ACSA-2 and GLAST classify subpopulations of multipotent and glial-restricted cerebellar precursors.

The formation of the cerebellum is highly coordinated to obtain its characteristic morphology and all cerebellar cell types. During mouse postnatal development, cerebellar progenitors with astroglial-like characteristics generate mainly astrocytes and oligodendrocytes. However, a subset of astroglial-like progenitors found in the prospective white matter (PWM) produces astroglia and interneurons. Characterizing these cerebellar astroglia-like progenitors and distinguishing their developmental fates is still elusive. Here, we reveal that astrocyte cell surface antigen-2 (ACSA-2), lately identified as ATPase, Na+/K+ transporting, beta 2 polypeptide, is expressed by glial precursors throughout postnatal cerebellar development. In contrast to common astrocyte markers, ACSA-2 appears on PWM cells but is absent on Bergmann glia (BG) precursors. In the adult cerebellum, ACSA-2 is broadly expressed extending to velate astrocytes in the granular layer, white matter astrocytes, and to a lesser extent to BG. Cell transplantation and transcriptomic analysis revealed that marker staining discriminates two postnatal progenitor pools. One subset is defined by the co-expression of ACSA-2 and GLAST and the expression of markers typical of parenchymal astrocytes. These are PWM precursors that are exclusively gliogenic. They produce predominantly white matter and granular layer astrocytes. Another subset is constituted by GLAST positive/ACSA-2 negative precursors that express neurogenic and BG-like progenitor genes. This population displays multipotency and gives rise to interneurons besides all glial types, including BG. In conclusion, this work reports about ACSA-2, a marker that in combination with GLAST enables for the discrimination and isolation of multipotent and glia-committed progenitors, which generate different types of cerebellar astrocytes.

Semi-quantitative distribution of excitatory amino acid (glutamate) transporters 1-3 (EAAT1-3) and the cystine-glutamate exchanger (xCT) in the adult murine spinal cord.

Proper glutamatergic neurotransmission requires a balance between glutamate release and removal. The removal is mainly catalyzed by the glutamate transporters EAAT1-3, while the glutamate-cystine exchanger (system xc- with specific subunit xCT) represents one of the release mechanisms. Previous studies of the spinal cord have focused on the cellular distribution of EAAT1-3 with special reference to the dorsal horn, but have not provided quantitative data and have not systematically compared multiple segments. Here we have studied the distribution of EAAT1-3 and xCT in sections of multiple spinal cord segments using knockout tissue as negative controls. EAAT2 and EAAT3 were evenly expressed in all gray matter areas at all segmental levels, albeit with slightly higher levels in laminae 1-4 (dorsal horn). Somewhat higher levels of EAAT2 were also seen in lamina 9 (ventral horn), while EAAT3 was also detected in the lateral spinal nucleus. EAAT1 was concentrated in laminae 1-3, lamina 10, the intermediolateral nucleus and the sacral parasympathetic nucleus, while xCT was concentrated in laminae 1-3, lamina 10 and the leptomeninges. The levels of these four transporters were low in white matter, which represents 42% of the spinal cord volume. Quantitative immunoblotting revealed that the average level of EAAT1 in the whole spinal cord was 0.6 ± 0.1% of that in the cerebellum, while the levels of EAAT2, EAAT3 and xCT were, respectively, 41.6 ± 12%, 39.8 ± 7.6%, and 30.8 ± 4.3% of the levels in the hippocampus (mean values ± SEM). Conclusions: Because the hippocampal tissue content of EAAT2 protein is two orders of magnitude higher than the content of the EAAT3, it follows that most of the gray matter in the spinal cord depends almost exclusively on EAAT2 for glutamate removal, while the lamina involved in the processing of autonomic and nociceptive information rely on a complex system of transporters.

Efficient Mass Spectral Analysis of Active Transporters Overexpressed in Escherichia coli.

