The neurobiology of autism

Efficacy of post-insult minocycline administration to alter long-term hypoxia-ischemia-induced damage to the serotonergic system in the immature rat brain

Neuroinflammation is a key mechanism contributing to long-term neuropathology observed after neonatal hypoxia-ischemia (HI). Minocycline, a second-generation tetracycline, is a potent inhibitor of neuroinflammatory mediators and is successful for at least short-term amelioration of neuronal injury after neonatal HI. However the long-term efficacy of minocycline to prevent injury to a specific neuronal network, such as the serotonergic (5-hydroxytryptamine, 5-HT) system, is not known. In a post-natal day 3 (P3) rat model of preterm HI we found significant reductions in 5-HT levels, 5-HT transporter expression and numbers of 5-HT-positive dorsal raphé neurons 6 weeks after insult compared to control animals. Numbers of activated microglia were significantly elevated in the thalamus and dorsal raphé although the greatest numbers were observed in the thalamus. Brain levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were also significantly elevated on P45 in the thalamus and frontal cortex. Post-insult administration of minocycline for 1 week (P3-P9) attenuated the P3 HI-induced increases in numbers of activated microglia and levels of TNF-α and IL-1β on P45 with concurrent changes in serotonergic outcomes. The parallel prevention of P3 HI-induced serotonergic changes suggests that inhibition of neuroinflammation within the first week after P3 HI injury was sufficient to prevent long-term neuroinflammation as well as serotonergic system damage still evident at 6 weeks. Thus early, post-insult administration of minocycline may target secondary neuroinflammation and represent a long-term therapy to preserve the integrity of the central serotonergic network in the preterm neonate.

Effects of neonatal systemic inflammation on blood-brain barrier permeability and behaviour in juvenile and adult rats

Several neurological disorders have been linked to inflammatory insults suffered during development. We investigated the effects of neonatal systemic inflammation, induced by LPS injections, on blood-brain barrier permeability, endothelial tight junctions and behaviour of juvenile (P20) and adult rats. LPS-treatment resulted in altered cellular localisation of claudin-5 and changes in ultrastructural morphology of a few cerebral blood vessels. Barrier permeability to sucrose was significantly increased in LPS treated animals when adult but not at P20 or earlier. Behavioural tests showed that LPS treated animals at P20 exhibited altered behaviour using prepulse inhibition (PPI) analysis, whereas adults demonstrated altered behaviour in the dark/light test. These data indicate that an inflammatory insult during brain development can change blood-brain barrier permeability and behaviour in later life. It also suggests that the impact of inflammation can occur in several phases (short- and long-term) and that each phase might lead to different behavioural modifications.

Understanding barrier mechanisms in the developing brain to aid therapy for the dysfunctional brain

The brain, both in the adult and during development, is protected by morphological barriers and functional mechanisms that provide a stable internal environment. Understanding these processes in the developing brain may lead to novel therapies for brain disorders, as some transport mechanisms, particularly those in the choroid plexus, may prove more amenable to devising novel delivery systems. Based on results from studies of the transfer of specific proteins across the blood–cerebrospinal fluid interface in the developing brain, the steps required to develop such a delivery system are outlined. Knowledge of barrier mechanisms in the developing brain may be relevant to treating neuropsychiatric conditions in children and adults for whom barrier dysfunction in the fetus, precipitated by adverse factors such as maternal infection, may contribute to the neuropathology underlying disorders such as autism and schizophrenia.

Autoantibodies to cerebellum in children with autism associate with behavior

Autism is a heterogeneous disorder with a poorly understood biological basis. Some children with autism harbor plasma autoantibodies that target brain proteins. Similarly, some mothers of children with autism produce antibodies specific to autism that target pairs of fetal brain proteins at 37/73 and 39/73 kDa. We explored the relationship between the presence of brain-specific autoantibodies and several behavioral characteristics of autism in 277 children with an autism spectrum disorder and 189 typically developing age-matched controls. Further, we used maternal autoantibody data to investigate potential familial relationships for the production of brain-directed autoantibodies. We demonstrated by Western blot that autoantibodies specific for a 45 kDa cerebellar protein in children were associated with a diagnosis of autism (p=0.017) while autoantibodies directed towards a 62 kDa protein were associated with the broader diagnosis of autism spectrum disorder (ASD) (p=0.043). Children with such autoantibodies had lower adaptive (p=0.0008) and cognitive function (p=0.005), as well as increased aberrant behaviors (p<0.05) compared to children without these antibodies. No correlation was noted for those mothers with the most specific pattern of anti-fetal brain autoantibodies and children with the autoantibodies to either the 45 or 62 kDa bands. Collectively, these data suggest that antibodies towards brain proteins in children are associated with lower adaptive and cognitive function as well as core behaviors associated with autism. It is unclear whether these antibodies have direct pathologic significance, or if they are merely a response to previous injury. Future studies are needed to determine the identities of the protein targets and explore their significance in autism.

Density and function of central serotonin (5-HT) transporters, 5-HT1A and 5-HT2A receptors, and effects of their targeting on BTBR T+tf/J mouse social behavior

BTBR mice are potentially useful tools for autism research because their behavior parallels core social interaction impairments and restricted-repetitive behaviors. Altered regulation of central serotonin (5-HT) neurotransmission may underlie such behavioral deficits. To test this, we compared 5-HT transporter (SERT), 5-HT(1A) and 5-HT(2A) receptor densities among BTBR and C57 strains. Autoradiographic [(3) H] cyanoimipramine (1 nM) binding to SERT was 20-30% lower throughout the adult BTBR brain as compared to C57BL/10J mice. In hippocampal membrane homogenates, [(3) H] citalopram maximal binding (B(max) ) to SERT was 95 ± 13 fmol/mg protein in BTBR and 171 ± 20 fmol/mg protein in C57BL/6J mice, and the BTBR dissociation constant (K(D) ) was 2.0 ± 0.3 nM versus 1.1 ± 0.2 in C57BL/6J mice. Hippocampal 5-HT(1A) and 5-HT(2A) receptor binding was similar among strains. However, 8-OH-DPAT-stimulated [(35) S] GTPγS binding in the BTBR hippocampal CA(1) region was 28% higher, indicating elevated 5-HT(1A) capacity to activate G-proteins. In BTBR mice, the SERT blocker, fluoxetine (10 mg/kg) and the 5-HT(1A) receptor partial-agonist, buspirone (2 mg/kg) enhanced social interactions. The D(2) /5-HT(2) receptor antagonist, risperidone (0.1 mg/kg) reduced marble burying, but failed to improve sociability. Overall, altered SERT and/or 5-HT(1A) functionality in hippocampus could contribute to the relatively low sociability of BTBR mice.

