Impairment of cortical GABAergic synaptic transmission in an environmental rat model of autism

Balancing efficacy and safety: The dual impact of antiseizure medications on the developing brain

The number of neurons in the developing brain is greater than typically found in adulthood, and the brain possesses delicate mechanisms to induce the death of excess cells and refine neural circuitry. The correct tuning between the processes of neuronal death and survival generates a mature and functional brain in its complexity and plastic capacity. Epilepsy is a highly prevalent neurological condition worldwide, including among young individuals. However, exposure to the main treatment approaches, the long-term use of Antiseizure Medication (ASM), during the critical period of development can induce a series of changes in this delicate balance. Acting by various mechanisms of action, ASMs may induce an increase in neuronal death, something that translates into deleterious neuropsychiatric effects in adulthood. Several investigations conducted in recent years have brought to light new aspects related to this dynamic, yet many questions, such as the cellular mechanisms of death and the pathophysiology of late effects, still have unresolved elements. In this review, we aimed to explore the mechanisms of action of the most widely used ASMs in the treatment of neonatal epilepsy, the broad aspects of neuronal death in the developing brain and the repercussions of this death and other effects in adulthood. We review the evidence indicating a relationship between exposure to ASMs and the manifestation of associated psychiatric comorbidities in adulthood and discuss some possible mechanisms underlying the induction of this process by morphological and physiological changes in the related behaviors.

The potential neuroprotective effects of Spirulina platensis in a valproic acid-induced experimental model of autism in the siblings of albino rats: targeting PIk3/AKT/mTOR signalling pathway

INTRODUCTION

Autism spectrum disorders (ASDs) are a group of neurodevelopmental disorders with poor social interaction, communication issues, aberrant motor movements, and limited repetitive interests and behaviour. Spirulina platensis (SP) contains several multi-nutrients and has a wide range of neuroprotective properties.

AIM

The target of the current experiment is to detect the protective effects of S. platensis on valproic-induced autism in adult female albino rats' siblings for the first time.

MATERIALS AND METHODS

Twelve Pregnant rats were separated into four main groups; Group I (control); Group II (S. platensis); Group III (autistic group); and Group IV (autistic SP-treated group). Fifteen offspring pups from each group were sacrificed, brain was divided for biochemical analysis as superoxide dismutase and malondialdehyde were evaluated spectrophotometrically while interleukin-6, interleukin-12, Bcl-2-associated X protein, B-cell lymphoma-2, Beclin-1, brain-derived neurotrophic factor were assessed by ELISA, other division of brain were used for gene expression of PI3k, Akt and mTOR pathway, last division of brain were stained using (H&E) and Giemsa stains. Tumour necrosis factor alpha (TNF-α ) and Synaptophysin (SYN) markers were used for immunohistochemical staining.

RESULTS

Autistic Group (III) showed an increment in levels of MDA, IL-6, IL12 and BAX while showing a decrement in SOD, Bcl-2 and Beclin-1 as well as increased PI3k, Akt and mTOR gene expression. Autistic Group (III) also exhibited hypocellularity and disorganization of hippocampal and prefrontal cortex cells. The autistic SP-treated group (IV) showed improvement in these biochemical markers and pathological changes. Our findings suggest that Spirulina platensis will be significant in managing autism.

Neuroprotective effects of Apigenin on prenatal Valproic acid-induced autism spectrum disorder in rats

Valproic acid (VPA) demonstrates teratogenic effects during pregnancy. Prenatal exposure to VPA may result in autism spectrum disorder (ASD) -like phenotypes. Apigenin, a natural flavonoid, has been shown to have neuroprotective impacts due to its antioxidant properties. This study aimed to investigate the protective effects of apigenin in prenatal Valproic acid-induced autism in rats. Female rats (220-240 g, 2-3 months) received a single dose of VPA (600 mg/kg, i.p.) on the 12.5th day of gestational. The male offspring were given oral apigenin (50 mg/kg, p.o.) or the vehicle for 30 days. Behavioral tests, biochemical assessments for oxidative stress markers and pro-inflammatory cytokines were performed. VPA-treated rats exhibited increased anxiety-like behavior, and repetitive behavior. Social interaction was reduced, and detection of the novel object was impaired. Also, VPA-treated rats have shown higher levels of oxidative stress malondialdehyde (MDA) and lower GPX and superoxide dismutase (SOD) levels. Furthermore, IL-6 and TNF-α increased in the prefrotalcortex decreased. On the other hand, apigenin-treated rats restored the cognitive consequences and lowered oxidative stress and inflammation in the prefrotalcortex.

Conclusion

Chronic apigenin treatment restored the behavioral and biochemical abnormalities caused by prenatal VPA exposure.

Spontaneous Calcium Transients Recorded from Striatal Astrocytes in a Preclinical Model of Autism

Autism spectrum disorder (ASD) is known as a group of neurodevelopmental conditions including stereotyped and repetitive behaviors, besides social and sensorimotor deficits. Anatomical and functional evidence indicates atypical maturation of the striatum. Astrocytes regulate the maturation and plasticity of synaptic circuits, and impaired calcium signaling is associated with repetitive behaviors and atypical social interaction. Spontaneous calcium transients (SCT) recorded in the striatal astrocytes of the rat were investigated in the preclinical model of ASD by prenatal exposure to valproic acid (VPA). Our results showed sensorimotor delay, augmented glial fibrillary acidic protein -a typical intermediate filament protein expressed by astrocytes- and diminished expression of GABAA-ρ3 through development, and increased frequency of SCT with a reduced latency that resulted in a diminished amplitude in the VPA model. The convulsant picrotoxin, a GABAA (γ-aminobutyric acid type A) receptor antagonist, reduced the frequency of SCT in both experimental groups but rescued this parameter to control levels in the preclinical ASD model. The amplitude and latency of SCT were decreased by picrotoxin in both experimental groups. Nipecotic acid, a GABA uptake inhibitor, reduced the mean amplitude only for the control group. Nevertheless, nipecotic acid increased the frequency but diminished the latency in both experimental groups. Thus, we conclude that striatal astrocytes exhibit SCT modulated by GABAA-mediated signaling, and prenatal exposure to VPA disturbs this tuning.

Three Decades of Valproate: A Current Model for Studying Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder with increased prevalence and incidence in recent decades. Its etiology remains largely unclear, but it seems to involve a strong genetic component and environmental factors that, in turn, induce epigenetic changes during embryonic and postnatal brain development. In recent decades, clinical studies have shown that inutero exposure to valproic acid (VPA), a commonly prescribed antiepileptic drug, is an environmental factor associated with an increased risk of ASD. Subsequently, prenatal VPA exposure in rodents has been established as a reliable translational model to study the pathophysiology of ASD, which has helped demonstrate neurobiological changes in rodents, non-human primates, and brain organoids from human pluripotent stem cells. This evidence supports the notion that prenatal VPA exposure is a valid and current model to replicate an idiopathic ASD-like disorder in experimental animals. This review summarizes and describes the current features reported with this animal model of autism and the main neurobiological findings and correlates that help elucidate the pathophysiology of ASD. Finally, we discuss the general framework of the VPA model in comparison to other environmental and genetic ASD models.

Abnormal auditory brainstem responses in an animal model of autism spectrum disorder

Auditory dysfunction is a common feature of autism spectrum disorder (ASD) and ranges from deafness to hypersensitivity. The auditory brainstem response (ABR) permits study of the amplitude and latency of synchronized electrical activity along the ascending auditory pathway in response to clicks and pure tone stimuli. Indeed, numerous studies have shown that subjects with ASD have ABR abnormalities. In utero exposure to the antiepileptic drug valproic acid (VPA) is associated with human cases of ASD and is used as an animal model of ASD. Previous studies have shown that VPA-exposed animals have significantly fewer neurons in the auditory brainstem and thalamus, reduced ascending projections to the auditory midbrain and thalamus and increased neuronal activation in response to pure tone stimuli. Accordingly, we hypothesized that VPA-exposed animals would have abnormal ABRs throughout their lifespans. We approached this hypothesis in two cohorts. First, we examined ABRs from both ears on postnatal day 22 (P22). Then, we examined monaural ABRs in animals at P28, 60, 120, 180, 240, 300 and 360. Our results suggest that at P22, VPA-exposed animals have elevated thresholds and increased peak latencies. However, by P60 these differences largely normalize with differences appearing only near hearing threshold. Additionally, our analysis revealed that maturation of ABR waves occurred at different trajectories in control and VPA-exposed animals. These results, together with our previous work, suggest that VPA exposure not only impacts total neuron number and connectivity, but also auditory evoked responses. Finally, our longitudinal analysis suggests that delayed maturation of auditory brainstem circuits may impact ABRs throughout the lifespan of the animal.

