Autistic-like syndrome in mu opioid receptor null mice is relieved by facilitated mGluR4 activity

The role of gene-environment interactions in social dysfunction: Focus on preclinical evidence from mouse studies

Human and animal research has demonstrated that genetic and environmental factors can strongly modulate behavioral function, including the expression of social behaviors and their dysfunctionalities. Several genes have been linked to pathologies characterized by alterations in social behaviors, e.g., aggressive/antisocial personality disorder (ASPD), or autism spectrum disorder (ASD). Environmental stimulation (e.g., physical exercise, environmental enrichment) or adversity (e.g., chronic stress, social isolation) may respectively improve or impair social interactions. While the independent contribution of genetic and environmental factors to social behaviors has been assessed in a variety of human and animal studies, the impact of their interactive effects on social functions has been less extensively investigated. Genetic mutations and environmental changes can indeed influence each other through complex mutual effects, e.g., inducing synergistic, antagonistic or interactive behavioral outcomes. This complexity is difficult to be disentangled in human populations, thus encouraging studies in animal models, especially in the mouse species which is the most suitable for genetic manipulations. Here we review the available preclinical evidence on the impact of gene-environment interactions on social behaviors and their dysfunction, focusing on studies in laboratory mice. We included findings combining naturally occurring mutations, selectively bred or transgenic mice with multiple environmental manipulations, including positive (environmental enrichment, physical exercise) and aversive (social isolation, maternal separation, and stress) experiences. The impact of these results is critically discussed in terms of their generalizability across mouse models and social tests, as well as their implications for human studies on social dysfunction.

Acute, chronic and conditioned effects of intranasal oxytocin in the mu-opioid receptor knockout mouse model of autism: Social context matters

Autism Spectrum Disorders (ASD) are neurodevelopmental disorders whose diagnosis relies on deficient social interaction and communication together with repetitive behaviours. Multiple studies have highlighted the potential of oxytocin (OT) to ameliorate behavioural abnormalities in animal models and subjects with ASD. Clinical trials, however, yielded disappointing results. Our study aimed at assessing the behavioural effects of different regimens of OT administration in the Oprm1 null mouse model of ASD. We assessed the effects of intranasal OT injected once at different doses (0.15, 0.3, and 0.6 IU) and time points (5, 15, and 30 min) following administration, or chronically, on ASD-related behaviours (social interaction and preference, stereotypies, anxiety, nociception) in Oprm1+/+ and Oprm1-/- mice. We then tested whether pairing intranasal OT injection with social experience would influence its outcome on ASD-like symptoms, and measured gene expression in the reward/social circuit. Acute intranasal OT at 0.3 IU improved social behaviour in Oprm1-/- mice 5 min after administration, with limited effects on non-social behaviours. Chronic (8-17 days) OT maintained rescuing effects in Oprm1 null mice but was deleterious in wild-type mice. Finally, improvements in the social behaviour of Oprm1-/- mice were greater and longer lasting when OT was administered in a social context. Under these conditions, the expression of OT and vasopressin receptor genes, as well as marker genes of striatal projection neurons, was suppressed. We detected no sex difference in OT effects. Our results highlight the importance of considering dosage and social context when evaluating the effects of OT treatment in ASD.

Differential temporal decline of cerebral oxytocin and μ-opioid receptor density during the aging process in mice

Aging is often associated with changes in social, sexual, emotional and pain functioning, as well as with the increased prevalence of certain psychopathologies. However, the neurodevelopmental basis underpinning these age-related changes remains to be determined. Considering the key roles of oxytocin (OTR) and μ-opioid (MOPr) receptor systems in regulating social, sexual, pain, reward and emotional processing, it seems plausible that they are also implicated in age-related behavioural alterations. Although the ontogeny of both receptors has been well characterized in rodent brains from early development till adulthood, little is known concerning the neuroadaptations occurring from middle age to old age. Therefore, we mapped the neuroadaptations in OTR and MOPr in the brains of mice at those developmental endpoints. Quantitative OTR and MOPr autoradiographic binding was carried out in the brains of male mice at 2, 6, 9, 12 and 18 months of age. A significant whole brain decline in OTR density was detected between 2 and 6 months of age, with no additional decline thereafter. Interestingly, for MOPrs, the decline in density was not detected until 9 months of age. Region-specific age-related decline in OTR density was concentrated in the lateral anterior olfactory nuclei (AOL) and, for MOPr, in the AOL and the nucleus accumbens for MOPr. Identifying the tipping point of these age-related variations in both receptors may assist with our understanding of the neurobiology underlining age-related changes in social, pain and emotional functioning/processing. It may also help us target interventions to specific developmental windows to abrogate certain age-related psychopathologies.

Deciphering autism heterogeneity: a molecular stratification approach in four mouse models

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by impairments in social interaction and communication, as well as restrained or stereotyped behaviors. The inherent heterogeneity within the autism spectrum poses challenges for developing effective pharmacological treatments targeting core features. Successful clinical trials require the identification of robust markers to enable patient stratification. In this study, we identified molecular markers within the oxytocin and immediate early gene families across five interconnected brain structures of the social circuit. We used wild-type and four heterogeneous mouse models, each exhibiting unique autism-like behaviors modeling the autism spectrum. While dysregulations in the oxytocin family were model-specific, immediate early genes displayed widespread alterations, reflecting global changes across the four models. Through integrative analysis, we identified Egr1, Foxp1, Homer1a, Oxt, and Oxtr as five robust and discriminant molecular markers that allowed the successful stratification of the four models. Importantly, our stratification demonstrated predictive values when challenged with a fifth mouse model or identifying subgroups of mice potentially responsive to oxytocin treatment. Beyond providing insights into oxytocin and immediate early gene mRNA dynamics, this proof-of-concept study represents a significant step toward the potential stratification of individuals with ASD. This work has implications for the success of clinical trials and the development of personalized medicine in autism.

Endogenous mu-opioid modulation of social connection in humans: a systematic review and meta-analysis

Social bonding, essential for health and survival in all social species, depends on mu-opioid signalling in non-human mammals. A growing neuroimaging and psychopharmacology literature also implicates mu-opioids in human social connectedness. To determine the role of mu-opioids for social connectedness in healthy humans, we conducted a preregistered ( https://osf.io/x5wmq ) multilevel random-effects meta-analysis of randomised double-blind placebo-controlled opioid antagonist studies. We included data from 8 publications and 2 unpublished projects, totalling 17 outcomes (N = 455) sourced from a final literature search in Web of Science, Scopus, PubMed and EMBASE on October 12, 2023, and through community contributions. All studies used naltrexone (25-100 mg) to block the mu-opioid system and measured social connectedness by self-report. Opioid antagonism slightly reduced feelings of social connectedness (Hedges' g [95% CI) = -0.20] [-0.32, -0.07]. Results were highly consistent within and between studies (I2 = 23%). However, there was some indication of bias in favour of larger effects among smaller studies (Egger's test: B = -2.16, SE = 0.93, z = -2.33, p = 0.02), and publication bias analysis indicated that the effect of naltrexone might be overestimated. The results clearly demonstrate that intact mu-opioid signalling is not essential for experiencing social connectedness, as robust feelings of connectedness are evident even during full pharmacological mu-opioid blockade. Nevertheless, antagonism reduced measures of social connection, consistent with a modulatory role of mu-opioids for human social connectedness. The modest effect size relative to findings in non-human animals, could be related to differences in measurement (subjective human responses versus behavioural/motivation indices in animals), species specific neural mechanisms, or naltrexone effects on other opioid receptor subtypes. In sum, these results help explain how mu-opioid dysregulation and social disconnection can contribute to disability, and conversely-how social connection can buffer risk of ill health.

The neurobiological mechanisms underlying the effects of exercise interventions in autistic individuals

Autism spectrum disorder is a pervasive and heterogeneous neurodevelopmental condition characterized by social communication difficulties and rigid, repetitive behaviors. Owing to the complex pathogenesis of autism, effective drugs for treating its core features are lacking. Nonpharmacological approaches, including education, social-communication, behavioral and psychological methods, and exercise interventions, play important roles in supporting the needs of autistic individuals. The advantages of exercise intervention, such as its low cost, easy implementation, and high acceptance, have garnered increasing attention. Exercise interventions can effectively improve the core features and co-occurring conditions of autism, but the underlying neurobiological mechanisms are unclear. Abnormal changes in the gut microbiome, neuroinflammation, neurogenesis, and synaptic plasticity may individually or interactively be responsible for atypical brain structure and connectivity, leading to specific autistic experiences and characteristics. Interestingly, exercise can affect these biological processes and reshape brain network connections, which may explain how exercise alleviates core features and co-occurring conditions in autistic individuals. In this review, we describe the definition, diagnostic approach, epidemiology, and current support strategies for autism; highlight the benefits of exercise interventions; and call for individualized programs for different subtypes of autistic individuals. Finally, the possible neurobiological mechanisms by which exercise improves autistic features are comprehensively summarized to inform the development of optimal exercise interventions and specific targets to meet the needs of autistic individuals.

