Neurite Outgrowth Stimulated by Oxytocin Is Modulated by Inhibition of the Calcium Voltage-Gated Channels

OXTR-mediated signaling in astrocytes contributes to anxiolysis

Astrocytes are an indispensable part of signal processing within the mammalian brain. Thus, the mode of action of a neuropeptide such as oxytocin (OXT) can only be fully understood considering this integral part of the CNS. Here, we show that OXT regulates astrocytic gene expression, intracellular signaling and specific proteins both in vitro and in vivo. This translates into rapid regulation of astroglial structural and functional properties including cytoskeletal plasticity, coverage of synapses and gap-junction coupling. At the molecular level, we identify the previously undescribed Sp1-Gem signaling cascade as the key driver for these cell type-specific OXT effects. Finally at the behavioral level, we found in vivo that OXT requires astrocytes to exert its well described anxiolytic properties within the hypothalamic paraventricular nucleus. Thus, our study points to OXT receptor-expressing astrocytes as a critical component of the brain OXT system.

Peptidergic Systems and Neuroblastoma

The peptidergic systems are involved in neuroblastoma. Peptides (angiotensin II, neuropeptide Y, neurotensin, substance P) act as oncogenic agents in neuroblastoma, whereas others (adrenomedullin, corticotropin-releasing factor, urocortin, orexin) exert anticancer effects against neuroblastoma. This plethora of peptidergic systems show the functional complexity of the mechanisms regulated by peptides in neuroblastoma. Peptide receptor antagonists act as antineuroblastoma agents since these compounds counteracted neuroblastoma cell growth and migration and the angiogenesis promoted by oncogenic peptides. Other therapeutic approaches (signaling pathway inhibitors, focal adhesion kinase inhibitors, peptide receptor knockdown, acetic acid analogs) that also counteract the beneficial effects mediated by the oncogenic peptides in neuroblastoma are discussed, and future research lines to be developed in neuroblastoma (interactions between oncogenic and anticancer peptides, combination therapy using peptide receptor antagonists and chemotherapy/radiotherapy) are also suggested. Although the data regarding the involvement of the peptidergic systems in neuroblastoma are, in many cases, fragmentary or very scarce for a particular peptidergic system, taken together, they are quite promising with respect to potentiating and developing this research line with the aim of developing new therapeutic strategies to treat neuroblastoma in the future. Peptidergic systems are potential and promising targets for the diagnosis and treatment of neuroblastoma.

KLF7 promotes neuroblastoma differentiation through the GTPase signaling pathway by upregulating neuroblast differentiation-associated protein AHNAKs and glycerophosphodiesterase GDPD5

The arrest of neural crest-derived sympathoadrenal neuroblast differentiation contributes to neuroblastoma formation, and overriding this blocked differentiation is a clear strategy for treating high-risk neuroblastoma. A better understanding of neuroblast or neuroblastoma differentiation is essential for developing new therapeutic approaches. It has been proposed that Krueppel-like factor 7 (KLF7) is a neuroblastoma super-enhancer-associated transcription factor gene. Moreover, KLF7 was found to be intensely active in postmitotic neuroblasts of the developing nervous system during embryogenesis. However, the role of KLF7 in the differentiation of neuroblast or neuroblastoma is unknown. Here, we find a strong association between high KLF7 expression and favorable clinical outcomes in neuroblastoma. KLF7 induces differentiation of neuroblastoma cells independently of the retinoic acid (RA) pathway and acts cooperatively with RA to induce neuroblastoma differentiation. KLF7 alters the GTPase activity and multiple differentiation-related genes by binding directly to the promoters of neuroblast differentiation-associated protein (AHNAK and AHNAK2) and glycerophosphodiester phosphodiesterase domain-containing protein 5 (GDPD5) and regulating their expression. Furthermore, we also observe that silencing KLF7 in neuroblastoma cells promotes the adrenergic-to-mesenchymal transition accompanied by changes in enhancer-mediated gene expression. Our results reveal that KLF7 is an inducer of neuroblast or neuroblastoma differentiation with prognostic significance and potential therapeutic value.

