Larvae of the small white butterfly,Pieris rapae,express a novel serotonin receptor

The biogenic amine serotonin ( 5‐hydroxytryptamine, 5‐HT) is a neurotransmitter in vertebrates and invertebrates. It acts in regulation and modulation of many physiological and behavioral processes through G‐protein‐coupled receptors. Five 5‐HT receptor subtypes have been reported in Drosophila that share high similarity with mammalian 5‐HT_1A, 5‐HT_1B, 5‐HT_2A, 5‐HT_2B, and 5‐HT₇ receptors. We isolated a cDNA (Pr5‐HT₈) from larval Pieris rapae, which shares relatively low similarity to the known 5‐HT receptor classes. After heterologous expression in HEK293 cells, Pr5‐HT₈ mediated increased [Ca²⁺]_i in response to low concentrations (< 10 nM) of 5‐HT. The receptor did not affect [cAMP]_i even at high concentrations (> 10 μM) of 5‐HT. Dopamine, octopamine, and tyramine did not influence receptor signaling. Pr5‐HT₈ was also activated by various 5‐HT receptor agonists including 5‐methoxytryptamine, (±)‐8‐Hydroxy‐2‐(dipropylamino) tetralin, and 5‐carboxamidotryptamine. Methiothepin, a non‐selective 5‐HT receptor antagonist, activated Pr5‐HT₈. WAY 10635, a 5‐HT_1A antagonist, but not SB‐269970, SB‐216641, or RS‐127445, inhibited 5‐HT‐induced [Ca²⁺]_i increases. We infer that Pr5‐HT₈ represents the first recognized member of a novel 5‐HT receptor class with a unique pharmacological profile. We found orthologs of Pr5‐HT₈ in some insect pests and vectors such as beetles and mosquitoes, but not in the genomes of honeybee or parasitoid wasps. This is likely to be an invertebrate‐specific receptor because there were no similar receptors in mammals.

     

Comparative effect of lurasidone and blonanserin on cortical glutamate,dopamine, and acetylcholine efflux: role of relative serotonin (5‐HT)2A and DA D2 antagonism and 5‐HT1A partial agonism

Atypical antipsychotic drugs (AAPDs) have been suggested to be more effective in improving cognitive impairment in schizophrenia than typical APDs, a conclusion supported by differences in receptor affinities and neurotransmitter efflux in the cortex and the hippocampus. More potent serotonin (5‐HT)_2A than dopamine (DA) D₂ receptors antagonism, and direct or indirect 5‐HT_1A agonism, characterize almost all AAPDs. Blonanserin, an AAPD, has slightly greater affinity for D₂ than 5‐HT_2A receptors. Using microdialysis and ultra performance liquid chromatography‐mass spectrometry/mass spectrometry, we compared the abilities of the typical APD, haloperidol, three AAPDs, blonanserin, lurasidone, and olanzapine, and a selective 5‐HT_1A partial agonist, tandospirone, and all, except haloperidol, were found to ameliorate the cognitive deficits produced by the N‐methyl‐d‐aspartate antagonist, phencyclidine, altering the efflux of neurotransmitters and metabolites in the rat cortex and nucleus accumbens. Blonanserin, lurasidone, olanzapine, and tandospirone, but not haloperidol, increased the efflux of cortical DA and its metabolites, homovanillic acid and 3,4‐dihydroxyphenylacetic acid. Olanzapine and lurasidone increased the efflux of acetylcholine; lurasidone increased glutamate as well. None of the compounds significantly altered the efflux of 5‐HT or its metabolite, 5‐hydroxyindole acetic acid, or GABA, serine, and glycine. The ability to increase cortical DA efflux was the only shared effect of the compounds which ameliorates the deficit in cognition in rodents following phencyclidine.

     

Drebrin depletion alters neurotransmitter receptor levels in protein complexes,dendritic spine morphogenesis and memory‐related synaptic plasticity in the mouse hippocampus

