India ink to 3D imaging: The legacy of Dr. Deepak "Dee" N. Pandya and his influence on generations of neuroanatomists.

Dr. Deepak "Dee" Pandya spent his career as an internal medicine physician as well as in his respective laboratories at the Bedford, Massachusetts Veterans Administration Hospital and at Boston University School of Medicine. His achievements mapping out the cytoarchitecture and connectivity of areas all over the nonhuman primate brain and small mammals are unparalleled. Dee made numerous discoveries and created painstakingly detailed reports, which impacted the field of neuroanatomy and expanded our perceptions of the many diverse inputs and suggestive functions of specific brain regions. The "old school" methods employed from microscopic work to detailed analyses yielded a product that was accurate and exciting all at the same time. We will all miss Dee's smile and tender manner, but more so, we will miss his wonderful and patient mentorship during the precious time we all spent with him. His mentorship resulted in all of his trainees becoming better scientists and left us with the understanding that people like Dee only come by once in a lifetime. In this tribute article for this special issue in the Journal of Comparative Neurology (JCN), the authors describe some of the tedious methods that were used to present our work as a way to provide insight into the extraordinary time and effort it took to produce and publish our articles with Dee in JCN. Dee's work with his colleagues set the stage for more modern methods of counting and mapping neuronal populations presented here, paving the way for such technologies as artificial intelligence and light sheet imaging to advance the field forward to reach new and exciting discoveries.

Transcriptomic analysis of isolated and pooled human postmortem cerebellar Purkinje cells in autism spectrum disorders.

At present, the neuronal mechanisms underlying the diagnosis of autism spectrum disorder (ASD) have not been established. However, studies from human postmortem ASD brains have consistently revealed disruptions in cerebellar circuitry, specifically reductions in Purkinje cell (PC) number and size. Alterations in cerebellar circuitry would have important implications for information processing within the cerebellum and affect a wide range of human motor and non-motor behaviors. Laser capture microdissection was performed to obtain pure PC populations from a cohort of postmortem control and ASD cases and transcriptional profiles were compared. The 427 differentially expressed genes were enriched for gene ontology biological processes related to developmental organization/connectivity, extracellular matrix organization, calcium ion response, immune function and PC signaling alterations. Given the complexity of PCs and their far-ranging roles in response to sensory stimuli and motor function regulation, understanding transcriptional differences in this subset of cerebellar cells in ASD may inform on convergent pathways that impact neuronal function.

Region-Specific Alterations of Perineuronal Net Expression in Postmortem Autism Brain Tissue.

Genetic variance in autism spectrum disorder (ASD) is often associated with mechanisms that broadly fall into the category of neuroplasticity. Parvalbumin positive neurons and their surrounding perineuronal nets (PNNs) are important factors in critical period plasticity and have both been implicated in ASD. PNNs are found in high density within output structures of the cerebellum and basal ganglia, two regions that are densely connected to many other brain areas and have the potential to participate in the diverse array of symptoms present in an ASD diagnosis. The dentate nucleus (DN) and globus pallidus (GP) were therefore assessed for differences in PNN expression in human postmortem ASD brain tissue. While Purkinje cell loss is a consistent neuropathological finding in ASD, in this cohort, the Purkinje cell targets within the DN did not show differences in number of cells with or without a PNN. However, the density of parvalbumin positive neurons with a PNN were significantly reduced in the GP internus and externus of ASD cases, which was not dependent on seizure status. It is unclear whether these alterations manifest during development or are a consequence of activity-dependent mechanisms that lead to altered network dynamics later in life.

Parvalbumin subtypes of cerebellar Purkinje cells contribute to differential intrinsic firing properties.

Purkinje cells (PCs) are central to cerebellar information coding and appreciation for the diversity of their firing patterns and molecular profiles is growing. Heterogeneous subpopulations of PCs have been identified that display differences in intrinsic firing properties without clear mechanistic insight into what underlies the divergence in firing parameters. Although long used as a general PC marker, we report that the calcium binding protein parvalbumin labels a subpopulation of PCs, based on high and low expression, with a conserved distribution pattern across the animals examined. We trained a convolutional neural network to recognize the parvalbumin subtypes and create maps of whole cerebellar distribution and find that PCs within these areas have differences in spontaneous firing that can be modified by altering calcium buffer content. These subtypes also show differential responses to potassium and calcium channel blockade, suggesting a mechanistic role for variability in PC intrinsic firing through differences in ion channel composition. It is proposed that ion channels drive the diversity in PC intrinsic firing phenotype and parvalbumin calcium buffering provides capacity for the highest firing rates observed. These findings open new avenues for detailed classification of PC subtypes.

