Somato-axodendritic release of oxytocin into the brain due to calcium amplification is essential for social memory

Characteristics of Cerebrospinal Fluid in Autism Spectrum Disorder - A Systematic Review

Autism Spectrum Disorder (ASD) is a range of neurodevelopmental conditions characterized by impaired social interaction, learning, and restricted or repetitive behaviors. The underlying causes of ASD are still debated, but researchers have found many physiological traits like gut problems and impaired immune system to help understand the etiology of ASD. Cerebrospinal fluid (CSF) plays a critical role in maintaining the homeostasis of the neuronal environment and has, therefore, been analyzed in multiple conditions impacting the central nervous system. The study of CSF is crucial to understanding neurological disorders as its composition changes with the disorders, and these changes may indicate various disorder-related physiological mechanisms. For this systematic review, we searched PubMed, Scopus, and Web of Science for studies published between 1977 and 2025 and selected 49 studies after manual screening. We took stock of the evidence supporting the hypothesis that ASD alters the properties and composition of CSF. We systematically report on the different attributes of CSF in the ASD population that could be potential biomarkers and assist in understanding the origins and progression of ASD. We found that in CSF, immune markers, proteins, extra-axial CSF, folate, oxytocin, and vasopressin showed changes in ASD compared to the neurotypicals. We observed gaps in the literature due to variations in age and sample size and noted biases related to sex (i.e., samples are predominantly including male participants) and age (i.e., a handful of studies were conducted on adults). Our review highlights the need for more research on CSF in ASD to improve our understanding of this disorder and identify CSF biomarkers.

Orgasms, sexual pleasure, and opioid reward mechanisms

INTRODUCTION

Sexual activity produces pleasure related to sexual arousal, desire, and genitosensory and erogenous stimulation. Orgasms produce a whole brain and body rush of ecstatic pleasure followed by relaxation and refractoriness. This pleasure results from the activation of neurochemical reward pathways in the brain. This is differentiated by spinal pathways that control climax, the particular motor movements of the pelvic floor and the experience of tension release.

OBJECTIVES

To relate the activation of key neurochemical reward and bonding systems, notably dopamine, oxytocin, and opioids, to the pleasure of sexual activity in general and orgasms in particular.

METHODS

A narrative review of the neurochemical and neuroanatomical mechanisms activated during sexual stimulation and orgasm in rats and humans, and how they are related overall to the generation of sexual pleasure and reward.

RESULTS

Appetitive sexual pleasure involves the activation of dopamine and oxytocin release in hypothalamic and mesolimbic regions that regulate sexual arousal and desire, and are reinforced by localized opioid activity. Orgasms are thought to result in part from a massive release of opioids into these regions that inhibits dopamine and oxytocin transmission, but that initiates molecular changes to sensitize both systems and induce sexually conditioned place and partner preferences. Serotonin is also activated at orgasm and contributes to feelings of satiety and refractoriness. Orgasm disorders are distressing, cause resentment and conflict in a relationship, and diminish overall sexual health and well-being.

CONCLUSIONS

Orgasms are an important component of sexual pleasure for humans and perhaps all vertebrates. Endogenous opioids like β-endorphin that bind to mu opioid receptors are likely responsible for sexual pleasure and reward.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Oxytocin transported from the blood across the blood-brain barrier by receptor for advanced glycation end-products (RAGE) affects brain function related to social behavior

Oxytocin (OT) is a neuropeptide that primarily functions as a hormone controlling female reproductive processes. Since numerous recent studies have shown that single and repetitive administrations of OT increase trust, social interaction, and maternal behaviors in humans and animals, OT is considered a key molecule that regulates social memory and behavior. Furthermore, OT binds to receptors for advanced glycation end-products (RAGE), and it has been demonstrated that loss of RAGE in the brain vascular endothelial cells of mice fails to increase brain OT concentrations following peripheral OT administration. This leads to the hypothesis that RAGE is involved in the direct transport of OT, allowing it access to the brain by transporting it across the blood-brain barrier; however, this hypothesis is only based on limited evidence. Herein, we review the recent results related to this hypothesis, such as the mode of transport of OT in the blood circulation to the brain via different forms of RAGE, including membrane-bound full-length RAGE and soluble RAGE. We further review the modulation of brain function and social behavior, which seem to be mediated by RAGE-dependent OT. Overall, this review mostly confirms that RAGE enables the recruitment of circulating OT to the brain, thereby influencing social behavior. The requirement for further studies considering the physiological aspects of RAGE is also discussed.

Acquiring Social Safety Engages Oxytocin Neurons in the Supraoptic Nucleus: Role of Magel2 Deficiency

INTRODUCTION

Exposure to social trauma may alter engagement with both fear-related and unrelated social stimuli long after. Intriguingly, how simultaneous discrimination of social fear and safety is affected in neurodevelopmental conditions remains underexplored. The role of the neuropeptide oxytocin is established in social behaviors and yet unexplored during such a challenge post-social trauma.

METHODS

Using Magel2 knockout mice, an animal model of Prader-Willi syndrome (PWS) and Schaaf-Yang syndrome (SYS), we tested memory of social fear and safety after a modified social fear conditioning task. Additionally, we tracked the activity of oxytocin neurons in the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus by fiber photometry, as animals were simultaneously presented with a choice between fear and safe social cue during recall.

RESULTS

Male Magel2 KO mice trained to fear females with electrical footshocks avoided both unfamiliar females and males during recalls, lasting even a week post-conditioning. On the contrary, trained Magel2 WT avoided only females during recalls, lasting days rather than a week post-conditioning. Inability to overcome social fear and avoidance of social safety in Magel2 KO mice were associated with the reduced engagement of oxytocin neurons in the SON but not the PVN.