Potential role of oxytocin in the regulation of memories and treatment of memory disorders

Oxytocin (OXT) is an "affiliative" hormone or neurohormone or neuropeptide consists of nine amino acids, synthesized in magnocellular neurons of paraventricular (PVN) and supraoptic nuclei (SON) of hypothalamus. OXT receptors are widely distributed in various region of brain and OXT has been shown to regulate various social and nonsocial behavior. Hippocampus is the main region which regulates the learning and memory. Hippocampus particularly regulates the acquisition of new memories and retention of acquired memories. OXT has been shown to regulate the synaptic plasticity, neurogenesis, and consolidation of memories. Further, findings from both preclinical and clinical studies have suggested that the OXT treatment improves performance in memory related task. Various trials have suggested the positive impact of intranasal OXT in the dementia patients. However, these studies are limited in number. In the present study authors have highlighted the role of OXT in the formation and retrieval of memories. Further, the study demonstrated the outcome of OXT treatment in various memory and related disorders.

Conductive and alignment-optimized porous fiber conduits with electrical stimulation for peripheral nerve regeneration

Autologous nerve transplantation (ANT) is currently considered the gold standard for treating long-distance peripheral nerve defects. However, several challenges associated with ANT, such as limited availability of donors, donor site injury, mismatched nerve diameters, and local neuroma formation, remain unresolved. To address these issues comprehensively, we have developed porous poly(lactic-co-glycolic acid) (PLGA) electrospinning fiber nerve guide conduits (NGCs) that are optimized in terms of alignment and conductive coating to facilitate peripheral nerve regeneration (PNR) under electrical stimulation (ES). The physicochemical and biological properties of aligned porous PLGA fibers and poly(3,4-ethylenedioxythiophene):polystyrene sodium sulfonate (PEDOT:PSS) coatings were characterized through assessments of electrical conductivity, surface morphology, mechanical properties, hydrophilicity, and cell proliferation. Material degradation experiments demonstrated the biocompatibility in vivo of electrospinning fiber films with conductive coatings. The conductive NGCs combined with ES effectively facilitated nerve regeneration. The designed porous aligned NGCs with conductive coatings exhibited suitable physicochemical properties and excellent biocompatibility, thereby significantly enhancing PNR when combined with ES. This combination of porous aligned NGCs with conductive coatings and ES holds great promise for applications in the field of PNR.

Microarray evidence that 8-cell human embryos express some hormone family members including oxytocin

OBJECTIVE

This study is to discover hormone pathways active in early cleaving human embryos.

METHODS

A list of 152 hormones and receptors were compiled to query the microarray database of mRNAs in 8-cell human embryos, two lines of human embryonic stem cells plus human fibroblasts before and after induced pluripotency.

RESULTS

Over half of the 152 hormones and receptors were silent on the arrays of all cell types, and more were detected at high or moderate levels on the 8-cell arrays than on the pluripotent cell or fibroblast arrays. Eight hormone family genes were uniquely detected at least 22-fold higher on the 8-cell arrays than the stem cell arrays: AVPI1, CCK, CORT, FSTL4, GIP, GPHA2, OXT, and PPY suggesting novel roles for these proteins in early development. Oxytocin was detected by pilot immunoassay in culture media collected from Day 3 embryos. Robust detection of CRHR1 and EPOR suggests the 8-cell embryo may be responsive to maternal CRH and EPO. The over-expression of POMC and GHITM suggests POMP peptide products may have undiscovered roles in early development and GHITM may contribute to mitochondrial remodeling. Under-detected on the 8-cell arrays at least tenfold were two key enzymes in steroid biosynthesis, DHCR24 and FDPS.

CONCLUSIONS

The 8-cell human embryo may be secreting oxytocin, which could stimulate its own progress down the fallopian tube as well as play a role in early neural precursor development. The 8-cell embryo does not synthesize reproductive steroid hormones. As previously reported for growth factor families, the early embryo over-expresses more hormones than hormone receptors.

Oxytocin, GABA, and dopamine interplay in autism

Oxytocin plays an important role in brain development and is associated with various neurotransmitter systems in the brain. Abnormalities in the production, secretion, and distribution of oxytocin in the brain, at least during some stages of the development, are critical for the pathogenesis of neuropsychiatric diseases, particularly in the autism spectrum disorder. The etiology of autism includes changes in local sensory and dopaminergic areas of the brain, which are also supplied by the hypothalamic sources of oxytocin. It is very important to understand their mutual relationship. In this review, the relationship of oxytocin with several components of the dopaminergic system, gamma-aminobutyric acid (GABA) inhibitory neurotransmission and their alterations in the autism spectrum disorder is discussed. Special attention has been paid to the results describing a reduced expression of inhibitory GABAergic markers in the brain in the context of dopaminergic areas in various models of autism. It is presumed that the altered GABAergic neurotransmission, due to the absence or dysfunction of oxytocin at certain developmental stages, disinhibits the dopaminergic signaling and contributes to the autism symptoms.