Structural analysis of purified active membrane proteins can be performed by mass spectrometry (MS). However, no large-scale expression systems for active eukaryotic membrane proteins are available. Moreover, because membrane proteins cannot easily be digested by trypsin and ionized, they are difficult to analyze by MS. We developed a method for mass spectral analysis of eukaryotic membrane proteins combined with an overexpression system in Escherichia coli. Vesicular glutamate transporter 2 (VGLUT2/SLC17A6) with a soluble α-helical protein and histidine tag on the N- and C-terminus, respectively, was overexpressed in E. coli, solubilized with detergent, and purified by Ni-NTA affinity chromatography. Proteoliposomes containing VGLUT2 retained glutamate transport activity. For MS analysis, the detergent was removed from purified VGLUT2 by trichloroacetic acid precipitation, and VGLUT2 was then subjected to reductive alkylation and tryptic digestion. The resulting peptides were detected with 88% coverage by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MS with or without liquid chromatography. Vesicular excitatory amino acid transporter and vesicular acetylcholine transporter were also detected with similar coverage by the same method. Thus this methodology could be used to analyze purified eukaryotic active transporters. Structural analysis with chemical modifiers by MS could have applications in functional binding analysis for drug discovery.

Expression of Glutamate Transporters in Mouse Liver, Kidney, and Intestine.

Glutamate transport activities have been identified not only in the brain, but also in the liver, kidney, and intestine. Although glutamate transporter distributions in the central nervous system are fairly well known, there are still uncertainties with respect to the distribution of these transporters in peripheral organs. Quantitative information is mostly lacking, and few of the studies have included genetically modified animals as specificity controls. The present study provides validated qualitative and semi-quantitative data on the excitatory amino acid transporter (EAAT)1-3 subtypes in the mouse liver, kidney, and intestine. In agreement with the current view, we found high EAAT3 protein levels in the brush borders of both the distal small intestine and the renal proximal tubules. Neither EAAT1 nor EAAT2 was detected at significant levels in murine kidney or intestine. In contrast, the liver only expressed EAAT2 (but 2 C-terminal splice variants). EAAT2 was detected in the plasma membranes of perivenous hepatocytes. These cells also expressed glutamine synthetase. Conditional deletion of hepatic EAAT2 did neither lead to overt neurological disturbances nor development of fatty liver.

Anti-ACSA-2 defines a novel monoclonal antibody for prospective isolation of living neonatal and adult astrocytes.

Astrocytes are the most abundant cell type of the central nervous system and cover a broad range of functionalities. We report here the generation of a novel monoclonal antibody, anti-astrocyte cell surface antigen-2 (Anti-ACSA-2). Flow cytometry, immunohistochemistry and immunocytochemistry revealed that Anti-ACSA-2 reacted specifically with a not yet identified glycosylated surface molecule of murine astrocytes at all developmental stages. It did not show any labeling of non-astroglial cells such as neurons, oligodendrocytes, NG2+ cells, microglia, endothelial cells, leukocytes, or erythrocytes. Co-labeling studies of GLAST and ACSA-2 showed largely overlapping expression. However, there were also notable differences in protein expression levels and frequencies of single-positive subpopulations of cells in some regions of the CNS such as cerebellum, most prominently at early postnatal stages. In the neurogenic niches, the dentate gyrus of the hippocampus and the subventricular zone (SVZ), again a general overlap with slight differences in expression levels were observed. ACSA-2 was unlike GLAST not sensitive to papain-based tissue dissociation and allowed for a highly effective, acute, specific, and prospective purification of viable astrocytes based on a new rapid sorting procedure using Anti-ACSA-2 directly coupled to superparamagnetic MicroBeads. In conclusion, ACSA-2 appears to be a new surface marker for astrocytes, radial glia, neural stem cells and bipotent glial progenitor cells which opens up the possibility of further dissecting the characteristics of astroglial subpopulations and lineages.

Intrinsic Astrocyte Heterogeneity Influences Tumor Growth in Glioma Mouse Models.

The influence of cellular origin on glioma pathogenesis remains elusive. We previously showed that mutations inactivating Rb and Pten and activating Kras transform astrocytes and induce tumorigenesis throughout the adult mouse brain. However, it remained unclear whether astrocyte subpopulations were susceptible to these mutations. We therefore used genetic lineage tracing and fate mapping in adult conditional, inducible genetically engineered mice to monitor transformation of glial fibrillary acidic protein (GFAP) and glutamate aspartate transporter (GLAST) astrocytes and immunofluorescence to monitor cellular composition of the tumor microenvironment over time. Because considerable regional heterogeneity exists among astrocytes, we also examined the influence of brain region on tumor growth. GFAP astrocyte transformation induced uniformly rapid, regionally independent tumor growth, but transformation of GLAST astrocytes induced slowly growing tumors with significant regional bias. Transformed GLAST astrocytes had reduced proliferative response in culture and in vivo and malignant progression was delayed in these tumors. Recruited glial cells, including proliferating astrocytes, oligodendrocyte progenitors and microglia, were the majority of GLAST, but not GFAP astrocyte-derived tumors and their abundance dynamically changed over time. These results suggest that intrinsic astrocyte heterogeneity, and perhaps regional brain microenvironment, significantly contributes to glioma pathogenesis.

