Modeling autism-relevant behavioral phenotypes in rats and mice: Do ‘autistic’ rodents exist?

Early-life exposure to PM2.5 leads to ASD-like phenotype in male offspring rats through activation of PI3K-AKT signaling pathway

Previous studies have shown that early-life exposure to fine particulate matter (PM2.5) is associated with an increasing risk of autism spectrum disorder (ASD), however, the specific sensitive period of ASD is unknown. Here, a model of dynamic whole-body concentrated PM2.5 exposure in pre- and early-postnatal male offspring rats (MORs) was established. And we found that early postnatal PM2.5 exposed rats showed more typical ASD behavioral characteristics than maternal pregnancy exposure rats, including poor social interaction, novelty avoidance and anxiety disorder. And more severe oxidative stress and inflammatory responses were observed in early postnatal PM2.5 exposed rats. Moreover, the expression level of phosphatase and tensin homolog deleted on chromosome ten (PTEN) was down-regulated and the ratios of p-PI3K/PI3K and p-AKT/AKT were up-regulated in early postnatal PM2.5 exposed rats. This study suggests that early postnatal exposure to PM2.5 is more susceptible to ASD-like phenotype in offspring than maternal pregnancy exposure and the activation of PI3K-AKT signaling pathway may represent underlying mechanisms.

Sociability: Comparing the Effect of Chlorpyrifos with Valproic Acid

In recent years, exposures to organophosphate pesticide have been highlighted as a possible cause or aggravating factor of autism spectrum disorder (ASD). The present study examined if Wistar rats prenatally exposed to chlorpyrifos (CPF) at a dose of 1 mg/kg in GD 12.5-15.5 could express similar behaviors to those exposed to valproic acid (VPA, 400 mg/kg) during the same administration window, which is an accepted animal model of autism. The 3-chambered test was employed to evaluate sociability and reaction to social novelty in two experiments, the first in adolescence and the second in adulthood. The results obtained in this study show that animals prenatally treated with CPF or VPA show a similar behavioral phenotype compared to the control group (CNT). In adolescence, the CPF animals showed a negative index in the reaction to social novelty, followed closely by the VPA, while both experimental groups showed a recovery in this aspect during adulthood. This study therefore provides evidence to suggest that prenatal exposure to CPF in rats could have similar effects on certain components of sociability to those seen in autistic models.

Group I and group II metabotropic glutamate receptors are upregulated in the synapses of infant rats prenatally exposed to valproic acid

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interaction and restricted/stereotyped behavior. Prenatal exposure to valproic acid (VPA) is associated with an increased risk of developing ASD in humans and autistic-like behaviors in rodents. Increasing evidence indicates that dysfunctions of glutamate receptors at synapses are associated with ASD. In the VPA rat model, an involvement of glutamate receptors in autism-like phenotypes has been suggested; however, few studies were carried out on metabotropic glutamate (mGlu) receptors.

OBJECTIVES

We examined the protein expression levels of group I (mGlu1 and mGlu5) and group II (mGlu2/3) mGlu receptors in rats prenatally exposed to VPA and evaluated the effect of mGlu receptor modulation on an early autism-like phenotype in these animals.

METHODS

We used western blotting analysis on synaptosomes obtained from forebrain of control and VPA rats at different ages (postnatal day P13, 35, 90) and carried out ultrasonic vocalization (USV) emission test in infant control and VPA rats.

RESULTS

The expression levels of all these receptors were significantly increased in infant VPA rats. No changes were detected in adolescent and adult rats. An acute treatment with the preferential mGlu2/3 antagonist, LY341495, attenuated the impairment in the USV emission in VPA rats. No effect was observed after a treatment with the mGlu5 selective antagonist, MTEP.

CONCLUSIONS

Our findings demonstrate that the expression of group I and group II mGlu receptors is upregulated at synapses of infant VPA rats and suggest that mGlu2/3 receptor modulation may have a therapeutic potential in ASD.

Altered Developmental Trajectory in Male and Female Rats in a Prenatal Valproic Acid Exposure Model of Autism Spectrum Disorder

Early motor and sensory developmental delays precede Autism Spectrum Disorder (ASD) diagnosis and may serve as early indicators of ASD. The literature on sensorimotor development in animal models is sparse, male centered, and has mixed findings. We characterized early development in a prenatal valproic acid (VPA) model of ASD and found sex-specific developmental delays in VPA rats. We created a developmental composite score combining 15 test readouts, yielding a reliable gestalt measure spanning physical, sensory, and motor development, that effectively discriminated between VPA and control groups. Considering the heterogeneity in ASD phenotype, the developmental composite offers a robust metric that can enable comparison across different animal models of ASD and can serve as an outcome measure for early intervention studies.

Amelioration of cognition impairments in the valproic acid-induced animal model of autism by ciproxifan, a histamine H3-receptor antagonist

Autism spectrum disorder is a neurodevelopmental disorder characterized by deficits in social communication and repetitive behavior. Many studies show that the number of cognitive impairmentscan be reduced by antagonists of the histamine H3 receptor (H3R). In this study, the effects of ciproxifan (CPX) (1 and 3 mg/kg, intraperitoneally) on cognitive impairments in rat pups exposed to valproic acid (VPA) (600 mg/kg, intraperitoneally) wereexamined on postnatal day 48-50 (PND 48-50) using marble-burying task (MBT), open field, novel object recognition (NOR), and Passive avoidance tasks. Famotidine (FAM) (10, 20, and 40 mg/kg, intraperitoneally) was also used to determine whether histaminergic neurotransmission exerts its procognitive effects via H2 receptors (H2Rs). Furthermore, a histological investigation was conducted to assess the degree of degeneration of hippocampal neurons. The results revealed that repetitive behaviors increased in VPA-exposed rat offspring in the MBT. In addition, VPA-exposed rat offspring exhibited more anxiety-like behaviors in the open field than saline-treated rats. It was found that VPA-exposed rat offspring showed memory deficits in NOR and Passive avoidance tasks. Our results indicated that 3 mg/kg CPX improved cognitive impairments induced by VPA, while 20 mg/kg FAM attenuated them. We concluded that 3 mg/kg CPX improved VPA-induced cognitive impairments through H3Rs. The histological assessment showed that the number of CA1 neurons decreased in the VPA-exposed rat offspring compared to the saline-exposed rat offspring, but this decrease was not significant. The histological assessment also revealed no significant differences in CA1 neurons in VPA-exposed rat offspring compared to saline-exposed rat offspring. However, CPX3 increased the number of CA1 neurons in the VPA + CPX3 group compared to the VPA + Saline group, but this increase was not significant. This study showed that rats prenatally exposed to VPA exhibit cognitive impairments in the MBT, open field, NOR, and Passive avoidance tests, which are ameliorated by CPX treatment on PND 48-50. In addition, morphological investigations showed that VPA treatment did not lead to neuronal degeneration in the CA1 subfield of the hippocampus in rat pups.