CONCLUSION

In a preclinical model of PWS/SYS, we demonstrated region-specific deficit in oxytocin neuron activity associated with behavioral generalization of social fear to social safety. Insights from this study add to our understanding of oxytocin action in the brain at the intersection of social trauma and PWS/SYS.

Remission of social behavior impairment by oral administration of a precursor of NAD in CD157, but not in CD38, knockout mice

Nicotinamide adenine dinucleotide (NAD) is a substrate of adenosine diphosphate (ADP)-ribosyl cyclase and is catalyzed to cyclic ADP-ribose (cADPR) by CD38 and/or CD157. cADPR, a Ca²⁺ mobilizing second messenger, is critical in releasing oxytocin from the hypothalamus into the brain. Although NAD precursors effectively play a role in neurodegenerative disorders, muscular dystrophy, and senescence, the beneficial effects of elevating NAD by NAD precursor supplementation on brain function, especially social interaction, and whether CD38 is required in this response, has not been intensely studied. Here, we report that oral gavage administration of nicotinamide riboside, a perspective NAD precursor with high bioavailability, for 12 days did not show any suppressive or increasing effects on sociability (mouse's interest in social targets compared to non-social targets) in both CD157KO and CD38KO male mice models in a three-chamber test. CD157KO and CD38KO mice displayed no social preference (that is, more interest towards a novel mouse than a familiar one) behavior. This defect was rescued after oral gavage administration of nicotinamide riboside for 12 days in CD157KO mice, but not in CD38KO mice. Social memory was not observed in CD157KO and CD38KO mice; subsequently, nicotinamide riboside administration had no effect on social memory. Together with the results that nicotinamide riboside had essentially no or little effect on body weight during treatment in CD157KO mice, nicotinamide riboside is less harmful and has beneficial effect on defects in recovery from social behavioral, for which CD38 is required in mice.

Endolysosomal TPCs regulate social behavior by controlling oxytocin secretion

Oxytocin (OT) is a prominent regulator of many aspects of mammalian social behavior and stored in large dense-cored vesicles (LDCVs) in hypothalamic neurons. It is released in response to activity-dependent Ca2+ influx, but is also dependent on Ca2+ release from intracellular stores, which primes LDCVs for exocytosis. Despite its importance, critical aspects of the Ca2+-dependent mechanisms of its secretion remain to be identified. Here we show that lysosomes surround dendritic LDCVs, and that the direct activation of endolysosomal two-pore channels (TPCs) provides the critical Ca2+ signals to prime OT release by increasing the releasable LDCV pool without directly stimulating exocytosis. We observed a dramatic reduction in plasma OT levels in TPC knockout mice, and impaired secretion of OT from the hypothalamus demonstrating the importance of priming of neuropeptide vesicles for activity-dependent release. Furthermore, we show that activation of type 1 metabotropic glutamate receptors sustains somatodendritic OT release by recruiting TPCs. The priming effect could be mimicked by a direct application of nicotinic acid adenine dinucleotide phosphate, the endogenous messenger regulating TPCs, or a selective TPC2 agonist, TPC2-A1-N, or blocked by the antagonist Ned-19. Mice lacking TPCs exhibit impaired maternal and social behavior, which is restored by direct OT administration. This study demonstrates an unexpected role for lysosomes and TPCs in controlling neuropeptide secretion, and in regulating social behavior.

Behavioral, Neural, and Molecular Mechanisms of Conditioned Mate Preference: The Role of Opioids and First Experiences of Sexual Reward

Although mechanisms of mate preference are thought to be relatively hard-wired, experience with appetitive and consummatory sexual reward has been shown to condition preferences for partner related cues and even objects that predict sexual reward. Here, we reviewed evidence from laboratory species and humans on sexually conditioned place, partner, and ejaculatory preferences in males and females, as well as the neurochemical, molecular, and epigenetic mechanisms putatively responsible. From a comprehensive review of the available data, we concluded that opioid transmission at μ opioid receptors forms the basis of sexual pleasure and reward, which then sensitizes dopamine, oxytocin, and vasopressin systems responsible for attention, arousal, and bonding, leading to cortical activation that creates awareness of attraction and desire. First experiences with sexual reward states follow a pattern of sexual imprinting, during which partner- and/or object-related cues become crystallized by conditioning into idiosyncratic "types" that are found sexually attractive and arousing. These mechanisms tie reward and reproduction together, blending proximate and ultimate causality in the maintenance of variability within a species.

Oxytocin Dynamics in the Body and Brain Regulated by the Receptor for Advanced Glycation End-Products, CD38, CD157, and Nicotinamide Riboside

Investigating the neurocircuit and synaptic sites of action of oxytocin (OT) in the brain is critical to the role of OT in social memory and behavior. To the same degree, it is important to understand how OT is transported to the brain from the peripheral circulation. To date, of these, many studies provide evidence that CD38, CD157, and receptor for advanced glycation end-products (RAGE) act as regulators of OT concentrations in the brain and blood. It has been shown that RAGE facilitates the uptake of OT in mother’s milk from the digestive tract to the cell surface of intestinal epithelial cells to the body fluid and subsequently into circulation in male mice. RAGE has been shown to recruit circulatory OT into the brain from blood at the endothelial cell surface of neurovascular units. Therefore, it can be said that extracellular OT concentrations in the brain (hypothalamus) could be determined by the transport of OT by RAGE from the circulation and release of OT from oxytocinergic neurons by CD38 and CD157 in mice. In addition, it has recently been found that gavage application of a precursor of nicotinamide adenine dinucleotide, nicotinamide riboside, for 12 days can increase brain OT in mice. Here, we review the evaluation of the new concept that RAGE is involved in the regulation of OT dynamics at the interface between the brain, blood, and intestine in the living body, mainly by summarizing our recent results due to the limited number of publications on related topics. And we also review other possible routes of OT recruitment to the brain.

