Evidence that oxytocin exerts anxiolytic effects via oxytocin receptor expressed in serotonergic neurons in mice

Disruptions of the oxytocin system impair sociability and cognitive flexibility in a subchronic phencyclidine model of schizophrenia

Previous research suggests that the oxytocin (Oxt) system may play a role in the etiology of schizophrenia. To investigate, we used a subchronic phencyclidine (PCP) mouse model to test how disruption of Oxt or the Oxt receptor (Oxtr) affects schizophrenia-related behaviors. Specifically, we assessed how subchronic PCP impacted hyperlocomotion, sociability, and passive stress coping in male Oxt and Oxtr knockout (-/-) and wildtype (+/+) mice. Additionally, we evaluated immediate early gene activation in Oxtr -/- and +/+ mice to identify brain regions where the Oxt system might impact schizophrenia-associated behaviors. Lastly, we investigated cognitive flexibility in Oxtr -/- and +/+ mice. We found that subchronic PCP treatment decreased social interactions in Oxt -/- mice as compared to Oxt +/+ mice, with no genotypic differences in the Oxtr line of mice. Increased c-Fos expression was observed in Oxtr -/- mice relative to Oxtr +/+ controls in the medial amygdala and the paraventricular nucleus of the hypothalamus following a forced swim test. Finally, we found deficits in cognitive flexibility in Oxtr -/- mice treated with PCP, relative to Oxtr +/+ mice. These findings are consistent with the hypothesis that Oxt may buffer against some of the schizophrenia-associated symptoms induced by subchronic PCP treatment. Based on the data, we speculate that compensatory mechanisms may be able to accommodate the loss of the Oxt system, depending on the origin of the dysfunction and the behavioral endpoint in question. These findings also add support to data linking disruption of Oxt system signaling to schizophrenia.

Differential Functions of Oxytocin Receptor-Expressing Neurons in the Ventromedial Hypothalamus in Social Stress Responses: Induction of Adaptive and Maladaptive Coping Behaviors

BACKGROUND

The flexibility to adjust actions and attitudes in response to varying social situations is a fundamental aspect of adaptive social behavior. Adaptive social behaviors influence an individual's vulnerability to social stress. While it has been proposed that oxytocin is a facilitator of active coping behaviors during social stress, the exact mechanisms remain unknown.

METHODS

Using a social defeat stress paradigm in male mice, we identified the distribution of oxytocin receptor (OXTR)-expressing neurons in the ventrolateral part of the ventromedial hypothalamus (vlVMH) that are activated during stress by detection of c-Fos protein expression. We then investigated the role of vlVMH OXTR-expressing neurons in social defeat stress responses by chemogenetic methods or deletion of local OXTRs. The social defeat posture was measured for quantification of adaptive social behavior during repeated social stress.

RESULTS

Social defeat stress activated OXTR-expressing neurons rather than estrogen receptor 1-expressing neurons in the rostral vlVMH. OXTR-expressing neurons in the vlVMH were glutamatergic. Chemogenetic activation of vlVMH OXTR-expressing neurons facilitated exhibition of the social defeat posture during exposure to social stress, while local OXTR deletion suppressed it. In contrast, overactivation of vlVMH-OXTR neurons induced generalized social avoidance after exposure to chronic social defeat stress. Neural circuits for the social defeat posture centered on OXTR-expressing neurons were identified by viral tracers and c-Fos mapping.

CONCLUSIONS

vlVMH OXTR-expressing neurons are a functionally unique population of neurons that promote active coping behavior during social stress, but their excessive and repetitive activation under chronic social stress impairs subsequent social behavior.

Oxytocin attenuates yohimbine-induced responding for oral oxycodone under a progressive ratio schedule in male and female rats

Opioid Use Disorder (OUD) has become an epidemic in the United States, with oxycodone (OXY) being one of the most widely misused opioids. Stress plays a key role in triggering opioid use, which can lead to addiction and relapse, underscoring the urgent need for effective therapeutic interventions. Recent studies suggest that the neuropeptide oxytocin (OXT) may reduce addiction-related behaviors and possess anxiolytic properties. The present study investigates the effect of peripheral administration of OXT on attenuating stress-induced motivation to seek oral OXY, as measured by progressive ratio (PR) responding in both male and female rats. Animals were first trained in an operant conditioning paradigm to orally self-administer a sucrose solution by pressing an active lever for access to the solution. As responding stabilized, subjects were switched to an OXY-sucrose solution, with sucrose concentration reduced overtime, until subjects were self-administering oral OXY alone. To test the effect of stress on OXY responding the pharmacological stressor, yohimbine (YOH), was administered prior to a progressive ratio test in which animals were required to produce increasingly higher responses to receive a single exposure to OXY. Through a within subjects design, when OXT was concurrently administered, this YOH-induced enhancement of OXY reward strength was attenuated in both male and female rats. These results suggest that OXT may serve as a potential therapeutic remedy to mitigate the deleterious effects of stress on OXY addiction in both sexes.

Exploring the impact of MDMA and oxytocin ligands on anxiety and social responses: A comprehensive behavioural and molecular study in the zebrafish model

BACKGROUND

Mental disorders, including anxiety and depression, impact nearly 1 billion people worldwide. Recent research has highlighted the potential of certain amphetamine compounds in the therapy of psychiatric disorders, with 3,4-methylenedioxymethamphetamine (MDMA) emerging as a promising candidate.

AIM

This study investigates the effects of MDMA on anxiety and social behaviours using 3-week-old zebrafish. Additionally, the role of oxytocin in regulating these behaviours was examined through the use of an oxytocin receptor agonist (WAY-267,464) and antagonist (L-368,899).

METHODS

Behavioural effects were assessed using the novel exploration test, light-dark preference test and social preference test. To explore the underlying mechanisms, changes in gene expression in serotonin, oxytocin and vasopressin systems and changes in AKT and EKR1/2 signalling pathways were analysed.

RESULTS

Acute MDMA exposure reduced thigmotactic behaviour and increased the social preference index, indicating anxiolytic and prosocial effects. However, these effects were biphasic - the lowest tested dose of 0.5 μM showed anxiogenic and prosocial effects. As the concentration increased, these effects reversed, with a peak at 2.5 μM. MDMA suppressed the expression of serotonin receptors (htr1b and htr2b) and transporter (scl6a4) genes while increasing oxytocin receptors (oxtra and oxtrb) genes, decreasing vasopressin receptor (avpr1aa) gene expression, and reducing AKT phosphorylation. The oxytocin receptor agonist mimicked MDMA's effects, while the antagonist had no significant effect on anxiety or social behaviour.

CONCLUSIONS

MDMA demonstrates therapeutic potential for treating anxiety disorders and social impairments. Moreover, 3-week-old zebrafish proved to be a valuable model for neurobehavioural research and high-throughput screening of psychiatric treatments.

Associations between different types of delivery, empathy, aggression, impulsivity and school bullying in children attending public and private schools in Pereira (Colombia)

This study aimed to correlate exposure to oxytocin during childbirth with behavioral determinants in teenage students. The Barratt Questionnaire (BQ), the Buss and Perry Aggression Questionnaire (BPAQ) and the Bryant Empathy Index (BEI), respectively measured impulsivity, aggression and empathy; the results were correlated with the roles of school bullying through the Velásquez and Pineda scale. Mothers were asked about birth circumstances. A total of 401 students were included (mean age 12 ± 1 years, 53,9 % were male, 53,3 % were attending a public school). 41,9 % of students had exogenous oxytocin exposure, 40,1 % had physiological oxytocin exposure, and 18 % had no oxytocin exposure. Regarding bullying, 75,1 % of students were classified as observers, 14,2 % were classified as victims, 6 % were classified as intimidators and 4,7 % exhibited an indifferent role. The mean value of the BPAQ was 78 ± 19, for the BEI was 78 ± 10 and for the BQ was 60 ± 10; all values were considered high. There were no significant differences among the type of delivery, sex and bullying roles or the type of delivery, aggressiveness and impulsivity according to sex; however, males had significantly lower empathy scores. There was no significant association between the type of delivery and the risk of assuming a bullying role. A regression model showed a significant association between attending a private school and a lower risk of developing a victim or intimidator role. This study could contribute to a better understanding of the processes involved in behavioral and emotional outcomes after birth, which can help to design prevention strategies to address increasing mental health problems in youth. Furthermore, this study could help emphasize the importance of promoting physiological delivery and find evidence that helps the scientific community design new work to deepen the relationship between oxytocin and behavior.