Altered GABAergic, glutamatergic and endocannabinoid signaling is accompanied by neuroinflammatory response in a zebrafish model of social withdrawal behavior

Introduction

Deficits in social communication are in the core of clinical symptoms characterizing many neuropsychiatric disorders such as schizophrenia and autism spectrum disorder. The occurrence of anxiety-related behavior, a common co-morbid condition in individuals with impairments in social domain, suggests the presence of overlapping neurobiological mechanisms between these two pathologies. Dysregulated excitation/inhibition balance and excessive neuroinflammation, in specific neural circuits, are proposed as common etiological mechanisms implicated in both pathologies.

Methods and Results

In the present study we evaluated changes in glutamatergic/GABAergic neurotransmission as well as the presence of neuroinflammation within the regions of the Social Decision-Making Network (SDMN) using a zebrafish model of NMDA receptor hypofunction, following sub-chronic MK-801 administration. MK-801-treated zebrafish are characterized by impaired social communication together with increased anxiety levels. At the molecular level, the behavioral phenotype was accompanied by increased mGluR5 and GAD67 but decreased PSD-95 protein expression levels in telencephalon and midbrain. In parallel, MK-801-treated zebrafish exhibited altered endocannabinoid signaling as indicated by the upregulation of cannabinoid receptor 1 (CB1R) in the telencephalon. Interestingly, glutamatergic dysfunction was positively correlated with social withdrawal behavior whereas defective GABAergic and endocannabinoid activity were positively associated with anxiety-like behavior. Moreover, neuronal and astrocytic IL-1β expression was increased in regions of the SDMN, supporting the role of neuroinflammatory responses in the manifestation of MK-801 behavioral phenotype. Colocalization of interleukin-1β (IL-1β) with β₂-adrenergic receptors (β₂-ARs) underlies the possible influence of noradrenergic neurotransmission to increased IL-1β expression in comorbidity between social deficits and elevated anxiety comorbidity.

Discussion

Overall, our results indicate the contribution of altered excitatory and inhibitory synaptic transmission as well as excessive neuroinflammatory responses in the manifestation of social deficits and anxiety-like behavior of MK-801-treated fish, identifying possible novel targets for amelioration of these symptoms.

A working taxonomy for describing the sensory differences of autism

BACKGROUND

Individuals on the autism spectrum have been long described to process sensory information differently than neurotypical individuals. While much effort has been leveraged towards characterizing and investigating the neurobiology underlying the sensory differences of autism, there has been a notable lack of consistency in the terms being used to describe the nature of those differences.

MAIN BODY

We argue that inconsistent and interchangeable terminology-use when describing the sensory differences of autism has become problematic beyond mere pedantry and inconvenience. We begin by highlighting popular terms that are currently being used to describe the sensory differences of autism (e.g. "sensitivity", "reactivity" and "responsivity") and discuss why poor nomenclature may hamper efforts towards understanding the aetiology of sensory differences in autism. We then provide a solution to poor terminology-use by proposing a hierarchical taxonomy for describing and referring to various sensory features.

CONCLUSION

Inconsistent terminology-use when describing the sensory features of autism has stifled discussion and scientific understanding of the sensory differences of autism. The hierarchical taxonomy proposed was developed to help resolve lack of clarity when discussing the sensory differences of autism and to place future research targets at appropriate levels of analysis.

Oxytocin protective effects on zebrafish larvae models of autism-like spectrum disorder

Objectives

Autism is a complicated neurodevelopmental disorder characterized by social interaction deficiencies, hyperactivity, anxiety, communication disorders, and a limited range of interests. The zebrafish (Danio rerio) is a social vertebrate used as a biomedical research model to understand social behavior mechanisms.

Materials and Methods

After spawning, the eggs were exposed to sodium valproate for 48 hr, after which the eggs were divided into eight groups. Except for the positive and control groups, there were six treatment groups based on oxytocin concentration (25, 50, and 100 μM) and time point (24 and 48 hr). Treatment was performed on days 6 and 7, examined by labeling oxytocin with fluorescein-5-isothiocyanate (FITC) and imaging with confocal microscopy and the expression levels of potential genes associated with the qPCR technique. Behavioral studies, including light-dark background preference test, shoaling behavior, mirror test, and social preference, were performed on 10, 11, 12, and 13 days post fertilization (dpf), respectively.

Results

The results showed that the most significant effect of oxytocin was at the concentration of 50 μM and the time point of 48 hr. Increased expression of shank3a, shank3b, and oxytocin receptor genes was also significant at this oxytocin concentration. Light-dark background preference results showed that oxytocin in the concentration of 50 µM significantly increased the number of crosses between dark and light areas compared with valproic acid (positive group). Also, oxytocin showed an increase in the frequency and time of contact between the two larvae. We showed a decrease in the distance in the larval group and an increase in time spent at a distance of one centimeter from the mirror.

Conclusion

Our findings showed that the increased gene expression of shank3a, shank3b, and oxytocin receptors improved autistic behavior. Based on this study some indications showed that oxytocin administration in the larval stage could significantly improve the autism-like spectrum.

Memantine/Aripiprazole Combination Alleviates Cognitive Dysfunction in Valproic Acid Rat Model of Autism: Hippocampal CREB/BDNF Signaling and Glutamate Homeostasis

Significant efforts are increasingly directed towards identifying novel therapeutic targets for autism spectrum disorder (ASD) with a rising role of aberrant glutamatergic transmission in the pathogenesis of ASD-associated cellular and behavioral deficits. This study aimed at investigating the role of chronic memantine (20 mg/kg/day) and aripiprazole (3 mg/kg/day) combination therapy in the management of prenatal sodium valproate (VPA)-induced autistic-like/cognitive deficits in male Wistar rats. Pregnant female rats received a single intraperitoneal injection of VPA (600 mg/kg) to induce autistic-like behaviors in their offspring. Prenatal VPA induced autistic-like symptoms (decreased social interaction and the appearance of stereotyped behavior) with deficits in spatial learning (in Morris water maze) and cognitive flexibility (in the attentional set-shifting task) in addition to decreased hippocampal protein levels of phosphorylated cAMP response element-binding protein (p-CREB), brain-derived neurotrophic factor (BDNF), and gene expression of glutamate transporter-1 (Glt-1) with a decline in GABA/glutamate ratio (both measured by HPLC). These were accompanied by the appearance of numerous neurofibrillary tangles (NFTs) with enhanced apoptosis in hippocampal sections. Memantine/aripiprazole combination increased the protein levels of p-CREB, BDNF, and Glt-1 gene expression with restoration of GABA/glutamate balance, attenuation of VPA-induced neurodegenerative changes and autistic-like symptoms, and improvement of cognitive performance. This study draws attention to the favorable cognitive effects of memantine/aripiprazole combination in autistic subjects which could be mediated via enhancing CREB/BDNF signaling with increased expression of astrocytic Glt-1 and restoration of GABA/glutamate balance, leading to inhibition of hippocampal NFTs formation and neuronal apoptosis.

GABAergic synaptic transmission and cortical oscillation patterns in the primary somatosensory area of a valproic acid rat model of autism spectrum disorder

Autism spectrum disorder (ASD) is characterized by impaired social communication and interaction associated with repetitive or stereotyped behaviour. Prenatal valproic acid (VPA) exposure in rodents is a commonly used model of ASD. Resveratrol (RSV) has been shown to prevent interneuronal and behavioural impairments in the VPA model. We investigated the effects of prenatal VPA exposure and RSV on the GABAergic synaptic transmission, brain oscillations and on the genic expression of interneuron-associated transcription factor LHX6 in the primary somatosensory area (PSSA). Prenatal VPA exposure decreased the sIPSC and mIPSC frequencies and the sIPSC decay kinetics onto layers 4/5 pyramidal cells of PSSA. About 40% of VPA animals exhibited absence-like spike-wave discharge (SWD) events associated with behaviour arrest and increased power spectrum density of delta, beta and gamma cortical oscillations. VPA animals had reduced LHX6 expression in PSSA, but VPA animals treated with RSV had no changes on synaptic inhibition or LHX6 expression in the PSSA. SWD events associated with behaviour arrest and the abnormal increment of cortical oscillations were also absent in VPA animals treated with RSV. These findings provide new venues to investigate the role of both RSV and VPA in the pathophysiology of ASD and highlight the VPA animal model as an interesting tool to investigate pathways related to the aetiology and possible future therapies to this neuropsychiatric disorder.