Drebrin an actin‐bundling key regulator of dendritic spine genesis and morphology, has been recently proposed as a regulator of hippocampal glutamatergic activity which is critical for memory formation and maintenance. Here, we examined the effects of genetic deletion of drebrin on dendritic spine and on the level of complexes containing major brain receptors. To this end, homozygous and heterozygous drebrin knockout mice generated in our laboratory and related wild‐type control animals were studied. Level of protein complexes containing dopamine receptor D1/dopamine receptor D2, 5‐hydroxytryptamine receptor 1A (5‐HT1_AR), and 5‐hydroxytryptamine receptor 7 (5‐HT7R) were significantly reduced in hippocampus of drebrin knockout mice whereas no significant changes were detected for GluR1, 2, and 3 and NR1 as examined by native gel‐based immunoblotting. Drebrin depletion also altered dendritic spine formation, morphology, and reduced levels of dopamine receptor D1 in dendritic spines as evaluated using immunohistochemistry/confocal microscopy. Electrophysiological studies further showed significant reduction in memory‐related hippocampal synaptic plasticity upon drebrin depletion. These findings provide unprecedented experimental support for a role of drebrin in the regulation of memory‐related synaptic plasticity and neurotransmitter receptor signaling, offer relevant information regarding the interpretation of previous studies and help in the design of future studies on dendritic spines.

     

Kisspeptin1 modulates odorant‐evoked fear response via two serotonin receptor subtypes (5‐HT1A and 5‐HT2) in zebrafish

Kiss1, a neuropeptide predominantly expressed in the habenula, modulates the serotonin (5‐HT) system to decrease odorant cue [alarm substance (AS)]‐evoked fear behaviour in the zebrafish. The purpose of this study was to assess the interaction of Kiss1 with the 5‐HT system as well as to determine the involvement of the 5‐HT receptor subtypes in AS‐evoked fear. We utilized 0. 28 mg/kg WAY 100635 (WAY), a selective 5‐HT_1A receptor antagonist, to observe the effects of Kiss1 administration on AS‐evoked fear. We found WAY significantly inhibited the anxiolytic effects of Kiss1 (p < 0.001) with an exception of freezing behaviour. Based on this, we utilized 92.79 mg/kg methysergide, a 5‐HT₁ and 5‐HT₂ receptor antagonist, and found that methysergide significantly blocked the anxiolytic effects of Kiss1 in the presence of the AS (p < 0.001). From this, we conclude that Kiss1 modulates AS‐evoked fear responses mediated by the 5‐HT_1A and 5‐HT₂ receptors.

     

Striatal serotonin 2C receptors decrease nigrostriatal dopamine release by increasing GABA‐A receptor tone in the substantia nigra

Drugs acting at the serotonin‐2C (5‐HT2C) receptor subtype have shown promise as therapeutics in multiple syndromes including obesity, depression, and Parkinson's disease. While it is established that 5‐HT2C receptor stimulation inhibits DA release, the neural circuits and the localization of the relevant 5‐HT2C receptors remain unknown. This study used dual‐probe in vivo microdialysis to investigate the relative contributions of 5‐HT2C receptors localized in the rat substantia nigra (SN) and caudate‐putamen (CP) in the control of nigrostriatal DA release. Systemic administration (3.0 mg/kg) of the 5‐HT2C receptor selective agonist Ro 60‐0175 [(αS)‐6‐Chloro‐5‐fluoro‐α‐methyl‐1H‐indole‐1‐ethanamine fumarate] decreased, whereas intrastriatal infusions of the selective 5‐HT2C antagonist SB 242084 [6‐Chloro‐2,3‐dihydro‐5‐methyl‐N‐[6‐[(2‐methyl‐3‐pyridinyl)oxy]‐3‐pyridinyl]‐1H‐indole‐1‐carboxyamide; 1.0 μM] increased, basal DA in the CP. Depending on the site within the SN pars reticulata (SNpr), infusions of SB 242084 had more modest but significant effects. Moreover, infusions of the GABA‐A receptor agonist muscimol (10 μM) into the SNpr completely reversed the increases in striatal DA release produced by intrastriatal infusions of SB 242084. These findings suggest a role for 5‐HT2C receptors regulating striatal DA release that is highly localized. 5‐HT2C receptors localized in the striatum may represent a primary site of action that is mediated by the actions on GABAergic activity in the SN.

     