VTA μ-opioidergic neurons facilitate low sociability in protracted opioid withdrawal

Opioids initiate dynamic maladaptation in brain reward and affect circuits that occur throughout chronic exposure and withdrawal that persist beyond cessation. Protracted withdrawal is characterized by negative affective behaviors such as heightened anxiety, irritability, dysphoria, and anhedonia, which pose a significant risk factor for relapse. While the ventral tegmental area (VTA) and mu-opioid receptors (MORs) are critical for opioid reinforcement, the specific contributions of VTAMOR neurons in mediating protracted withdrawal-induced negative affect is not fully understood. In our study, we elucidate the role of VTAMOR neurons in mediating negative affect and altered brain-wide neuronal activities following opioid exposure and withdrawal in male and female mice. Utilizing a chronic oral morphine administration model, we observe increased social deficit, anxiety-related, and despair-like behaviors during protracted withdrawal. VTAMOR neurons show heightened neuronal FOS activation at the onset of withdrawal and connect to an array of brain regions that mediate reward and affective processes. Viral re-expression of MORs selectively within the VTA of MOR knockout mice demonstrates that the disrupted social interaction observed during protracted withdrawal is facilitated by this neural population, without affecting other protracted withdrawal behaviors. Lastly, VTAMORs contribute to heightened neuronal FOS activation in the anterior cingulate cortex (ACC) in response to an acute morphine challenge, suggesting their unique role in modulating ACC-specific neuronal activity. These findings identify VTAMOR neurons as critical modulators of low sociability during protracted withdrawal and highlight their potential as a mechanistic target to alleviate negative affective behaviors associated with opioid withdrawal.

Effect of intrahippocampal microinjection of VU0155041, a positive allosteric modulator of mGluR4, on long term potentiation in a valproic acid-induced autistic male rat model

The precise cause of autism spectrum disorder (ASD) is not fully understood. Despite the involvement of glutamatergic dysregulation in autism, the specific contribution of mGlu4 receptors to synaptic plasticity remains unclear. Using the positive allosteric modulator VU0155041, we aimed to restore long-term potentiation (LTP) in the perforant path-dentate gyrus (PP-DG) pathway in VPA-induced autistic rat model. High-frequency stimulation was applied to the PP-DG synapse to induce LTP, while the VU0155041 was administered into the DG. Unexpectedly, VU0155041 failed to alleviate the observed LTP reduction in VPA-exposed rats, further resulting in a significant decrease in population spike LTP. This unexpected outcome prompts discussion on the complex nature of mGlu4 receptor modulation, highlighting potential interference with physiological processes underlying synaptic plasticity.

The NMDA receptor modulator zelquistinel durably relieves behavioral deficits in three mouse models of autism spectrum disorder

Autism spectrum disorders (ASD) are complex neurodevelopmental disorders characterized by deficient social communication and interaction together with restricted, stereotyped behaviors. Currently approved treatments relieve comorbidities rather than core symptoms. Since excitation/inhibition balance and synaptic plasticity are disrupted in ASD, molecules targeting excitatory synaptic transmission appear as highly promising candidates to treat this pathology. Among glutamatergic receptors, the NMDA receptor has received particular attention through the last decade to develop novel allosteric modulators. Here, we show that positive NMDA receptor modulation by zelquistinel, a spirocyclic β-lactam platform chemical, relieves core symptoms in two genetic and one environmental mouse models of ASD. A single oral dose of zelquistinel rescued, in a dose-response manner, social deficits and stereotypic behavior in Shank3Δex13-16-/- mice while chronic intraperitoneal administration promoted a long-lasting relief of such autistic-like features in these mice. Subchronic oral mid-dose zelquistinel treatment demonstrated durable effects in Shank3Δex13-16-/-, Fmr1-/- and in utero valproate-exposed mice. Carry-over effects were best maintained in the Fmr1 null mouse model, with social parameters being still fully recovered two weeks after treatment withdrawal. Among recently developed NMDA receptor subunit modulators, zelquistinel displays a promising therapeutic potential to relieve core symptoms in ASD patients, with oral bioavailability and long-lasting effects boding well for clinical applications. Efficacy in three mouse models with different etiologies supports high translational value. Further, this compound represents an innovative pharmacological tool to investigate plasticity mechanisms underlying behavioral deficits in animal models of ASD.

Balance Between Projecting Neuronal Populations of the Nucleus Accumbens Controls Social Behavior in Mice

BACKGROUND

Deficient social interactions are a hallmark of major neuropsychiatric disorders, and accumulating evidence points to altered social reward and motivation as key underlying mechanisms of these pathologies. In the present study, we further explored the role of the balance of activity between D1 and D2 receptor-expressing striatal projection neurons (D1R- and D2R-SPNs) in the control of social behavior, challenging the hypothesis that excessive D2R-SPN activity, rather than deficient D1R-SPN activity, compromises social behavior.

METHODS

We selectively ablated D1R- and D2R-SPNs using an inducible diphtheria toxin receptor-mediated cell targeting strategy and assessed social behavior as well as repetitive/perseverative behavior, motor function, and anxiety levels. We tested the effects of optogenetic stimulation of D2R-SPNs in the nucleus accumbens (NAc) and pharmacological compounds repressing D2R-SPN.

RESULTS

Targeted deletion of D1R-SPNs in the NAc blunted social behavior in mice, facilitated motor skill learning, and increased anxiety levels. These behaviors were normalized by pharmacological inhibition of D2R-SPN, which also repressed transcription in the efferent nucleus, the ventral pallidum. Ablation of D1R-SPNs in the dorsal striatum had no impact on social behavior but impaired motor skill learning and decreased anxiety levels. Deletion of D2R-SPNs in the NAc produced motor stereotypies but facilitated social behavior and impaired motor skill learning. We mimicked excessive D2R-SPN activity by optically stimulating D2R-SPNs in the NAc and observed a severe deficit in social interaction that was prevented by D2R-SPN pharmacological inhibition.

CONCLUSIONS

Repressing D2R-SPN activity may represent a promising therapeutic strategy to relieve social deficits in neuropsychiatric disorders.

Effects of ketamine on rat social behavior as analyzed by DeepLabCut and SimBA deep learning algorithms

Traditional methods of rat social behavior assessment are extremely time-consuming and susceptible to the subjective biases. In contrast, novel digital techniques allow for rapid and objective measurements. This study sought to assess the feasibility of implementing a digital workflow to compare the effects of (R,S)-ketamine and a veterinary ketamine preparation Vetoquinol (both at 20 mg/kg) on the social behaviors of rat pairs. Historical and novel videos were used to train the DeepLabCut neural network. The numerical data generated by DeepLabCut from 14 video samples, representing various body parts in time and space were subjected to the Simple Behavioral Analysis (SimBA) toolkit, to build classifiers for 12 distinct social and non-social behaviors. To validate the workflow, previously annotated by the trained observer historical videos were analyzed with SimBA classifiers, and regression analysis of the total time of social interactions yielded R 2 = 0.75, slope 1.04; p < 0.001 (N = 101). Remarkable similarities between human and computer annotations allowed for using the digital workflow to analyze 24 novel videos of rats treated with vehicle and ketamine preparations. Digital workflow revealed similarities in the reduction of social behavior by both compounds, and no substantial differences between them. However, the digital workflow also demonstrated ketamine-induced increases in self-grooming, increased transitions from social contacts to self-grooming, and no effects on adjacent lying time. This study confirms and extends the utility of deep learning in analyzing rat social behavior and highlights its efficiency and objectivity. It provides a faster and objective alternative to human workflow.

Stress-Induced Changes in the Endogenous Opioid System Cause Dysfunction of Pain and Emotion Regulation

Early life stress, such as child abuse and neglect, and psychosocial stress in adulthood are risk factors for psychiatric disorders, including depression and anxiety. Furthermore, exposure to these stresses affects the sensitivity to pain stimuli and is associated with the development of chronic pain. However, the mechanisms underlying the pathogenesis of stress-induced depression, anxiety, and pain control remain unclear. Endogenous opioid signaling is reportedly associated with analgesia, reward, addiction, and the regulation of stress responses and anxiety. Stress alters the expression of various opioid receptors in the central nervous system and sensitivity to opioid receptor agonists and antagonists. μ-opioid receptor-deficient mice exhibit attachment disorders and autism-like behavioral expression patterns, while those with δ-opioid receptor deficiency exhibit anxiety-like behavior. In contrast, deficiency and antagonists of the κ-opioid receptor suppress the stress response. These findings strongly suggest that the expression and dysfunction of the endogenous opioid signaling pathways are involved in the pathogenesis of stress-induced psychiatric disorders and chronic pain. In this review, we summarize the latest basic and clinical research studies on the effects of endogenous opioid signaling on early-life stress, psychosocial stress-induced psychiatric disorders, and chronic pain.