Postnatal expression profiles of atypical cadherin FAT1 suggest its role in autism.

Genetic studies have linked FAT1 (FAT atypical cadherin 1) with autism spectrum disorder (ASD); however, the role that FAT1 plays in ASD remains unknown. In mice, the function of Fat1 has been primarily implicated in embryonic nervous system development with less known about its role in postnatal development. We show for the first time that FAT1 protein is expressed in mouse postnatal brains and is enriched in the cerebellum, where it localizes to granule neurons and Golgi cells in the granule layer, as well as inhibitory neurons in the molecular layer. Furthermore, subcellular characterization revealed FAT1 localization in neurites and soma of granule neurons, as well as being present in the synaptic plasma membrane and postsynaptic densities. Interestingly, FAT1 expression was decreased in induced pluripotent stem cell (iPSC)-derived neural precursor cells (NPCs) from individuals with ASD. These findings suggest a novel role for FAT1 in postnatal development and may be particularly important for cerebellum function. As the cerebellum is one of the vulnerable brain regions in ASD, our study warrants further investigation of FAT1 in the disease etiology.

Regulation of Neural Circuit Development by Cadherin-11 Provides Implications for Autism.

Autism spectrum disorder (ASD) is a neurologic condition characterized by alterations in social interaction and communication, and restricted and/or repetitive behaviors. The classical Type II cadherins cadherin-8 (Cdh8, CDH8) and cadherin-11 (Cdh11, CDH11) have been implicated as autism risk gene candidates. To explore the role of cadherins in the etiology of autism, we investigated their expression patterns during mouse brain development and in autism-specific human tissue. In mice, expression of cadherin-8 and cadherin-11 was developmentally regulated and enriched in the cortex, hippocampus, and thalamus/striatum during the peak of dendrite formation and synaptogenesis. Both cadherins were expressed in synaptic compartments but only cadherin-8 associated with the excitatory synaptic marker neuroligin-1. Induced pluripotent stem cell (iPSC)-derived cortical neural precursor cells (NPCs) and cortical organoids generated from individuals with autism showed upregulated CDH8 expression levels, but downregulated CDH11. We used Cdh11 knock-out (KO) mice of both sexes to analyze the function of cadherin-11, which could help explain phenotypes observed in autism. Cdh11-/- hippocampal neurons exhibited increased dendritic complexity along with altered neuronal and synaptic activity. Similar to the expression profiles in human tissue, levels of cadherin-8 were significantly elevated in Cdh11 KO brains. Additionally, excitatory synaptic markers neuroligin-1 and postsynaptic density (PSD)-95 were both increased. Together, these results strongly suggest that cadherin-11 is involved in regulating the development of neuronal circuitry and that alterations in the expression levels of cadherin-11 may contribute to the etiology of autism.

Increased Dopamine Type 2 Gene Expression in the Dorsal Striatum in Individuals With Autism Spectrum Disorder Suggests Alterations in Indirect Pathway Signaling and Circuitry.