Wnt/planar cell polarity signaling controls the anterior-posterior organization of monoaminergic axons in the brainstem

Monoaminergic neurons [serotonergic (5-HT) and dopaminergic (mdDA)] in the brainstem project axons along the anterior-posterior axis. Despite their important physiological functions and implication in disease, the molecular mechanisms that dictate the formation of these projections along the anterior-posterior axis remain unknown. Here we reveal a novel requirement for Wnt/planar cell polarity signaling in the anterior-posterior organization of the monoaminergic system. We find that 5-HT and mdDA axons express the core planar cell polarity components Frizzled3, Celsr3, and Vangl2. In addition, monoaminergic projections show anterior-posterior guidance defects in Frizzled3, Celsr3, and Vangl2 mutant mice. The only known ligands for planar cell polarity signaling are Wnt proteins. In culture, Wnt5a attracts 5-HT but repels mdDA axons, and Wnt7b attracts mdDA axons. However, mdDA axons from Frizzled3 mutant mice are unresponsive to Wnt5a and Wnt7b. Both Wnts are expressed in gradients along the anterior-posterior axis, consistent with their role as directional cues. Finally, Wnt5a mutants show transient anterior-posterior guidance defects in mdDA projections. Furthermore, we observe during development that the cell bodies of migrating descending 5-HT neurons eventually reorient along the direction of their axons. In Frizzled3 mutants, many 5-HT and mdDA neuron cell bodies are oriented abnormally along the direction of their aberrant axon projections. Overall, our data suggest that Wnt/planar cell polarity signaling may be a global anterior-posterior guidance mechanism that controls axonal and cellular organization beyond the spinal cord.

Channel-opening kinetic mechanism for human wild-type GluK2 and the M867I mutant kainate receptor

GluK2 is a kainate receptor subunit that is alternatively spliced at the C-terminus. Previous studies implicated GluK2 in autism. In particular, the methionine-to-isoleucine replacement at amino acid residue 867 (M867I) that can only occur in the longest isoform of the human GluK2 (hGluK2), as the disease (autism) mutation, is thought to cause gain-of-function. However, the kinetic properties of the wild-type hGluK2 and the functional consequence of this gain-of-function mutation at the molecular level are not well understood. To investigate whether the M867I mutation affects the channel properties of the human GluK2 kainate receptor, we have systematically characterized the rate and the equilibrium constants pertinent to channel opening and channel desensitization for this mutant and the wild-type hGluK2 receptor, along with the wild-type rat GluK2 kainate receptor (rGluK2) as the control. Our results show that the M867I mutation does not affect either the rate or the equilibrium constants of the channel opening but does slow down the channel desensitization rate by ~1.6-fold at saturating glutamate concentrations. It is possible that a consequence of this mutation on the desensitization rate is linked to facilitating the receptor trafficking and membrane expression, given the close proximity of M867 to the forward trafficking motif in the C-terminal sequence. By comparing the kinetic data of the wild-type human and rat GluK2 receptors, we also find that the human GluK2 has a ~3-fold smaller channel-opening rate constant but an identical channel-closing rate constant and thus a channel-opening probability of 0.85 vs 0.96 for rGluK2. Furthermore, the intrinsic equilibrium dissociation constant K(1) for hGluK2, like the EC(50) value, is ~2-fold lower than rGluK2. Our results therefore suggest that the human GluK2 is relatively a slowly activating channel but more sensitive to glutamate, as compared to the rat ortholog, despite the fact that the human and rat forms share 99% sequence homology.

Isolation of detergent resistant microdomains from cultured neurons: detergent dependent alterations in protein composition

Background

Membrane rafts are small highly dynamic sterol- and sphingolipid-enriched membrane domains that have received considerable attention due to their role in diverse cellular functions. More recently the involvement of membrane rafts in neuronal processes has been highlighted since these specialized membrane domains have been shown to be involved in synapse formation, neuronal polarity and neurodegeneration. Detergent resistance followed by gradient centrifugation is often used as first step in screening putative membrane raft components. Traditional methods of raft isolation employed the nonionic detergent Triton X100. However successful separation of raft from non-raft domains in cells is dependent on matching the detergent used for raft isolation to the specific tissue under investigation.

Results

We report here the isolation of membrane rafts from primary neuronal culture using a panel of different detergents that gave rise to membrane fractions that differed in respect to cholesterol and protein content. In addition, proteomic profiling of neuronal membrane rafts isolated with different detergents, Triton X100 and CHAPSO, revealed heterogeneity in their protein content.

Conclusions

These data demonstrate that appropriate selection of detergent for raft isolation is an important consideration for investigating raft protein composition of cultured neurons.

