A Role for Oxytocin in the Etiology and Treatment of Schizophrenia

Linking childhood trauma to the psychopathology of schizophrenia: the role of oxytocin

Childhood trauma has been linked to schizophrenia, but underlying biological mechanisms remain elusive. This study explored the potential role of plasma oxytocin as a mediator in the relationship between childhood trauma and the psychopathology of schizophrenia. 160 patients with schizophrenia and 80 age- and sex-matched healthy controls were assessed for childhood trauma experiences using the Childhood Trauma Questionnaire and structured interviews. Psychopathology was evaluated using the Positive and Negative Syndrome Scale and plasma oxytocin levels were measured. Results showed that patients with schizophrenia had lower oxytocin levels and higher childhood trauma scores than healthy controls. There was a significant correlation between childhood trauma scores and psychopathology, with plasma oxytocin levels being inversely associated with psychopathology, except for positive symptoms. Hierarchical regression analysis indicated that both childhood trauma scores and plasma oxytocin levels significantly predicted psychopathology. Plasma oxytocin levels partially mediated the relationship between childhood trauma and schizophrenia psychopathology. This study underscores the potential role of oxytocin in bridging the gap between childhood trauma and schizophrenia.

Intranasal Peptide Therapeutics: A Promising Avenue for Overcoming the Challenges of Traditional CNS Drug Development

The central nervous system (CNS) has, among all organ systems in the human body, the highest failure rate of traditional small-molecule drug development, ranging from 80-100% depending on the area of disease research. This has led to widespread abandonment by the pharmaceutical industry of research and development for CNS disorders, despite increased diagnoses of neurodegenerative disorders and the continued lack of adequate treatment options for brain injuries, stroke, neurodevelopmental disorders, and neuropsychiatric illness. However, new approaches, concurrent with the development of sophisticated bioinformatic and genomic tools, are being used to explore peptide-based therapeutics to manipulate endogenous pathways and targets, including "undruggable" intracellular protein-protein interactions (PPIs). The development of peptide-based therapeutics was previously rejected due to systemic off-target effects and poor bioavailability arising from traditional oral and systemic delivery methods. However, targeted nose-to-brain, or intranasal (IN), approaches have begun to emerge that allow CNS-specific delivery of therapeutics via the trigeminal and olfactory nerve pathways, laying the foundation for improved alternatives to systemic drug delivery. Here we review a dozen promising IN peptide therapeutics in preclinical and clinical development for neurodegenerative (Alzheimer's, Parkinson's), neuropsychiatric (depression, PTSD, schizophrenia), and neurodevelopmental disorders (autism), with insulin, NAP (davunetide), IGF-1, PACAP, NPY, oxytocin, and GLP-1 agonists prominent among them.

Treatments for Social Interaction Impairment in Animal Models of Schizophrenia: A Critical Review and Meta-analysis

BACKGROUND

While pharmacological treatments for positive symptoms of schizophrenia are widely used, their beneficial effect on negative symptoms, particularly social impairment, is insufficiently studied. Therefore, there is an increasing interest in preclinical research of potentially beneficial treatments, with mixed results. The current review aims to evaluate the efficacy of available treatments for social deficits in different animal models of schizophrenia.

STUDY DESIGN

A systematic literature search generated 145 outcomes for the measures "total time" and "number" of social interactions. Standardized mean differences (SMD) and 95% confidence interval (CI) were calculated, and heterogeneity was tested using Q statistics in a random-effect meta-analytic model. Given the vast heterogeneity in effect sizes, the animal model, treatment group, and sample size were all examined as potential moderators.

STUDY RESULTS

The results showed that in almost all models, treatment significantly improved social deficit (total time: SMD = 1.24; number: SMD = 1.1). The moderator analyses discovered significant subgroup differences across models and treatment subgroups. Perinatal and adult pharmacological models showed the most substantial influence of treatments on social deficits, reflecting relative pharmacological validity. Furthermore, atypical antipsychotic drugs had the highest SMD within each model subgroup.

CONCLUSIONS

Our findings indicate that the improvement in social interaction behaviors is dependent on the animal model and treatment family used. Implications for the preclinical and clinical fields are discussed.