Maternal Immune Activation Induced by Prenatal Lipopolysaccharide Exposure Leads to Long-Lasting Autistic-like Social, Cognitive and Immune Alterations in Male Wistar Rats

Several studies have supported the association between maternal immune activation (MIA) caused by exposure to pathogens or inflammation during critical periods of gestation and an increased susceptibility to the development of various psychiatric and neurological disorders, including autism and other neurodevelopmental disorders (NDDs), in the offspring. In the present work, we aimed to provide extensive characterization of the short- and long-term consequences of MIA in the offspring, both at the behavioral and immunological level. To this end, we exposed Wistar rat dams to Lipopolysaccharide and tested the infant, adolescent and adult offspring across several behavioral domains relevant to human psychopathological traits. Furthermore, we also measured plasmatic inflammatory markers both at adolescence and adulthood. Our results support the hypothesis of a deleterious impact of MIA on the neurobehavioral development of the offspring: we found deficits in the communicative, social and cognitive domains, together with stereotypic-like behaviors and an altered inflammatory profile at the systemic level. Although the precise mechanisms underlying the role of neuroinflammatory states in neurodevelopment need to be clarified, this study contributes to a better understanding of the impact of MIA on the risk of developing behavioral deficits and psychiatric illness in the offspring.

FMR1 deletion in rats induces hyperactivity with no changes in striatal dopamine transporter availability

Autism Spectrum Disorder (ASD) is a pervasive neurodevelopmental disorder emerging in early life characterized by impairments in social interaction, poor verbal and non-verbal communication, and repetitive patterns of behaviors. Among the best-known genetic risk factors for ASD, there are mutations causing the loss of the Fragile X Messenger Ribonucleoprotein 1 (FMRP) leading to Fragile X syndrome (FXS), a common form of inherited intellectual disability and the leading monogenic cause of ASD. Being a pivotal regulator of motor activity, motivation, attention, and reward processing, dopaminergic neurotransmission has a key role in several neuropsychiatric disorders, including ASD. Fmr1 ^Δexon 8 rats have been validated as a genetic model of ASD based on FMR1 deletion, and they are also a rat model of FXS. Here, we performed behavioral, biochemical and in vivo SPECT neuroimaging experiments to investigate whether Fmr1 ^Δexon 8 rats display ASD-like repetitive behaviors associated with changes in striatal dopamine transporter (DAT) availability assessed through in vivo SPECT neuroimaging. At the behavioral level, Fmr1 ^Δexon 8 rats displayed hyperactivity in the open field test in the absence of repetitive behaviors in the hole board test. However, these behavioral alterations were not associated with changes in striatal DAT availability as assessed by non-invasive in vivo SPECT and Western blot analyses.

Social Behavioral Deficits in Krushinsky-Molodkina Rats, an Animal Model of Audiogenic Epilepsy

In clinical practice, epilepsy is often comorbid with the autism spectrum disorders (ASDs). This warrants a search of animal models to uncover putative overlapping neuronal mechanisms. The Krushinsky-Molodkina (KM) rat strain is one of the oldest inbred animal models for human convulsive epilepsies. We analyzed the behavioral response of adult seizure-naive KM males in three-chambered tests for social preference. We found that a presence of social stimuli (encaged unfamiliar Wistar rats of the same age and sex) evoked a reduced or reversed exploratory response in freely moving KM individuals. The epilepsy-prone rats demonstrated remarkably shortened bouts of social contacts and displayed less locomotion around the stranger rat-containing boxes, together with a pronounced freezing response. The decrease in social preference was not due to a general decrease in activity, since relative measures of activity, the index of sociability, were decreased, too. The susceptibility to audiogenic seizures was verified in the KM cohort but not seen in the control Wistar group. We propose the KM rat strain as a new animal model for comorbid ASD and epilepsy.

The inhibition of NCS-1 binding to Ric8a rescues fragile X syndrome mice model phenotypes

Fragile X syndrome (FXS) is caused by the loss of function of Fragile X mental retardation protein (FMRP). FXS is one of the leading monogenic causes of intellectual disability (ID) and autism. Although it is caused by the failure of a single gene, FMRP that functions as an RNA binding protein affects a large number of genes secondarily. All these genes represent hundreds of potential targets and different mechanisms that account for multiple pathological features, thereby hampering the search for effective treatments. In this scenario, it seems desirable to reorient therapies toward more general approaches. Neuronal calcium sensor 1 (NCS-1), through its interaction with the guanine-exchange factor Ric8a, regulates the number of synapses and the probability of the release of a neurotransmitter, the two neuronal features that are altered in FXS and other neurodevelopmental disorders. Inhibitors of the NCS-1/Ric8a complex have been shown to be effective in restoring abnormally high synapse numbers as well as improving associative learning in FMRP mutant flies. Here, we demonstrate that phenothiazine FD44, an NCS-1/Ric8a inhibitor, has strong inhibition ability in situ and sufficient bioavailability in the mouse brain. More importantly, administration of FD44 to two different FXS mouse models restores well-known FXS phenotypes, such as hyperactivity, associative learning, aggressive behavior, stereotype, or impaired social approach. It has been suggested that dopamine (DA) may play a relevant role in the behavior and in neurodevelopmental disorders in general. We have measured DA and its metabolites in different brain regions, finding a higher metabolic rate in the limbic area, which is also restored with FD44 treatment. Therefore, in addition to confirming that the NCS-1/Ric8a complex is an excellent therapeutic target, we demonstrate the rescue effect of its inhibitor on the behavior of cognitive and autistic FXS mice and show DA metabolism as a FXS biochemical disease marker.

Autism spectrum disorder-like behavior induced in rat offspring by perinatal exposure to di-(2-ethylhexyl) phthalate

Autism spectrum disorders (ASD), also known as childhood autism, is a common neurological developmental disorder. Although it is generally believed that genetic factors are a primary cause for ASD development, more and more studies show that an increasing number of ASD diagnoses are related to environmental exposure. Epidemiological studies indicated that perinatal exposure to endocrine disruptors might cause neurodevelopmental disorders in children. Di-(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in many products. To explore the neurodevelopmental effect induced by perinatal exposure to DEHP on rat offspring, and the potential mechanisms, female Wistar rats were exposed to 1, 10, and 100 mg/kg/day DEHP during pregnancy and lactation, while valproic acid (VPA) was used as a positive control. The behavior tests showed that rat pups exposed to VPA and 100 mg/kg/day DEHP were not good as those from the control group in both their socialability and social novelty. Expression of mTOR pathway-related components increased while the number of autophagosomes decreased in the brain tissue of the rat offspring exposed to 100 mg/kg/day DEHP. In addition, perinatal exposure to DEHP at all dosages decreased the level of autophagy proteins LC3II and Beclin1 in the brain tissue of rat pups. Our results indicated that perinatal DEHP exposure would induce ASD-like behavioral changes in rat offspring, which might be mediated by activation of the mTOR signaling pathway, and inhibition of autophagy in the brain.