The rates of postmortem proteolysis of glutamate transporters differ dramatically between cells and between transporter subtypes.

Glutamate transporters (GLT-1, GLAST, EAAC1) limit the actions of excitatory amino acids. Because a disturbed transporter operation can cause or aggravate neurological diseases, transporters are of considerable neuropathological interest. Human samples, however, are seldom obtained fresh. Here, we used mice brains to study how fast glutamate transporters are degraded after death. Immunoblots showed that terminal GLT-1 epitopes (within residues 1-26 and 518-573) had mostly disappeared after 24 hr. GLAST termini (1-25 and 522-543) degraded slightly slower. In contrast, epitopes within central parts of GLT-1 (493-508) and the EAAC1 C-terminus (510-523) were readily detectable after 72 hr. The decline in immunoreactivity of the GLT-1 and GLAST termini was also seen in tissue sections, but proteolysis did not happen synchronously in all cells. At 24 hr, scattered cells remained strongly immunopositive, while the majority of cells were completely immunonegative. GLAST and GLT-1 co-localized in neocortical tissue, but at 12 hr, many GLAST-positive cells had lost the GLT-1 termini. The uneven disappearance of labeling was not observed with the antibodies to GLT-1 residues 493-508. The immunoreactivity to this epitope correlated better with the reported glutamate uptake activity. Thus, postmortem delay may affect epitopes differently, possibly causing erroneous conclusions about relative expression levels.

Aroclor 1254 selectively inhibits expression of glial GLT-1 glutamate transporter in the forebrain of chronically exposed adult rat.

Aroclor 1254, a commercially produced mixture of polychlorinated biphenyls, is known to cause many adverse conditions, including neurotoxicity. It has been recently postulated that upregulation of N-methyl-d-aspartate receptors (NMDARs) and enhanced glutamate signalling which leads to excitotoxicity, is the mechanism of Aroclor-induced neurotoxicity. To obtain insights into the mechanisms underlying glutamatergic overstimulation, we investigated the function and expression of sodium-dependent glutamate transporters which are known to regulate extracellular glutamate concentrations in the brain. Exposure to Aroclor 1254 was found to significantly lower the uptake of radioactive glutamate into gliosomal fractions obtained from adult rat brains. It also markedly decreased the expression of both protein and mRNA of GLT-1, the main glial glutamate transporter. This indicates that downregulation of GLT-1 may potentially lead to disturbances in glutamate clearance. The expression of GLAST, another astroglial glutamate transporter, was unchanged under conditions of Aroclor toxicity. Conversely, we observed enhanced glutamate uptake into nerve-endings fractions paralleled by increased EAAC1 protein expression. This may reflect the induction of protective mechanisms.

Investigation of the association between SLC1A3 gene polymorphisms and normal tension glaucoma.

PURPOSE: To investigate whether the solute carrier family 1, member 3 (SLC1A3) gene, which encodes the glutamate aspartate transporter, is associated with normal tension glaucoma (NTG) in Japanese patients. METHODS: Two hundred and ninety-five Japanese patients with NTG and 518 Japanese healthy controls were recruited. Patients exhibiting comparatively early NTG onset were selected because early onset suggests that genetic factors may show stronger involvement. We genotyped 5 single-nucleotide polymorphisms (SNPs) in SLC1A3 and assessed the allelic and genotypic diversity among cases and controls. RESULTS: There were no statistically significant differences in the frequency of SLC1A3 alleles and genotypes between cases and controls. CONCLUSIONS: Our study showed no association between SLC1A3 and NTG, suggesting that the SLC1A3 gene may not be an associated factor in NTG pathogenesis.

Riluzole normalizes early-life stress-induced visceral hypersensitivity in rats: role of spinal glutamate reuptake mechanisms.