Spatiotemporal Mapping of the Oxytocin Receptor at Single-Cell Resolution in the Postnatally Developing Mouse Brain

The oxytocin receptor (OXTR) has garnered increasing attention for its role in regulating both mature behaviors and brain development. It has been established that OXTR mediates a range of effects that are region-specific or period-specific. However, the current studies of OXTR expression patterns in mice only provide limited help due to limitations in resolution. Therefore, our objective was to generate a comprehensive, high-resolution spatiotemporal expression map of Oxtr mRNA across the entire developing mouse brain. We applied RNAscope in situ hybridization to investigate the spatiotemporal expression pattern of Oxtr in the brains of male mice at six distinct postnatal developmental stages (P7, P14, P21, P28, P42, P56). We provide detailed descriptions of Oxtr expression patterns in key brain regions, including the cortex, basal forebrain, hippocampus, and amygdaloid complex, with a focus on the precise localization of Oxtr+ cells and the variance of expression between different neurons. Furthermore, we identified some neuronal populations with high Oxtr expression levels that have been little studied, including glutamatergic neurons in the ventral dentate gyrus, Vgat+Oxtr+ cells in the basal forebrain, and GABAergic neurons in layers 4/5 of the cortex. Our study provides a novel perspective for understanding the distribution of Oxtr and encourages further investigations into its functions.

High-throughput evolution of near-infrared oxytocin nanosensors enables oxytocin imaging in mice and prairie voles

Oxytocin is a neuropeptide involved in regulating social and emotional behavior. Current techniques for oxytocin imaging are generally limited in spatial and temporal resolution, real-time imaging capacity, selectivity for oxytocin over vasopressin, and application in young and non-model organisms. To address these issues, we developed a method to evolve purely synthetic molecular recognition for oxytocin on the surface of near-infrared fluorescent single-walled carbon nanotubes (SWCNT) using single-stranded DNA (ssDNA). The best-performing nanosensor nIROT-SELEC reversibly undergoes up to a 172% fluorescence increase in response to oxytocin with micromolar dissociation, nanomolar limit of detection, and and high selectivity over oxytocin analogs, receptor agonists and antagonists, and co-released neurochemicals. We next demonstrated the versatility of nIROT-SELEC by performing live imaging of synaptic evoked oxytocin released in acute brain slices of mice and prairie voles. Our method for high throughput evolution of neuropeptide nanosensors holds promise to enable synaptic scale visualization of neuropeptide signaling in the brain cross different species and developmental stages, to advance the study of neurochemical signaling for its role in both health and disease.

Social Bonds Retain Oxytocin-Mediated Brain-Liver Axis to Retard Atherosclerosis

BACKGROUNDS

Social interaction with others is essential to life. Although social isolation and loneliness have been implicated as increased risks of cardiometabolic and cardiovascular diseases and all-cause mortality, the cellular and molecular mechanisms by which social connection maintains cardiometabolic and cardiovascular health remain largely unresolved.

METHODS

To investigate how social connection protects against cardiometabolic and cardiovascular diseases, atherosclerosis-prone, high-fat diet-fed Apoe-/- mouse siblings were randomly assigned to either individual or grouped housing for 12 weeks. Histological, flow cytometric, biochemical, gene, and protein analyses were performed to assess atherosclerotic lesions, systemic metabolism, inflammation, and stress response. The effects of oxytocin on hepatocytes and subsequent cardiometabolic and cardiovascular function were investigated by in vivo and in vitro approaches.

RESULTS

Apoe-/- mice housed individually developed larger vulnerable atherosclerotic lesions by disrupted lipid metabolism compared with those of mice in regular group housing, irrespective of body weight, eating behavior, feeding conditions, sympathetic nervous activity, glucocorticoid response, or systemic inflammation. Mechanistically, the chronic isolation reduced the hypothalamic production of oxytocin, which controls bile acid production and LPL (lipoprotein lipase) activity through the peripheral OXTR (oxytocin receptor) in hepatocytes, whose downstream targets include Cyp7a1, Angptl4, and Angptl8. While hepatocyte-specific OXTR-null mice and mice receiving adeno-associated virus targeting OXTR on hepatocytes led to severe dyslipidemia and aggravated atherosclerosis, oral oxytocin supplementation to socially isolated mice, but not to hepatocyte-specific OXTR conditional knockout mice, improved lipid profiles and retarded atherosclerosis development.

CONCLUSIONS

These results identify a novel brain-liver axis that links sociality to hepatic lipid metabolism, thus proposing a potential therapeutic strategy for loneliness-associated atherosclerosis progression.

Oxytocin alleviates high-fat diet-induced anxiety by decreasing glutamatergic synaptic transmission in the ventral dentate gyrus in adolescent mice

A high-fat diet (HFD)-induced obesity is associated with mental disorders in adolescence. However, the mechanisms underlying these associations remain unclear. In this study, we hypothesized that synaptic remodeling occurs in the ventral hippocampus (vHP) of obese mice. To investigate this, we established a postnatal model of HFD-induced obesity in mice and observed increased body weight, elevated plasma luteinizing hormone and testosterone levels, premature puberty, and enhanced anxiety-like behavior in male subjects. We also examined the effect of HFD on the c-Fos protein expression in the ventral dentate gyrus (vDG) and explored the influence of intracerebroventricular (i.c.v) oxytocin injections on HFD-induced anxiety. Our results indicated an increase in c-Fos-positive cells in the vDG following HFD consumption. Additionally, we recorded the spontaneous synaptic activity of miniature excitatory postsynaptic currents (mEPSCs) in the vDG. Notably, HFD resulted in an elevated mEPSC frequency without affecting mEPSC amplitude. Subsequently, investigations demonstrated that i.c.v oxytocin injections reversed anxiety-like behavior induced by HFD. Moreover, the application of oxytocin in a bath solution reduced the mEPSC frequency in the vDG. These findings suggest that postnatal HFD intake induces synaptic dysfunction in the vDG, associated with the hyperactivity of vDG neurons, potentially contributing to the anxiety-like behavior in juvenile obesity.

Beyond fur color: differences in socio-emotional behavior and the oxytocin system between male BL6 and CD1 mice in adolescence and adulthood

Introduction

The development of stress-related psychopathologies, often associated with socio-emotional dysfunctions, is crucially determined by genetic and environmental factors, which shape the individual vulnerability or resilience to stress. Especially early adolescence is considered a vulnerable time for the development of psychopathologies. Various mouse strains are known to age-dependently differ in social, emotional, and endocrine stress responses based on genetic and epigenetic differences. This highlights the importance of the qualified selection of an adequate strain and age for any biomedical research. Neuropeptides like oxytocin (OXT) can contribute to individual and strain-dependent differences in emotional and social behaviors.

Methods

In this study, we compared anxiety- and fear-related, as well as social behavior and pain perception between male adolescent and adult mice of two commonly used strains, C57BL/6N (BL6) and CD1.

Results

We revealed BL6 mice as being more anxious, less social, and more susceptible toward non-social and social trauma, both in adolescence and adulthood. Furthermore, during development from adolescence toward adulthood, BL6 mice lack the reduction in fear- and anxiety-related behavior seen in adult CD1 mice and show even higher social fear-responses and perception of noxious stimuli during adulthood. Analysis of the OXT system, by means of receptor autoradiography and immunohistochemistry, showed strain- and age-specific differences in OXT receptor (OXTR) binding in relevant brain regions, but no differences in the number of hypothalamic OXT neurons. However, intracerebroventricular infusion of OXT did neither reduce the high level of anxiety-related nor of social fear-related behavior in adult BL6 mice.

Discussion

In summary, we show that male BL6 mice present an anxious and stress vulnerable phenotype in adolescence, which further exacerbates in adulthood, whereas CD1 mice show a more resilient socio-emotional state both in adolescence as well as during adulthood. These consistent behavioral differences between the two strains might only be partly mediated by differences in the OXT system but highlight the influence of early-life environment on socio-emotional behavior.

Oxytocin receptor control social information about fear expression of others in mice

The social functions of oxytocin are diverse, and the specific aspects of information processing involved in emotional contagion remain unclear. We compared some fear-related behaviors among oxytocin receptor knockout mice and oxytocin-receptor-reduced mice with that of wild-type mice. In the observational fear assay, which reflects fear emotional contagion, mice that observed other individuals receiving electric shocks exhibited vicarious freezing. Mice with reduced or knockout oxytocin receptor expression showed reduced vicarious freezing. In the emotional discrimination assay, which reflects the ability to perceive others' emotional cues, we compared approach and scent-sniffing behaviors toward fear and emotionally neutral individuals. While wild-type mice were able to detect the fear emotion of others, mice with reduced or knocked-out oxytocin receptors showed reduced discrimination ability. In the fear behavior assays, which do not present social cues, we did not find these differences in oxytocin receptor expression in the brain. These findings indicate that oxytocin plays a role in emotional contagion by perceiving the emotions of others.