Sex Differences in Autism Spectrum Disorder: Diagnostic, Neurobiological, and Behavioral Features

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder with a worldwide prevalence of about 1%, characterized by impairments in social interaction, communication, repetitive patterns of behaviors, and can be associated with hyper- or hypo-reactivity of sensory stimulation and cognitive disability. ASD comorbid features include internalizing and externalizing symptoms such as anxiety, depression, hyperactivity, and attention problems. The precise etiology of ASD is still unknown and it is undoubted that the disorder is linked to some extent to both genetic and environmental factors. It is also well-documented and known that one of the most striking and consistent finding in ASD is the higher prevalence in males compared to females, with around 70% of ASD cases described being males. The present review looked into the most significant studies that attempted to investigate differences in ASD males and females thus trying to shade some light on the peculiar characteristics of this prevalence in terms of diagnosis, imaging, major autistic-like behavior and sex-dependent uniqueness. The study also discussed sex differences found in animal models of ASD, to provide a possible explanation of the neurological mechanisms underpinning the different presentation of autistic symptoms in males and females.

Reinforced behavioral variability in the valproate rat model of autism spectrum disorder

Individuals diagnosed with autism spectrum disorder (ASD) tend to display restricted, repetitive behaviors and deficits in social interaction. Rats exposed to valproate (VPA) in utero have been shown to model symptoms of ASD. In previous research, VPA rats engaged in less social interaction and more repetitive responding than controls. The purpose of the present study was to further investigate behavioral variability in the VPA rat model of ASD by testing VPA and control rats in a reinforced-behavioral-variability operant task. In this procedure, rats emitted sequences of lever presses, some of which produced food. During baseline, food was delivered probabilistically, and variability was not required. Next, rats were exposed either to a variability contingency, in which food was only delivered following sequences that differed sufficiently from previous sequences (i.e., variability required), or to a yoked contingency, in which variability was not required. We hypothesized that VPA rats would behave less variably than controls in this task. However, VPA and control rats responded similarly variably when variability was required. Furthermore, VPA rats behaved slightly more variably than controls during baseline and yoked conditions, when variability was not required. These findings contribute to the complex literature surrounding the VPA rat model of ASD.

Phosphodiesterase 2A inhibition corrects the aberrant behavioral traits observed in genetic and environmental preclinical models of Autism Spectrum Disorder

Pharmacological inhibition of phosphodiesterase 2A (PDE2A), which catalyzes the hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), has recently been proposed as a novel therapeutic tool for Fragile X Syndrome (FXS), the leading monogenic cause of Autism Spectrum Disorder (ASD). Here, we investigated the role of PDE2A in ASD pathogenesis using two rat models that reflect one of either the genetic or environmental factors involved in the human disease: the genetic Fmr1-Δexon 8 rat model and the environmental rat model based on prenatal exposure to valproic acid (VPA, 500 mg/kg). Prior to behavioral testing, the offspring was treated with the PDE2A inhibitor BAY607550 (0.05 mg/kg at infancy, 0.1 mg/kg at adolescence and adulthood). Socio-communicative symptoms were assessed in both models through the ultrasonic vocalization test at infancy and three-chamber test at adolescence and adulthood, while cognitive impairments were assessed by the novel object recognition test in Fmr1-Δexon 8 rats (adolescence and adulthood) and by the inhibitory avoidance test in VPA-exposed rats (adulthood). PDE2A enzymatic activity in VPA-exposed infant rats was also assessed. In line with the increased PDE2A enzymatic activity previously observed in the brain of Fmr1-KO animals, we found an altered upstream regulation of PDE2A activity in the brain of VPA-exposed rats at an early developmental age (p < 0.05). Pharmacological inhibition of PDE2A normalized the communicative (p < 0.01, p < 0.05), social (p < 0.001, p < 0.05), and cognitive impairment (p < 0.001) displayed by both Fmr1-Δexon 8 and VPA-exposed rats. Altogether, these data highlight a key role of PDE2A in brain development and point to PDE2A inhibition as a promising pharmacological approach for the deficits common to both FXS and 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.

Modeling dopamine dysfunction in autism spectrum disorder: From invertebrates to vertebrates

Autism Spectrum Disorder (ASD) is a highly heterogeneous neurodevelopmental disorder characterized by deficits in social communication and by patterns of restricted interests and/or repetitive behaviors. The Simons Foundation Autism Research Initiative's Human Gene and CNV Modules now list over 1000 genes implicated in ASD and over 2000 copy number variant loci reported in individuals with ASD. Given this ever-growing list of genetic changes associated with ASD, it has become evident that there is likely not a single genetic cause of this disorder nor a single neurobiological basis of this disorder. Instead, it is likely that many different neurobiological perturbations (which may represent subtypes of ASD) can result in the set of behavioral symptoms that we called ASD. One such of possible subtype of ASD may be associated with dopamine dysfunction. Precise regulation of synaptic dopamine (DA) is required for reward processing and behavioral learning, behaviors which are disrupted in ASD. Here we review evidence for DA dysfunction in ASD and in animal models of ASD. Further, we propose that these studies provide a scaffold for scientists and clinicians to consider subcategorizing the ASD diagnosis based on the genetic changes, neurobiological difference, and behavioral features identified in individuals with ASD.

Chronic consumption of a high linoleic acid diet during pregnancy, lactation and post-weaning period increases depression-like behavior in male, but not female offspring

Polyunsaturated fatty acids (PUFAs) play an essential role in brain development. Emerging data have suggested a possible link between an imbalance in PUFAs and cognitive behavioral deficits in offspring. A diet rich in high linoleic acid (HLA), typically from preconception to lactation, leads to an increase in the ratio of omega-6 (n-6) to omega-3 (n-3) fatty acids in the fetus. Arising research has suggested that a deficiency in omega-3 fatty acids is a potential risk factor for inducing autism spectrum disorder (ASD)-like behavioral deficits. However, the impact of a high n- diet during preconception, pregnancy, lactation, and post-weaning on the brain development of adolescent offspring are yet to be determined. This study examined whether consumption of an HLA diet during pregnancy, lactation, and post-weaning induced social and cognitive impairments in female and male offspring rats that resemble autistic phenotypes in humans. Female Wistar Kyoto rats were fed with either HLA or low linoleic acid (LLA) control diet for 10 weeks before mating, then continued with the same diet throughout the pregnancy and lactation period. Female and male offspring at 5 weeks old were subjected to behavioral tests to assess social interaction behavior and depression-/anxiety-like behavior. Our result showed that chronic consumption of an HLA diet did not affect sociability and social recognition memory, but induced depression-like behavior in male but not in female offspring.