Serum Oxytocin in Cows Is Positively Correlated with Caregiver Interactions in the Impossible Task Paradigm

Simple Summary

A possible relationship between circulating hormones (e.g., oxytocin and cortisol) and social behaviors toward humans in cows was studied using the impossible task paradigm test. Serum oxytocin levels correlated positively with the duration and negatively correlated with the latency of the cows’ social interactions with the caregiver. The implications of these findings for productivity as well as for animal welfare can be numerous and worth further investigation.

Abstract

This study explored a possible relationship between the circulating oxytocin, cortisol, and the willingness of dairy cows to engage in social behaviors with humans in an experimental context. The behaviors of twenty-nine cows were recorded during the impossible task paradigm, a procedure aimed at creating a violation of expectancy, in the presence of the caregiver and a stranger. The results showed that serum oxytocin levels were positively correlated with duration and negatively correlated with the latency of the cows’ social interactions with the caregiver. This research provides a clear correlation between circulating oxytocin and a willingness to engage in social contact with the caregiver, excluding the possible effect of different cortisol levels on such behavior.

"Live together, die alone": The effect of re-socialization on behavioural performance and social-affective brain-related proteins after a long-term chronic social isolation stress

Loneliness affects group-living mammals triggering a cascade of stress-dependent physiological disorders. Indeed, social isolation stress is a major risk factor for several neuropsychiatric disorders including anxiety and depression. Furthermore, social isolation has a negative impact on health and fitness. However, the neurobiological consequences of long-term chronic social isolation stress (LTCSIS) manifested during the adulthood of affected individuals are not fully understood. Our study assessed the impact of LTCSIS and social buffering (re-socialization) on the behavioural performance and social-affective brain-related proteins in diurnal, social, and long-lived Octodon degus (degus). Thereby, anxiety-like and social behaviour, and social recognition memory were assessed in male and female animals subjected to a variety of stress-inducing treatments applied from post-natal and post-weaning until their adulthood. Additionally, we evaluated the relationship among LTCSIS, Oxytocin levels (OXT), and OXT-Ca2+-signalling proteins in the hypothalamus, the hippocampus, and the prefrontal cortex. Our findings suggest that LTCSIS induces anxiety like-behaviour and impairs social novelty preference whereas sociability is unaffected. On the other hand, re-socialization can revert both isolation-induced anxiety and social memory impairment. However, OXT and its signalling remained reduced in the abovementioned brain areas, suggesting that the observed changes in OXT-Ca2+ pathway proteins were permanent in male and female degus. Based on these findings, we conclude degus experience social stress differently, suggesting the existence of sex-related mechanisms to cope with specific adaptive challenges.

In Vivo Electrophysiology of Peptidergic Neurons in Deep Layers of the Lumbar Spinal Cord after Optogenetic Stimulation of Hypothalamic Paraventricular Oxytocin Neurons in Rats

The spinal ejaculation generator (SEG) is located in the central gray (lamina X) of the rat lumbar spinal cord and plays a pivotal role in the ejaculatory reflex. We recently reported that SEG neurons express the oxytocin receptor and are activated by oxytocin projections from the paraventricular nucleus of hypothalamus (PVH). However, it is unknown whether the SEG responds to oxytocin in vivo. In this study, we analyzed the characteristics of the brain–spinal cord neural circuit that controls male sexual function using a newly developed in vivo electrophysiological technique. Optogenetic stimulation of the PVH of rats expressing channel rhodopsin under the oxytocin receptor promoter increased the spontaneous firing of most lamina X SEG neurons. This is the first demonstration of the in vivo electrical response from the deeper (lamina X) neurons in the spinal cord. Furthermore, we succeeded in the in vivo whole-cell recordings of lamina X neurons. In vivo whole-cell recordings may reveal the features of lamina X SEG neurons, including differences in neurotransmitters and response to stimulation. Taken together, these results suggest that in vivo electrophysiological stimulation can elucidate the neurophysiological response of a variety of spinal neurons during male sexual behavior.

Transport of oxytocin to the brain after peripheral administration by membrane-bound or soluble forms of receptors for advanced glycation end-products

Oxytocin (OT) is a neuropeptide hormone. Single and repetitive administration of OT increases social interaction and maternal behaviour in humans and mammals. Recently, it was found that the receptor for advanced glycation end-products (RAGE) is an OT-binding protein and plays a critical role in the uptake of OT to the brain after peripheral OT administration. Here, we address some unanswered questions on RAGE-dependent OT transport. First, we found that, after intranasal OT administration, the OT concentration increased in the extracellular space of the medial prefrontal cortex (mPFC) of wild-type male mice, as measured by push-pull microperfusion. No increase of OT in the mPFC was observed in RAGE knockout male mice. Second, in a reconstituted in vitro blood-brain barrier system, inclusion of the soluble form of RAGE (endogenous secretory RAGE [esRAGE]), an alternative splicing variant, in the luminal (blood) side had no effect on the transport of OT to the abluminal (brain) chamber. Third, OT concentrations in the cerebrospinal fluid after i.p. OT injection were slightly higher in male mice overexpressing esRAGE (esRAGE transgenic) compared to those in wild-type male mice, although this did not reach statistical significance. Although more extensive confirmation is necessary because of the small number of experiments in the present study, the reported data support the hypothesis that RAGE may be involved in the transport of OT to the mPFC from the circulation. These results suggest that the soluble form of RAGE in the plasma does not function as a decoy in vitro.

