Involvement of Oxytocin Receptor/Erk/MAPK Signaling in the mPFC in Early Life Stress-Induced Autistic-Like Behaviors

Combination of rTMS and oxytocin agonist attenuate depression-like behavior after postpartum depression in mice

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) categorizes postpartum depression (PPD) as a subtype of Major Depressive Disorder (MDD) with peripartum onset, generally arising within the initial trimester following delivery. This acute psychiatric condition is characterized by feelings of worthlessness, insomnia, extreme anxiety, or maternal neglect. Intranasal oxytocin (OT) and transcranial magnetic stimulation (TMS) have the potential to address impaired social cognition; nonetheless, their neuronal underpinnings, along with their safety and efficacy, are little comprehended. This study examines the effects of rTMS stimulation with an oxytocin agonist or antagonist in a PPD model. We employed the maternal separation with early weaning (MSEW) strategy for 21 days to attain our objective. Oxytocin acetate (agonist) and atosiban (antagonist) were administered by injection twice daily for three consecutive days following the model according to the established protocol. A single session of rTMS involved the application of high-frequency stimulation (20 Hz) one hour following the final injection. Behavioral testing and brain collection were conducted 12 h post-rTMS. The results indicated that treatment with OT followed by rTMS stimulation decreased neuronal cell death and microglial activation, meanwhile enhancing synaptic plasticity through the upregulation of PSD95, Synapsin I, and Synaptophysin. Simultaneously, both OT therapy and repetitive transcranial magnetic stimulation demonstrated a significant capacity to alter autophagy activity and astrocyte function. Nonetheless, OTA therapy followed by rTMS did not exhibit the same pattern of outcomes. Our findings indicate that the combination of rTMS stimulation and an oxytocin agonist in a PPD model may mitigate depression-like behavior.

Role of Sex and Early Life Stress Experience on Porcine Cardiac and Brain Tissue Expression of the Oxytocin and H2S Systems

Early life stress (ELS) significantly increases the risk of chronic cardiovascular diseases and may cause neuroinflammation. This post hoc study, based on the material available from a previous study showing elevated "serum brain injury markers" in male control animals, examines the effect of sex and/or ELS on the cerebral and cardiac expression of the H2S and oxytocin systems. Following approval by the Regional Council of Tübingen, a randomized controlled study was conducted on 12 sexually mature, uncastrated German Large White swine of both sexes. The control animals were separated from their mothers at 28-35 days, while the ELS group was separated at day 21. At 20-24 weeks, animals underwent anesthesia, ventilation, and surgical instrumentation. An immunohistochemical analysis of oxytocin, its receptor, and the H2S-producing enzymes cystathionine-β-synthase and cystathionine-γ-lyase was performed on hypothalamic, prefrontal cortex, and myocardial tissue samples. Data are expressed as the % of positive tissue staining, and differences between groups were tested using a two-way ANOVA. The results showed no significant differences in the oxytocin and H2S systems between groups; however, sex influenced the oxytocin system, and ELS affected the oxytocin and H2S systems in a sex-specific manner. No immunohistochemical correlate to the elevated "serum brain injury markers" in male controls was identified.

Exposure to polystyrene microplastics reduces sociality and brain oxytocin levels through the gut-brain axis in mice

The rising global prevalence of microplastics (MPs) has highlighted their diverse toxicological effects. The oxytocin (OT) system in mammals, deeply intertwined with social behaviors, is recognized to be vulnerable to environmental stressors. We hypothesized that MP exposure might disrupt this system, a topic not extensively studied. We investigated the effects of MPs on behavioral neuroendocrinology via the gut-brain axis by exposing adolescent male C57BL/6 mice to varied sizes (5 μm and 50 μm) and concentrations (100 μg/L and 1000 μg/L) of polystyrene MPs over 10 weeks. The results demonstrated that exposure to 50 μm MPs significantly reduced colonic mucin production and induced substantial alterations in gut microbiota. Notably, the 50 μm-100 μg/L group showed a significant reduction in OT content within the medial prefrontal cortex and associated deficits in sociality, along with damage to the blood-brain barrier. Importantly, blocking the vagal pathway ameliorated these behavioral impairments, emphasizing the pivotal role of the gut-brain axis in mediating neurobehavioral outcomes. Our findings confirm the toxicity of MPs on sociality and the corresponding neuroendocrine systems, shedding light on the potential hazards and adverse effects of environmental MPs exposure on social behavior and neuroendocrine frameworks in social mammals, including humans.