Social Deficits or Interactional Differences? Interrogating Perspectives on Social Functioning in Autism

Social dysfunction is a key characteristic of autism. Determining and treating autism-related social deficits have been challenging. The medical model views interpersonal difficulties in autism as a localized set of deficits to be managed, whereas the neurodiversity movement calls for the accommodation of differences by the larger community. One common assumption underlying these perspectives is a misalignment in social behaviors between autistic individuals and neurotypicals. This paper reviews and interrogates current perspectives on social functioning in autism to uncover the intricacies of such a notion. Even though extant literature has alluded to a misalignment in social behaviors between autistic and neurotypical individuals, it is uncertain where this disparity lies. Implications for future research and practice are discussed.

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.

Assessment of behavioral, morphological and electrophysiological changes in prenatal and postnatal valproate induced rat models of autism spectrum disorder

Autism spectrum disorders (ASD) are neurodevelopmental disorders, that are characterized by core symptoms, such as alterations of social communication and restrictive or repetitive behavior. The etiology and pathophysiology of disease is still unknown, however, there is a strong interaction between genetic and environmental factors. An intriguing point in autism research is identification the vulnerable time periods of brain development that lack compensatory homeostatic corrections. Valproic acid (VPA) is an antiepileptic drug with a pronounced teratogenic effect associated with a high risk of ASD, and its administration to rats during the gestation is used for autism modeling. It has been hypothesized that valproate induced damage and functional alterations of autism target structures may occur and evolve during early postnatal life. Here, we used prenatal and postnatal administrations of VPA to investigate the main behavioral features which are associated with autism spectrum disorders core symptoms were tested in early juvenile and adult rats. Neuroanatomical lesion of autism target structures and electrophysiological studies in specific neural circuits. Our results showed that prenatal and early postnatal administration of valproate led to the behavioral alterations that were similar to ASD. Postnatally treated group showed tendency to normalize in adulthood. We found pronounced structural changes in the brain target regions of prenatally VPA-treated groups, and an absence of abnormalities in postnatally VPA-treated groups, which confirmed the different severity of VPA across different stages of brain development. The results of this study clearly show time dependent effect of VPA on neurodevelopment, which might be explained by temporal differences of brain regions' development process. Presumably, postnatal administration of valproate leads to the dysfunction of synaptic networks that is recovered during the lifespan, due to the brain plasticity and compensatory ability of circuit refinement. Therefore, investigations of compensatory homeostatic mechanisms activated after VPA administration and directed to eliminate the defects in postnatal brain, may elucidate strategies to improve the course of disease.

The role of the endocannabinoid system as a therapeutic target for autism spectrum disorder: Lessons from behavioral studies on mouse models

Recent years have seen an impressive amount of research devoted to understanding the etiopathology of Autism Spectrum Disorder (ASD) and developing therapies for this syndrome. Because of the lack of biomarkers of ASD, this work has been largely based on the behavioral characterization of rodent models, based on a multitude of genetic and environmental manipulations. Here we highlight how the endocannabinoid system (ECS) has recently emerged within this context of mouse behavioral studies as an etiopathological factor in ASD and a valid potential therapeutic target. We summarize the most recent results showing alterations of the ECS in rodent models of ASD, and demonstrating ASD-like behaviors in mice with altered ECS, induced either by genetic or pharmacological manipulations. We also give a critical overview of the most relevant advances in designing treatments and novel mouse models for ASD targeting the ECS, highlighting the relevance of thorough and innovative behavioral approaches to investigate the mechanisms acting underneath the complex features of ASD.

GABAB Receptor Agonist R-Baclofen Reverses Altered Auditory Reactivity and Filtering in the Cntnap2 Knock-Out Rat

Altered sensory information processing, and auditory processing, in particular, is a common impairment in individuals with autism spectrum disorder (ASD). One prominent hypothesis for the etiology of ASD is an imbalance between neuronal excitation and inhibition. The selective GABA_B receptor agonist R-Baclofen has been shown previously to improve social deficits and repetitive behaviors in several mouse models for neurodevelopmental disorders including ASD, and its formulation Arbaclofen has been shown to ameliorate social avoidance symptoms in some individuals with ASD. The present study investigated whether R-Baclofen can remediate ASD-related altered sensory processing reliant on excitation/inhibition imbalance in the auditory brainstem. To assess a possible excitation/inhibition imbalance in the startle-mediating brainstem underlying ASD-like auditory-evoked behaviors, we detected and quantified brain amino acid levels in the nucleus reticularis pontis caudalis (PnC) of rats with a homozygous loss-of-function mutation in the ASD-linked gene Contactin-associated protein-like 2 (Cntnap2) and their wildtype (WT) littermates using Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI MS). Abnormal behavioral read-outs of brainstem auditory signaling in Cntnap2 KO rats were accompanied by increased levels of GABA, glutamate, and glutamine in the PnC. We then compared the effect of R-Baclofen on behavioral read-outs of brainstem auditory signaling in Cntnap2 KO and WT rats. Auditory reactivity, sensory filtering, and sensorimotor gating were tested in form of acoustic startle response input-output functions, short-term habituation, and prepulse inhibition before and after acute administration of R-Baclofen (0.75, 1.5, and 3 mg/kg). Systemic R-Baclofen treatment improved disruptions in sensory filtering in Cntnap2 KO rats and suppressed exaggerated auditory startle responses, in particular to moderately loud sounds. Lower ASR thresholds in Cntnap2 KO rats were increased in a dose-dependent fashion, with the two higher doses bringing thresholds close to controls, whereas shorter ASR peak latencies at the threshold were further exacerbated. Impaired prepulse inhibition increased across various acoustic prepulse conditions after administration of R-Baclofen in Cntnap2 KO rats, whereas R-Baclofen did not affect prepulse inhibition in WT rats. Our findings suggest that GABA_B receptor agonists may be useful for pharmacologically targeting multiple aspects of sensory processing disruptions involving neuronal excitation/inhibition imbalances in ASD.