Emerging role of aripiprazole for treatment of irritability associated with autistic disorder in children and adolescents

Autistic disorder is a largely misunderstood and difficult to treat neurodevelopmental disorder. Three core domains of functioning are affected by autistic disorder, ie, socialization, communication, and behavior. Signs of autistic disorder may be present early, but are frequently overlooked, resulting in a delay in its diagnosis and a subsequent delay in treatment. No one definitive therapy is available, and treatment consists of early educational and behavioral interventions, as well as drug therapy. Atypical antipsychotics have often been used in the treatment of autistic disorder to target irritability, aggression, and self-injurious behavior, all of which can interfere with other aspects of treatment. One atypical antipsychotic, aripiprazole, has recently been approved for treatment of irritability associated with autistic disorder. Based on the results from two randomized, controlled trials, with efficacy data from nearly 300 patients, treatment with aripiprazole was associated with reductions in irritability, global improvements in behavior, and improvements in quality of life from both the patient and caregiver perspectives. Dosage of aripiprazole ranged from 5 mg to 15 mg per day. Aripiprazole was well tolerated during clinical trials, with most adverse events considered mild or moderate. Clinically relevant weight gain occurred in about 30% of patients given aripiprazole, although when compared with other atypical antipsychotics, aripiprazole appears to have fewer metabolic effects and a lower risk of weight gain. However, pediatric patients taking any atypical antipsychotic should be carefully monitored for potential adverse events, because the long-term effects of antipsychotic therapy in this population are not well known. When used appropriately, aripiprazole has the potential to be an effective treatment for children with autistic disorder to improve irritability and aggressive behavior and improve quality of life.

Autistic spectrum disorder in a 9-year-old girl with macrocephaly

A 9-year-old girl was brought for consultation due to autism and a large head circumference. Her birth weight was 6 pounds after a 37-week gestation to a healthy G3P1SAb 2 mother. She had been a healthy child with the exception of the development of a lipomatous lesion on the left thigh, requiring surgical removal at age 3(1/2) years. Autism was diagnosed at age 5 yr by a developmental pediatrician. She did not have cognitive disabilities or a history of seizures. The family history was notable for maternal infertility with no history of developmental disabilities, large body or head size, or malignancy in close relatives.On physical examination, she was a mildly obese girl with a large head. Her weight was 50.4 kg (>95%), height was 142 cm (90%), and head circumference was 60.3 cm (significantly >95%; 4SDs above the mean). Examination of her skin was notable for a 2 x 6 cm scar on her left thigh and three café au lait macules on her trunk. She was Tanner Stage I. Mild hypotonia with normal deep tendon reflexes was observed; the remainder of the neurological examination was normal.Laboratory studies included high-resolution chromosomes, fragile X, metabolic screens, and methylation for Prader Willie Syndrome and Angelman Syndrome; all these studies were normal. Molecular testing of the PTEN gene (phosphatase and tensin homolog protein) revealed a R355X mutation, consistent with the diagnosis of Bannayan-Riley-Ruvalcaba Syndrome (BRRS). In parents and siblings, PTEN test results were negative for mutations.Endocrine evaluation revealed an abnormal thyroid nodule on ultrasound. Computed tomography and positron emission tomography scans raised suspicion of malignancy. She underwent a total thyroidectomy; the pathology report revealed a thyroid adenoma with Hurthle cells. She was treated with thyroid hormone replacement therapy.

Emerging pharmacotherapies for neurodevelopmental disorders

A growing and interdisciplinary translational neuroscience research effort for neurodevelopmental disorders (NDDs) is investigating the mechanisms of dysfunction and testing effective treatment strategies in animal models and, when possible, in the clinic. NDDs with a genetic basis have received particular attention. Transgenic animals that mimic genetic insults responsible for disease in man have provided insight about mechanisms of dysfunction, and, surprisingly, have shown that cognitive deficits can be addressed in adult animals. This review will present recent translational research based on animal models of genetic NDDs, as well as pharmacotherapeutic strategies under development to address deficits of brain function for Down syndrome, fragile X syndrome, Rett syndrome, neurofibromatosis-1, tuberous sclerosis, and autism. Although these disorders vary in underlying causes and clinical presentation, common pathways and mechanisms for dysfunction have been observed. These include abnormal gene dosage, imbalance among neurotransmitter systems, and deficits in the development, maintenance and plasticity of neuronal circuits. NDDs affect multiple brain systems and behaviors that may be amenable to drug therapies that target distinct deficits. A primary goal of translational research is to replace symptomatic and supportive drug therapies with pharmacotherapies based on a principled understanding of the causes of dysfunction. Based on this principle, several recently developed therapeutic strategies offer clear promise for clinical development in man.

Volumetric and voxel-based morphometry findings in autism subjects with and without macrocephaly

This study sought to replicate Herbert et al. (2003a), which found increased overall white matter (WM) volume in subjects with autism, even after controlling for head size differences. To avoid the possibility that greater WM volume in autism is merely an epiphenomena of macrocephaly overrepresentation associated with the disorder, the current study included control subjects with benign macrocephaly. The control group also included subjects with a reading disability to insure cognitive heterogeneity. WM volume in autism was significantly larger, even when controlling for brain volume, rate of macrocephaly, and other demographic variables. Autism and controls differed little on whole-brain WM voxel-based morphometry (VBM) analyses suggesting that the overall increase in WM volume was non-localized. Autism subjects exhibited a differential pattern of IQ relationships with brain volumetry findings from controls. Current theories of brain overgrowth and their importance in the development of autism are discussed in the context of these findings.

Autism spectrum disorders and epigenetics

OBJECTIVE

Current research suggests that the causes of autism spectrum disorders (ASD) are multifactorial and include both genetic and environmental factors. Several lines of evidence suggest that epigenetics also plays an important role in ASD etiology and that it might, in fact, integrate genetic and environmental influences to dysregulate neurodevelopmental processes. The objective of this review is to illustrate how epigenetic modifications that are known to alter gene expression without changing primary DNA sequence may play a role in the etiology of ASD.

METHOD

In this review, we summarize current knowledge about epigenetic modifications to genes and genomic regions possibly involved in the etiology of ASD.