Negative modulation of the GABAAρ1 receptor function by l‐cysteine

l ‐Cysteine is an endogenous sulfur‐containing amino acid with multiple and varied roles in the central nervous system, including neuroprotection and the maintenance of the redox balance. However, it was also suggested as an excitotoxic agent implicated in the pathogenesis of neurological disorders such as Parkinson′s and Alzheimer′s disease. l ‐Cysteine can modulate the activity of ionic channels, including voltage‐gated calcium channels and glutamatergic NMDA receptors, whereas its effects on GABAergic neurotransmission had not been studied before. In the present work, we analyzed the effects of l ‐cysteine on responses mediated by homomeric GABA_Aρ1 receptors, which are known for mediating tonic γ‐aminobutyric acid (GABA) responses in retinal neurons. GABA_Aρ1 receptors were expressed in Xenopus laevis oocytes and GABA‐evoked chloride currents recorded by two‐electrode voltage‐clamp in the presence or absence of l ‐cysteine. l ‐Cysteine antagonized GABA_Aρ1 receptor‐mediated responses; inhibition was dose‐dependent, reversible, voltage independent, and susceptible to GABA concentration. Concentration‐response curves for GABA were shifted to the right in the presence of l ‐cysteine without a substantial change in the maximal response. l ‐Cysteine inhibition was insensitive to chemical protection of the sulfhydryl groups of the ρ1 subunits by the irreversible alkylating agent N‐ethyl maleimide. Our results suggest that redox modulation is not involved during l ‐cysteine actions and that l ‐cysteine might be acting as a competitive antagonist of the GABA_Aρ1 receptors.

     

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.

     

Allosteric modulation of sigma‐1 receptors by SKF83959 inhibits microglia‐mediated inflammation

Recent studies have shown that sigma‐1 receptor orthodox agonists can inhibit neuroinflammation. SKF83959 (3‐methyl‐6‐chloro‐7,8‐hydroxy‐1‐[3‐methylphenyl]‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepine), an atypical dopamine receptor‐1 agonist, has been recently identified as a potent allosteric modulator of sigma‐1 receptor. Here, we investigated the anti‐inflammatory effects of SKF83959 in lipopolysaccharide (LPS)‐stimulated BV2 microglia. Our results indicated that SKF83959 significantly suppressed the expression/release of the pro‐inflammatory mediators, such as tumor necrosis factor‐α (TNF‐α), interleukin‐1β (IL‐1β), inducible nitric oxide synthase (iNOS), and inhibited the generation of reactive oxygen species. All of these responses were blocked by selective sigma‐1 receptor antagonists (BD1047 or BD1063) and by ketoconazole (an inhibitor of enzyme cytochrome c₁₇ to inhibit the synthesis of endogenous dehydroepiandrosterone, DHEA). Additionally, we found that SKF83959 promoted the binding activity of DHEA with sigma‐1 receptors, and enhanced the inhibitory effects of DHEA on LPS‐induced microglia activation in a synergic manner. Furthermore, in a microglia‐conditioned media system, SKF83959 inhibited the cytotoxicity of conditioned medium generated by LPS‐activated microglia toward HT‐22 neuroblastoma cells. Taken together, our study provides the first evidence that allosteric modulation of sigma‐1 receptors by SKF83959 inhibits microglia‐mediated inflammation.

     

Assembly,trafficking and function of α1β2γ2 GABAA receptors are regulated by N‐terminal regions,in a subunit‐specific manner

GABA_A receptors are pentameric ligand‐gated ion channels that mediate inhibitory fast synaptic transmission in the central nervous system. Consistent with recent pentameric ligand‐gated ion channels structures, sequence analysis predicts an α‐helix near the N‐terminus of each GABA_A receptor subunit. Preceding each α‐helix are 8–36 additional residues, which we term the N‐terminal extension. In homomeric GABA_C receptors and nicotinic acetylcholine receptors, the N‐terminal α‐helix is functionally essential. Here, we determined the role of the N‐terminal extension and putative α‐helix in heteromeric α1β2γ2 GABA_A receptors. This role was most prominent in the α1 subunit, with deletion of the N‐terminal extension or further deletion of the putative α‐helix both dramatically reduced the number of functional receptors at the cell surface. Conversely, deletion of the β2 or γ2 N‐terminal extension had little effect on the number of functional cell surface receptors. Additional deletion of the putative α‐helix in the β2 or γ2 subunits did, however, decrease both functional cell surface receptors and incorporation of the γ2 subunit into mature receptors. In the β2 subunit only, α‐helix deletions affected GABA sensitivity and desensitization. Our findings demonstrate that N‐terminal extensions and α‐helices make key subunit‐specific contributions to assembly, consistent with both regions being involved in inter‐subunit interactions.

