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

Oxytocin Levels in Children with Separation Anxiety and Their Mothers before and after Treatment

Objective

The purpose of this study was to compare the plasma oxytocin levels of children with separation anxiety disorder (SAD) and their mothers with those of healthy controls and to examine the relationship between oxytocin levels and changes in anxiety three months after treatment.

Methods

Thirty children aged 6-12 years with SAD, 30 healthy children, and mothers of both groups were included in the study. All cases were evaluated with semi-structured interview and Clinical Global Impression Scale. All cases and mothers of both groups filled out scales to determine various psychological variables (anxiety, depression, and attachment). The patient group children were re-evaluated with their mothers after three months, following treatment. Plasma oxytocin levels were evaluated from both groups and their mothers before and after treatment.

Results

The plasma oxytocin levels of mothers of children with SAD were significantly lower than those of the controls and increased significantly three months after their children were treated. No difference was found between the plasma oxytocin levels of children with SAD and the control group, and these children's levels decreased significantly after treatment. A positive correlation was found between changes in the plasma oxytocin levels of children with SAD and the change in anxiety scores.

Conclusion

Our results show that the change in plasma oxytocin levels in both children and mothers after treatment suggests that oxytocin may be important in the etiology of SAD.

Potential of Heterogeneous Compounds as Antidepressants: A Narrative Review

Depression is a globally widespread disorder caused by a complicated interplay of social, psychological, and biological factors. Approximately 280 million people are suffering from depression worldwide. Traditional frontline antidepressants targeting monoamine neurotransmitters show unsatisfactory effects. The development and application of novel antidepressants for dissimilar targets are on the agenda. This review characterizes the antidepressant effects of multiple endogenous compounds and/or their targets to provide new insight into the working mechanism of antidepressants. We also discuss perspectives and challenges for the generation of novel antidepressants.

Tryptophan Hydroxylase 2 Knockout Male Rats Exhibit a Strengthened Oxytocin System, Are Aggressive, and Are Less Anxious

The central serotoninergic system is critical for stress responsivity and social behavior, and its dysregulations have been centrally implicated in virtually all neuropsychiatric disorders. Genetic serotonin depletion animal models could provide a tool to elucidate the causes and mechanisms of diseases and to develop new treatment approaches. Previously, mice lacking tryptophan hydroxylase 2 (Tph2) have been developed, showing altered behaviors and neurotransmission. However, the effect of congenital serotonin deficiency on emotional and social behavior in rats is still largely unknown, as are the underlying mechanisms. In this study, we used a Tph2 knockout (Tph2^-/-) male rat model to study how the lack of serotonin in the rat brain affects anxiety-like and social behaviors. Since oxytocin is centrally implicated in these behaviors, we furthermore explored whether the effects of Tph2 knockout on behavior would relate to changes in the oxytocin system. We show that Tph2^-/- rats display reduced anxiety-like behavior and a high level of aggression in social interactions. In addition, oxytocin receptor expression was increased in the infralimbic and prelimbic cortices, paraventricular nucleus, dorsal raphe nucleus, and some subregions of the hippocampus, which was paralleled by increased levels of oxytocin in the medial frontal cortex and paraventricular nucleus but not the dorsal raphe nucleus, central amygdala, and hippocampus. In conclusion, our study demonstrated reduced anxiety but exaggerated aggression in Tph2^-/- male rats and reveals for the first time a potential involvement of altered oxytocin system function. Meanwhile, the research of oxytocin could be distinguished in almost any psychiatric disorder including anxiety and mental disorders. This research potentially proposes a new target for the treatment of such disorders, from a genetic serotonin deficiency aspect.

Oxytocin inhibits hindpaw hyperalgesia induced by orofacial inflammation combined with stress

Oxytocin (OT) is recognized as a critical neuropeptide in pain-related disorders. Chronic pain caused by the comorbidity of temporomandibular disorder (TMD) and fibromyalgia syndrome (FMS) is common, but whether OT plays an analgesic role in the comorbidity of TMD and FMS is unknown. Female rats with masseter muscle inflammation combined with 3-day forced swim (FS) stress developed somatic hypersensitivity, which modeled the comorbidity of TMD and FMS. Using this model, the effects of spinal OT administration on mechanical allodynia and thermal hyperalgesia in hindpaws were examined. Furthermore, the protein levels of OT receptors and 5-HT2A receptors in the L4-L5 spinal dorsal horn were analyzed by Western blot. The OT receptor antagonist atosiban and 5-HT2A receptor antagonist ritanserin were intrathecally injected prior to OT injection in the separate groups. Intrathecal injection of 0.125 μg and 0.5 μg OT attenuated the hindpaw hyperalgesia. The expression of OT receptors and 5-HT2A receptors in the L4-L5 spinal dorsal horn significantly increased following intrathecal injection of 0.5 μg OT. Intrathecal administration of either the OT receptor antagonist atosiban or 5-HT2A receptor antagonist ritanserin blocked the analgesic effect of OT. These results suggest that OT may inhibit hindpaw hyperalgesia evoked by orofacial inflammation combined with stress through OT receptors and/or 5-HT2A receptors, thus providing a therapeutic prospect for drugs targeting the OT system and for patients with comorbidity of TMD and FMS.

Antidepressant- and anxiolytic-like activities of Rosmarinus officinalis extract in rodent models: Involvement of oxytocinergic system

BACKGROUND

Oxytocin (OXT), a neuropeptide involved in mammal reproductive and prosocial behaviors, has been reported to interact with various stressor-provoked neurobiological changes, including neuroendocrine, neurotransmitter, and inflammatory processes. In view of disturbances in psychosocial relationships due to social isolation and physical distancing measures amid the COVID-19 pandemic, being one of the triggering factors for the recent rise in depression and anxiety, OXT is a potential candidate for a new antidepressant.

METHODS

In this present study, we have aimed to investigate the effects of oral administration of Rosmarinus officinalis extract (RE), extracted from distillation residue of rosemary essential oil, on central OXT level in the context of other stress biomarkers and neurotransmitter levels in mice models. Tail suspension test (TST) and elevated plus maze test (EPMT) following LPS injection were employed to assess depressive- and anxiety-like behavior in mice, respectively.

FINDINGS

Pretreatment with RE for seven days significantly improved behavior in TST and EPMT. Whole-genome microarray analysis reveals that RE significantly reversed TST stress-induced alterations in gene expressions related to oxytocinergic and neurotransmitter pathways and inflammatory processes. In both models, RE significantly increased central Oxt and Oxtr expressions, as well as OXT protein levels. RE also significantly attenuated stress-induced changes in serum corticosterone, brain and serum BDNF levels, and brain neurotransmitters levels in both models.

INTERPRETATION

Altogether, our study is the first to report antidepressant- and anxiolytic-like activities of RE through modulating oxytocinergic system in mice brain and thus highlights the prospects of RE in the treatment of depressive disorders of psychosocial nature.