Oxytocin signaling in the treatment of drug addiction: Therapeutic opportunities and challenges

Drug addiction is one of the leading causes of mortality worldwide. Despite great advances were achieved in understanding the neurobiology of drug addiction, the therapeutic options are severely limited, with poor effectiveness and serious side effects. The neuropeptide oxytocin (OXT) is well known for its effects on uterine contraction, sexual/maternal behaviors, social affiliation, stress and learning/memory by interacting with the OXT receptor and other neuromodulators. Emerging evidence suggests that the acute or chronic exposure to drugs can affect the OXT system. Additionally, OXT administration can ameliorate a wide range of abused drug-induced neurobehavioral changes. Overall, OXT not only suppresses drug reward in the binge stage of drug addiction, but also reduces stress responses and social impairments during the withdrawal stage and, finally, prevents drug/cue/stress-induced reinstatement. More importantly, clinical studies have also shown that OXT can exert beneficial effects on reducing substance use disorders of a series of drugs, such as heroin, cocaine, alcohol, cannabis and nicotine. Thus, the present review focuses on the role of OXT in treating drug addiction, including the preclinical and clinical therapeutic potential of OXT and its analogs on the neurobiological perspectives of drugs, to provide a better insight of the efficacy of OXT as a clinical addiction therapeutic agent.

CD157 and Brain Immune System in (Patho)physiological Conditions: Focus on Brain Plasticity

Ectoenzyme and receptor BST-1/CD157 has been considered as a key molecule involved in the regulation of functional activity of cells in various tissues and organs. It is commonly accepted that CD157 catalyzes NAD+ hydrolysis and acts as a component of integrin adhesion receptor complex. Such properties are important for the regulatory role of CD157 in neuronal and glial cells: in addition to recently discovered role in the regulation of emotions, motor functions, and social behavior, CD157 might serve as an important component of innate immune reactions in the central nervous system. Activation of innate immune system in the brain occurs in response to infectious agents as well as in brain injury and neurodegeneration. As an example, in microglial cells, association of CD157 with CD11b/CD18 complex drives reactive gliosis and neuroinflammation evident in brain ischemia, chronic neurodegeneration, and aging. There are various non-substrate ligands of CD157 belonging to the family of extracellular matrix proteins (fibronectin, collagen I, finbrinogen, and laminin) whose activity is required for controlling cell adhesion and migration. Therefore, CD157 could control structural and functional integrity of the blood-brain barrier and barriergenesis. On the other hand, contribution of CD157 to the regulation of brain development is rather possible since in the embryonic brain, CD157 expression is very high, whereas in the adult brain, CD157 is expressed on neural stem cells and, presumably, is involved in the neurogenesis. Besides, CD157 could mediate astrocytes' action on neural stem and progenitor cells within neurogenic niches. In this review we will summarize how CD157 may affect brain plasticity acting as a molecule at the crossroad of neurogenesis, cerebral angiogenesis, and immune regulation.

Oxytocin Influences Male Sexual Activity via Non-synaptic Axonal Release in the Spinal Cord

Oxytocinergic neurons in the paraventricular nucleus of the hypothalamus that project to extrahypothalamic brain areas and the lumbar spinal cord play an important role in the control of erectile function and male sexual behavior in mammals. The gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord is an important component of the neural circuits that control penile reflexes in rats, circuits that are commonly referred to as the "spinal ejaculation generator (SEG)." We have examined the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system in rats. Here, we show that SEG/GRP neurons express oxytocin receptors and are activated by oxytocin during male sexual behavior. Intrathecal injection of oxytocin receptor antagonist not only attenuates ejaculation but also affects pre-ejaculatory behavior during normal sexual activity. Electron microscopy of potassium-stimulated acute slices of the lumbar cord showed that oxytocin-neurophysin-immunoreactivity was detected in large numbers of neurosecretory dense-cored vesicles, many of which are located close to the plasmalemma of axonal varicosities in which no electron-lucent microvesicles or synaptic membrane thickenings were visible. These results suggested that, in rats, release of oxytocin in the lumbar spinal cord is not limited to conventional synapses but occurs by exocytosis of the dense-cored vesicles from axonal varicosities and acts by diffusion-a localized volume transmission-to reach oxytocin receptors on GRP neurons and facilitate male sexual function.

A Novel Role of CD38 and Oxytocin as Tandem Molecular Moderators of Human Social Behavior

Oxytocin is an important modulator of human affiliative behaviors, including social skills, human pair bonding, and friendship. CD38 will be discussed as an immune marker and then in more detail the mechanisms of CD38 on releasing brain oxytocin. Mention is made of the paralogue of oxytocin, vasopressin, that has often overlapping and complementary functions with oxytocin on social behavior. Curiously, vasopressin does not require CD38 to be released from the brain. This review discusses the social salience hypothesis of oxytocin action, a novel view of how this molecule influences much of human social behaviors often in contradictory ways. The oxytocinergic-vasopressinergic systems are crucial modulators of broad aspects of human personality. Of special interest are studies of these two hormones in trust related behavior observed using behavioral economic games. This review also covers the role of oxytocin in parenting and parental attachment. In conclusion, the effects of oxytocin on human behavior depend on the individual's social context and importantly as well, the individual's cultural milieu, viz. East and West. ACRONYMS: ACC = Anterior Cingulate ADP = Adenosine diphosphate AQ = Autism Quotient cADPR = Cyclic ADP-ribose CNS = Central nervous system DA = Dopamine eQTLC = Expression Quantitative Trait Loci LC-NE = Locus Coeruleus-Norepinephrine MRI = Magnetic Resonance Imaging OFC = Orbitofrontal cortices OXT = Oxytocin RAGE = Receptor for advanced glycation end-products SARM1 = Sterile Alpha and toll/interleukin-1 receptor motif-containing 1 TRPM2= Transient Receptor Potential Cation Channel Subfamily M Member 2 AVP = Vasopressin.