Oxytocin Receptor Expression in Hair Follicle Stem Cells: A Promising Model for Biological and Therapeutic Discovery in Neuropsychiatric Disorders

The intricate nature of the human brain and the limitations of existing model systems to study molecular and cellular causes of neuropsychiatric disorders represent a major challenge for basic research. The promising progress in patient-derived stem cell technology and in our knowledge on the role of the brain oxytocin (OXT) system in health and disease offer new possibilities in that direction. In this study, the rat hair follicle stem cells (HFSCs) were isolated and expanded in vitro. The expression of oxytocin receptors (OXTR) was evaluated in these cells. The cellular viability was assessed 12 h post stimulation with OXT. The activation of OXTR-coupled intracellular signaling cascades, following OXT treatment was determined. Also, the influence of OXT on neurite outgrowth and cytoskeletal rearrangement were defined. The assessment of OXTR protein expression revealed this receptor is expressed abundantly in HFSCs. As evidenced by the cell viability assay, no adverse or cytotoxic effects were detected following 12 h treatment with different concentrations of OXT. Moreover, OXTR stimulation by OXT resulted in ERK1/2, CREB, and eEF2 activation, neurite length alterations, and cytoskeletal rearrangements that reveal the functionality of this receptor in HFSCs. Here, we introduced the rat HFSCs as an easy-to-obtain stem cell model that express functional OXTR. This cell-based model can contribute to our understanding of the progression and treatment of neuropsychiatric disorders with oxytocinergic system deficiency.

Oxytocin modulates steroidogenesis-associated genes and estradiol levels in the placenta

Oxytocin (OXT) plays a significant role during pregnancy, especially toward the end of pregnancy. Some studies have reported that OXT is involved in the stimulation of steroidogenesis in several organs. However, the effects of OXT on placental steroidogenesis have not yet been established. In this study, we investigated the regulation of steroid hormones and steroidogenic enzymes by OXT-associated signaling in vitro and in vivo. OXT increased the gene expression of steroidogenic enzymes, which convert pregnenolone to progesterone and dehydroepiandrosterone (DHEA) in vitro. In OXT-administered pregnant rats, pregnenolone and DHEA levels were significantly enhanced in the plasma and the expression of the enzymes synthesizing DHEA, testosterone, and estradiol (E2) was increased in placental tissues. Furthermore, OXT was found to affect placental cell differentiation, which is closely related to steroid hormone synthesis. After treatment of the pregnant rats with atosiban, an antagonist of the OXT receptor, the concentration of E2 in the plasma and the expression of E2-synthesizing enzyme were reduced. This regulation may be due to OXT-mediated differentiation, because OXT increases the expression of corticotropin-releasing hormone, which is a biomarker of placental cell differentiation. Our findings suggest that OXT contributes to maintaining pregnancy by regulating the differentiation of placental cells and steroidogenesis during pregnancy.

Oxytocin action on components of endoplasmic reticulum in hippocampal neuronal cells

Despite the known importance of the endoplasmic reticulum (ER) in protein synthesis and vesicular transport, it is not clear whether neuropeptide and neuromodulator oxytocin can directly affect components of the ER in neuronal cells. Therefore, in the present study, we hypothesize that incubation of hippocampal neuronal cells in a presence of oxytocin 1) plays a role in the regulation of the expression of selected ER chaperone components and molecules involved in unfolded protein response pathway 2) affects distribution of the intracellular fluorescence signal highly selective for the ER. We found that oxytocin (1 μM) after 60 min significantly decreased the gene expression of oxidoreductase Ero1β, chaperone glucose-regulated proteins (Grp) 78 and Grp94. A significant decrease in GRP78 protein levels in response to oxytocin treatment occurred after 30, 60 and 120 min. We also observed a time-dependent increase in calreticulin protein levels with a statistically significant increase observed after 360 min. We found that the dynamics of the ER network changes significantly within 2 h of incubation under the influence of oxytocin. In conclusion we have shown that ER chaperones, oxidoreductases and trafficking molecules in neuronal cells are changing in response to oxytocin treatment in a short-term scenario potentially relevant for growth of dendrites and axons.