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

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

Multiple Aspects of Inappropriate Action of Renin-Angiotensin, Vasopressin, and Oxytocin Systems in Neuropsychiatric and Neurodegenerative Diseases

The cardiovascular system and the central nervous system (CNS) closely cooperate in the regulation of primary vital functions. The autonomic nervous system and several compounds known as cardiovascular factors, especially those targeting the renin-angiotensin system (RAS), the vasopressin system (VPS), and the oxytocin system (OTS), are also efficient modulators of several other processes in the CNS. The components of the RAS, VPS, and OTS, regulating pain, emotions, learning, memory, and other cognitive processes, are present in the neurons, glial cells, and blood vessels of the CNS. Increasing evidence shows that the combined function of the RAS, VPS, and OTS is altered in neuropsychiatric/neurodegenerative diseases, and in particular in patients with depression, Alzheimer's disease, Parkinson's disease, autism, and schizophrenia. The altered function of the RAS may also contribute to CNS disorders in COVID-19. In this review, we present evidence that there are multiple causes for altered combined function of the RAS, VPS, and OTS in psychiatric and neurodegenerative disorders, such as genetic predispositions and the engagement of the RAS, VAS, and OTS in the processes underlying emotions, memory, and cognition. The neuroactive pharmaceuticals interfering with the synthesis or the action of angiotensins, vasopressin, and oxytocin can improve or worsen the effectiveness of treatment for neuropsychiatric/neurodegenerative diseases. Better knowledge of the multiple actions of the RAS, VPS, and OTS may facilitate programming the most efficient treatment for patients suffering from the comorbidity of neuropsychiatric/neurodegenerative and cardiovascular diseases.

Differential H3K9me2 heterochromatin levels and concordant mRNA expression in postmortem brain tissue of individuals with schizophrenia, bipolar, and controls

The existence of repressive and durable chromatin assemblies along gene promoters or networks, especially in the brain, is of theoretical and therapeutic relevance in a subset of individuals diagnosed with schizophrenia who experience a chronic, persistent, and treatment-resistant trajectory. We used chromatin immunoprecipitation followed by deep sequencing (ChIP-Seq) to generate an epigenomic map that includes differential sites occupied by di-methylated lysine 9 of histone 3 (H3K9me2), a repressive modification that is yet unexplored in human postmortem brain tissue. We have discovered over 150 significantly differential promoter sites in the postmortem prefrontal cortex tissue of individuals diagnosed with schizophrenia (n = 15) when compared to controls (n = 15). Potentially dysregulated gene categories include postsynaptic proteins, processing enzymes (for proproteins, lipids, and oxidative stress), cadherin family genes, the complement system, and peptide hormones. Ten genes with significantly increased or decreased H3K9me2 promoter occupation were selected through statistical analysis, function, or previous GWAS association, and Quantitative RT-PCR (qRT-PCR) was performed on an extended sample of postmortem brain tissue, adding an additional 17 controls, 7 individuals with schizophrenia, and 19 individuals with bipolar samples (n = 32 control, 22 schizophrenia, 19 bipolar). This approach revealed that mRNA expression levels correlated with chromatin modification levels in eight of 10 selected genes, and mRNA expression in the total sample could be predicted by the occupancy of H3K9me2. Utilization of this method and replication in a larger sample open a pathway to durable and restrictive epigenomic assemblies whose accumulation across the lifespan of individuals diagnosed with schizophrenia may explain treatment resistance, and advance therapeutic options.

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.

Neural and Molecular Contributions to Pathological Jealousy and a Potential Therapeutic Role for Intranasal Oxytocin

Romantic jealousy, especially in its pathological form, is a significant contributor to both domestic abuse, including partner sexual coercion and even murder, although relatively little research has been conducted on it. Both obsessive and delusional forms have been identified although only the latter is currently recognized as a pathological disorder. Studies in both clinical and healthy populations have identified altered fronto-striatal responsivity as being associated primarily with romantic jealousy and to date drug based treatments have targeted both dopaminergic and serotonergic systems. However, there is increasing interest in a potential role for the neuropeptide oxytocin, which can also modulate dopaminergic and serotonin systems in the brain and has been shown to altered in other psychotic conditions, such as schizophrenia and obsessive compulsive disorder. Recent studies in healthy populations have reported that when oxytocin is administered intranasally it can influence the brain to promote strengthening of romantic bonds and reduce romantic jealousy in both men and women evoked in either imagined or real contexts. These findings indicate a possible therapeutic use of intranasal oxytocin administration in pathological jealousy.