Chronic intranasal oxytocin reverses stress-induced social avoidance in female prairie voles

Social anxiety disorder (SAD) is a prevalent mental illness in both men and women, but current treatment approaches with selective serotonin reuptake inhibitors (SSRI) have limited success. The neuropeptide oxytocin (OXT) has become a therapeutic target due to its prosocial and anxiolytic effects. Nevertheless, no research has focused on the impact of chronic OXT treatment in animal models of SAD. Social defeat stress is an animal model of social conflict that reliably induces a social avoidance phenotype, reflecting symptoms observed in individuals suffering from SAD. Here, we used the socially monogamous prairie vole, which exhibits aggressive behavior in both sexes, to examine the effects of OXT and SSRI treatment following social defeat stress in males and females. Defeated voles became avoidant in unfamiliar social situations as early as one day after defeat experience, and this phenotype persisted for at least eight weeks. OXT receptor (OXTR) binding in mesocorticolimbic and paralimbic regions was reduced in defeated females during the eight-week recovery period. In males, serotonin 1A receptor binding was decreased in the basolateral amygdala and dorsal raphe nucleus starting at one week and four weeks post-defeat, respectively. Chronic intranasal treatment with OXT had a negative effect on sociability and mesolimbic OXTR binding in non-defeated females. However, chronic intranasal OXT promoted social engagement and increased mesolimbic OXTR binding in defeated females but not males. SSRI treatment led to only modest effects. This study identifies a sex-specific and stress-dependent function of intranasal OXT on mesolimbic OXTR and social behaviors.

Intranasal Oxytocin Improves Lean Muscle Mass and Lowers LDL Cholesterol in Older Adults with Sarcopenic Obesity: A Pilot Randomized Controlled Trial

OBJECTIVES

Obesity is associated with sarcopenia in older adults, and weight loss can lead to further muscle mass loss. Oxytocin decreases with age, and animal studies suggest that oxytocin administration has trophic effects on skeletal muscle cells and reduces adiposity. We conducted a clinical trial to examine the safety and preliminary efficacy of intranasal oxytocin for older adults with sarcopenic obesity.

DESIGN

A double-blind, placebo-controlled randomized controlled trial of intranasal oxytocin (24 IU 4 times per day) for 8 weeks.

SETTING AND PARTICIPANTS

Twenty-one older (67.5 ± 5.4 years), obese (30-43 kg/m2), sedentary (<2 strenuous exercise per week) adults with slow gait speed (<1 m/s, proxy measure of sarcopenia) were recruited.

MEASURES

Generalized estimating equations were used to evaluate the effect of oxytocin on safety/tolerability of oxytocin administration and whole body muscle and fat mass.

RESULTS

At baseline, body mass index (BMI) was 36.8 ± 3.6 kg/m2, fat mass 46.09 ± 6.99 kg, lean mass 50.98 ± 11.77 kg, fasting plasma glucose (FPG) 92.0 ± 8.9 mg/dL, hemoglobin A1c (HbA1c) 5.7% ± 0.4%, low density lipoprotein (LDL) 111.3 ± 41.5 mg/dL, high-density lipoprotein (HDL) 47.85 ± 10.96 mg/dL, and triglycerides 140.55 ± 83.50 mg/dL. Oxytocin administration was well tolerated without any significant adverse events. Oxytocin led to a significant increase of 2.25 kg in whole body lean mass compared with placebo (P < .01) with a trend toward decreasing fat mass, and a significantly reduced plasma LDL cholesterol by -19.3 mg/dL (P = .023) compared against placebo. There were no significant changes in BMI, appetite scores, glycemia, plasma HDL, triglycerides, or depressive symptoms.

CONCLUSIONS AND IMPLICATIONS

This proof-of-concept study indicates that oxytocin may be useful for the treatment of sarcopenic obesity in older adults. Oxytocin administration may also provide additional cardiovascular benefits.

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.

The relationship between oxytocin blood concentrations and antidepressants over pregnancy and the postpartum

Antidepressant treatment of perinatal depression is increasingly common and accepted in clinical guidelines. It has been suggested that serotonergic antidepressants may effect changes in the oxytocinergic system, including oxytocin levels, and that this may be one of the beneficial mechanisms of action for these drugs. Furthermore, oxytocin has been associated with the quality of the parent-child relationship, which may be important in treatment of perinatal depression. This study will explore if there is a relationship between antidepressant use over the perinatal period and oxytocin levels. Data from a pregnancy cohort study are used from 279 women across three groups: women taking antidepressants in pregnancy (n = 48), women with untreated depression (n = 31) and healthy control women (n = 200). Data included antidepressant use, maternal depression and oxytocin plasma concentrations in pregnancy and up to 12 months postpartum. We found that concurrent oxytocin blood concentrations were not associated with perinatal antidepressant use. However, oxytocin blood concentrations increased more steeply in those on antidepressants across the perinatal period compared to control women. A steeper increase for Selective Serotonergic Reuptake Inhibitors was observed, however, this effect was on the boarder of statistical significance. In conclusion, although antidepressant use and oxytocin was not associated at any time point, women taking antidepressants during pregnancy had larger increases in oxytocin over the perinatal period. Future research could examine specific agents and class of antidepressant and the relationship to parenting.

Genetic association with boldness and maternal performance in a free-ranging population of grey seals (Halichoerus grypus)

Individual variation in quantitative traits clearly influence many ecological and evolutionary processes. Moderate to high heritability estimates of personality and life-history traits suggest some level of genetic control over these traits. Yet, we know very little of the underlying genetic architecture of phenotypic variation in the wild. In this study, we used a candidate gene approach to investigate the association of genetic variants with repeated measures of boldness and maternal performance traits (weaning mass and lactation duration) collected over an 11- and 28-year period, respectively, in a free-ranging population of grey seals on Sable Island National Park Reserve, Canada. We isolated and re-sequenced five genes: dopamine receptor D4 (DRD4), serotonin transporter (SERT), oxytocin receptor (OXTR), and melanocortin receptors 1 (MC1R) and 5 (MC5R). We discovered single nucleotide polymorphisms (SNPs) in each gene; and, after accounting for loci in linkage disequilibrium and filtering due to missing data, we were able to test for genotype-phenotype relationships at seven loci in three genes (DRD4, SERT, and MC1R). We tested for association between these loci and traits of 180 females having extreme shy-bold phenotypes using mixed-effects models. One locus within SERT was significantly associated with boldness (effect size = 0.189) and a second locus within DRD4 with weaning mass (effect size = 0.232). Altogether, genotypes explained 6.52-13.66% of total trait variation. Our study substantiates SERT and DRD4 as important determinants of behaviour, and provides unique insight into the molecular mechanisms underlying maternal performance variation in a marine predator.

