The SLC32 transporter, a key protein for the synaptic release of inhibitory amino acids

Impact of anesthetics on rat hippocampus and neocortex: A comprehensive proteomic study based on label-free mass spectrometry

Anesthesia is regarded as an important milestone in medicine. However, the negative effect on memory and learning has been observed. In addition, the impact of anesthetics on postoperative cognitive functions is still discussed. In this work, in vivo experiment simulating a general anesthesia and ICU sedation was designed to assess the impact of two intravenous (midazolam, dexmedetomidine) and two inhalational (isoflurane, desflurane) agents on neuronal centers for cognition (neocortex), learning, and memory (hippocampus). More than 3600 proteins were quantified across both neocortex and hippocampus. Proteomic study revealed relatively mild effects of anesthetics, nevertheless, protein dysregulation uncovered possible different effect of isoflurane (and midazolam) compared to desflurane (and dexmedetomidine) to neocortical and hippocampal proteins. Isoflurane induced the upregulation of hippocampal NMDAR and other proteins of postsynaptic density and downregulation of GABA signaling, whereas desflurane and dexmedetomidine rather targeted mitochondrial VDAC isoforms and protein regulating apoptotic activity.

Influence of a Polyherbal Choline Source in Dogs: Body Weight Changes, Blood Metabolites, and Gene Expression

Choline chloride is used to provide choline in dog foods; however, in other domestic species, it has been replaced with a polyherbal containing phosphatidylcholine. A polyherbal containing Achyrantes aspera, Trachyspermum ammi, Citrullus colocynthis, Andrographis paniculata, and Azadirachta indica was evaluated in adult dogs through body weight changes, subcutaneous fat thickness, blood metabolites, and gene expression. Forty dogs (4.6 ± 1.6 years old) who were individually housed in concrete kennels were randomly assigned to the following treatments: unsupplemented diet (377 mg choline/kg), choline chloride (3850 mg/kg equivalent to 2000 mg choline/kg diet), and polyherbal (200, 400, and 800 mg/kg) for 60 days. Blood samples were collected on day 59 for biochemistry, biometry, and gene expression analysis through microarray assays. Intake, final body weight, and weight changes were similar for the two choline sources. Feed intake variation among dogs (p = 0.01) and dorsal fat (p = 0.03) showed a quadratic response to herbal choline. Dogs that received the polyherbal diet had reduced blood cholesterol levels (Quadratic, p = 0.02). The gene ontology analysis indicated that 15 biological processes were modified (p ≤ 0.05) with implications for preventing cardiovascular and metabolic diseases, cancer prevention, inflammatory and immune response, and behavior and cognitive process. According to these results that were observed in a 60 day trial, the polyherbal form could replace choline chloride in dog diets at a concentration of 400 mg/kg.

A conditional GABAergic synaptic vesicle marker for Drosophila

BACKGROUND

Throughout the animal kingdom, GABA is the principal inhibitory neurotransmitter of the nervous system. It is essential for maintaining the homeostatic balance between excitation and inhibition required for the brain to operate normally. Identification of GABAergic neurons and their GABA release sites are thus essential for understanding how the brain regulates the excitability of neurons and the activity of neural circuits responsible for numerous aspects of brain function including information processing, locomotion, learning, memory, and synaptic plasticity, among others.

NEW METHOD

Since the structure and features of GABA synapses are critical to understanding their function within specific neural circuits of interest, here we developed and characterized a conditional marker of GABAergic synaptic vesicles for Drosophila, 9XV5-vGAT.

RESULTS

9XV5-vGAT is validated for conditionality of expression, specificity for localization to synaptic vesicles, specificity for expression in GABAergic neurons, and functionality. Its utility for GABAergic neurotransmitter phenotyping and identification of GABA release sites was verified for ellipsoid body neurons of the central complex. In combination with previously reported conditional SV markers for acetylcholine and glutamate, 9XV5-vGAT was used to demonstrate fast neurotransmitter phenotyping of subesophageal ganglion neurons.

COMPARISON WITH EXISTING METHODS

This method is an alternative to single cell transcriptomics for neurotransmitter phenotyping and can be applied to any neurons of interest represented by a binary transcription system driver.

CONCLUSION

A conditional GABAergic synaptic vesicle marker has been developed and validated for GABA neurotransmitter phenotyping and subcellular localization of GABAergic synaptic vesicles.

Transcriptome analysis of Kentucky bluegrass subject to drought and ethephon treatment

Kentucky bluegrass (Poa pratensis L.) is an excellent cool-season turfgrass utilized widely in Northern China. However, turf quality of Kentucky bluegrass declines significantly due to drought. Ethephon seeds-soaking treatment has been proved to effectively improve the drought tolerance of Kentucky bluegrass seedlings. In order to investigate the effect of ethephon leaf-spraying method on drought tolerance of Kentucky bluegrass and understand the underlying mechanism, Kentucky bluegrass plants sprayed with and without ethephon are subjected to either drought or well watered treatments. The relative water content and malondialdehyde conent were measured. Meanwhile, samples were sequenced through Illumina. Results showed that ethephon could improve the drought tolerance of Kentucky bluegrass by elevating relative water content and decreasing malondialdehyde content under drought. Transcriptome analysis showed that 58.43% transcripts (254,331 out of 435,250) were detected as unigenes. A total of 9.69% (24,643 out of 254,331) unigenes were identified as differentially expressed genes in one or more of the pairwise comparisons. Differentially expressed genes due to drought stress with or without ethephon pre-treatment showed that ethephon application affected genes associated with plant hormone, signal transduction pathway and plant defense, protein degradation and stabilization, transportation and osmosis, antioxidant system and the glyoxalase pathway, cell wall and cuticular wax, fatty acid unsaturation and photosynthesis. This study provides a theoretical basis for revealing the mechanism for how ethephon regulates drought response and improves drought tolerance of Kentucky bluegrass.

TDP-43 regulates GAD1 mRNA splicing and GABA signaling in Drosophila CNS

Alterations in the function of the RNA-binding protein TDP-43 are largely associated with the pathogenesis of amyotrophic lateral sclerosis (ALS), a devastating disease of the human motor system that leads to motoneurons degeneration and reduced life expectancy by molecular mechanisms not well known. In our previous work, we found that the expression levels of the glutamic acid decarboxylase enzyme (GAD1), responsible for converting glutamate to γ-aminobutyric acid (GABA), were downregulated in TBPH-null flies and motoneurons derived from ALS patients carrying mutations in TDP-43, suggesting that defects in the regulation of GAD1 may lead to neurodegeneration by affecting neurotransmitter balance. In this study, we observed that TBPH was required for the regulation of GAD1 pre-mRNA splicing and the levels of GABA in the Drosophila central nervous system (CNS). Interestingly, we discovered that pharmacological treatments aimed to potentiate GABA neurotransmission were able to revert locomotion deficiencies in TBPH-minus flies, revealing novel mechanisms and therapeutic strategies in ALS.