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.

RAGE regulates oxytocin transport into the brain

Oxytocin, a nonapeptide hormone, has a key role in female reproductive functions as well as in social memory in the brain. In our recent Communications Biology article, we reported that oxytocin is transported from the peripheral blood into the brain by the receptor for advanced glycation end-products (RAGE) in endothelial cells at the blood−brain barrier. Additionally, we found that oral oxytocin is absorbed by RAGE on intestinal epithelial cells at the blood−intestinal barrier. From a physiological perspective, we herein outline the continuing research regarding oxytocin and social behaviour.

Yamamoto and Higashido discuss the possible routes of the hormone oxytocin in the body, and highlight their recent study in Communications Biology where they showed that the RAGE receptor is a transporter for oxytocin across the blood−brain barrier.

One Single Nucleotide Polymorphism of the TRPM2 Channel Gene Identified as a Risk Factor in Bipolar Disorder Associates with Autism Spectrum Disorder in a Japanese Population

The transient receptor potential melastatin 2 (TRPM2) is a non-specific cation channel, resulting in Ca2+ influx at warm temperatures from 34 °C to 47 °C, thus including the body temperature range in mammals. TRPM2 channels are activated by β-NAD+, ADP-ribose (ADPR), cyclic ADPR, and 2'-deoxyadenosine 5'-diphosphoribose. It has been shown that TRPM2 cation channels and CD38, a type II or type III transmembrane protein with ADP-ribosyl cyclase activity, simultaneously play a role in heat-sensitive and NAD+ metabolite-dependent intracellular free Ca2+ concentration increases in hypothalamic oxytocinergic neurons. Subsequently, oxytocin (OT) is released to the brain. Impairment of OT release may induce social amnesia, one of the core symptoms of autism spectrum disorder (ASD). The risk of single nucleotide polymorphisms (SNPs) and variants of TRPM2 have been reported in bipolar disorder, but not in ASD. Therefore, it is reasonable to examine whether SNPs or haplotypes in TRPM2 are associated with ASD. Here, we report a case-control study with 147 ASD patients and 150 unselected volunteers at Kanazawa University Hospital in Japan. The sequence-specific primer-polymerase chain reaction method together with fluorescence correlation spectroscopy was applied. Of 14 SNPs examined, one SNP (rs933151) displayed a significant p-value (OR = 0.1798, 95% CI = 0.039, 0.83; Fisher's exact test; p = 0.0196). The present research data suggest that rs93315, identified as a risk factor for bipolar disorder, is a possible association factor for ASD.

CD38, CD157, and RAGE as Molecular Determinants for Social Behavior

Recent studies provide evidence to support that cluster of differentiation 38 (CD38) and CD157 meaningfully act in the brain as neuroregulators. They primarily affect social behaviors. Social behaviors are impaired in Cd38 and Cd157 knockout mice. Single-nucleotide polymorphisms of the CD38 and CD157/BST1 genes are associated with multiple neurological and psychiatric conditions, including autism spectrum disorder, Parkinson’s disease, and schizophrenia. In addition, both antigens are related to infectious and immunoregulational processes. The most important clues to demonstrate how these molecules play a role in the brain are oxytocin (OT) and the OT system. OT is axo-dendritically secreted into the brain from OT-containing neurons and causes activation of OT receptors mainly on hypothalamic neurons. Here, we overview the CD38/CD157-dependent OT release mechanism as the initiation step for social behavior. The receptor for advanced glycation end-products (RAGE) is a newly identified molecule as an OT binding protein and serves as a transporter of OT to the brain, crossing over the blood–brain barrier, resulting in the regulation of brain OT levels. We point out new roles of CD38 and CD157 during neuronal development and aging in relation to nicotinamide adenine dinucleotide⁺ levels in embryonic and adult nervous systems. Finally, we discuss how CD38, CD157, and RAGE are crucial for social recognition and behavior in daily life.

Clinical potential of oxytocin in autism spectrum disorder: current issues and future perspectives

The effects of oxytocin on social cognition and behavior have recently attracted considerable attention. In particular, oxytocin has been proposed as a novel therapeutic for psychiatric disorders with social deficits such as autism spectrum disorders. This review provides a brief overview of behavioral and neural responses to oxytocin manipulations in humans and animal models. Although the differences in findings between human and animal studies should be interpreted carefully, shared behavioral phenotypes have been recognized, such as social bonding, social responses, and recognition and usage of social cues. Previous literature suggests that the neural effects of oxytocin in humans and animals overlap in the prefrontal, limbic, and paralimbic cortices. Oxytocin-induced alterations in these regions may indicate a fundamental basis for how oxytocin modulates social behaviors and facilitate the discovery of new pharmaceutical targets for treating social deficits.

A multiscale analysis in CD38-/- mice unveils major prefrontal cortex dysfunctions

Autism spectrum disorder (ASD) is characterized by early onset of behavioral and cognitive alterations. Low plasma levels of oxytocin (OT) have also been found in ASD patients; recently, a critical role for the enzyme CD38 in the regulation of OT release was demonstrated. CD38 is important in regulating several Ca²⁺-dependent pathways, but beyond its role in regulating OT secretion, it is not known whether a deficit in CD38 expression leads to functional modifications of the prefrontal cortex (PFC), a structure involved in social behavior. Here, we report that CD38^-/- male mice show an abnormal cortex development, an excitation-inhibition balance shifted toward a higher excitation, and impaired synaptic plasticity in the PFC such as those observed in various mouse models of ASD. We also show that a lack of CD38 alters social behavior and emotional responses. Finally, examining neuromodulators known to control behavioral flexibility, we found elevated monoamine levels in the PFC of CD38^-/- adult mice. Overall, our study unveiled major changes in PFC physiologic mechanisms and provides new evidence that the CD38^-/- mouse could be a relevant model to study pathophysiological brain mechanisms of mental disorders such as ASD.-Martucci, L. L., Amar, M., Chaussenot, R., Benet, G., Bauer, O., de Zélicourt, A., Nosjean, A., Launay, J.-M., Callebert, J., Sebrié, C., Galione, A., Edeline, J.-M., de la Porte, S., Fossier, P., Granon, S., Vaillend, C., Cancela, J.-M., A multiscale analysis in CD38^-/- mice unveils major prefrontal cortex dysfunctions.