Early Environmental Upheaval and the Risk for Schizophrenia

Why does prenatal exposure to wars, natural disasters, urbanicity, or winter increase the risk for schizophrenia? Research from the last two decades has provided rich insight about the underlying chains of causation at play during environmental upheaval, from conception to early infancy. In this review, we appraise the evidence linking schizophrenia spectrum disorder to prenatal maternal stress, obstetric complications, early infections, and maternal nutrition and other lifestyle factors. We discuss putative mechanisms, including the maternal stress system, perinatal hypoxia, and maternal-offspring immune activation. We propose that gene-environment interactions, timing during development, and sex differentiate the neuropsychiatric outcomes. Future research should pursue the translation of animal studies to humans and the longitudinal associations between early exposures, intermediate phenotypes, and psychiatric disorders. Finally, to paint a comprehensive model of risk and to harness targets for prevention, we argue that risk factors should be situated within the individual's personal ecosystem.

Epigenetic mechanisms in schizophrenia and other psychotic disorders: a systematic review of empirical human findings

Schizophrenia and other psychotic disorders are highly debilitating psychiatric conditions that lack a clear etiology and exhibit polygenic inheritance underlain by pleiotropic genes. The prevailing explanation points to the interplay between predisposing genes and environmental exposure. Accumulated evidence suggests that epigenetic regulation of the genome may mediate dynamic gene-environment interactions at the molecular level by modulating the expression of psychiatric phenotypes through transcription factors. This systematic review summarizes the current knowledge linking schizophrenia and other psychotic disorders to epigenetics, based on PubMed and Web of Science database searches conducted according to the PRISMA guidelines. Three groups of mechanisms in case-control studies  of human tissue (i.e., postmortem brain and bio-fluids) were considered: DNA methylation, histone modifications, and non-coding miRNAs. From the initial pool of 3,204 records, 152 studies met our inclusion criteria (11,815/11,528, 233/219, and 2,091/1,827 cases/controls for each group, respectively). Many of the findings revealed associations with epigenetic modulations of genes regulating neurotransmission, neurodevelopment, and immune function, as well as differential miRNA expression (e.g., upregulated miR-34a, miR-7, and miR-181b). Overall, actual evidence moderately supports an association between epigenetics and schizophrenia and other psychotic disorders. However, heterogeneous results and cross-tissue extrapolations call for future work. Integrating epigenetics into systems biology may critically enhance research on psychosis and thus our understanding of the disorder. This may have implications for psychiatry in risk stratification, early recognition, diagnostics, precision medicine, and other interventional approaches targeting epigenetic fingerprints.

Nicotinamide riboside supplementation corrects deficits in oxytocin, sociability and anxiety of CD157 mutants in a mouse model of autism spectrum disorder

Oxytocin (OT) is a critical molecule for social recognition and memory that mediates social and emotional behaviours. In addition, OT acts as an anxiolytic factor and is released during stress. Based on the activity of CD38 as an enzyme that produces the calcium-mobilizing second messenger cyclic ADP-ribose (cADPR), CD157, a sister protein of CD38, has been considered a candidate mediator for the production and release of OT and its social engagement and anti-anxiety functions. However, the limited expression of CD157 in the adult mouse brain undermined confidence that CD157 is an authentic and/or actionable molecular participant in OT-dependent social behaviour. Here, we show that CD157 knockout mice have low levels of circulating OT in cerebrospinal fluid, which can be corrected by the oral administration of nicotinamide riboside, a recently discovered vitamin precursor of nicotinamide adenine dinucleotide (NAD). NAD is the substrate for the CD157- and CD38-dependent production of cADPR. Nicotinamide riboside corrects social deficits and fearful and anxiety-like behaviours in CD157 knockout males. These results suggest that elevating NAD levels with nicotinamide riboside may allow animals with cADPR- and OT-forming deficits to overcome these deficits and function more normally.

Demographic, clinical and social characteristics of forensic patients diagnosed with schizophrenia at the Free State Psychiatric Complex, Bloemfontein, South Africa

Schizophrenia, prevalent in forensic mental health settings, is chronic and devastating, with a generally unfavourable course and prognosis. The aim of this study was to determine the demographic, clinical and social characteristics of forensic patients diagnosed with schizophrenia at the Free State Psychiatric Complex. A data collection form was used to gather information from the clinical records of patients diagnosed with schizophrenia between 1 January 2011 and 31 December 2015. The majority of the 110 participants were young male adults aged between 18 and 35 years with a low educational level. Cognitive impairment and positive symptoms were the most prominent clinical features. Aggressive and violent behaviour was notably prevalent. The majority of our sample had committed crimes against humans, while fewer had committed other types of crimes. It was concluded that causal factors included young adulthood, male gender, substance abuse, a poor social support system and lower educational level.