Functional and Biochemical Consequences of Disease Variants in Neurotransmitter Transporters: A Special Emphasis on Folding and Trafficking Deficits

Neurotransmitters, such as γ-aminobutyric acid, glutamate, acetyl choline, glycine and the monoamines, facilitate the crosstalk within the central nervous system. The designated neurotransmitter transporters (NTTs) both release and take up neurotransmitters to and from the synaptic cleft. NTT dysfunction can lead to severe pathophysiological consequences, e.g. epilepsy, intellectual disability, or Parkinson’s disease. Genetic point mutations in NTTs have recently been associated with the onset of various neurological disorders. Some of these mutations trigger folding defects in the NTT proteins. Correct folding is a prerequisite for the export of NTTs from the endoplasmic reticulum (ER) and the subsequent trafficking to their pertinent site of action, typically at the plasma membrane. Recent studies have uncovered some of the key features in the molecular machinery responsible for transporter protein folding, e.g., the role of heat shock proteins in fine-tuning the ER quality control mechanisms in cells. The therapeutic significance of understanding these events is apparent from the rising number of reports, which directly link different pathological conditions to NTT misfolding. For instance, folding-deficient variants of the human transporters for dopamine or GABA lead to infantile parkinsonism/dystonia and epilepsy, respectively. From a therapeutic point of view, some folding-deficient NTTs are amenable to functional rescue by small molecules, known as chemical and pharmacological chaperones.

Effects of febrile seizures in mesial temporal lobe epilepsy with hippocampal sclerosis on gene expression using bioinformatical analysis

Background

To investigate the effect of long-term febrile convulsions on gene expression in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) and explore the molecular mechanism of MTLE-HS.

Methods

Microarray data of MTLE-HS were obtained from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) between MTLE-HS with and without febrile seizure history were screened by the GEO2R software. Pathway enrichment and gene ontology of the DEGs were analyzed using the DAVID online database and FunRich software. Protein–protein interaction (PPI) networks among DEGs were constructed using the STRING database and analyzed by Cytoscape.

Results

A total of 515 DEGs were identified in MTLE-HS samples with a febrile seizure history compared to MTLE-HS samples without febrile seizure, including 25 down-regulated and 490 up-regulated genes. These DEGs were expressed mostly in plasma membrane and synaptic vesicles. The major molecular functions of those genes were voltage-gated ion channel activity, extracellular ligand-gated ion channel activity and calcium ion binding. The DEGs were mainly involved in biological pathways of cell communication signal transduction and transport. Five genes (SNAP25, SLC32A1, SYN1, GRIN1,andGRIA1) were significantly expressed in the MTLE-HS with prolonged febrile seizures.

Conclusion

The pathogenesis of MTLE-HS involves multiple genes, and prolonged febrile seizures could cause differential expression of genes. Thus, investigations of those genes may provide a new perspective into the mechanism of MTLE-HS.

The voltage-gated potassium channel Shaker promotes sleep via thermosensitive GABA transmission

Genes and neural circuits coordinately regulate animal sleep. However, it remains elusive how these endogenous factors shape sleep upon environmental changes. Here, we demonstrate that Shaker (Sh)-expressing GABAergic neurons projecting onto dorsal fan-shaped body (dFSB) regulate temperature-adaptive sleep behaviors in Drosophila. Loss of Sh function suppressed sleep at low temperature whereas light and high temperature cooperatively gated Sh effects on sleep. Sh depletion in GABAergic neurons partially phenocopied Sh mutants. Furthermore, the ionotropic GABA receptor, Resistant to dieldrin (Rdl), in dFSB neurons acted downstream of Sh and antagonized its sleep-promoting effects. In fact, Rdl inhibited the intracellular cAMP signaling of constitutively active dopaminergic synapses onto dFSB at low temperature. High temperature silenced GABAergic synapses onto dFSB, thereby potentiating the wake-promoting dopamine transmission. We propose that temperature-dependent switching between these two synaptic transmission modalities may adaptively tune the neural property of dFSB neurons to temperature shifts and reorganize sleep architecture for animal fitness.

Ji-hyung Kim and Yoonhee Ki et al. show that low temperatures suppress sleep in Drosophila by increasing GABA transmission in Shaker-expressing GABAergic neurons projecting onto the dorsal fan-shaped body, while high temperatures potentiate dopamine-induced arousal by reducing GABA transmission. This study highlights a role for Shaker in sleep modulation via a temperature-dependent switch in GABA signaling.

The solute carrier transporters and the brain: Physiological and pharmacological implications

Solute carriers (SLCs) are the largest family of transmembrane transporters that determine the exchange of various substances, including nutrients, ions, metabolites, and drugs across biological membranes. To date, the presence of about 287 SLC genes have been identified in the brain, among which mutations or the resultant dysfunctions of 71 SLC genes have been reported to be correlated with human brain disorders. Although increasing interest in SLCs have focused on drug development, SLCs are currently still under-explored as drug targets, especially in the brain. We summarize the main substrates and functions of SLCs that are expressed in the brain, with an emphasis on selected SLCs that are important physiologically, pathologically, and pharmacologically in the blood-brain barrier, astrocytes, and neurons. Evidence suggests that a fraction of SLCs are regulated along with the occurrences of brain disorders, among which epilepsy, neurodegenerative diseases, and autism are representative. Given the review of SLCs involved in the onset and procession of brain disorders, we hope these SLCs will be screened as promising drug targets to improve drug delivery to the brain.

Physiopathological Role of the Vesicular Nucleotide Transporter (VNUT) in the Central Nervous System: Relevance of the Vesicular Nucleotide Release as a Potential Therapeutic Target

Vesicular storage of neurotransmitters, which allows their subsequent exocytotic release, is essential for chemical transmission in the central nervous system. Neurotransmitter uptake into secretory vesicles is carried out by vesicular transporters, which use the electrochemical proton gradient generated by a vacuolar H⁺-ATPase to drive neurotransmitter vesicular accumulation. ATP and other nucleotides are relevant extracellular signaling molecules that participate in a variety of biological processes. Although the active transport of nucleotides into secretory vesicles has been characterized from the pharmacological and biochemical point of view, the protein responsible for such vesicular accumulation remained unidentified for some time. In 2008, the human SLC17A9 gene, the last identified member of the SLC17 transporters, was found to encode the vesicular nucleotide transporter (VNUT). VNUT is expressed in various ATP-secreting cells and is able to transport a wide variety of nucleotides in a vesicular membrane potential-dependent manner. VNUT knockout mice lack vesicular storage and release of ATP, resulting in blockage of the purinergic transmission. This review summarizes the current studies on VNUT and analyzes the physiological relevance of the vesicular nucleotide transport in the central nervous system. The possible role of VNUT in the development of some pathological processes, such as chronic neuropathic pain or glaucoma is also discussed. The putative involvement of VNUT in these pathologies raises the possibility of the use of VNUT inhibitors for therapeutic purposes.

Transcriptome analysis reveals the activation of neuroendocrine-immune system in shrimp hemocytes at the early stage of WSSV infection

Background

Functional communications between nervous, endocrine and immune systems are well established in both vertebrates and invertebrates. Circulating hemocytes act as fundamental players in this crosstalk, whose functions are conserved during the evolution of the main groups of metazoans. However, the roles of the neuroendocrine-immune (NEI) system in shrimp hemocytes during pathogen infection remain largely unknown.

