Glutamine as a precursor for transmitter glutamate, aspartate and GABA in the cerebellum: a role for phosphate-activated glutaminase

Astrocyte coverage of excitatory synapses correlates to measures of synapse structure and function in ferret primary visual cortex

Most excitatory synapses in the mammalian brain are contacted or ensheathed by astrocyte processes, forming tripartite synapses. Astrocytes are thought to be critical regulators of the structural and functional dynamics of synapses. While the degree of synaptic coverage by astrocytes is known to vary across brain regions and animal species, the reason for and implications of this variability remains unknown. Further, how astrocyte coverage of synapses relates to in vivo functional properties of individual synapses has not been investigated. Here, we characterized astrocyte coverage of synapses of pyramidal neurons in the ferret visual cortex and, using correlative light and electron microscopy, examined their relationship to synaptic strength and sensory-evoked Ca2+ activity. Nearly, all synapses were contacted by astrocytes, and most were contacted along the axon-spine interface. Structurally, we found that the degree of synaptic astrocyte coverage directly scaled with synapse size and postsynaptic density complexity. Functionally, we found that the amount of astrocyte coverage scaled with how selectively a synapse responds to a particular visual stimulus and, at least for the largest synapses, scaled with the reliability of visual stimuli to evoke postsynaptic Ca2+ events. Our study shows astrocyte coverage is highly correlated with structural metrics of synaptic strength of excitatory synapses in the visual cortex and demonstrates a previously unknown relationship between astrocyte coverage and reliable sensory activation.

Mechanistic stoichiometric relationship between the rates of neurotransmission and neuronal glucose oxidation: Reevaluation of and alternatives to the pseudo-malate-aspartate shuttle model

The ~1:1 stoichiometry between the rates of neuronal glucose oxidation (CMRglc-ox-N) and glutamate (Glu)/γ-aminobutyric acid (GABA)-glutamine (Gln) neurotransmitter (NT) cycling between neurons and astrocytes (VNTcycle) has been firmly established. However, the mechanistic basis for this relationship is not fully understood, and this knowledge is critical for the interpretation of metabolic and brain imaging studies in normal and diseased brain. The pseudo-malate-aspartate shuttle (pseudo-MAS) model established the requirement for glycolytic metabolism in cultured glutamatergic neurons to produce NADH that is shuttled into mitochondria to support conversion of extracellular Gln (i.e., astrocyte-derived Gln in vivo) into vesicular neurotransmitter Glu. The evaluation of this model revealed that it could explain half of the 1:1 stoichiometry and it has limitations. Modifications of the pseudo-MAS model were, therefore, devised to address major knowledge gaps, that is, submitochondrial glutaminase location, identities of mitochondrial carriers for Gln and other model components, alternative mechanisms to transaminate α-ketoglutarate to form Glu and shuttle glutamine-derived ammonia while maintaining mass balance. All modified models had a similar 0.5 to 1.0 predicted mechanistic stoichiometry between VNTcycle and the rate of glucose oxidation. Based on studies of brain β-hydroxybutyrate oxidation, about half of CMRglc-ox-N may be linked to glutamatergic neurotransmission and localized in pre-synaptic structures that use pseudo-MAS type mechanisms for Glu-Gln cycling. In contrast, neuronal compartments that do not participate in transmitter cycling may use the MAS to sustain glucose oxidation. The evaluation of subcellular compartmentation of neuronal glucose metabolism in vivo is a critically important topic for future studies to understand glutamatergic and GABAergic neurotransmission.

Astrocyte coverage of excitatory synapses correlates to measures of synapse structure and function in primary visual cortex

Most excitatory synapses in the mammalian brain are contacted by astrocytes, forming the tripartite synapse. This interface is thought to be critical for glutamate turnover and structural or functional dynamics of synapses. While the degree of synaptic contact of astrocytes is known to vary across brain regions and animal species, the implications of this variability remain unknown. Furthermore, precisely how astrocyte coverage of synapses relates to in vivo functional properties of individual dendritic spines has yet to be investigated. Here, we characterized perisynaptic astrocyte processes (PAPs) contacting synapses of pyramidal neurons of the ferret visual cortex and, using correlative light and electron microscopy, examined their relationship to synaptic strength and to sensory-evoked Ca2+ activity. Nearly all synapses were contacted by PAPs, and most were contacted along the axon-spine interface (ASI). Structurally, we found that the degree of PAP coverage scaled with synapse size and complexity. Functionally, we found that PAP coverage scaled with the selectivity of Ca2+ responses of individual synapses to visual stimuli and, at least for the largest synapses, scaled with the reliability of visual stimuli to evoke postsynaptic Ca2+ events. Our study shows astrocyte coverage is highly correlated with structural properties of excitatory synapses in the visual cortex and implicates astrocytes as a contributor to reliable sensory activation.