Maternal High Fat Diet-Induced Obesity Modifies Histone Binding and Expression of Oxtr in Offspring Hippocampus in a Sex-Specific Manner

Maternal obesity during pregnancy increases risk for neurodevelopmental disorders in offspring, although the underlying mechanisms remain unclear. Epigenetic deregulation associates with many neurodevelopmental disorders, and recent evidence indicates that maternal nutritional status can alter chromatin marks in the offspring brain. Thus, maternal obesity may disrupt epigenetic regulation of gene expression during offspring neurodevelopment. Using a C57BL/6 mouse model, we investigated whether maternal high fat diet (mHFD)-induced obesity alters the expression of genes previously implicated in the etiology of neurodevelopmental disorders within the Gestational Day 17.5 (GD 17.5) offspring hippocampus. We found significant two-fold upregulation of oxytocin receptor (Oxtr) mRNA in the hippocampus of male, but not female, GD 17.5 offspring from mHFD-induced obese dams (p < 0.05). To determine whether altered histone binding at the Oxtr gene promoter may underpin these transcriptional changes, we then performed chromatin immunoprecipitation (ChIP). Consistent with the Oxtr transcriptional changes, we observed increased binding of active histone mark H3K9Ac at the Oxtr transcriptional start site (TSS) in the hippocampus of mHFD male (p < 0.05), but not female, offspring. Together, these data indicate an increased vulnerability of male offspring to maternal obesity-induced changes in chromatin remodeling processes that regulate gene expression in the developing hippocampus, and contributes to our understanding of how early life nutrition affects the offspring brain epigenome.

Sex-dependent regulation of social reward by oxytocin: an inverted U hypothesis

The rewarding properties of social interactions are essential for the expression of social behavior and the development of adaptive social relationships. Here, we review sex differences in social reward, and more specifically, how oxytocin (OT) acts in the mesolimbic dopamine system (MDS) to mediate the rewarding properties of social interactions in a sex-dependent manner. Evidence from rodents and humans suggests that same-sex social interactions may be more rewarding in females than in males. We propose that there is an inverted U relationship between OT dose, social reward, and neural activity within structures of the MDS in both males and females, and that this dose-response relationship is initiated at lower doses in females than males. As a result, depending on the dose of OT administered, OT could reduce social reward in females, while enhancing it in males. Sex differences in the neural mechanisms regulating social reward may contribute to sex differences in the incidence of a large number of psychiatric and neurodevelopmental disorders. This review addresses the potential significance of a sex-dependent inverted U dose-response function for OT's effects on social reward and in the development of gender-specific therapies for these disorders.

The past and future of novel, non-dopamine-2 receptor therapeutics for schizophrenia: A critical and comprehensive review

Since the discovery of chlorpromazine in the 1950's, antipsychotic drugs have been the cornerstone of treatment of schizophrenia, and all attenuate dopamine transmission at the dopamine-2 receptor. Drug development for schizophrenia since that time has led to improvements in side effects and tolerability, and limited improvements in efficacy, with the exception of clozapine. However, the reasons for clozapine's greater efficacy remain unclear, despite the great efforts and resources invested therewith. We performed a comprehensive review of the literature to determine the fate of previously tested, non-dopamine-2 receptor experimental treatments. Overall we included 250 studies in the review from the period 1970 to 2017 including treatments with glutamatergic, serotonergic, cholinergic, neuropeptidergic, hormone-based, dopaminergic, metabolic, vitamin/naturopathic, histaminergic, infection/inflammation-based, and miscellaneous mechanisms. Despite there being several promising targets, such as allosteric modulation of the NMDA and α7 nicotinic receptors, we cannot confidently state that any of the mechanistically novel experimental treatments covered in this review are definitely effective for the treatment of schizophrenia and ready for clinical use. We discuss potential reasons for the relative lack of progress in developing non-dopamine-2 receptor treatments for schizophrenia and provide recommendations for future efforts pursuing novel drug development for schizophrenia.