Vitamin B6 Deficiency Induces Autism-Like Behaviors in Rats by Regulating mTOR-Mediated Autophagy in the Hippocampus

Vitamin B6 (VB₆) exhibits therapeutic effects towards autism spectrum disorder (ASD), but its specific mechanism is poorly understood. Rat dams were treated with VB₆ standard, VB₆ deficiency, or VB₆ supplementary diet, and the same treatment was provided to their offspring, with their body weights monitored. Three-chambered social test and open field test were employed to evaluate the effect of VB₆ on autism-like behaviors. Gamma-aminobutyric acid (GABA) generation and synaptic inhibition of neurons in the hippocampus of rat were detected via immunofluorescence staining, followed by the measurement of GABA concentration through high-performance liquid chromatography (HPLC). The role of VB₆ in the autophagy and apoptosis of cells was determined via Western blot and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). In order to conduct rescue experiments, the inhibition of mammalian target of rapamycin (mTOR) or the activation of GABA was achieved by drug administration to the offspring rats with VB₆ deficiency. As a result, no evident difference in weight was observed in the offspring with varied VB₆ treatments. VB₆ deficiency impaired social interaction; aggravated self-grooming and bowel frequency; decreased GABA concentration, VIAAT, GAD67, vGAT expressions, and LC3 II/LC3 I ratio; increased p62 level and p-mTOR/mTOR ratio; and promoted cell apoptosis. Inhibition of mTOR reversed the effect of VB₆ deficiency on cell autophagy. GABA activation or mTOR inhibition offset the role of VB₆ deficiency in autism-like behaviors and hippocampal GABA expression. Collectively, VB₆ deficiency induces autism-like behaviors in rats by regulating mTOR-mediated autophagy in the hippocampus.

The Role of Zinc and NMDA Receptors in Autism Spectrum Disorders

NMDA-type glutamate receptors are critical for synaptic plasticity in the central nervous system. Their unique properties and age-dependent arrangement of subunit types underpin their role as a coincidence detector of pre- and postsynaptic activity during brain development and maturation. NMDAR function is highly modulated by zinc, which is co-released with glutamate and concentrates in postsynaptic spines. Both NMDARs and zinc have been strongly linked to autism spectrum disorders (ASDs), suggesting that NMDARs are an important player in the beneficial effects observed with zinc in both animal models and children with ASDs. Significant evidence is emerging that these beneficial effects occur via zinc-dependent regulation of SHANK proteins, which form the backbone of the postsynaptic density. For example, dietary zinc supplementation enhances SHANK2 or SHANK3 synaptic recruitment and rescues NMDAR deficits and hypofunction in Shank3^ex13-16-/- and Tbr1^+/- ASD mice. Across multiple studies, synaptic changes occur in parallel with a reversal of ASD-associated behaviours, highlighting the zinc-dependent regulation of NMDARs and glutamatergic synapses as therapeutic targets for severe forms of ASDs, either pre- or postnatally. The data from rodent models set a strong foundation for future translational studies in human cells and people affected by ASDs.

Abnormal vestibular brainstem structure and function in an animal model of autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that includes several key neuropathological changes and behavioral impairments. In utero exposure to the anti-epileptic valproic acid (VPA) increases risk of an ASD diagnosis in human subjects and timed in utero exposure to VPA is a clinically relevant animal model of ASD. Many human subjects with ASD have cerebellar hypoplasia, fewer Purkinje cells, difficulties with balance, ophthalmic dysfunction and abnormal responses to vestibular stimulation and such vestibular difficulties are likely under reported in ASD. We have recently shown that animals exposed to VPA in utero have fewer neurons in their auditory brainstem, reduced axonal projections to the auditory midbrain and thalamus, reduced expression of the calcium binding protein calbindin (CB) in the brainstem and cerebellum, smaller and occasionally ectopic cerebellar Purkinje cells and ataxia on several motor tasks. Based on these findings, we hypothesized that in utero VPA exposure similarly impacts structure and function of the vestibular brainstem. We investigated this hypothesis using quantitative morphometric analyses, immunohistochemistry for CB, a battery of vestibular challenges, recording of vestibular-evoked myogenic potentials and spontaneous eye movements. Our results indicate that VPA exposure results in fewer neurons in the vestibular nuclei, fewer CB-positive puncta, difficulty on certain motor tasks, longer latency VEMPs and significantly more horizontal eye movements. These findings indicate that the vestibular nuclei are impacted by in utero VPA exposure and provide a basis for further study of vestibular circuits in human cases of ASD.

Epigenetic regulation of GABAergic differentiation in the developing brain

In the vertebrate brain, GABAergic cell development and neurotransmission are important for the establishment of neural circuits. Various intrinsic and extrinsic factors have been identified to affect GABAergic neurogenesis. However, little is known about the epigenetic control of GABAergic differentiation in the developing brain. Here, we report that the number of GABAergic neurons dynamically changes during the early tectal development in the Xenopus brain. The percentage of GABAergic neurons is relatively unchanged during the early stages from stage 40 to 46 but significantly decreased from stage 46 to 48 tadpoles. Interestingly, the histone acetylation of H3K9 is developmentally decreased from stage 42 to 48 (about 3.5 days). Chronic application of valproate acid (VPA), a broad-spectrum histone deacetylase (HDAC) inhibitor, at stage 46 for 48 h increases the acetylation of H3K9 and the number of GABAergic cells in the optic tectum. VPA treatment also reduces apoptotic cells. Electrophysiological recordings show that a VPA induces an increase in the frequency of mIPSCs and no changes in the amplitude. Behavioral studies reveal that VPA decreases swimming activity and visually guided avoidance behavior. These findings extend our understanding of histone modification in the GABAergic differentiation and neurotransmission during early brain development.

Acute rapamycin rescues the hyperexcitable phenotype of accumbal medium spiny neurons in the valproic acid rat model of autism spectrum disorder

We previously demonstrated that prenatal exposure to valproic acid (VPA), an environmental model of autism spectrum disorder (ASD), leads to a hyperexcitable phenotype associated with downregulation of inward-rectifying potassium currents in nucleus accumbens (NAc) medium spiny neurons (MSNs) of adolescent rats. Aberrant mTOR pathway function has been associated with autistic-like phenotypes in multiple animal models, including gestational exposure to VPA. The purpose of this work was to probe the involvement of the mTOR pathway in VPA-induced alterations of striatal excitability. Adolescent male Wistar rats prenatally exposed to VPA were treated acutely with the mTOR inhibitor rapamycin and used for behavioral tests, ex vivo brain slice electrophysiology, single-neuron morphometric analysis, synaptic protein quantification and gene expression analysis in the NAc. We report that postnatal rapamycin ameliorates the social deficit and reverts the abnormal excitability, but not the inward-rectifying potassium current defect, of accumbal MSNs. Synaptic transmission and neuronal morphology were largely unaffected by prenatal VPA exposure or postnatal rapamycin treatment. Transcriptome analysis revealed extensive deregulation of genes implied in neurodevelopmental disorders and ionic mechanisms exerted by prenatal VPA, which was partially reverted by postnatal rapamycin. The results of this work support the existence of antagonistic interaction between mTOR and VPA-induced pathways on social behavior, neurophysiological phenotype and gene expression profile, thus prompting further investigation of the mTOR pathway in the quest for specific therapeutic targets in ASD.

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.

Alterations in the intrinsic discharge activity of CA1 pyramidal neurons associated with possible changes in the NADPH diaphorase activity in a rat model of autism induced by prenatal exposure to valproic acid

Autism spectrum disorder is a neurodevelopmental disorder characterized by sensory abnormalities, social skills impairment and cognitive deficits. Although recent evidence indicated that induction of autism-like behavior in animal models causes abnormal neuronal excitability, the impact of autism on neuronal properties is still an important issue. Thus, new findings at the cellular level may shed light on the pathophysiology of autism and may help to find effective treatment strategies. Here, we investigated the behavioral, electrophysiological and histochemical impacts of prenatal exposure to valproic acid (VPA) in rats. Findings revealed that VPA exposure caused a significant increase in the hot plate response latency. The novel object recognition ability was also impaired in VPA-exposed rats. Along with these behavioral alterations, neurons from VPA-exposed animals exhibited altered excitability features in response to depolarizing current injections relative to control neurons. In the VPA-exposed group, these changes consisted of a significant increase in the amplitude, evoked firing frequency and the steady-state standard deviation of spike timing of action potentials (APs). Moreover, the half-width, the AHP amplitude and the decay time constant of APs were significantly decreased in this group. These changes in the evoked electrophysiological properties were accompanied by intrinsic hyperexcitability and lower spike-frequency adaptation and also a significant increase in the number of NADPH-diaphorase stained neurons in the hippocampal CA1 area of the VPA-exposed rats. Taken together, findings demonstrate that abnormal nociception and recognition memory is associated with alterations in the neuronal responsiveness and nitrergic system in a rat model of autism-like.