Genetic and epigenetic studies of opioid abuse disorder - the potential for future diagnostics

INTRODUCTION

Opioid use disorder (OUD) is a global problem that often begins with prescribed medications. The available treatment and maintenance plans offer solutions for the consumption rate by individuals leaving the outstanding problem of relapse, which is a major factor hindering the long-term efficacy of treatments.

AREAS COVERED

Understanding the neurobiology of addiction and relapse would help identifying the core causes of relapse and distinguish vulnerable from resilient individuals, which would lead to more targeted and effective treatment and provide diagnostics to screen individuals who have a propensity to OUD. In this review, we cover the neurobiology of the reward system highlighting the role of multiple brain regions and opioid receptors in the development of the disorder. We also review the current knowledge of the epigenetics of addiction and the available screening tools for aberrant use of opioids.

EXPERT OPINION

Relapse remains an anticipated limitation in the way of recovery even after long period of abstinence. This highlights the need for diagnostic tools that identify vulnerable patients and prevent the cycle of addiction. Finally, we discuss the limitations of the available screening tools and propose possible solutions for the discovery of addiction diagnostics.

The activation of mGluR4 rescues parallel fiber synaptic transmission and LTP, motor learning and social behavior in a mouse model of Fragile X Syndrome

BACKGROUND

Fragile X syndrome (FXS), the most common inherited intellectual disability, is caused by the loss of expression of the Fragile X Messenger Ribonucleoprotein (FMRP). FMRP is an RNA-binding protein that negatively regulates the expression of many postsynaptic as well as presynaptic proteins involved in action potential properties, calcium homeostasis and neurotransmitter release. FXS patients and mice lacking FMRP suffer from multiple behavioral alterations, including deficits in motor learning for which there is currently no specific treatment.

METHODS

We performed electron microscopy, whole-cell patch-clamp electrophysiology and behavioral experiments to characterise the synaptic mechanisms underlying the motor learning deficits observed in Fmr1KO mice and the therapeutic potential of positive allosteric modulator of mGluR4.

RESULTS

We found that enhanced synaptic vesicle docking of cerebellar parallel fiber to Purkinje cell Fmr1KO synapses was associated with enhanced asynchronous release, which not only prevents further potentiation, but it also compromises presynaptic parallel fiber long-term potentiation (PF-LTP) mediated by β adrenergic receptors. A reduction in extracellular Ca2+ concentration restored the readily releasable pool (RRP) size, basal synaptic transmission, β adrenergic receptor-mediated potentiation, and PF-LTP. Interestingly, VU 0155041, a selective positive allosteric modulator of mGluR4, also restored both the RRP size and PF-LTP in mice of either sex. Moreover, when injected into Fmr1KO male mice, VU 0155041 improved motor learning in skilled reaching, classical eyeblink conditioning and vestibuloocular reflex (VOR) tests, as well as the social behavior alterations of these mice.

LIMITATIONS

We cannot rule out that the activation of mGluR4s via systemic administration of VU0155041 can also affect other brain regions. Further studies are needed to stablish the effect of a specific activation of mGluR4 in cerebellar granule cells.

CONCLUSIONS

Our study shows that an increase in synaptic vesicles, SV, docking may cause the loss of PF-LTP and motor learning and social deficits of Fmr1KO mice and that the reversal of these changes by pharmacological activation of mGluR4 may offer therapeutic relief for motor learning and social deficits in FXS.

[Oxytocin and its receptor: molecular and therapeutic approaches]

It is known since the fifties that oxytocin is a neurohormone synthesized in the brain and released in blood circulation to trigger uterus contraction during delivery. It is also involved in milk ejection during breast-feeding. Over the past 25 years, many other central and peripheral functions have been discovered, in particular for attachment between child and parents as well as between individuals and interaction between a human being and its social group. Over this period, we have studied the functional supramolecular architecture of the hormone bound to its receptor. This information was used to design pharmacological probes and drug candidates. This led to the discovery of the first non-peptide oxytocin receptor full agonist. This molecule, LIT-001, restores social interaction in an animal model of autism and paves the way for a treatment of this neurodevelopmental disorder.

The mu opioid receptor and the orphan receptor GPR151 contribute to social reward in the habenula

The mu opioid receptor (MOR) and the orphan GPR151 receptor are inhibitory G protein coupled receptors that are enriched in the habenula, a small brain region involved in aversion processing, addiction and mood disorders. While MOR expression in the brain is widespread, GPR151 expression is restricted to the habenula. In a previous report, we created conditional ChrnB4-Cre × Oprm1fl/fl (so-called B4MOR) mice, where MORs are deleted specifically in Chrnb4-positive neurons restricted to the habenula, and shown a role for these receptors in naloxone aversion. Here we characterized the implication of habenular MORs in social behaviors. B4MOR-/- mice and B4MOR+/+ mice were compared in several social behavior measures, including the chronic social stress defeat (CSDS) paradigm, the social preference (SP) test and social conditioned place preference (sCPP). In the CSDS, B4MOR-/- mice showed lower preference for the social target (unfamiliar mouse of a different strain) at baseline, providing a first indication of deficient social interactions in mice lacking habenular MORs. In the SP test, B4MOR-/- mice further showed reduced sociability for an unfamiliar conspecific mouse. In the sCPP, B4MOR-/- mice also showed impaired place preference for their previous familiar littermates after social isolation. We next created and tested Gpr151-/- mice in the SP test, and also found reduced social preference compared to Gpr151+/+ mice. Altogether our results support the underexplored notion that the habenula regulates social behaviors. Also, our data suggest that the inhibitory habenular MOR and GPR151 receptors normally promote social reward, possibly by dampening the aversive habenula activity.

Mechanism of opioid addiction and its intervention therapy: Focusing on the reward circuitry and mu-opioid receptor

Opioid abuse and addiction have become a global pandemic, posing tremendous health and social burdens. The rewarding effects and the occurrence of withdrawal symptoms are the two mainstays of opioid addiction. Mu-opioid receptors (MORs), a member of opioid receptors, play important roles in opioid addiction, mediating both the rewarding effects of opioids and opioid withdrawal syndrome (OWS). The underlying mechanism of MOR-mediated opioid rewarding effects and withdrawal syndrome is of vital importance to understand the nature of opioid addiction and also provides theoretical basis for targeting MORs to treat drug addiction. In this review, we first briefly introduce the basic concepts of MORs, including their structure, distribution in the nervous system, endogenous ligands, and functional characteristics. We focused on the brain circuitry and molecular mechanism of MORs-mediated opioid reward and withdrawal. The neuroanatomical and functional elements of the neural circuitry of the reward system underlying opioid addiction were thoroughly discussed, and the roles of MOR within the reward circuitry were also elaborated. Furthermore, we interrogated the roles of MORs in OWS, along with the structural basis and molecular adaptions of MORs-mediated withdrawal syndrome. Finally, current treatment strategies for opioid addiction targeting MORs were also presented.

Chronic sodium bromide treatment relieves autistic-like behavioral deficits in three mouse models of autism

Autism Spectrum Disorders (ASD) are neurodevelopmental disorders whose diagnosis relies on deficient social interaction and communication together with repetitive behavior. To date, no pharmacological treatment has been approved that ameliorates social behavior in patients with ASD. Based on the excitation/inhibition imbalance theory of autism, we hypothesized that bromide ions, long used as an antiepileptic medication, could relieve core symptoms of ASD. We evaluated the effects of chronic sodium bromide (NaBr) administration on autistic-like symptoms in three genetic mouse models of autism: Oprm1^-/-, Fmr1^-/- and Shank3^Δex13-16-/- mice. We showed that chronic NaBr treatment relieved autistic-like behaviors in these three models. In Oprm1^-/- mice, these beneficial effects were superior to those of chronic bumetanide administration. At transcriptional level, chronic NaBr in Oprm1 null mice was associated with increased expression of genes coding for chloride ions transporters, GABA_A receptor subunits, oxytocin and mGlu4 receptor. Lastly, we uncovered synergistic alleviating effects of chronic NaBr and a positive allosteric modulator (PAM) of mGlu4 receptor on autistic-like behavior in Oprm1^-/- mice. We evidenced in heterologous cells that bromide ions behave as PAMs of mGlu4, providing a molecular mechanism for such synergy. Our data reveal the therapeutic potential of bromide ions, alone or in combination with a PAM of mGlu4 receptor, for the treatment of ASDs.