The association of oxytocin with major depressive disorder: role of confounding effects of antidepressants

Major depressive disorder is a genetic susceptible disease, and a psychiatric syndrome with a high rate of incidence and recurrence. Because of its complexity concerning etiology and pathogenesis, the cure rate of first-line antidepressants is low. In recent years, accumulative evidences revealed that oxytocin act as a physiological or pathological participant in a variety of complex neuropsychological activities, including major depressive disorder. Six electronic databases (Web of Science, PubMed, Scopus, Google Scholar, CNKI, and Wanfang) were employed for researching relevant publications. At last, 226 articles were extracted. The current review addresses the correlation of the oxytocin system and major depressive disorder. Besides, we summarize the mechanisms by which the oxytocin system exerts potential antidepressant effects, including regulating neuronal activity, influencing neuroplasticity and regeneration, altering neurotransmitter release, down regulating hypothalamic-pituitary-adrenal axis, anti-inflammatory, antioxidation, and genetic effects. Increasing evidence shows that oxytocin and its receptor gene may play a potential role in major depressive disorder. Future research should focus on the predictive ability of the oxytocin system as a biomarker, as well as its role in targeted prevention and early intervention of major depressive disorder.

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.

Developmental Fluoxetine Exposure Alters Behavior and Neuropeptide Receptors in the Prairie Vole

Developmental exposure to selective serotonin reuptake inhibitor (SSRI) increases the risk of Autism Spectrum Disorder (ASD), however, the underlying neurobiology of this effect is not fully understood. Here we used the socially monogamous prairie vole as a translational model of developmental SSRI exposure. Paired female prairie voles (n = 20) were treated with 5 mg/kg subcutaneous fluoxetine (FLX) or saline (SAL) daily from birth of the second litter until the day of birth of the 4th litter. This design created three cohorts of FLX exposure: postnatal exposure in litter 2, both prenatal and postnatal exposure in litter 3, and prenatal exposure in litter 4. Post-weaning, subjects underwent behavioral testing to detect changes in sociality, repetitive behavior, pair-bond formation, and anxiety-like behavior. Quantitative receptor autoradiography was performed for oxytocin, vasopressin 1a, and serotonin 1a receptor density in a subset of brains. We observed increased anxiety-like behavior and reduced sociality in developmentally FLX exposed adults. FLX exposure decreased oxytocin receptor binding in the nucleus accumbens core and central amygdala, and vasopressin 1a receptor binding in the medial amygdala. FLX exposure did not affect serotonin 1A receptor binding in any areas examined. Changes to oxytocin and vasopressin receptors may underlie the behavioral changes observed and have translational implications for the mechanism of the increased risk of ASD subsequent to prenatal SSRI exposure.

Molecular, biochemical and behavioural evidence for a novel oxytocin receptor and serotonin 2C receptor heterocomplex

The complexity of oxytocin-mediated functions is strongly associated with its modulatory effects on other neurotransmission systems, including the serotonin (5-hydroxytryptamine, 5-HT) system. Signalling between oxytocin (OT) and 5-HT has been demonstrated during neurodevelopment and in the regulation of specific emotion-based behaviours. It is suggested that crosstalk between neurotransmitters is driven by interaction between their specific receptors, particularly the oxytocin receptor (OTR) and the 5-hydroxytryptamine 2C receptor (5-HTR_2C), but evidence for this and the downstream signalling consequences that follow are lacking. Considering the overlapping central expression profiles and shared involvement of OTR and 5-HTR_2C in certain endocrine functions and behaviours, including eating behaviour, social interaction and locomotor activity, we investigated the existence of functionally active OTR/5-HTR_2C heterocomplexes. Here, we demonstrate evidence for a potential physical interaction between OTR and 5-HTR_2Cin vitro in a cellular expression system using flow cytometry-based FRET (fcFRET). We could recapitulate this finding under endogenous expression levels of both receptors via in silico analysis of single cell transcriptomic data and ex vivo proximity ligation assay (PLA). Next, we show that co-expression of the OTR/5-HTR_2C pair resulted in a significant depletion of OTR-mediated Gαq-signalling and significant changes in receptor trafficking. Of note, attenuation of OTR-mediated downstream signalling was restored following pharmacological blockade of the 5-HTR_2C. Finally, we demonstrated a functional relevance of this novel heterocomplex, in vivo, as 5-HTR_2C antagonism increased OT-mediated hypoactivity in mice. Overall, we provide compelling evidence for the formation of functionally active OTR/5-HTR_2C heterocomplexes, adding another level of complexity to OTR and 5-HTR_2C signalling functionality. This article is part of the special issue on Neuropeptides.

Psychopharmacology and ethnicity: A comparative study on Senegalese and Italian men

Objectives: Ethnicity represents a crucial factor in influencing response to psychotropic drugs. Some data indicate that functional polymorphisms of two candidate genes of the serotonin (5-HT) transporter (SERT) may affect the response to selective 5-HT reuptake inhibitors (SSRIs). The present study aimed to compare the platelet SERT, through the specific [³H]paroxetine ([³H]Par) binding, and plasma oxytocin (OT) levels in 20 Senegalese and in 20 Italian men.Methods: No subjects had family or personal history of any major psychiatric disorder, or had ever regularly taken psychotropic drugs, or were suffering from any physical illness.Results: Senegalese men showed statistically significant higher density (B_max, fmol/mg protein, mean ± SD) of [³H]Par binding sites (2105.00 ± 473.15 vs 1139.85 ± 213.58, P < 0.001), as well as more elevated plasma OT levels (pg/ml, mean ± SD) (OT: 18.08 ± 4.46 vs 6.62 ± 2.91) than Italian men.Conclusions: These differences, possibly due to genetic or dietary reasons, or even to gender, might affect the response to psychopharmacological compounds. Our findings would suggest specific caution when administering psychotropic compounds to non-European individuals, and the need of further studies in this emerging field of neuropsychopharmacology.

Effect of amisulpride, olanzapine, quetiapine, and aripiprazole single administration on c-Fos expression in vasopressinergic and oxytocinergic neurons of the rat hypothalamic supraoptic nucleus

OBJECTIVE

The goal of this study was to reveal the impact of four types of atypical antipsychotics including amisulpride (AMI), olanzapine (OLA), quetiapine (QUE), and aripiprazole (ARI), with different receptor-affinity profile and dissociation constant, on the activity of hypothalamic supraoptic nucleus (SON) vasopressinergic and oxytocinergic neurons.

METHODS

Male Sprague Dawley rats received a single injection of vehicle (VEH) (0.1 ml/100g), AMI (20 mg/kg), OLA (5 mg/kg), QUE (15 mg/kg/) or ARI (10 mg/kg). Ninety min after treatment, the animals were fixed by transcardial perfusion, the brains removed, and cryocut into serial coronal sections of 35 µm thickness. The sections were processed for c-Fos staining using an avidin-biotin-peroxidase complex and visualized by nickel intensified diaminobenzidine to reach black end product. Afterwards, the sections were exposed to vasopressin (AVP) and oxytocin (OXY) antibodies and the reaction product visualized by biotin-labeled fluorescent Alexa Fluor 568 dye. The data were evaluated from c-Fos and AVP or OXY merged sections.