Prosocial effects of an oxytocin metabolite, but not synthetic oxytocin receptor agonists, in a mouse model of autism

Currently, there are no established pharmaceutical strategies that effectively treat social deficits in autism spectrum disorder (ASD). Oxytocin, a neurohormone that plays a role in multiple types of social behaviors, has been proposed as a possible therapeutic against social impairment and other symptoms in ASD. However, from the standpoint of pharmacotherapy, oxytocin has several liabilities as a standard clinical treatment, including rapid metabolism, low brain penetrance, and activity at the vasopressin (antidiuretic hormone) receptors. The present studies describe findings from a preclinical screening program to evaluate oxytocin receptor (OXTR) agonists and oxytocin metabolites for potential clinical use as more optimal treatments. We first investigated two synthetic oxytocin analogs, TC-OT-39 and carbetocin, using in vitro cell-based assays for pharmacological characterization and behavioral tests in the BALB/cByJ mouse model of ASD-like social deficits. Although both TC-OT-39 and carbetocin selectively activate the OXTR, neither synthetic agonist had prosocial efficacy in the BALB/cByJ model. We next evaluated two oxytocin metabolites: OT(4-9) and OT(5-9). While OT(5-9) failed to affect social deficits, the metabolite OT(4-9) led to significant social preference in the BALB/cByJ model, in a dose-dependent manner. The increased sociability was observed at both 24 h and 12 days following the end of a subchronic regimen with OT(4-9) (2.0 mg/kg). Overall, these results suggest that the prosocial effects of oxytocin could be mediated by downstream activity of oxytocin metabolites, raising the possibility of new pathways to target for drug discovery relevant to ASD.

Selective and non-selective OT receptor agonists induce different locomotor behaviors in male rats via central OT receptors and peripheral V1a receptors

Oxytocin (OT) continues to inspire much research due to its diverse physiological effects. While the best-understood actions of OT are uterine contraction and milk ejection, OT is also implicated in maternal and bonding behaviors, and potentially in CNS disorders such as autism, schizophrenia, and pain. The dissection of the mechanism of action of OT is complicated by the fact that this peptide activates not only its cognate receptor but also vasopressin type 1a (V1a) receptors. In this study, we evaluated OT and a selective OT receptor (OTR) agonist, FE 204409, in an automated assay that measures rat locomotor activity. The results showed: 1) Subcutaneous (sc) administration of OT decreased locomotor behavior (distance traveled, stereotypy, and rearing). This effect was reversed by a V1a receptor (V1aR) antagonist ([Pmp1,Tyr(ME)2]AVP, sc), suggesting that OT acts through peripheral V1aR to inhibit locomotor activity. 2) A selective OTR agonist (FE 204409, sc) increased stereotypy. This effect was reversed by an OTR antagonist dosed icv, suggesting a central OTR site of action. Our findings identify distinct behavioral effects for OT and the selective agonist FE 204409, adding to the growing body of evidence that the V1aR mediates many effects attributed to OT and that peptides administered systemically at supra-physiological doses may activate receptors in the brain. Our studies further emphasize the importance of utilizing selective agonists and antagonists to assess therapeutic indications.

Oxytocin Reduces Alcohol Cue-Reactivity in Alcohol-Dependent Rats and Humans

Approved pharmacological treatments for alcohol use disorder are limited in their effectiveness, and new drugs that can easily be translated into the clinic are warranted. One of those candidates is oxytocin because of its interaction with several alcohol-induced effects. Alcohol-dependent rats as well as post-mortem brains of human alcoholics and controls were analyzed for the expression of the oxytocin system by qRT-PCR, in situ hybridization, receptor autoradiography ([¹²⁵I]OVTA binding), and immunohistochemistry. Alcohol self-administration and cue-induced reinstatement behavior was measured after intracerebroventricular injection of 10 nM oxytocin in dependent rats. Here we show a pronounced upregulation of oxytocin receptors in brain tissues of alcohol-dependent rats and deceased alcoholics, primarily in frontal and striatal areas. This upregulation stems most likely from reduced oxytocin expression in hypothalamic nuclei. Pharmacological validation showed that oxytocin reduced cue-induced reinstatement response in dependent rats-an effect that was not observed in non-dependent rats. Finally, a clinical pilot study (German clinical trial number DRKS00009253) using functional magnetic resonance imaging in heavy social male drinkers showed that intranasal oxytocin (24 IU) decreased neural cue-reactivity in brain networks similar to those detected in dependent rats and humans with increased oxytocin receptor expression. These studies suggest that oxytocin might be used as an anticraving medication and thus may positively affect treatment outcomes in alcoholics.

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.