Results

In this study, we sequenced six cDNA libraries prepared with hemocytes from Litopenaeus vannamei which were injected by WSSV (white spot syndrome virus) or PBS for 6 h using Illumina Hiseq 4000 platform. As a result, 3444 differentially expressed genes (DEGs), including 3240 up-regulated genes and 204 down-regulated genes, were identified from hemocytes after WSSV infection. Among these genes, 349 DEGs were correlated with innate immunity and categorized into seven groups based on their predictive function. Interestingly, 18 genes encoded putative neuropeptide precursors were induced significantly by WSSV infection. Furthermore, some genes were mapped to several typical processes in the NEI system, including proteolytic processing of prohormones, amino acid neurotransmitter pathways, biogenic amine biosynthesis and acetylcholine signaling pathway.

Conclusions

The data suggested that WSSV infection triggers the activation of NEI in shrimp, which throws a light on the pivotal roles of NEI system mediated by hemocytes in shrimp antiviral immunity.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5614-4) contains supplementary material, which is available to authorized users.

Mapping the malaria parasite druggable genome by using in vitro evolution and chemogenomics

Chemogenetic characterization through in vitro evolution combined with whole-genome analysis can identify antimalarial drug targets and drug-resistance genes. We performed a genome analysis of 262 Plasmodium falciparum parasites resistant to 37 diverse compounds. We found 159 gene amplifications and 148 nonsynonymous changes in 83 genes associated with drug-resistance acquisition, where gene amplifications contributed to one-third of resistance acquisition events. Beyond confirming previously identified multidrug-resistance mechanisms, we discovered hitherto unrecognized drug target-inhibitor pairs, including thymidylate synthase and a benzoquinazolinone, farnesyltransferase and a pyrimidinedione, and a dipeptidylpeptidase and an arylurea. This exploration of the P. falciparum resistome and druggable genome will likely guide drug discovery and structural biology efforts, while also advancing our understanding of resistance mechanisms available to the malaria parasite.

Proton electrochemical gradient: Driving and regulating neurotransmitter uptake

Accumulation of neurotransmitters in the lumen of synaptic vesicles (SVs) relies on the activity of the vacuolar-type H⁺ -ATPase. This pump drives protons into the lumen, generating a proton electrochemical gradient (Δμ_H+ ) across the membrane. Recent work has demonstrated that the balance between the chemical (ΔpH) and electrical (ΔΨ) components of Δμ_H+ is regulated differently by some distinct vesicle types. As different neurotransmitter transporters use ΔpH and ΔΨ with different relative efficiencies, regulation of this gradient balance has the potential to influence neurotransmitter uptake. Nevertheless, the underlying mechanisms responsible for this regulation remain poorly understood. In this review, we provide an overview of current neurotransmitter uptake models, with a particular emphasis on the distinct roles of the electrical and chemical gradients and current hypotheses for regulatory mechanisms.

Correcting miR92a-vGAT-Mediated GABAergic Dysfunctions Rescues Human Tau-Induced Anxiety in Mice

Patients with Alzheimer's disease (AD) commonly show anxiety behaviors, but the molecular mechanisms are not clear and no efficient intervention exists. Here, we found that overexpression of human wild-type, full-length tau (termed htau) in hippocampus significantly decreased the extracellular γ-aminobutyric acid (GABA) level with inhibition of γ oscillation and the evoked inhibitory postsynaptic potential (eIPSP). With tau accumulation, the mice show age-dependent anxiety behaviors. Among the factors responsible for GABA synthesis, release, uptake, and transport, we found that accumulation of htau selectively suppressed expression of the intracellular vesicular GABA transporter (vGAT). Tau accumulation increased miR92a, which targeted vGAT mRNA 3' UTR and inhibited vGAT translation. Importantly, we found that upregulating GABA tones by intraperitoneal injection of midazolam (a GABA agonist), ChR2-mediated photostimulating and overexpressing vGAT, or blocking miR92a by using specific antagomir or inhibitor efficiently rescued the htau-induced GABAergic dysfunctions with attenuation of anxiety. Finally, we also demonstrated that vGAT level decreased while the miR92a increased in the AD brains. These findings demonstrate that the AD-like tau accumulation induces anxiety through disrupting miR92a-vGAT-GABA signaling, which reveals molecular mechanisms underlying the anxiety behavior in AD patients and potentially leads to the development of new therapeutics for tauopathies.

The dynamics of GABA signaling: Revelations from the circadian pacemaker in the suprachiasmatic nucleus

Virtually every neuron within the suprachiasmatic nucleus (SCN) communicates via GABAergic signaling. The extracellular levels of GABA within the SCN are determined by a complex interaction of synthesis and transport, as well as synaptic and non-synaptic release. The response to GABA is mediated by GABA_A receptors that respond to both phasic and tonic GABA release and that can produce excitatory as well as inhibitory cellular responses. GABA also influences circadian control through the exclusively inhibitory effects of GABA_B receptors. Both GABA and neuropeptide signaling occur within the SCN, although the functional consequences of the interactions of these signals are not well understood. This review considers the role of GABA in the circadian pacemaker, in the mechanisms responsible for the generation of circadian rhythms, in the ability of non-photic stimuli to reset the phase of the pacemaker, and in the ability of the day-night cycle to entrain the pacemaker.

Glycinergic transmission: glycine transporter GlyT2 in neuronal pathologies

Glycinergic neurons are major contributors to the regulation of neuronal excitability, mainly in caudal areas of the nervous system. These neurons control fluxes of sensory information between the periphery and the CNS and diverse motor activities like locomotion, respiration or vocalization. The phenotype of a glycinergic neuron is determined by the expression of at least two proteins: GlyT2, a plasma membrane transporter of glycine, and VIAAT, a vesicular transporter shared by glycine and GABA. In this article, we review recent advances in understanding the role of GlyT2 in the pathophysiology of inhibitory glycinergic neurotransmission. GlyT2 mutations are associated to decreased glycinergic function that results in a rare movement disease termed hyperekplexia (HPX) or startle disease. In addition, glycinergic neurons control pain transmission in the dorsal spinal cord and their function is reduced in chronic pain states. A moderate inhibition of GlyT2 may potentiate glycinergic inhibition and constitutes an attractive target for pharmacological intervention against these devastating conditions.

Impact of Low Dose Oral Exposure to Bisphenol A (BPA) on the Neonatal Rat Hypothalamic and Hippocampal Transcriptome: A CLARITY-BPA Consortium Study

Bisphenol A (BPA) is an endocrine disrupting, high volume production chemical found in a variety of products. Evidence of prenatal exposure has raised concerns that developmental BPA may disrupt sex-specific brain organization and, consequently, induce lasting changes on neurophysiology and behavior. We and others have shown that exposure to BPA at doses below the no-observed-adverse-effect level can disrupt the sex-specific expression of estrogen-responsive genes in the neonatal rat brain including estrogen receptors (ERs). The present studies, conducted as part of the Consortium Linking Academic and Regulatory Insights of BPA Toxicity program, expanded this work by examining the hippocampal and hypothalamic transcriptome on postnatal day 1 with the hypothesis that genes sensitive to estrogen and/or sexually dimorphic in expression would be altered by prenatal BPA exposure. NCTR Sprague-Dawley dams were gavaged from gestational day 6 until parturition with BPA (0-, 2.5-, 25-, 250-, 2500-, or 25 000-μg/kg body weight [bw]/d). Ethinyl estradiol was used as a reference estrogen (0.05- or 0.5-μg/kg bw/d). Postnatal day 1 brains were microdissected and gene expression was assessed with RNA-sequencing (0-, 2.5-, and 2500-μg/kg bw BPA groups only) and/or quantitative real-time PCR (all exposure groups). BPA-related transcriptional changes were mainly confined to the hypothalamus. Consistent with prior observations, BPA induced sex-specific effects on hypothalamic ERα and ERβ (Esr1 and Esr2) expression and hippocampal and hypothalamic oxytocin (Oxt) expression. These data demonstrate prenatal BPA exposure, even at doses below the current no-observed-adverse-effect level, can alter gene expression in the developing brain.