Role of sexually dimorphic oxytocin receptor-expressing neurons in the anteroventral periventricular nucleus on maternal behavior

Oxytocin is a neuropeptide produced by magnocellular neurosecretory neurons located primarily in the supraoptic nucleus and paraventricular nucleus of the hypothalamus. The long axons of these neurons project to the neurohypophysis where oxytocin is released into the general circulation in response to the physiological demands. Oxytocin plays critical roles in female reproductive physiology, specifically in uterine contraction during labor and milk ejection while nursing. Oxytocin is also called "the love hormone" due to its modulatory roles in prosocial behaviors, including social recognition, maternal behavior, and pair bonding. Oxytocin influences behaviors by binding to oxytocin receptors (OXTR) located in various parts of the brain. Previously, we discovered a group of estrogen-dependent OXTR neurons that is exclusively present in the anteroventral periventricular nucleus (AVPV) of females but not of males. The female-specific expression of OXTR in the AVPV is a rare case of neurochemically-demonstrated, all-or-none sexual dimorphism in the brain. In this review, the cellular characterization and functional significance of the sexually dimorphic OXTR neurons in the AVPV as well as the clinical implications of the research will be discussed.

Distinct medial amygdala oxytocin receptor neurons projections respectively control consolation or aggression in male mandarin voles

The individuals often show consolation to distressed companions or show aggression to the intruders. The circuit mechanisms underlying switching between consolation and aggression remain unclear. In the present study, using male mandarin voles, we identified that two distinct subtypes of oxytocin receptor (OXTR) neurons in the medial amygdala (MeA) projecting to the anterior insula (AI) and ventrolateral aspect of ventromedial hypothalamus (VMHvl) response differently to stressed siblings or unfamiliar intruders using c-Fos or calcium recording. Oxytocin release and activities of PVN neurons projecting to MeA increased upon consoling and attacking. OXTR antagonist injection to the MeA reduced consoling and attacking. Apoptosis, optogenetic or pharmacogenetic manipulation of these two populations of neurons altered behavioral responses to these two social stimuli respectively. Here, we show that two subtypes of OXTR neurons in the MeA projecting to the AI or VMHvl causally control consolation or aggression that may underlie switch between consolation and aggression.

Paraventricular oxytocin neurons impact energy intake and expenditure: projections to the bed nucleus of the stria terminalis reduce sucrose consumption

Background

The part played by oxytocin and oxytocin neurons in the regulation of food intake is controversial. There is much pharmacological data to support a role for oxytocin notably in regulating sugar consumption, however, several recent experiments have questioned the importance of oxytocin neurons themselves.

Methods

Here we use a combination of histological and chemogenetic techniques to investigate the selective activation or inhibition of oxytocin neurons in the hypothalamic paraventricular nucleus (OxtPVH). We then identify a pathway from OxtPVH neurons to the bed nucleus of the stria terminalis using the cell-selective expression of channel rhodopsin.

Results

OxtPVH neurons increase their expression of cFos after both physiological (fast-induced re-feeding or oral lipid) and pharmacological (systemic administration of cholecystokinin or lithium chloride) anorectic signals. Chemogenetic activation of OxtPVH neurons is sufficient to decrease free-feeding in Oxt Cre:hM3Dq mice, while inhibition in Oxt Cre:hM4Di mice attenuates the response to administration of cholecystokinin. Activation of OxtPVH neurons also increases energy expenditure and core-body temperature, without a significant effect on locomotor activity. Finally, the selective, optogenetic stimulation of a pathway from OxtPVH neurons to the bed nucleus of the stria terminalis reduces the consumption of sucrose.

Conclusion

Our results support a role for oxytocin neurons in the regulation of whole-body metabolism, including a modulatory action on food intake and energy expenditure. Furthermore, we demonstrate that the pathway from OxtPVH neurons to the bed nucleus of the stria terminalis can regulate sugar consumption.

Is Oxytocin a Contributor to Behavioral and Metabolic Features in Prader-Willi Syndrome?

Prader-Willi Syndrome (PWS) is a rare genetic disorder typically characterized by decreased social interaction, hyperphagia, poor behavioral control and temper tantrums, together with a high risk of morbid obesity unless food intake is controlled. The genetic defects that cause PWS include paternal 15q deletion (estimated in 60% of cases), chromosome 15 maternal uniparental disomy (UPD) (estimated in 35% of cases) and imprinting defects and translocations. Several studies indicate an oxytocin deficiency in PWS. Oxytocin is a hypothalamic nonapeptide with receptors located in the brain and in various other tissues in the body. It acts as a neuropeptide in several brain areas of great importance for behavioral and metabolic effects, as well as a neurohypophyseal hormone released into the circulation. Oxytocin in both rats and humans has strong and long-lasting behavioral and metabolic effects. Thus, an oxytocin deficiency might be involved in several of the behavioral and metabolic symptoms characterizing PWS. Treatment with oxytocin has, in some studies, shown improvement in psycho-social behavior and hyperphagia in individuals with PWS. This review focus on the behavioral and metabolic effects of oxytocin, the symptoms of a potential oxytocin deficiency in PWS and the effects of oxytocin treatment.

Navigating Central Oxytocin Transport: Known Realms and Uncharted Territories

Complex mechanisms govern the transport and action of oxytocin (Oxt), a neuropeptide and hormone that mediates diverse physiologic processes. While Oxt exerts site-specific and rapid effects in the brain via axonal and somatodendritic release, volume transmission via CSF and the neurovascular interface can act as an additional mechanism to distribute Oxt signals across distant brain regions on a slower timescale. This review focuses on modes of Oxt transport and action in the CNS, with particular emphasis on the roles of perivascular spaces, the blood-brain barrier (BBB), and circumventricular organs in coordinating the triadic interaction among circulating blood, CSF, and parenchyma. Perivascular spaces, critical conduits for CSF flow, play a pivotal role in Oxt diffusion and distribution within the CNS and reciprocally undergo Oxt-mediated structural and functional reconstruction. While the BBB modulates the movement of Oxt between systemic and cerebral circulation in a majority of brain regions, circumventricular organs without a functional BBB can allow for diffusion, monitoring, and feedback regulation of bloodborne peripheral signals such as Oxt. Recognition of these additional transport mechanisms provides enhanced insight into the systemic propagation and regulation of Oxt activity.

Limbic oxytocin receptor expression alters molecular signaling and social avoidance behavior in female prairie voles (Microtus ochrogaster)

Introduction

The social defeat paradigm is the most representative animal model to study social anxiety disorder (SAD) and its underlying neuronal mechanisms. We have previously reported that defeat progressively reduces oxytocin receptors (OXTR) in limbic regions of the brain over an eight-week period in female prairie voles (Microtus ochrogaster). Oxytocin receptors activate the mitogen-activated protein kinase (MAPK) pathway, which has been previously associated with the anxiolytic effects of oxytocin. Here, we assessed the functional significance of OXTR in stress-induced social avoidance and the response of the MAPK signaling pathway in the nucleus accumbens (NAc), anterior cingulate cortex (ACC), and basolateral amygdala (BLA) of female prairie voles.

Methods

In experiment 1, Sexually naïve adult female prairie voles were defeated for three consecutive days and tested a week after for social preference/avoidance (SPA) test. Control subjects were similarly handled without defeat conditioning. In experiment 2, sexually and stress naïve adult female prairie voles were bilaterally injected into the NAc, ACC, or the BLA with a CRISPR/Cas9 virus targeting the Oxtr coding sequence to induce OXTR knockdown. Two weeks post-surgery, subjects were tested for SPA behavior. Viral control groups were similarly handled but injected with a control virus. A subgroup of animals from each condition in both experiments were similarly treated and euthanized without being tested for SPA behavior. Brains were harvested for OXTR autoradiography, western blot analysis of MAPK proteins and quantification of local oxytocin content in the NAc, BLA, ACC, and PVN through ELISA.

Results

Social defeat reduced OXTR binding in the NAc and affected MAPK pathway activity and oxytocin availability. These results were region-specific and sensitive to exposure to the SPA test. Additionally, OXTR knockdown in the NAc, ACC, and BLA induced social avoidance and decreased basal MAPK activity in the NAc. Finally, we found that OXTR knockdown in these regions was associated with less availability of oxytocin in the PVN.

Conclusion

Dysregulation of the oxytocin system and MAPK signaling pathway in the NAc, ACC, and BLA are important in social behavior disruptions in female voles. This dysregulation could, therefore, play an important role in the etiology of SAD in women.