Insulin-regulated aminopeptidase immunoreactivity is abundantly present in human hypothalamus and posterior pituitary gland, with reduced expression in paraventricular and suprachiasmatic neurons in chronic schizophrenia

The vasopressin- and oxytocin-degrading enzyme insulin-regulated aminopeptidase (IRAP) is expressed in various organs including the brain. However, knowledge about its presence in human hypothalamus is fragmentary. Functionally, for a number of reasons (genetic linkage, hydrolysis of oxytocin and vasopressin, its role as angiotensin IV receptor in learning and memory and others) IRAP might play a role in schizophrenia. We studied the regional and cellular localization of IRAP in normal human brain with special emphasis on the hypothalamus and determined numerical densities of IRAP-expressing cells in the paraventricular, supraoptic and suprachiasmatic nuclei in schizophrenia patients and controls. By using immunohistochemistry and Western blot analysis, IRAP was immunolocalized in postmortem human brains. Cell countings were performed to estimate numbers and numerical densities of IRAP immunoreactive hypothalamic neurons in schizophrenia patients and control cases. Shape, size and regional distribution of IRAP-expressing cells, as well the lack of co-localization with the glia marker glutamine synthetase, show that IRAP is expressed in neurons. IRAP immunoreactive cells were observed in the hippocampal formation, cerebral cortex, thalamus, amygdala and, abundantly, hypothalamus. Double labeling experiments (IRAP and oxytocin/neurophysin 1, IRAP with vasopressin/neurophysin 2) revealed that IRAP is present in oxytocinergic and in vasopressinergic neurons. In schizophrenia patients, the numerical density of IRAP-expressing neurons in the paraventricular and the suprachiasmatic nuclei is significantly reduced, which might be associated with the reduction in neurophysin-containing neurons in these nuclei in schizophrenia. The pathophysiological role of lowered hypothalamic IRAP expression in schizophrenia remains to be established.

Oxytocin and Vasopressin: Powerful Regulators of Social Behavior

For many, the terms oxytocin and vasopressin immediately evoke images of animals interacting with one another, as both of these neuropeptides have been implicated as being part of the neurochemical "glue" that socially binds animals. However, social environments and social interactions are complex and include behaviors that bring animals together as well as behaviors that keep animals apart. It is at the intersection of social context, social experience, and an individual's sex that oxytocin and vasopressin act to modulate social behavior and social cognition. In this review, this complexity will be explored across mammalian species, with a focus on social memory, cooperative behaviors, and competitive behaviors. Implications for humans as well as future directions will also be considered.

Symptomatic thinking: the current state of Phase III and IV clinical trials for cognition in schizophrenia

Research indicates that relieving the cognitive and negative symptoms of schizophrenia is crucial for improving patient quality of life. However effective pharmacotherapies for cognitive and negative symptoms do not currently exist. A review of ongoing Phase III clinical trials indicates that, despite numerous compounds being investigated for cognition in schizophrenia, few are actually novel and most are not backed by empirically driven preclinical research efforts. Based on these trials, and a general disinvestment in development of novel therapies for schizophrenia, the likelihood of a major advancement in treating cognitive differences in schizophrenia does not look promising. Possible ways in which the remaining resources for development of novel treatment for schizophrenia can best be leveraged are discussed.

PRELIMINARY INSIGHTS IN OXYTOCIN ASSOCIATION WITH THE ONSET OF DIABETIC NEUROPATHY

Diabetes is one of the most prevalent chronic disorders, associating numerous somatic and behavioral modifications. Oxytocin has been widely studied for its involvement in social behavior and psychiatric disorders. This pilot study presents a series of 3 patients with type 1 diabetes and diabetic neuropathy in which the values of plasma oxytocin, neurotensin, β-endorphins, α-MSH, substance P and orexin A were measured in comparison to 3 healthy controls with matching ages. In the diabetic patients group, there was a strong negative correlation between the value of plasma glucose and oxytocin (r=-0.99, p=0.04), respectively neurotensin (r=-0.99, p=0.03). These values did not correlate in the control group. The results suggest that oxytocin, in conjunction with neurotensin, could be investigated as a potential early detection marker of diabetic neuropathy and, to our knowledge, this is the first report focusing on plasma oxytocin levels in patients with diabetic neuropathy.

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.