The Putative SLC Transporters Mfsd5 and Mfsd11 Are Abundantly Expressed in the Mouse Brain and Have a Potential Role in Energy Homeostasis

Background

Solute carriers (SLCs) are membrane bound transporters responsible for the movement of soluble molecules such as amino acids, ions, nucleotides, neurotransmitters and oligopeptides over cellular membranes. At present, there are 395 SLCs identified in humans, where about 40% are still uncharacterized with unknown expression and/or function(s). Here we have studied two uncharacterized atypical SLCs that belong to the Major Facilitator Superfamily Pfam clan, Major facilitator superfamily domain 5 (MFSD5) and Major facilitator superfamily domain 11 (MFSD11). We provide fundamental information about the histology in mice as well as data supporting their disposition to regulate expression levels to keep the energy homeostasis.

Results

In mice subjected to starvation or high-fat diet, the mRNA expression of Mfsd5 was significantly down-regulated (P<0.001) in food regulatory brain areas whereas Mfsd11 was significantly up-regulated in mice subjected to either starvation (P<0.01) or high-fat diet (P<0.001). qRT-PCR analysis on wild type tissues demonstrated that both Mfsd5 and Mfsd11 have a wide central and peripheral mRNA distribution, and immunohistochemistry was utilized to display the abundant protein expression in the mouse embryo and the adult mouse brain. Both proteins are expressed in excitatory and inhibitory neurons, but not in astrocytes.

Conclusions

Mfsd5 and Mfsd11 are both affected by altered energy homeostasis, suggesting plausible involvement in the energy regulation. Moreover, the first histological mapping of MFSD5 and MFSD11 shows ubiquitous expression in the periphery and the central nervous system of mice, where the proteins are expressed in excitatory and inhibitory mouse brain neurons.

Age-related gene expression change of GABAergic system in visual cortex of rhesus macaque

Degradation of visual function is a common phenomenon during aging and likely mediated by change in the impaired central visual pathway. Treatment with GABA or its agonist could recover the ability of visual neurons in the primary visual cortex of senescent macaques. However, little is known about how GABAergic system change is related to the aged degradation of visual function in nonhuman primate. With the use of quantitative PCR method, we measured the expression change of 24 GABA related genes in the primary visual cortex (Brodmann's 17) of different age groups. In this study, both of mRNA and protein of glutamic acid decarboxylase (GAD65) were measured by real-time RT-PCR and Western blot, respectively. Results revealed that the level of GAD65 message was not significantly altered, but the proteins were significantly decreased in the aged monkey. As GAD65 plays an important role in GABA synthesis, the down-regulation of GAD65 protein was likely the key factor leading to the observed GABA reduction in the primary visual cortex of the aged macaques. In addition, 7 of 14 GABA receptor genes were up-regulated and one GABA receptor gene was significantly reduced during aging process even after Banjamini correction for multiple comparisons (P<0.05). These results suggested that the dysregulation of GAD65 protein might contribute to some age-related neural visual dysfunctions and most of GABA receptor genes induce a clear indication of compensatory effect for the reduced GABA release in the healthy aged monkey cortex.

Structure, Function, and Drug Interactions of Neurotransmitter Transporters in the Postgenomic Era

Vesicular neurotransmitter transporters are responsible for the accumulation of neurotransmitters in secretory vesicles and play essential roles in chemical transmission. The SLC17 family contributes to sequestration of anionic neurotransmitters such as glutamate, aspartate, and nucleotides. Identification and subsequent cellular and molecular biological studies of SLC17 transporters unveiled the principles underlying the actions of these transporters. Recent progress in reconstitution methods in combination with postgenomic approaches has advanced studies on neurotransmitter transporters. This review summarizes the molecular properties of SLC17-type transporters and recent findings regarding the novel SLC18 transporter.

The GABAA Receptor as a Therapeutic Target for Neurodevelopmental Disorders

Intellectual disability, autism spectrum disorder, and epilepsy are prime examples of neurodevelopmental disorders that collectively affect a significant percentage of the world population. Recent technological breakthroughs allowed the elucidation of the genetic causes of many of these disorders. As neurodevelopmental disorders are genetically heterogeneous, the development of rational therapy is extremely challenging. Fortunately, many causative genes are interconnected and cluster in specific cellular pathways. Targeting a common node in such a network would allow us to interfere with a series of related neurodevelopmental disorders at once. Here, we argue that the GABAergic system is disturbed in many neurodevelopmental disorders, including fragile X syndrome, Rett syndrome, and Dravet syndrome, and is a key candidate target for therapeutic intervention. Many drugs that modulate the GABAergic system have already been tested in animal models with encouraging outcomes and are readily available for clinical trials.

Conditional targeting of medium spiny neurons in the striatal matrix

The striatum serves as the main input to the basal ganglia, and is key for the regulation of motor behaviors, compulsion, addiction, and various cognitive and emotional states. Its deterioration is associated with degenerative disorders such as Huntington's disease. Despite its apparent anatomical uniformity, it consists of intermingled cell populations, which have precluded straightforward anatomical sub-classifications adhering to functional dissections. Approximately 95% of the striatal neurons are inhibitory projection neurons termed medium spiny neurons (MSNs). They are commonly classified according to their expression of either dopamine receptor D1 or D2, which also determines their axonal projection patterns constituting the direct and indirect pathway in the basal ganglia. Immunohistochemical patterns have further indicated compartmentalization of the striatum to the striosomes and the surrounding matrix, which integrate MSNs of both the D1 and D2 type. Here, we present a transgenic mouse line, Gpr101-Cre, with Cre recombinase activity localized to matrix D1 and D2 MSNs. Using two Gpr101-Cre founder lines with different degrees of expression in the striatum, we conditionally deleted the vesicular inhibitory amino acid transporter (VIAAT), responsible for storage of GABA and glycine in synaptic vesicles. Partial ablation of VIAAT (in ~36% of MSNs) resulted in elevated locomotor activity compared to control mice, when provoked with the monoamine reuptake inhibitor cocaine. Near complete targeting of matrix MSNs led to profoundly changed motor behaviors, which increased in severity as the mice aged. Moreover, these mice had exaggerated muscle rigidity, retarded growth, increased rate of spontaneous deaths, and defective memory. Therefore, our data provide a link between dysfunctional GABA signaling of matrix MSNs to specific behavioral alterations, which are similar to the symptoms of Huntington's disease.

Protonophore properties of hyperforin are essential for its pharmacological activity

Hyperforin is a pharmacologically active component of the medicinal plant Hypericum perforatum (St. John's wort), recommended as a treatment for a range of ailments including mild to moderate depression. Part of its action has been attributed to TRPC6 channel activation. We found that hyperforin induces TRPC6-independent H⁺ currents in HEK-293 cells, cortical microglia, chromaffin cells and lipid bilayers. The latter demonstrates that hyperforin itself acts as a protonophore. The protonophore activity of hyperforin causes cytosolic acidification, which strongly depends on the holding potential, and which fuels the plasma membrane sodium-proton exchanger. Thereby the free intracellular sodium concentration increases and the neurotransmitter uptake by Na⁺ cotransport is inhibited. Additionally, hyperforin depletes and reduces loading of large dense core vesicles in chromaffin cells, which requires a pH gradient in order to accumulate monoamines. In summary the pharmacological actions of the “herbal Prozac” hyperforin are essentially determined by its protonophore properties shown here.