RESULTS

The present study shows that all four antipsychotics applied induced c-Fos expression in the SON. With respect to the stimulation efficacy of the individual antipsychotics, estimated based on the quantity of c-Fos-labeled AVP and OXY neurons, could be a preferential action assigned to QUE over moderate effect of ARI and lower effect to OLA and reduced effect of AMI (VEH < AMI < OLA < ARI < QUE).

CONCLUSION

The present data for the first time provide an insight into the quantitative pattern of brain activity within the clusters of SON AVP and OXY cells in response to different atypical antipsychotics single treatment.

Parasympathetic nervous activity is associated with oxytocin in multiparous, but not primiparous, women during the perinatal period

Oxytocin (OXT) is thought to have antidepressant/anxiolytic effects in postpartum women. Primiparous women tend toward an attenuated lactation compared with multiparous women. However, so far, little is known about the relationship between OXT and autonomic nervous activity (ANA) in perinatal women and whether it may be different in primiparous and multiparous women. Therefore, the objective of this study was to answer this question by determining both ANA and salivary OXT levels in primiparous and multiparous perinatal women. In 18 primiparous and 18 multiparous women, who underwent a physical and physiological examination, ANA measurement by heart rate variability and saliva sampling were performed during the perinatal period. Saliva OXT concentration was determined by a highly sensitive ELISA. OXT release into saliva was obtained from multiplying saliva OXT concentration by saliva flow rate. In the postpartum period, multiparous women had higher parasympathetic nervous activity (PNA) and lower physical stress index (PSI) compared with primiparous women. Furthermore, multiparous postpartal women had higher OXT compared with primiparous or multiparous prepartal women. In addition, in multiparous perinatal women, OXT correlated positively with PNA, but negatively with PSI. These results suggest that after parturition, multiparous mothers may switch over to the "feed and breed" system more quickly due to increased OXT compared with primiparous mothers. Our findings support antidepressant/anxiolytic and anti-stress effects of OXT. In postpartal women exposed to synthetic OXT, ANA measurement may provide a clue to clarify the effects of exogenous OXT on postpartum psychiatric disorders.

Maternal behaviour in domestic dogs

Mammalian parental care, in most of the cases, is given by the female, who provides food, warmth, and protection. In domestic dogs, maternal behaviour shown by the dam mainly consists of contact, nursing, grooming/licking, play, punishment, thermoregulation, and motion. Peer-reviewed literature published between 1952 and 2018 was retrieved from CAB Abstracts, PubMed, ISI Web of Knowledge, Scopus and book chapters. Keywords for this search included the following terms: behaviour, bonding, altricial, precocial, offspring, maternal, whelping, nursing, domestic dogs, female dog, aggression, puppies, anogenital licking. In this review, we reported and discussed scientific information about maternal behaviour in domestic bitches, comparing altricial vs precocial species; the importance of the bonding, grooming/licking and nursing, and their impacts on puppies' behaviour; altered maternal behaviours such as aggression, cannibalism, rejection, and also the relation between hormones and maternal care behaviours. We concluded that the level of interactions between the dam and the puppies influences the physiological, cognitive and behavioural development of the litter, and the main hormones in the bitch for inducing maternal care behaviours are estradiol, oxytocin, prolactin and progesterone.

Differences in how macaques monitor others: Does serotonin play a central role?

Primates must balance the need to monitor other conspecifics to gain social information while not losing other resource opportunities. We consolidate evidence across the fields of primatology, psychology, and neuroscience to examine individual, population, and species differences in how primates, particularly macaques, monitor conspecifics. We particularly consider the role of serotonin in mediating social competency via social attention, aggression, and dominance behaviors. Finally, we consider how the evolution of variation in social tolerance, aggression, and social monitoring might be explained by differences in serotonergic function in macaques. This article is categorized under: Economics > Interactive Decision-Making Psychology > Comparative Psychology Neuroscience > Behavior Cognitive Biology > Evolutionary Roots of Cognition.

Are neuropeptides relevant for the mechanism of action of SSRIs?

Selective serotonin reuptake inhibitors (SSRIs) are drugs of first choice in the therapy of moderate to severe depression and anxiety disorders. Their primary mechanism of action is via influence of the serotonergic (5-HT) system, but a growing amount of data provides evidence for other non-monoaminergic players in SSRI effects. It is assumed that neuropeptides, which play a role as neuromodulators in the CNS, are involved in their mechanism of action. In this review we focus on six neuropeptides: corticotropin-releasing factor - CRF, galanin - GAL, oxytocin - OT, vasopressin - AVP, neuropeptide Y - NPY, and orexins - OXs. First, information about their roles in depression and anxiety disorders are presented. Then, findings describing their interactions with the 5-HT system are summarized. These data provide background for analysis of the results of published preclinical and clinical studies related to SSRI effects on the neuropeptide systems. We also report findings showing how modulation of neuropeptide transmission influences behavioral and neurochemical effects of SSRIs. Finally, future research necessary for enriching our knowledge of SSRI mechanisms of action is proposed. Recognition of new molecular targets for antidepressants will have a significant effect on the development of novel therapeutic strategies for mood-related disorders.

Neural correlates of emotion processing comparing antidepressants and exogenous oxytocin in postpartum depressed women: An exploratory study

Despite common use of antidepressants to treat postpartum depression, little is known about the impact of antidepressant use on postpartum brain activity. Additionally, although oxytocin has been investigated as a potential treatment for postpartum depression, the interaction between antidepressants and exogenous oxytocin on brain activity is unknown. We explored postpartum depressed women's neural activation in areas identified as important to emotion and reward processing and potentially, antidepressant response: the amygdala, nucleus accumbens and ventral tegmental area. We conducted a secondary analysis of a functional imaging study of response to sexual, crying infant and smiling infant images in 23 postpartum depressed women with infants under six months (11 women taking antidepressants, 12 unmedicated). Participants were randomized to receive a single dose of oxytocin or placebo nasal spray. There was significantly higher amygdala activation to sexual stimuli than either neutral or infant-related stimuli among women taking antidepressants or receiving oxytocin nasal spray. Among unmedicated women receiving placebo, amygdala activation was similar across stimuli types. There were no significant effects of antidepressants nor oxytocin nasal spray on reward area processing (i.e., in the nucleus accumbens or ventral tegmental area). Among postpartum women who remain depressed, there may be significant interactions between the effects of antidepressant use and exogenous oxytocin on neural activity associated with processing emotional information. Observed effect sizes were moderate to large, strongly suggesting the need for further replication with a larger sample.

