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

Adjunctive intranasal oxytocin improves verbal memory in people with schizophrenia

INTRODUCTION

Cognitive deficits are a prominent, disabling component of schizophrenia and current pharmacological treatments have demonstrated limited efficacy in their amelioration. Oxytocin - though it has shown promise as a novel antipsychotic in multiple clinical trials - has as-yet poorly characterized effects on cognition, with some evidence indicating an amnestic profile.

METHOD

As part of a previously reported trial of chronic adjunctive oxytocin in schizophrenia, we measured its effect on two cognitive tests: the CVLT (California Verbal Learning Test) and the LNS (Letter Number Sequence). Tests were performed at baseline and after 3 weeks of treatment.

RESULTS

We found no evidence for an amnestic effect and, in fact, significantly better performance with oxytocin on several subtests of the CVLT; namely total Recall trials 1-5 (p=0.027), short delayed free recall (p=0.032) and total recall discrimination (p=0.020). In contrast we found no difference between placebo and oxytocin on LNS performance.

CONCLUSIONS

This is the first report we are aware of documenting a beneficial effect of oxytocin on cognition in schizophrenia. Though from a small sample (n=15), these data both offset past concerns about oxytocin's amnestic effects, and may auger another potential benefit in addition to the already-demonstrated salutary effects on other components of the illness.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Menstrual exacerbation of schizophrenia symptoms

OBJECTIVE

To better understand premenstrual exacerbations of schizophrenia in women and weigh treatment options.

METHOD

A PubMed literature search was conducted, using the search terms 'schizophrenia', 'psychosis', 'menstrual exacerbation', 'hormones' and assessing relevance to premenstrual exacerbation of schizophrenia symptoms.

RESULTS

Exacerbations are usually distinguishable from periodic or menstrual psychosis, a relatively rare condition. Controversy continues about whether low estrogen periods of the month lead to an increase in schizophrenia symptoms among women of reproductive age or whether some women suffer from both schizophrenia and premenstrual dysphoric disorder (PMDD). No treatment trials of specific interventions have been conducted so that physicians must decide on a case-by-case basis whether to raise antipsychotic doses premenstrually, try estrogens or estrogen/progesterone combinations or selective estrogen receptor modulators, or target PMDD symptoms.

CONCLUSION

Clinicians need to be aware of premenstrual symptom aggravation in a large minority of women with schizophrenia. Treatment strategies will depend on the nature of the symptoms that are exacerbated. Optimal treatment needs to be adjusted to the individual woman.

The effects of oxytocin and its analog, carbetocin, on genetic deficits in sensorimotor gating

Converging evidence from preclinical and clinical studies suggest that oxytocin has therapeutic potential for schizophrenia and other neuropsychiatric disorders. Prepulse inhibition of the startle reflex (PPI) is a measure of sensorimotor gating, an important brain function involved in filtering environmental information. We previously demonstrated that systemically administered oxytocin reversed psychostimulant-induced PPI deficits in rats suggesting that oxytocin can produce antipsychotic-like central effects. That finding was supported by a recent trial in humans, which found that intranasal oxytocin reduced symptoms of schizophrenia. The goal of this study was to extend this line of investigation by testing the effects of oxytocin, and a structural analog of oxytocin, carbetocin, on non-pharmacological deficits in PPI. In experiment 1, Brown Norway (BN) rats, a rat strain that has naturally low PPI, were given either saline or one of three doses of oxytocin (0.04-1.0 mg/kg, sc). In experiment 2, BN rats were given either saline, one of three doses of carbetocin (0.04-1.0 mg/kg) or oxytocin (1 mg/kg). PPI and acoustic startle response (ASR) of rats were tested. Oxytocin significantly increased PPI (P<0.01) and decreased ASR levels (P<0.01) in BN rats in a dose-dependent fashion. In contrast, carbetocin had no effect on PPI levels or ASR. The facilitation of BN PPI by oxytocin is similar to what we have previously observed with clozapine and thus further supports oxytocin having antipsychotic properties. In contrast to oxytocin, our data do not support the use of carbetocin as an antipsychotic drug.

