of the startle reflex. Another schizophrenia-relevant abnormality that is the basis of a predictive animal test for APD efficacy is deficient latent inhibition (LI). LI is the normal suppression of a classically conditioned response when the subject is pre-exposed to the conditioned stimulus (CS) before it is paired with the unconditioned stimulus (UCS). Conditioned taste aversion (CTA), the normal avoidance of ingesting a food or liquid by animals when its taste is associated with an aversive experience, was used to test whether OT facilitates LI consistent with APDs.

METHODS

Brown Norway rats, known to naturally display attenuated LI, were aversively conditioned on two consecutive exposures to flavored drinking water (0.1% saccharin) by pairing it with malaise-inducing lithium chloride injections. Concurrent with conditioning, rats received subcutaneous OT (0.02, 0.1, 0.5mg/kg) or saline. Some rats were pre-exposed to the flavored water prior to its aversive conditioning (pre-exposed) while others were not (non pre-exposed). Two days after aversive conditioning the amount of flavored water consumed during a 20-min session was recorded.

RESULTS

As expected, LI, defined as greater consumption by pre-exposed vs. non pre-exposed rats was only weakly exhibited in Brown Norway rats and OT enhanced LI by reducing CTA in pre-exposed rats in a dose-dependent manner, with the 0.02 mg/kg dose producing the strongest effect.

CONCLUSIONS

The facilitation of LI by OT is consistent with the effects produced by APDs and provides further support for the notion that OT has therapeutic potential for schizophrenia.

Testing synaptic plasticity in dynamic mate choice decisions: N-methyl D-aspartate receptor blockade disrupts female preference

Social behaviours such as mate choice require context-specific responses, often with evolutionary consequences. Increasing evidence indicates that the behavioural plasticity associated with mate choice involves learning. For example, poeciliids show age-dependent changes in female preference functions and express synaptic-plasticity-associated molecular markers during mate choice. Here, we test whether social cognition is necessary for female preference behaviour by blocking the central player in synaptic plasticity, NMDAR (N-methyl d-aspartate receptor), in a poeciliid fish, Xiphophorus nigrensis. After subchronic exposure to NMDAR antagonist MK-801, female preference behaviours towards males were dramatically reduced. Overall activity levels were unaffected, but there was a directional shift from 'social' behaviours towards neutral activity. Multivariate gene expression patterns significantly discriminated between females with normal versus disrupted plasticity processes and correlated with preference behaviours-not general activity. Furthermore, molecular patterns support a distinction between 'preference' (e.g. neuroserpin, neuroligin-3, NMDAR) and 'sociality' (isotocin and vasotocin) gene clusters, highlighting a possible conservation between NMDAR disruption and nonapeptides in modulating behaviour. Our results suggest that mate preference may involve greater social memory processing than overall sociality, and that poeciliid preference functions integrate synaptic-plasticity-oriented 'preference' pathways with overall sociality to invoke dynamic, context-specific responses towards favoured males and away from unfavoured males.

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.

Dopamine D2 heteroreceptor complexes and their receptor-receptor interactions in ventral striatum: novel targets for antipsychotic drugs

This review is focused on the D2 heteroreceptor complexes within the ventral striatum with their receptor-receptor interactions and relevance for the treatment of schizophrenia. A "guide-and-clasp" manner for receptor-receptor interactions is proposed where "adhesive guides" may be amino acid triplet homologies, which were determined for different kinds of D2 heteroreceptor complexes. The first putative D2 heteroreceptor complex to be discovered in relation to schizophrenia was the A2A-D2 heteroreceptor complex where antagonistic A2A-D2 receptor-receptor interactions were demonstrated after A2A agonist treatment in the ventral striatum. The A2A agonist CGS 21680 with atypical antipsychotic properties may at least in part act by increasing β-arrestin2 signaling over the D2 protomer in the A2A-D2 heteroreceptor complex in the ventral striatum. The antagonistic NTS1-D2 interactions in the NTS1-D2 heteroreceptor complex in the ventral striatum are proposed as one molecular mechanism for the potential antipsychotic effects of NT. Indications were obtained that the psychotic actions of the 5-HT2AR hallucinogens LSD and DOI can involve enhancement of D2R protomer signaling via a biased agonist action at the 5-HT2A protomer in the D2-5-HT2A heteroreceptor complex in the ventral striatum. Facilitatory allosteric D2likeR-OTR interactions in heteroreceptor complexes in nucleus accumbens may have a role in social and emotional behaviors. By blocking the D2 protomers of these heteroreceptor complexes, antipsychotics can fail to reduce the negative symptoms of schizophrenia. The discovery of different types of D2 heteroreceptor complexes gives an increased understanding of molecular mechanisms involved in causing schizophrenia and new strategies for its treatment and understanding the side effects of antipsychotics.