Glutamate Signaling and Filopodiagenesis of Astrocytoma Cells in Brain Cancers: Survey and Questions

Astrocytes are non-excitable cells in the CNS that can cause life-threatening astrocytoma tumors when they transform to cancerous cells. Perturbed homeostasis of the neurotransmitter glutamate is associated with astrocytoma tumor onset and progression, but the factors that govern this phenomenon are less known. Herein, we review possible mechanisms by which glutamate may act in facilitating the growth of projections in astrocytic cells. This review discusses the similarities and differences between the morphology of astrocytes and astrocytoma cells, and the role that dysregulation in glutamate and calcium signaling plays in the aberrant morphology of astrocytoma cells. Converging reports suggest that ionotropic glutamate receptors and voltage-gated calcium channels expressed in astrocytes may be responsible for the abnormal filopodiagenesis or process extension leading to astrocytoma cells’ infiltration throughout the brain.

A randomized controlled trial of intranasal oxytocin in Phelan-McDermid syndrome

Background

Phelan-McDermid syndrome (PMS) is a rare neurodevelopmental disorder caused by haploinsufficiency of the SHANK3 gene and characterized by global developmental delays, deficits in speech and motor function, and autism spectrum disorder (ASD). Monogenic causes of ASD such as PMS are well suited to investigations with novel therapeutics, as interventions can be targeted based on established genetic etiology. While preclinical studies have demonstrated that the neuropeptide oxytocin can reverse electrophysiological, attentional, and social recognition memory deficits in Shank3-deficient rats, there have been no trials in individuals with PMS. The purpose of this study is to assess the efficacy and safety of intranasal oxytocin as a treatment for the core symptoms of ASD in a cohort of children with PMS.

Methods

Eighteen children aged 5–17 with PMS were enrolled. Participants were randomized to receive intranasal oxytocin or placebo (intranasal saline) and underwent treatment during a 12-week double-blind, parallel group phase, followed by a 12-week open-label extension phase during which all participants received oxytocin. Efficacy was assessed using the primary outcome of the Aberrant Behavior Checklist-Social Withdrawal (ABC-SW) subscale as well as a number of secondary outcome measures related to the core symptoms of ASD. Safety was monitored throughout the study period.

Results

There was no statistically significant improvement with oxytocin as compared to placebo on the ABC-SW (Mann–Whitney U = 50, p = 0.055), or on any secondary outcome measures, during either the double-blind or open-label phases. Oxytocin was generally well tolerated, and there were no serious adverse events.

Limitations

The small sample size, potential challenges with drug administration, and expectancy bias due to relying on parent reported outcome measures may all contribute to limitations in interpreting results.

Conclusion

Our results suggest that intranasal oxytocin is not efficacious in improving the core symptoms of ASD in children with PMS.

Trial registration NCT02710084.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13229-021-00459-1.

Alterations in Dendritic Spine Maturation and Neurite Development Mediated by FAM19A1

Neurogenesis and functional brain activity require complex associations of inherently programmed secretory elements that are regulated precisely and temporally. Family with sequence similarity 19 A1 (FAM19A1) is a secreted protein primarily expressed in subsets of terminally differentiated neuronal precursor cells and fully mature neurons in specific brain substructures. Several recent studies have demonstrated the importance of FAM19A1 in brain physiology; however, additional information is needed to support its role in neuronal maturation and function. In this study, dendritic spine morphology in Fam19a1-ablated mice and neurite development during in vitro neurogenesis were examined to understand the putative role of FAM19A1 in neural integrity. Adult Fam19a1-deficient mice showed low dendritic spine density and maturity with reduced dendrite complexity compared to wild-type (WT) littermates. To further explore the effect of FAM19A1 on neuronal maturation, the neurite outgrowth pattern in primary neurons was analyzed in vitro with and without FAM19A1. In response to FAM19A1, WT primary neurons showed reduced neurite complexity, whereas Fam19a1-decifient primary neurons exhibited increased neurite arborization, which was reversed by supplementation with recombinant FAM19A1. Together, these findings suggest that FAM19A1 participates in dendritic spine development and neurite arborization.