BACKGROUND & AIMS: The molecular basis underlying visceral hypersensitivity in functional irritable bowel syndrome remains elusive, resulting in poor treatment effectiveness. Because alterations in spinal non-neuronal (astrocytic) glutamate reuptake are suspected to participate in chronic pain, we asked whether such processes occur in visceral hypersensitivity. METHODS: Visceral hypersensitivity was induced in Sprague-Dawley rats by maternal separation. Separated adults were given a systemic administration of riluzole (5 mg/kg), an approved neuroprotective agent activating glutamate reuptake. Visceral hypersensitivity was assessed using colorectal distension (40 mm Hg). Somatic nociception was quantified using Hot Plate, Randall-Sellito, and Hargreaves tests. Spinal proteins were quantified using immunofluorescence and Western blot. The dependence of visceral sensory function upon spinal glutamate transport was evaluated by intrathecal injection of glutamate transport antagonist DL-threo-beta-benzyloxyaspartate (TBOA). For in vitro testing of riluzole and TBOA, primary cultures of astrocytes were used. RESULTS: We show that riluzole counteracts stress-induced visceral hypersensitivity without affecting visceral response in nonseparated rats or altering nociceptive responses to somatic pain stimulation. In addition, maternal separation produces a reduction in glial excitatory amino acid transporter (EAAT)-1 with no change in EAAT-2 or gamma-amino butyric acid transporters. Stress was not associated with changes in glial fibrillary acidic protein or astrocytic morphology per se. Furthermore, visceral normosensitivity relies on spinal EAAT, as intrathecal TBOA is sufficient to induce hypersensitivity in normal rats. CONCLUSIONS: We identify spinal EAAT as a therapeutic target, and establish riluzole as a candidate to counteract gastrointestinal hypersensitivity in disorders such as irritable bowel syndrome.

The expression of astroglial glutamate transporters in patients with focal cortical dysplasia: an immunohistochemical study.

PURPOSE: An abnormal increase in the extracellular glutamate is thought to play a crucial role in the initiation, spread, and maintenance of seizure activity.In normal conditions, the majority of this excess glutamate is cleared via glial glutamate transporters (EAAT-1 and EAAT-2). We aimed to examine the immunohistochemical expression of these transporters in the dysplastic tissues of patients with focal cortical dysplasia (FCD). METHODS: The parafin-embedded dysplastic tissues of 33 patients who were operated on due to medically intractable epilepsy and histopathologically diagnosed with FCD between 2001 and 2006 were stained immunohistochemically with appropriate antibodies, and the distribution and intensity of immunoreactivity (IR) of EAAT-1 and EAAT-2 were examined.The findings were compared with the histologically normal tissues of five patients who underwent temporal lobectomy for epilepsy surgery and 10 fresh postmortem cases. RESULTS: In the majority of the patients, the EAAT-1 and EAAT-2 IR were decreased, their astrocytic expression were lower, and the pattern of distribution were more diffused when compared to the control groups.Analyzing these findings according to the types of FCD revealed that as the severity of the dysplasia increased, the IR and astrocytic expression of both transporters are decreased and their distribution tend to be more "diffused." CONCLUSION: The results of this study suggest a relationship between the decreased glutamate transporter expressions in dysplastic tissues which,in turn, may cause increased extracellular concentrations of glutamate and FCD pathophysiology.Further studies with larger patient populations,investigating the expression of glutamate transporters at mRNA and protein levels, are required to clarify their roles in the pathophysiology of FCD.

Astrocyte phenotype in relation to Alzheimer-type pathology in the ageing brain.

Astrocyte pathology occurs in association with Alzheimer's disease (AD) and in brain ageing, but is poorly characterised. We sought to define the detailed cellular pathology of astrocytes, the extent of population variation and the relationship to Alzheimer-type changes in a population-based cohort. Three staining patterns were associated with GFAP and excitatory amino acid transporter 2 (EAAT2): minimal, moderate or extensive immunoreactivity. GFAP and EAAT2 expression were inversely related (p=0.015), with trends to increased expression of GFAP (p=0.019) and decreased expression of EAAT2 (p=ns) with increasing Braak stage. GFAP and EAAT2 correlated incompletely with beta-amyloid and tau immunoreactivity. However, gliosis increased with increasing burden of neuritic (p=0.011), but not diffuse (p=ns), plaques. Double-staining revealed distinct subsets of astrocytes; GFAP(+)EAAT(-), GFAP(-)EAAT(+), or GFAP(+)EAAT(+). In contrast to the variation in GFAP and EAAT2, levels of EAAT1 and S100B showed consistent staining patterns. Alzheimer-type pathology only partially explains the variation in gliosis and astrocyte functional markers, suggesting that other factors contribute to the population variance in astrocyte pathology.