Clinical trials of intranasal delivery for treating neurological disorders--a critical review

INTRODUCTION

The intranasal delivery of therapeutics to the brain has achieved great success in preclinical studies. These findings are important because there are many neurological disorders without feasible treatments, due to a lack of effective drug delivery methods to the brain. Translating such intranasal delivery strategies from bench to bedside is an important step for curing these neurological diseases.

AREAS COVERED

This review summarizes recent clinical trials that have investigated the intranasal delivery of drugs to the brain to treat neurological disorders and their potential mechanisms of action. In addition, the potential opportunities as well as challenges of intranasal delivery in clinical trials are discussed.

EXPERT OPINION

The intranasal delivery of drugs to the brain is a novel method with great potential, and it may provide an extraordinary approach to overcome the existing barriers of drug delivery for treating some neurological disorders. Intranasal delivery of central nervous system therapeutics has shown promise in several clinical trials, which demonstrates both the need and importance of further research.

Neurohypophyseal hormones manipulation modulate social and anxiety-related behavior in zebrafish

RATIONALE

Oxytocin (OT) and arginine-vasopressin (AVP) regulate social behavior in mammals. Zebrafish (Danio rerio) allows higher throughput and ease in studying human brain disorders.

OBJECTIVES

This study investigated in zebrafish the effect of non-mammalian homologs isotocin (IT) and vasotocin (AVT) in comparison with OT/AVP on social behavior and fear response to predator. The mechanism was studied using the most human selective OT and AVP receptor antagonists.

METHODS

Zebrafish were injected i.m. with increasing doses (0.001-40 ng/kg) of the neuropeptides. DesGly-NH(2)-d(CH(2))(5)-[D-Tyr(2),Thr(4)]OVT) for OT receptor, SR 49059 for V1a subtype receptor, and SSR-149415 for V1b subtype receptor were injected i.m. 10 min before each agonist.

RESULTS

All the peptides increased social preference and reduced fear to predator response in a dose-dependent manner interpolated by symmetrical parabolas. AVT/AVP were more potent to elicit anxiolytic than social effect while IT and OT were equally potent. All the antagonists dose-dependently inhibited both the effects induced by the neuropeptides. The ratio between the ED50 obtained for blocking the OT-induced effects on social preference and fear response to predator was very high only for desglyDTTyrOVT (160). SR49059 showed the highest ratio in blocking AVP-induced effects (807). The less selective antagonist appeared to be SSR149415.

CONCLUSIONS

For the first time, IT/AVT and OT/AVP were found to modulate in zebrafish, social behavior, unrelated to sex, and fear to predator response through at least two different receptors. Zebrafish is confirmed as a valid, reliable model to study deficit in social behavior characteristic of some psychiatric disorders.

Forensic aspects of water intoxication: four case reports and review of relevant literature

Water intoxication (WI) is a rare condition that originates from over-consumption of water, with a potentially fatal outcome. Increased water intake (polydipsia) is followed by urination of high amount of diluted urine (polyuria) which are the main initial symptoms of WI. We present four case reports of WI. Two of them are unusual pediatric clinical cases using medical documentation and police case files, one of which is related to child abuse, and the other to a psychiatric disorder. The other two cases are fatal adult cases submitted to autopsy from a psychiatric hospital. Also, we present a diagnostic algorithm for polydipsia and polyuria before death. WI is usually seen in patients with psychiatric disorders, victims of child abuse or torture, drug abusers or it can be iatrogenically induced.

Neurobiology of sociability

Sociability consists of behaviors that bring animals together and those that keep animals apart. Remarkably, while the neural circuitry that regulates these two "faces" of sociability differ from one another, two neurohormones, oxytocin (Oxt) and vasopressin (Avp), have been consistently implicated in the regulation of both. In this chapter the the structure and function of the Oxt and Avp systems, the ways in which affiliative and aggressive behavior are studied and the roles of Oxt and Avp in the regulation of sociability will be briefly reviewed. Finally, work implicating Oxt and Avp in sociability in humans, with a focus on neuropsychiatric disorders will be highlighted.