Conserved and differing functions of the endocrine system across different social systems - oxytocin as a case study

A key goal of the field of endocrinology has been to understand the hormonal mechanisms that drive social behavior and influence reactions to others, such as oxytocin. However, it has sometimes been challenging to understand which aspects and influences of hormonal action are conserved and common among mammalian species, and which effects differ based on features of these species, such as social system. This challenge has been exacerbated by a focus on a relatively small number of traditional model species. In this review, we first demonstrate the benefits of using non-traditional models for the study of hormones, with a focus on oxytocin as a case study in adding species with diverse social systems. We then expand our discussion to explore differing effects of oxytocin (and its response to behavior) within a species, with a particular focus on relationship context and social environment among primate species. Finally, we suggest key areas for future exploration of oxytocin's action centrally and peripherally, and how non-traditional models can be an important resource for understanding the breadth of oxytocin's potential effects.

Oxytocin receptors in the nucleus accumbens shell are necessary for the onset of maternal behavior

In rodents, oxytocin (Oxt) contributes to the onset of maternal care by shifting the perception of pups from aversive to attractive. Both Oxt receptor knockout (Oxtr -/-) and forebrain-specific Oxtr knockout (FB/FB) dams abandon their first litters, likely due to a failure of the brain to 'switch' to a more maternal state. Whether this behavioral shift is neurochemically similar in virgin females, who can display maternal behaviors when repeatedly exposed to pups, or what neuroanatomical substrate is critical for the onset of maternal care remains unknown. To understand similarities and differences in Oxtr signaling in virgin pup-sensitized Oxtr FB/FB as opposed to post-parturient Oxtr -/- and Oxtr FB/FB dams, maternal behavior (pup-sensitized females only) and immediate early gene activation were assessed. Pup-sensitized Oxtr FB/FB females retrieved pups faster on day one of testing and had reduced c-Fos expression in the dorsal lateral septum as compared to virgin pup-sensitized Oxtr +/+ females. This differs from what was observed in post-parturient Oxtr -/- and Oxtr FB/FB dams, where increased c-Fos expression was observed in the nucleus accumbens (NAcc) shell. Based on these data, we then disrupted Oxtr signaling in the NAcc shell or the posterior paraventricular thalamus (pPVT) (control region) of female Oxtr floxed mice using a Cre recombinase expressing adeno-associated virus. Knockout of the Oxtr only in the NAcc shell prevented the onset of maternal care post-parturient females. Our data suggest that a pup-sensitized brain may differ from a post-parturient brain and that Oxtr signaling in the NAcc shell is critical to the onset of maternal behavior.

Body weight modulates the impact of oxytocin on chronic cold-immobilization stress response

By activating the stress system, stress modulates various physiological parameters including food intake, energy consumption, and, consequently, body weight. The role of oxytocin in the regulation of stress and obesity cannot be disregarded. Based on these findings, we aimed to investigate the effect of intranasal oxytocin on stress response in high-fat-diet (HFD)--fed and control-diet-fed rats exposed to chronic stress. Cold-immobilization stress was applied for 5 consecutive days to male Sprague-Dawley rats fed either with a control diet (n=20) or HFD (n=20) for 6 weeks. Half of the animals in each group received oxytocin. Stress response was evaluated via plasma and salivary cortisol levels as well as elevated plus maze scores. Prefrontal cortex and hypothalamic oxytocin receptor (OxtR) expression levels were identified using western blot analysis. The results showed higher stress response in HFD-fed animals than in control animals both under basal and post-stress conditions. Oxytocin application had a prominent anxiolytic effect in the control group but an insignificant effect in the HFD group. While OxtR expression levels in the prefrontal cortex did not vary according to the body weight and oxytocin application, OxtR levels in the hypothalamus were higher in the HFD- and/or oxytocin-treated animals. Our results indicated that the peripheral and central effects of oxytocin vary with body weight. Moreover, obesity masks the anxiolytic effects of oxytocin, probably by reinforcing the stress condition via central OxtRs. In conclusion, elucidating the mechanisms underlying the central effect of oxytocin is important to cope with stress and obesity.

Human placental lactogen (human chorionic somatomammotropin) and oxytocin during pregnancy: Individual patterns and associations with maternal-fetal attachment, anxiety, and depression

Previous studies support links among maternal-fetal attachment, psychological symptoms, and hormones during pregnancy and the post-partum period. Other studies connect maternal feelings and behaviors to oxytocin and suggest that an increase in oxytocin during pregnancy may prime maternal-fetal attachment. To date, researchers have not examined a possible association between maternal-fetal attachment with human placental lactogen although animal models are suggestive. In the current study, we sought to describe oxytocin and human placental lactogen levels as related to psychological constructs across pregnancy. Seventy women participated in the study. At each of three time-points (early, mid, and late pregnancy), the women had their blood drawn to assess oxytocin and human placental lactogen levels, and they completed psychological assessments measuring maternal-fetal attachment, anxiety, and depression. Our results indicate that oxytocin levels were statistically similar across pregnancy, but that human placental lactogen significantly increased across pregnancy. Results did not indicate significant associations of within-person (comparing individuals to themselves) oxytocin or human placental lactogen levels with maternal-fetal attachment. Additionally, results did not show between-person (comparing individuals to other individuals) oxytocin or human placental lactogen levels with maternal-fetal attachment. Oxytocin levels were not associated with anxiety; rather the stage of pregnancy moderated the effect of the within-person OT level on depression. Notably, increasing levels of human placental lactogen were significantly associated with increasing levels of both anxiety and depression in between subject analyses. The current study is important because it describes typical hormonal and maternal fetal attachment levels during each stage of pregnancy, and because it suggests an association between human placental lactogen and psychological symptoms during pregnancy. Future research should further elucidate these relationships.

Cerebellar damage with inflammation upregulates oxytocin receptor expression in Bergmann Glia

The cerebellum plays an important role in cognitive and social functioning. Childhood damage in the cerebellum increases the risk of autism spectrum disorder. Cerebellar inflammation induces social avoidance in mice. Oxytocin regulates social relationship and expression pattern of the oxytocin receptor in the brain is related to social behaviors. However, the expression patterns of the oxytocin receptor in the cerebellum remain controversial. Here, we report that the expression patterns of the oxytocin receptor in the cerebellum are highly variable among knock-in transgenic lines. We used Oxtr-Cre knock-in mice combined with a fluorescent reporter line and found that oxytocin receptor expression in Bergmann glia was more variable than that in Purkinje cells. We found that physical damage with inflammation induced the selective upregulation of the oxytocin receptor in Bergmann glia. Our findings indicate high variability in oxytocin receptor expression in the cerebellum and suggest that the oxytocin receptor can affect neural processing in pathological conditions, such as inflammation.

Increased reactivity of the paraventricular nucleus of the hypothalamus and decreased threat responding in male rats following psilocin administration

Psychedelics have experienced renewed interest following positive clinical effects, however the neurobiological mechanisms underlying effects remain unclear. The paraventricular nucleus of the hypothalamus (PVN) plays an integral role in stress response, autonomic function, social behavior, and other affective processes. We investigated the effect of psilocin, the psychoactive metabolite of psilocybin, on PVN reactivity in Sprague Dawley rats. Psilocin increased stimulus-independent PVN activity as measured by c-Fos expression in male and female rats. Psilocin increased PVN reactivity to an aversive air-puff stimulus in males but not females. Reactivity was restored at 2- and 7-days post-injection with no group differences. Additionally, prior psilocin injection did not affect PVN reactivity following acute restraint stress. Experimental groups sub-classified by baseline threat responding indicate that increased male PVN reactivity is driven by active threat responders. These findings identify the PVN as a significant site of psychedelic drug action with implications for threat responding behavior.

The bilevel chamber revealed differential involvement of vasopressin and oxytocin receptors in female mouse sexual behavior

Arginine vasopressin (AVP) and oxytocin (OT) are well-known as neuropeptides that regulate various social behaviors in mammals. However, little is known about their role in mouse female sexual behavior. Thus, we investigated the role of AVP (v1a and v1b) and OT receptors on female sexual behavior. First, we devised a new apparatus, the bilevel chamber, to accurately observe female mouse sexual behavior. This apparatus allowed for a more precisely measurement of lordosis as receptivity and rejection-like behavior (newly defined in this study), a reversed expression of proceptivity. To address our research question, we evaluated female sexual behavior in mice lacking v1a (aKO), v1b (bKO), both v1a and v1b (dKO), and OT (OTRKO) receptors. aKO females showed decreased rejection-like behavior but a normal level of lordosis, whereas bKO females showed almost no lordosis and no change in rejection-like behavior. In addition, dKO females showed normal lordosis levels, suggesting that the v1b receptor promotes lordosis, but not necessarily, while the v1a receptor latently suppresses it. In contrast, although OTRKO did not influence lordosis, it significantly increased rejection-like behavior. In summary, the present results demonstrated that the v1a receptor inhibits proceptivity and receptivity, whereas the v1b and OT receptors facilitate receptivity and proceptivity, respectively.