Identifying functional gene regulatory network phenotypes underlying single cell transcriptional variability

Recent analysis of single-cell transcriptomic data has revealed a surprising organization of the transcriptional variability pervasive across individual neurons. In response to distinct combinations of synaptic input-type, a new organization of neuronal subtypes emerged based on transcriptional states that were aligned along a gradient of correlated gene expression. Individual neurons traverse across these transcriptional states in response to cellular inputs. However, the regulatory network interactions driving these changes remain unclear. Here we present a novel fuzzy logic-based approach to infer quantitative gene regulatory network models from highly variable single-cell gene expression data. Our approach involves developing an a priori regulatory network that is then trained against in vivo single-cell gene expression data in order to identify causal gene interactions and corresponding quantitative model parameters. Simulations of the inferred gene regulatory network response to experimentally observed stimuli levels mirrored the pattern and quantitative range of gene expression across individual neurons remarkably well. In addition, the network identification results revealed that distinct regulatory interactions, coupled with differences in the regulatory network stimuli, drive the variable gene expression patterns observed across the neuronal subtypes. We also identified a key difference between the neuronal subtype-specific networks with respect to negative feedback regulation, with the catecholaminergic subtype network lacking such interactions. Furthermore, by varying regulatory network stimuli over a wide range, we identified several cases in which divergent neuronal subtypes could be driven towards similar transcriptional states by distinct stimuli operating on subtype-specific regulatory networks. Based on these results, we conclude that heterogenous single-cell gene expression profiles should be interpreted through a regulatory network modeling perspective in order to separate the contributions of network interactions from those of cellular inputs.

Histological analysis of SLC38A6 (SNAT6) expression in mouse brain shows selective expression in excitatory neurons with high expression in the synapses

SLC38A6 is one of the newly found members of the solute carrier 38 family consisting of total 11 members, of which only 6 have been characterized so far. Being the only glutamine transporter family expressed in the brain, this family of proteins are most probably involved in the regulation of the glutamate-glutamine cycle, responsible for preventing excitotoxicity. We used immunohistochemistry to show that SLC38A6 is primarily expressed in excitatory neurons and is not expressed in the astrocytes. Using proximity ligation assay, we have quantified the interactions of this SLC38 family protein with other proteins with known localization in the cells, showing that this transporter is expressed at the synapses. Moreover, this study has enabled us to come up with a model suggesting sub-cellular localization of SLC38A6 at the synaptic membrane of the excitatory neurons.

PAT4 is abundantly expressed in excitatory and inhibitory neurons as well as epithelial cells

PAT4, the fourth member of the SLC36/proton dependent amino acid transporter (PAT) family, is a high-affinity, low capacity electroneutral transporter of neutral amino acids like proline and tryptophan. It has also been associated with the function of mTORC1, a complex in the mammalian target of rapamycin (mTOR) pathway. We performed in situ hybridization and immunohistological analysis to determine the expression profile of PAT4, as well as an RT-PCR study on tissue from mice exposed to leucine. We performed a phylogenetic analysis to determine the evolutionary origin of PAT4. The in situ hybridization and the immunohistochemistry on mouse brain sections and hypothalamic cells showed abundant PAT4 expression in the mouse brain intracellularly in both inhibitory and excitatory neurons, partially co-localizing with lysosomal markers and epithelial cells lining the ventricles. Its location in epithelial cells around the ventricles indicates a transport of substrates across the blood brain barrier. Phylogenetic analysis showed that PAT4 belongs to an evolutionary old family most likely predating animals, and PAT4 is the oldest member of that family.

Vesicular neurotransmitter transporters: an approach for studying transporters with purified proteins

Vesicular storage and subsequent release of neurotransmitters are the key processes of chemical signal transmission. In this process, vesicular neurotransmitter transporters are responsible for loading the signaling molecules. The use of a "clean biochemical" approach with purified, recombinant transporters has helped in the identification of novel vesicular neurotransmitter transporters and in the analysis of the control of signal transmission.

The Concise Guide to PHARMACOLOGY 2013/14: transporters

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Transporters are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Evolutionary origin of amino acid transporter families SLC32, SLC36 and SLC38 and physiological, pathological and therapeutic aspects

About 25% of all solute carriers (SLCs) are likely to transport amino acids as their primary substrate. One of the major phylogenetic clusters of amino acid transporters from the SLC family is the β-family, which is part of the PFAM APC clan. The β-family includes three SLC families, SLC32, SLC36 and SLC38 with one, four and eleven members in humans, respectively. The most well characterized genes within these families are the vesicular inhibitory amino acid transporter (VIAAT, SLC32A1), PAT1 (SLC36A1), PAT2 (SLC36A2), PAT4 (SLC36A4), SNAT1 (SLC38A1), SNAT2 (SLC38A2), SNAT3 (SLC38A3), and SNAT4 (SLC38A4). Here we review the structural characteristics and functional role of these transporters. We also mined the complete protein sequence datasets for nine different genomes to clarify the evolutionary history of the β-family of transporters. We show that all three main branches of the this family are found as far back as green algae suggesting that genes from these families existed in the early eukaryote before the split of animals and plants and that they are present in most animal species. We also address the potential of further drug development within this field highlighting the important role of these transporters in neurotransmission and transport of amino acids as nutrients.

Are vesicular neurotransmitter transporters potential treatment targets for temporal lobe epilepsy?

The vesicular neurotransmitter transporters (VNTs) are small proteins responsible for packing synaptic vesicles with neurotransmitters thereby determining the amount of neurotransmitter released per vesicle through fusion in both neurons and glial cells. Each transporter subtype was classically seen as a specific neuronal marker of the respective nerve cells containing that particular neurotransmitter or structurally related neurotransmitters. More recently, however, it has become apparent that common neurotransmitters can also act as co-transmitters, adding complexity to neurotransmitter release and suggesting intriguing roles for VNTs therein. We will first describe the current knowledge on vesicular glutamate transporters (VGLUT1/2/3), the vesicular excitatory amino acid transporter (VEAT), the vesicular nucleotide transporter (VNUT), vesicular monoamine transporters (VMAT1/2), the vesicular acetylcholine transporter (VAChT) and the vesicular γ-aminobutyric acid (GABA) transporter (VGAT) in the brain. We will focus on evidence regarding transgenic mice with disruptions in VNTs in different models of seizures and epilepsy. We will also describe the known alterations and reorganizations in the expression levels of these VNTs in rodent models for temporal lobe epilepsy (TLE) and in human tissue resected for epilepsy surgery. Finally, we will discuss perspectives on opportunities and challenges for VNTs as targets for possible future epilepsy therapies.