Centrally administered kisspeptin suppresses feeding via nesfatin-1 and oxytocin in male rats

Kisspeptin (KP), known as a hypothalamic neuropeptide, plays a critical role in the regulation of not only reproduction but also food intake. The anorectic neuropeptides, nesfatin-1 and oxytocin (OXT), are expressed in central nervous system, particulaly in various hypothalamic nuclei, and peripheral tissue. We examined the effects of the intracerebroventricular (icv) administration of KP-10 on feeding and nesfatin-1-immunoreactive (ir) or OXT-ir neurons in the rat hypothalamus, using Fos double immunohistochemistry in male rats. Cumulative food intake was remarkably decreased 0.5-3 h after icv administration of KP-10 (6.0 μg) compared to the vehicle treated and the KP-10 (3.8 μg) treated group. The icv administration of KP-10 significantly increased the number of nesfatin-1-ir neurons expressing Fos in the supraoptic nucleus (SON), paraventricular nucleus (PVN), arcuate nucleus (ARC), dorsal raphe nucleus, locus coeruleus, and nucleus tractus solitarius. The decreased food intake induced by KP-10 was significantly attenuated by pretreatment with the icv administration of antisense RNA against nucleobindin-2. After icv administration of KP-10, the percentages of OXT-ir neurons expressing FOS were remarkably higher in the SON and PVN than for vehicle treatment. The KP-10-induced anorexia was partially abolished by pretreatment with OXT receptor antagonist (OXTR-A). The percentage of nesfatin-1-ir neurons expressing Fos-ir in the ARC was also decreased by OXTR-A pretreatment. These results indicate that central administration of KP-10 activates nesfatin-1- and OXT neurons, and may play an important role in the suppression of feeding in male rats.

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.

Neural Circuits for Social Cognition: Implications for Autism

Social neuroscience, the study of the neurobiological basis of social behavior, has become a major area of current research in behavioral neuroscience and psychiatry, since many psychiatric disorders are characterized by social deficits. Social behavior refers to the behavioral response with regard to socially relevant information, and requires the perception and integration of social cues through a complex cognition process (i.e. social cognition) that involves attention, memory, motivation and emotion. Neurobiological and molecular mechanisms underlying social behavior are highly conserved across species, and inter- and intra-specific variability observed in social behavior can be explained to large extent by differential activity of this conserved neural network. Human functional magnetic resonance imaging (fMRI) studies have greatly informed about the brain structures and their connectivity networks that are important for social cognition. Animal research has been crucial for identifying specific circuits and molecular mechanisms that modulate this structural network. From a molecular neurobiology perspective, activity in these brain structures is coordinated by neuronal circuits modulated by several neurotransmitters and neuromodulators. Thus, quantitative variation in the levels, release and/or receptor density of these molecules could affect the observed behavioral response. The present review presents an overall framework of the components of the social brain circuitry and its modulation. By integrating multiple research approaches, from human fMRI studies to animal models we can start shedding light into how dysfunction in these circuits could lead to disorders of social-functioning such as Autism.

Interactive effects of 5-HTTLPR genotype and rearing environment on affective attitude towards own infant in Japanese mothers

Maternal positive attitude towards one's own infant is the cornerstone of effective parenting. Previous research has revealed an influence of both genetic and environmental factors on maternal parenting behavior, but little is known of the potential gene-environment interaction in shaping a mother's affective attitude. To address this gap, we investigated the effect of a mother's childhood rearing environment and a serotonin transporter gene polymorphism (5-HTTLPR) on affective attitude towards her infant. Our analyses found an interactive effect between rearing environment and 5-HTTLPR genotype on maternal attitude. Specifically, a poor rearing environment (characterized by low maternal care and high paternal overprotection) decreased positive attitude towards one's own infant in mothers with homozygous short allele genotype. In contrast, this detrimental effect was almost eliminated in long allele carriers. Altogether, our results indicate that the 5-HTTLPR gene moderates the influence of experienced rearing environment on maternal parental behavior in a manner consistent with the notion that the short 5-HTTLPR allele amplifies environmental influence.

The Non-Peptide Arginine-Vasopressin v1a Selective Receptor Antagonist, SR49059, Blocks the Rewarding, Prosocial, and Anxiolytic Effects of 3,4-Methylenedioxymethamphetamine and Its Derivatives in Zebra Fish

3,4-Methylenedioxymethamphetamine (MDMA) and its derivatives, 2,5-dimethoxy-4-bromo-amphetamine hydrobromide (DOB) and para-methoxyamphetamine (PMA), are recreational drugs whose pharmacological effects have recently been attributed to serotonin 5HT_2A/C receptors. However, there is growing evidence that the oxytocin (OT)/vasopressin system can modulate some the effects of MDMA. In this study, MDMA (2.5-10 mg/kg), DOB (0.5 mg/kg), or PMA (0.005, 0.1, or 0.25 mg/kg) were administered intramuscularly to adult zebra fish, alone or in combination with the V_1a vasopressin antagonist, SR49059 (0.01-1 ng/kg), before carrying out conditioned place preference (CPP), social preference, novel tank diving, and light-dark tests in order to evaluate subsequent rewarding, social, and emotional-like behavior. The combination of SR49059 and each drug progressively blocked: (1) rewarding behavior as measured by CPP in terms of time spent in drug-paired compartment; (2) prosocial effects measured on the basis of the time spent in the proximity of a nacre fish picture; and (3) anxiolytic effects in terms of the time spent in the upper half of the novel tank and in the white compartment of the tank used for the light-dark test. Antagonism was obtained at SR49059 doses which, when given alone, did not change motor function. In comparison with a control group, receiving vehicle alone, there was a three to five times increase in the brain release of isotocin (the analog of OT in fish) after treatment with the most active doses of MDMA (10 mg/kg), DOB (0.5 mg/kg), and PMA (0.1 mg/kg) as evaluated by means of bioanalytical reversed-phase high-performance liquid chromatography. Taken together, these findings show that the OT/vasopressin system is involved in the rewarding, prosocial, and anxiolytic effects of MDMA, DOB, and PMA in zebra fish and underline the association between this system and the behavioral alterations associated with disorders related to substance abuse.

Fibroblast growth factor 2 alters the oxytocin receptor in a developmental model of anxiety-like behavior in male rat pups

We aimed to determine the short-term effects of early-life stress in the form of maternal separation (MS) on anxiety-like behavior in male rat pups. In order to assess anxiety, we measured 40kHz separation-induced ultrasonic vocalizations (USV) on postnatal day (PND) 11. We further aimed to evaluate the potential involvement of two neurochemical systems known to regulate social and anxiety-like behaviors throughout life: oxytocin (OT) and fibroblast growth factor 2 (FGF2). For these purposes, we tested the effects of neonatal administration (on PND1) of an acute dose of FGF2 on USV and its potential interaction with MS. In addition, we validated the anxiolytic effects of OT and measured oxytocin receptor (OTR) gene expression, binding and epigenetic regulation via histone acetylation. Our results show that MS potentiated USV while acute administration of OT and FGF2 attenuated them. Further, we found that both FGF2 and MS increased OTR gene expression and the association of acH3K14 with the OTR promoter in the bed nucleus of the stria terminalis (BNST). Comparable changes, though not as pronounced, were also found for the central amygdala (CeA). Our findings suggest that FGF2 may exert its anxiolytic effects in male MS rats by a compensatory increase in the acetylation of the OTR promoter to overcome reduced OT levels in the BNST.