     

Ethanol,not detectably metabolized in brain,significantly reduces brain metabolism,probably via action at specific GABA(A) receptors and has measureable metabolic effects at very low concentrations

Ethanol is a known neuromodulatory agent with reported actions at a range of neurotransmitter receptors. Here, we measured the effect of alcohol on metabolism of [3‐¹³C]pyruvate in the adult Guinea pig brain cortical tissue slice and compared the outcomes to those from a library of ligands active in the GABAergic system as well as studying the metabolic fate of [1,2‐¹³C]ethanol. Analyses of metabolic profile clusters suggest that the significant reductions in metabolism induced by ethanol (10, 30 and 60 mM) are via action at neurotransmitter receptors, particularly α4β3δ receptors, whereas very low concentrations of ethanol may produce metabolic responses owing to release of GABA via GABA transporter 1 (GAT1) and the subsequent interaction of this GABA with local α5‐ or α1‐containing GABA(A)R. There was no measureable metabolism of [1,2‐¹³C]ethanol with no significant incorporation of ¹³C from [1,2‐¹³C]ethanol into any measured metabolite above natural abundance, although there were measurable effects on total metabolite sizes similar to those seen with unlabelled ethanol.

     

Adenosine A2A receptors are required for glutamate mGluR5‐ and dopamine D1 receptor‐evoked ERK1/2 phosphorylation in rat hippocampus: involvement of NMDA receptor

Interaction between mGluR5 and NMDA receptors (NMDAR ) is vital for synaptic plasticity and cognition. We recently demonstrated that stimulation of mGluR5 enhances NMDAR responses in hippocampus by phosphorylating NR2B(Tyr1472) subunit, and this reaction was enabled by adenosine A_2A receptors (A_2AR) (J Neurochem, 135, 2015, 714). In this study, by using in vitro phosphorylation and western blot analysis in hippocampal slices of male Wistar rats, we show that mGluR5 stimulation or mGluR5/NMDAR s co‐stimulation synergistically activate ERK 1/2 signaling leading to c‐Fos expression. Interestingly, both reactions are under the permissive control of endogenous adenosine acting through A_2ARs. Moreover, mGluR5‐mediated ERK 1/2 phosphorylation depends on NMDAR , which however exhibits a metabotropic way of function, since no ion influx through its ion channel is required. Furthermore, our results demonstrate that mGluR5 and mGluR5/NMDAR ‐evoked ERK 1/2 activation correlates well with the mGluR5/NMDAR ‐evoked NR2B(Tyr1472) phosphorylation, since both phenomena coincide temporally, are Src dependent, and are both enabled by A_2ARs. This indicates a functional involvement of NR2B(Tyr1472) phosphorylation in the ERK 1/2 activation. Our biochemical results are supported by electrophysiological data showing that in CA 1 region of hippocampus, the theta burst stimulation (TBS)‐induced long‐term potentiation coincides temporally with an increase in ERK 1/2 activation and both phenomena are dependent on the tripartite A_2A, mGlu5, and NMDAR s. Furthermore, we show that the dopamine D1 receptors evoked ERK 1/2 activation as well as the NR2B(Tyr1472) phosphorylation are also regulated by endogenous adenosine and A_2ARs. In conclusion, our results highlight the A_2ARs as a crucial regulator not only for NMDAR responses, but also for regulating ERK 1/2 signaling and its downstream pathways, leading to gene expression, synaptic plasticity, and memory consolidation.

     

Polyphenols from green tea prevent antineuritogenic action of Nogo‐A via 67‐kDa laminin receptor and hydrogen peroxide

Axonal regeneration after injury to the CNS is hampered by myelin‐derived inhibitors, such as Nogo‐A. Natural products, such as green tea, which are neuroprotective and safe for long‐term therapy, would complement ongoing various pharmacological approaches. In this study, using nerve growth factor‐differentiated neuronal‐like Neuroscreen‐1 cells, we show that extremely low concentrations of unfractionated green tea polyphenol mixture (GTPP) and its active ingredient, epigallocatechin‐3‐gallate (EGCG), prevent both the neurite outgrowth‐inhibiting activity and growth cone‐collapsing activity of Nogo‐66 (C‐terminal domain of Nogo‐A). Furthermore, a synergistic interaction was observed among GTPP constituents. This preventive effect was dependent on 67‐kDa laminin receptor (67LR) to which EGCG binds with high affinity. The antioxidants N‐acetylcysteine and cell‐permeable catalase abolished this preventive effect of GTPP and EGCG, suggesting the involvement of sublethal levels of H₂O₂ in this process. Accordingly, exogenous sublethal concentrations of H₂O₂, added as a bolus dose (5 μM) or more effectively through a steady‐state generation (1–2 μM), mimicked GTPP in counteracting the action of Nogo‐66. Exogenous H₂O₂ mediated this action by bypassing the requirement of 67LR. Taken together, these results show for the first time that GTPP and EGCG, acting through 67LR and elevating intracellular sublethal levels of H₂O₂, inhibit the antineuritogenic action of Nogo‐A.