RESULTS

Several genetic syndromes comorbid with ASD, which include Rett, Fragile X, Prader-Willi, Angelman, and CHARGE (Coloboma of the eye, Heart defects, Atresia of the nasal choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and deafness), all demonstrate dysregulation of epigenetic marks or epigenetic mechanisms. We report also on genes or genomic regions exhibiting abnormal epigenetic regulation in association with either syndromic (15q11-13 maternal duplication) or nonsyndromic forms of ASD. Finally, we discuss the state of current knowledge regarding the etiologic role of environmental factors linked to both the development of ASD and epigenetic dysregulation.

CONCLUSION

Data reviewed in this article highlight a variety of situations in which epigenetic dysregulation is associated with the development of ASD, thereby supporting a role for epigenetics in the multifactorial etiologies of ASD.

Central tetrahydrobiopterin concentration in neurodevelopmental disorders

Tetrahydrobiopterin (BH₄) is a naturally occurring cofactor essential for critical metabolic pathways. Studies suggest that BH₄ supplementation may ameliorate autism symptoms; the biological mechanism for such an effect is unknown. To help understand the relation between central BH₄ concentration and systemic metabolism and to develop a biomarker of central BH₄ concentration, the relationship between cerebrospinal fluid BH₄ concentration and serum amino acids was studied. BH₄ concentration was found to be distributed in two groups, a lower and higher BH₄ concentration group. Two serum amino acids, citrulline and methionine, differentiated these groups, and the ratio of serum citrulline-to-methionine was found to correlate with the cerebrospinal fluid BH₄ concentration (r = −0.67, p < 0.05). Both citrulline and methionine are substrates in inflammation and oxidative stress pathways – two pathways that utilize BH₄ and are abnormally activated in autism. These data suggests that central BH₄ concentration may be related to systemic inflammation and oxidative stress pathways.

Tetrahydrobiopterin as a novel therapeutic intervention for autism

Tetrahydrobiopterin (BH(4)) is an essential cofactor for several critical metabolic pathways that have been reported to be abnormal in autism spectrum disorder (ASD). In addition, the cerebrospinal fluid concentration of BH(4) is reported to be depressed in children with ASD. Over the past 25 years, several clinical trials have suggested that treatment with BH(4) improves ASD symptomatology in some individuals. Two ongoing clinical protocols may help further define the efficacy of BH(4) treatment in children with ASD. First, children with ASD who had low concentrations of cerebrospinal fluid or urine pterins were treated in an open-label manner with 20 mg/kg per day of BH(4). The majority of children (63%) responded positively to treatment, with minimal adverse events (AEs). Second, a double-blind placebo-controlled study examining the efficacy of 20 mg/kg per day of BH(4) treatment in children with ASD is currently underway. Safety studies from the commercially available forms of BH(4) document the low incidence of AEs, particularly serious AEs. Studies have also documented the ability of BH(4) to cross the blood-brain barrier. Based on the importance of BH(4) in neurodevelopmental metabolic pathways, the safety of BH(4) treatment, and the evidence for a therapeutic benefit of BH(4) treatment in children with ASD, we conclude that BH(4) represents a novel therapy for ASD, one that may gain wider use after further clinical studies have established efficacy and treatment guidelines.

Immune dysfunction in autism: a pathway to treatment

Autism is a complex and clinically heterogeneous disorder with a spectrum of symptoms. Clinicians, schools, and service agencies worldwide have reported a dramatic increase in the number of children identified with autism. Despite expanding research, the etiology and underlying biological processes of autism remain poorly understood, and the relative contribution from genetic, epigenetic, and environmental factors remains unclear. Although autism affects primarily brain function (especially affect, social functioning, and cognition), it is unknown to what extent other organs and systems are disrupted. Published findings have identified widespread changes in the immune systems of children with autism, at both systemic and cellular levels. Brain specimens from autism subjects exhibit signs of active, ongoing inflammation, as well as alterations in gene pathways associated with immune signaling and immune function. Moreover, many genetic studies have indicated a link between autism and genes that are relevant to both the nervous system and the immune system. Alterations in these pathways can affect function in both systems. Together, these reports suggest that autism may in fact be a systemic disorder with connections to abnormal immune responses. Such immune system dysfunction may represent novel targets for treatment. A better understanding of the involvement of the immune response in autism, and of how early brain development is altered, may have important therapeutic implications.

Mechanisms underlying synapse-specific clustering of GABA(A) receptors

A principle that arises from a body of previous work is that each presynaptic terminal recognises its postsynaptic partner and that each postsynaptic site recognises the origin of the synaptic bouton innervating it. In response, the presynaptic terminal sequesters the proteins whose interactions result in the dynamic transmitter release pattern and chemical modulation appropriate for that connection. In parallel, the postsynaptic site sequesters, inserts or captures the receptors and postsynaptic density proteins appropriate for that type of synapse. The focus of this review is the selective clustering of GABA(A) receptors (GABA(A)R) at synapses made by each class of inhibitory interneurone. This provides a system in which the mechanisms underlying transynaptic recognition can be explored. There are many synaptic proteins, often with several isoforms created by post-translational modifications. Complex cascades of interactions between these proteins, on either side of the synaptic cleft, are essential for normal function, normal transmitter release and postsynaptic responsiveness. Interactions between presynaptic and postsynaptic proteins that have binding domains in the synaptic cleft are proposed here to result in a local cleft structure that captures and stabilises only the appropriate subtype of GABA(A)Rs, allowing others to drift away from that synapse, either to be captured by another synapse, or internalised.

Guidance molecules in axon pruning and cell death

Axon pruning and neuronal cell death constitute two major regressive events that enable the establishment of fully mature brain architecture and connectivity. Although the cellular mechanisms for these two events are thought to be distinct, recent evidence has indicated the direct involvement of axon guidance molecules, including semaphorins, netrins, and ephrins, in controlling both processes. Here, we review how axon guidance cues regulate regressive events in paradigmatic models of neural development, from early control of apoptosis of neural progenitors, to later maintenance of neuronal survival and stereotyped pruning of axonal branches. These new findings are also discussed in the context of neural diseases and the potential links between axon pruning and degeneration.