Oxytocin and oxytocin receptor gene polymorphisms and risk for schizophrenia: a case-control study

OBJECTIVES

Dysfunctions of the "social brain" belong to the core features of schizophrenia. The neurohormone oxytocin (OXT), mediated through its specific receptor (OXTR), is involved in the regulation of social behaviour and social cognition. Previous research has suggested a role of OXT system genes in disorders of social reciprocity. Preliminary evidence points to an association of peripheral OXT levels as well as OXT and OXTR gene polymorphisms with psychotic symptoms and treatment response in schizophrenia. This study aims to determine a possible contribution of OXT and OXTR genetic variations to schizophrenia susceptibility.

METHODS

Using n = 406 individuals diagnosed with schizophrenia according to DSM-IV and n = 406 healthy controls matched for age and gender in a case-control design, two single nucleotide polymorphisms (SNPs) within the OXT gene (rs2740204, rs2740210) and four SNPs within the OXTR gene (rs53576, rs237880, rs237885, rs237902) that were previously investigated in other studies were genotyped.

RESULTS

Chi(2)-testing suggested significant associations of OXTR SNPs rs53576(A > G) (P = 0.008) and rs237885(T > G) (P = 0.025) with a diagnosis of schizophrenia. Post-hoc ANCOVA revealed significant associations of OXTR SNPs rs53576 with general psychopathology and rs237902 with negative symptom scores in schizophrenic patients.

CONCLUSIONS

Our findings support hypotheses about an involvement of oxytocinergic gene variants in schizophrenia vulnerability and warrant independent replication.

Characterization of the effects of oxytocin on fear recognition in patients with schizophrenia and in healthy controls

Individuals who suffer from schizophrenia often show a marked deficit in recognition of emotional facial expressions, as part of broader impairment of social cognition. Research has shown that recognition of negative emotions, specifically fear recognition, is particularly impaired among patients with schizophrenia. Recently we reported that intranasal administration of OT (IN OT) increased the ability to correctly recognize fear in a group of healthy men. The aim of the current study was to examine the effects of IN OT administration on fear recognition among patients with schizophrenia. Based on previous research, we also sought to examine a possible selective effect of OT dependent on baseline performance, hypothesizing that IN OT would have a greater enhancement effect on less proficient individuals. It was thus hypothesized that patients will show more improvement in fear recognition following the administration of IN OT as compared to controls. Sixty six participants (31 schizophrenia patients, 35 healthy controls) were enrolled in the current study. All participants received treatment of a single dose of 24 IU IN OT and an equivalent amount of placebo, 1 week apart. The participants' ability to accurately recognize fear and happiness was evaluated using a face morphing task. Overall, as a group, both patients and healthy control participants were more accurate in recognizing fearful facial expressions, but not happy faces, following IN OT administration, as compared to their performance following placebo. IN OT did not differentially affect emotion recognition in patients and healthy controls. Yet, the results indicated a selective effect for IN OT, in which the hormone improves fear recognition only among individuals whose baseline performance was below the median, regardless of their psychiatric status.

Differential correlations between plasma oxytocin and social cognitive capacity and bias in schizophrenia

Social cognitive impairment is related to poor social functioning in schizophrenia. This impairment includes both deficits in emotion perception and theory of mind (ToM), and cognitive biases including attributional bias and jumping to conclusions. Oxytocin (OXT) is a hormone that has been implicated in human social behavior, and that has also been associated with regulation of inflammation. In a cross-sectional study involving 60 patients with schizophrenia and 20 healthy controls, we examined associations between OXT and social cognitive capacity and bias. Secondary analyses examined associations between OXT and inflammation. We found significant correlations between OXT and social cognitive bias in the control group and in patients with delusions, but not in patients without delusions. Social cognitive capacity only correlated significantly with OXT in patients with delusions. A correlation between OXT and inflammation was observed only in patients without delusions. Findings suggest that OXT may be implicated in social cognition both in controls and in patients with delusions, but that this association may be blunted in patients without delusions. Inflammation appears to be related to OXT rather independently of social cognition. Future longitudinal and intervention studies with OXT are needed to clarify causality in the identified associations.