Methanolic Extract of Aerva javanica Leaves Prevents LPS-Induced Depressive Like Behavior in Experimental Mice

Aim

Depression is a chronic recurrent neuropsychiatric disorder associated with inflammation. This study explored the pharmacological activities of Aerva javanica leaves crude extract (Aj.Cr) on lipopolysaccharide (LPS)-induced depressive-like behavior in experimental mice.

Methods

Aj.Cr was evaluated for its phenolic and flavonoid contents, bioactive potential, amino acid profiling and enzyme inhibition assays using different analytical techniques followed by in-silico molecular docking was performed. In addition, three ligands identified in HPLC analysis and standard galantamine were docked to acetyl cholinesterase (AchE) enzyme to assess the ligand interaction along with their binding affinities. In in-vivo analysis, mice were given normal saline (10 mL/kg), imipramine (10 mg/kg) and Aj.Cr (100, 300, and 500 mg/kg) orally for 14-consecutive days. On the 14th day, respective treatment was given 30-minutes before intra-peritoneal administration of (0.83 mg/kg) LPS. Open field, forced swim and tail suspension tests were performed 24-hours after LPS injection, followed by a sucrose preference test 48-hours later. Serum corticosterone levels, as well as levels of nitric oxide (NO), malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), tumor necrosis factor-alpha (TNF-), interleukin-1β (IL-1β), interleukin-6 (IL-6), brain-derived neurotrophic factor (BDNF) and catecholamines were determined in brain tissues.

Results

In-vitro results revealed that crude extract of Aj.Cr possesses anti-depressant agents with solid antioxidant potential. In-vivo analysis showed that LPS significantly increased depressive-like behavior followed by alteration in serum and tissue biomarkers as compared to normal control (p < 0.001). While imipramine and Aj.Cr (100, 300, and 500 mg/kg) treated groups significantly (p<0.05) improved the depressive-like behavior and biomarkers when compared to the LPS group.

Conclusion

The mitigation of LPS-induced depressive-like behavior by Aj.Cr may be linked to the modulation of oxidative stress, neuro-inflammation and catecholamines due to the presence of potent bioactive compounds exerting anti-depressant effects.

The role of neuroimmune and inflammation in pediatric uremia-induced neuropathy

Uremic neuropathy in children encompasses a wide range of central nervous system (CNS), peripheral nervous system (PNS), autonomic nervous system (ANS), and psychological abnormalities, which is associated with progressive renal dysfunction. Clinically, the diagnosis of uremic neuropathy in children is often made retrospectively when symptoms improve after dialysis or transplantation, due to there is no defining signs or laboratory and imaging findings. These neurological disorders consequently result in increased morbidity and mortality among children population, making uremia an urgent public health problem worldwide. In this review, we discuss the epidemiology, potential mechanisms, possible treatments, and the shortcomings of current research of uremic neuropathy in children. Mechanistically, the uremic neuropathy may be caused by retention of uremic solutes, increased oxidative stress, neurotransmitter imbalance, and disturbance of the blood-brain barrier (BBB). Neuroimmune, including the change of inflammatory factors and immune cells, may also play a crucial role in the progression of uremic neuropathy. Different from the invasive treatment of dialysis and kidney transplantation, intervention in neuroimmune and targeted anti-inflammatory therapy may provide a new insight for the treatment of uremia.

GABA, but Not Bestrophin-1, Is Localized in Astroglial Processes in the Mouse Hippocampus and the Cerebellum

GABA is proposed to act as a gliotransmitter in the brain. Differences in GABA release from astroglia are thought to underlie differences in tonic inhibition between the cerebellum and the CA1 hippocampus. Here we used quantitative immunogold cytochemistry to localize and compare the levels of GABA in astroglia in these brain regions. We found that the density of GABA immunogold particles was similar in delicate processes of Bergman glia in the cerebellum and astrocytes in the CA1 hippocampus. The astrocytic GABA release is proposed to be mediated by, among others, the Ca²⁺ activated Cl^- channel bestrophin-1. The bestrophin-1 antibodies did not show any significant bestrophin-1 signal in the brain of wt mice, nor in bestrophin-1 knockout mice. The bestrophin-1 signal was low both on Western blots and immunofluorescence laser scanning microscopic images. These results suggest that GABA is localized in astroglia, but in similar concentrations in the cerebellum and CA1 hippocampus, and thus cannot account for differences in tonic inhibition between these brain regions. Furthermore, our data seem to suggest that the GABA release from astroglia previously observed in the hippocampus and cerebellum occurs via mechanisms other than bestrophin-1.