Synaptically evoked glutamate transporter currents in Spinal Dorsal Horn Astrocytes.

BACKGROUND: Removing and sequestering synaptically released glutamate from the extracellular space is carried out by specific plasma membrane transporters that are primarily located in astrocytes. Glial glutamate transporter function can be monitored by recording the currents that are produced by co-transportation of Na+ ions with the uptake of glutamate. The goal of this study was to characterize glutamate transporter function in astrocytes of the spinal cord dorsal horn in real time by recording synaptically evoked glutamate transporter currents. RESULTS: Whole-cell patch clamp recordings were obtained from astrocytes in the spinal substantia gelatinosa (SG) area in spinal slices of young adult rats. Glutamate transporter currents were evoked in these cells by electrical stimulation at the spinal dorsal root entry zone in the presence of bicuculline, strychnine, DNQX and D-AP5. Transporter currents were abolished when synaptic transmission was blocked by TTX or Cd2+. Pharmacological studies identified two subtypes of glutamate transporters in spinal astrocytes, GLAST and GLT-1. Glutamate transporter currents were graded with stimulus intensity, reaching peak responses at 4 to 5 times activation threshold, but were reduced following low-frequency (0.1 - 1 Hz) repetitive stimulation. CONCLUSION: These results suggest that glutamate transporters of spinal astrocytes could be activated by synaptic activation, and recording glutamate transporter currents may provide a means of examining the real time physiological responses of glial cells in spinal sensory processing, sensitization, hyperalgesia and chronic pain.

Rottlerin inhibits (Na+, K+)-ATPase activity in brain tissue and alters D-aspartate dependent redistribution of glutamate transporter GLAST in cultured astrocytes.

The naturally occurring toxin rottlerin has been used by other laboratories as a specific inhibitor of protein kinase C-delta (PKC-delta) to obtain evidence that the activity-dependent distribution of glutamate transporter GLAST is regulated by PKC-delta mediated phosphorylation. Using immunofluorescence labelling for GLAST and deconvolution microscopy we have observed that D-aspartate-induced redistribution of GLAST towards the plasma membranes of cultured astrocytes was abolished by rottlerin. In brain tissue in vitro, rottlerin reduced apparent activity of (Na+, K+)-dependent ATPase (Na+, K+-ATPase) and increased oxygen consumption in accordance with its known activity as an uncoupler of oxidative phosphorylation ("metabolic poison"). Rottlerin also inhibited Na+, K+-ATPase in cultured astrocytes. As the glutamate transport critically depends on energy metabolism and on the activity of Na+, K+-ATPase in particular, we suggest that the metabolic toxicity of rottlerin and/or the decreased activity of the Na+, K+-ATPase could explain both the glutamate transport inhibition and altered GLAST distribution caused by rottlerin even without any involvement of PKC-delta-catalysed phosphorylation in the process.

Distribution of glutamate transporter GLAST in membranes of cultured astrocytes in the presence of glutamate transport substrates and ATP.

Neurotransmitter L-glutamate released at central synapses is taken up and "recycled" by astrocytes using glutamate transporter molecules such as GLAST and GLT. Glutamate transport is essential for prevention of glutamate neurotoxicity, it is a key regulator of neurotransmitter metabolism and may contribute to mechanisms through which neurons and glia communicate with each other. Using immunocytochemistry and image analysis we have found that extracellular D-aspartate (a typical substrate for glutamate transport) can cause redistribution of GLAST from cytoplasm to the cell membrane. The process appears to involve phosphorylation/dephosphorylation and requires intact cytoskeleton. Glutamate transport ligands L-trans-pyrrolidine-2,4-dicarboxylate and DL-threo-3-benzyloxyaspartate but not anti,endo-3,4-methanopyrrolidine dicarboxylate have produced similar redistribution of GLAST. Several representative ligands for glutamate receptors whether of ionotropic or metabotropic type, were found to have no effect. In addition, extracellular ATP induced formation of GLAST clusters in the cell membranes by a process apparently mediated by P2 receptors. The present data suggest that GLAST can rapidly and specifically respond to changes in the cellular environment thus potentially helping to fine-tune the functions of astrocytes.