Haloperidol rescues the schizophrenia-like phenotype in adulthood after rotenone administration in neonatal rats

Neuropsychiatric disorders are multifactorial disturbances that encompass several hypotheses, including changes in neurodevelopment. It is known that brain development disturbances during early life can predict psychosis in adulthood. As we have previously demonstrated, rotenone, a mitochondrial complex I inhibitor, could induce psychiatric-like behavior in 60-day-old rats after intraperitoneal injections from the 5th to the 11th postnatal day. Because mitochondrial deregulation is related to psychiatric disorders and the establishment of animal models is a high-value preclinical tool, we investigated the responsiveness of the rotenone (Rot)-treated newborn rats to pharmacological agents used in clinical practice, haloperidol (Hal), and methylphenidate (MPD). Taken together, our data show that Rot-treated animals exhibit hyperlocomotion, decreased social interaction, and diminished contextual fear conditioning response at P60, consistent with positive, negative, and cognitive deficits of schizophrenia (SZ), respectively, that were reverted by Hal, but not MPD. Rot-treated rodents also display a prodromal-related phenotype at P35. Overall, our results seem to present a new SZ animal model as a consequence of mitochondrial inhibition during a critical neurodevelopmental period. Therefore, our study is crucial not only to elucidate the relevance of mitochondrial function in the etiology of SZ but also to fulfill the need for new and trustworthy experimentation models and, likewise, provide possibilities to new therapeutic avenues for this burdensome disorder.

Hyperactivation of the amygdala correlates with impaired social play behavior of prepubertal male rats in a maternal immune activation model

Maternal infection during pregnancy is an environmental risk factor for neurodevelopmental dysfunction, such as autism spectrum disorder (ASD). This study investigated the effect of maternal immune activation (MIA) on the behavior profile of prepubertal offspring and whether MIA alters the neuronal activation pattern of brain areas related to social play behavior. Pregnant Wistar rats received 500 μg/kg of lipopolysaccharide or saline solution on gestational day 16. Their offspring were tested using behavioral tasks to capture some of the core and associated ASD-like symptoms. Neuronal activation, indexed via c-fos expression after social play behavior, was evaluated in several brain areas. MIA had a number of adverse effects on dams and reduced the number of successful births and litter size. MIA induced sex-specific autistic-like features by a reduction in ultrasonic vocalizations in response to separation from the mother and nest, reduction in discrimination between neutral odors and their nest odor, moderate effect in stereotypies in the hole-board test, impaired risk assessment phenotype, and reduction in social play behavior without changes in locomotor activity only in prepubertal male offspring. A decrease in social play behavior may be associated with a decrease in the number of c-fos-positive cells in the prefrontal cortex and striatum, but hyperactivation of the basolateral and basomedial amygdala. Prenatal immune challenge results in ASD-like symptoms such as impaired risk assessment behavior, communication, and social interactions in male prepubertal offspring. Impaired social play behavior is correlated with neuronal hyperactivation in the amygdala.

Maternal overweight induced by reduced litter size impairs the behavioral neurodevelopment of offspring

AIMS

We assessed the influence of maternal overweight on the behavioral neurodevelopment of male and female offspring in prepubertal age by reducing the litter size.

MAIN METHODS

To reduce litter size in Wistar rats, the offspring of generation 0 (G0) were culled for 12 pups (6 males and 6 females: normal litter, NL-G1) or 4 pups (2 males and 2 females: small litter, SL-G1). In G1 dams, overweight was characterized, maternal behavior and locomotor activity were assessed. At G2, we quantified the ultrasonic vocalizations in post-natal day 5 (PND5); we evaluated olfactory discrimination in the homing behavior test on PND13; and in PND28-32 (prepubertal age), we performed the following tests: social play behavior, hole board, object recognition, and open field. At the end of the experiments, hippocampus and prefrontal cortex were dissected to quantify the synaptophysin by western blotting.

KEY FINDINGS

Our data demonstrated that a reduction in litter size was able to induce maternal overweight without altering the parameters related to overweight in the offspring. The SL-G2 offspring showed deficits in early social communication, olfactory discrimination, social play behavior, and the exploration of objects, in addition to increasing repetitive and stereotyped movements. There were also changes in the synaptophysin levels in the hippocampus and prefrontal cortex of the offspring from reduced litter dams. In conclusion, maternal overweight caused by litter reduction impairs behavioral neurodevelopment, inducing autism-like symptoms in the offspring.

SIGNIFICANCE

This study alerts the public about the negative consequences of maternal overweight in the descendants.

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.

An overview of modeling and behavioral assessment of autism in the rodent

Autism Spectrum Disorders (ASDs) are common neurodevelopmental disorders with a growing incidence that generally present in the first 3 years of life. Behavioral symptoms, including impaired social interaction and increased repetitive or stereotypic movements, are hallmark characteristics of autism. Animal models are research tools used to study the biology of the disease and to develop new therapeutic approaches. The complexity of the etiology of autism makes it challenging to develop a comprehensive animal model that accurately mimics different clinical aspects of autism. Here, we reviewed the literature on modeling and behavioral assessment of autism in the rodent, and focused on ASD behavioral phenotypes that can be modeled in rodents. These animal models can be effective in gaining a better understanding of the pathophysiology of the disease.

Healing autism spectrum disorder with cannabinoids: a neuroinflammatory story

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with a multifactorial etiology. Latest researches are raising the hypothesis of a link between the onset of the main behavioral symptoms of ASD and the chronic neuroinflammatory condition of the autistic brain; increasing evidence of this connection is shedding light on new possible players in the pathogenesis of ASD. The endocannabinoid system (ECS) has a key role in neurodevelopment as well as in normal inflammatory responses and it is not surprising that many preclinical and clinical studies account for alterations of the endocannabinoid signaling in ASD. These findings lay the foundation for a better understanding of the neurochemical mechanisms underlying ASD and for new therapeutic attempts aimed at exploiting the renowned anti-inflammatory properties of cannabinoids to treat pathologies encompassed in the autistic spectrum. This review discusses the current preclinical and clinical evidence supporting a key role of the ECS in the neuroinflammatory state that characterizes ASD, providing hints to identify new biomarkers in ASD and promising therapies for the future.

Understanding and Treating Niemann-Pick Type C Disease: Models Matter

Biomedical research aims to understand the molecular mechanisms causing human diseases and to develop curative therapies. So far, these goals have been achieved for a small fraction of diseases, limiting factors being the availability, validity, and use of experimental models. Niemann–Pick type C (NPC) is a prime example for a disease that lacks a curative therapy despite substantial breakthroughs. This rare, fatal, and autosomal-recessive disorder is caused by defects in NPC1 or NPC2. These ubiquitously expressed proteins help cholesterol exit from the endosomal–lysosomal system. The dysfunction of either causes an aberrant accumulation of lipids with patients presenting a large range of disease onset, neurovisceral symptoms, and life span. Here, we note general aspects of experimental models, we describe the line-up used for NPC-related research and therapy development, and we provide an outlook on future topics.