Association study between single nucleotide polymorphisms in promoter region of AVPR1A and Korean autism spectrum disorders

To determine the association between arginine vasopressin receptor 1A gene (AVPR1A) and autism spectrum disorders (ASDs), we examined 3 single nucleotide polymorphisms (SNPs), namely, rs7294536, rs3759292, and rs10877969, in the promoter region of AVPR1A by using a family-based association test (FBAT) in 151 Korean trios. Our results demonstrated a statistically significant association between autism and SNPs (additive model: rs7294536, chi(2)=9.328, df=2, P=0.002; rs10877969, chi(2)=11.529, df=2, P<0.001) as well as between autism and haplotype analysis (additive model: chi(2)=14.122, df=3, P=0.003). In addition, we found that ADI-R scores calculated by using a diagnostic algorithm for failure to develop peer relationships (A2) were higher in subjects having the AA genotype than in subjects having the AG and GG genotypes of rs7294536. Thus, our study provides evidence for a possible association between these SNPs and the phenotype of ASDs.

Variations of plasma leptin and adiponectin levels in autistic patients

Autism is a neurodevelopmental disorder with pathogenesis not completely understood. Although a genetic origin has been recognized, it has been hypothesized a role for environmental factors, immune dysfunctions, and alterations of neurotransmitter systems. In young autistic patients we investigated plasma leptin and adiponectin levels over a year period. Thirty-five patients, mean age at the basal time 14.1+/-5.4 years, were enrolled. Controls were 35 healthy subjects, sex and age matched. Blood samples were withdrawn in the morning at the baseline and 1 year after. In patients leptin concentrations significantly increased, while adiponectin did not significantly change. Leptin values in patients were significantly higher than those found in controls at each time; adiponectin values did not differ at each time between patients and controls. Since patients were not obese, we could hypothesize that leptin might participate to clinical manifestations other than weight balance. The role of adiponectin in autism is still debatable.

Combined effect of maternal serotonin transporter genotype and prenatal stress in modulating offspring social interaction in mice

Several studies suggest that prenatal stress is a possible risk factor in the development of autism spectrum disorders. However, many children exposed to stress prenatally are born healthy and develop typically, suggesting that other factors must contribute to autism. Genes that contribute to stress reactivity may, therefore, exacerbate prenatal stress-mediated behavioral changes in the adult offspring. One candidate gene linked to increased stress reactivity encodes the serotonin transporter. Specifically, an insertion/deletion (long/short allele) polymorphism upstream of the serotonin transporter gene correlates with differential expression and function of the serotonin transporter and a heightened response to stressors. Heterozygous serotonin transporter knockout mice show reductions in serotonin transporter expression similar to the human short polymorphism. In this study, the role of prenatal stress and maternal serotonin transporter genotype were assessed in mice to determine whether their combined effect produces reductions in social behavior in the adult offspring. Pregnant serotonin transporter heterozygous knockout and wild-type dams were placed in either a control condition or subjected to chronic variable stress. The adult offspring were subsequently assessed for social interaction and anxiety using a three-chamber social approach task, ultrasonic vocalization detection, elevated-plus maze and an open field task. Results indicated that prenatal stress and reduced serotonin transporter expression of the dam may have the combined effect of producing changes in social interaction and social interest in the offspring consistent with those observed in autism spectrum disorder. This data indicates a possible combined effect of maternal serotonin transporter genotype and prenatal stress contributing to the production of autistic-like behaviors in offspring.

Branching out: mechanisms of dendritic arborization

Type-specific dendrite morphology is a hallmark of the neuron and has important functional implications in determining what signals a neuron receives and how these signals are integrated. During the past two decades, studies on dendritic arborization neurons in Drosophila melanogaster have started to identify mechanisms of dendrite morphogenesis that may have broad applicability to vertebrate species. Transcription factors, receptor-ligand interactions, various signalling pathways, local translational machinery, cytoskeletal elements, Golgi outposts and endosomes have been identified as contributors to the organization of dendrites of individual neurons and the placement of these dendrites in the neuronal circuitry. Further insight into these mechanisms will improve our understanding of how the nervous system functions and might help to identify the underlying causes of some neurological and neurodevelopmental disorders.

Staging perspectives in neurodevelopmental aspects of neuropsychiatry: agents, phases and ages at expression

Neurodevelopmental risk factors have assumed a critical role in prevailing notions concerning the etiopathogenesis of neuropsychiatric disorders. Staging, diagnostic elements at which phase of disease is determined, provides a means of conceptualizing the degree and extent of factors affecting brain development trajectories, but is concurrently specified through the particular interactions of genes and environment unique to each individual case. For present purposes, staging perspectives in neurodevelopmental aspects of the disease processes are considered from conditions giving rise to neurodevelopmental staging in affective states, adolescence, dopamine disease states, and autism spectrum disorders. Three major aspects influencing the eventual course of individual developmental trajectories appear to possess an essential determinant influence upon outcome: (i) the type of agent that interferes with brain development, whether chemical, immune system activating or absent (anoxia/hypoxia), (ii) the phase of brain development at which the agent exerts disruption, whether prenatal, postnatal, or adolescent, and (iii) the age of expression of structural and functional abnormalities. Clinical staging may be assumed at any or each developmental phase. The present perspective offers both a challenge to bring further order to diagnosis, intervention, and prognosis and a statement regarding the extreme complexities and interwoven intricacies of epigenetic factors, biomarkers, and neurobehavioral entities that aggravate currents notions of the neuropsychiatric disorders.