Expression and distribution of 'high affinity' glutamate transporters GLT1, GLAST, EAAC1 and of GCPII in the rat peripheral nervous system.

l-Glutamate is one of the major excitatory neurotransmitters in the mammalian central nervous system, but recently it has been shown to have a role also in the transduction of sensory input at the periphery, and in particular in the nociceptive pathway. An excess of glutamate is implicated in cases of peripheral neuropathies as well. Conventional therapeutic approaches for treating these diseases have focused on blocking glutamate receptors with small molecules or on reducing its synthesis of the receptors through the inhibition of glutamate carboxypeptidase II (GCPII), the enzyme that generates glutamate. In vivo studies have demonstrated that the pharmacological inhibition of GCPII can either prevent or treat the peripheral nerve changes in both BB/Wor and chemically induced diabetes in rats. In this study, we characterized the expression and distribution of glutamate transporters GLT1, GLAST, EAAC1 and of the enzyme GCPII in the peripheral nervous system of female Wistar rats. Immunoblotting results demonstrated that all glutamate transporters and GCPII are present in dorsal root ganglia (DRG) and the sciatic nerve. Immunofluorescence localization studies revealed that both DRG and sciatic nerves were immunopositive for all glutamate transporters and for GCPII. In DRG, satellite cells were positive for GLT1 and GCPII, whereas sensory neurons were positive for EAAC1. GLAST was localized in both neurons and satellite cells. In the sciatic nerve, GLT1 and GCPII were expressed in the cytoplasm of Schwann cells, whereas GLAST and EAAC1 stained the myelin layer. Our results give for the first time a complete characterization of the glutamate transporter system in the peripheral nervous system. Therefore, they are important both for understanding glutamatergic signalling in the PNS and for establishing new strategies to treat peripheral neuropathies.

Aberrant expression of the glutamate transporter excitatory amino acid transporter 1 (EAAT1) in Alzheimer's disease.

Glutamate-mediated toxicity has been implicated in the neurodegeneration observed in Alzheimer's disease. In particular, glutamate transport dysfunction may increase susceptibility to glutamate toxicity, thereby contributing to neuronal cell injury and death. In this study, we examined the cellular localization of the glial glutamate transporter excitatory amino acid transporter 1 (EAAT1) in the cerebral cortex of control, Alzheimer's disease, and non-Alzheimer dementia cases. We found that EAAT1 was strongly expressed in a subset of cortical pyramidal neurons in dementia cases showing Alzheimer-type pathology. In addition, tau (which is a marker of neurofibrillary pathology) colocalized to those same pyramidal cells that expressed EAAT1. These findings suggest that EAAT1 changes are related to tau expression (and hence neurofibrillary tangle formation) in dementia cases showing Alzheimer-type pathology. This study implicates aberrant glutamate transporter expression as a mechanism involved in neurodegeneration in Alzheimer's disease.

Postmortem brain abnormalities of the glutamate neurotransmitter system in autism.

BACKGROUND: Studies examining the brains of individuals with autism have identified anatomic and pathologic changes in regions such as the cerebellum and hippocampus. Little, if anything, is known, however, about the molecules that are involved in the pathogenesis of this disorder. OBJECTIVE: To identify genes with abnormal expression levels in the cerebella of subjects with autism. METHOD: Brain samples from a total of 10 individuals with autism and 23 matched controls were collected, mainly from the cerebellum. Two cDNA microarray technologies were used to identify genes that were significantly up- or downregulated in autism. The abnormal mRNA or protein levels of several genes identified by microarray analysis were investigated using PCR with reverse transcription and Western blotting. alpha-Amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)- and NMDA-type glutamate receptor densities were examined with receptor autoradiography in the cerebellum, caudate-putamen, and prefrontal cortex. RESULTS: The mRNA levels of several genes were significantly increased in autism, including excitatory amino acid transporter 1 and glutamate receptor AMPA 1, two members of the glutamate system. Abnormalities in the protein or mRNA levels of several additional molecules in the glutamate system were identified on further analysis, including glutamate receptor binding proteins. AMPA-type glutamate receptor density was decreased in the cerebellum of individuals with autism (p < 0.05). CONCLUSIONS: Subjects with autism may have specific abnormalities in the AMPA-type glutamate receptors and glutamate transporters in the cerebellum. These abnormalities may be directly involved in the pathogenesis of the disorder.