Monocytic Infiltrates Contribute to Autistic-like Behaviors in a Two-Hit Model of Neurodevelopmental Defects

Growing evidence suggests that early-life interactions among genetic, immune, and environment factors may modulate neurodevelopment and cause psycho-cognitive deficits. Maternal immune activation (MIA) induces autism-like behaviors in offspring, but how it interplays with perinatal brain injury (especially birth asphyxia or hypoxia ischemia [HI]) is unclear. Herein we compared the effects of MIA (injection of poly[I:C] to dam at gestational day 12.5), HI at postnatal day 10, and the combined MIA/HI insult in murine offspring of both sexes. We found that MIA induced autistic-like behaviors without microglial activation but amplified post-HI NFκB signaling, pro-inflammatory responses, and brain injury in offspring. Conversely, HI neither provoked autistic-like behaviors nor concealed them in the MIA offspring. Instead, the dual MIA/HI insult added autistic-like behaviors with diminished synaptic density and reduction of autism-related PSD-95 and Homer-1 in the hippocampus, which were missing in the singular MIA or HI insult. Further, the dual MIA/HI insult enhanced the brain influx of Otx2-positive monocytes that are associated with an increase of perineuronal net-enwrapped parvalbumin neurons. Using CCR2-CreER mice to distinguish monocytes from the resident microglia, we found that the monocytic infiltrates gradually adopted a ramified morphology and expressed the microglial signature genes (Tmem119, P2RY12, and Sall1) in post-MIA/HI brains, with some continuing to express the proinflammatory cytokine TNFα. Finally, genetic or pharmacological obstruction of monocytic influx significantly reduced perineuronal net-enwrapped parvalbumin neurons and autistic-like behaviors in MIA/HI offspring. Together, these results suggest a pathologic role of monocytes in the two-hit (immune plus neonatal HI) model of neurodevelopmental defects.SIGNIFICANCE STATEMENT In autism spectrum disorders (ASDs), prenatal infection or maternal immune activation (MIA) may act as a primer for multiple genetic and environmental factors to impair neurodevelopment. This study examined whether MIA cooperates with neonatal cerebral hypoxia ischemia to promote ASD-like aberrations in mice using a novel two-hit model. It was shown that the combination of MIA and neonatal hypoxia ischemia produces autistic-like behaviors in the offspring, and has synergistic effects in inducing neuroinflammation, monocytic infiltrates, synaptic defects, and perineuronal nets. Furthermore, genetic or pharmacological intervention of the MCP1-CCR2 chemoattractant pathway markedly reduced monocytic infiltrates, perineuronal nets, and autistic-like behaviors. These results suggest reciprocal escalation of immune and neonatal brain injury in a subset of ASD that may benefit from monocyte-targeted treatments.

The role of neuroglia in autism spectrum disorders

Neuroglia are a large class of neural cells of ectodermal (astroglia, oligodendroglia, and peripheral glial cells) and mesodermal (microglia) origin. Neuroglial cells provide homeostatic support, protection, and defense to the nervous tissue. Pathological potential of neuroglia has been acknowledged since their discovery. Research of the recent decade has shown the key role of all classes of glial cells in autism spectrum disorders (ASD), although molecular mechanisms defining glial contribution to ASD are yet to be fully characterized. This narrative conceptualizes recent findings of the broader roles of glial cells, including their active participation in the control of cerebral environment and regulation of synaptic development and scaling, highlighting their putative involvement in the etiopathogenesis of ASD.

Social and Cognitive Impairments in Rat Offspring after Ultrasound-Induced Prenatal Stress

We studied the possibility of developing an autism model based on chronic prenatal psychological stress caused by variable frequency ultrasound 20-45 kHz. The offspring of female rats stressed during pregnancy demonstrated reduced time of social contacts in the social interaction test, increased anxiety in the open-field test, and memory impairment in the Morris water maze test in comparison with the control (intact) rat offspring. We also found a reducing trend in the BDNF gene expression in the amygdala in males of the experimental group. The results showed the possibility of developing the animal autism model based on prenatal stress.

Effects of PM2.5 and gases exposure during prenatal and early-life on autism-like phenotypes in male rat offspring

BACKGROUND

Epidemiological studies have reported associations between elevated air pollution and autism spectrum disorders (ASD). However, we hypothesized that exposure to air pollution that mimics real world scenarios, is a potential contributor to ASD. The exact etiology and molecular mechanisms underlying ASD are not well understood. Thus, we assessed whether changes in OXTR levels may be part of the mechanism linking PM_2.5/gaseous pollutant exposure and ASD. The current in-vivo study investigated the effect of exposure to fine particulate matter (PM_2.5) and gaseous pollutants on ASD using behavioral and molecular experiments. Four exposure groups of Wistar rats were included in this study: 1) particulate matter and gaseous pollutants exposed (PGE), 2) gaseous pollutants only exposed (GE), 3) autism-like model (ALM) with VPA induction, and 4) clean air exposed (CAE) as the control. Pregnant dams and male pups were exposed to air pollutants from embryonic day (E0) to postnatal day (PND21).

RESULTS

The average ± SD concentrations of air pollutants were: PM_2.5: 43.8 ± 21.1 μg/m³, CO: 13.5 ± 2.5 ppm, NO₂: 0.341 ± 0.100 ppm, SO₂: 0.275 ± 0.07 ppm, and O₃: 0.135 ± 0.01 ppm. The OXTR protein level, catalase activity (CAT), and GSH concentrations in the ALM, PGE, and GE rats were lower than those in control group (CAE). However, the decrements in the GE rats were smaller than other groups. Also in behavioral assessments, the ALM, PGE, and GE rats demonstrated a repetitive /restricted behavior and poor social interaction, but the GE rats had weaker responses compared to other groups of rats. The PGE and GE rats showed similar trends in these tests compared to the VPA rats.

CONCLUSIONS

This study suggested that exposure to ambient air pollution contributed to ASD and that OXTR protein may serve as part of the mechanism linking them.

Segmented Iba1-Positive Processes of Microglia in Autism Model Marmosets

Autism spectrum disorder (ASD) is one of the most widespread neurodevelopmental disorders, characterized by impairment in social interactions, and restricted stereotyped behaviors. Using immunohistochemistry and positron emission tomography (PET), several studies have provided evidence of the existence of activated microglia in ASD patients. Recently, we developed an animal model of ASD using the new world monkey common marmoset (Callithrix jacchus) and demonstrated ASD-like social impairment after the in utero administration of valproic acid (VPA). To characterize microglia in this marmoset model of ASD from early toddler to adult, morphological analyses of microglia in VPA marmosets and age-matched unexposed (UE) marmosets were performed using immunohistochemistry for microglia-specific markers, Iba1, and P2RY12. The most robust morphological difference between VPA marmosets and UE marmosets throughout the life span evaluated were the microglia processes in VPA marmosets being frequently segmented by thin and faintly Iba1-positive structures. The segmentation of microglial processes was only rarely observed in UE marmosets. This feature of segmentation of microglial processes in VPA marmosets can also be observed in images from previous studies on ASD conducted in humans and animal models. Apoptotic cells have been shown to have segmented processes. Therefore, our results might suggest that microglia in patients and animals with ASD symptoms could frequently be in the apoptotic phase with high turnover rates of microglia found in some pathological conditions.