The serotonergic system: its role in pathogenesis and early developmental treatment of autism

Autism is a severe childhood disorder already presenting in the first 3 years of life and, therefore, strongly correlated with neurodevelopmental alterations in prenatal, as well as postnatal period. Neurotransmitters hold a pivotal role in development by providing the stimulation needed for synapses and neuronal networks to be formed during the critical period of neuroplasticity. Aberrations of the serotonergic system modify key processes in the developing brain and are strongly implicated in the pathophysiology of developmental disorders. Evidence for the role of serotonin in autism emerges from neuropathological, imaging and genetic studies. Due to its developmental arrest, autism requires early intervention that would, among others, target the disrupted serotonergic system and utilize brain plasticity to elicit clinically important brain changes in children.

[Autism, genetics and synaptic function alterations]

Autism is a neurodevelopmental disorder characterized by a deficit of language and communication both associated with a restricted repertoire of activities and interests. The current prevalence of autistic disorder stricto sensu is estimated at 1/500 whereas autism spectrum disorders (ASD) increases up to 1/150 to 1/200. Mental deficiency (MD) and epilepsy are present in numerous autistic individuals. Consequently, autism is as a major public health issue. Autism was first considered as a non biological disease; however various rational approaches for analysing epidemiological data suggested the possibility of the influence of genetic factors. In 2003, this hypothesis was clearly illustrated by the characterization of genetic mutations transmitted through a mendelian manner. Subsequently, the glutamate synapse appeared as a preferential causal target in autism because the identified genes encoded proteins present in this structure. Strikingly, the findings that an identical genetic dysfunction of the synapse might also explain some MD suggested the possibility of a genetic comorbidity between these neurodevelopmental conditions. To date, various identified genes are considered indifferently as "autism" or "MD" genes. The characterization of mutations in the NLGN4X gene in patients with Asperger syndrome, autism without MD, or MD without autism, was the first example. It appears that a genetic continuum between ASD on one hand, and between autism and MD on the other hand, is present. Consequently, it is likely that genes already involved in MD will be found mutated in autistic patients and will represent future target for finding new factors in autism.

Minding the calcium store: Ryanodine receptor activation as a convergent mechanism of PCB toxicity

Chronic low-level polychlorinated biphenyl (PCB) exposures remain a significant public health concern since results from epidemiological studies indicate that PCB burden is associated with immune system dysfunction, cardiovascular disease, and impairment of the developing nervous system. Of these various adverse health effects, developmental neurotoxicity has emerged as a particularly vulnerable endpoint in PCB toxicity. Arguably the most pervasive biological effects of PCBs could be mediated by their ability to alter the spatial and temporal fidelity of Ca2+ signals through one or more receptor-mediated processes. This review will focus on our current knowledge of the structure and function of ryanodine receptors (RyRs) in muscle and nerve cells and how PCBs and related non-coplanar structures alter these functions. The molecular and cellular mechanisms by which non-coplanar PCBs and related structures alter local and global Ca2+ signaling properties and the possible short and long-term consequences of these perturbations on neurodevelopment and neurodegeneration are reviewed.

Neurodevelopmental effects of chronic exposure to elevated levels of pro-inflammatory cytokines in a developing visual system

Background

Imbalances in the regulation of pro-inflammatory cytokines have been increasingly correlated with a number of severe and prevalent neurodevelopmental disorders, including autism spectrum disorder, schizophrenia and Down syndrome. Although several studies have shown that cytokines have potent effects on neural function, their role in neural development is still poorly understood. In this study, we investigated the link between abnormal cytokine levels and neural development using the Xenopus laevis tadpole visual system, a model frequently used to examine the anatomical and functional development of neural circuits.

Results

Using a test for a visually guided behavior that requires normal visual system development, we examined the long-term effects of prolonged developmental exposure to three pro-inflammatory cytokines with known neural functions: interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α. We found that all cytokines affected the development of normal visually guided behavior. Neuroanatomical imaging of the visual projection showed that none of the cytokines caused any gross abnormalities in the anatomical organization of this projection, suggesting that they may be acting at the level of neuronal microcircuits. We further tested the effects of TNF-α on the electrophysiological properties of the retinotectal circuit and found that long-term developmental exposure to TNF-α resulted in enhanced spontaneous excitatory synaptic transmission in tectal neurons, increased AMPA/NMDA ratios of retinotectal synapses, and a decrease in the number of immature synapses containing only NMDA receptors, consistent with premature maturation and stabilization of these synapses. Local interconnectivity within the tectum also appeared to remain widespread, as shown by increased recurrent polysynaptic activity, and was similar to what is seen in more immature, less refined tectal circuits. TNF-α treatment also enhanced the overall growth of tectal cell dendrites. Finally, we found that TNF-α-reared tadpoles had increased susceptibility to pentylenetetrazol-induced seizures.

Conclusions

Taken together our data are consistent with a model in which TNF-α causes premature stabilization of developing synapses within the tectum, therefore preventing normal refinement and synapse elimination that occurs during development, leading to increased local connectivity and epilepsy. This experimental model also provides an integrative approach to understanding the effects of cytokines on the development of neural circuits and may provide novel insights into the etiology underlying some neurodevelopmental disorders.

Adenosine A(2A) receptor gene (ADORA2A) variants may increase autistic symptoms and anxiety in autism spectrum disorder

Autism spectrum disorders (ASDs) are heterogeneous disorders presenting with increased rates of anxiety. The adenosine A(2A) receptor gene (ADORA2A) is associated with panic disorder and is located on chromosome 22q11.23. Its gene product, the adenosine A(2A) receptor, is strongly expressed in the caudate nucleus, which also is involved in ASD. As autistic symptoms are increased in individuals with 22q11.2 deletion syndrome, and large 22q11.2 deletions and duplications have been observed in ASD individuals, in this study, 98 individuals with ASD and 234 control individuals were genotyped for eight single-nucleotide polymorphisms in ADORA2A. Nominal association with the disorder was observed for rs2236624-CC, and phenotypic variability in ASD symptoms was influenced by rs3761422, rs5751876 and rs35320474. In addition, association of ADORA2A variants with anxiety was replicated for individuals with ASD. Findings point toward a possible mediating role of ADORA2A variants on phenotypic expression in ASD that need to be replicated in a larger sample.