The impact of oxytocin on neurite outgrowth and synaptic proteins in Magel2-deficient mice

Oxytocin contributes to the regulation of cytoskeletal and synaptic proteins and could, therefore, affect the mechanisms of neurodevelopmental disorders, including autism. Both the Prader-Willi syndrome and Schaaf-Yang syndrome exhibit autistic symptoms involving the MAGEL2 gene. Magel2-deficient mice show a deficit in social behavior that is rescued following the postnatal administration of oxytocin. Here, in Magel2-deficient mice, we showed that the neurite outgrowth of primary cultures of immature hippocampal neurons is reduced. Treatment with oxytocin reversed this abnormality. In the hippocampus of Magel2-deficient pups, we further demonstrated that several transcripts of neurite outgrowth-associated proteins, synaptic vesicle proteins, and cell-adhesion molecules are decreased. In the juvenile stage, when neurons are mature, normalization or even overexpression of most of these markers was observed, suggesting a delay in the neuronal maturation of Magel2-deficient pups. Moreover, we found reduced transcripts of the excitatory postsynaptic marker, Psd95 in the hippocampus and we observed a decrease of PSD95/VGLUT2 colocalization in the hippocampal CA1 and CA3 regions in Magel2-deficient mice, indicating a defect in glutamatergic synapses. Postnatal administration of oxytocin upregulated postsynaptic transcripts in pups; however, it did not restore the level of markers of glutamatergic synapses in Magel2-deficient mice. Overall, Magel2 deficiency leads to abnormal neurite outgrowth and reduced glutamatergic synapses during development, suggesting abnormal neuronal maturation. Oxytocin stimulates the expression of numerous genes involved in neurite outgrowth and synapse formation in early development stages. Postnatal oxytocin administration has a strong effect on development that should be considered for certain neuropsychiatric conditions in infancy.

Abnormal neuronal morphology and altered synaptic proteins are restored by oxytocin in autism-related SHANK3 deficient model

Oxytocin has been suggested as a potential therapeutic agent in autism and other neuropsychiatric conditions. Although, the link between the deficit in "SH3 domain and ankyrin repeat containing protein 3" (SHANK3) and autism spectrum disorders is highly studied topic, developmental mechanisms are still poorly understood. In this study, we clearly confirm that SHANK3 deficiency is accompanied with abnormalities in neurite number and length, which are reversed by oxytocin treatment (1 μM, 48h) in primary hippocampal neurons. Transient silencing for the SHANK3 gene (siSHANK3) in neuron-like cell line (SH-SY5Y) revealed a significant decrease in the expression levels of Neurexins 1α, 1β, 2α and 2β. Oxytocin treatment compensated reduced levels of Synapsin I, PSD95 and Neuroligin 3 in siSHANK3 cells suggesting a marked potential of oxytocin to ameliorate defects present in conditions of SHANK3 deficiency. Further analysis of hippocampal tissue revealed that oxytocin application (0.1 μg/μl, s.c. at P2 and P3 day) affects levels of synaptic proteins and GTPases in both WT and SHANK3 deficient mice on day P5. Oxytocin stimulated the mRNA expression of RhoB and Rac1 in both WT and SHANK3 deficient mice. Our data suggest that autism relevant synaptic pathologies could be reversed by oxytocin treatment.

Modulation of Neuronal Cell Affinity on PEDOT-PSS Nonwoven Silk Scaffolds for Neural Tissue Engineering

Peripheral nerve injury is a common consequence of trauma with low regenerative potential. Electroconductive scaffolds can provide appropriate cell growth microenvironments and synergistic cell guidance cues for nerve tissue engineering. In the present study, electrically conductive scaffolds were prepared by conjugating poly (3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT-PSS) or dimethyl sulfoxide (DMSO)-treated PEDOT-PSS on electrospun silk scaffolds. Conductance could be tuned by the coating concentration and was further boosted by DMSO treatment. Analogue NG108-15 neuronal cells were cultured on the scaffolds to evaluate neuronal cell growth, proliferation, and differentiation. Cellular viability was maintained on all scaffold groups while showing comparatively better metabolic activity and proliferation than neat silk. DMSO-treated PEDOT-PSS functionalized scaffolds partially outperformed their PEDOT-PSS counterparts. Differentiation assessments suggested that these PEDOT-PSS assembled silk scaffolds could support neurite sprouting, indicating that they show promise to be used as a future platform to restore electrochemical coupling at the site of injury and preserve normal nerve function.