Vesicular GABA transporter (VGAT) transports β-alanine

Vesicular GABA transporter (VGAT) is expressed in GABAergic and glycinergic neurons, and is responsible for vesicular storage and subsequent exocytosis of these inhibitory amino acids. In this study, we show that VGAT recognizes β-alanine as a substrate. Proteoliposomes containing purified VGAT transport β-alanine using Δψ but not ΔpH as a driving force. The Δψ-driven β-alanine uptake requires Cl(-). VGAT also facilitates Cl(-) uptake in the presence of β-alanine. A previously described VGAT mutant (Glu213Ala) that disrupts GABA and glycine transport similarly abrogates β-alanine uptake. These findings indicated that VGAT transports β-alanine through a mechanism similar to those for GABA and glycine, and functions as a vesicular β-alanine transporter. Vesicular GABA transporter (VGAT) is expressed in GABAergic and glycinergic neurons, and is responsible for vesicular storage and subsequent exocytosis of these inhibitory amino acids. In the present study, we showed that proteoliposomes containing purified VGAT transport β-alanine using Δψ as a driving force. VGAT also facilitates Cl(-) uptake. Our findings indicated that VGAT functions as a vesicular β-alanine transporter.

Characterization of the transporterB0AT3 (Slc6a17) in the rodent central nervous system

BACKGROUND

The vesicular B0AT3 transporter (SLC6A17), one of the members of the SLC6 family, is a transporter for neutral amino acids and is exclusively expressed in brain. Here we provide a comprehensive expression profile of B0AT3 in mouse brain using in situ hybridization and immunohistochemistry.

RESULTS

We confirmed previous expression data from rat brain and used a novel custom made antibody to obtain detailed co-labelling with several cell type specific markers. B0AT3 was highly expressed in both inhibitory and excitatory neurons. The B0AT3 expression was highly overlapping with those of vesicular glutamate transporter 2 (VGLUT2) and vesicular glutamate transporter 1 (VGLUT1). We also show here that Slc6a17mRNA is up-regulated in animals subjected to short term food deprivation as well as animals treated with the serotonin reuptake inhibitor fluoxetine and the dopamine/noradrenaline reuptake inhibitor bupropion.

CONCLUSIONS

This suggests that the B0AT3 transporter have a role in regulation of monoaminergic as well as glutamatergic synapses.

Systematic analysis of γ-aminobutyric acid (GABA) metabolism and function in the social amoeba Dictyostelium discoideum

While GABA has been suggested to regulate spore encapsulation in the social amoeba Dictyostelium discoideum, the metabolic profile and other potential functions of GABA during development remain unclear. In this study, we investigated the homeostasis of GABA metabolism by disrupting genes related to GABA metabolism and signaling. Extracellular levels of GABA are tightly regulated during early development, and GABA is generated by the glutamate decarboxylase, GadB, during growth and in early development. However, overexpression of the prespore-specific homologue, GadA, in the presence of GadB reduces production of extracellular GABA. Perturbation of extracellular GABA levels delays the process of aggregation. Cytosolic GABA is degraded by the GABA transaminase, GabT, in the mitochondria. Disruption of a putative vesicular GABA transporter (vGAT) homologue DdvGAT reduces secreted GABA. We identified the GABAB receptor-like family member GrlB as the major GABA receptor during early development, and either disruption or overexpression of GrlB delays aggregation. This delay is likely the result of an abolished pre-starvation response and late expression of several "early" developmental genes. Distinct genes are employed for GABA generation during sporulation. During sporulation, GadA alone is required for generating GABA and DdvGAT is likely responsible for GABA secretion. GrlE but not GrlB is the GABA receptor during late development.

Neurons with GABAergic phenotype in the visual system of Drosophila

The visual system of Drosophila contains ~60,000 neurons per hemisphere that are organized in parallel, retinotopically arranged columns. The neuroanatomy of these neurons has been mapped in considerable detail at both the light and ultrastructural level. However, studies providing direct evidence for synaptic signaling and the neurotransmitter used by individual neurons are relatively sparse. Here we characterize those neurons in the Drosophila optic lobes that possibly release gamma aminobutyric acid (GABA), the major inhibitory neurotransmitter of the insect central nervous system. We identified 26 different types of neurons of the lamina, medulla, lobula, and lobula plate. Based on the previous Golgi-staining analysis (Fischbach and Dittrich [1989] Cell Tissue Res 258:441-475), the identified neurons are further classified into 11 major subgroups representing lamina monopolar (L), medulla intrinsic (Mi, Mt), bushy T (T), transmedullary (Tm), transmedullary Y (TmY), Y, lobula-complex intrinsic (Lccn), lobula columnar (Lcn), lobula plate intrinsic (Lpi), and lobula tangential (Lt) cell types. This detailed map of neurons with GABAergic phenotype will contribute to the future neurogenetic dissection of information processing circuits in the fly visual system.

Unraveling the central proopiomelanocortin neural circuits

Central proopiomelanocortin (POMC) neurons form a potent anorexigenic network, but our understanding of the integration of this hypothalamic circuit throughout the central nervous system (CNS) remains incomplete. POMC neurons extend projections along the rostrocaudal axis of the brain, and can signal with both POMC-derived peptides and fast amino acid neurotransmitters. Although recent experimental advances in circuit-level manipulation have been applied to POMC neurons, many pivotal questions still remain: how and where do POMC neurons integrate metabolic information? Under what conditions do POMC neurons release bioactive molecules throughout the CNS? Are GABA and glutamate or neuropeptides released from POMC neurons more crucial for modulating feeding and metabolism? Resolving the exact stoichiometry of signals evoked from POMC neurons under different metabolic conditions therefore remains an ongoing endeavor. In this review, we analyze the anatomical atlas of this network juxtaposed to the physiological signaling of POMC neurons both in vitro and in vivo. We also consider novel genetic tools to further characterize the function of the POMC circuit in vivo. Our goal is to synthesize a global view of the POMC network, and to highlight gaps that require further research to expand our knowledge on how these neurons modulate energy balance.

Whole-genome studies identify solute carrier transporters in cellular susceptibility to paclitaxel

OBJECTIVE

The clinical use of paclitaxel is limited by variable responses and the potential for significant toxicity. To date, studies of associations between variants in candidate genes and paclitaxel effects have yielded conflicting results. We aimed to evaluate the relationships between global gene expression and paclitaxel sensitivity.

METHODS

We utilized well-genotyped lymphoblastoid cell lines derived from the International HapMap Project to evaluate the relationships between cellular susceptibility to paclitaxel and global gene expression. Cells were exposed to varying concentrations of paclitaxel to evaluate paclitaxel-induced cytotoxicity and apoptosis. Among the top genes, we identified solute carrier (SLC) genes associated with paclitaxel sensitivity and narrowed down the list to those that had single nucleotide polymorphisms associated with both the expression level of the SLC gene and also with paclitaxel sensitivity. We performed an independent validation in an independent set of cell lines and also conducted functional studies using RNA interference.

RESULTS

Of all genes associated with paclitaxel-induced cytotoxicity at P less than 0.05 (1713 genes), there was a significant enrichment in SLC genes (31 genes). A subset of SLC genes, namely SLC31A2, SLC43A1, SLC35A5, and SLC41A2, was associated with paclitaxel sensitivity and had regulating single nucleotide polymorphisms that were also associated with paclitaxel-induced cytotoxicity. Multivariate modeling demonstrated that those four SLC genes together explained 20% of the observed variability in paclitaxel susceptibility. Using RNA interference, we demonstrated increased paclitaxel susceptibility with knockdown of three SLC genes, SLC31A2, SLC35A5, and SLC41A2.