Implicit association to infant faces: Genetics, early care experiences, and cultural factors influence caregiving propensities

Genetics, early experience, and culture shape caregiving, but it is still not clear how genetics, early experiences, and cultural factors might interact to influence specific caregiving propensities, such as adult responsiveness to infant cues. To address this gap, 80 Italian adults (50% M; 18-25 years) were (1) genotyped for two oxytocin receptor gene polymorphisms (rs53576 and rs2254298) and the serotonin transporter gene polymorphism (5-HTTLPR), which are implicated in parenting behaviour, (2) completed the Adult Parental Acceptance/Rejection Questionnaire to evaluate their recollections of parental behaviours toward them in childhood, and (3) were administered a Single Category Implicit Association Test to evaluate their implicit responses to faces of Italian infants, Japanese infants, and Italian adults. Analysis of implicit associations revealed that Italian infant faces were evaluated as most positive; participants in the rs53576 GG group had the most positive implicit associations to Italian infant faces; the serotonin polymorphism moderated the effect of early care experiences on adults' implicit association to both Italian infant and adult female faces. Finally, 5-HTTLPR S carriers showed less positive implicit responses to Japanese infant faces. We conclude that adult in-group preference extends to in-group infant faces and that implicit responses to social cues are influenced by interactions of genetics, early care experiences, and cultural factors. These findings have implications for understanding processes that regulate adult caregiving.

Orgasm, Serotonin Reuptake Inhibition, and Plasma Oxytocin in Obsessive-Compulsive Disorder. Gleaning From a Distant Randomized Clinical Trial

Introduction

Serotonin reuptake inhibitors (SRIs) are widely used for the treatment of psychiatric disorders, including obsessive-compulsive disorder (OCD). SRIs commonly cause delayed orgasm, the mechanism of which is poorly understood. Oxytocin is involved in sexual function and is interconnected with serotonin within the brain. SRIs are reported to affect the oxytocin system, but possible relations between SRI-induced changes of sexual function and oxytocin are unexplored in humans. In a randomized, double-blinded, placebo-controlled trial of OCD, the anti-obsessive efficacy and adverse events of SRIs and oxytocin measurements were studied.

Aims

To identify possible correlates between oxytocin levels and sexual function; find out whether sexual side effects correlate with levels of oxytocin and/or paroxetine and clomipramine; and test whether changes in sexual functioning are related to an anti-obsessive response.

Methods

Reported sexual function and oxytocin plasma levels at rest were studied in 31 adults (15 men and 16 women) with OCD who participated in a randomized, double-blinded trial comparing the SRIs clomipramine and paroxetine with placebo. Sexual adverse effects were quantified by a clinician-administered semistructured interview. Anti-obsessive response was based on the Yale-Brown Obsessive-Compulsive Scale.

Main Outcome Measures

Ratings on the Sexual Symptom Checklist, plasma oxytocin, serum paroxetine and clomipramine levels, and Yale-Brown Obsessive-Compulsive Scale scores.

Results

Baseline oxytocin levels were positively correlated with baseline OCD severity, but not with sexual functioning. Impaired orgasm at week 6 was reported by 73% of SRI-treated and 20% of placebo-treated patients (P = .03). Impaired orgasm was related to higher oxytocin levels after 4 weeks of SRI treatment (P < .01) but not to SRI concentrations. In men, an association between impaired orgasm and anti-obsessive treatment response was found (P = .028).

Conclusion

This pilot study suggests that some collateral effects of SRIs, particularly delayed orgasm, might be influenced by changes within the oxytocinergic system and are related to anti-obsessive mechanisms. Early-onset delayed orgasm in SRI-treated patients could serve as a predictor for OCD treatment response.

Variants in Adjacent Oxytocin/Vasopressin Gene Region and Associations with ASD Diagnosis and Other Autism Related Endophenotypes

BACKGROUND

There has been increasing interest in oxytocin (peptide: OT, gene: OXT) as a treatment pathway for neurodevelopmental disorders such as Autism Spectrum Disorder (ASD). Neurodevelopmental disorders affect functional, social, and intellectual abilities. With advances in molecular biology, research has connected multiple gene regions to the clinical presentation of ASD. Studies have also shown that the neuropeptide hormones OT and arginine vasopressin (AVP) influence mammalian social and territorial behaviors and may have treatment potential for neurodevelopmental disorders. Published data examining molecular and phenotypic variation in ASD, such as cognitive abilities, are limited. Since most studies have focused on the receptors in the OT-AVP system, we investigated genetic variation within peptide genes for association with phenotypic ASD features that help identify subgroups within the spectrum.

METHODS

In this study, TDT analysis was carried out utilizing FBAT in 207 probands (156 trios) and a European Ancestry (EA) subsample (108 trios).The evolutionarily related and adjacent genes of OXT and AVP were studied for associations between the tagged single nucleotide polymorphisms and ASD diagnosis, social abilities, restrictive and repetitive behaviors, and IQ for cognitive abilities. Additionally, relationships with whole blood serotonin (WB5HT) were explored because of the developmental relationships connecting plasma levels of OT and WB5HT within ASD.

RESULTS

RESULTS indicate significant association between OXT rs6084258 (p = 0.001) and ASD. Associations with several endophenotypes were also noted: OXT rs6133010 was associated with IQ (full scale IQ, p = 0.008; nonverbal IQ, p = 0.010, verbal IQ, p = 0.006); and OXT rs4813625 and OXT rs877172 were associated with WB5HT levels (EA, p = 0.027 and p = 0.033, respectively). Additionally, we measured plasma OT (pOT) levels in a subsample (N = 54). RESULTS show the three polymorphisms, OXT rs6084258, OXT rs11697250, and OXT rs877172, have significant association with pOT (EA, p = 0.011, p = 0.010, and p = 0.002, respectively).

CONCLUSIONS

These findings suggest that SNPs near OXT and AVP are associated with diagnosis of ASD, social behaviors, restricted and repetitive behaviors, IQ, pOT, and WB5HT. Future studies need to replicate these findings and examine gene-interactions in other neurodevelopmental disorders. Mechanisms of action may influence early social and cognitive development that may or may not be limited to ASD diagnosis.

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.