The Opioid System in Depression

Opioid receptors are widely distributed throughout the brain and play an essential role in modulating aspects of human mood, reward, and well-being. Accumulating evidence indicates the endogenous opioid system is dysregulated in depression and that pharmacological modulators of mu, delta, and kappa opioid receptors hold potential for the treatment of depression. Here we review animal and clinical data, highlighting evidence to support: dysregulation of the opioid system in depression, evidence for opioidergic modulation of behavioural processes and brain regions associated with depression, and evidence for opioidergic modulation in antidepressant responses. We evaluate clinical trials that have examined the safety and efficacy of opioidergic agents in depression and consider how the opioid system may be involved in the effects of other treatments, including ketamine, that are currently understood to exert antidepressant effects through non-opioidergic actions. Finally, we explore key neurochemical and molecular mechanisms underlying the potential therapeutic effects of opioid system engagement, that together provides a rationale for further investigation into this relevant target in the treatment of depression.

Pu-erh tea increases the metabolite Cinnabarinic acid to improve circadian rhythm disorder-induced obesity

Obesity is one of the circadian rhythm disorders (CRD)-mediated metabolic disorder syndromes. Pu-erh tea is a viable dietary intervention for CRD, however its effect on CRD-induced obesity is unclear. Here, we found that Pu-erh tea improved obesity in CRD-induced mice, which stemmed from the production of Cinnabarinic acid (CA). CA promoted adipose tissue lipolysis and thermogenic response (HSL, ATGL, Pparα, CKB, UCP1) and increased adipocyte sensitivity to hormones and neurotransmitters by targeting the expression of adipose tissue receptor proteins (Q6KAT8, P51655, A2AKQ0, M0QWX7, Q6ZQ33, and mGluR4). This improved mitochondrial activity and facilitated adipose tissue metabolic processes, thereby accelerating glucolipid metabolism. Also, CA-induced alterations in gut microbes and short-chain fatty acids further improved CRD-mediated lipid accumulation. These results suggest that the increase of CA caused by Pu-erh tea, targeted to adipose tissue via the metabolite-blood circulation-adipose tissue axis, maybe a key mechanism for reducing the development of CRD-induced obesity.

The partial µ-opioid agonist buprenorphine in autism spectrum disorder: a case report

Background

There are currently no approved medications for impaired social cognition and function, core symptoms of autism spectrum disorder. We describe marked improvement of these symptoms with long-term low-dose administration of the partial µ-opioid agonist buprenorphine. We discuss these observations in the context of a role for endogenous opioid systems in social attachment, and theories integrating those findings mechanistically with autism spectrum disorder.

Case presentation

M, a 43-year-old Caucasian male, is medically healthy. Despite social difficulties since childhood, he completed high school with better-than-average grades, but failed university education. A psychiatric evaluation in his twenties diagnosed attention deficit hyperactivity disorder but also noted symptoms of coexisting autism spectrum disorder. M accidentally came across buprenorphine in his late twenties and experienced progressively improved social functioning on a low daily dosage (0.5–1.0 mg/day), an effect maintained for 15 years. He lived independently and maintained a part-time occupation. After abrupt discontinuation of treatment, his autistic symptoms returned, and function deteriorated. Following evaluation by our team, buprenorphine was resumed, with gradual return to prior level of functioning. An attempt to formally evaluate M both on and off medication was agreed with him and approved by the Swedish Ethics Authority, but medication had to be resumed when the patient worsened following discontinuation.

Conclusions

According to the µ-opioid receptor balance model, both excessive and deficient μ-receptor activity may negatively influence social behavior, and accordingly both opioid agonist and opioid antagonist treatment may be able to improve social functioning, depending on an individual’s opioid tone before treatment. Our case report is consistent with these hypotheses, and given the extensive unmet medical needs in individuals with autism spectrum disorders, randomized controlled trial appears warranted.

SEX-DEPENDENT IMPACT OF MICROBIOTA STATUS ON CEREBRAL μ -OPIOID RECEPTOR DENSITY IN FISCHER RATS

μ‐opioid receptors (MOPr) play a critical role in social play, reward and pain, in a sex‐ and age‐dependent manner. There is evidence to suggest that sex and age differences in brain MOPr density may be responsible for this variability; however, little is known about the factors driving these differences in cerebral MOPr density. Emerging evidence highlights gut microbiota's critical influence and its bidirectional interaction with the brain on neurodevelopment. Therefore, we aimed to determine the impact of gut microbiota on MOPr density in male and female brains at different developmental stages. Quantitative [³H]DAMGO autoradiographic binding was carried out in the forebrain of male and female conventional (CON) and germ‐free (GF) rats at postnatal days (PND) 8, 22 and 116–150. Significant ‘microbiota status X sex’, ‘age X brain region’ interactions and microbiota status‐ and age‐dependent effects on MOPr binding were uncovered. Microbiota status influenced MOPr levels in males but not females, with higher MOPr levels observed in GF versus CON rats overall regions and age groups. In contrast, no overall sex differences were observed in GF or CON rats. Interestingly, within‐age planned comparison analysis conducted in frontal cortical and brain regions associated with reward revealed that this microbiota effect was restricted only to PND22 rats. Thus, this pilot study uncovers the critical sex‐dependent role of gut microbiota in regulating cerebral MOPr density, which is restricted to the sensitive developmental period of weaning. This may have implications in understanding the importance of microbiota during early development on opioid signalling and associated behaviours.

Autistic Traits and Empathy for Others' Pain Among the General Population: Test of the Mediating Effects of First-Hand Pain Sensitivity

Autism spectrum disorders (ASD) are characterized by reduced pain empathy-a process that is grounded in first-hand pain perception. Because autistic traits are continuously distributed in the general population, we hypothesized that first-hand pain sensitivity would mediate the link between autistic traits and pain empathy. After controlling for alexithymia, higher autistic traits were associated with lower cognitive and emotional empathy in response to others' pain, as well as lower sensitivity to cold and heat pain (higher cold pain tolerance and lower laser heat pain-intensity ratings). Importantly, pain sensitivity fully mediated the link between autistic traits and pain empathy. These findings highlight the role of atypical first-hand pain sensitivity in the lack of pain empathy observed in people with high autistic traits or ASD.

Role of Oxytocin and Vasopressin in Neuropsychiatric Disorders: Therapeutic Potential of Agonists and Antagonists

Oxytocin (OT) and vasopressin (AVP) are hypothalamic neuropeptides classically associated with their regulatory role in reproduction, water homeostasis, and social behaviors. Interestingly, this role has expanded in recent years and has positioned these neuropeptides as therapeutic targets for various neuropsychiatric diseases such as autism, addiction, schizophrenia, depression, and anxiety disorders. Due to the chemical-physical characteristics of these neuropeptides including short half-life, poor blood-brain barrier penetration, promiscuity for AVP and OT receptors (AVP-R, OT-R), novel ligands have been developed in recent decades. This review summarizes the role of OT and AVP in neuropsychiatric conditions, as well as the findings of different OT-R and AVP-R agonists and antagonists, used both at the preclinical and clinical level. Furthermore, we discuss their possible therapeutic potential for central nervous system (CNS) disorders.

μ-Opioid Receptor (Oprm1) Copy Number Influences Nucleus Accumbens Microcircuitry and Reciprocal Social Behaviors

The μ-opioid receptor regulates reward derived from both drug use and natural experiences, including social interaction, through actions in the nucleus accumbens. Here, we studied nucleus accumbens microcircuitry and social behavior in male and female mice with heterozygous genetic knockout of the μ-opioid receptor (Oprm1+/-). This genetic condition models the partial reduction of μ-opioid receptor signaling reported in several neuropsychiatric disorders. We first analyzed inhibitory synapses in the nucleus accumbens, using methods that differentiate between medium spiny neurons (MSNs) expressing the D1 or D2 dopamine receptor. Inhibitory synaptic transmission was increased in D2-MSNs of male mutants, but not female mutants, while the expression of gephyrin mRNA and the density of inhibitory synaptic puncta at the cell body of D2-MSNs was increased in mutants of both sexes. Some of these changes were more robust in Oprm1+/- mutants than Oprm1-/- mutants, demonstrating that partial reductions of μ-opioid signaling can have large effects. At the behavioral level, social conditioned place preference and reciprocal social interaction were diminished in Oprm1+/- and Oprm1-/- mutants of both sexes. Interaction with Oprm1 mutants also altered the social behavior of wild-type test partners. We corroborated this latter result using a social preference task, in which wild-type mice preferred interactions with another typical mouse over Oprm1 mutants. Surprisingly, Oprm1-/- mice preferred interactions with other Oprm1-/- mutants, although these interactions did not produce a conditioned place preference. Our results support a role for partial dysregulation of μ-opioid signaling in social deficits associated with neuropsychiatric conditions.SIGNIFICANCE STATEMENT Activation of the μ-opioid receptor plays a key role in the expression of normal social behaviors. In this study, we examined brain function and social behavior of female and male mice, with either partial or complete genetic deletion of μ-opioid receptor expression. We observed abnormal social behavior following both genetic manipulations, as well as changes in the structure and function of synaptic input to a specific population of neurons in the nucleus accumbens, which is an important brain region for social behavior. Synaptic changes were most robust when μ-opioid receptor expression was only partially lost, indicating that small reductions in μ-opioid receptor signaling can have a large impact on brain function and behavior.