Oxytocin to modulate emotional processing in schizophrenia: A randomized, double-blind, cross-over clinical trial

Deficits in social cognition, including emotional processing, are hallmarks of schizophrenia and antipsychotic agents seem to be ineffectual to improve these symptoms. However, oxytocin does seem to have beneficial effects on social cognition. The aim of this study was to examine the effects of four months of treatment with intranasal oxytocin, in 31 patients with schizophrenia, on distinct aspects of social cognition. This was assessed using standardized and experimental tests in a randomized, double-blind, placebo-controlled, cross-over trial. All patients underwent clinical and experimental assessment before treatment, four months after treatment and at the end of treatment. Social cognition abilities were assessed with the Mayer-Salovey-Caruso Emotional Intelligence Test (MSCEIT) and the Reading the Mind in the Eyes task (RMET). Furthermore, an Emotional Priming Paradigm (EPP) was developed to examine the effects of oxytocin on implicit perceptual sensitivity to affective information and explicit facial affect recognition. We found that oxytocin improved performance on MSCEIT compared to placebo in Branch 3-Understanding Emotion (p-value=0.004; Cohen׳s d=1.12). In the EPP task, we observed a significant reduction of reaction times for facial affect recognition (p-value=0.021; Cohen׳s d=0.88). No effects were found for implicit priming or for theory of mind abilities. Further study is required in order to highlight the potential for possible integration of oxytocin with antipsychotic agents as well as to evaluate psycho-social treatment as a multi-dimensional approach to increase explicit emotional processing abilities and compensate social cognition deficits related to schizophrenia.

Cocaine abstinence induces emotional impairment and brain region-specific upregulation of the oxytocin receptor binding

The key problem in treating cocaine addiction is the maintenance of a drug-free state as negative emotional symptoms during abstinence often trigger relapse. The mechanisms underpinning the emotional dysregulation during abstinence are currently not well-understood. There is evidence suggesting a role of the neuropeptide oxytocin in the modulation of drug addiction processes. However, its involvement during long-term abstinence from cocaine use remains unclear. In this study, we aimed to behaviourally characterize a mouse model of long-term cocaine withdrawal and assess the effect of chronic cocaine administration and long-term cocaine abstinence on the central oxytocinergic system and the hypothalamic-pituitary-adrenal axis. Fourteen-day escalating-dose cocaine administration (3 × 15-30 mg/kg/day) and 14-day withdrawal increased plasma corticosterone levels and oxytocin receptor (OTR) binding in piriform cortex, lateral septum and amygdala. A specific cocaine withdrawal-induced increase in OTR binding was observed in the medial septum. These biochemical alterations occurred concomitantly with the emergence of memory impairment, contextual psychomotor sensitization and an anhedonic and anxiogenic phenotype during withdrawal. Our study established a clear relationship between cocaine abstinence and emotional impairment in a novel translationally relevant model of cocaine withdrawal and demonstrated for the first time brain region-specific neuroadaptations of the oxytocin system, which may contribute to abstinence-induced negative emotional state.

Oxytocin Receptor (OXTR) Methylation and Cognition in Psychotic Disorders

Previous reports have identified an association between cognitive impairment and genetic variation in psychotic disorders. In particular, this association may be related to abnormal regulation of genes responsible for broad cognitive functions such as the oxytocin receptor (OXTR). Within psychotic disorders, it is unknown if OXTR methylation, which can have important implications for gene regulation, is related to cognitive function. The current study examined peripheral blood OXTR methylation and general cognition in people with schizophrenia, schizoaffective disorder, and psychotic disorder not otherwise specified (N = 101). Using hierarchical multiple regression analysis, methylation at the Chr3:8767638 site was significantly associated with composite cognitive performance independent of demographic and medication factors while controlling for multiple testing in this combined diagnostic sample (adjusted p = 0.023).

Comparison of Plasma Neurosteroid and Prolactin Levels in Patients with Schizophrenia and Healthy Individuals

Background. The present study aimed to compare plasma levels of cortisol, testosterone, dehydroepiandrosterone (DHEA), and prolactin in patients with schizophrenia and healthy individuals. Method. A total of 100 patients with schizophrenia disorder (69 men and 31 women) and 190 healthy individuals (94 men and 96 women) participated in this cross-sectional study. They were tested for hormone levels and completed demographic questionnaires. Data were analyzed using multivariate analysis of variance (MANOVA) and one-way analysis of variance. Results. Serum testosterone level was significantly higher in men with schizophrenia than in healthy men. Women with schizophrenia had a significantly higher level of testosterone and lower level of prolactin compared to healthy women. There were no significant differences in hormone levels across various subtypes of schizophrenia. No significant differences also were observed in hormones levels in patients with first-episode schizophrenia disorder compared to those in patients with recurrent episodes. Conclusion. This study indicated that abnormal testosterone and prolactin levels might be associated with pathophysiology of schizophrenia disorder.