AgRP neurons mediate activity-dependent development of oxytocin connectivity and autonomic regulation

During postnatal life, the adipocyte-derived hormone leptin is required for proper targeting of neural inputs to the paraventricular nucleus of the hypothalamus (PVH) and impacts the activity of neurons containing agouti-related peptide (AgRP) in the arcuate nucleus of the hypothalamus. Activity-dependent developmental mechanisms are known to play a defining role during postnatal organization of neural circuits, but whether leptin-mediated postnatal neuronal activity specifies neural projections to the PVH or impacts downstream connectivity is largely unexplored. Here, we blocked neuronal activity of AgRP neurons during a discrete postnatal period and evaluated development of AgRP inputs to defined regions in the PVH, as well as descending projections from PVH oxytocin neurons to the dorsal vagal complex (DVC) and assessed their dependence on leptin or postnatal AgRP neuronal activity. In leptin-deficient mice, AgRP inputs to PVH neurons were significantly reduced, as well as oxytocin-specific neuronal targeting by AgRP. Moreover, downstream oxytocin projections from the PVH to the DVC were also impaired, despite the lack of leptin receptors found on PVH oxytocin neurons. Blocking AgRP neuron activity specifically during early postnatal life reduced the density of AgRP inputs to the PVH, as well as the density of projections from PVH oxytocin neurons to the DVC, and these innervation deficits were associated with dysregulated autonomic function. These findings suggest that postnatal targeting of descending PVH oxytocin projections to the DVC requires leptin-mediated AgRP neuronal activity, and represents a novel activity-dependent mechanism for hypothalamic specification of metabolic circuitry, with consequences for autonomic regulation.

Significance statement

Hypothalamic neural circuits maintain homeostasis by coordinating endocrine signals with autonomic responses and behavioral outputs to ensure that physiological responses remain in tune with environmental demands. The paraventricular nucleus of the hypothalamus (PVH) plays a central role in metabolic regulation, and the architecture of its neural inputs and axonal projections is a defining feature of how it receives and conveys neuroendocrine information. In adults, leptin regulates multiple aspects of metabolic physiology, but it also functions during development to direct formation of circuits controlling homeostatic functions. Here we demonstrate that leptin acts to specify the input-output architecture of PVH circuits through an activity-dependent, transsynaptic mechanism, which represents a novel means of sculpting neuroendocrine circuitry, with lasting effects on how the brain controls energy balance.

Intranasal oxytocin as a treatment for anxiety and autism: From subclinical to clinical applications

Animal and human studies have demonstrated that intranasal oxytocin (OT) can penetrate the brain and induce cognitive, emotional, and behavioral changes, particularly in social functioning. Consequently, numerous investigations have explored the potential of OT as a treatment for anxiety and autism, conditions characterized by social deficits. Although both subclinical and clinical studies provide converging evidence of the therapeutic effects of OT in reducing anxiety levels and improving social symptoms in autism, results are not always consistent. Additionally, the pharmacological mechanism of OT requires further elucidation for its effective clinical application. Therefore, this review aims to examine the contentious findings concerning the effects of OT on anxiety and autism, offer interpretations of the inconsistent results from the perspectives of individual differences and varying approaches to OT administration, and shed light on the underlying mechanisms of OT. Ultimately, standardization of dosage, frequency of administration, formulation characteristics, and nasal spray devices is proposed as essential for future human studies and clinical applications of OT treatment.

Effects of systemic oxytocin receptor activation and blockade on risky decision making in female and male rats

The neuropeptide oxytocin is traditionally known for its roles in parturition, lactation, and social behavior. Other data, however, show that oxytocin can modulate behaviors outside of these contexts, including drug self-administration and some aspects of cost-benefit decision making. Here we used a pharmacological approach to investigate the contributions of oxytocin signaling to decision making under risk of explicit punishment. Female and male Long-Evans rats were trained on a risky decision-making task in which they chose between a small, "safe" food reward and a large, "risky" food reward that was accompanied by varying probabilities of mild footshock. Once stable choice behavior emerged, rats were tested in the task following acute intraperitoneal injections of oxytocin or the oxytocin receptor antagonist L-368,899. Neither drug affected task performance in males. In females, however, both oxytocin and L-368,899 caused a dose-dependent reduction in preference for large risky reward. Control experiments showed that these effects could not be accounted for by alterations in food motivation or shock sensitivity. Together, these results reveal a sex-dependent effect of oxytocin signaling on risky decision making in rats.

From Parental Behavior to Sexual Function: Recent Advances in Oxytocin Research

Purpose of Review

Oxytocin plays many diverse roles in physiological and behavioral processes, including social activity, parental nurturing, stress responses, and sexual function. In this narrative review, we provide an update on the most noteworthy recent findings in this fascinating field.

Recent Findings

The development of techniques such as serial two-photon tomography and fiber photometry have provided a window into oxytocin neuroanatomy and real-time neuronal activity during social interactions. fMRI and complementary mapping techniques offer new insights into oxytocin's influence on brain activity and connectivity. Indeed, oxytocin has recently been found to influence the acquisition of maternal care behaviors and to mediate the influence of social touch on brain development and social interaction. Additionally, oxytocin plays a crucial role in male sexual function, affecting erectile activity and ejaculation, while its role in females remains controversial. Recent studies also highlight oxytocin's interaction with other neuropeptides, such as melanin-concentrating hormone, serotonin, and arginine vasopressin, influencing social and affective behaviors. Finally, an update is provided on the status of clinical trials involving oxytocin as a therapeutic intervention.

Summary

The exploration of oxytocin's complexities and its interplay with other neuropeptides holds promise for targeted treatment in various health and disease contexts. Overall, these findings contribute to the discovery of new and specific pathways to allow therapeutic targeting of oxytocin to treat disorders.

The psychophysiology of music-based interventions and the experience of pain

In modern times there is increasing acceptance that music-based interventions are useful aids in the clinical treatment of a range of neurological and psychiatric conditions, including helping to reduce the perception of pain. Indeed, the belief that music, whether listening or performing, can alter human pain experiences has a long history, dating back to the ancient Greeks, and its potential healing properties have long been appreciated by indigenous cultures around the world. The subjective experience of acute or chronic pain is complex, influenced by many intersecting physiological and psychological factors, and it is therefore to be expected that the impact of music therapy on the pain experience may vary from one situation to another, and from one person to another. Where pain persists and becomes chronic, aberrant central processing is a key feature associated with the ongoing pain experience. Nonetheless, beneficial effects of exposure to music on pain relief have been reported across a wide range of acute and chronic conditions, and it has been shown to be effective in neonates, children and adults. In this comprehensive review we examine the various neurochemical, physiological and psychological factors that underpin the impact of music on the pain experience, factors that potentially operate at many levels - the periphery, spinal cord, brainstem, limbic system and multiple areas of cerebral cortex. We discuss the extent to which these factors, individually or in combination, influence how music affects both the quality and intensity of pain, noting that there remains controversy about the respective roles that diverse central and peripheral processes play in this experience. Better understanding of the mechanisms that underlie music's impact on pain perception together with insights into central processing of pain should aid in developing more effective synergistic approaches when music therapy is combined with clinical treatments. The ubiquitous nature of music also facilitates application from the therapeutic environment into daily life, for ongoing individual and social benefit.

In need of a specific antibody against the oxytocin receptor for neuropsychiatric research: A KO validation study

Antibodies are one of the most utilized tools in biomedical research. However, few of them are rigorously evaluated, as there are no accepted guidelines or standardized methods for determining their validity before commercialization. Often, an antibody is considered validated if it detects a band by Western blot of the expected molecular weight and, in some cases, if blocking peptides result in loss of staining. Neither of these approaches are unquestionable proof of target specificity. Since the oxytocin receptor has recently become a popular target in neuropsychiatric research, the need for specific antibodies to be used in brain has arisen. In this work, we have tested the specificity of six commercially available oxytocin receptor antibodies, indicated by the manufacturers to be suitable for Western blot and with an available image showing the correct size band (45-55 KDa). Antibodies were first tested by Western blot in brain lysates of wild-type and oxytocin receptor knockout mice. Uterus tissue was also tested as control for putative differential tissue specificity. In brain, the six tested antibodies lacked target specificity, as both wild-type and receptor knockout samples resulted in a similar staining pattern, including the expected 45-55 KDa band. Five of the six antibodies detected a selective band in uterus (which disappeared in knockout tissue). These five specific antibodies were also tested for immunohistochemistry in uterus, where only one was specific. However, when the uterine-specific antibody was tested in brain tissue, it lacked specificity. In conclusion, none of the six tested commercial antibodies are suitable to detect oxytocin receptor in brain by either Western blot or immunohistochemistry, although some do specifically detect it in uterus. The present work highlights the need to develop standardized antibody validation methods, including a proper negative control, in order to grant quality and reproducibility of the generated data.