Genetic models of sensorimotor gating: relevance to neuropsychiatric disorders

Sensorimotor gating, or the ability of a sensory event to suppress a motor response, can be measured operationally via prepulse inhibition (PPI) of the startle response. PPI is deficient in schizophrenia patients as well as other neuropsychiatric disorders, can be measured across species, and has been used widely as a translational tool in preclinical neuropharmacological and genetic research. First developed to assess drug effects in pharmacological and developmental models, PPI has become one of the standard behavioral measures in genetic models of schizophrenia and other neuropsychiatric disorders that exhibit PPI deficits. In this chapter we review the literature on genetic models of sensorimotor gating and discuss the utility of PPI as a tool in phenotyping mutant mouse models. We highlight the approaches to genetic mouse models of neuropsychiatric disease, discuss some of the important caveats to these approaches, and provide a comprehensive table covering the more recent genetic models that have evaluated PPI.

Adolescent oxytocin exposure causes persistent reductions in anxiety and alcohol consumption and enhances sociability in rats

Previous studies have suggested that administration of oxytocin (OT) can have modulatory effects on social and anxiety-like behavior in mammals that may endure beyond the time of acute OT administration. The current study examined whether repeated administration of OT to male Wistar rats (n = 48) during a key developmental epoch (early adolescence) altered their physiology and behavior in later-life. Group housed rats were given intraperitoneal injections of either 1 mg/kg OT or vehicle during early adolescence (post natal-days [PND] 33–42). OT treatment caused a transient inhibition of body weight gain that recovered quickly after the cessation of treatment. At PND 50, the rats pre-treated with OT displayed less anxiety-like behavior on the emergence test, while at PND 55 they showed greater levels of social interaction. A subgroup of OT pre-treated rats examined at PND 63 showed a strong trend towards increased plasma OT levels, and also displayed significantly increased OT receptor mRNA in the hypothalamus. Rats pre-treated with OT and their controls showed similar induction of beer intake in daily 70 min test sessions (PND 63 onwards) in which the alcohol concentration of beer was gradually increased across days from 0.44% to 4.44%. However, when given ad libitum access to beer in their home cages from PND 72 onwards (early adulthood), consumption of beer but not water was significantly less in the OT pre-treated rats. A “booster” shot of OT (1 mg/kg) given after 25 days of ad libitum access to beer had a strong acute inhibitory effect on beer intake without affecting water intake. Overall these results suggest that exogenous OT administered during adolescence can have subtle yet enduring effects on anxiety, sociability and the motivation to consume alcohol. Such effects may reflect the inherent neuroplasticity of brain OT systems and a feed-forward effect whereby exogenous OT upregulates endogenous OT systems.

Disparate effects of pramipexole on locomotor activity and sensorimotor gating in Sprague-Dawley rats

Prepulse inhibition (PPI) of acoustic startle and locomotor activity are both widely studied in the preclinical development of dopaminergic agents, including those acting at D3 dopamine receptors. In mice, the dopamine D3 receptor-preferential agonist pramipexole (PPX) alters locomotor activity in a biphasic manner at doses that have no effect on PPI. The present study examined the time-course of PPX effects on locomotion and PPI in rats. In adult male Sprague-Dawley rats, PPX (0, 0.1, 0.3, 1.0mg/kg) was injected prior to measurement of locomotor activity for 90 min in photobeam chambers. Based on disparate early vs. late effects of PPX on locomotion, the effects of PPX (0 vs. 0.3mg/kg) on PPI were tested 20 and 80 min after injection. All doses of PPX decreased locomotor activity for 30 min compared to vehicle, and the higher doses stimulated hyperlocomotion later in the session; the late hyperlocomotion, but not the early hypolocomotion, was blocked by the D2-selective antagonist, L741626 (1.0mg/kg sc). In contrast to its locomotor effects, PPX caused a similar reduction in PPI at 20 and 80 min after administration. These findings suggest both a temporal and pharmacological dissociation between PPX effects on locomotor activity and PPI; these two behavioral measures contribute non-redundant information to the investigation of D3-related behavioral pharmacology.