     

The Neuroplastin adhesion molecules: key regulators of neuronal plasticity and synaptic function

The Neuroplastins Np65 and Np55 are neuronal and synapse‐enriched immunoglobulin superfamily molecules that play important roles in a number of key neuronal and synaptic functions including, for Np65, cell adhesion. In this review we focus on the physiological roles of the Neuroplastins in promoting neurite outgrowth, regulating the structure and function of both inhibitory and excitatory synapses in brain, and in neuronal and synaptic plasticity. We discuss the underlying molecular and cellular mechanisms by which the Neuroplastins exert their physiological effects and how these are dependent upon the structural features of Np65 and Np55, which enable them to bind to a diverse range of protein partners. In turn this enables the Neuroplastins to interact with a number of key neuronal signalling cascades. These include: binding to and activation of the fibroblast growth factor receptor; Np65 trans‐homophilic binding leading to activation of p38 MAPK and internalization of glutamate (GluR1) receptor subunits; acting as accessory proteins for monocarboxylate transporters, thus affecting neuronal energy supply, and binding to GABA_A α1, 2 and 5 subunits, thus regulating the composition and localization of GABA_A receptors. An emerging theme is the role of the Neuroplastins in regulating the trafficking and subcellular localization of specific binding partners. We also discuss the involvement of Neuroplastins in a number of pathophysiological conditions, including ischaemia, schizophrenia and breast cancer and the role of a single nucleotide polymorphism in the human Neuroplastin (NPTN) gene locus in impairment of cortical development and cognitive functions.

     

Endothelin‐1 increases the expression of VEGF‐R1/Flt‐1 receptors in rat cultured astrocytes through ETB receptors

Expressions of vascular endothelial growth factor (VEGF) receptors in astrocytes are increased in damaged brains. To clarify the regulatory mechanisms of VEGF receptors, the effects of endothelin‐1 (ET‐1) were examined in rat cultured astrocytes. Expressions of VEGF‐R1 and ‐R2 receptor mRNA were at similar levels, whereas the mRNA expressions of VEGF‐R3 and Tie‐2, a receptor for angiopoietins, were lower. Placenta growth factor, a selective agonist of the VEGF‐R1 receptor, induced phosphorylation of focal adhesion kinase (FAK) and extracellular signal regulated kinase 1/2 (ERK1/2). Phosphorylations of FAK and ERK 1/2 were also stimulated by VEGF‐E, a selective VEGF‐R2 agonist. Increased phosphorylations of FAK and ERK1/2 by VEGF₁₆₅ were reduced by selective antagonists for VEGF‐R1 and ‐R2. Treatment with ET‐1 increased VEGF‐R1 mRNA and protein levels. The effects of ET‐1 on VEGF‐R1 mRNA were mimicked by Ala^1,3,11,15‐ET‐1, a selective agonist for ET_B receptors, and inhibited by BQ788, an ET_B antagonist. ET‐1 did not affect the mRNA levels of VEGF‐R2, ‐R3, and Tie‐2. Pre‐treatment with ET‐1 potentiated the effects of placenta growth factor on phosphorylations of FAK and ERK1/2. These findings suggest that ET‐1 induces up‐regulation of VEGF‐R1 receptors in astrocytes, and potentiates VEGF signals in damaged nerve tissues.

     

Actin dynamics in growth cone motility and navigation

Motile growth cones lead growing axons through developing tissues to synaptic targets. These behaviors depend on the organization and dynamics of actin filaments that fill the growth cone leading margin [peripheral (P‐) domain]. Actin filament organization in growth cones is regulated by actin‐binding proteins that control all aspects of filament assembly, turnover, interactions with other filaments and cytoplasmic components, and participation in producing mechanical forces. Actin filament polymerization drives protrusion of sensory filopodia and lamellipodia, and actin filament connections to the plasma membrane link the filament network to adhesive contacts of filopodia and lamellipodia with other surfaces. These contacts stabilize protrusions and transduce mechanical forces generated by actomyosin activity into traction that pulls an elongating axon along the path toward its target. Adhesive ligands and extrinsic guidance cues bind growth cone receptors and trigger signaling activities involving Rho GTPases, kinases, phosphatases, cyclic nucleotides, and [Ca⁺⁺] fluxes. These signals regulate actin‐binding proteins to locally modulate actin polymerization, interactions, and force transduction to steer the growth cone leading margin toward the sources of attractive cues and away from repellent guidance cues.