The effects of gestational stress and Selective Serotonin reuptake inhibitor antidepressant treatment on structural plasticity in the postpartum brain--A translational model for postpartum depression

This article is part of a Special Issue "Parental Care". Postpartum depression (PPD) is a common complication following childbirth experienced by one in every five new mothers. Although the neural basis of PPD remains unknown, previous research in rats has shown that gestational stress, a risk factor for PPD, induces depressive-like behavior during the postpartum period. Moreover, the effect of gestational stress on postpartum mood is accompanied by structural modifications within the nucleus accumbens (NAc) and the medial prefrontal cortex (mPFC)-limbic regions that have been linked to PPD. Mothers diagnosed with PPD are often prescribed selective serotonin reuptake inhibitor (SSRI) antidepressant medications and yet little is known about their effects in models of PPD. Thus, here we investigated whether postpartum administration of Citalopram, an SSRI commonly used to treat PPD, would ameliorate the behavioral and morphological consequences of gestational stress. In addition, we examined the effects of gestational stress and postpartum administration of Citalopram on structural plasticity within the basolateral amygdala (BLA) which together with the mPFC and NAc forms a circuit that is sensitive to stress and is involved in mood regulation. Our results show that postpartum rats treated with Citalopram do not exhibit gestational stress-induced depressive-like behavior in the forced swim test. In addition, Citalopram was effective in reversing gestational stress-induced structural alterations in the postpartum NAc shell and mPFC. We also found that gestational stress increased spine density within the postpartum BLA, an effect which was not reversed by Citalopram treatment. Overall, these data highlight the usefulness of gestational stress as a valid and informative translational model for PPD. Furthermore, they suggest that structural alterations in the mPFC-NAc pathway may underlie stress-induced depressive-like behavior during the postpartum period and provide much needed information on how SSRIs may act in the maternal brain to treat PPD.

Genetic mechanisms of parenting

This article is part of a Special Issue "Parental Care". The complexities of parenting behavior in humans have been studied for decades. Only recently did we begin to probe the genetic and epigenetic mechanisms underlying these complexities. Much of the research in this field continues to be informed by animal studies, where genetic manipulations and invasive tools allow to peek into and directly observe the brain during the expression of maternal behavior. In humans, studies of adult twins who are parents can suggest dimensions of parenting that might be more amenable to a genetic influence. Candidate gene studies can test specific genes in association with parental behavior based on prior knowledge of those genes' function. Gene-by-environment interactions of a specific kind indicating differential susceptibility to the environment might explain why some parents are more resilient and others are more vulnerable to stressful life events. Epigenetic studies can provide the bridge often necessary to explain why some individuals behave differently from others despite common genetic influences. There is a much-needed expansion in parenting research to include not only mothers as the focus-as has been the case almost exclusively to date-but also fathers, grandparents, and other caregivers.

A refined high carbohydrate diet is associated with changes in the serotonin pathway and visceral obesity

Consumption of palatable foods high in refined carbohydrate has been implicated as a contributing factor to the epidemic levels of obesity. Such foods may disrupt appetite regulation in the hypothalamus through alterations in hunger and satiety signalling. This investigation examined whether a palatable high refined carbohydrate (HRC) diet with the potential to induce obesity was linked to modulation of serotonin and dopamine signalling within the hypothalamus of rats. Male Wistar rats were allowed ad libitum access to either a palatable refined carbohydrate enriched (HRC) diet or standard chow (SC). Visceral fat percentage was used as a measure of the animals' weight gain during the trial. Real-time PCR was applied to determine any variation in levels of expression of the serotonin (Slc6A4 or Sert) and dopamine transporter (Slc6A3 or Dat) genes. After 29 weeks, the HRC group showed a significant increase in visceral fat percentage accompanied by increased expression of Sert. Higher levels of circulating triglycerides were also seen. This investigation determined that a refined high carbohydrate diet is associated with visceral obesity, increased circulating lipids in the blood and distorted serotonergic signalling, which possibly alters satiety and hunger signals.

A review of animal models of obsessive-compulsive disorder: a focus on developmental, immune, endocrine and behavioral models

INTRODUCTION

Obsessive-compulsive disorder (OCD) is a neuropsychiatric condition characterized by intrusive thoughts (obsessions) and/or repetitive behaviors (compulsions). Several models of OCD exist, many which employ behaviors such as over-grooming or hoarding as correlates for compulsive behaviors - often using a response to serotonergic agents as evidence for their validity. Recent discoveries in the genetics of OCD and the identification of aberrancies of glutamatergic, hormonal, and immune pathways in the OCD phenotype highlight a need to review existing of animal models of OCD. The focus of attention to these pathways may lead to possible new targets for drug discovery.

AREAS COVERED

In this review, the authors describe frameworks for animal models in OCD conceptualized as either biological (e.g., developmental, genetic, and endocrine pathways), or behavioral (e.g., repetitive grooming, and stereotypies). In addition, the authors give special attention to the emerging role of glutamate in OCD.

EXPERT OPINION

While many animal models for OCD demonstrate pathologic repetitive behavior phenotypes, which are relieved by serotoninergic agents, animal models based on reversal learning, perseverative responding, and neurodevelopmental mechanisms represent robust new paradigms. Glutamatergic influences in these new animal models suggest that drug discovery using neuroprotective approaches may represent a new stage for pharmacologic developments in OCD.

Oxytocin and vasopressin: linking pituitary neuropeptides and their receptors to social neurocircuits

Oxytocin and vasopressin are pituitary neuropeptides that have been shown to affect social processes in mammals. There is growing interest in these molecules and their receptors as potential precipitants of, and/or treatments for, social deficits in neurodevelopmental disorders, including autism spectrum disorder. Numerous behavioral-genetic studies suggest that there is an association between these peptides and individual social abilities; however, an explanatory model that links hormonal activity at the receptor level to complex human behavior remains elusive. The following review summarizes the known associations between the oxytocin and vasopressin neuropeptide systems and social neurocircuits in the brain. Following a micro- to macro- level trajectory, current literature on the synthesis and secretion of these peptides, and the structure, function and distribution of their respective receptors is first surveyed. Next, current models regarding the mechanism of action of these peptides on microcircuitry and other neurotransmitter systems are discussed. Functional neuroimaging evidence on the acute effects of exogenous administration of these peptides on brain activity is then reviewed. Overall, a model in which the local neuromodulatory effects of pituitary neuropeptides on brainstem and basal forebrain regions strengthen signaling within social neurocircuits proves appealing. However, these findings are derived from animal models; more research is needed to clarify the relevance of these mechanisms to human behavior and treatment of social deficits in neuropsychiatric disorders.