Autism spectrum disorder (ASD) is behaviorally defined and diagnosed by delayed and/or impeded language, stereotyped repetitive behaviors, and difficulties with social interactions. Additionally, there are disruptions in motor processing, which includes the intent to execute movements, interrupted/inhibited action chain sequences, impaired execution of speech, and repetitive motor behaviors. Cortical loops through basal ganglia (BG) structures are known to play critical roles in the typical functioning of these actions. Specifically, corticostriate projections to the dorsal striatum (caudate and putamen) convey abundant input from motor, cognitive and limbic cortices and subsequently project to other BG structures. Excitatory dopamine (DA) type 1 receptors are predominantly expressed on GABAergic medium spiny neurons (MSNs) in the dorsal striatum as part of the "direct pathway" to GPi and SNpr whereas inhibitory DA type 2 receptors are predominantly expressed on MSNs that primarily project to GPe. This study aimed to better understand how this circuitry may be altered in ASD, especially concerning the neurochemical modulation of GABAergic MSNs within the two major BG pathways. We utilized two classical methods to analyze the postmortem BG in ASD in comparison to neurotypical cases: ligand binding autoradiography to quantify densities of GABA-A, GABA-B, 5-HT2, and DA type 1 and 2 receptors and in situ hybridization histochemistry (ISHH) to quantify mRNA for D1, D2 receptors and three key GABAergic subunits (α1, ß2, and γ2), as well as the GABA synthesizing enzymes (GAD65/67). Results demonstrated significant increases in D2 mRNA within MSNs in both the caudate and putamen, which was further verified by proenkephalin mRNA that is co-expressed with the D2 receptor in the indirect pathway MSNs. In contrast, all other GABAergic, serotonergic and dopaminergic markers in the dorsal striatum had comparable labeling densities. These results indicate alterations in the indirect pathway of the BG, with possible implications for the execution of competing motor programs and E/I imbalance in the direct/indirect motor feedback pathways through thalamic and motor cortical areas. Results also provide insights regarding the efficacy of FDA-approved drugs used to treat individuals with ASD acting on specific DA and 5-HT receptor subtypes.

Development of a 3-D Organoid System Using Human Induced Pluripotent Stem Cells to Model Idiopathic Autism.

Autism spectrum condition (ASC) is a complex set of behavioral and neurological responses reflecting a likely interaction between autism susceptibility genes and the environment. Autism represents a spectrum in which heterogeneous genetic backgrounds are expressed with similar heterogeneity in the affected domains of communication, social interaction, and behavior. The impact of gene-environment interactions may also account for differences in underlying neurology and wide variation in observed behaviors. For these reasons, it has been difficult for geneticists and neuroscientists to build adequate systems to model the complex neurobiology causes of autism. In addition, the development of therapeutics for individuals with autism has been painstakingly slow, with most treatment options reduced to repurposed medications developed for other neurological diseases. Adequately developing therapeutics that are sensitive to the genetic and neurobiological diversity of individuals with autism necessitates personalized models of ASC that can capture some common pathways that reflect the neurophysiological and genetic backgrounds of varying individuals. Testing cohorts of individuals with and without autism for these potentially convergent pathways on a scalable platform for therapeutic development requires large numbers of samples from a diverse population. To date, human induced pluripotent stem cells (iPSCs) represent one of the best systems for conducting these types of assays in a clinically relevant and scalable way. The discovery of the four Yamanaka transcription factors (OCT3/4, SOX2, c-Myc, and KLF4) [1] allows for the induction of iPSCs from fibroblasts [2], peripheral blood mononuclear cells (PBMCs, i.e. lymphocytes and monocytes) [3, 4], or dental pulp cells [5] that retain the original genetics of the individual from which they were derived [6], making iPSCs a powerful tool to model neurophysiological conditions. iPSCs are a readily renewable cell type that can be developed on a small scale for boutique-style proof-of-principle phenotypic studies and scaled to an industrial level for drug screening and other high-content assays. This flexibility, along with the ability to represent the true genetic diversity of autism, underscores the importance of using iPSCs to model neurophysiological aspects of ASC.

Differential serotonin transporter (5-HTT) and 5-HT2 receptor density in limbic and neocortical areas of adults and children with autism spectrum disorders: implications for selective serotonin reuptake inhibitor efficacy.

As selective serotonin reuptake inhibitors (SSRIs) are among the most commonly prescribed medications in autism, we aimed to determine whether targets for SSRIs are differentially affected in three cortical areas in children and adults with autism compared to neurotypical individuals. Utilizing a large cohort of postmortem brain tissue (n = 14-19 per group), saturation ligand binding assays were conducted on sections from the anterior cingulate cortex (ACC), posterior cingulate cortex, and fusiform gyrus (FG). Specific binding to the 5-HT transporter (5-HTT) as well as to 5-HT2 and 1A receptors (5-HT2, 5-HT1A ) was quantified in superficial and deep layers of each region using the ligands [3 H]-citalopram (5-HTT), [3 H]-ketanserin (5-HT2 ), and [3 H]-8-OH-DPAT (5-HT1A ). A Welch's t-test was utilized to compare receptor densities (Bmax ), revealing a statistically significant decrease in 5-HTT within the ACC of the entire autism cohort. There was also a decrease in 5-HT2 receptor density in the ACC in the adult cohort, but not in child postmortem autism cases as compared to controls. Comparing linear regression lines of Bmax values plotted against age, shows a significantly lower intercept for 5-HTT in autism (p = 0.025). 5-HT2 density increases with age in control cases, whereas in autism there is a decrease with age and significantly different slopes between regression lines (p = 0.032). This suggests a deficit in 5-HTT within the ACC in individuals with autism, while decreases in 5-HT2 density are age-dependent. There were no differences in receptor densities in the posterior cingulate cortex or FG in autism and no differences in ligand affinity (KD ) across all regions and ligands examined.