Decoding Molecular Bases of Rodent Social Hetero-Grooming Behavior Using in Silico Analyses and Bioinformatics Tools

Highly prevalent in laboratory rodents, 'social' hetero-grooming behavior is translationally relevant to modeling a wide range of neuropsychiatric disorders. Here, we comprehensively evaluated all known to date mouse genes linked to aberrant hetero-grooming phenotype, and applied bioinformatics tools to construct a network of their established protein-protein interactions (PPI). We next identified several distinct molecular clusters within this complex network, including neuronal differentiation, cytoskeletal, WNT-signaling and synapsins-associated pathways. Using additional bioinformatics analyses, we further identified 'central' (hub) proteins within these molecular clusters, likely key for mouse hetero-grooming behavior. Overall, a more comprehensive characterization of intricate molecular pathways linked to aberrant rodent grooming may markedly advance our understanding of underlying cellular mechanisms and related neurological disorders, eventually helping discover novel targets for their pharmacological or gene therapy interventions.

Examining the Role of Oxytocinergic Signaling and Neuroinflammatory Markers in the Therapeutic Effects of MDMA in a Rat Model for PTSD

MDMA-assisted psychotherapy has shown potential as an effective treatment for post-traumatic stress disorder (PTSD). Preclinical studies involving rodents have demonstrated that MDMA can facilitate the extinction of fear memories. It has been noted that MDMA impacts oxytocin neurons and pro-inflammatory cytokines. Thus, the aim of this study was to explore the role of oxytocinergic signaling and neuroinflammatory markers in the therapeutic effects of MDMA. To achieve this, male rats were subjected to a model of PTSD involving exposure to shock and situational reminders. MDMA was microinjected into the medial prefrontal cortex (mPFC) before extinction training, followed by behavioral tests assessing activity levels, anxiety, and social function. Our findings indicate that MDMA treatment facilitated fear extinction and mitigated the shock-induced increase in freezing, as well as deficits in social behavior. Shock exposure led to altered expression of the gene coding for OXT-R and neuroinflammation in the mPFC and basolateral amygdala (BLA), which were restored by MDMA treatment. Importantly, the OXT-R antagonist L-368,899 prevented MDMA's therapeutic effects on extinction and freezing behavior. In conclusion, MDMA's therapeutic effects in the PTSD model are associated with alterations in OXT-R expression and neuroinflammation, and MDMA's effects on extinction and anxiety may be mediated by oxytocinergic signaling.

Effects of paternal deprivation on empathetic behavior and the involvement of oxytocin receptors in the anterior cingulate cortex

Paternal deprivation (PD) impairs social cognition and sociality and increases levels of anxiety-like behavior. However, whether PD affects the levels of empathy in offspring and its underlying mechanisms remain unknown. The present study found that PD increased anxiety-like behavior in mandarin voles (Microtus mandarinus), impaired sociality, reduced the ability of emotional contagion, and the level of consolation behavior. Meanwhile, PD reduced OT neurons in the paraventricular nucleus (PVN) in both male and female mandarin voles. PD decreased the level of OT receptor (OTR) mRNA in the anterior cingulate cortex (ACC) of male and female mandarin voles. Besides, OTR overexpression in the ACC reversed the PD-induced changes in anxiety-like behavior, social preference, emotional contagion, and consolation behavior. Interference of OTR expression in the ACC increased levels of anxiety-like behaviors, while it reduced levels of sociality, emotional contagion, and consolation. These results revealed that the OTR in the ACC is involved in the effects of PD on empathetic behaviors, and provide mechanistic insight into how social experiences affect empathetic behaviors.

Therapeutic uses of oxytocin in stress-related neuropsychiatric disorders

Oxytocin (OXT), produced and secreted in the paraventricular nucleus and supraoptic nucleus of magnocellular and parvocellular neurons. The diverse presence and activity of oxytocin suggests a potential for this neuropeptide in the pathogenesis and treatment of stress-related neuropsychiatric disorders (anxiety, depression and post-traumatic stress disorder (PTSD)). For a more comprehensive understanding of the mechanism of OXT's anti-stress action, the signaling cascade of OXT binding to targeting stress were summarized. Then the advance of OXT treatment in depression, anxiety, PTSD and the major projection region of OXT neuron were discussed. Further, the efficacy of endogenous and exogenous OXT in stress responses were highlighted in this review. To augment the level of OXT in stress-related neuropsychiatric disorders, current biological strategies were summarized to shed a light on the treatment of stress-induced psychiatric disorders. We also conclude some of the major puzzles in the therapeutic uses of OXT in stress-related neuropsychiatric disorders. Although some questions remain to be resolved, OXT has an enormous potential therapeutic use as a hormone that regulates stress responses.