Generational synaptic functions of GABAA receptor β3 subunit deteriorations in an animal model of social deficit

BACKGROUND

Disruption of normal brain development is implicated in numerous psychiatric disorders with neurodevelopmental origins, including autism spectrum disorder (ASD). Widespread abnormalities in brain structure and functions caused by dysregulations of neurodevelopmental processes has been recently shown to exert adverse effects across generations. An imbalance between excitatory/inhibitory (E/I) transmission is the putative hypothesis of ASD pathogenesis, supporting by the specific implications of inhibitory γ-aminobutyric acid (GABA)ergic system in autistic individuals and animal models of ASD. However, the contribution of GABAergic system in the neuropathophysiology across generations of ASD is still unknown. Here, we uncover profound alterations in the expression and function of GABA_A receptors (GABA_ARs) in the amygdala across generations of the VPA-induced animal model of ASD.

METHODS

The F2 generation was produced by mating an F1 VPA-induced male offspring with naïve females after a single injection of VPA on embryonic day (E12.5) in F0. Autism-like behaviors were assessed by animal behavior tests. Expression and functional properties of GABA_ARs and related proteins were examined by using western blotting and electrophysiological techniques.

RESULTS

Social deficit, repetitive behavior, and emotional comorbidities were demonstrated across two generations of the VPA-induced offspring. Decreased synaptic GABA_AR and gephyrin levels, and inhibitory transmission were found in the amygdala from two generations of the VPA-induced offspring with greater reductions in the F2 generation. Weaker association of gephyrin with GABA_AR was shown in the F2 generation than the F1 generation. Moreover, dysregulated NMDA-induced enhancements of gephyrin and GABA_AR at the synapse in the VPA-induced offspring was worsened in the F2 generation than the F1 generation. Elevated glutamatergic modifications were additionally shown across generations of the VPA-induced offspring without generation difference.

CONCLUSIONS

Taken together, these findings revealed the E/I synaptic abnormalities in the amygdala from two generations of the VPA-induced offspring with GABAergic deteriorations in the F2 generation, suggesting a potential therapeutic role of the GABAergic system to generational pathophysiology of ASD.

The GABAB receptor agonist STX209 reverses the autism‑like behaviour in an animal model of autism induced by prenatal exposure to valproic acid

Autism spectrum disorder (ASD) is a lifelong neurodevelopmental condition characterized by impaired social interaction, compromised communication, and restrictive or stereotyped behaviours and interests. Due to the complex pathophysiology of ASD, there are currently no available medical therapies for improving the associated social deficits. Consequently, the present study investigated the effects of STX209, a selective γ‑aminobutyric acid type B receptor (GABABR2) agonist, on an environmental rodent model of autism. The mouse model of autism induced by prenatal exposure to valproic acid (VPA) was used to assess the therapeutic potential of STX209 on autism‑like behaviour in the present study. This study investigated the effects of STX209 on VPA model mice via behavioral testing and revealed a significant reversal of core/associated autism‑like behavior, including sociability and preference for social novelty, novelty recognition, locomotion and exploration activity and marble‑burying deficit. This may be associated with STX209 correcting dendritic arborization, spine density and GABABR2 expression in hippocampus of VPA model mice. However, expression of glutamic acid decarboxylase 65/67 in the hippocampus were not altered by STX209. The present results demonstrated that STX209 administration ameliorated autism‑like symptoms in mice exposed to VPA prenatally, suggesting that autism‑like symptoms in children with a history of prenatal VPA exposure may also benefit from treatment with the GABABR2 agonist STX209.

Prenatal GABAB Receptor Agonist Administration Corrects the Inheritance of Autism-Like Core Behaviors in Offspring of Mice Prenatally Exposed to Valproic Acid

This study was performed to evaluate the effects of prenatal baclofen (a GABAB receptor agonist) treatment on the inheritance of autism-like behaviors in valproic acid (VPA)-exposed mice. VPA model mice (first generation, F1) that were prenatally exposed to VPA exhibited robust core autism-like behaviors, and we found that oral administration of baclofen to F1 mice corrected their autism-like behavioral phenotypes at an early age. Based on a previous epigenetics study, we mated the F1 male offspring with litter females to produce the second generation (F2). The F2 male mice showed obvious inheritance of autism-like phenotypes from F1 mice, implying the heritability of autism symptoms in patients with prenatal VPA exposure. Furthermore, we found prenatal baclofen administration was associated with beneficial effects on the autism-like phenotype in F2 male mice. This may have involved corrections in the density of total/mature dendritic spines in the hippocampus (HC) and medial prefrontal cortex (mPFC), normalizing synaptic plasticity. In this research, GABAB receptor agonist administration corrected the core autism-like behaviors of F1 mice and protected against the inheritance of neurodevelopmental disorders in the offspring of F1 mice, suggesting the potential of early intervention with GABAB receptor agonists in the treatment of neurodevelopmental disorders.

Excitatory and Inhibitory Synaptic Imbalance Caused by Brain-Derived Neurotrophic Factor Deficits During Development in a Valproic Acid Mouse Model of Autism

Environmental factors, such as medication during pregnancy, are one of the major causes of autism spectrum disorder (ASD). Valproic acid (VPA) intake during pregnancy has been reported to dramatically elevate autism risk in offspring. Recently, researchers have proposed that VPA exposure could induce excitatory or inhibitory synaptic dysfunction. However, it remains to be determined whether and how alterations in the excitatory/inhibitory (E/I) balance contribute to VPA-induced ASD in a mouse model. In the present study, we explored changes in the E/I balance during different developmental periods in a VPA mouse model. We found that typical markers of pre- and postsynaptic excitatory and inhibitory function involved in E/I balance markedly decreased during development, reflecting difficulties in the development of synaptic plasticity in VPA-exposed mice. The expression of brain-derived neurotrophic factor (BDNF), a neurotrophin that promotes the formation and maturation of glutamatergic and GABAergic synapses during postnatal development, was severely reduced in the VPA-exposed group. Treatment with exogenous BDNF during the critical E/I imbalance period rescued synaptic functions and autism-like behaviors, such as social defects. With these results, we experimentally showed that social dysfunction in the VPA mouse model of autism might be caused by E/I imbalance stemming from BDNF deficits during the developmental stage.

Autism Spectrum Disorder: Focus on Glutamatergic Neurotransmission

Disturbances in the glutamatergic system have been increasingly documented in several neuropsychiatric disorders, including autism spectrum disorder (ASD). Glutamate-centered theories of ASD are based on evidence from patient samples and postmortem studies, as well as from studies documenting abnormalities in glutamatergic gene expression and metabolic pathways, including changes in the gut microbiota glutamate metabolism in patients with ASD. In addition, preclinical studies on animal models have demonstrated glutamatergic neurotransmission deficits and altered expression of glutamate synaptic proteins. At present, there are no approved glutamatergic drugs for ASD, but several ongoing clinical trials are currently focusing on evaluating in autistic patients glutamatergic pharmaceuticals already approved for other conditions. In this review, we provide an overview of the literature concerning the role of glutamatergic neurotransmission in the pathophysiology of ASD and as a potential target for novel treatments.

Degraded cortical temporal processing in the valproic acid-induced rat model of autism

Hearing disorders, such as abnormal speech perception, are frequently reported in individuals with autism. However, the mechanisms underlying these auditory-associated signature deficits in autism remain largely unknown. In this study, we documented significant behavioral impairments in the sound temporal rate discrimination task for rats prenatally exposed to valproic acid (VPA), a well-validated animal model for studying the pathology of autism. In parallel, there was a large-scale degradation in temporal information-processing in their primary auditory cortices (A1) at both levels of spiking outputs and synaptic inputs. Substantially increased spine density of excitatory neurons and decreased numbers of parvalbumin- and somatostatin-labeled inhibitory inter-neurons were also recorded in the A1 after VPA exposure. Given the fact that cortical temporal processing of sound is associated with speech perception in humans, these results in the animal model of VPA exposure provide insight into a possible neurological mechanism underlying auditory and language-related deficits in individuals with autism.

A Multi-Target and Multi-Channel Mechanism of Action for Jiawei Yinhuo Tang in the Treatment of Social Communication Disorders in Autism: Network Pharmacology and Molecular Docking Studies

BACKGROUND

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder with complex pathogenesis. Currently, the pathogenesis of ASD is not fully understood. Moreover, current treatments do not effectively alleviate the primary symptoms of ASD social disorder (SCDA). Jiawei Yinhuo Tang (JWYHT) is an improved version of the classic prescription Yinhuo Tang. Although this medication has been shown to improve social behavior in ASD patients, the mechanism by which it works remains unknown.