Cariprazine alleviates core behavioral deficits in the prenatal valproic acid exposure model of autism spectrum disorder

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication and interaction and restricted, repetitive behaviors. The unmet medical need in ASD is considerable since there is no approved pharmacotherapy for the treatment of these deficits in social communication, interaction, and behavior. Cariprazine, a dopamine D₃-preferring D₃/D₂ receptor partial agonist, is already approved for the treatment of schizophrenia and bipolar I disorder in adults; investigation in patients with ASD is warranted.

OBJECTIVES

The aim of this study was to investigate the effects of cariprazine, compared with risperidone and aripiprazole, in the rat prenatal valporic acid (VPA) exposure model on behavioral endpoints representing the core and associated symptoms of ASD.

METHODS

To induce the ASD model, time-mated Wistar rat dams were treated with VPA during pregnancy. Male offspring were assigned to groups and studied in a behavioral test battery at different ages, employing social play, open field, social approach-avoidance, and social recognition memory tests. Animals were dosed orally, once a day for 8 days, with test compounds (cariprazine, risperidone, aripiprazole) or vehicle before behavioral assessment.

RESULTS

Cariprazine showed dose-dependent efficacy on all behavioral endpoints. In the social play paradigm, only cariprazine was effective. On the remaining behavioral endpoints, including the reversal of hyperactivity, risperidone and aripiprazole displayed similar efficacy to cariprazine.

CONCLUSIONS

In the present study, cariprazine effectively reversed core behavioral deficits and hyperactivity present in juvenile and young adult autistic-like rats. These findings indicate that cariprazine may be useful in the treatment of ASD symptoms.

The microbial metabolite p-Cresol induces autistic-like behaviors in mice by remodeling the gut microbiota

BACKGROUND

Autism spectrum disorders (ASD) are associated with dysregulation of the microbiota-gut-brain axis, changes in microbiota composition as well as in the fecal, serum, and urine levels of microbial metabolites. Yet a causal relationship between dysregulation of the microbiota-gut-brain axis and ASD remains to be demonstrated. Here, we hypothesized that the microbial metabolite p-Cresol, which is more abundant in ASD patients compared to neurotypical individuals, could induce ASD-like behavior in mice.

RESULTS

Mice exposed to p-Cresol for 4 weeks in drinking water presented social behavior deficits, stereotypies, and perseverative behaviors, but no changes in anxiety, locomotion, or cognition. Abnormal social behavior induced by p-Cresol was associated with decreased activity of central dopamine neurons involved in the social reward circuit. Further, p-Cresol induced changes in microbiota composition and social behavior deficits could be transferred from p-Cresol-treated mice to control mice by fecal microbiota transplantation (FMT). We also showed that mice transplanted with the microbiota of p-Cresol-treated mice exhibited increased fecal p-Cresol excretion, compared to mice transplanted with the microbiota of control mice. In addition, we identified possible p-Cresol bacterial producers. Lastly, the microbiota of control mice rescued social interactions, dopamine neurons excitability, and fecal p-Cresol levels when transplanted to p-Cresol-treated mice.

CONCLUSIONS

The microbial metabolite p-Cresol induces selectively ASD core behavioral symptoms in mice. Social behavior deficits induced by p-Cresol are dependant on changes in microbiota composition. Our study paves the way for therapeutic interventions targeting the microbiota and p-Cresol production to treat patients with ASD. Video abstract.

Mu-opioid receptor agonism differentially alters social behaviour and immediate early gene expression in male adolescent rats prenatally exposed to valproic acid versus controls

Mu-opioid receptors (MOPs) mediate and modulate social reward and social interaction. However, few studies have examined the functionality of this system in rodent models of social impairment. Deficits in social motivation and cognition are observed in rodents following pre-natal exposure to the anti-epileptic valproic acid (VPA), however it is not known whether MOP functionality is altered in these animals. The present study examined the effects of acute administration of the prototypical MOP agonist morphine (1 mg/kg) on social behavioural responding in the 3-chamber test and immediate early gene expression in adolescent rats (postnatal day 28-43) prenatally exposed to VPA vs saline-exposed controls. Pharmacokinetic analysis of morphine concentration, MOP binding and expression were also examined. The data revealed that sociability and social novelty preference in the 3-chamber test were reduced in rats prenatally exposed to VPA compared to saline-exposed control counterparts. Morphine reduced both sociability and social novelty preference behaviour in saline-, but not VPA-, exposed rats. Analysis of immediate early gene expression revealed that morphine reduced the expression of cfos in the prefrontal cortex of both saline- and VPA-exposed rats and reduced expression of cfos and junb in the hippocampus of VPA-exposed rats only. Pharmacokinetic analysis revealed similar concentrations of morphine in the plasma and brain of both saline- and VPA-exposed rats and similar thalamic MOP occupancy levels. Gene and protein expression of MOP in prefrontal cortex and hippocampus did not differ between saline and VPA-exposed rats. These data indicate differential effects of morphine on social responding and immediate early gene expression in the hippocampus of VPA-exposed rats compared with saline-exposed controls. This study provides support for altered MOP functionality in rats prenatally exposed to VPA, which may underlie the social deficits observed in the model.

Facilitating mGluR4 activity reverses the long-term deleterious consequences of chronic morphine exposure in male mice

Understanding the neurobiological underpinnings of abstinence from drugs of abuse is critical to allow better recovery and ensure relapse prevention in addicted subjects. By comparing the long-term transcriptional consequences of morphine and cocaine exposure, we identified the metabotropic glutamate receptor subtype 4 (mGluR4) as a promising pharmacological target in morphine abstinence. We evaluated the behavioral and molecular effects of facilitating mGluR4 activity in abstinent mice. Transcriptional regulation of marker genes of medium spiny neurons (MSNs) allowed best discriminating between 4-week morphine and cocaine abstinence in the nucleus accumbens (NAc). Among these markers, Grm4, encoding mGluR4, displayed down-regulated expression in the caudate putamen and NAc of morphine, but not cocaine, abstinent mice. Chronic administration of the mGluR4 positive allosteric modulator (PAM) VU0155041 (2.5 and 5 mg/kg) rescued social behavior, normalized stereotypies and anxiety and blunted locomotor sensitization in morphine abstinent mice. This treatment improved social preference but increased stereotypies in cocaine abstinent mice. Finally, the beneficial behavioral effects of VU0155041 treatment in morphine abstinent mice were correlated with restored expression of key MSN and neural activity marker genes in the NAc. This study reports that chronic administration of the mGluR4 PAM VU0155041 relieves long-term deleterious consequences of morphine exposure. It illustrates the neurobiological differences between opiate and psychostimulant abstinence and points to pharmacological repression of excessive activity of D2-MSNs in the NAc as a promising therapeutic lever in drug addiction.

16p11.2 deletion is associated with hyperactivation of human iPSC-derived dopaminergic neuron networks and is rescued by RHOA inhibition in vitro

Reciprocal copy number variations (CNVs) of 16p11.2 are associated with a wide spectrum of neuropsychiatric and neurodevelopmental disorders. Here, we use human induced pluripotent stem cells (iPSCs)-derived dopaminergic (DA) neurons carrying CNVs of 16p11.2 duplication (16pdup) and 16p11.2 deletion (16pdel), engineered using CRISPR-Cas9. We show that 16pdel iPSC-derived DA neurons have increased soma size and synaptic marker expression compared to isogenic control lines, while 16pdup iPSC-derived DA neurons show deficits in neuronal differentiation and reduced synaptic marker expression. The 16pdel iPSC-derived DA neurons have impaired neurophysiological properties. The 16pdel iPSC-derived DA neuronal networks are hyperactive and have increased bursting in culture compared to controls. We also show that the expression of RHOA is increased in the 16pdel iPSC-derived DA neurons and that treatment with a specific RHOA-inhibitor, Rhosin, rescues the network activity of the 16pdel iPSC-derived DA neurons. Our data suggest that 16p11.2 deletion-associated iPSC-derived DA neuron hyperactivation can be rescued by RHOA inhibition.