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 Receptor in Cerebellar Purkinje Cells Does Not Engage in Autism-Related Behaviors

The classical motor center cerebellum is one of the most consistent structures of abnormality in autism spectrum disorders (ASD), and neuropeptide oxytocin is increasingly explored as a potential pharmacotherapy for ASD. However, whether oxytocin targets the cerebellum for therapeutic effects remains unclear. Here, we report a localization of oxytocin receptor (OXTR) in Purkinje cells (PCs) of cerebellar lobule Crus I, which is functionally connected with ASD-implicated circuits. OXTR activation neither affects firing activities, intrinsic excitability, and synaptic transmission of normal PCs nor improves abnormal intrinsic excitability and synaptic transmission of PCs in maternal immune activation (MIA) mouse model of autism. Furthermore, blockage of OXTR in Crus I in wild-type mice does not induce autistic-like social, stereotypic, cognitive, and anxiety-like behaviors. These results suggest that oxytocin signaling in Crus I PCs seems to be uninvolved in ASD pathophysiology, and contribute to understanding of targets and mechanisms of oxytocin in ASD treatment.

Investigation of metal modulation of oxytocin structure receptor-mediated signaling

Oxytocin is a 9-amino acid peptide hormone. Since its discovery in 1954, it has most commonly been studied in relation to its role in stimulating parturition and lactation. However, it is now known that oxytocin has a widely diverse set of functions throughout the body including neuromodulation, bone growth, and inflammation. Previous research has suggested that divalent metal ions may be required for oxytocin activity, but the exact metal species and specific pathways have yet to be fully elucidated. In this work, we focus on characterizing copper and zinc bound forms of oxytocin and related analogs through far-UV circular dichroism. We report that Cu(ii) and Zn(ii) bind uniquely to oxytocin and all analogs investigated. Furthermore, we investigate how these metal bound forms may affect downstream signaling of MAPK activation upon receptor binding. We find that both Cu(ii) and Zn(ii) bound oxytocin attenuates the activation of the MAPK pathway upon receptor binding relative to oxytocin alone. Interestingly, we observed that Zn(ii) bound forms of linear oxytocin facilitate increased MAPK signaling. This study lays the foundation for future work on elucidating the metal effects on oxytocin's diverse bioactivity.

Involvement of oxytocin receptor deficiency in psychiatric disorders and behavioral abnormalities

Oxytocin and its target receptor (oxytocin receptor, OXTR) exert important roles in the regulation of complex social behaviors and cognition. The oxytocin/OXTR system in the brain could activate and transduce several intracellular signaling pathways to affect neuronal functions or responses and then mediate physiological activities. The persistence and outcome of the oxytocin activity in the brain are closely linked to the regulation, state, and expression of OXTR. Increasing evidence has shown that genetic variations, epigenetic modification states, and the expression of OXTR have been implicated in psychiatric disorders characterized by social deficits, especially in autism. Among these variations and modifications, OXTR gene methylation and polymorphism have been found in many patients with psychiatric disorders and have been considered to be associated with those psychiatric disorders, behavioral abnormalities, and individual differences in response to social stimuli or others. Given the significance of these new findings, in this review, we focus on the progress of OXTR's functions, intrinsic mechanisms, and its correlations with psychiatric disorders or deficits in behaviors. We hope that this review can provide a deep insight into the study of OXTR-involved psychiatric disorders.

OXTRHigh stroma fibroblasts control the invasion pattern of oral squamous cell carcinoma via ERK5 signaling

The Pattern Of Invasion (POI) of tumor cells into adjacent normal tissues clinically predicts postoperative tumor metastasis/recurrence of early oral squamous cell carcinoma (OSCC), but the mechanisms underlying the development of these subtypes remain unclear. Focusing on the highest score of POIs (Worst POI, WPOI) present within each tumor, we observe a disease progression-driven shift of WPOI towards the high-risk type 4/5, associated with a mesenchymal phenotype in advanced OSCC. WPOI 4-5-derived cancer-associated fibroblasts (CAFs^WPOI4-5), characterized by high oxytocin receptor expression (OXTR^High), contribute to local-regional metastasis. OXTR^High CAFs induce a desmoplastic stroma and CCL26 is required for the invasive phenotype of CCR3⁺ tumors. Mechanistically, OXTR activates nuclear ERK5 transcription signaling via Gαq and CDC37 to maintain high levels of OXTR and CCL26. ERK5 ablation reprograms the pro-invasive phenotype of OXTR^High CAFs. Therefore, targeting ERK5 signaling in OXTR^High CAFs is a potential therapeutic strategy for OSCC patients with WPOI 4-5.