Oxidative stress from diverse developmental neurotoxicants: antioxidants protect against lipid peroxidation without preventing cell loss

Oxidative stress has been hypothesized to provide a mechanism by which apparently unrelated chemicals can nevertheless produce similar developmental neurotoxic outcomes. We used differentiating PC12 cells to compare the effects of agents from four different classes and then to evaluate antioxidant amelioration: fipronil, perfluorooctanesulfonamide (PFOSA), dieldrin and chlorpyrifos. The rank order for lipid peroxidation corresponded to the ability to evoke cell loss: fipronil>PFOSA>dieldrin>chlorpyrifos. The same sequence was found for an index of cell enlargement (protein/DNA ratio) but the effects on neurite outgrowth (membrane/total protein) diverged, with fipronil producing a decrease and PFOSA an increase. Cotreatment with antioxidants reduced (ascorbate) or eliminated (Vitamin E) lipid peroxidation caused by each of the agents but failed to protect against cell loss, with the sole exception of chlorpyrifos, for which we earlier showed partial protection by Vitamin E; addition of higher NGF concentrations protected neither against oxidative stress nor cell loss. Despite the failure to prevent cell loss, ascorbate protected the cells from the effects of PFOSA on neuritic outgrowth; NGF, and to a lesser extent, ascorbate, offset the effects of fipronil on both cell enlargement and neuritogenesis. At the same time, the ameliorant treatments also worsened some of the other toxicant effects. Our results point out the problems in concluding that, just because a neurotoxicant produces oxidative stress, antioxidant therapy will be effective in preventing damage. Instead, additional mechanisms for each agent may provide alternative routes to neurotoxicity, or may be additive or synergistic with oxidative stress.

Autism susceptibility candidate 2 (Auts2) encodes a nuclear protein expressed in developing brain regions implicated in autism neuropathology

Autism susceptibility candidate 2 (Auts2) is a gene associated with autism and mental retardation, whose function is unknown. Expression of Auts2 mRNA and protein were studied in the developing mouse brain by in situ hybridization, immunohistochemistry, and western blotting. Auts2 mRNA was highly expressed in the developing cerebral cortex and cerebellum, regions often affected by neuropathological changes in autism, and a few other brain regions. On embryonic day (E) 12, Auts2 mRNA was expressed in the cortical preplate, where it colocalized with Tbr1, a transcription factor specific for postmitotic projection neurons. From E16 to postnatal day 21, Auts2 was expressed most abundantly in frontal cortex, hippocampus and cerebellum, including Purkinje cells and deep nuclei. High levels of Auts2 were also detected in developing dorsal thalamus, olfactory bulb, inferior colliculus and substantia nigra. Auts2 protein showed similar regional expression patterns as the mRNA. At the cellular level, Auts2 protein was localized in the nuclei of neurons and some neuronal progenitors.

Autism spectrum and obsessive-compulsive disorders: OC behaviors, phenotypes and genetics

Autism spectrum disorders (ASDs) are a phenotypically and etiologically heterogeneous set of disorders that include obsessive-compulsive behaviors (OCB) that partially overlap with symptoms associated with obsessive-compulsive disorder (OCD). The OCB seen in ASD vary depending on the individual's mental and chronological age as well as the etiology of their ASD. Although progress has been made in the measurement of the OCB associated with ASD, more work is needed including the potential identification of heritable endophenotypes. Likewise, important progress toward the understanding of genetic influences in ASD has been made by greater refinement of relevant phenotypes using a broad range of study designs, including twin and family-genetic studies, parametric and nonparametric linkage analyses, as well as candidate gene studies and the study of rare genetic variants. These genetic analyses could lead to the refinement of the OCB phenotypes as larger samples are studied and specific associations are replicated. Like ASD, OCB are likely to prove to be multidimensional and polygenic. Some of the vulnerability genes may prove to be generalist genes influencing the phenotypic expression of both ASD and OCD while others will be specific to subcomponents of the ASD phenotype. In order to discover molecular and genetic mechanisms, collaborative approaches need to generate shared samples, resources, novel genomic technologies, as well as more refined phenotypes and innovative statistical approaches. There is a growing need to identify the range of molecular pathways involved in OCB related to ASD in order to develop novel treatment interventions.

A meta-analysis of the corpus callosum in autism

BACKGROUND

Previous magnetic resonance imaging (MRI) studies have reported reductions in corpus callosum (CC) total area and CC regions in individuals with autism. However, studies have differed concerning the magnitude and/or region contributing to CC reductions. The present study determined the significance and magnitude of reductions in CC total and regional area measures in autism.

METHOD

PubMed and PsycINFO databases were searched to identify MRI studies examining corpus callosum area in autism. Ten studies contributed data from 253 patients with autism (mean age = 14.58, SD = 6.00) and 250 healthy control subjects (mean age = 14.47, SD = 5.31). Of these 10 studies, 8 reported area measurements for corpus callosum regions (anterior, mid/body, and posterior), and 6 reported area for Witelson subdivisions. Meta-analytic procedures were used to quantify differences in total and region CC area measurements.

RESULTS

Total CC area was reduced in autism and the magnitude of the reduction was medium (weighted mean d = .48, 95% confidence interval [CI] = .30-.66). All regions showed reductions in size with the magnitude of the effect decreasing caudally (anterior d = .49, mid/body d = .43, posterior d = .37). Witelson subdivision 3 (rostral body) showed the largest effect, indicating greatest reduction in the region containing premotor/supplementary motor neurons.

CONCLUSIONS

Corpus callosum reductions are present in autism and support the aberrant connectivity hypothesis. Future diffusion tensor imaging studies examining specific fiber tracts connecting the hemispheres are needed to identify the cortical regions most affected by CC reductions.