Loss of Mevalonate/Cholesterol Homeostasis in the Brain: A Focus on Autism Spectrum Disorder and Rett Syndrome

The mevalonate (MVA)/cholesterol pathway is crucial for central nervous system (CNS) development and function and consequently, any dysfunction of this fundamental metabolic pathway is likely to provoke pathologic changes in the brain. Mutations in genes directly involved in MVA/cholesterol metabolism cause a range of diseases, many of which present neurologic and psychiatric symptoms. This raises the question whether other diseases presenting similar symptoms are related albeit indirectly to the MVA/cholesterol pathway. Here, we summarized the current literature suggesting links between MVA/cholesterol dysregulation and specific diseases, namely autism spectrum disorder and Rett syndrome.

Role of the endocannabinoid system in neurological disorders

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that begins in infancy. Although the etiology and pathogenesis are poorly understood, many studies have shown that ASD is closely related to structural and functional defects in the nervous system, especially synaptic transmission. The endocannabinoid (eCB) system is an important regulatory system of the central nervous system that regulates neurotransmission and synaptic plasticity and plays an important role in emotional and social responses and cognitive function. The relationship between eCB system and ASD has attracted increasing attention from scholars. In this review, we discuss the complex lipid signaling network of the eCB system, intracellular transport pathways, abnormal expression and association with various neurological diseases, and direct and indirect evidence for the link between eCB and ASD. Collectively, the findings to date indicate that the eCB system plays a key role in the pathophysiology of ASD and can provide new insights into potential interventions and rehabilitation strategies for ASD.

Neuroglia in the autistic brain: evidence from a preclinical model

Background

Neuroglial cells that provide homeostatic support and form defence of the nervous system contribute to all neurological disorders. We analyzed three major types of neuroglia, astrocytes, oligodendrocytes, and microglia in the brains of an animal model of autism spectrum disorder, in which rats were exposed prenatally to antiepileptic and mood stabilizer drug valproic acid; this model being of acknowledged clinical relevance.

Methods

We tested the autistic-like behaviors of valproic acid-prenatally exposed male rats by performing isolation-induced ultrasonic vocalizations, the three-chamber test, and the hole board test. To account for human infancy, adolescence, and adulthood, such tasks were performed at postnatal day 13, postnatal day 35, and postnatal day 90, respectively. After sacrifice, we examined gene and protein expression of specific markers of neuroglia in hippocampus, prefrontal cortex, and cerebellum, these brain regions being associated with autism spectrum disorder pathogenesis.

Results

Infant offspring of VPA-exposed dams emitted less ultrasonic vocalizations when isolated from their mothers and siblings and, in adolescence and adulthood, they showed altered sociability in the three chamber test and increased stereotypic behavior in the hole board test. Molecular analyses indicate that prenatal valproic acid exposure affects all types of neuroglia, mainly causing transcriptional modifications. The most prominent changes occur in prefrontal cortex and in the hippocampus of autistic-like animals; these changes are particularly evident during infancy and adolescence, while they appear to be mitigated in adulthood.

Conclusions

Neuroglial pathological phenotype in autism spectrum disorder rat model appears to be rather mild with little signs of widespread and chronic neuroinflammation.

Altered Auditory Processing, Filtering, and Reactivity in the Cntnap2 Knock-Out Rat Model for Neurodevelopmental Disorders

Sensory processing, and auditory processing in particular, is altered in individuals with neurodevelopmental disorders such as autism spectrum disorders (ASDs). The typical maturation of the auditory system is perturbed in these individuals during early development, which may underlie altered auditory reactivity that persists in later life. Of the many genes that regulate the auditory system development, loss-of-function mutations in the CNTNAP2 gene are strongly associated with language processing deficits and ASD. Therefore, using a novel Cntnap2 knock-out rat model, we tested the impact of Cntnap2 loss on auditory processing, filtering, and reactivity throughout development and young adulthood in male and female animals. Although hearing thresholds were not altered in Cntnap2 knock-out animals, we found a reduction in response amplitudes and a delay in response latency of the auditory brainstem response (ABR) in juvenile Cntnap2 knock-out rats compared with age-matched controls. Amplitudes and latency of the ABR largely normalized by adulthood, indicating a delayed maturation of auditory processing pathways in Cntnap2 knock-out rats. Despite the reduced ABR amplitudes, adolescent Cntnap2 knock-out animals displayed increased startle reactivity accompanied by disruptions in sensory filtering and sensorimotor gating across various conditions, most of which persisted in adulthood. All of these observations show striking parallels to disruptions reported in ASD. Our results also imply that developmental disruptions of sensory signal processing are associated with persistent changes in neural circuitries responsible for implicit auditory evoked behavior, emphasizing the need for interventions that target sensory processing disruptions early during development in ASD.SIGNIFICANCE STATEMENT This is the first study of brainstem auditory processing in a novel knock-out rat model with very high construct and face validity for autism spectrum disorders. Electrophysiological and behavioral measures of implicit auditory-evoked responses were systematically taken across developmental stages. Auditory processing, filtering, and reactivity disruptions show striking similarities to observations in autism. We also show for the first time that, whereas auditory brainstem responses normalize by adulthood, disruptions in brainstem-mediated auditory-evoked behavior persist. This indicates that early developmental perturbations in sensory processing can cause permanent maladaptive changes in circuitries responsible for auditory reactivity, underlining the importance for interventions early during development aiming at normalizing sensory processing.

Sex-specific autistic endophenotypes induced by prenatal exposure to valproic acid involve anandamide signalling

BACKGROUND AND PURPOSE

Autism spectrum disorder (ASD) is more commonly diagnosed in males than in females. Prenatal exposure to the antiepileptic drug valproic acid (VPA) is an environmental risk factor of ASD. Male rats prenatally exposed to VPA show socio-emotional autistic-like dysfunctions that have been related to changes in the activity of the endocannabinoid anandamide. Here, we have investigated if prenatal VPA induced sex-specific autistic endophenotypes involving anandamide signalling.

EXPERIMENTAL APPROACH

We studied sex-specific differences in the ASD-like socio-emotional, cognitive and repetitive symptoms displayed during development of Wistar rats of both sexes, prenatally exposed to VPA. The involvement of anandamide was followed by Western blotting of cannabinoid CB₁ receptors and by inhibiting its metabolism.