METHODS

In this study, network pharmacology bioinformatics analysis was used to identify the key targets, biological functions, and signal pathways of JWYHT in SCDA. Then, molecular docking and molecular dynamic simulation were used to validate the activity and stability of the active ingredient and the target protein during the binding process.

RESULTS

The analysis identified 157 key targets and 9 core targets of JWYHT (including proto-oncogene (FOS), caspase 3 (CASP3), mitogen-activated protein kinase-3 (MAPK3), interleukin-6 (IL6), mitogen-activated protein kinase-1 (MAPK1), tumor necrosis factor (TNF), mitogen-activated protein kinase-8 (MAPK8), AKT serine/threonine kinase 1 (AKT1), and 5-hydroxytryptamine receptor 1B (5HT1B)) in SCDA. In addition, the Kyoto Encyclopedia of Gene and Genome results, as well as the staggering network analyses, revealed 20 biological processes and 20 signal pathways targeted by JWYHT in SCDA. Finally, molecular docking analysis was used to determine the binding activity of the main active components of JWYHT to the key targets. The binding activity and stability of methyl arachidonate and MAPK8 were demonstrated using molecular dynamics simulation.

CONCLUSION

This study demonstrates that JWYHT regulates neuronal development, synaptic transmission, intestinal and cerebral inflammatory response, and other processes in SCDA.

Alterations of the Hippocampal Networks in Valproic Acid-Induced Rat Autism Model

Autism Spectrum Disorder (ASD) is one of the most frequently diagnosed neurodevelopmental disorders, characterized among others by impairments in social interactions and repetitive behavior. According to one of the leading hypotheses about its origin, ASD is caused by the imbalance of excitatory and inhibitory circuit activity. ASD-related morphological and functional changes can be observed in several brain regions i.e., in the prefrontal cortex and the hippocampus. It is well-established that prenatal valproic-acid (VPA) exposure of rats on day 12.5 leads to neurodevelopmental alterations with autism-like clinical and behavioral symptoms. The aim of this study was to investigate potential changes in the excitability of neuronal networks and individual neurons of the hippocampus elicited by prenatal VPA treatment. As there are marked sex differences in ASD, offspring of both sexes were systematically tested, using two different age groups, to elucidate eventual differences in neurodevelopment after VPA treatment. Excitatory connections and long-term synaptic plasticity as well as intrinsic excitability of CA1 pyramidal cells were examined. Pregnant female Wistar rats received saline or 500 mg/kg VPA i. p. on gestation day 12.5. Brain slices of 6-week-old and 3-month-old offspring were investigated using extra- and intracellular electrophysiological techniques. Field potential- and whole-cell patch clamp recordings were carried out to measure network excitability and single cell activity in the CA1 region hippocampus. Enhanced excitability of hippocampal networks was detected in the 6-week-old VPA-treated male rats; however, this change could not be observed in 3-month-old males. Intrinsic excitability of single neurons, however, was increased in 3-month-old males. In 6-week-old treated females, the most prominent effect of VPA was an increase in voltage sag, to a similar degree to the neurons of the older age group. In 3-month-old females, a network excitability increase could be demonstrated, in a lesser degree than in younger males. It can be concluded, that VPA treatment had diverse effects on hippocampal excitability depending on the sex and the age of the animals. We found that certain alterations manifested in 6-week-old rats were compensated later, on the other hand, other changes persisted until the age of 3 months.

Sex differences in neuronal systems function and behaviour: beyond a single diagnosis in autism spectrum disorders

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that is associated with functional brain alterations that underlie the expression of behaviour. Males are diagnosed up to four times more than females, and sex differences have been identified in memory, cognitive flexibility, verbal fluency, and social communication. Unfortunately, there exists a lack of information on the sex-dependent mechanisms of ASD, as well as biological markers to distinguish sex-specific symptoms in ASD. This can often result in a standardized diagnosis for individuals across the spectrum, despite significant differences in the various ASD subtypes. Alterations in neuronal connectivity and oscillatory activity, such as is observed in ASD, are highly coupled to behavioural states. Yet, despite the well-identified sexual dimorphisms that exist in ASD, these functional patterns have rarely been analyzed in the context of sex differences or symptomology. This review summarizes alterations in neuronal oscillatory function in ASD, discusses the age, region, symptom and sex-specific differences that are currently observed across the spectrum, and potential targets for regulating neuronal oscillatory activity in ASD. The need to identify sex-specific biomarkers, in order to facilitate specific diagnostic criteria and allow for more targeted therapeutic approaches for ASD will also be discussed.

Spontaneous Visual Preference for Face-Like Stimuli Is Impaired in Newly-Hatched Domestic Chicks Exposed to Valproic Acid During Embryogenesis

Faces convey a great amount of socially relevant information related to emotional and mental states, identity and intention. Processing of face information is a key mechanism for social and cognitive development, such that newborn babies are already tuned to recognize and orient to faces and simple schematic face-like patterns since the first hours of life. Similar to neonates, also non-human primates and domestic chicks have been shown to express orienting responses to faces and schematic face-like patterns. More importantly, existing studies have hypothesized that early disturbances of these mechanisms represent one of the earliest biomarker of social deficits in autism spectrum disorders (ASD). We used VPA exposure to induce neurodevelopmental changes associated with ASD in domestic chicks and tested whether VPA could impact the expression of the animals’ approach responses to schematic face-like stimuli. We found that VPA impairs the chicks’ preference responses to these social stimuli. Based on the results shown here and on previous studies, we propose the domestic chick as animal model to investigate the biological mechanisms underlying face processing deficits in ASD.

Brain and plasma amino acid concentration in infant rats prenatally exposed to valproic acid

Autism spectrum disorder is associated with alterations in GABAergic and glutamatergic neurotransmission. Here, we aimed to determine the concentration of GABA, glutamate, glutamine, aspartate, taurine, and glycine in brain tissue and plasma of rats prenatally exposed to valproic acid (VPA), a well-characterized experimental model of autism. Pregnant rats were injected with VPA (600mg/Kg) during the twelfth-embryonic-day. Control rats were injected with saline. On the fourteen-postnatal-day, rats from both groups (males and females) were anesthetized, euthanized by decapitation and their brain dissected out. The frontal cortex, hippocampus, amygdala, brain stem and cerebellum were dissected and homogenized. Homogenates were centrifuged and supernatants were used to quantify amino acid concentrations by HPLC coupled with fluorometric detection. Blood samples were obtained by a cardiac puncture; plasma was separated and deproteinized to quantify amino acid concentration by HPLC. We found that, in VPA rats, glutamate and glutamine concentrations were increased in hippocampus and glycine concentration was increased in cortex. We did not find changes in other regions or in plasma amino acid concentration in the VPA group with respect to control group. Our results suggest that VPA exposure in utero may impair inhibitory and excitatory amino acid transmission in the infant brain.

Combined the GABA-A and GABA-B receptor agonists attenuates autistic behaviors in a prenatal valproic acid-induced mouse model of autism

Autism spectrum disorder (ASD) is an immensely challenging developmental disorder characterized primarily by two core behavioral symptoms of social communication deficits and restricted/repetitive behaviors. Investigating the etiological process and identifying an appropriate therapeutic target remain as formidable challenges to overcome ASD due to numerous risk factors and complex symptoms associated with the disorder. Among the various mechanisms that contribute to ASD, the maintenance of excitation and inhibition balance emerged as a key factor to regulate proper functioning of neuronal circuitry. In this study, we employed prenatally exposed to valproic acid (VPA) to establish a validated ASD mouse model and found impaired inhibitory gamma-aminobutyric acid (GABAergic) neurotransmission through a presynaptic mechanism in these model mice, which was accompanied with decreased GABA release and GABA-A and GABA-B receptor subunits expression. And acute administration of individual GABA-A or GABA-B receptor agonists partially reversed autistic-like behaviors in the model mice. Furthermore, acute administration of the combined GABA-A and GABA-B receptor agonists palliated sociability deficits, anxiety and repetitive behaviors in the animal model of autistic-like behaviors, demonstrating the therapeutic potential of above cocktail in the treatment of ASD.