Intranasal oxytocin reduces psychotic symptoms and improves Theory of Mind and social perception in schizophrenia

Oxytocin has numerous prosocial and antipsychotic-like effects in animals. Prosocial effects of acute intranasal oxytocin administration have also been reported in human subjects. We conducted a randomized, placebo-controlled trial testing the effects of twice daily intranasal oxytocin treatment for 14 days on psychotic symptoms and social cognition in patients with schizophrenia. PANSS scores declined significantly and several social cognition measures improved significantly or nearly significantly in oxytocin (N=11) but not placebo (N=9) recipients. Our results suggest that, in addition to reducing classic psychotic symptoms, oxytocin may diminish certain social cognition deficits that are not improved by current antipsychotic medications.

Startle response related genes

The startle reaction (also known as the startle response, the startle reflex, or the alarm reaction) is the psychological and physiological response to a sudden unexpected stimulus, such as a flash of light, a loud noise (acoustic startle reflex), or a quick movement near the face. Abnormalities of startle response have been observed in many stress-related mental disorders, such as schizophrenia and post-traumatic stress disorder (PTSD). However, the molecular mechanisms of startle in stress-associated conditions--for example, whether the startle reaction is associated with any gene variance--is still unknown. In this paper, we will carry out a systematic review by retrieving, assessing, and combining, when applicable, individual studies investigating association of the molecular variation of candidate gene with the startle response. The systematic review is based on the search for numerous publications using the keywords "startle gene" on September 15, 2010 using PubMed, which comprises more than 20 million citations for biomedical literature from MEDLINE and life science journals. A total of 486 publications regarding genes associated with startle have been obtained and reviewed here. There are fewer than 20 publications associating genes with the startle response between 1979, when the first valuable paper was published, and 1999. However, publications have dramatically increase from 2001 and reaches over 70 in 2009. We have characterized them into three categories: startle-associated gene studies in humans, in animals, as well as in both human and animals. This review of research strategy may provide the information for identifying a biomarker for startle response, with the objective of translating research into clinical utility: diagnosis and treatment of stress-induced mental disorders.

Divergent effects of two different doses of intranasal oxytocin on facial affect discrimination in schizophrenic patients with and without polydipsia

RATIONALE

Hyponatremia and dexamethasone resistance in polydipsic schizophrenic patients are attributable to changes in hippocampal-modulated antidiuretic and stress hormone activity, respectively. The relationship of the neuroendocrine findings to the psychiatric illness, however, is unknown. An impaired ability to identify facial emotions has been linked to core features of schizophrenia and to diminished levels of the closely related hormone, oxytocin, in the polydipsic subset. Intranasal oxytocin enhances facial affect discrimination in healthy subjects.

OBJECTIVE

The aim of this study is to explore if oxytocin reverses impaired facial affect discrimination in schizophrenic patients with, relative to that in patients without, polydipsia.

METHODS

Intranasal oxytocin (10 or 20 IU) and placebo were administered on three occasions to five polydipsic schizophrenic patients, eight nonpolydipsic patients, and 11 healthy controls. Subsequently, subjects rated the presence and intensity of six facial emotions.

RESULTS

Emotion recognition fell in both patient groups following 10 IU of oxytocin due to an increased propensity to identify all emotions regardless of whether they were displayed. By contrast, emotion recognition improved following 20 IU in polydipsic relative to nonpolydipsic patients due primarily to divergent effects on the bias to identify fear in nonfearful faces.

CONCLUSION

The effects of 20 IU oxytocin support the hypothesis that altered neuroendocrine function in polydipsic patients contributes to their psychiatric illness. Further studies are warranted to confirm these findings and assess if oxytocin treatment improves social functioning in this subset. This is the first psychopharmacologic study to compare different doses of oxytocin in the same subject, thus the significance of the opposing responses is unclear.