CONCLUSION

Our findings are novel and lend further support to the role of transporters, specifically solute carriers, in mediating cellular susceptibility to paclitaxel.

GABA system dysfunction in autism and related disorders: from synapse to symptoms

Autism spectrum disorders (ASDs) are neurodevelopmental syndromes characterised by repetitive behaviours and restricted interests, impairments in social behaviour and relations, and in language and communication. These symptoms are also observed in a number of developmental disorders of known origin, including Fragile X Syndrome, Rett Syndrome, and Foetal Anticonvulsant Syndrome. While these conditions have diverse etiologies, and poorly understood pathologies, emerging evidence suggests that they may all be linked to dysfunction in particular aspects of GABAergic inhibitory signalling in the brain. We review evidence from genetics, molecular neurobiology and systems neuroscience relating to the role of GABA in these conditions. We conclude by discussing how these deficits may relate to the specific symptoms observed.

Regulation of GABA and glutamate release from proopiomelanocortin neuron terminals in intact hypothalamic networks

Hypothalamic proopiomelanocortin (POMC) neurons and their peptide products mediate important aspects of energy balance, analgesia, and reward. In addition to peptide products, there is evidence that POMC neurons can also express the amino acid transmitters GABA and glutamate, suggesting these neurons may acutely inhibit or activate downstream neurons. However, the release of amino acid transmitters from POMC neurons has not been thoroughly investigated in an intact system. In the present study, the light-activated cation channel channelrhodopsin-2 (ChR2) was used to selectively evoke transmitter release from POMC neurons. Whole-cell electrophysiologic recordings were made in brain slices taken from POMC-Cre transgenic mice that had been injected with a viral vector containing a floxed ChR2 sequence. Brief pulses of blue light depolarized POMC-ChR2 neurons and induced the release of GABA and glutamate onto unidentified neurons within the arcuate nucleus, as well as onto other POMC neurons. To determine whether the release of GABA and glutamate from POMC terminals can be readily modulated, opioid and GABA(B) receptor agonists were applied. Agonists for μ- and κ-, but not δ-opioid receptors inhibited transmitter release from POMC neurons, as did the GABA(B) receptor agonist baclofen. This regulation indicates that opioids and GABA released from POMC neurons may act at presynaptic receptors on POMC terminals in an autoregulatory manner to limit continued transmission. The results show that, in addition to the relatively slow and long-lasting actions of peptides, POMC neurons can rapidly affect the activity of downstream neurons via GABA and glutamate release.

Expanding neurotransmitters in the hypothalamic neurocircuitry for energy balance regulation

The current epidemic of obesity and its associated metabolic syndromes impose unprecedented challenges to our society. Despite intensive research on obesity pathogenesis, an effective therapeutic strategy to treat and cure obesity is still lacking. Exciting studies in last decades have established the importance of the leptin neural pathway in the hypothalamus in the regulation of body weight homeostasis. Important hypothalamic neuropeptides have been identified as critical neurotransmitters from leptin-sensitive neurons to mediate leptin action. Recent research advance has significantly expanded the list of neurotransmitters involved in body weight-regulating neural pathways, including fast-acting neurotransmitters, gamma-aminobutyric acid (GABA) and glutamate. Given the limited knowledge on the leptin neural pathway for body weight homeostasis, understanding the function of neurotransmitters released from key neurons for energy balance regulation is essential for delineating leptin neural pathway and eventually for designing effective therapeutic drugs against the obesity epidemic.

Hippocampal CA3 transcriptome signature correlates with initial precipitating injury in refractory mesial temporal lobe epilepsy

BACKGROUND

Prolonged febrile seizures constitute an initial precipitating injury (IPI) commonly associated with refractory mesial temporal lobe epilepsy (RMTLE). In order to investigate IPI influence on the transcriptional phenotype underlying RMTLE we comparatively analyzed the transcriptomic signatures of CA3 explants surgically obtained from RMTLE patients with (FS) or without (NFS) febrile seizure history. Texture analyses on MRI images of dentate gyrus were conducted in a subset of surgically removed sclerotic hippocampi for identifying IPI-associated histo-radiological alterations.

METHODOLOGY/PRINCIPAL FINDINGS

DNA microarray analysis revealed that CA3 global gene expression differed significantly between FS and NFS subgroups. An integrative functional genomics methodology was used for characterizing the relations between GO biological processes themes and constructing transcriptional interaction networks defining the FS and NFS transcriptomic signatures and its major gene-gene links (hubs). Co-expression network analysis showed that: i) CA3 transcriptomic profiles differ according to the IPI; ii) FS distinctive hubs are mostly linked to glutamatergic signalization while NFS hubs predominantly involve GABAergic pathways and neurotransmission modulation. Both networks have relevant hubs related to nervous system development, what is consistent with cell genesis activity in the hippocampus of RMTLE patients. Moreover, two candidate genes for therapeutic targeting came out from this analysis: SSTR1, a relevant common hub in febrile and afebrile transcriptomes, and CHRM3, due to its putative role in epilepsy susceptibility development. MRI texture analysis allowed an overall accuracy of 90% for pixels correctly classified as belonging to FS or NFS groups. Histological examination revealed that granule cell loss was significantly higher in FS hippocampi.

CONCLUSIONS/SIGNIFICANCE

CA3 transcriptional signatures and dentate gyrus morphology fairly correlate with IPI in RMTLE, indicating that FS-RMTLE represents a distinct phenotype. These findings may shed light on the molecular mechanisms underlying refractory epilepsy phenotypes and contribute to the discovery of novel specific drug targets for therapeutic interventions.

Mutations in an amino acid transporter gene are responsible for sex-linked translucent larval skin of the silkworm, Bombyx mori

The sex-linked translucent (os) mutation in the silkworm, Bombyx mori, confers slightly translucent larval skin resulting from a decrease in the incorporation of uric acid into epidermal cells. By positional cloning, we narrowed a region linked to the os phenotype to approximately 157 kb located on scaffold Bm_scaf72 on the Z chromosome (chromosome 1). The region contained four gene models. Sequencing analysis revealed that one of the candidate genes had a 7-bp deletion in the coding region. We also found a 111-bp deletion or single-nucleotide substitution in the same gene using independent os mutant strains. Because all the mutations caused the generation of abnormal transcripts followed by translation of a truncated protein, we conclude that the mutation of this candidate gene is responsible for the translucent larval skin of the os mutant. Sequence analysis indicated that the gene responsible for the os mutation had homology to amino acid transporters of the solute carrier family of proteins. Our results suggest that solute carrier proteins are involved in uric acid transport in insects and other invertebrates.

SLC6 neurotransmitter transporters: structure, function, and regulation

The neurotransmitter transporters (NTTs) belonging to the solute carrier 6 (SLC6) gene family (also referred to as the neurotransmitter-sodium-symporter family or Na(+)/Cl(-)-dependent transporters) comprise a group of nine sodium- and chloride-dependent plasma membrane transporters for the monoamine neurotransmitters serotonin (5-hydroxytryptamine), dopamine, and norepinephrine, and the amino acid neurotransmitters GABA and glycine. The SLC6 NTTs are widely expressed in the mammalian brain and play an essential role in regulating neurotransmitter signaling and homeostasis by mediating uptake of released neurotransmitters from the extracellular space into neurons and glial cells. The transporters are targets for a wide range of therapeutic drugs used in treatment of psychiatric diseases, including major depression, anxiety disorders, attention deficit hyperactivity disorder and epilepsy. Furthermore, psychostimulants such as cocaine and amphetamines have the SLC6 NTTs as primary targets. Beginning with the determination of a high-resolution structure of a prokaryotic homolog of the mammalian SLC6 transporters in 2005, the understanding of the molecular structure, function, and pharmacology of these proteins has advanced rapidly. Furthermore, intensive efforts have been directed toward understanding the molecular and cellular mechanisms involved in regulation of the activity of this important class of transporters, leading to new methodological developments and important insights. This review provides an update of these advances and their implications for the current understanding of the SLC6 NTTs.