Basal ganglia and autism - a translational perspective.

The basal ganglia are a collection of nuclei below the cortical surface that are involved in both motor and non-motor functions, including higher order cognition, social interactions, speech, and repetitive behaviors. Motor development milestones that are delayed in autism such as gross motor, fine motor and walking can aid in early diagnosis of autism. Neuropathology and neuroimaging findings in autism cases revealed volumetric changes and altered cell density in select basal ganglia nuclei. Interestingly, in autism, both the basal ganglia and the cerebellum are impacted both in their motor and non-motor domains and recently, found to be connected via the pons through a short disynaptic pathway. In typically developing individuals, the basal ganglia plays an important role in: eye movement, movement coordination, sensory modulation and processing, eye-hand coordination, action chaining, and inhibition control. Genetic models have proved to be useful toward understanding cellular and molecular changes at the synaptic level in the basal ganglia that may in part contribute to these autism-related behaviors. In autism, basal ganglia functions in motor skill acquisition and development are altered, thus disrupting the normal flow of feedback to the cortex. Taken together, there is an abundance of emerging evidence that the basal ganglia likely plays critical roles in maintaining an inhibitory balance between cortical and subcortical structures, critical for normal motor actions and cognitive functions. In autism, this inhibitory balance is disturbed thus impacting key pathways that affect normal cortical network activity. Autism Res 2017, 10: 1751-1775. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Habit learning, action selection and performance are modulated by the basal ganglia, a collection of groups of neurons located below the cerebral cortex in the brain. In autism, there is emerging evidence that parts of the basal ganglia are structurally and functionally altered disrupting normal information flow. The basal ganglia through its interconnected circuits with the cerebral cortex and the cerebellum can potentially impact various motor and cognitive functions in the autism brain.

Decreased parvalbumin mRNA levels in cerebellar Purkinje cells in autism.

Recent neuropathology studies in human brains indicate that several areas of the prefrontal cortex have decreased numbers of parvalbumin interneurons or decreased parvalbumin expression in Autism Spectrum disorders (ASD) [Hashemi, Ariza, Rogers, Noctor, & Martinez-Cerdeno, 2017; Zikopoulos & Barbas, ]. These data suggest that a deficit in parvalbumin may be a key neuropathology of ASD and contribute to altered GABAergic inhibition. However, it is unclear if a deficit in parvalbumin is a phenomenon that occurs in regions other than the cerebral cortex. The cerebellum is a major region where neuropathology was first detected in ASD over three decades ago [Bauman & Kemper, ]. In view of the documented association between parvalbumin-expressing neurons and autism, the objective of the present study was to determine if parvalbumin gene expression is also altered in Purkinje neurons of the cerebellum. Radioisotopic in situ hybridization histochemistry was used on human tissue sections from control and ASD brains in order to detect and measure parvalbumin mRNA levels at the single cell level in Purkinje cells of Crus II of the lateral cerebellar hemispheres. Results indicate that parvalbumin mRNA levels are significantly lower in Purkinje cells in ASD compared to control brains. This decrease was not influenced by post-mortem interval or age at death. This result indicates that decreased parvalbumin expression is a more widespread feature of ASD. We discuss how this decrease may be implicated in altered cerebellar output to the cerebral cortex and in key ASD symptoms. Autism Res 2017, 10: 1787-1796. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: The cerebellum of the brain controls movement and cognition, including memory and language. This study investigated mechanisms of cerebellar function in Autism. Our hypothesis is that parvalbumin, a molecule that controls and coordinate many cellular brain functions, contributes to the excitatory/inhibitory imbalance in Autism. We report that parvalbumin expression is depressed in Purkinje cells of the cerebellum in autism. This finding contributes to elucidate the cellular and molecular underpinings of autism and should provide a direction for future therapies.