Oxytocin and excitation/inhibition balance in social recognition

Social recognition is the sensitive domains of complex behavior critical for identification, interpretation and storage of socially meaningful information. Social recognition develops throughout childhood and adolescent, and is affected in a wide variety of psychiatric disorders. Recently, new data appeared on the molecular mechanisms of these processes, particularly, the excitatory-inhibitory (E/I) ratio which is modified during development, and then E/I balance is established in the adult brain. While E/I imbalance has been proposed as a mechanism for schizophrenia, it also seems to be the common mechanism in autism spectrum disorder (ASD). In addition, there is a strong suggestion that the oxytocinergic system is related to GABA-mediated E/I control in the context of brain socialization. In this review, we attempt to summarize the underpinning molecular mechanisms of E/I balance and its imbalance, and related biomarkers in the brain in healthiness and pathology. In addition, because there are increasing interest on oxytocin in the social neuroscience field, we will pay intensive attention to the role of oxytocin in maintaining E/I balance from the viewpoint of its effects on improving social impairment in psychiatric diseases, especially in ASD.

The Oxytocin Receptor: From Intracellular Signaling to Behavior

The many facets of the oxytocin (OXT) system of the brain and periphery elicited nearly 25,000 publications since 1930 (see FIGURE 1 , as listed in PubMed), which revealed central roles for OXT and its receptor (OXTR) in reproduction, and social and emotional behaviors in animal and human studies focusing on mental and physical health and disease. In this review, we discuss the mechanisms of OXT expression and release, expression and binding of the OXTR in brain and periphery, OXTR-coupled signaling cascades, and their involvement in behavioral outcomes to assemble a comprehensive picture of the central and peripheral OXT system. Traditionally known for its role in milk let-down and uterine contraction during labor, OXT also has implications in physiological, and also behavioral, aspects of reproduction, such as sexual and maternal behaviors and pair bonding, but also anxiety, trust, sociability, food intake, or even drug abuse. The many facets of OXT are, on a molecular basis, brought about by a single receptor. The OXTR, a 7-transmembrane G protein-coupled receptor capable of binding to either Gαior Gαqproteins, activates a set of signaling cascades, such as the MAPK, PKC, PLC, or CaMK pathways, which converge on transcription factors like CREB or MEF-2. The cellular response to OXT includes regulation of neurite outgrowth, cellular viability, and increased survival. OXTergic projections in the brain represent anxiety and stress-regulating circuits connecting the paraventricular nucleus of the hypothalamus, amygdala, bed nucleus of the stria terminalis, or the medial prefrontal cortex. Which OXT-induced patterns finally alter the behavior of an animal or a human being is still poorly understood, and studying those OXTR-coupled signaling cascades is one initial step toward a better understanding of the molecular background of those behavioral effects.

A rat model for pituitary stalk electric lesion-induced central diabetes insipidus: application of 3D printing and further outcome assessments

A stable and reproducible rat injury model is not currently available to study central diabetes insipidus (CDI) and the neurohypophyseal system. In addition, a system is needed to assess the severity of CDI and measure the accompanying neurobiological alterations. In the present study, a 3D-printed lesion knife with a curved head was designed to fit into the stereotaxic instrument. The neuro-anatomical features of the brain injury were determined by in vivo magnetic resonance imaging (MRI) and arginine vasopressin (AVP) immunostaining on brain sections. Rats that underwent pituitary stalk electrical lesion (PEL) exhibited a tri-phasic pattern of CDI. MRI revealed that the hyperintenseT1-weighted signal of the pituitary stalk was interrupted, and the brain sections showed an enlarged end proximal to the injury site after PEL. In addition, the number of AVP-positive cells in supraoptic nucleus (SON) and paraventricular nucleus (PVN) decreased after PEL, which confirmed the success of the CDI model. Unlike hand-made tools, the 3D-printed lesion knives were stable and reproducible. Next, we used an ordinal clustering method for staging and the k-means’ clustering method to construct a CDI index to evaluate the severity and recovery of CDI that could be used in other multiple animals, even in clinical research. In conclusion, we established a standard PEL model with a 3D-printed knife tool and proposed a CDI index that will greatly facilitate further research on CDI.

Transient receptor potential melastatin-2 and temperature participate in the process of CD38-regulated oxytocin secretion

In recent studies, oxytocin showed potential for the treatment of mental diseases. CD38 is essential for oxytocin release, and hence plays a critical role in social behavior. CD38 catalyzes β-NAD into cyclic ADP ribose (cADPR), which could elevate the intracellular Ca by Ca-permeable channels for oxytocin secretion. The temperature-sensitive cation channel, transient receptor potential melastatin-2 (TRPM2), is a cation-nonselective cation and has been shown to affect oxytocin indirectly. The aim of the present study was to verify the participation of temperature and TRPM2 in CD38-regulated oxytocin release. The crude membranes were prepared to isolate the nerve terminals from the posterior pituitary. At 34°C, 37°C, and 39°C, agonists (β-NAD, ADPR, cADPR) and antagonists (8-Br-cADPR, 2-APB) were used to stimulate the nerve terminals. Oxytocin releases were investigated by enzyme-linked immunosorbent assay. In addition, the expression of TRPM2 and CD38 in the hypothalamus and pituitary was detected by western blotting and quantitative PCR. CD38 agonists (β-NAD, cADPR) and antagonist (8-Br-cADPR) could increase or reduce the oxytocin release, respectively. TRPM2 agonist (ADPR) and antagonist (2-APB) alone could also regulate oxytocin release. Furthermore, temperature could increase agonist stimulation and attenuate the antagonist inhibition on oxytocin release. In addition, CD38 and TRPM2 were expressed in the hypothalamus and pituitary at both the mRNA and the protein level. TRPM2 in pituitary nerve terminals plays a role in oxytocin release. Temperature- enhanced oxytocin release by CD38 and TRPM2. TRPM2 might be involved in the process of CD38-regulated oxytocin release.