Autism

Autism spectrum disorders are characterised by severe deficits in socialisation, communication, and repetitive or unusual behaviours. Increases over time in the frequency of these disorders (to present rates of about 60 cases per 10,000 children) might be attributable to factors such as new administrative classifications, policy and practice changes, and increased awareness. Surveillance and screening strategies for early identification could enable early treatment and improved outcomes. Autism spectrum disorders are highly genetic and multifactorial, with many risk factors acting together. Genes that affect synaptic maturation are implicated, resulting in neurobiological theories focusing on connectivity and neural effects of gene expression. Several treatments might address core and comorbid symptoms. However, not all treatments have been adequately studied. Improved strategies for early identification with phenotypic characteristics and biological markers (eg, electrophysiological changes) might hopefully improve effectiveness of treatment. Further knowledge about early identification, neurobiology of autism, effective treatments, and the effect of this disorder on families is needed.

Inducible gene manipulations in serotonergic neurons

An impairment of the serotonergic (5-HT) system has been implicated in the etiology of many neuropsychiatric disorders. Despite the considerable genetic evidence, the exact molecular and pathophysiological mechanisms underlying this dysfunction remain largely unknown. To address the lack of instruments for the molecular dissection of gene function in serotonergic neurons we have developed a new mouse transgenic tool that allows inducible Cre-mediated recombination of genes selectively in 5-HT neurons of all raphe nuclei. In this transgenic mouse line, the tamoxifen-inducible CreERT2 recombinase is expressed under the regulatory control of the mouse tryptophan hydroxylase 2 (Tph2) gene locus (177 kb). Tamoxifen treatment efficiently induced recombination selectively in serotonergic neurons with minimal background activity in vehicle-treated mice. These genetic manipulations can be initiated at any desired time during embryonic development, neonatal stage or adulthood. To illustrate the versatility of this new tool, we show that Brainbow-1.0L(TPH2-CreERT2) mice display highly efficient recombination in serotonergic neurons with individual 5-HT neurons labeling with multiple distinct fluorescent colors. This labeling is well suited for visualization and tracing of serotonergic neurons and their network architecture. Finally, the applicability of TPH2-CreERT2 for loxP-flanked candidate gene manipulation is evidenced by our successful knockout induction of the ubiquitously expressed glucocorticoid-receptor exclusively in 5-HT neurons of adult mice. The TPH2-CreERT2 line will allow detailed analysis of gene function in both developing and adult serotonergic neurons.

Animal models of autism spectrum disorders: information for neurotoxicologists

Recent findings derived from large-scale datasets and biobanks link multiple genes to autism spectrum disorders. Consequently, novel rodent mutants with deletions, truncations and in some cases, overexpression of these candidate genes have been developed and studied both behaviorally and biologically. At the Annual Neurotoxicology Meeting in Rochester, NY in October of 2008, a symposium of clinicians and basic scientists gathered to present the behavioral features of autism, as well as strategies to model those behavioral features in mice and primates. The aim of the symposium was to provide researchers with up-to-date information on both the genetics of autism and how they are used in differing in vivo and in vitro animal models as well as to provide a background on the environmental exposures being tested on several animal models. In addition, researchers utilizing complementary approaches, presented on cell culture, in vitro or more basic models, which target neurobiological mechanisms, including Drosophila. Following the presentation, a panel convened to explore the opportunities and challenges of using model systems to investigate genetic and environment interactions in autism spectrum disorders. The following paper represents a summary of each presentation, as well as the discussion that followed at the end of the symposium.

Pathogenesis of autism: a patchwork of genetic causes

Autism spectrum disorders (ASDs) are relatively infrequent but are devastating developmental conditions characterized by marked deficiencies in social, communicative and other behavioral domains. It has been known for a substantial period of time that these disorders are genetic in nature. However, elucidating the specific mechanisms of these disorders has been difficult. A major reason for such difficulty is the recognized genetic heterogeneity of ASDs. Specifically, many genetic mechanisms related to structural variations in the genome have been reported as possible genetic causes of these disorders. This review briefly exemplifies these genetic mechanisms, presents a concise overview of the evidence for the genetic basis of ASDs and provides an appraisal of the specific structural genetic variants thought to contribute to the pathogenesis of these complex disorders.

Syndromic autism: causes and pathogenetic pathways

BACKGROUND

Autism is a severe neurodevelopmental disorder known to have many different etiologies. In the last few years, significant progresses have been made in comprehending the causes of autism and their multiple impacts on the developing brain. This article aims to review the current understanding of the etiologies and the multiple pathogenetic pathways that are likely to lead to the autistic phenotype.

DATA SOURCES

The PubMed database was searched with the keywords "autism" and "chromosomal abnormalities", "metabolic diseases", "susceptibility loci".

RESULTS

Genetic syndromes, defined mutations, and metabolic diseases account for less than 20% of autistic patients. Alterations of the neocortical excitatory/inhibitory balance and perturbations of interneurons' development represent the most probable pathogenetic mechanisms underlying the autistic phenotype in fragile X syndrome and tuberous sclerosis complex. Chromosomal abnormalities and potential candidate genes are strongly implicated in the disruption of neural connections, brain growth and synaptic/dendritic morphology. Metabolic and mitochondrial defects may have toxic effects on the brain cells, causing neuronal loss and altered modulation of neurotransmission systems.

CONCLUSIONS

A wide variety of cytogenetic abnormalities have been recently described, particularly in the low functioning individuals with dysmorphic features. Routine metabolic screening studies should be performed in the presence of autistic regression or suggestive clinical findings. As etiologies of autism are progressively discovered, the number of individuals with idiopathic autism will progressively shrink. Studies of genetic and environmentally modulated epigenetic factors are beginning to provide some clues to clarify the complexities of autism pathogenesis. The role of the neuropediatrician will be to understand the neurological basis of autism, and to identify more homogenous subgroups with specific biologic markers.