A Subset of Autism-Associated Genes Regulate the Structural Stability of Neurons.

Autism spectrum disorder (ASD) comprises a range of neurological conditions that affect individuals' ability to communicate and interact with others. People with ASD often exhibit marked qualitative difficulties in social interaction, communication, and behavior. Alterations in neurite arborization and dendritic spine morphology, including size, shape, and number, are hallmarks of almost all neurological conditions, including ASD. As experimental evidence emerges in recent years, it becomes clear that although there is broad heterogeneity of identified autism risk genes, many of them converge into similar cellular pathways, including those regulating neurite outgrowth, synapse formation and spine stability, and synaptic plasticity. These mechanisms together regulate the structural stability of neurons and are vulnerable targets in ASD. In this review, we discuss the current understanding of those autism risk genes that affect the structural connectivity of neurons. We sub-categorize them into (1) cytoskeletal regulators, e.g., motors and small RhoGTPase regulators; (2) adhesion molecules, e.g., cadherins, NCAM, and neurexin superfamily; (3) cell surface receptors, e.g., glutamatergic receptors and receptor tyrosine kinases; (4) signaling molecules, e.g., protein kinases and phosphatases; and (5) synaptic proteins, e.g., vesicle and scaffolding proteins. Although the roles of some of these genes in maintaining neuronal structural stability are well studied, how mutations contribute to the autism phenotype is still largely unknown. Investigating whether and how the neuronal structure and function are affected when these genes are mutated will provide insights toward developing effective interventions aimed at improving the lives of people with autism and their families.

Human Inducible Pluripotent Stem Cells and Autism Spectrum Disorder: Emerging Technologies.

Autism Spectrum Disorder (ASD) is a behaviorally defined neurodevelopmental condition. Symptoms of ASD cover the spectrum from mild qualitative differences in social interaction to severe communication and social and behavioral challenges that require lifelong support. Attempts at understanding the pathophysiology of ASD have been hampered by a multifactorial etiology that stretches the limits of current behavioral and cell based models. Recent progress has implicated numerous autism-risk genes but efforts to gain a better understanding of the underlying biological mechanisms have seen slow progress. This is in part due to lack of appropriate models for complete molecular and pharmacological studies. The advent of induced pluripotent stem cells (iPSC) has reinvigorated efforts to establish more complete model systems that more reliably identify molecular pathways and predict effective drug targets and candidates in ASD. iPSCs are particularly appealing because they can be derived from human patients and controls for research purposes and provide a technology for the development of a personalized treatment regimen for ASD patients. The pluripotency of iPSCs allow them to be reprogrammed into a number of CNS cell types and phenotypically screened across many patients. This quality is already being exploited in protocols to generate 2-dimensional (2-D) and three-dimensional (3-D) models of neurons and developing brain structures. iPSC models make powerful platforms that can be interrogated using electrophysiology, gene expression studies, and other cell-based quantitative assays. iPSC technology has limitations but when combined with other model systems has great potential for helping define the underlying pathophysiology of ASD. Autism Res 2016, 9: 513-535. © 2015 International Society for Autism Research, Wiley Periodicals, Inc.

Autism spectrum disorders and neuropathology of the cerebellum.

The cerebellum contains the largest number of neurons and synapses of any structure in the central nervous system. The concept that the cerebellum is solely involved in fine motor function has become outdated; substantial evidence has accumulated linking the cerebellum with higher cognitive functions including language. Cerebellar deficits have been implicated in autism for more than two decades. The computational power of the cerebellum is essential for many, if not most of the processes that are perturbed in autism including language and communication, social interactions, stereotyped behavior, motor activity and motor coordination, and higher cognitive functions. The link between autism and cerebellar dysfunction should not be surprising to those who study its cellular, physiological, and functional properties. Postmortem studies have revealed neuropathological abnormalities in cerebellar cellular architecture while studies on mouse lines with cell loss or mutations in single genes restricted to cerebellar Purkinje cells have also strongly implicated this brain structure in contributing to the autistic phenotype. This connection has been further substantiated by studies investigating brain damage in humans restricted to the cerebellum. In this review, we summarize advances in research on idiopathic autism and three genetic forms of autism that highlight the key roles that the cerebellum plays in this spectrum of neurodevelopmental disorders.