Enhanced responsiveness to selective serotonin reuptake inhibitors during lactation

The physiology of mood regulation in the postpartum is poorly understood despite the fact that postpartum depression (PPD) is a common pathology. Serotonergic mechanisms and their dysfunction are widely presumed to be involved, which has led us to investigate whether lactation induces changes in central or peripheral serotonin (5-HT) systems and related affective behaviors. Brain sections from lactating (day 10 postpartum) and age-matched nulliparous (non-pregnant) C57BL/6J mice were processed for 5-HT immunohistochemistry. The total number of 5-HT immunostained cells and optical density were measured. Lactating mice exhibited lower immunoreactive 5-HT and intensity in the dorsal raphe nucleus when compared with nulliparous controls. Serum 5-HT was quantified from lactating and nulliparous mice using radioimmunoassay. Serum 5-HT concentrations were higher in lactating mice than in nulliparous controls. Affective behavior was assessed in lactating and non-lactating females ten days postpartum, as well as in nulliparous controls using the forced swim test (FST) and marble burying task (MBT). Animals were treated for the preceding five days with a selective serotonin reuptake inhibitor (SSRI, citalopram, 5mg/kg/day) or vehicle. Lactating mice exhibited a lower baseline immobility time during the FST and buried fewer marbles during the MBT as compared to nulliparous controls. Citalopram treatment changed these behaviors in lactating mice with further reductions in immobility during the FST and decreased marble burying. In contrast, the same regimen of citalopram treatment had no effect on these behaviors in either non-lactating postpartum or nulliparous females. Our findings demonstrate changes in both central and peripheral 5-HT systems associated with lactation, independent of pregnancy. They also demonstrate a significant interaction of lactation and responsiveness to SSRI treatment, which has important implications in the treatment of PPD. Although recent evidence has cast doubt on the effectiveness of SSRIs, these results support their therapeutic use in the treatment of PPD.

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.

The utility of zebrafish to study the mechanisms by which ethanol affects social behavior and anxiety during early brain development

Exposure to moderate levels of ethanol during brain development has a number of effects on social behavior but the molecular mechanisms that mediate this are not well understood. Gaining a better understanding of these factors may help to develop therapeutic interventions in the future. Zebrafish offer a potentially useful model in this regard. Here, we introduce a zebrafish model of moderate prenatal ethanol exposure. Embryos were exposed to 20mM ethanol for seven days (48hpf-9dpf) and tested as adults for individual social behavior and shoaling. We also tested their basal anxiety with the novel tank diving test. We found that the ethanol-exposed fish displayed reductions in social approach and shoaling, and an increase in anxiety in the novel tank test. These behavioral differences corresponded to differences in hrt1aa, slc6a4 and oxtr expression. Namely, acute ethanol caused a spike in oxtr and ht1aa mRNA expression, which was followed by down-regulation at 7dpf, and an up-regulation in slc6a4 at 72hpf. This study confirms the utility of zebrafish as a model system for studying the molecular basis of developmental ethanol exposure. Furthermore, it proposes a putative developmental mechanism characterized by ethanol-induced OT inhibition leading to suppression of 5-HT and up-regulation of 5-HT1A, which leads, in turn, to possible homeostatic up-regulation of 5-HTT at 72hpf and subsequent imbalance of the 5-HT system.

Oxytocin treatment in pediatric populations

The role of endogenous oxytocin as neuromodulator of birth, lactation and social behaviors is well-recognized. Moreover, the use of oxytocin as a facilitator of social and other behaviors is becoming more and more accepted. Many positive effects have been attributed to intranasal oxytocin administration in animals and humans; with current research highlighting encouraging advances in its potential for use in mental health disorders. The new frontier will be investigating the effective use of oxytocin in pediatric populations. Limited animal data is available on this. Large-scale human studies focusing on autism are currently under way, but many other possibilities seem to lie in the future. However, we need to know more about the risks and effects of repeated use on the developing brain and body. This paper will provide an overview of the current understanding of the role of endogenous oxytocin and its related neuropeptide systems in influencing behaviors, in particular attachment, and will review (a) the literature on the use of intranasal oxytocin in young animals, children (age range birth-12 years) and adolescents (age range 13-19 years), (b) the expected benefits and risks based on the current research, and (c) the risks of oxytocin in children with severe psychopathology and early life trauma. The paper will conclude with a clinical perspective on these findings.

Switching brain serotonin with oxytocin

Serotonin (5-HT) and oxytocin (OXT) are two neuromodulators involved in human affect and sociality and in disorders like depression and autism. We asked whether these chemical messengers interact in the regulation of emotion-based behavior by administering OXT or placebo to 24 healthy subjects and mapping cerebral 5-HT system by using 2'-methoxyphenyl-(N-2'-pyridinyl)-p-[(18)F]fluoro-benzamidoethylpiperazine ([(18)F]MPPF), an antagonist of 5-HT1A receptors. OXT increased [(18)F]MPPF nondisplaceable binding potential (BPND) in the dorsal raphe nucleus (DRN), the core area of 5-HT synthesis, and in the amygdala/hippocampal complex, insula, and orbitofrontal cortex. Importantly, the amygdala appears central in the regulation of 5-HT by OXT: [(18)F]MPPF BPND changes in the DRN correlated with changes in right amygdala, which were in turn correlated with changes in hippocampus, insula, subgenual, and orbitofrontal cortex, a circuit implicated in the control of stress, mood, and social behaviors. OXT administration is known to inhibit amygdala activity and results in a decrease of anxiety, whereas high amygdala activity and 5-HT dysregulation have been associated with increased anxiety. The present study reveals a previously unidentified form of interaction between these two systems in the human brain, i.e., the role of OXT in the inhibitory regulation of 5-HT signaling, which could lead to novel therapeutic strategies for mental disorders.

Decreased serotonin transporter immunoreactivity in the human hypothalamic infundibular nucleus of overweight subjects

Context: That serotonin plays a role in the regulation of feeding behavior and energy metabolism has been known for a long time. Serotonin transporters (SERT) play a crucial role in serotonin signaling by regulating its availability in the synaptic cleft. The neuroanatomy underlying serotonergic signaling in humans is largely unknown, and until now, SERT immunoreactivity in relation to body weight has not been investigated.

Objective: To clarify the distribution of SERT immunoreactivity throughout the human hypothalamus and to compare SERT immunoreactivity in the infundibular nucleus (IFN), the human equivalent of the arcuate nucleus, in lean and overweight subjects.

Design: First, we investigated the distribution of serotonin transporters (SERT) over the rostro-caudal axis of six post-mortem hypothalami by means of immunohistochemistry. Second, we estimated SERT immunoreactivity in the IFN of lean and overweight subjects. Lastly, double-labeling of SERT with Neuropeptide Y (NPY) and melanocortin cell populations was performed to further identify cells showing basket-like SERT staining.

Results: SERT-immunoreactivity was ubiquitously expressed in fibers throughout the hypothalamus and was the strongest in the IFN. Immunoreactivity in the IFN was lower in overweight subjects (p = 0.036). Basket-like staining in the IFN was highly suggestive of synaptic innervation. A very small minority of cells showed SERT double labeling with NPY, agouti-related protein and α–melanocyte stimulating hormone.

Conclusions: SERT is ubiquitously expressed in the human hypothalamus. Strong SERT immunoreactivity, was observed in the IFN a region important for appetite regulation, in combination with lower SERT immunoreactivity in the IFN of overweight and obese subjects, may point toward a role for hypothalamic SERT in human obesity.

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.