The neurochemistry of social reward during development: What have we learned from rodent models?

Social rewards are fundamental to survival and overall health. Several studies suggest that adequate social stimuli during early life are critical for developing appropriate socioemotional and cognitive skills, whereas adverse social experiences negatively affect the proper development of brain and behavior, by increasing the susceptibility to develop neuropsychiatric conditions. Therefore, a better understanding of the neural mechanisms underlying social interactions, and their rewarding components in particular, is an important challenge of current neuroscience research. In this context, preclinical research has a crucial role: Animal models allow to investigate the neurobiological aspects of social reward in order to shed light on possible neurochemical alterations causing aberrant social reward processing in neuropsychiatric diseases, and they allow to test the validity and safety of innovative therapeutic strategies. Here, we discuss preclinical research that has investigated the rewarding properties of two forms of social interaction that occur in different phases of the lifespan of mammals, that is, mother-infant interaction and social interactions with peers, by focusing on the main neurotransmitter systems mediating their rewarding components. Together, the research performed so far helped to elucidate the mechanisms of social reward and its psychobiological components throughout development, thus increasing our understanding of the neurobiological substrates sustaining social functioning in health conditions and social dysfunction in major psychiatric disorders.

Seasonal Variation in the Brain μ-Opioid Receptor Availability

Seasonal rhythms influence mood and sociability. The brain μ-opioid receptor (MOR) system modulates a multitude of seasonally varying socioemotional functions, but its seasonal variation remains elusive with no previously reported in vivo evidence. Here, we first conducted a cross-sectional study with previously acquired human [¹¹C]carfentanil PET imaging data (132 male and 72 female healthy subjects) to test whether there is seasonal variation in MOR availability. We then investigated experimentally whether seasonal variation in daylength causally influences brain MOR availability in rats. Rats (six male and three female rats) underwent daylength cycle simulating seasonal changes; control animals (two male and one female rats) were kept under constant daylength. Animals were scanned repeatedly with [¹¹C]carfentanil PET imaging. Seasonally varying daylength had an inverted U-shaped functional relationship with brain MOR availability in humans. Brain regions sensitive to daylength spanned the socioemotional brain circuits, where MOR availability peaked during spring. In rats, MOR availabilities in the brain neocortex, thalamus, and striatum peaked at intermediate daylength. Varying daylength also affected the weight gain and stress hormone levels. We conclude that cerebral MOR availability in humans and rats shows significant seasonal variation, which is predominately associated with seasonal photoperiodic variation. Given the intimate links between MOR signaling and socioemotional behavior, these results suggest that the MOR system might underlie seasonal variation in human mood and social behavior.SIGNIFICANCE STATEMENT Seasonal rhythms influence emotion and sociability. The central μ-opioid receptor (MOR) system modulates numerous seasonally varying socioemotional functions, but its seasonal variation remains elusive. Here we used positron emission tomography to show that MOR levels in both human and rat brains show daylength-dependent seasonal variation. The highest MOR availability was observed at intermediate daylengths. Given the intimate links between MOR signaling and socioemotional behavior, these results suggest that the MOR system might underlie seasonal variation in human mood and social behavior.

Risk of Substance Use Disorder and Its Associations With Comorbidities and Psychotropic Agents in Patients With Autism

IMPORTANCE

The risk of substance use disorder (SUD) in patients with autism spectrum disorder (ASD) remains unclear.

OBJECTIVE

To investigate the risk of SUD in patients with ASD and its associations with comorbidities, psychotropic agents (PAs), and mortality.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective, population-based, cohort study of 1 936 512 participants used data from the Taiwan National Health Insurance Research Database and was conducted from January 1, 2000, to December 31, 2015. Included participants attended at least 3 outpatient visits within the 1-year study period for symptomatic ASD as determined by the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnostic codes. Individuals diagnosed with ASD before 2000, those diagnosed with SUD before the first visit for ASD, and those with missing data were excluded from the analysis. Patients with ASD and non-ASD controls were matched 1:4 by age, sex, and index date.

EXPOSURES

Symptomatic ASD evaluated for at least 3 outpatient visits within the 1-year study period.

MAIN OUTCOMES AND MEASURES

Adjusted hazard ratios (aHRs) with 95% CIs for SUD, including alcohol use disorder (AUD) and drug use disorder (DUD), and the risk of mortality were calculated. Data were analyzed from March 1 to July 13, 2020.

RESULTS

A total of 6599 individuals with ASD (mean [SD] age, 11.9 [5.1] years; 5094 boys [77.2%]; mean [SD] follow-up period, 8.1 [8.3] years; median follow-up period, 4.3 [interquartile range [IQR], 2.3-5.3] years) and 26 396 controls (mean [SD] age, 12.1 [5.8] years; 20 376 boys [77.2%]; mean [SD] follow-up period, 8.6 [8.9] years; median follow-up period, 4.4 [IQR, 2.4-5.4] years) were enrolled in the study. According to multivariable-adjusted analysis, the aHRs for SUD (2.33; 95% CI, 1.89-2.87), AUD (2.07; 95% CI, 1.60-2.63), and DUD (3.00; 95% CI, 2.15-4.58) were significantly higher in the ASD group than in the non-ASD controls. The aHRs for SUD in the ASD subgroups with 1 PA (0.60; 95% CI, 0.43-0.66) and with multiple PAs (0.37; 95% CI, 0.28-0.49) were significantly lower than those in the ASD subgroup with no PAs. Comparisons between patients with ASD and non-ASD controls with the same comorbidities showed higher aHRs for SUD among patients with ASD (range, 1.17-2.55); moreover, the ASD subgroup not receiving any PAs had an aHR of 6.39 (95% CI, 5.11-7.87) for SUD when they had comorbid tic disorder and aHRs of 5.48 (95% CI, 5.12-5.70) for AUD and 5.42 (95% CI, 5.12-5.80) for DUD when they had comorbid impulse control disorder. The mortality risk was significantly higher in patients with ASD and concomitant SUD than in non-ASD controls without SUD (aHR, 3.17; 95% CI, 2.69-3.89).

CONCLUSIONS AND RELEVANCE

These findings suggest that patients with ASD are vulnerable to the development of SUD. Comorbid ASD and SUD were associated with an increase in mortality risk.

Cariprazine alleviates core behavioral deficits in the prenatal valproic acid exposure model of autism spectrum disorder

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication and interaction and restricted, repetitive behaviors. The unmet medical need in ASD is considerable since there is no approved pharmacotherapy for the treatment of these deficits in social communication, interaction, and behavior. Cariprazine, a dopamine D₃-preferring D₃/D₂ receptor partial agonist, is already approved for the treatment of schizophrenia and bipolar I disorder in adults; investigation in patients with ASD is warranted.

OBJECTIVES

The aim of this study was to investigate the effects of cariprazine, compared with risperidone and aripiprazole, in the rat prenatal valporic acid (VPA) exposure model on behavioral endpoints representing the core and associated symptoms of ASD.

METHODS

To induce the ASD model, time-mated Wistar rat dams were treated with VPA during pregnancy. Male offspring were assigned to groups and studied in a behavioral test battery at different ages, employing social play, open field, social approach-avoidance, and social recognition memory tests. Animals were dosed orally, once a day for 8 days, with test compounds (cariprazine, risperidone, aripiprazole) or vehicle before behavioral assessment.

RESULTS

Cariprazine showed dose-dependent efficacy on all behavioral endpoints. In the social play paradigm, only cariprazine was effective. On the remaining behavioral endpoints, including the reversal of hyperactivity, risperidone and aripiprazole displayed similar efficacy to cariprazine.

CONCLUSIONS

In the present study, cariprazine effectively reversed core behavioral deficits and hyperactivity present in juvenile and young adult autistic-like rats. These findings indicate that cariprazine may be useful in the treatment of ASD symptoms.