L-type Voltage-Gated Calcium Channel Modulators Inhibit Glutamate-Induced Morphology Changes in U118-MG Astrocytoma Cells

The excitatory neurotransmitter glutamate evokes physiological responses within the astrocytic network that lead to fine morphological changes. However, the mechanism by which astrocytes couple glutamate sensing with cellular calcium rise remains unclear. We tested a possible connection between L-type voltage-gated calcium channels (Cav) and glutamate-induced response in U118-MG astrocytoma cells. While astrocytoma cells differ from primary astrocytes, they demonstrate the same response to glutamate. In this study, the extension of U118-MG processes upon glutamate exposure was shown to depend on extracellular calcium entry via L-type Cav's. Drugs known to bind to the pore-forming subunit of Cav's decreased the astrocytic filopodia extension caused by glutamate, and ligands of the α2δ auxiliary subunit inhibited all process growth (e.g., gabapentinoids). The observed phenotypic responses suggest that α2δ is a main contributor to the role of Cavs in glutamate-dependent filopodiagenesis, thereby opening new avenues of research on the role of α2δ in astrocytic neurochemical signaling.

Neuronal morphology alterations in autism and possible role of oxytocin

Current understanding of the neuroanatomical abnormalities in autism includes gross anatomical changes in several brain areas and microstructural alterations in neuronal cells as well. There are many controversies in the interpretation of the imaging data, evaluation of volume and size of particular brain areas, and their functional translation into a broad autism phenotype. Critical questions of neuronal pathology in autism include the concept of the reversible plasticity of morphological changes, volume alterations of brain areas, and both short- and long-term consequences of adverse events present during the brain development. At the cellular level, remodeling of the actin cytoskeleton is considered as one of the critical factors associated with the autism spectrum disorders. Alterations in the composition of the neuronal cytoskeleton, in particular abnormalities in the polymerization of actin filaments and their associated proteins underlie the functional consequences in behavior resulting in symptoms and clinical correlates of autism spectrum disorder. In the present review, a special attention is devoted to the role of oxytocin in experimental models of neurodevelopmental disorders manifesting alterations in neuronal morphology.

Anxiolytic and Anxiogenic? How the Transcription Factor MEF2 Might Explain the Manifold Behavioral Effects of Oxytocin

The neuromodulator oxytocin, since its first synthesis by du Vigneaud in 1953, has mainly been associated with beneficial physiological effects, as well as positive social and emotional behaviors. This overall positive picture of oxytocin as the "love-, cuddle-, or bonding-hormone" has repeatedly been challenged since then. Oxytocin-induced effects that would be perceived as negative by the individual, such as increased anxiety or potentiation of stress-induced ACTH release, as well as the regulation of negative approach-related emotions, such as envy and schadenfreude (gloating) have been described. The general consent is that oxytocin, instead of acting unidirectional, induces changes in the salience network to shift the emphasis of emotional contexts, and therefore can, e.g., produce both anxiolytic as well as anxiogenic behavioral outcomes. However, the underlying mechanisms leading to alterations in the salience network are still unclear. With the aim to understand the manifold effects of oxytocin on a cellular/molecular level, a set of oxytocin receptor-coupled signaling cascades and downstream effectors regulating transcription and translation has been identified. Those oxytocin-driven effectors, such as MEF2 and CREB, are known modulators of the neuronal and glial cytoarchitecture. We hypothesize that, by determining cellular morphology and connectivity, MEF2 is one of the key factors that might contribute to the diverse behavioral effects of oxytocin.

Molecular Mechanisms of Oxytocin Signaling at the Synaptic Connection

Aberrant regulation of oxytocin signaling is associated with the etiology of neurodevelopmental disorders. Synaptic dysfunctions in neurodevelopmental disorders are becoming increasingly known, and their pathogenic mechanisms could be a target of potential therapeutic intervention. Therefore, it is important to pay attention to the role of oxytocin and its receptor in synapse structure, function, and neuron connectivity. An early alteration in oxytocin signaling may disturb neuronal maturation and may have short-term and long-term pathological consequences. At the molecular level, neurodevelopmental disorders include alterations in cytoskeletal rearrangement and neuritogenesis resulting in a diversity of synaptopathies. The presence of oxytocin receptors in the presynaptic and postsynaptic membranes and the direct effects of oxytocin on neuronal excitability by regulating the activity of ion channels in the cell membrane implicate that alterations in oxytocin signaling could be involved in synaptopathies. The ability of oxytocin to modulate neurogenesis, synaptic plasticity, and certain parameters of cytoskeletal arrangement is discussed in the present review.

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.