Valproic acid-exposed astrocytes impair inhibitory synapse formation and function

Valproic acid (VPA) is widely prescribed to treat epilepsy. Maternal VPA use is, however, clinically restricted because of the severe risk that VPA may cause neurodevelopmental disorders in offspring, such as autism spectrum disorder. Understanding the negative action of VPA may help to prevent VPA-induced neurodevelopmental disorders. Astrocytes play a vital role in neurodevelopment and synapse function; however, the impact of VPA on astrocyte involvement in neurodevelopment and synapse function has not been examined. In this study, we examined whether exposure of cultured astrocytes to VPA alters neuronal morphology and synapse function of co-cultured neurons. We show that synaptic transmission by inhibitory neurons was small because VPA-exposed astrocytes reduced the number of inhibitory synapses. However, synaptic transmission by excitatory neurons and the number of excitatory synapses were normal with VPA-exposed astrocytes. VPA-exposed astrocytes did not affect the morphology of inhibitory neurons. These data indicate that VPA-exposed astrocytes impair synaptogenesis specifically of inhibitory neurons. Our results indicate that maternal use of VPA would affect not only neurons but also astrocytes and would result in perturbed astrocyte-mediated neurodevelopment.

The Parvalbumin Hypothesis of Autism Spectrum Disorder

The prevalence of autism spectrum disorder (ASD)-a type of neurodevelopmental disorder-is increasing and is around 2% in North America, Asia, and Europe. Besides the known genetic link, environmental, epigenetic, and metabolic factors have been implicated in ASD etiology. Although highly heterogeneous at the behavioral level, ASD comprises a set of core symptoms including impaired communication and social interaction skills as well as stereotyped and repetitive behaviors. This has led to the suggestion that a large part of the ASD phenotype is caused by changes in a few and common set of signaling pathways, the identification of which is a fundamental aim of autism research. Using advanced bioinformatics tools and the abundantly available genetic data, it is possible to classify the large number of ASD-associated genes according to cellular function and pathways. Cellular processes known to be impaired in ASD include gene regulation, synaptic transmission affecting the excitation/inhibition balance, neuronal Ca2+ signaling, development of short-/long-range connectivity (circuits and networks), and mitochondrial function. Such alterations often occur during early postnatal neurodevelopment. Among the neurons most affected in ASD as well as in schizophrenia are those expressing the Ca2+-binding protein parvalbumin (PV). These mainly inhibitory interneurons present in many different brain regions in humans and rodents are characterized by rapid, non-adaptive firing and have a high energy requirement. PV expression is often reduced at both messenger RNA (mRNA) and protein levels in human ASD brain samples and mouse ASD (and schizophrenia) models. Although the human PVALB gene is not a high-ranking susceptibility/risk gene for either disorder and is currently only listed in the SFARI Gene Archive, we propose and present supporting evidence for the Parvalbumin Hypothesis, which posits that decreased PV level is causally related to the etiology of ASD (and possibly schizophrenia).

Gestational Exposure to Sodium Valproate Disrupts Fasciculation of the Mesotelencephalic Dopaminergic Tract, With a Selective Reduction of Dopaminergic Output From the Ventral Tegmental Area

Gestational exposure to valproic acid (VPA) is known to cause behavioral deficits of sociability, matching similar alterations in human autism spectrum disorder (ASD). Available data are scarce on the neuromorphological changes in VPA-exposed animals. Here, we focused on alterations of the dopaminergic system, which is implicated in motivation and reward, with relevance to social cohesion. Whole brains from 7-day-old mice born to mothers given a single injection of VPA (400 mg/kg b.wt.) on E13.5 were immunostained against tyrosine hydroxylase (TH). They were scanned using the iDISCO method with a laser light-sheet microscope, and the reconstructed images were analyzed in 3D for quantitative morphometry. A marked reduction of mesotelencephalic (MT) axonal fascicles together with a widening of the MT tract were observed in VPA treated mice, while other major brain tracts appeared anatomically intact. We also found a reduction in the abundance of dopaminergic ventral tegmental (VTA) neurons, accompanied by diminished tissue level of DA in ventrobasal telencephalic regions (including the nucleus accumbens (NAc), olfactory tubercle, BST, substantia innominata). Such a reduction of DA was not observed in the non-limbic caudate-putamen. Conversely, the abundance of TH+ cells in the substantia nigra (SN) was increased, presumably due to a compensatory mechanism or to an altered distribution of TH+ neurons occupying the SN and the VTA. The findings suggest that defasciculation of the MT tract and neuronal loss in VTA, followed by diminished dopaminergic input to the ventrobasal telencephalon at a critical time point of embryonic development (E13-E14) may hinder the patterning of certain brain centers underlying decision making and sociability.

The early overgrowth theory of autism spectrum disorder: Insight into convergent mechanisms from valproic acid exposure and translational models

The development of new approaches for the clinical management of autism spectrum disorder (ASD) can only be realized through a better understanding of the neurobiological changes associated with ASD. One strategy for gaining deeper insight into the neurobiological mechanisms associated with ASD is to identify converging pathogenic processes associated with human idiopathic clinicopathology that are conserved in translational models of ASD. In this chapter, we first present the early overgrowth theory of ASD. Second, we introduce valproic acid (VPA), one of the most robust and well-known environmental risk factors associated with ASD, and we summarize the rapidly growing body of animal research literature using VPA as an ASD translational model. Lastly, we will detail the mechanisms of action of VPA and its impact on functional neural systems, as well as discuss future research directions that could have a lasting impact on the field.

5-aminolevulinic acid inhibits oxidative stress and ameliorates autistic-like behaviors in prenatal valproic acid-exposed rats

Autism spectrum disorders (ASDs) constitute a neurodevelopmental disorder characterized by social deficits, repetitive behaviors, and learning disability. Oxidative stress and mitochondrial dysfunction are associated with ASD brain pathology. Here, we used oxidative stress in prenatal valproic acid (VPA)-exposed rats as an ASD model. After maternal VPA exposure (600 mg/kg, p.o.) on embryonic day (E) 12.5, temporal analyses of oxidative stress in the brain using an anti-4-hydroxy-2-nonenal antibody revealed that oxidative stress was increased in the hippocampus after birth. This was accompanied by aberrant enzymatic activity in the mitochondrial electron transport chain and reduced adenosine triphosphate (ATP) levels in the hippocampus. VPA-exposed rats exhibited impaired spatial reference and object recognition memory alongside impaired social behaviors and repetitive behaviors. ASD-like behaviors including learning and memory were rescued by chronic oral administration of 5-aminolevulinic acid (5-ALA; 30 mg/kg/day) and intranasal administration of oxytocin (OXT; 12 μg/kg/day), a neuropeptide that improves social behavior in ASD patients. 5-ALA but not OXT treatment ameliorated oxidative stress and mitochondrial dysfunction in the hippocampus of VPA-exposed rats. Fewer parvalbumin-positive interneurons were observed in VPA-exposed rats. Both 5-ALA and OXT treatments augmented the number of parvalbumin-positive interneurons. Collectively, our results indicate that oral 5-ALA administration ameliorated oxidative stress and mitochondrial dysfunction, suggesting that 5-ALA administration improves ASD-like neuropathology and behaviors via mechanisms different to those of OXT.

Inhibition within a premotor circuit controls the timing of vocal turn-taking in zebra finches

Vocal turn-taking is a fundamental organizing principle of human conversation but the neural circuit mechanisms that structure coordinated vocal interactions are unknown. The ability to exchange vocalizations in an alternating fashion is also exhibited by other species, including zebra finches. With a combination of behavioral testing, electrophysiological recordings, and pharmacological manipulations we demonstrate that activity within a cortical premotor nucleus orchestrates the timing of calls in socially interacting zebra finches. Within this circuit, local inhibition precedes premotor neuron activation associated with calling. Blocking inhibition results in faster vocal responses as well as an impaired ability to flexibly avoid overlapping with a partner. These results support a working model in which premotor inhibition regulates context-dependent timing of vocalizations and enables the precise interleaving of vocal signals during turn-taking.

Control over when to initiate or withhold vocalizations is essential for vocal turn-taking. Here the authors investigate vocal interactions in zebra finches and show that inhibition within the premotor nucleus HVC plays an important role in the precise timing of vocal motor responses.