Manipulation of Glutamatergic Neuronal Activity in the Primary Motor Cortex Regulates Cardiac Function in Normal and Myocardial Infarction Mice

Cardiac function is under neural regulation; however, brain regions in the cerebral cortex responsible for regulating cardiac function remain elusive. In this study, retrograde trans-synaptic viral tracing is used from the heart to identify a specific population of the excitatory neurons in the primary motor cortex (M1) that influences cardiac function in mice. Optogenetic activation of M1 glutamatergic neurons increases heart rate, ejection fraction, and blood pressure. By contrast, inhibition of M1 glutamatergic neurons decreased cardiac function and blood pressure as well as tyrosine hydroxylase (TH) expression in the heart. Using viral tracing and optogenetics, the median raphe nucleus (MnR) is identified as one of the key relay brain regions in the circuit from M1 that affect cardiac function. Then, a mouse model of cardiac injury is established caused by myocardial infarction (MI), in which optogenetic activation of M1 glutamatergic neurons impaired cardiac function in MI mice. Moreover, ablation of M1 neurons decreased the levels of norepinephrine and cardiac TH expression, and enhanced cardiac function in MI mice. These findings establish that the M1 neurons involved in the regulation of cardiac function and blood pressure. They also help the understanding of the neural mechanisms underlying cardiovascular regulation.

The Influence of Social Dynamics on Biological Aging and the Health of Historically Marginalized Populations: A Biopsychosocial Model for Health Disparities

Historically marginalized populations are susceptible to social isolation resulting from their unique social dynamics; thus, they incur a higher risk of developing chronic diseases across the course of life. Research has suggested that the cumulative effect of aging trajectories per se, across the lifespan, determines later-in-life disease risks. Emerging evidence has shown the biopsychosocial effects of social stress and social support on one's wellbeing in terms of inflammation. Built upon previous multidisciplinary findings, here, we provide an overarching model that explains how the social dynamics of marginalized populations shape their rate of biological aging through the inflammatory process. Under the framework of social stress and social support theories, this model aims to facilitate our understanding of the biopsychosocial impacts of social dynamics on the wellbeing of historically marginalized individuals, with a special emphasis on biological aging. We leverage this model to advance our mechanistic understanding of the health disparity observed in historically marginalized populations and inform future remediation strategies.

Systemic Co-Administration of Low-Dose Oxytocin and Glucagon-Like Peptide 1 Additively Decreases Food Intake and Body Weight

INTRODUCTION

GLP-1 receptor agonists are the number one drug prescribed for the treatment of obesity and type 2 diabetes. These drugs are not, however, without side effects, and in an effort to maximize therapeutic effect while minimizing adverse effects, gut hormone co-agonists received considerable attention as new drug targets in the fight against obesity. Numerous previous reports identified the neuropeptide oxytocin (OXT) as a promising anti-obesity drug. The aims of this study were to evaluate OXT as a possible co-agonist for GLP-1 and examine the effects of its co-administration on food intake (FI) and body weight (BW) in mice.

METHODS

FI and c-Fos levels were measured in the feeding centers of the brain in response to an intraperitoneal injection of saline, OXT, GLP-1, or OXT/GLP-1. The action potential frequency and cytosolic Ca2+ ([Ca2+]i) in response to OXT, GLP-1, or OXT/GLP-1 were measured in ex vivo paraventricular nucleus (PVN) neuronal cultures. Finally, FI and BW changes were compared in diet-induced obese mice treated with saline, OXT, GLP-1, or OXT/GLP-1 for 13 days.

RESULTS

Single injection of OXT/GLP-1 additively decreased FI and increased c-Fos expression specifically in the PVN and supraoptic nucleus. Seventy percent of GLP-1 receptor-positive neurons in the PVN also expressed OXT receptors, and OXT/GLP-1 co-administration dramatically increased firing and [Ca2+]i in the PVN OXT neurons. The chronic OXT/GLP-1 co-administration decreased BW without changing FI.

CONCLUSION

Chronic OXT/GLP-1 co-administration decreases BW, possibly via the activation of PVN OXT neurons. OXT might be a promising candidate as an incretin co-agonist in obesity treatment.

Traditional Pediatric Massage Enhanced Hippocampal GR, BDNF and IGF-1 Expressions and Exerted an Anti-depressant Effect in an Adolescent Rat Model of CUMS-induced Depression

This study aimed to investigate the anti-depressant effect of traditional pediatric massage (TPM) in adolescent rats and its possible mechanism. The adolescent depression model in rats was established by using chronic unpredictable mild stress (CUMS). All rats were randomly divided into five groups (seven per group), including the groups of control (CON), CUMS, CUMS with TPM, CUMS with back stroking massage (BSM) and CUMS with fluoxetine (FLX). The tests of sucrose preference, Morris water maze and elevated plus maze were used to evaluate depression-related behaviors. Plasma corticosterone (CORT) level was measured by ELISA. The gene and protein expressions of glucocorticoid receptor (GR), brain-derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1) were measured by RT-qPCR and IHC respectively. The results showed that CUMS induced depression-related behaviors in the adolescent rats, along with decreased weight gain and reduced hippocampal expressions of GR, IGF-1 and BDNF. TPM could effectively prevent depression-related behaviors in CUMS-exposed adolescent rats, manifested as increasing weight gain, sucrose consumption, ratio of open-arm entry, times of crossing the specific quadrant and shortening escape latency. TPM also decreased CORT level in plasma, together with enhancing expressions of GR, IGF-1 and BDNF in the hippocampus. These results may support the clinical application of TPM to prevent and treat adolescent depression.

Quantification of surface-localized and total oxytocin receptor in myometrial smooth muscle cells

Oxytocin acts through the oxytocin receptor (OXTR) to modulate uterine contractility. We previously identified OXTR genetic variants and showed that, in HEK293T cells, two of the OXTR protein variants localized to the cell surface less than wild-type OXTR. Here, we sought to measure OXTR in the more native human myometrial smooth muscle cell (HMSMC) line on both the cell-surface and across the whole cell, and used CRISPR editing to add an HA tag to the endogenous OXTR gene for anti-HA measurement. Quantitative flow cytometry revealed that these cells possessed 55,000 ± 3200 total OXTRs and 4900 ± 390 cell-surface OXTRs per cell. To identify any differential wild-type versus variant localization, we transiently transfected HMSMCs to exogenously express wild-type or variant OXTR with HA and green fluorescent protein tags. Total protein expression of wild-type OXTR and all tested variants were similar. However, the two variants with lower surface localization in HEK293T cells also presented lower surface localization in HMSMCs. Overall, we confirm the differential surface localization of variant OXTR in a more native cell type, and further demonstrate that the quantitative flow cytometry technique is adaptable to whole-cell measurements.

µ-Opioid receptor antagonism facilitates the anxiolytic-like effect of oxytocin in mice

Mood and anxiety disorders are leading causes of disability worldwide and are major contributors to the global burden of diseases. Neuropeptides, such as oxytocin and opioid peptides, are important for emotion regulation. Previous studies have demonstrated that oxytocin reduced depression- and anxiety-like behavior in male and female mice, and opioid receptor activation reduced depression-like behavior. However, it remains unclear whether the endogenous opioid system interacts with the oxytocin system to facilitate emotion regulation in male and female mice. We hypothesized that opioid receptor blockade would inhibit the anxiolytic- and antidepressant-like effects of oxytocin. In this study, we systemically administered naloxone, a preferential μ-opioid receptor antagonist, and then intracerebroventricularly administered oxytocin. We then tested mice on the elevated zero maze and the tail suspension tests, respective tests of anxiety- and depression-like behavior. Contrary to our initial hypothesis, naloxone potentiated the anxiolytic-like, but not the antidepressant-like, effect of oxytocin. Using a selective μ-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, and a selective κ-opioid receptor antagonist, norbinaltorphimine, we demonstrate that μ-opioid receptor blockade potentiated the anxiolytic-like effect of oxytocin, whereas κ-opioid receptor blockade inhibited the oxytocin-induced anxiolytic-like effects. The present results suggest that endogenous opioids can regulate the oxytocin system to modulate anxiety-like behavior. Potential clinical implications of these findings are discussed.