Men perform comparably to women in a perspective taking task after administration of intranasal oxytocin but not after placebo

Oxytocin (OT) is thought to play an important role in human interpersonal information processing and behavior. By inference, OT should facilitate empathic responding, i.e., the ability to feel for others and to take their perspective. In two independent double-blind, placebo-controlled between-subjects studies, we assessed the effect of intranasally administered OT on affective empathy and perspective taking, whilst also examining potential sex differences (e.g., women being more empathic than men). In study 1, we provided 96 participants (48 men) with an empathy scenario and recorded self-reports of empathic reactions to the scenario, while in study 2, a sample of 120 individuals (60 men) performed a computerized implicit perspective taking task. Whilst results from Study 1 showed no influence of OT on affective empathy, we found in Study 2 that OT exerted an effect on perspective taking ability in men. More specifically, men responded faster than women in the placebo group but they responded as slowly as women in the OT group. We conjecture that men in the OT group adopted a social perspective taking strategy, such as did women in both groups, but not men in the placebo group. On the basis of results across both studies, we suggest that self-report measures (such as used in Study 1) might be less sensitive to OT effects than more implicit measures of empathy such as that used in Study 2. If these assumptions are confirmed, one could infer that OT effects on empathic responses are more pronounced in men than women, and that any such effect is best studied using more implicit measures of empathy rather than explicit self-report measures.

Sniffing around oxytocin: review and meta-analyses of trials in healthy and clinical groups with implications for pharmacotherapy

The popularity of oxytocin (OT) has grown exponentially during the past decade, and so has the number of OT trials in healthy and clinical groups. We take stock of the evidence from these studies to explore potentials and limitations of pharmacotherapeutic applications. In healthy participants, intranasally administered OT leads to better emotion recognition and more trust in conspecifics, but the effects appear to be moderated by context (perceived threat of the 'out-group'), personality and childhood experiences. In individuals with untoward childhood experiences, positive behavioral or neurobiological effects seem lowered or absent. In 19 clinical trials, covering autism, social anxiety, postnatal depression, obsessive-compulsive problems, schizophrenia, borderline personality disorder and post-traumatic stress, the effects of OT administration were tested, with doses ranging from 15 IU to more than 7000 IU. The combined effect size was d=0.32 (N=304; 95% confidence interval (CI): 0.18-0.47; P<0.01). However, of all disorders, only studies on autism spectrum disorder showed a significant combined effect size (d=0.57; N=68; 95% CI: 0.15-0.99; P<0.01). We hypothesize that for some of the other disorders, etiological factors rooted in negative childhood experiences may also have a role in the diminished effectiveness of treatment with OT.

Peripheral vasopressin but not oxytocin relates to severity of acute psychosis in women with acutely-ill untreated first-episode psychosis

BACKGROUND

In women with chronic schizophrenia, higher levels of peripheral oxytocin have been associated with lower levels of positive but not negative symptoms. Sex-specific associations between endogenous levels of oxytocin (OT) and arginine vasopressin (AVP) with clinical symptoms and cognition in untreated early course patients have not been examined.

METHOD

Clinical ratings and neuropsychological testing were performed in thirty-eight acutely ill, unmedicated first-episode schizophrenia patients (14 women, 24 men). Serum hormone assays were obtained in patients and thirty-eight demographically similar healthy controls.

RESULTS

Patients demonstrated increased AVP levels compared to controls (p = 0.01). Higher AVP levels were associated with greater positive symptoms (r = 0.58, p = 0.03) and worse verbal learning (r = -0.63, p = 0.02) in female, but not male, patients. OT levels did not statistically differ between patients and controls, and were unrelated to clinical symptoms or cognition in patients.

CONCLUSION

Results suggest an association of endogenous AVP with increased positive symptom severity and worse cognition in untreated female, but not male, schizophrenia patients. Findings support the role of neuroendocrine alterations in acute psychosis and the importance of examining sex-specific neuroendocrine alterations early in the course of schizophrenia.

Alternative pharmacologic targets for the treatment of schizophrenia: results from phase I and II trials

PURPOSE OF REVIEW

The current article provides a brief review of the clinical efficacy and safety outcomes from selected phase I and II clinical trials of compounds in development acting on targets beyond the dopamine D2 receptor in patients with schizophrenia.