Metabolic control of vesicular glutamate transport and release

Fasting has been used to control epilepsy since antiquity, but the mechanism of coupling between metabolic state and excitatory neurotransmission remains unknown. Previous work has shown that the vesicular glutamate transporters (VGLUTs) required for exocytotic release of glutamate undergo an unusual form of regulation by Cl(-). Using functional reconstitution of the purified VGLUTs into proteoliposomes, we now show that Cl(-) acts as an allosteric activator, and the ketone bodies that increase with fasting inhibit glutamate release by competing with Cl(-) at the site of allosteric regulation. Consistent with these observations, acetoacetate reduced quantal size at hippocampal synapses and suppresses glutamate release and seizures evoked with 4-aminopyridine in the brain. The results indicate an unsuspected link between metabolic state and excitatory neurotransmission through anion-dependent regulation of VGLUT activity.

Mutation of the Drosophila vesicular GABA transporter disrupts visual figure detection

The role of gamma amino butyric acid (GABA) release and inhibitory neurotransmission in regulating most behaviors remains unclear. The vesicular GABA transporter (VGAT) is required for the storage of GABA in synaptic vesicles and provides a potentially useful probe for inhibitory circuits. However, specific pharmacologic agents for VGAT are not available, and VGAT knockout mice are embryonically lethal, thus precluding behavioral studies. We have identified the Drosophila ortholog of the vesicular GABA transporter gene (which we refer to as dVGAT), immunocytologically mapped dVGAT protein expression in the larva and adult and characterized a dVGAT(minos) mutant allele. dVGAT is embryonically lethal and we do not detect residual dVGAT expression, suggesting that it is either a strong hypomorph or a null. To investigate the function of VGAT and GABA signaling in adult visual flight behavior, we have selectively rescued the dVGAT mutant during development. We show that reduced GABA release does not compromise the active optomotor control of wide-field pattern motion. Conversely, reduced dVGAT expression disrupts normal object tracking and figure-ground discrimination. These results demonstrate that visual behaviors are segregated by the level of GABA signaling in flies, and more generally establish dVGAT as a model to study the contribution of GABA release to other complex behaviors.

Guinea pig horizontal cells express GABA, the GABA-synthesizing enzyme GAD 65, and the GABA vesicular transporter

Gamma-aminobutyric acid (GABA) is likely expressed in horizontal cells of all species, although conflicting physiological findings have led to considerable controversy regarding its role as a transmitter in the outer retina. This study has evaluated key components of the GABA system in the outer retina of guinea pig, an emerging retinal model system. The presence of GABA, its rate-limiting synthetic enzyme glutamic acid decarboxylase (GAD(65) and GAD(67) isoforms), the plasma membrane GABA transporters (GAT-1 and GAT-3), and the vesicular GABA transporter (VGAT) was evaluated by using immunohistochemistry with well-characterized antibodies. The presence of GAD(65) mRNA was also evaluated by using laser capture microdissection and reverse transcriptase-polymerase chain reaction. Specific GABA, GAD(65), and VGAT immunostaining was localized to horizontal cell bodies, as well as to their processes and tips in the outer plexiform layer. Furthermore, immunostaining of retinal whole mounts and acutely dissociated retinas showed GAD(65) and VGAT immunoreactivity in both A-type and B-type horizontal cells. However, these cells did not contain GAD(67), GAT-1, or GAT-3 immunoreactivity. GAD(65) mRNA was detected in horizontal cells, and sequencing of the amplified GAD(65) fragment showed approximately 85% identity with other mammalian GAD(65) mRNAs. These studies demonstrate the presence of GABA, GAD(65), and VGAT in horizontal cells of the guinea pig retina, and support the idea that GABA is synthesized from GAD(65), taken up into synaptic vesicles by VGAT, and likely released by a vesicular mechanism from horizontal cells.

Immunocytochemical evidence for SNARE protein-dependent transmitter release from guinea pig horizontal cells

Horizontal cells are lateral interneurons that participate in visual processing in the outer retina but the cellular mechanisms underlying transmitter release from these cells are not fully understood. In non-mammalian horizontal cells, GABA release has been shown to occur by a non-vesicular mechanism. However, recent evidence in mammalian horizontal cells favors a vesicular mechanism as they lack plasmalemmal GABA transporters and some soluble NSF attachment protein receptor (SNARE) core proteins have been identified in rodent horizontal cells. Moreover, immunoreactivity for GABA and the molecular machinery to synthesize GABA have been found in guinea pig horizontal cells, suggesting that if components of the SNARE complex are expressed they could contribute to the vesicular release of GABA. In this study we investigated whether these vesicular and synaptic proteins are expressed by guinea pig horizontal cells using immunohistochemistry with well-characterized antibodies to evaluate their cellular distribution. Components of synaptic vesicles including vesicular GABA transporter, synapsin I and synaptic vesicle protein 2A were localized to horizontal cell processes and endings, along with the SNARE core complex proteins, syntaxin-1a, syntaxin-4 and synaptosomal-associated protein 25 (SNAP-25). Complexin I/II, a cytosolic protein that stabilizes the activated SNARE fusion core, strongly immunostained horizontal cell soma and processes. In addition, the vesicular Ca(2+)-sensor, synaptotagmin-2, which is essential for Ca(2+)-mediated vesicular release, was also localized to horizontal cell processes and somata. These morphological findings from guinea pig horizontal cells suggest that mammalian horizontal cells have the capacity to utilize a regulated Ca(2+)-dependent vesicular pathway to release neurotransmitter, and that this mechanism may be shared among many mammalian species.

Glycinergic synapse development, plasticity, and homeostasis in zebrafish

The zebrafish glial glycine transporter 1 (GlyT1) mutant provides an animal model in which homeostatic plasticity at glycinergic synapses restores rhythmic motor behaviors. GlyT1 mutants, initially paralyzed by the build-up of the inhibitory neurotransmitter glycine, stage a gradual recovery that is associated with reductions in the strength of evoked glycinergic responses. Gradual motor recovery suggests sequential compensatory mechanisms that culminate in the down-regulation of the neuronal glycine receptor. However, how motor recovery is initiated and how other forms of plasticity contribute to behavioral recovery are still outstanding questions that we discuss in the context of (1) glycinergic synapses as they function in spinal circuits that produce rhythmic motor behaviors, (2) the proteins involved in regulating glycinergic synaptic strength, (3) current models of glycinergic synaptogenesis, and (4) plasticity mechanisms that modulate the strength of glycinergic synapses. Concluding remarks (5) explore the potential for distinct plasticity mechanisms to act in concert at different spatial and temporal scales to achieve a dynamic stability that results in balanced motor behaviors.