Understanding the Biological Relationship between Migraine and Depression

Migraine is a highly prevalent neurological disorder. Among the risk factors identified, psychiatric comorbidities, such as depression, seem to play an important role in its onset and clinical course. Patients with migraine are 2.5 times more likely to develop a depressive disorder; this risk becomes even higher in patients suffering from chronic migraine or migraine with aura. This relationship is bidirectional, since depression also predicts an earlier/worse onset of migraine, increasing the risk of migraine chronicity and, consequently, requiring a higher healthcare expenditure compared to migraine alone. All these data suggest that migraine and depression may share overlapping biological mechanisms. Herein, this review explores this topic in further detail: firstly, by introducing the common epidemiological and risk factors for this comorbidity; secondly, by focusing on providing the cumulative evidence of common biological aspects, with a particular emphasis on the serotoninergic system, neuropeptides such as calcitonin-gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), substance P, neuropeptide Y and orexins, sexual hormones, and the immune system; lastly, by remarking on the future challenges required to elucidate the etiopathological mechanisms of migraine and depression and providing updated information regarding new key targets for the pharmacological treatment of these clinical entities.

Is the efficacy of oxytocin for autism diminished at higher dosages or repeated doses?: Potential mechanisms and candidate solutions

No approved pharmacological intervention currently exists to address the core symptoms of autism spectrum disorder, a prevalent neurodevelopmental condition. However, there is a growing body of empirical evidence highlighting oxytocin's modulatory effects on social and communicative behaviors. Numerous single-dose trials have consistently demonstrated the efficacy of oxytocin in ameliorating behavioral and neural measurements associated with the core symptoms of autism spectrum disorder. Nevertheless, prior investigations involving the repeated administration of oxytocin have yielded disparate findings concerning its effectiveness, particularly in relation to clinical measures of the core symptoms of autism spectrum disorder. Recent studies have also raised the possibility of diminishing efficacy of oxytocin over time, particularly when higher or recurrent dosages of oxytocin are administered. This review article aims to provide an overview of previous studies examining this issue. Furthermore, it aims to discuss the potential mechanisms underlying these effects, including the interaction between oxytocin and vasopressin, as well as potential strategies for addressing the challenges mentioned. This review's overall objective is to provide insights into the potential development of innovative therapeutics to mitigate the core symptoms of autism spectrum disorder, representing potential breakthroughs in the treatment of this complex neurodevelopmental condition.

Oxytocin Receptor-Expressing Neurons in the Medial Preoptic Area Are Essential for Lactation, whereas Those in the Lateral Septum Are Not Critical for Maternal Behavior

INTRODUCTION

In nurturing systems, the oxytocin (Oxt)-oxytocin receptor (Oxtr) system is important for parturition, and essential for lactation and parental behavior. Among the nerve nuclei that express Oxtr, the lateral septal nucleus (LS) and medial preoptic area (MPOA) are representative regions that control maternal behavior.

METHODS

We investigated the role of Oxtr- and Oxtr-expressing neurons, located in the LS and MPOA, in regulating maternal behavior by regulating Oxtr expression in a region-specific manner using recombinant mice and adeno-associated viruses. We quantified the prolactin (Prl) concentrations in the pituitary gland and plasma when Oxtr expression in the MPOA was reduced.

RESULTS

The endogenous Oxtr gene in the neurons of the LS did not seem to play an essential role in maternal behavior. Conversely, decreased Oxtr expression in the MPOA increased the frequency of pups being left outside the nest and reduced their survival rate. Deletion of Oxtr in MPOA neurons prevented elevation of Prl levels in plasma and pituitary at postpartum day 2.

DISCUSSION/CONCLUSION

Oxtr-expressing neurons in the MPOA are involved in the postpartum production of Prl. We confirmed the essential functions of Oxtr-expressing neurons and the Oxtr gene itself in the MPOA for the sustainability of maternal behavior, which involved Oxtr-dependent induction of Prl.

Functional Dimerization of Serotonin Receptors: Role in Health and Depressive Disorders

Understanding the neurobiological underpinnings of depressive disorder constitutes a pressing challenge in the fields of psychiatry and neurobiology. Depression represents one of the most prevalent forms of mental and behavioral disorders globally. Alterations in dimerization capacity can influence the functional characteristics of serotonin receptors and may constitute a contributing factor to the onset of depressive disorders. The objective of this review is to consolidate the current understanding of interactions within the 5-HT receptor family and between 5-HT receptors and members of other receptor families. Furthermore, it aims to elucidate the role of such complexes in depressive disorders and delineate the mechanisms through which antidepressants exert their effects.

Chronic oxytocin-driven alternative splicing of Crfr2α induces anxiety

The neuropeptide oxytocin (OXT) has generated considerable interest as potential treatment for psychiatric disorders, including anxiety and autism spectrum disorders. However, the behavioral and molecular consequences associated with chronic OXT treatment and chronic receptor (OXTR) activation have scarcely been studied, despite the potential therapeutic long-term use of intranasal OXT. Here, we reveal that chronic OXT treatment over two weeks increased anxiety-like behavior in rats, with higher sensitivity in females, contrasting the well-known anxiolytic effect of acute OXT. The increase in anxiety was transient and waned 5 days after the infusion has ended. The behavioral effects of chronic OXT were paralleled by activation of an intracellular signaling pathway, which ultimately led to alternative splicing of hypothalamic corticotropin-releasing factor receptor 2α (Crfr2α), an important modulator of anxiety. In detail, chronic OXT shifted the splicing ratio from the anxiolytic membrane-bound (mCRFR2α) form of CRFR2α towards the soluble CRFR2α (sCRFR2α) form. Experimental induction of alternative splicing mimicked the anxiogenic effects of chronic OXT, while sCRFR2α-knock down reduced anxiety-related behavior of male rats. Furthermore, chronic OXT treatment triggered the release of sCRFR2α into the cerebrospinal fluid with sCRFR2α levels positively correlating with anxiety-like behavior. In summary, we revealed that the shifted splicing ratio towards expression of the anxiogenic sCRFR2α underlies the adverse effects of chronic OXT treatment on anxiety.

Loss of oxytocin receptors in hilar mossy cells impairs social discrimination

Hippocampal oxytocin receptor (OXTR) signaling is crucial for discrimination of social stimuli to guide social recognition, but circuit mechanisms and cell types involved remain incompletely understood. Here, we report a role for OXTR-expressing hilar mossy cells (MCs) of the dentate gyrus in social stimulus discrimination by regulating granule cell (GC) activity. Using a Cre-loxP recombination approach, we found that ablation of Oxtr from MCs impairs discrimination of social, but not object, stimuli in adult male mice. Ablation of MC Oxtr increases spontaneous firing rate of GCs, synaptic excitation to inhibition ratio of MC-to-GC circuit, and GC firing when temporally associated with the lateral perforant path inputs. Using mouse hippocampal slices, we found that bath application of OXTR agonist [Thr4,Gly7]-oxytocin causes membrane depolarization and increases MC firing activity. Optogenetic activation of MC-to-GC circuit ameliorates social discrimination deficit in MC OXTR deficient mice. Together, our results uncover a previously unknown role of MC OXTR signaling for discrimination of social stimuli and delineate a MC-to-GC circuit responsible for social information processing.

Sexually dimorphic oxytocin receptor-expressing (OXTR) neurons in the anteroventral periventricular nucleus (AVPV) in the postpartum female mouse are involved in maternal behavior

Maternal care is crucial for the survival and development of offspring. Oxytocin modulates maternal behavior by binding to oxytocin receptors (OXTRs) in various parts of the brain. Previously, we showed that OXTRs are expressed in the anteroventral periventricular nucleus (AVPV) of female, but not male mice. Because the AVPV is involved in the regulation of maternal behavior and oxytocin enhances its induction, this finding leads to the hypothesis that the female specific population of OXTR neurons in the AVPV regulates maternal behavior. To address this hypothesis, OXTR-Venus reporter mice were used to assess if expression levels of OXTR in the AVPV are changed during the postpartum period. The total number of OXTR-Venus neurons was significantly greater in postpartum dams compared to virgin females. To assess efferent projections of the AVPV-OXTR neurons, a Cre-dependent fluorescent protein (tdTomato) expressing a viral vector was injected into one side of the AVPV of female OXTR-Cre mice. Fibers expressing tdTomato were found in hypothalamic areas containing oxytocin neurons (the supraoptic and paraventricular nuclei) and the midbrain areas (the ventral tegmental area and periaqueductal gray) that are involved in the regulation of maternal motivation. To assess if activity of the AVPV-OXTR neurons is involved in the regulation of maternal behaviors, a chemogenetic approach was employed. Specific inhibition of activity of AVPV-OXTR neurons completely abolished pup retrieval and nest building behaviors. Collectively, these findings demonstrate that AVPV-OXTR neurons in postpartum female mice constitute an important node in the neural circuitry that regulates maternal behavior.