Worst pattern of invasion (WPOI) is a parameter used to quantify tumor invasiveness of oral squamous cell carcinoma (OSCC). Here the authors show that a fibroblast subset characterized by the expression of the oxytocin receptor is enriched in highly invasive WPOI 4-5 OSCC tumors and can be targeted to reduce the desmoplastic stroma and tumor metastasis.

Effects of early life adversities upon memory processes and cognition in rodent models

Exposure to stressors in early postnatal life induces long-lasting modifications in brainfunction.Thisplasticity,an essential characteristic of the brain that enables adaptation to the environment, may also induce impairments in some psychophysiological functions, including learning and memory. Early life stress (ELS) has long-term effects on thehypothalamic-pituitary-adrenal axisresponse to stressors, and has been reported to lead toneuroinflammation,altered levelsof neurotrophic factors, modifications inneurogenesis andsynaptic plasticity,with changes in neurotransmitter systems and network functioning. In this review, we focus on early postnatal stress in animal models and their effects on learning and memory.Many studies have reported ELS-induced impairments in different types of memories, including spatial memory, fear memory, recognition (both for objects and social) memory, working memory and reversal learning. Studies are not always in agreement, however, no effects, or sometimes facilitation, being reported, depending on the nature and intensity of the early intervention, as well as the age when the outcome was evaluated and the sex of the animals. When considering processes occurring after consolidation, related with memory maintenance or modification, there are a very reduced number of reports. Future studies addressing the mechanisms underlying memory changes for ELS should shed some light on the understanding of the different effects induced by stressors of different types and intensities on cognitive functions.

Infant ultrasonic vocalizations predict adolescent social behavior in rats: Effects of early life adversity

Early life adversity (ELA) increases risk for psychopathologies that often manifest during adolescence and involve disrupted social functioning. ELA affects development of the prefrontal cortex (PFC), which plays a role in social behavior. PFC oxytocin and vasopressin are important regulators of, first, mother-infant attachment, and, later, social behavior, and are implicated in psychiatric disorders. Here, we tested whether infant social communication is predictive of PFC development and adolescent social behavior. We used the limited bedding (LB) ELA model in rats during postnatal days (P)2-14, and measured isolation-induced ultrasonic vocalizations (USVs) at P10 to characterize differences in an early social response. Rats were tested for dyadic social interaction in adolescence (P34). Adolescent oxytocin receptor (Oxtr) and arginine-vasopressin receptor 1a mRNA were measured in the PFC. Relationships between infant USVs, adolescent behavior, and gene expression were assessed. LB-reared rats exhibited fewer USVs at P10. While social behaviors were not robustly affected by rearing, fewer total and complex-type infant USVs predicted fewer interactions in adolescence. LB increased Oxtr in both sexes but Oxtr was not directly predicted by USVs. Findings support the use of USVs as indicators of differential early life experience in rodents, toward further characterization of early factors associated with vulnerability.

Effects of chronic triclosan exposure on social behaviors in adult mice

Triclosan (TCS), a newly identified environmental endocrine disruptor (EED) in household products, has been reported to have toxic effects on animals and humans. The effects of TCS exposure on individual social behaviors and the potential underlying mechanisms are still unknown. This study investigated the behavioral effects of 42-day exposure to TCS (0, 50, 100 mg/kg) in drinking water using the open field test (OFT), social dominance test (SDT), social interaction test (SIT), and novel object recognition task (NOR). Using 16S rRNA sequencing analysis and transmission electron microscopy (TEM), we observed the effects of TCS exposure on the gut microbiota and ultrastructure of hippocampal neurons and synapses. Behavioral results showed that chronic TCS exposure reduced the social dominance of male and female mice. TCS exposure also reduced social interaction in male mice and impaired memory formation in female mice. Analysis of the gut microbiota showed that TCS exposure increased the relative abundance of the Proteobacteria and Actinobacteria phyla in female mice. Ultrastructural analysis revealed that TCS exposure induced ultrastructural damage to hippocampal neurons and synapses. These findings suggest that TCS exposure may affect social behaviors, which may be caused by altered gut microbiota and impaired plasticity of hippocampal neurons and synapses.