International Union of Basic and Clinical Pharmacology. CXI. Pharmacology, Signaling, and Physiology of Metabotropic Glutamate Receptors

Metabotropic glutamate (mGlu) receptors respond to glutamate, the major excitatory neurotransmitter in the mammalian brain, mediating a modulatory role that is critical for higher-order brain functions such as learning and memory. Since the first mGlu receptor was cloned in 1992, eight subtypes have been identified along with many isoforms and splice variants. The mGlu receptors are transmembrane-spanning proteins belonging to the class C G protein-coupled receptor family and represent attractive targets for a multitude of central nervous system disorders. Concerted drug discovery efforts over the past three decades have yielded a wealth of pharmacological tools including subtype-selective agents that competitively block or mimic the actions of glutamate or act allosterically via distinct sites to enhance or inhibit receptor activity. Herein, we review the physiologic and pathophysiological roles for individual mGlu receptor subtypes including the pleiotropic nature of intracellular signal transduction arising from each. We provide a comprehensive analysis of the in vitro and in vivo pharmacological properties of prototypical and commercially available orthosteric agonists and antagonists as well as allosteric modulators, including ligands that have entered clinical trials. Finally, we highlight emerging areas of research that hold promise to facilitate rational design of highly selective mGlu receptor-targeting therapeutics in the future. SIGNIFICANCE STATEMENT: The metabotropic glutamate receptors are attractive therapeutic targets for a range of psychiatric and neurological disorders. Over the past three decades, intense discovery efforts have yielded diverse pharmacological tools acting either competitively or allosterically, which have enabled dissection of fundamental biological process modulated by metabotropic glutamate receptors and established proof of concept for many therapeutic indications. We review metabotropic glutamate receptor molecular pharmacology and highlight emerging areas that are offering new avenues to selectively modulate neurotransmission.

Nuclear receptor corepressors in intellectual disability and autism

Autism spectrum disorder (ASD) is characterized by neurocognitive dysfunctions, such as impaired social interaction and language learning. Gene-environment interactions have a pivotal role in ASD pathogenesis. Nuclear receptor corepressors (NCORs) are transcription co-regulators physically associated with histone deacetylases (HDACs) and many known players in ASD etiology such as transducin β-like 1 X-linked receptor 1 and methyl-CpG binding protein 2. The epigenome-modifying NCOR complex is sensitive to many ASD risk factors, including HDAC inhibitor valproic acid and a variety of endocrine factors, xenobiotic chemicals, or metabolites that can directly bind to multiple nuclear receptors. Here, we review recent studies of NCORs in neurocognition using animal models and human genetics approaches. We discuss functional interplays between NCORs and other known players in ASD etiology. It is conceivable that the NCOR complex may bridge the in utero environmental risk factors of ASD with epigenetic remodeling and can serve as a converging point for many gene-environment interactions in the pathogenesis of ASD and intellectual disability.

Game theoretic centrality: a novel approach to prioritize disease candidate genes by combining biological networks with the Shapley value

Background

Complex human health conditions with etiological heterogeneity like Autism Spectrum Disorder (ASD) often pose a challenge for traditional genome-wide association study approaches in defining a clear genotype to phenotype model. Coalitional game theory (CGT) is an exciting method that can consider the combinatorial effect of groups of variants working in concert to produce a phenotype. CGT has been applied to associate likely-gene-disrupting variants encoded from whole genome sequence data to ASD; however, this previous approach cannot take into account for prior biological knowledge. Here we extend CGT to incorporate a priori knowledge from biological networks through a game theoretic centrality measure based on Shapley value to rank genes by their relevance–the individual gene’s synergistic influence in a gene-to-gene interaction network. Game theoretic centrality extends the notion of Shapley value to the evaluation of a gene’s contribution to the overall connectivity of its corresponding node in a biological network.

Results

We implemented and applied game theoretic centrality to rank genes on whole genomes from 756 multiplex autism families. Top ranking genes with the highest game theoretic centrality in both the weighted and unweighted approaches were enriched for pathways previously associated with autism, including pathways of the immune system. Four of the selected genes HLA-A, HLA-B, HLA-G, and HLA-DRB1–have also been implicated in ASD and further support the link between ASD and the human leukocyte antigen complex.

Conclusions

Game theoretic centrality can prioritize influential, disease-associated genes within biological networks, and assist in the decoding of polygenic associations to complex disorders like autism.

Opposing effects of antibiotics and germ-free status on neuropeptide systems involved in social behaviour and pain regulation

Background

Recent research has revealed that the community of microorganisms inhabiting the gut affects brain development, function and behaviour. In particular, disruption of the gut microbiome during critical developmental windows can have lasting effects on host physiology. Both antibiotic exposure and germ-free conditions impact the central nervous system and can alter multiple aspects of behaviour. Social impairments are typically displayed by antibiotic-treated and germ-free animals, yet there is a lack of understanding of the underlying neurobiological changes. Since the μ-opioid, oxytocin and vasopressin systems are key modulators of mammalian social behaviour, here we investigate the effect of experimentally manipulating the gut microbiome on the expression of these pathways.

Results

We show that social neuropeptide signalling is disrupted in germ-free and antibiotic-treated mice, which may contribute to the behavioural deficits observed in these animal models. The most notable finding is the reduction in neuroreceptor gene expression in the frontal cortex of mice administered an antibiotic cocktail post-weaning. Additionally, the changes observed in germ-free mice were generally in the opposite direction to the antibiotic-treated mice.

Conclusions

Antibiotic treatment when young can impact brain signalling pathways underpinning social behaviour and pain regulation. Since antibiotic administration is common in childhood and adolescence, our findings highlight the potential adverse effects that antibiotic exposure during these key neurodevelopmental periods may have on the human brain, including the possible increased risk of neuropsychiatric conditions later in life. In addition, since antibiotics are often considered a more amenable alternative to germ-free conditions, our contrasting results for these two treatments suggest that they should be viewed as distinct models.

Brain Opioid Activity and Oxidative Injury: Different Molecular Scenarios Connecting Celiac Disease and Autistic Spectrum Disorder

Celiac Disease (CD) is an immune-mediated disease triggered by the ingestion of wheat gliadin and related prolamins from other cereals, such as barley and rye. Immunity against these cereal-derived proteins is mediated by pro-inflammatory cytokines produced by both innate and adaptive system response in individuals unable to adequately digest them. Peptides generated in this condition are absorbed across the gut barrier, which in these patients is characterized by the deregulation of its permeability. Here, we discuss a possible correlation between CD and Autistic Spectrum Disorder (ASD) pathogenesis. ASD can be induced by an excessive and inappropriate brain opioid activity during the neonatal period. Cereal-derived peptides produced in celiac patients cross the blood-brain barrier and bind to endogenous opioid receptors interfering with neurotransmission and generating deleterious effects on brain maturation, learning and social relations. Moreover, an increase in oxidative stress and a decrease in the antioxidant capacity, as well as an extended mitochondrial impairment in the brain, could represent a possible connection between ASD and CD. Therefore, we critically discuss the proposed relationship between ASD and CD and the possible usefulness of a gluten-free diet in ASD patients.

Transcriptomics of Gabra4 knockout mice reveals common NMDAR pathways underlying autism, memory, and epilepsy

Autism spectrum disorder (ASD) is a neuronal developmental disorder with impaired social interaction and communication, often with abnormal intelligence and comorbidity with epilepsy. Disturbances in synaptic transmission, including the GABAergic, glutamatergic, and serotonergic systems, are known to be involved in the pathogenesis of this disorder, yet we do not know if there is a common molecular mechanism. As mutations in the GABAergic receptor subunit gene GABRA4 are reported in patients with ASD, we eliminated the Gabra4 gene in mice and found that the Gabra4 knockout mice showed autistic-like behavior, enhanced spatial memory, and attenuated susceptibility to pentylenetetrazol-induced seizures, a constellation of symptoms resembling human high-functioning autism. To search for potential molecular pathways involved in these phenotypes, we performed a hippocampal transcriptome profiling, constructed a hippocampal interactome network, and revealed an upregulation of the NMDAR system at the center of the converged pathways underlying high-functioning autism-like and anti-epilepsy phenotypes.

Beyond the Ligand: Extracellular and Transcellular G Protein-Coupled Receptor Complexes in Physiology and Pharmacology

G protein-coupled receptors (GPCRs) remain one of the most successful targets of U.S. Food and Drug Administration-approved drugs. GPCR research has predominantly focused on the characterization of the intracellular interactome's contribution to GPCR function and pharmacology. However, emerging evidence uncovers a new dimension in the biology of GPCRs involving their extracellular and transcellular interactions that critically impact GPCR function and pharmacology. The seminal examples include a variety of adhesion GPCRs, such as ADGRLs/latrophilins, ADGRBs/brain angiogenesis inhibitors, ADGRG1/GPR56, ADGRG6/GPR126, ADGRE5/CD97, and ADGRC3/CELSR3. However, recent advances have indicated that class C GPCRs that contain large extracellular domains, including group III metabotropic glutamate receptors (mGluR4, mGluR6, mGluR7, mGluR8), γ-aminobutyric acid receptors, and orphans GPR158 and GPR179, can also participate in this form of transcellular regulation. In this review, we will focus on a variety of identified extracellular and transcellular GPCR-interacting partners, including teneurins, neurexins, integrins, fibronectin leucine-rich transmembranes, contactin-6, neuroligin, laminins, collagens, major prion protein, amyloid precursor protein, complement C1q-likes, stabilin-2, pikachurin, dystroglycan, complement decay-accelerating factor CD55, cluster of differentiation CD36 and CD90, extracellular leucine-rich repeat and fibronectin type III domain containing 1, and leucine-rich repeat, immunoglobulin-like domain and transmembrane domains. We provide an account on the diversity of extracellular and transcellular GPCR complexes and their contribution to key cellular and physiologic processes, including cell migration, axon guidance, cellular and synaptic adhesion, and synaptogenesis. Furthermore, we discuss models and mechanisms by which extracellular GPCR assemblies may regulate communication at cellular junctions. SIGNIFICANCE STATEMENT: G protein-coupled receptors (GPCRs) continue to be the prominent focus of pharmacological intervention for a variety of human pathologies. Although the majority of GPCR research has focused on the intracellular interactome, recent advancements have identified an extracellular dimension of GPCR modulation that alters accepted pharmacological principles of GPCRs. Herein, we describe known endogenous allosteric modulators acting on GPCRs both in cis and in trans.