Pathology from evolutionary conflict, with a theory of X chromosome versus autosome conflict over sexually antagonistic traits

Evolutionary conflicts cause opponents to push increasingly hard and in opposite directions on the regulation of traits. One can see only the intermediate outcome from the balance of the exaggerated and opposed forces. Intermediate expression hides the underlying conflict, potentially misleading one to conclude that trait regulation is designed to achieve efficient and robust expression, rather than arising by the precarious resolution of conflict. Perturbation often reveals the underlying nature of evolutionary conflict. Upon mutation or knockout of one side in the conflict, the other previously hidden and exaggerated push on the trait may cause extreme, pathological expression. In this regard, pathology reveals hidden evolutionary design. We first review several evolutionary conflicts between males and females, including conflicts over mating, fertilization, and the growth rate of offspring. Perturbations of these conflicts lead to infertility, misregulated growth, cancer, behavioral abnormalities, and psychiatric diseases. We then turn to antagonism between the sexes over traits present in both males and females. For many traits, the different sexes favor different phenotypic values, and constraints prevent completely distinct expression in the sexes. In this case of sexual antagonism, we present a theory of conflict between X-linked genes and autosomal genes. We suggest that dysregulation of the exaggerated conflicting forces between the X chromosome and the autosomes may be associated with various pathologies caused by extreme expression along the male-female axis. Rapid evolution of conflicting X-linked and autosomal genes may cause divergence between populations and speciation.

Potential for oxytocin use in children and adolescents with mental illness

BACKGROUND

Oxytocin, long known for its role in childbirth and breastfeeding, has recently come under investigation for its psychoactive properties. We investigated its potential for use in adolescent psychiatric populations for anxiety, depression, attachment disorders, and conduct disorder.

METHODS

We conducted a thorough search of the literature using the Pubmed and Psychinfo databases and reviewed both the Journal of the American Academy of Child and Adolescent Psychiatry from January 2000 until June 2010 and the new research abstracts from the 2009 and 2008 American Academy of Child and Adolescent Psychiatry conferences. We also surveyed the studies, both ongoing and recruiting, currently receiving National Institutes of Health funding to study oxytocin.

RESULTS

We found numerous articles outlining benefits of intranasal oxytocin administration on individual traits, both in healthy and psychiatric populations. We also found ongoing phase II clinical trials for oxytocin uses as an antipsychotic or anxiolytic.

CONCLUSIONS

Given the research already conducted, we recommend investigation into the therapeutic use of oxytocin in adolescent populations for anxiety, psychosis, attachment disorders, and conduct disorder.

Oxytocin reduces background anxiety in a fear-potentiated startle paradigm

Oxytocin reportedly decreases anxious feelings in humans and may therefore have therapeutic value for anxiety disorders, such as post-traumatic stress disorder (PTSD). As PTSD patients have exaggerated startle responses, a fear-potentiated startle paradigm in rats may have face validity as an animal model to examine the efficacy of oxytocin in treating these symptoms. Oxytocin (0, 0.01, 0.1, or 1.0 μg, subcutaneously) was given either 30 min before fear conditioning, immediately after fear conditioning, or 30 min before fear-potentiated startle testing to assess its effects on acquisition, consolidation, and expression of conditioned fear, respectively. Startle both in the presence and absence of the fear-conditioned light was significantly diminished by oxytocin when administered at acquisition, consolidation, or expression. There was no specific effect of oxytocin on light fear-potentiated startle. In an additional experiment, oxytocin had no effects on acoustic startle without previous fear conditioning. Further, in a context-conditioned test, previous light-shock fear conditioning did not increase acoustic startle during testing when the fear-conditioned light was not presented. The data suggest that oxytocin did not diminish cue-specific conditioned nor contextually conditioned fear, but reduced background anxiety. This suggests that oxytocin has unique effects of decreasing background anxiety without affecting learning and memory of a specific traumatic event. Oxytocin may have antianxiety properties that are particularly germane to the hyper-vigilance and exaggerated startle typically seen in PTSD patients.