Chemogenetic Activation of Oxytocin Neurons Improves Pain in a Reserpine-induced Fibromyalgia Rat Model

Fibromyalgia (FM) is a syndrome characterized by chronic pain with depression as a frequent comorbidity. However, efficient management of the pain and depressive symptoms of FM is lacking. Given that endogenous oxytocin (OXT) contributes to the regulation of pain and depressive disorders, herein, we investigated the role of OXT in an experimental reserpine-induced FM model. In FM model, OXT-monomeric red fluorescent protein 1 (OXT-mRFP1) transgenic rats exhibited increased depressive behavior and sensitivity in a mechanical nociceptive test, suggesting reduced pain tolerance. Additionally, the development of the FM-like phenotype in OXT-mRFP1 FM model rats was accompanied by a significant reduction in OXT mRNA expression in the magnocellular neurons of the paraventricular nucleus. OXT-mRFP1 FM model rats also had significantly fewer tryptophan hydroxylase (TPH)- and tyrosine hydroxylase (TH)-immunoreactive (ir) neurons as well as reduced serotonin and norepinephrine levels in the dorsal raphe and locus coeruleus. To investigate the effects of stimulating the endogenous OXT pathway, rats expressing OXT-human muscarinic acetylcholine receptor (hM3Dq)-mCherry designer receptors exclusively activated by designer drugs (DREADDs) were also assessed in the FM model. Treatment of these rats with clozapine-N-oxide (CNO), an hM3Dq-activating drug, significantly improved characteristic FM model-induced pathophysiological pain, but did not alter depressive-like behavior. The chemogenetically induced effects were reversed by pre-treatment with an OXT receptor antagonist, confirming the specificity of action via the OXT pathway. These results indicate that endogenous OXT may have analgesic effects in FM, and could be a potential target for effective pain management strategies for this disorder.

The role of the oxytocin system in the resilience of patients with breast cancer

Breast cancer is a grave traumatic experience that can profoundly compromise patients' psychological resilience, impacting their overall quality of life. The oxytocin system represents one of the essential neurobiological bases of psychological resilience and plays a critical role in regulating resilience in response to social or traumatic events during adulthood. Oxytocin, through its direct interaction with peripheral or central oxytocin receptors, has been found to have a significant impact on regulating social behavior. However, the precise mechanism by which the activation of peripheral oxytocin receptors leads to improved social is still not completely comprehended and requires additional research. Its activation can modulate psychological resilience by influencing estrogen and its receptors, the hypothalamic-pituitary-adrenal axis, thyroid function, 5-hydroxytryptamine metabolism levels, and arginine pressure release in breast cancer patients. Various interventions, including psychotherapy and behavioral measures, have been employed to improve the psychological resilience of breast cancer patients. The potential effectiveness of such interventions may be underpinned by their ability to modulate oxytocin release levels. This review provides an overview of the oxytocin system and resilience in breast cancer patients and identifies possible future research directions and interventions.

The Relationship Between Oxytocin and Alcohol Dependence

The hypothalamic neuropeptide oxytocin (OT) is well known for its prosocial, anxiolytic, and ameliorating effects on various psychiatric conditions, including alcohol use disorder (AUD). In this chapter, we will first introduce the basic neurophysiology of the OT system and its interaction with other neuromodulatory and neurotransmitter systems in the brain. Next, we provide an overview over the current state of research examining the effects of acute and chronic alcohol exposure on the OT system as well as the effects of OT system manipulation on alcohol-related behaviors in rodents and humans. In rodent models of AUD, OT has been repeatedly shown to reduce ethanol consumption, particularly in models of acute alcohol exposure. In humans however, the results of OT administration on alcohol-related behaviors are promising but not yet conclusive. Therefore, we further discuss several physiological and methodological limitations to the effective application of OT in the clinic and how they may be mitigated by the application of synthetic OT receptor (OTR) agonists. Finally, we discuss the potential efficacy of cutting-edge pharmacology and gene therapies designed to specifically enhance endogenous OT release and thereby rescue deficient expression of OT in the brains of patients with severe forms of AUD and other incurable mental disorders.

Behavior and heart rate variability after intranasal administration of oxytocin in Holstein steers

Oxytocin (OXT) is a neuropeptide that regulates memory, emotion, stress response, and behavior in the brain. In our previous study with cattle, we demonstrated the anti-stress effect of intracerebroventricularly administered OXT on the central nervous system. However, it is important to investigate the effects of this peptide after intranasal administration, as it offers convenience and non-invasiveness for practical use. Therefore, this study investigated the effects of intranasal OXT on the behavior and autonomic nervous system of Holstein steers. The experiment followed a within-subjects design, including a total of six steers. Each steer received intranasal administration of either 1 mL of saline (SAL), 100 µg OXT (OXT100), or 200 µg OXT (OXT200). However, due to some issues, the sample size for the OXT200 group was reduced to five. After these treatments, we conducted electrocardiography recordings to analyze heart rate variability (HRV) and also made behavioral observations for 90 min. OXT200 tended to increase the time spent ruminating while lying down (Steel's multiple comparison test; P=0.053). In contrast, OXT treatment did not affect HRV indices. In conclusion, the current OXT dosage did not significantly affects behavior or the autonomic nervous system. However, the observed tendency to increase rumination may suggest a central effect of OXT.

Sex and hormonal status influence the anxiolytic-like effect of oxytocin in mice

Anxiety and depression are highly prevalent psychiatric disorders, affecting approximately 18% of the United States population. Evidence indicates that central oxytocin mediates social cognition, social bonding, and social anxiety. Although it is well-established that oxytocin ameliorates social deficits, less is known about the therapeutic effects of oxytocin in non-social contexts. We hypothesized that positive effects of oxytocin in social contexts are attributable to intrinsic effects of oxytocin on neural systems that are related to emotion regulation. The present study investigated the effect of intracerebroventricular (ICV) oxytocin administration (i.e., central action) on anxiety- and depression-like behavior in C57Bl/6J mice using non-social tests. Male and female mice received an ICV infusion of vehicle or oxytocin (100, 200, or 500 ng), then were tested in the elevated zero maze (for anxiety-like behavior) and the tail suspension test (for depression-like behavior). Oxytocin dose-dependently increased open zone occupancy and entries in the elevated zero maze and reduced immobility duration in the tail suspension test in both sexes. Oxytocin decreased anxiety and depression-like behavior in male and female mice. The observed effect of oxytocin on anxiolytic-like behavior appeared to be driven by the males. Given the smaller anxiolytic-like effect of oxytocin in the female mice and the established interaction between oxytocin and reproductive hormones (estrogen and progesterone), we also explored whether oxytocin sensitivity in females varies across estrous cycle phases and in ovariectomized females that were or were not supplemented with estrogen or progesterone. Oxytocin reduced anxiety-like behavior in female mice in proestrus/estrus, ovariectomized females (supplemented or not with estrogen or progesterone), but not females in metestrus/diestrus. Additionally, oxytocin reduced depression-like behavior in all groups tested with slight differences across the various hormonal statuses. These results suggest that the effect of oxytocin in depression- and anxiety-like behavior in mice can be influenced by sex and hormonal status.

Microbes, oxytocin and stress: Converging players regulating eating behavior

Oxytocin is a peptide-hormone extensively studied for its multifaceted biological functions and has recently gained attention for its role in eating behavior, through its action as an anorexigenic neuropeptide. Moreover, the gut microbiota is involved in oxytocinergic signaling through the brain-gut axis, specifically in the regulation of social behavior. The gut microbiota is also implicated in appetite regulation and is postulated to play a role in central regulation of hedonic eating. In this review, we provide an overview on oxytocin and its individual links with the microbiome, the homeostatic and non-homeostatic regulation of eating behavior as well as social behavior and stress.

Oxytocin measurements in saliva: an analytical perspective

Oxytocin has traditionally been known for its physiological effects on muscle contraction associated with birth and lactation, but in the last years is widely used as a biomarker of "positive experiences" in psychology and behavior. Different types of samples have been used for oxytocin measurements with saliva samples having the particular advantage of an easy and non-stressful collection. However, the low concentration of oxytocin in saliva can represent a limitation for its use. For this reason, sensitive assays and even a previous sample treatment in some cases are required for saliva oxytocin quantification. In addition, the lack of standardized and generally agreed-upon approach to peripheral oxytocin measurement leads to large discrepancies between different laboratories, that use different sample treatment protocols and different assays. The main objectives of this review are to describe the current status of the use of saliva for oxytocin measurement, provide details of the different sample processing techniques that can be applied and inform about the analytical techniques and assays available in different animal species, and also in humans for comparative purposes. It is expected that this information can contribute to an increase in the knowledge about the measurements of oxytocin in saliva and to its wider use in the future.