KEY RESULTS

Female rats were less vulnerable to the deleterious effects of prenatal VPA exposure on social communication, emotional reactivity and cognitive performance than male rats. Conversely, as observed in male rats, prenatal VPA exposure induced selective deficits in social play behaviour and stereotypies in the female rat offspring. At the neurochemical level, prenatal VPA exposure altered phosphorylation of CB₁ receptors in a sex-specific, age-specific and tissue-specific manner. Enhancing anandamide signalling through inhibition of its degradation reversed the behavioural deficits displayed by VPA-exposed animals of both sexes.

CONCLUSIONS AND IMPLICATIONS

These findings highlight sexually dimorphic consequences of prenatal VPA exposure that may be related to sex-specific effects of VPA on endocannabinoid neurotransmission in the course of development and introduce a new therapeutic target for reversing autistic-like symptoms in both sexes.

Development and Characterization of Human Cerebral Organoids: An Optimized Protocol

Studies of human neurodevelopmental disorders and stem cell–based regenerative transplants have been hampered by the lack of a model of the developing human brain. Stem cell–derived neurons suffer major limitations, including the ability to recapitulate the 3-dimensional architecture of a brain tissue and the representation of multiple layers and cell types that contribute to the overall brain functions in vivo. Recently, cerebral organoid technology was introduced; however, such technology is still in its infancy, and its low reproducibility and limitations significantly reduce the reliability of such a model as it currently exists, especially considering the complexity of cerebral-organoid protocols. Here we have tested and compared multiple protocols and conditions for growth of organoids, and we describe an optimized methodology, and define the necessary and sufficient factors that support the development of optimal organoids. Our optimization criteria included organoids’ overall growth and size, stratification and representation of the various cell types, inter-batch variability, analysis of neuronal maturation, and even the cost of the procedure. Importantly, this protocol encompasses a plethora of technical tips that allow researchers to easily reproduce it and obtain reliable organoids with the least variability, and showcases a robust array of approaches to characterize successful organoids. This optimized protocol provides a reliable system for genetic or pharmacological (drug development) screens and may enhance understanding and therapy of human neurodevelopmental disorders, including harnessing the therapeutic potential of stem cell–derived transplants.

Altered Brain Cholesterol/Isoprenoid Metabolism in a Rat Model of Autism Spectrum Disorders

Autism spectrum disorders (ASDs) present a wide range of symptoms characterized by altered sociability, compromised communication and stereotypic/repetitive behaviors. These symptoms are caused by developmental changes, but the mechanisms remain largely unknown. Some lines of evidence suggest an impairment of the cholesterol/isoprenoid metabolism in the brain as a possible cause, but systematic analyses in rodent models of ASDs are lacking. Prenatal exposure to the antiepileptic drug valproate (VPA) is a risk factor for ASDs in humans and generates a well-established model for the disease in rodents. Here, we studied cholesterol/isoprenoid metabolism in different brain areas of infant, adolescent and adult rats prenatally exposed to VPA. VPA-treated rats present autistic-like symptoms, they show changes in cholesterol/isoprenoid homeostasis in some brain areas, a decreased number of oligodendrocytes and impaired myelination in the hippocampus. Together, our data suggest a relation between brain cholesterol/isoprenoid homeostasis and ASDs.

Impaired repair of DNA damage is associated with autistic-like traits in rats prenatally exposed to valproic acid

Prenatal exposure to the antiepileptic and mood stabilizer valproic acid (VPA) is an environmental risk factor for autism spectrum disorders (ASD), although recent epidemiological studies show that the public awareness of this association is still limited. Based on the clinical findings, prenatal VPA exposure in rodents is a widely used preclinical model of ASD. However, there is limited information about the precise biochemical mechanisms underlying the link between ASD and VPA. Here, we tested the effects of increasing doses of VPA on behavioral features resembling core and secondary symptoms of ASD in rats. Only when administered prenatally at the dose of 500mg/kg, VPA induced deficits in communication and social discrimination in rat pups, and altered social behavior and emotionality in the adolescent and adult offspring in the absence of gross malformations. This dose of VPA inhibited histone deacetylase in rat embryos and favored the formation of DNA double strand breaks (DSB), but impaired their repair. The defective DSB response was no more visible in one-day-old pups, thus supporting the hypothesis that unrepaired VPA-induced DNA damage at the time of neural tube closure may underlie the autistic-like traits displayed in the course of development by rats prenatally exposed to VPA. These experiments help to understand the neurodevelopmental trajectories affected by prenatal VPA exposure and identify a biochemical link between VPA exposure during gestation and ASD.

The Endocannabinoid System and Autism Spectrum Disorders: Insights from Animal Models

Autism spectrum disorder (ASD) defines a group of neurodevelopmental disorders whose symptoms include impaired communication and social interaction with restricted or repetitive motor movements, frequently associated with general cognitive deficits. Although it is among the most severe chronic childhood disorders in terms of prevalence, morbidity, and impact to the society, no effective treatment for ASD is yet available, possibly because its neurobiological basis is not clearly understood hence specific drugs have not yet been developed. The endocannabinoid (EC) system represents a major neuromodulatory system involved in the regulation of emotional responses, behavioral reactivity to context, and social interaction. Furthermore, the EC system is also affected in conditions often present in subsets of patients diagnosed with ASD, such as seizures, anxiety, intellectual disabilities, and sleep pattern disturbances. Despite the indirect evidence suggestive of an involvement of the EC system in ASD, only a few studies have specifically addressed the role of the EC system in the context of ASD. This review describes the available data on the investigation of the presence of alterations of the EC system as well as the effects of its pharmacological manipulations in animal models of ASD-like behaviors.

Advances in nonhuman primate models of autism: Integrating neuroscience and behavior

Given the prevalence and societal impact of autism spectrum disorders (ASD), there is an urgent need to develop innovative preventative strategies and treatments to reduce the alarming number of cases and improve core symptoms for afflicted individuals. Translational efforts between clinical and preclinical research are needed to (i) identify and evaluate putative causes of ASD, (ii) determine the underlying neurobiological mechanisms, (iii) develop and test novel therapeutic approaches and (iv) ultimately translate basic research into safe and effective clinical practices. However, modeling a uniquely human brain disorder, such as ASD, will require sophisticated animal models that capitalize on unique advantages of diverse species including drosophila, zebra fish, mice, rats, and ultimately, species more closely related to humans, such as the nonhuman primate. Here we discuss the unique contributions of the rhesus monkey (Macaca mulatta) model to ongoing efforts to understand the neurobiology of the disorder, focusing on the convergence of brain and behavior outcome measures that parallel features of human ASD.