Reduced serotonin receptor subtypes in a limbic and a neocortical region in autism.

Autism is a behaviorally defined, neurological disorder with symptom onset before the age of 3. Abnormalities in social-emotional behaviors are a core deficit in autism, and are characterized by impaired reciprocal-social interaction, lack of facial expressions, and the inability to recognize familiar faces. The posterior cingulate cortex (PCC) and fusiform gyrus (FG) are two regions within an extensive limbic-cortical network that contribute to social-emotional behaviors. Evidence indicates that changes in brains of individuals with autism begin prenatally. Serotonin (5-HT) is one of the earliest expressed neurotransmitters, and plays an important role in synaptogenesis, neurite outgrowth, and neuronal migration. Abnormalities in 5-HT systems have been implicated in several psychiatric disorders, including autism, as evidenced by immunology, imaging, genetics, pharmacotherapy, and neuropathology. Although information is known regarding peripheral 5-HT in autism, there is emerging evidence that 5-HT systems in the central nervous system, including various 5-HT receptor subtypes and transporters, are affected in autism. The present study demonstrated significant reductions in 5-HT1A receptor-binding density in superficial and deep layers of the PCC and FG, and in the density of 5-HT(2A) receptors in superficial layers of the PCC and FG. A significant reduction in the density of serotonin transporters (5-HTT) was also found in the deep layers of the FG, but normal levels were demonstrated in both layers of the PCC and superficial layers of the FG. This study provides potential substrates for decreased 5-HT modulation/innervation in the autism brain, and implicate two 5-HT receptor subtypes as potential neuromarkers for novel or existing pharmacotherapies.

Decreased parvalbumin mRNA expression in dorsolateral prefrontal cortex in Parkinson's disease.

It has recently been shown that expression of the rate-limiting GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) is decreased in Brodmann area 9 (BA9) of the dorsolateral prefrontal cortex (DLPFC) in Parkinson's disease (PD) compared to control brains (Lanoue, A.C., Dumitriu, A., Myers, R.H., Soghomonian, JJ., 2010. Exp. Neurol. 206 (1), 207-217). A subpopulation of cortical GABAergic interneurons expresses the calcium-binding protein parvalbumin and plays a critical role in the control of pyramidal neuron excitability and the generation of cortical gamma frequency oscillations. In view of its key role in the physiology of the cerebral cortex, we sought to determine whether the expression of parvalbumin and the number of parvalbumin-expressing neurons are altered in BA9 of PD brains. First, isotopic in situ hybridization histochemistry was used to examine mRNA expression of parvalbumin on post-mortem brain sections. Second, immunohistochemistry and design-based stereology were used to determine the density of parvalbumin-positive interneurons in BA9. Quantification of mRNA labeling at the single cell level showed a significant decrease in parvalbumin expression in PD cases. In contrast, neuronal density of parvalbumin-positive neurons was not significantly different between PD and controls. Results confirm that the GABAergic system is altered in the DLPFC in PD and identify the contribution of parvalbumin-expressing neurons in these alterations. We speculate that these effects could contribute to altered cortical excitability and oscillatory activity previously documented in PD.

Consensus paper: pathological role of the cerebellum in autism.

There has been significant advancement in various aspects of scientific knowledge concerning the role of cerebellum in the etiopathogenesis of autism. In the current consensus paper, we will observe the diversity of opinions regarding the involvement of this important site in the pathology of autism. Recent emergent findings in literature related to cerebellar involvement in autism are discussed, including: cerebellar pathology, cerebellar imaging and symptom expression in autism, cerebellar genetics, cerebellar immune function, oxidative stress and mitochondrial dysfunction, GABAergic and glutamatergic systems, cholinergic, dopaminergic, serotonergic, and oxytocin-related changes in autism, motor control and cognitive deficits, cerebellar coordination of movements and cognition, gene-environment interactions, therapeutics in autism, and relevant animal models of autism. Points of consensus include presence of abnormal cerebellar anatomy, abnormal neurotransmitter systems, oxidative stress, cerebellar motor and cognitive deficits, and neuroinflammation in subjects with autism. Undefined areas or areas requiring further investigation include lack of treatment options for core symptoms of autism, vermal hypoplasia, and other vermal abnormalities as a consistent feature of autism, mechanisms underlying cerebellar contributions to cognition, and unknown mechanisms underlying neuroinflammation.