Oxytocin and vasopressin neural networks: Implications for social behavioral diversity and translational neuroscience

Oxytocin- and vasopressin-related systems are present in invertebrate and vertebrate bilaterian animals, including humans, and exhibit conserved neuroanatomical and functional properties. In vertebrates, these systems innervate conserved neural networks that regulate social learning and behavior, including conspecific recognition, social attachment, and parental behavior. Individual and species-level variation in central organization of oxytocin and vasopressin systems has been linked to individual and species variation in social learning and behavior. In humans, genetic polymorphisms in the genes encoding oxytocin and vasopressin peptides and/or their respective target receptors have been associated with individual variation in social recognition, social attachment phenotypes, parental behavior, and psychiatric phenotypes such as autism. Here we describe both conserved and variable features of central oxytocin and vasopressin systems in the context of social behavioral diversity, with a particular focus on neural networks that modulate social learning, behavior, and salience of sociosensory stimuli during species-typical social contexts.

Effects of Three Lipidated Oxytocin Analogs on Behavioral Deficits in CD38 Knockout Mice

Oxytocin (OT) is a nonapeptide that plays an important role in social behavior. Nasal administration of OT has been shown to improve trust in healthy humans and social interaction in autistic subjects. As is consistent with the nature of a peptide, OT has some unfavorable characteristics: it has a short half-life in plasma and shows poor permeability across the blood-brain barrier. Analogs with long-lasting effects may overcome these drawbacks. To this end, we have synthesized three analogs: lipo-oxytocin-1 (LOT-1), in which two palmitoyl groups are conjugated to the cysteine and tyrosine residues, lipo-oxytocin-2 (LOT-2) and lipo-oxytocin-3 (LOT-3), which include one palmitoyl group conjugated at the cysteine or tyrosine residue, respectively. The following behavioral deficits were observed in CD38 knockout (CD38^−/−) mice: a lack of paternal nurturing in CD38^−/− sires, decreased ability for social recognition, and decreased sucrose consumption. OT demonstrated the ability to recover these disturbances to the level of wild-type mice for 30 min after injection. LOT-2 and LOT-3 partially recovered the behaviors for a short period. Conversely, LOT-1 restored the behavioral parameters, not for 30 min, but for 24 h. These data suggest that the lipidation of OT has some therapeutic benefits, and LOT-1 would be most useful because of its long-last activity.

Communication Impairment in Ultrasonic Vocal Repertoire during the Suckling Period of Cd157 Knockout Mice: Transient Improvement by Oxytocin

Communication consists of social interaction, recognition, and information transmission. Communication ability is the most affected component in children with autism spectrum disorder (ASD). Recently, we reported that the CD157/BST1 gene is associated with ASD, and that CD157 knockout (Cd157^−/−) mice display severe impairments in social behavior that are improved by oxytocin (OXT) treatment. Here, we sought to determine whether Cd157^−/− mice can be used as a suitable model for communication deficits by measuring ultrasonic vocalizations (USVs), especially in the early developmental stage. Call number produced in pups due to isolation from dams was higher at postnatal day (PND) 3 in knockout pups than wild-type mice, but was lower at PNDs 7 and 10. Pups of both genotypes had similarly limited voice repertoires at PND 3. Later on, at PNDs 7 and 10, while wild-type pups emitted USVs consisting of six different syllable types, knockout pups vocalized with only two types. This developmental impairment in USV emission was rescued within 30 min by intraperitoneal OXT treatment, but quickly returned to control levels after 120 min, showing a transient effect of OXT. USV impairment was partially observed in Cd157^+/− heterozygous mice, but not in Cd157^−/− adult male mice examined while under courtship. These results demonstrate that CD157 gene deletion results in social communication insufficiencies, and suggests that CD157 is likely involved in acoustic communication. This unique OXT-sensitive developmental delay in Cd157^−/− pups may be a useful model of communicative interaction impairment in ASD.

An immunohistochemical, enzymatic, and behavioral study of CD157/BST-1 as a neuroregulator

Background

Recent rodent and human studies provide evidence in support of the fact that CD157, well known as bone marrow stromal cell antigen-1 (BST-1) and a risk factor in Parkinson’s disease, also meaningfully acts in the brain as a neuroregulator and affects social behaviors. It has been shown that social behaviors are impaired in CD157 knockout mice without severe motor dysfunction and that CD157/BST1 gene single nucleotide polymorphisms are associated with autism spectrum disorder in humans. However, it is still necessary to determine how this molecule contributes to the brain’s physiological and pathophysiological functions.

Methods

To gain fresh insights about the relationship between the presence of CD157 in the brain and its enzymatic activity, and aberrant social behavior, CD157 knockout mice of various ages were tested.