     

Hyperthermia‐induced seizures alter adenosine A1 and A2A receptors and 5′‐nucleotidase activity in rat cerebral cortex

Febrile seizure is one of the most common convulsive disorders in children. The neuromodulator adenosine exerts anticonvulsant actions through binding adenosine receptors. Here, the impact of hyperthermia‐induced seizures on adenosine A₁ and A_2A receptors and 5′‐nucleotidase activity has been studied at different periods in the cerebral cortical area by using radioligand binding, real‐time PCR, and 5′‐nucleotidase activity assays. Hyperthermic seizures were induced in 13‐day‐old rats using a warmed air stream from a hair dryer. Neonates exhibited rearing and falling over associated with hindlimb clonus seizures (stage 5 on Racine scale criteria) after hyperthermic induction. A significant increase in A₁ receptor density was observed using [³H]DPCPX as radioligand, and mRNA coding A₁ was observed 48 h after hyperthermia‐induced seizures. In contrast, a significant decrease in A_2A receptor density was detected, using [³H]ZM241385 as radioligand, 48 h after hyperthermia‐evoked convulsions. These short‐term changes in A₁ and A_2A receptors were also accompanied by a loss of 5′‐nucleotidase activity. No significant variations either in A₁ or A_2A receptor density or 5′‐nucleotidase were observed 5 and 20 days after hyperthermic seizures. Taken together, both regulation of A₁ and A_2A receptors and loss of 5′‐nucleotidase in the cerebral cortex suggest the existence of a neuroprotective mechanism against seizures.

     

Subanesthetic ketamine reverses neuronal and astroglial metabolic activity deficits in a social defeat model of depression

Depression is one of the most debilitating neuropsychiatric disorders. Most of the current antidepressants have long remission time and low recovery rate. This study explores the impact of ketamine on neuronal and astroglial metabolic activity in prefrontal cortex in a social defeat (SD) model of depression. C57BL/6 mice were subjected to a social defeat paradigm for 5 min a day for 10 consecutive days. Ketamine (10 mg/kg, intraperitoneal) was administered to mice for two consecutive days following the last defeat stress. Mice were infused with [1,6‐¹³C₂]glucose or [2‐¹³C]acetate to assess neuronal and astroglial metabolic activity, respectively, together with proton‐observed carbon‐edited nuclear magnetic resonance spectroscopy in prefrontal cortex tissue extract. The ¹³C labeling of amino acids from glucose and acetate was decreased in SD mice. Ketamine treatment in SD mice restored sucrose preference, social interaction and immobility time to control values. Acute subanesthetic ketamine restored the ¹³C labeling of brain amino acids from glucose as well as acetate in SD mice to the respective control values, suggesting that rates of neuronal and astroglial tricarboxylic acid (TCA) cycle and neurotransmitter cycling were re‐established to normal levels. The finding of improved energy metabolism in SD mice suggests that fast anti‐depressant action of ketamine is linked with improved neurotransmitter cycling.

     

Blocking the GABA transporter GAT‐1 ameliorates spinal GABAergic disinhibition and neuropathic pain induced by paclitaxel

Paclitaxel is a chemotherapeutic agent widely used for treating carcinomas. Patients receiving paclitaxel often develop neuropathic pain and have a reduced quality of life which hinders the use of this life‐saving drug. In this study, we determined the role of GABA transporters in the genesis of paclitaxel‐induced neuropathic pain using behavioral tests, electrophysiology, and biochemical techniques. We found that tonic GABA receptor activities in the spinal dorsal horn were reduced in rats with neuropathic pain induced by paclitaxel. In normal controls, tonic GABA receptor activities were mainly controlled by the GABA transporter GAT‐1 but not GAT‐3. In the spinal dorsal horn, GAT‐1 was expressed at presynaptic terminals and astrocytes while GAT‐3 was only expressed in astrocytes. In rats with paclitaxel‐induced neuropathic pain, the protein expression of GAT‐1 was increased while GAT‐3 was decreased. This was concurrently associated with an increase in global GABA uptake. The paclitaxel‐induced attenuation of GABAergic tonic inhibition was ameliorated by blocking GAT‐1 but not GAT‐3 transporters. Paclitaxel‐induced neuropathic pain was significantly attenuated by the intrathecal injection of a GAT‐1 inhibitor. These findings suggest that targeting GAT‐1 transporters for reversing disinhibition in the spinal dorsal horn may be a useful approach for treating paclitaxel‐induced neuropathic pain.