Maternal Separation Modifies the Activity of Social Processing Brain Nuclei Upon Social Novelty Exposure

Maternal separation has been shown to disrupt proper brain development and maturation, having profound consequences on the neuroendocrine systems in charge of the stress response, and has been shown to induce behavioral and cognitive abnormalities. At the behavioral level, maternal separation has been shown to increase offensive play-fighting in juvenile individuals and reduce social interest in adulthood. Since most of the studies that have evaluated the consequences of maternal separation on social behavior have focused on behavioral analysis, there is a need for a further understanding of the neuronal mechanisms underlying the changes in social behavior induced by maternal separation. Therefore, the aim of the present research was to assess the long-term effects of maternal separation on social interaction behavior and to assess the activity of several brain regions involved in the processing of social cues and reward upon social novelty exposure, using c-Fos immunohistochemistry as a marker of neuronal activity. Male Wistar rats were subjected to 4 h maternal separation during the neonatal period, 9:00 h-13:00 h from postnatal day 1 to 21, and exposed to social novelty during adulthood. After social novelty exposure, brains were fixed and coronal sections of the medial amygdala, lateral septum (LS), paraventricular nucleus of the hypothalamus, nucleus accumbens, and medial prefrontal cortex were obtained for c-Fos immunohistochemistry. Maternally separated rats spent less time investigating the novel peer, suggesting that maternal separation reduces social approach motivation. Furthermore, maternal separation reduced the number of c-Fos positive cells of the medial amygdala, paraventricular nucleus of the hypothalamus, LS, nucleus accumbens, and medial prefrontal cortex upon social novelty exposure. These findings suggest that maternal separation can reduce the plastic capacity of several brain nuclei, which constitute a physiological basis for the emergence of behavioral disorders presented later in life reported to be linked to early life adversity.

Epigenetics of childhood trauma: Long term sequelae and potential for treatment

Childhood trauma (CT) can have persistent effects on the brain and is one of the major risk factors for neuropsychiatric diseases in adulthood. Recent advances in the field of epigenetics suggest that epigenetic factors such as DNA methylation and histone modifications, as well as regulatory processes involving non-coding RNA are associated with the long-term sequelae of CT. This narrative review summarizes current knowledge on the epigenetic basis of CT and describes studies in animal models and human subjects examining how the epigenome and transcriptome are modified by CT in the brain. It discusses psychological and pharmacological interventions that can counteract epigenetic changes induced by CT and the need to establish longitudinal assessment after CT for developing more effective diagnostics and treatment strategies based on epigenetic targets.

The oxytocin system and early-life experience-dependent plastic changes

Early-life experience influences social and emotional behaviour in adulthood. Affiliative tactile stimuli in early life facilitate the development of social and emotional behaviour, whereas early-life adverse stimuli have been shown to increase the risk of various diseases in later life. On the other hand, oxytocin has been shown to have organizational actions during early-life stages. However, the detailed mechanisms of the effects of early-life experience and oxytocin remain unclear. Here, we review the effects of affiliative tactile stimuli during the neonatal period and neonatal oxytocin treatment on the activity of the oxytocin-oxytocin receptor system and social or emotional behaviour in adulthood. Both affiliative tactile stimuli and early-life adverse stimuli in the neonatal period acutely activate the oxytocin-oxytocin receptor system in the brain but modulate social behaviour and anxiety-related behaviour apparently in an opposite direction in adulthood. Accumulating evidence suggests that affiliative tactile stimuli and exogenous application of oxytocin in early-life stages induce higher activity of the oxytocin-oxytocin receptor system in adulthood, although the effects are dependent on experimental procedures, sex, dosages and brain regions examined. On the other hand, early-life stressful stimuli appear to induce reduced activity of the oxytocin-oxytocin receptor system, possibly leading to adverse actions in adulthood. It is possible that activation of a specific oxytocin system can induce beneficial actions against early-life maltreatments and thus could be used for the treatment of developmental psychiatric disorders.

Effect of early life social adversity on drug abuse vulnerability: Focus on corticotropin-releasing factor and oxytocin

Early life adversity can set the trajectory for later psychiatric disorders, including substance use disorders. There are a host of neurobiological factors that may play a role in the negative trajectory. The current review examines preclinical evidence suggesting that early life adversity specifically involving social factors (maternal separation, adolescent social isolation and adolescent social defeat) may influence drug abuse vulnerability by strengthening corticotropin-releasing factor (CRF) systems and weakening oxytocin (OT) systems. In adulthood, pharmacological and genetic evidence indicates that both CRF and OT systems are directly involved in drug reward processes. With early life adversity, numerous studies show an increase in drug abuse vulnerability measured in adulthood, along a concomitant strengthening of CRF systems and a weakening of OT systems. Mechanistic studies, while relatively few in number, are generally consistent with the theme that strengthened CRF systems and weakened OT systems mediate, at least in part, the link between early life adversity and drug abuse vulnerability. Establishing a direct role of CRF and OT in mediating the relation between early life social stressors and drug abuse vulnerability will inform clinical researchers and practitioners toward the development of intervention strategies to reduce risk among those suffering from early life adversities. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.