Results

CD157 immunoreactivity colocalized with nestin-positive cells and elements in the ventricular zones in E17 embryos. Brain CD157 mRNA levels were high in neonates but low in adults. Weak but distinct immunoreactivity was detected in several areas in the adult brain, including the amygdala. CD157 has little or no base exchange activity, but some ADP-ribosyl cyclase activity, indicating that CD157 formed cyclic ADP-ribose but much less nicotinic acid adenine dinucleotide phosphate, with both mobilizing Ca²⁺ from intracellular Ca²⁺ pools. Social avoidance in CD157 knockout mice was rescued by a single intraperitoneal injection of oxytocin.

Conclusions

CD157 may play a role in the embryonic and adult nervous systems. The functional features of CD157 can be explained in part through the production of cyclic ADP-ribose rather than nicotinic acid adenine dinucleotide phosphate. Further experiments are required to elucidate how the embryonic expression of CD157 in neural stem cells contributes to behaviors in adults or to psychiatric symptoms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-017-0350-7) contains supplementary material, which is available to authorized users.

Structure-specific effects of lipidated oxytocin analogs on intracellular calcium levels, parental behavior, and oxytocin concentrations in the plasma and cerebrospinal fluid in mice

Oxytocin (OT) is a neuroendocrine nonapeptide that plays an important role in social memory and behavior. Nasal administration of OT has been shown to improve trust in healthy humans and social interaction in autistic subjects in some clinical trials. As a central nervous system (CNS) drug, however, OT has two unfavorable characteristics: OT is short‐acting and shows poor permeability across the blood–brain barrier, because it exists in charged form in the plasma and has short half‐life. To overcome these drawbacks, an analog with long‐lasting effects is required. We previously synthesized the analog, lipo‐oxytocin‐1 (LOT‐1), in which two palmitoyl groups are conjugated to the cysteine and tyrosine residues. In this study, we synthesized and evaluated the analogs lipo‐oxytocin‐2 (LOT‐2) and lipo‐oxytocin‐3 (LOT‐3), which feature the conjugation of one palmitoyl group at the cysteine and tyrosine residues, respectively. In human embryonic kidney‐293 cells overexpressing human OT receptors, these three LOTs demonstrated comparably weak effects on the elevation of intracellular free calcium concentrations after OT receptor activation, compared to the effects of OT. The three LOTs and OT exhibited different time‐dependent effects on recovery from impaired pup retrieval behavior in sires of CD38‐knockout mice. Sires treated with LOT‐1 showed the strongest effect, whereas others had no or little effects at 24 h after injection. These results indicated that LOTs have structure‐specific agonistic effects, and suggest that lipidation of OT might have therapeutic benefits for social impairment.

Neurotransmitter release: vacuolar ATPase V0 sector c-subunits in possible gene or cell therapies for Parkinson's, Alzheimer's, and psychiatric diseases

We overview the 16-kDa proteolipid mediatophore, the transmembrane c-subunit of the V0 sector of the vacuolar proton ATPase (ATP6V0C) that was shown to mediate the secretion of acetylcholine. Acetylcholine, serotonin, and dopamine (DA) are released from cell soma and/or dendrites if ATP6V0C is expressed in cultured cells. Adeno-associated viral vector-mediated gene transfer of ATP6V0C into the caudate putamen enhanced the depolarization-induced overflow of endogenous DA in Parkinson-model mice. Motor impairment was ameliorated in hemiparkinsonian model mice when ATP6V0C was expressed with DA-synthesizing enzymes. The review discusses application in the future as a potential tool for gene therapy, cell transplantation therapy, and inducible pluripotent stem cell therapy in neurological diseases, from the view point of recent findings regarding vacuolar ATPase.

Cyclic ADP-Ribose and Heat Regulate Oxytocin Release via CD38 and TRPM2 in the Hypothalamus during Social or Psychological Stress in Mice

Hypothalamic oxytocin (OT) is released into the brain by cyclic ADP-ribose (cADPR) with or without depolarizing stimulation. Previously, we showed that the intracellular free calcium concentration ([Ca²⁺]_i) that seems to trigger OT release can be elevated by β-NAD⁺, cADPR, and ADP in mouse oxytocinergic neurons. As these β-NAD⁺ metabolites activate warm-sensitive TRPM2 cation channels, when the incubation temperature is increased, the [Ca²⁺]_i in hypothalamic neurons is elevated. However, it has not been determined whether OT release is facilitated by heat in vitro or hyperthermia in vivo in combination with cADPR. Furthermore, it has not been examined whether CD38 and TRPM2 exert their functions on OT release during stress or stress-induced hyperthermia in relation to the anxiolytic roles and social behaviors of OT under stress conditions. Here, we report that OT release from the isolated hypothalami of male mice in culture was enhanced by extracellular application of cADPR or increasing the incubation temperature from 35°C to 38.5°C, and simultaneous stimulation showed a greater effect. This release was inhibited by a cADPR-dependent ryanodine receptor inhibitor and a nonspecific TRPM2 inhibitor. The facilitated release by heat and cADPR was suppressed in the hypothalamus isolated from CD38 knockout mice and CD38- or TRPM2-knockdown mice. In the course of these experiments, we noted that OT release differed markedly between individual mice under stress with group housing. That is, when male mice received cage-switch stress and eliminated due to their social subclass, significantly higher levels of OT release were found in subordinates compared with ordinates. In mice exposed to anxiety stress in an open field, the cerebrospinal fluid (CSF) OT level increased transiently at 5 min after exposure, and the rectal temperature also increased from 36.6°C to 37.8°C. OT levels in the CSF of mice with lipopolysaccharide-induced fever (+0.8°C) were higher than those of control mice. The TRPM2 mRNA levels and immunoreactivities increased in the subordinate group with cage-switch stress. These results showed that cADPR/CD38 and heat/TRPM2 are co-regulators of OT secretion and suggested that CD38 and TRPM2 are potential therapeutic targets for OT release in psychiatric diseases caused by social stress.