The neuropathology of autism.

Autism is a behaviorally defined neurodevelopmental disorder that affects over 1% of new births in the United States and about 2% of boys. The etiologies are unknown and they are genetically complex. There may be epigenetic effects, environmental influences, and other factors that contribute to the mechanisms and affected neural pathway(s). The underlying neuropathology of the disorder has been evolving in the literature to include specific brain areas in the cerebellum, limbic system, and cortex. Part(s) of structures appear to be affected most rather than the entire structure, for example, select nuclei of the amygdala, the fusiform face area, and so forth. Altered cortical organization characterized by more frequent and narrower minicolumns and early overgrowth of the frontal portion of the brain, affects connectivity. Abnormalities include cytoarchitectonic laminar differences, excess white matter neurons, decreased numbers of GABAergic cerebellar Purkinje cells, and other events that can be traced developmentally and cause anomalies in circuitry. Problems with neurotransmission are evident by recent receptor and binding site studies especially in the inhibitory GABA system likely contributing to an imbalance of excitatory/inhibitory transmission. As postmortem findings are related to core behavior symptoms, and technology improves, researchers are gaining a much better perspective of contributing factors to the disorder.

Alterations in GABAergic biomarkers in the autism brain: research findings and clinical implications.

Autism is a pervasive developmental disorder characterized by repetitive stereotyped behavior, social-emotional deficits, and delayed or absent language abilities. There are known neuropathologies in the autism brain affecting limbic, cerebellar, and cortical structures but the neurochemical profile of affected individuals, revealed in postmortem tissue studies, is only recently emerging. One major component that appears highly impacted in autism is the GABAergic system. It is now apparent that there are widespread significant effects in many distributed regions in the autism brain revealed by histochemical, autoradiographic, and biochemical studies. The key synthesizing enzymes for GABA, glutamic acid decarboxylase type 65 and 67 (GAD65 and GAD67), are decreased in the cerebellum and closer examination of mRNA levels revealed that it is largely due to decreases in Purkinje cells and a subpopulation of larger dentate neurons as measured by in situ hybridization studies. Other cell types had either normal GAD levels (Golgi cells, smaller dentate interneurons, and stellate cells) or increased levels (basket cells). GABA receptor density, number, and protein expression are all decreased in the cerebellum and in select cortical areas. GABA(A) and GABA(B) subunit protein expression was significantly reduced in cerebellum, BA 9 and BA 40. Benzodiazepine binding sites were significantly reduced in the hippocampus and anterior cingulate cortex (BA 24). Taken together, data from these studies suggest that there is a marked dysregulation of the inhibitory GABA system in the autism brain affecting particular biomarkers localized to specific cell types and lamina likely influencing circuitry and behavior.

Prenatal protein malnutrition alters the proportion but not numbers of parvalbumin-immunoreactive interneurons in the hippocampus of the adult Sprague-Dawley rat.

Prenatal protein malnutrition alters the structure and function of the adult rat hippocampal formation. The current study examines the effect of prenatal protein malnutrition on numbers of parvalbumin-immunoreactive (PV-IR) GABAergic interneurons, which are important for perisomatic inhibition of hippocampal pyramidal neurons. Brain sections from prenatally protein malnourished and normally nourished rats were stained for parvalbumin and PV-IR neurons were quantified using stereology in the dentate gyrus, CA3/2 and CA1 subfields, and the subiculum for both cerebral hemispheres. Results demonstrated that prenatal malnutrition did not affect the number of PV-IR interneurons in the hippocampus. Since prenatal protein malnutrition reduces total neuron numbers in the CA1 subfield (1), this results in an altered ratio of PV-IR interneurons to total neuronal numbers (from 1:22.9 in controls to 1:20.5 in malnourished rats). Additionally, there was no hemispheric asymmetry of either PV-IR neuron numbers or ratio of PV-IR:total neuron numbers.