Peripheral oxytocin is associated with reduced symptom severity in schizophrenia

BACKGROUND

Emerging evidence from clinical trials suggests that oral estrogen and intranasal oxytocin might reduce symptom severity in schizophrenia. Whether increases in endogenous hormones are similarly associated with improved symptoms is unknown. We investigated the effects of menstrual cycle phase and related fluctuations in peripheral hormone levels on clinical symptoms in women with chronic schizophrenia.

METHOD

Twenty-three women with schizophrenia were administered the Positive and Negative Syndrome Scale (PANSS), a measure of clinical symptom severity, at two menstrual cycle phases: 1) early follicular (Days 2-4; low estrogen/progesterone) and 2) midluteal (Days 20-22; high estrogen/progesterone). Twenty-seven males with schizophrenia and 58 controls (31 female) completed testing at comparable intervals. Men were included to examine whether the relationships between clinical symptoms and hormone levels in women generalize to men. Plasma hormone assays of estrogen, oxytocin, progesterone, and testosterone were obtained.

RESULTS

Female patients showed less severe symptoms during the midluteal versus early follicular phase (p's<0.01). Oxytocin did not fluctuate across phases, but in female patients (p's<0.01) higher oxytocin levels were associated with less severe positive symptoms and overall psychopathology. In both sexes, higher oxytocin levels were associated with more prosocial behaviors (p<0.05).

CONCLUSION

Consistent with previous findings in acutely ill patients, our results suggest that clinical symptoms vary across the menstrual cycle in patients with chronic schizophrenia. Similar to recent findings regarding benefits of intranasal oxytocin, these new findings indicate that high levels of endogenous oxytocin might improve positive symptom severity and general psychopathology in women and social behaviors in both sexes.

Adjunctive intranasal oxytocin reduces symptoms in schizophrenia patients

BACKGROUND

Both human and animal studies suggest oxytocin may have antipsychotic properties. Therefore, we conducted a clinical trial to directly test this notion.

METHODS

Nineteen schizophrenia patients with residual symptoms despite being on a stable dose of at least one antipsychotic were enrolled in a randomized, double-blind, crossover study. They received 3 weeks of daily intranasal oxytocin (titrated to 40 IU twice a day) and placebo adjunctive to their antipsychotics. Order of intranasal treatment was randomly assigned and there was a 1-week washout between treatments.

RESULTS

Analysis of the 15 subjects who completed all the study visits revealed that oxytocin significantly reduced scores on the Positive and Negative Symptom Scale (p < .001) and Clinical Global Impression-Improvement Scale (p < .001) compared with placebo at the 3-week end point. No benefit was seen at the early time points. Oxytocin was well tolerated and produced no adverse effects based upon patient reports or laboratory analysis.

CONCLUSIONS

The results support the hypothesis that oxytocin has antipsychotic properties and is well tolerated. Higher doses and longer duration of treatment may produce larger benefits and should be evaluated in future studies.

Schizophrenia severity and clozapine treatment outcome association with oxytocinergic genes

Antipsychotic drugs are the best means available for symptomatically treating individuals suffering from schizophrenia; however, there is a significant variability in clinical response to these psychotropic medications. Previous findings connect oxytocin (OXT) with schizophrenia and antipsychotic action. Therefore, we evaluated if OXT and OXT receptor (OXTR) genes might play a role in the symptom severity and clozapine treatment response in schizophrenia subjects. The rs2740204 variant in the OXT gene was significantly associated with treatment response (after 1000 permutations p=0.042) and nominally associated with negative symptoms in our sample. Furthermore, variants in the OXTR were nominally associated with severity of overall symptoms accessed using the Brief Psychiatric Rating Scale (rs237885, rs237887) as well as on the improvement of the positive symptoms (rs11706648, rs4686301, rs237899). Additional association studies in independent samples will be able evaluate whether OXT and OXTR genes are truly playing a role in the clozapine treatment outcome.