Treating Negative Symptoms in Schizophrenia: an Update

Interest in the negative symptoms of schizophrenia has increased rapidly over the last several decades, paralleling a growing interest in functional, in addition to clinical, recovery, and evidence underscoring the importance negative symptoms play in the former. Efforts continue to better define and measure negative symptoms, distinguish their impact from that of other symptom domains, and establish effective treatments as well as trials to assess these. Multiple interventions have been the subject of investigation, to date, including numerous pharmacological strategies, brain stimulation, and non-somatic approaches. Level and quality of evidence vary considerably, but to this point, no specific treatment can be recommended. This is particularly problematic for individuals burdened with negative symptoms in the face of mild or absent positive symptoms. Presently, clinicians will sometimes turn to interventions that are seen as more “benign” and in line with routine clinical practice. Strategies include use of atypical antipsychotics, ensuring the lowest possible antipsychotic dose that maintains control of positive symptoms (this can involve a shift from antipsychotic polypharmacy to monotherapy), possibly an antidepressant trial (given diagnostic uncertainty and the frequent use of these drugs in schizophrenia), and non-somatic interventions (e.g., cognitive behavioral therapy, CBT). The array and diversity of strategies currently under investigation highlight the lack of evidence-based treatments and our limited understanding regarding negative symptoms underlying etiology and pathophysiology. Their onset, which can precede the first psychotic break, also means that treatments are delayed. From this perspective, identification of biomarkers and/or endophenotypes permitting earlier diagnosis and intervention may serve to improve treatment efficacy as well as outcomes.

A Role for the Transcription Factor Nk2 Homeobox 1 in Schizophrenia: Convergent Evidence from Animal and Human Studies

Schizophrenia is a highly heritable disorder with diverse mental and somatic symptoms. The molecular mechanisms leading from genes to disease pathology in schizophrenia remain largely unknown. Genome-wide association studies (GWASs) have shown that common single-nucleotide polymorphisms associated with specific diseases are enriched in the recognition sequences of transcription factors that regulate physiological processes relevant to the disease. We have used a “bottom-up” approach and tracked a developmental trajectory from embryology to physiological processes and behavior and recognized that the transcription factor NK2 homeobox 1 (NKX2-1) possesses properties of particular interest for schizophrenia. NKX2-1 is selectively expressed from prenatal development to adulthood in the brain, thyroid gland, parathyroid gland, lungs, skin, and enteric ganglia, and has key functions at the interface of the brain, the endocrine-, and the immune system. In the developing brain, NKX2-1-expressing progenitor cells differentiate into distinct subclasses of forebrain GABAergic and cholinergic neurons, astrocytes, and oligodendrocytes. The transcription factor is highly expressed in mature limbic circuits related to context-dependent goal-directed patterns of behavior, social interaction and reproduction, fear responses, responses to light, and other homeostatic processes. It is essential for development and mature function of the thyroid gland and the respiratory system, and is involved in calcium metabolism and immune responses. NKX2-1 interacts with a number of genes identified as susceptibility genes for schizophrenia. We suggest that NKX2-1 may lie at the core of several dose dependent pathways that are dysregulated in schizophrenia. We correlate the symptoms seen in schizophrenia with the temporal and spatial activities of NKX2-1 in order to highlight promising future research areas.

Oxytocin, Vasopressin, and the Motivational Forces that Drive Social Behaviors

The motivation to engage in social behaviors is influenced by past experience and internal state, but also depends on the behavior of other animals. Across species, the oxytocin (Oxt) and vasopressin (Avp) systems have consistently been linked to the modulation of motivated social behaviors. However, how they interact with other systems, such as the mesolimbic dopamine system, remains understudied. Further, while the neurobiological mechanisms that regulate prosocial/cooperative behaviors have been extensively examined, far less is understood about competitive behaviors, particularly in females. In this chapter, we highlight the specific contributions of Oxt and Avp to several cooperative and competitive behaviors and discuss their relevance to the concept of social motivation across species, including humans. Further, we discuss the implications for neuropsychiatric diseases and suggest future areas of investigation.