ELFN2 is a postsynaptic cell adhesion molecule with essential roles in controlling group III mGluRs in the brain and neuropsychiatric behavior

The functional characterization of the GPCR interactome has predominantly focused on intracellular binding partners; however, the recent emergence of transsynaptic GPCR complexes represents an additional dimension to GPCR function that has previously been unaccounted for in drug discovery. Here, we characterize ELFN2 as a novel postsynaptic adhesion molecule with a distinct expression pattern throughout the brain and a selective binding with group III metabotropic glutamate receptors (mGluRs) in trans. Using a transcellular GPCR signaling platform, we report that ELFN2 critically alters group III mGluR secondary messenger signaling by directly altering G protein coupling kinetics and efficacy. Loss of ELFN2 in mice results in the selective downregulation of group III mGluRs and dysregulated glutamatergic synaptic transmission. Elfn2 knockout (Elfn2 KO) mice also feature a range of neuropsychiatric manifestations including seizure susceptibility, hyperactivity, and anxiety/compulsivity, which can be rescued by pharmacological augmentation of group III mGluRs. Thus, we conclude that extracellular transsynaptic scaffolding by ELFN2 in the brain is a cardinal organizational feature of group III mGluRs essential for their signaling properties and brain function.

Using maternal rescue of pups in a cup to investigate mother-infant interactions in mice/rodents

Efficient parental care is indispensable for survival of the mammalian offspring, and therefore both parents and offspring cooperate to achieve the best performance. For example, when parents transport altricial offspring, the offspring immediately respond by reducing its cry and movement in both human infants and rodent pups. This coordinated set of central, motor and cardiac responses is designated as the Transport Response (TR) and is shown to facilitate maternal carrying in rodents. The present study aims to investigate the core behavioural characteristics of mother-infant interaction, and to investigate the mechanisms underlying the mother-pup cooperation using pharmacological and genetic manipulations (i.e. Oprm1-/). Along with the clear developmental changes of the pups' immobility and posture during maternal carrying as previously reported, there were also adaptations in maternal strategies, particularly in positioning of foothold and oral grasp over the pup's body, with the pups' age and pup's behaviour. Tree-based models elucidated that both of these maternal variables as well as percentage of pups' struggle predict the time required for pup retrieval from a cup. When the sensory-motor control in pups was disturbed by pharmacological or genetic manipulations, these core behaviours were inefficiently performed and impede maternal retrieval. Mother-infant mutual fit is a complex construct where several intermingled mechanisms are involved. Thus mothers and infants, when interacting, should be considered together as one whole system in which any change in one side or the other, affects the output of the whole dyad. The outcome of the interaction relays on a specific dynamic pattern of infant and maternal behaviours, which mutually change and adapt to fit each other's needs. Key features to reach a successful outcome of the interaction were the maternal retrieving strategy and infants' Transport Response behaviour.

Opioid receptors: drivers to addiction?

Drug addiction is a worldwide societal problem and public health burden, and results from recreational drug use that develops into a complex brain disorder. The opioid system, one of the first discovered neuropeptide systems in the history of neuroscience, is central to addiction. Recently, opioid receptors have been propelled back on stage by the rising opioid epidemics, revolutions in G protein-coupled receptor research and fascinating developments in basic neuroscience. This Review discusses rapidly advancing research into the role of opioid receptors in addiction, and addresses the key questions of whether we can kill pain without addiction using mu-opioid-receptor-targeting opiates, how mu- and kappa-opioid receptors operate within the neurocircuitry of addiction and whether we can bridge human and animal opioid research in the field of drug abuse.

Heterozygous loss of epilepsy gene KCNQ2 alters social, repetitive and exploratory behaviors

KCNQ/K_v7 channels conduct voltage‐dependent outward potassium currents that potently decrease neuronal excitability. Heterozygous inherited mutations in their principle subunits K_v7.2/KCNQ2 and K_v7.3/KCNQ3 cause benign familial neonatal epilepsy whereas patients with de novo heterozygous K_v7.2 mutations are associated with early‐onset epileptic encephalopathy and neurodevelopmental disorders characterized by intellectual disability, developmental delay and autism. However, the role of K_v7.2‐containing K_v7 channels in behaviors especially autism‐associated behaviors has not been described. Because pathogenic K_v7.2 mutations in patients are typically heterozygous loss‐of‐function mutations, we investigated the contributions of K_v7.2 to exploratory, social, repetitive and compulsive‐like behaviors by behavioral phenotyping of both male and female KCNQ2^+/− mice that were heterozygous null for the KCNQ2 gene. Compared with their wild‐type littermates, male and female KCNQ2^+/− mice displayed increased locomotor activity in their home cage during the light phase but not the dark phase and showed no difference in motor coordination, suggesting hyperactivity during the inactive light phase. In the dark phase, KCNQ2^+/− group showed enhanced exploratory behaviors, and repetitive grooming but decreased sociability with sex differences in the degree of these behaviors. While male KCNQ2^+/− mice displayed enhanced compulsive‐like behavior and social dominance, female KCNQ2^+/− mice did not. In addition to elevated seizure susceptibility, our findings together indicate that heterozygous loss of K_v7.2 induces behavioral abnormalities including autism‐associated behaviors such as reduced sociability and enhanced repetitive behaviors. Therefore, our study is the first to provide a tangible link between loss‐of‐function K_v7.2 mutations and the behavioral comorbidities of K_v7.2‐associated epilepsy.

The Role of Metabotropic Glutamate Receptors in Social Behavior in Rodents

The appropriate display of social behavior is critical for the well-being and survival of an individual. In many psychiatric disorders, including social anxiety disorder, autism spectrum disorders, depression and schizophrenia social behavior is severely impaired. Selective targeting of metabotropic glutamate receptors (mGluRs) has emerged as a novel treatment strategy for these disorders. In this review, we describe some of the behavioral paradigms used to assess different types of social behavior, such as social interaction, social memory, aggressive behavior and sexual behavior. We then focus on the effects of pharmacological modulation of mGluR1-8 on these types of social behavior. Indeed, accumulating evidence indicates beneficial effects of selective ligands of specific mGluRs in ameliorating innate or pharmacologically-induced deficits in social interaction and social memory as well as in reducing aggression in rodents. We emphasize the importance of future studies investigating the role of selective mGluR ligands on different types of social behavior to provide a better understanding of the neural mechanisms involved which, in turn, might promote the development of selective mGluR-targeted tools for the improved treatment of psychiatric disorders associated with social deficits.

The Application of Adeno-Associated Viral Vector Gene Therapy to the Treatment of Fragile X Syndrome

Viral vector-mediated gene therapy has grown by leaps and bounds over the past several years. Although the reasons for this progress are varied, a deeper understanding of the basic biology of the viruses, the identification of new and improved versions of viral vectors, and simply the vast experience gained by extensive testing in both animal models of disease and in clinical trials, have been key factors. Several studies have investigated the efficacy of adeno-associated viral (AAV) vectors in the mouse model of fragile X syndrome where AAVs have been used to express fragile X mental retardation protein (FMRP), which is missing or highly reduced in the disorder. These studies have demonstrated a range of efficacies in different tests from full correction, to partial rescue, to no effect. Here we provide a backdrop of recent advances in AAV gene therapy as applied to central nervous system disorders, outline the salient features of the fragile X studies, and discuss several key issues for moving forward. Collectively, the findings to date from the mouse studies on fragile X syndrome, and data from clinical trials testing AAVs in other neurological conditions, indicate that AAV-mediated gene therapy could be a viable strategy for treating fragile X syndrome.