The effects of pramipexole on prepulse inhibition and locomotor activity in C57BL/6J mice

Pramipexole (PRA) is a preferential D3R agonist that, in rats and humans, modifies prepulse inhibition (PPI) of the acoustic startle reflex, an operational measure of sensorimotor gating. The ability to use similar PPI measures across species, and the relative ease of genetic manipulations in mice, suggests that molecular studies of the D3R regulation of sensorimotor gating might be best pursued in mice. Here, we evaluate the effects of PRA on PPI and locomotion in C57BL/6J mice, the background strain for many gene knockout mouse models. Male C57BL/6J mice were tested for PPI and locomotor activity after injection of PRA. No significant effects of PRA on PPI were observed at any dose (0.1-10.0 mg/kg), but a significant reduction in startle magnitude was observed after 10 mg/kg PRA. In contrast, the D1/2 agonist, apomorphine (5 mg/kg) significantly reduced PPI in these mice. At doses of PRA that did not alter startle magnitude (0.3, 1, 3 mg/kg), significant decreases in the amount of locomotor and investigatory behavior were observed. Distinct from findings in rats and humans, it seems that either: (i) PRA does not activate D3Rs in C57BL/6J mice, or (ii) D3R agonists are not sufficient to alter PPI in this mouse strain.

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

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

Modeling the positive symptoms of schizophrenia in genetically modified mice: pharmacology and methodology aspects

In recent years, there have been huge advances in the use of genetically modified mice to study pathophysiological mechanisms involved in schizophrenia. This has allowed rapid progress in our understanding of the role of several proposed gene mechanisms in schizophrenia, and yet this research has also revealed how much still remains unresolved. Behavioral studies in genetically modified mice are reviewed with special emphasis on modeling psychotic-like behavior. I will particularly focus on observations on locomotor hyperactivity and disruptions of prepulse inhibition (PPI). Recommendations are included to address pharmacological and methodological aspects in future studies. Mouse models of dopaminergic and glutamatergic dysfunction are then discussed, reflecting the most important and widely studied neurotransmitter systems in schizophrenia. Subsequently, psychosis-like behavior in mice with modifications in the most widely studied schizophrenia susceptibility genes is reviewed. Taken together, the available studies reveal a wealth of available data which have already provided crucial new insight and mechanistic clues which could lead to new treatments or even prevention strategies for schizophrenia.

Evidence for a role of progesterone in menstrual cycle-related variability in prepulse inhibition in healthy young women

Prepulse inhibition (PPI) of the startle response is sensitive to sex, with healthy young women showing less PPI compared with age-matched men, and varies according to the menstrual cycle phase in women. Relatively less is known regarding sex and hormonal influences in prepulse facilitation (PPF). Menstrual phase-related variability in PPI is suggested to be mediated by fluctuating estrogen level, based on the observations of more PPI in women during the follicular, relative to the luteal, phase. No study has directly assessed the relationship between fluctuating hormones and PPI or PPF levels over the human ovarian cycle. To examine the roles of circulating ovarian hormones in PPI and PPF, 16 non-smoking regularly menstruating healthy women were tested during both the follicular and luteal phases on PPI and PPF and provided saliva samples for measurement of 17beta-estradiol (estrogen), progesterone and testosterone. The results showed higher levels of 17beta-estradiol and progesterone during the luteal, relative to the follicular, phase; and more PPI during the follicular phase and more PPF during the luteal phase with comparable startle amplitude and habituation during the two phases. A larger increase in progesterone was associated with a smaller decrease in PPI from the follicular to the luteal phase. No significant associations were found between changes in PPI/PPF and estrogen levels. The findings confirm lower PPI during the luteal, compared with the follicular, phase and suggest a role for progesterone, more specifically an antipsychotic-like PPI-restoration action of progesterone, during the luteal phase in PPI of young women.