RECENT FINDINGS

A number of experimental pharmacological targets have been studied in clinical trials. Among those, glutamatergic and nicotinergic pathways have received most attention. Glycine transporter 1 inhibitors used adjunctively with antipsychotics suggest efficacy for negative symptoms of schizophrenia. Adjunctive alpha7 nicotinic acetylcholine receptor agonists and minocycline may improve negative symptoms and cognitive deficits. Adjunctive oxytocin may benefit psychotic symptoms and social cognitive deficits. Adjunctive erythropoietin may improve cognitive function.

SUMMARY

Experimental therapeutic research for schizophrenia is rapidly expanding and a number of compounds with novel mechanisms of action are demonstrating encouraging evidence for efficacy across a range of symptoms. However, much work still needs to be conducted before these new agents can be considered for routine clinical treatment. In particular, further assessment of efficacy and longer term safety and tolerability monitoring are required.

Intranasal oxytocin as an adjunct to risperidone in patients with schizophrenia : an 8-week, randomized, double-blind, placebo-controlled study

BACKGROUND

Impairment of oxytocinergic function and/or oxytocin receptor genetic abnormalities has been demonstrated in patients with schizophrenia. Oxytocin reverses emotional recognition deficit and might restore sense of trust in patients with schizophrenia. Some short-term studies have shown efficacy and tolerability of oxytocin in patients with schizophrenia. However, there is a lack of evidence on the efficacy and tolerability of oxytocin in patients with schizophrenia beyond 3 weeks.

OBJECTIVE

The objective of this study was to assess the efficacy and tolerability of oxytocin intranasal spray (given as an adjuvant to risperidone) in patients with schizophrenia.

STUDY DESIGN

This was an 8-week, randomized, double-blind, placebo-controlled study.

STUDY SETTING

Inpatients of two large referral psychiatric hospitals in Iran were recruited for the study.

PATIENTS

Forty patients (male and female gender) aged 18-50 years with a diagnosis of schizophrenia (DSM-IV-TR) who were on a stable dose of risperidone for a minimum of 1 month and who were chronically partially responsive to antipsychotic monotherapy were included in the study.

INTERVENTIONS

The patients were randomly assigned to oxytocin intranasal spray (Syntocinon(®); Novartis, Basel, Switzerland) or placebo intranasal spray containing normal saline (ACER, Tehran, Iran) for 8 weeks. Oxytocin spray was administered as 20 IU (five sprays) twice a day for the first week followed by 40 IU (ten sprays) twice a day for the following 7 weeks. Placebo spray was administered at the same dose as the oxytocin spray. In addition, participants were on a stable dose of risperidone (5 or 6 mg/day).

OUTCOMES

The patients were assessed using Positive and Negative Syndrome Scale (PANSS) at baseline and at weeks 0, 2, 4, 6 and 8. Primary outcomes were the differences in the PANSS scores between the two groups at the end of the trial. Adverse effects were recorded using a checklist and the Extrapyramidal Symptom Rating Scale (ESRS) at baseline and at weeks 1, 2, 4, 6 and 8.

RESULTS

All patients had at least one post-baseline measurement and 37 patients (19 in the oxytocin and 18 in the placebo group) completed the study. Repeated measure analysis of variance showed significant effect for time X treatment interaction on the PANSS total [F(2.291,87.065) = 22.124, p < 0.001], positive [F(1.285,48.825) = 11.655, p = 0.001], negative [F(2.754,104.649) = 11.818, p < 0.001] and general psychopathology [F(1.627,61.839) = 4.022, p = 0.03] subscale scores. By week 8, patients in the oxytocin group showed significantly greater improvement on the positive (Cohen's d = 1.2, 20 % vs. 4 % reduction in score, p < 0.001), negative (Cohen's d = 1.4, 7 % vs. 2 % reduction in score, p < 0.001) and general psychopathology (Cohen's d = 0.8, 8 % vs. 2 % reduction in score, p = 0.021) subscales and total (Cohen's d = 1.9, 11 % vs. 2 % reduction in score, p < 0.001) PANSS scores than the placebo group. Adverse effects including the sodium concentration change were similar between the two groups.

CONCLUSION

Oxytocin as an adjunct to risperidone tolerably and efficaciously improves positive symptoms of schizophrenia. In addition, effects on negative and total psychopathology scores were statistically significant, but likely to be clinically insignificant. The interesting findings from the present pilot study need further replication in a larger population of patients.