Baclofen as an adjuvant therapy for autism: a randomized, double-blind, placebo-controlled trial

Increasing evidence suggests that the function of the GABAergic system is abnormally low in autism spectrum disorder (ASD). Baclofen, which functions as a selective agonist for GABA_B receptors, does appear promising for the treatment of ASD. We conducted a 10-week randomized-controlled study aimed at evaluating the potential of baclofen as an adjuvant therapy to enhance the effect of risperidone in children with ASD. Sixty-four children (3-12 years) with moderate-to-severe irritability symptoms of ASD were included. We used the Aberrant Behavior Checklist-Community Edition (ABC-C) for the outcome measures on each of the follow-up visits (weeks 0, 5, and 10). Analysis of the combined data revealed significant improvement for all the ABC subscales (irritability: F = 51.644, df = 1.66, p < 0.001, lethargy: F = 39.734, df = 1.38, p < 0.001, stereotypic behavior: F = 25.495, df = 1.56, p < 0.001, hyperactivity: F = 54.135, df = 1.35, p < 0.001, and inappropriate speech: F = 19.277, df = 1.47, p = 0.004). Combined treatment with baclofen and risperidone exerted a greater effect on improvement of hyperactivity symptoms at both midpoint [Cohen's d, 95% confidence interval (CI) = - 3.14, - 5.56 to - 0.72] and endpoint (d, 95% CI = - 4.45, - 8.74 to - 0.16) when compared with treatment with placebo plus risperidone. The two treatments achieved comparable results for other outcome measures. Our data support safety and efficacy of baclofen as an adjuvant to risperidone for improvement of hyperactivity symptoms in children with ASD.

Elevated Level of PKMζ Underlies the Excessive Anxiety in an Autism Model

Anxiety affects the life quality of a significant percentage of autism patients. To understand the possible biological basis of this high anxiety level, we used a valproic acid (VPA) model of autism. Anxiety level is significantly higher in VPA-injected mice, at both P35 and P70. In addition, protein kinase Mζ (PKMζ) level in the basolateral amygdala (BLA) is significantly higher in VPA mice at both ages. Consistent with this finding, infusion of a PKMζ-blocking peptide z-pseudosubstrate inhibitory peptide (ZIP) into BLA significantly reduced anxiety levels in VPA mice. Furthermore, viral overexpression of PKMζ in the BLA led to elevated anxiety level in Wild Type (WT) mice, with concomitant higher intrinsic excitability of BLA excitatory neurons. Altogether, our results indicate a key contribution of BLA PKMζ level to anxiety, especially in autism; and this finding may provide a further understanding of the pathogenesis as well as treatment of anxiety symptoms in autism patients.

Early alterations in a mouse model of Rett syndrome: the GABA developmental shift is abolished at birth

Genetic mutations of the Methyl-CpG-binding protein-2 (MECP2) gene underlie Rett syndrome (RTT). Developmental processes are often considered to be irrelevant in RTT pathogenesis but neuronal activity at birth has not been recorded. We report that the GABA developmental shift at birth is abolished in CA3 pyramidal neurons of Mecp2^-/y mice and the glutamatergic/GABAergic postsynaptic currents (PSCs) ratio is increased. Two weeks later, GABA exerts strong excitatory actions, the glutamatergic/GABAergic PSCs ratio is enhanced, hyper-synchronized activity is present and metabotropic long-term depression (LTD) is impacted. One day before delivery, maternal administration of the NKCC1 chloride importer antagonist bumetanide restored these parameters but not respiratory or weight deficits, nor the onset of mortality. Results suggest that birth is a critical period in RTT with important alterations that can be attenuated by bumetanide raising the possibility of early treatment of the disorder.

Motor cortex excitability and inhibitory imbalance in autism spectrum disorder assessed with transcranial magnetic stimulation: a systematic review

Cortical excitation/inhibition (E/I) imbalances contribute to various clinical symptoms observed in autism spectrum disorder (ASD). However, the detailed pathophysiologic underpinning of E/I imbalance remains uncertain. Transcranial magnetic stimulation (TMS) motor-evoked potentials (MEP) are a non-invasive tool for examining cortical inhibition in ASD. Here, we conducted a systematic review on TMS neurophysiology in motor cortex (M1) such as MEPs and short-interval intracortical inhibition (SICI) between individuals with ASD and controls. Out of 538 initial records, we identified six articles. Five studies measured MEP, where four studies measured SICI. There were no differences in MEP amplitudes between the two groups, whereas SICI was likely to be reduced in individuals with ASD compared with controls. Notably, SICI largely reflects GABA(A) receptor-mediated function. Conversely, other magnetic resonance spectroscopy and postmortem methodologies assess GABA levels. The present review demonstrated that there may be neurophysiological deficits in GABA receptor-mediated function in ASD. In conclusion, reduced GABAergic function in the neural circuits could underlie the E/I imbalance in ASD, which may be related to the pathophysiology of clinical symptoms of ASD. Therefore, a novel treatment that targets the neural circuits related to GABA(A) receptor-mediated function in regions involved in the pathophysiology of ASD may be promising.

Clinical effectiveness of repetitive transcranial magnetic stimulation treatment in children and adolescents with neurodevelopmental disorders: A systematic review

Neurodevelopmental disorders, including autism spectrum disorder, are common in children and adolescents, but treatment strategies remain limited. Although repetitive transcranial magnetic stimulation has been studied for neurodevelopmental disorders, there is no clear consensus on its therapeutic effects. This systematic review examined literature on repetitive transcranial magnetic stimulation for children and adolescents with neurodevelopmental disorders published up to 2018 using the PubMed database. The search identified 264 articles and 14 articles met eligibility criteria. Twelve of these studies used conventional repetitive transcranial magnetic stimulation and two studies used theta burst stimulation. No severe adverse effects were reported in these studies. In patients with autism spectrum disorder, low-frequency repetitive transcranial magnetic stimulation and intermittent theta burst stimulation applied to the dorsolateral prefrontal cortex may have therapeutic effects on social functioning and repetitive behaviors. In patients with attention deficit/hyperactivity disorder, low-frequency repetitive transcranial magnetic stimulation applied to the left dorsolateral prefrontal cortex and high-frequency repetitive transcranial magnetic stimulation applied to the right dorsolateral prefrontal cortex may target inattention, hyperactivity, and impulsivity. In patients with tic disorders, low-frequency repetitive transcranial magnetic stimulation applied to the bilateral supplementary motor area improved tic symptom severity. This systematic review suggests that repetitive transcranial magnetic stimulation may be a promising intervention for children and adolescents with neurodevelopmental disorders. The results warrant further large randomized controlled trials of repetitive transcranial magnetic stimulation in children with neurodevelopmental disorders.

Negative geotaxis: An early age behavioral hallmark to VPA rat model of autism

Background

Negative geotaxis (NG) is an important parameter, commonly used in study of different CNS diseases and neurodevelopmental disorders. Neurobehavioural change following brain injury was easily identified by negative geotaxis.

Purpose

Although NG is evaluated in the settings of ASD, most of the studies are conducted for short duration (1-3 day) and the overall trend of acquisition of NG is not evaluated. In this context, we wanted to evaluate the trend of acquisition of negative geotaxis as a behavioural marker of autism in Valproic acid (VPA) model of ASD.

Methods

Dams in the VPA group were treated with intraperitoneal injections of VPA 600 mg/kg single dose on gestational day 12.5, while the control animals received normal saline of similar volume. Developmental parameters {body weight (PND 8, 10 & 12), body length (PND 4, 5, 6 8, 10), eye opening (PND 10, 12, 14, 15 and 16) and motor development (grid walking test on PND 20)} were monitored. Negative geotaxis test was performed at PND 6, 10, 15 and 17.

Results

The results of the present experiments demonstrate that VPA exposed rats exhibited delayed developmental parameters, aberration of the pattern of acquisition of negative geotaxis, enhanced negative geotaxis in early postnatal period (PND 6) and enhanced negative geotaxis in absence of visual clues (PND 17).

Conclusion

NG can be a valuable biomarker in early detection of autistic behavior and in absence of visual clues. The abberant negative geotaxis developmental pattern can serve as a marker to detect ASD. Thus NG can serve as an important early age biomarker of ASD. Further studies are required to validate this finding.

Gastrodin Rescues Autistic-Like Phenotypes in Valproic Acid-Induced Animal Model

Autism spectrum disorder (ASD) is an immensely challenging developmental disorder characterized by impaired social interaction, restricted/repetitive behavior, and anxiety. GABAergic dysfunction has been postulated to underlie these autistic symptoms. Gastrodin is widely used clinically in the treatment of neurological disorders and showed to modulate GABAergic signaling in the animal brain. The present study aimed to determine whether treatment with gastrodin can rescue valproic acid (VPA) induced autistic-like phenotypes, and to determine its possible mechanism of action. Our results showed that administration of gastrodin effectively alleviated the autistic-associated behavioral abnormalities as reflected by an increase in social interaction and decrement in repetitive/stereotyped behavior and anxiety in mice as compared to those in untreated animals. Remarkably, the amelioration in autistic-like phenotypes was accompanied by the restoration of inhibitory synaptic transmission, α5 GABA_A receptor, and type 1 GABA transporter (GAT1) expression in the basolateral amygdala (BLA) of VPA-treated mice. These findings indicate that gastrodin may alleviate the autistic symptoms caused by VPA through regulating GABAergic synaptic transmission, suggesting that gastrodin may be a potential therapeutic target in autism.