The mechanism of life-threatening water imbalance in schizophrenia and its relationship to the underlying psychiatric illness

Impaired water excretion was noted to coincide with psychotic exacerbations in the first decades of the past century. In the ensuing decades, life-threatening water intoxication and elevated plasma levels of the antidiuretic hormone, arginine vasopressin (AVP) were reported in a subset of persons with schizophrenia. Subsequent studies demonstrated that the osmotic set point for AVP secretion was transiently reset in these patients by an unknown process and that this was further exacerbated by acute psychosis. More recent studies indicate that the AVP dysfunction is a manifestation of a hippocampal-mediated impairment in the regulation of both AVP and HPA axis responses to psychological, but not other types of, stimuli. Of potential significance, is that schizophrenic patients without water imbalance exhibit the opposite pattern of responses. Preliminary data indicate those with water imbalance also demonstrate a closely linked deficit in central oxytocin activity which may account for their diminished social function. These latter behavioral deficits are perhaps the most disabling and treatment resistant features of schizophrenia, which recent studies suggest, may respond to oxytocin agonists. Together these findings support the view that schizophrenia is a heterogeneous disorder, and provide novel biomarkers and approaches for exploring the pathophysiology and treatment of severe mental illness.

Association between arginine vasopressin 1a receptor (AVPR1a) promoter region polymorphisms and prepulse inhibition

Arginine vasopressin and the arginine vasopressin 1a (AVPR1a) gene contribute to a range of social behaviors both in lower vertebrates and in humans. Human promoter-region microsatellite repeat regions (RS1 and RS3) in the AVPR1a gene region have been associated with autism spectrum disorders, prosocial behavior and social cognition. Prepulse inhibition (PPI) of the startle response to auditory stimuli is a largely autonomic response that resonates with social cognition in both animal models and humans. Reduced PPI has been observed in disorders including schizophrenia that are distinguished by deficits in social skills. In the current investigation association was examined between PPI and the AVPR1a RS1 and RS repeat regions and PPI in a group of 113 nonclinical subjects. Using a robust family-based strategy, association was observed between AVPR1a promoter-region repeat length, especially RS3) and PPI (30 ms: global p=0.04; 60 ms p=0.006; 120 ms p=0.008). Notably, longer RS3 alleles were associated with greater levels of prepulse inhibition. Using a short/long classification scheme for the repeat regions, significant association was also observed between all three PPI intervals (30, 60 and 120 ms) and both RS1 and RS3 polymorphisms (PBAT: FBAT-PC(2) statistic p=0.047). Tests of within-subject effects (SPSS GLM) showed significant sexxRS3 interactions at 30 ms (p=0.045) and 60 ms (p=0.01). Longer alleles, especially in male subjects, are associated with significantly higher PPI response, consistent with a role for the promoter repeat region in partially molding social behavior in both animals and humans. This is the first report in humans demonstrating a role of the AVPR1a gene in contributing to the PPI response to auditory stimuli.

Oxytocin: the great facilitator of life

Oxytocin (Oxt) is a nonapeptide hormone best known for its role in lactation and parturition. Since 1906 when its uterine-contracting properties were described until 50 years later when its sequence was elucidated, research has focused on its peripheral roles in reproduction. Only over the past several decades have researchers focused on what functions Oxt might have in the brain, the subject of this review. Immunohistochemical studies revealed that magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei are the neurons of origin for the Oxt released from the posterior pituitary. Smaller cells in various parts of the brain, as well as release from magnocellular dendrites, provide the Oxt responsible for modulating various behaviors at its only identified receptor. Although Oxt is implicated in a variety of "non-social" behaviors, such as learning, anxiety, feeding and pain perception, it is Oxt's roles in various social behaviors that have come to the fore recently. Oxt is important for social memory and attachment, sexual and maternal behavior, and aggression. Recent work implicates Oxt in human bonding and trust as well. Human disorders characterized by aberrant social interactions, such as autism and schizophrenia, may also involve Oxt expression. Many, if not most, of Oxt's functions, from social interactions (affiliation, aggression) and sexual behavior to eventual parturition, lactation and maternal behavior, may be viewed as specifically facilitating species propagation.