Association of Autism Spectrum Disorder With Prenatal Exposure to Medication Affecting Neurotransmitter Systems

IMPORTANCE

Prenatal exposure to certain medications has been hypothesized to influence the risk of autism spectrum disorders (ASD). However, the underlying effects on the neurotransmitter systems have not been comprehensively assessed.

OBJECTIVE

To investigate the association of early-life interference with different neurotransmitter systems by prenatal medication exposure on the risk of ASD in offspring.

DESIGN, SETTING, AND PARTICIPANTS

This case-control study included children born from January 1, 1997, through December 31, 2007, and followed up for ASD until January 26, 2015, within a single Israeli health maintenance organization. Using publicly available data, 55 groups of medications affecting neurotransmitter systems and prescribed to pregnant women in this sample were identified. Children prenatally exposed to medications were compared with nonexposed children. Data were analyzed from March 1, 2017, through June 20, 2018.

MAIN OUTCOME AND MEASURES

Hazard ratios (HRs) and 95% CIs of ASD risk associated with exposure to medication groups using Cox proportional hazards regression, adjusted for the relevant confounders (eg, birth year, maternal age, maternal history of psychiatric and neurologic disorders, or maternal number of all medical diagnoses 1 year before pregnancy).

RESULTS

The analytic sample consisted of 96 249 individuals (1405 cases; 94 844 controls; mean [SD] age at the end of follow-up, 11.6 [3.1] years; 48.8% female), including 1405 with ASD and 94 844 controls. Of 34 groups of medications, 5 showed nominally statistically significant association with ASD in fully adjusted models. Evidence of confounding effects of the number of maternal diagnoses on the association between offspring exposure to medication and ASD was found. Adjusting for this factor, lower estimates of ASD risk among children exposed to cannabinoid receptor agonists (HR, 0.72; 95% CI, 0.55-0.95; P = .02), muscarinic receptor 2 agonists (HR, 0.49; 95% CI, 0.24-0.98; P = .04), opioid receptor κ and ε agonists (HR, 0.67; 95% CI, 0.45-0.99; P = .045), or α2C-adrenergic receptor agonists (HR, 0.43; 95% CI, 0.19-0.96; P = .04) were observed. Exposure to antagonists of neuronal nicotinic acetylcholine receptor α was associated with higher estimates of ASD risk (HR, 12.94; 95% CI, 1.35-124.25; P = .03).

CONCLUSIONS AND RELEVANCE

Most of the medications affecting neurotransmitter systems in this sample had no association with the estimates of ASD risk. Replication and/or validation using experimental techniques are required.

Social behavior, neuroimmune markers and glutamic acid decarboxylase levels in a rat model of valproic acid-induced autism

Autism is a complex neurodevelopmental disorder characterized by impaired social communication and social interactions, and repetitive behaviors. The etiology of autism remains unknown and its molecular basis is not yet well understood. Pregnant Sprague-Dawley (SD) rats were administered 600 mg/kg of valproic acid (VPA) by intraperitoneal injection on day 12.5 of gestation. Both 11- to 13-week-old male and female rat models of VPA-induced autism showed impaired sociability and impaired preference for social novelty as compared to the corresponding control SD rats. Significantly reduced mRNA expressions of social behavior-related genes, such as those encoding the serotonin receptor, brain-derived neurotrophic factor and neuroligin3, and significantly increased expression levels of proinflammatory cytokines, such as interleukin-1 β and tumor necrosis factor-α, were noted in the hippocampi of both male and female rats exposed to VPA in utero. The hippocampal expression level of gamma amino butyric acid (GABA) enzyme glutamic acid decarboxylase (GAD) 67 protein was reduced in both male and female VPA-exposed rats as compared to the corresponding control animals. Our results indicate that developmental exposure to VPA affects the social behavior in rats by modulating the expression levels of social behavior-related genes and inflammatory mediators accompanied with changes in GABA enzyme in the hippocampus.

Deep Brain Stimulation Modified Autism-Like Deficits via the Serotonin System in a Valproic Acid-Induced Rat Model

Deep brain stimulation (DBS) is known to be a promising treatment for resistant depression, which acts via the serotonin (5-hydroxytryptamine, 5-HT) system in the infralimbic prefrontal cortex (ILPFC). Previous study revealed that dysfunction of brain 5-HT homeostasis is related to a valproate (VPA)-induced rat autism spectrum disorder (ASD) model. Whether ILPFC DBS rescues deficits in VPA-induced offspring through the 5-HT system is not known. Using VPA-induced offspring, we therefore explored the effect of DBS in autistic phenotypes and further investigated the underlying mechanism. Using combined behavioral and molecular approaches, we observed that applying DBS and 5-HT_1A receptor agonist treatment with 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) reversed sociability deficits, anxiety and hyperactivity in the VPA-exposed offspring. We then administered the selective 5-HT_1A receptor antagonist N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide maleate (WAY 100635), following which the effect of DBS in terms of improving autistic behaviors was blocked in the VPA-exposed offspring. Furthermore, we found that both 8-OH-DPAT and DBS treatment rescued autistic behaviors by decreasing the expressions of NR2B subunit of N-methyl-D-aspartate receptors (NMDARs) and the β₃ subunit of γ-aminobutyric acid type A receptors (GABA_AR) in the PFC region. These results provided the first evidence of characteristic behavioral changes in VPA-induced offspring caused by DBS via the 5-HT system in the ILPFC.

A Developmental Study of Abnormal Behaviors and Altered GABAergic Signaling in the VPA-Treated Rat Model of Autism

Although studies have investigated the role of gamma-aminobutyric acid (GABA)ergic signaling in rodent neural development and behaviors relevant to autism, behavioral ontogeny, as underlain by the changes in GABAergic system, is poorly characterized in different brain regions. Here, we employed a valproic acid (VPA) rat model of autism to investigate the autism-like behaviors and GABAergic glutamic acid decarboxylase 67 (GAD67) expression underlying these altered behaviors in multiple brain areas at different developmental stages from birth to adulthood. We found that VPA-treated rats exhibited behavioral abnormalities relevant to autism, including delayed nervous reflex development, altered motor coordination, delayed sensory development, autistic-like and anxiety behaviors and impaired spatial learning and memory. We also found that VPA rats had the decreased expression of GAD67 in the hippocampus (HC) and cerebellum from childhood to adulthood, while decreased GAD67 expression of the temporal cortex (TC) was only observed in adulthood. Conversely, GAD67 expression was increased in the prefrontal cortex (PFC) from adolescence to adulthood. The dysregulated GAD67 expression could alter the excitatory-inhibitory balance in the cerebral cortex, HC and cerebellum. Our findings indicate an impaired GABAergic system could be a major etiological factor occurring in the cerebral cortex, HC and cerebellum of human cases of autism, which suggests enhancement of GABA signaling would be a promising therapeutic target for its treatment.

Dexmedetomidine and propofol sedation requirements in an autistic rat model

Background

Autism is a challenging neurodevelopmental disorder. Previous clinical observations have suggested altered sedation requirements for children with autism. Our study aimed to test this observation experimentally in an animal model and to explore its possible mechanisms.

Methods

Eight adult pregnant female Sprague-Dawley rats were randomly divided into two groups. Four were injected with intraperitoneal sodium valproate on gestational day 12 and four were injected with normal saline. On postnatal day 28, the newborn male rats were subjected to the open-field test to confirm autistic features. Each rat was injected intraperitoneally with a single dose of propofol (50 mg/kg) or dexmedetomidine (0.2 mg/kg). The times to loss of righting reflex (LORR) and to return of righting reflex (RORR) were recorded. On the following day, all rats were re-sedated and underwent electroencephalography (EEG). Thereafter, the rats were euthanized and their hippocampal gamma-aminobutyric acid type A (GABA_A) and glutamate N-methyl-D-aspartate (NMDA) receptor gene expressions were assessed.

Results

Autistic rats showed significantly longer LORR times and shorter RORR times than did the controls (median LORR times: 12.0 versus 5.0 min for dexmedetomidine and 22.0 versus 8.0 min for propofol; P < 0.05). EEG showed a low-frequency, high-amplitude wave pattern 2 min after LORR in the control rats. Autistic rats showed a high-frequency, low-amplitude awake pattern. Hippocampal GABA_A receptor gene expression was significantly lower and NMDA gene expression was greater in autistic rats.

Conclusions

This study supports the clinical observations of increased anesthetic sedative requirements in children with autism and our biochemical analyses using GABA_A and glutamate receptor gene expression highlight possible underlying mechanisms.