Slc38a1 Conveys Astroglia-Derived Glutamine into GABAergic Interneurons for Neurotransmitter GABA Synthesis

GABA signaling is involved in a wide range of neuronal functions, such as synchronization of action potential firing, synaptic plasticity and neuronal development. Sustained GABA signaling requires efficient mechanisms for the replenishment of the neurotransmitter pool of GABA. The prevailing theory is that exocytotically released GABA may be transported into perisynaptic astroglia and converted to glutamine, which is then shuttled back to the neurons for resynthesis of GABA-i.e., the glutamate/GABA-glutamine (GGG) cycle. However, an unequivocal demonstration of astroglia-to-nerve terminal transport of glutamine and the contribution of astroglia-derived glutamine to neurotransmitter GABA synthesis is lacking. By genetic inactivation of the amino acid transporter Solute carrier 38 member a1 (Slc38a1)-which is enriched on parvalbumin+ GABAergic neurons-and by intraperitoneal injection of radiolabeled acetate (which is metabolized to glutamine in astroglial cells), we show that Slc38a1 mediates import of astroglia-derived glutamine into GABAergic neurons for synthesis of GABA. In brain slices, we demonstrate the role of Slc38a1 for the uptake of glutamine specifically into GABAergic nerve terminals for the synthesis of GABA depending on demand and glutamine supply. Thus, while leaving room for other pathways, our study demonstrates a key role of Slc38a1 for newly formed GABA, in harmony with the existence of a GGG cycle.

Metabolism of Amino Acids in the Brain and Their Roles in Regulating Food Intake

Amino acids (AAs) and their metabolites play an important role in neurological health and function. They are not only the building blocks of protein but are also neurotransmitters. In the brain, glutamate and aspartate are the major excitatory neurotransmitters, whereas γ-aminobutyrate (GABA, a metabolite of glutamate) and glycine are the major inhibitory neurotransmitters. Nitric oxide (NO, a metabolite of arginine), H₂S (a metabolite of cysteine), serotonin (a metabolite of tryptophan) and histamine (a metabolite of histidine), as well as dopamine and norepinephrine (metabolites of tyrosine) are neurotransmitters to modulate synaptic plasticity, neuronal activity, learning, motor control, motivational behavior, emotion, and executive function. Concentrations of glutamine (a precursor of glutamate and aspartate), branched-chain AAs (precursors of glutamate, glutamine and aspartate), L-serine (a precursor of glycine and D-serine), methionine and phenylalanine in plasma are capable of affecting neurotransmission through the syntheses of glutamate, aspartate, and glycine, as well as the competitive transport of tryptophan and tyrosine across from the blood-brain barrier. Adequate consumption of AAs is crucial to maintain their concentrations and the production of neurotransmitters in the central nervous system. Thus, the content and balance of AAs in diets have a profound impact on food intake by animals. Knowledge of AA transport and metabolism in the brain is beneficial for improving the health and well-being of humans and animals.

Intermittent Fasting Applied in Combination with Rotenone Treatment Exacerbates Dopamine Neurons Degeneration in Mice

Intermittent fasting (IF) was suggested to be a powerful nutritional strategy to prevent the onset of age-related neurodegenerative diseases associated with compromised brain bioenergetics. Whether the application of IF in combination with a mitochondrial insult could buffer the neurodegenerative process has never been explored yet. Herein, we defined the effects of IF in C57BL/6J mice treated once per 24 h with rotenone (Rot) for 28 days. Rot is a neurotoxin that inhibits the mitochondrial complex I and causes dopamine neurons degeneration, thus reproducing the neurodegenerative process observed in Parkinson's disease (PD). IF (24 h alternate-day fasting) was applied alone or in concomitance with Rot treatment (Rot/IF). IF and Rot/IF groups showed the same degree of weight loss when compared to control and Rot groups. An accelerating rotarod test revealed that only Rot/IF mice have a decreased ability to sustain the test at the higher speeds. Rot/IF group showed a more marked decrease of dopaminergic neurons and increase in alpha-synuclein (α-syn) accumulation with respect to Rot group in the substantia nigra (SN). Through lipidomics and metabolomics analyses, we found that in the SN of Rot/IF mice a significant elevation of excitatory amino acids, inflammatory lysophospholipids and sphingolipids occurred. Collectively, our data suggest that, when applied in combination with neurotoxin exposure, IF does not exert neuroprotective effects but rather exacerbate neuronal death by increasing the levels of excitatory amino acids and inflammatory lipids in association with altered brain membrane composition.

NMR-Based Metabolic Profiling Reveals Neurochemical Alterations in the Brain of Rats Treated with Sorafenib

Sorafenib, an active multi-kinase inhibitor, has been widely used as a chemotherapy drug to treat advanced clear-cell renal cell carcinoma patients. In spite of the relative safety, sorafenib has been shown to exert a negative impact on cognitive functioning in cancer patients, specifically on learning and memory; however, the underlying mechanism remains unclear. In this study, an NMR-based metabolomics approach was applied to investigate the neurochemical effects of sorafenib in rats. Male rats were once daily administrated with 120 mg/kg sorafenib by gavage for 3, 7, and 28 days, respectively. NMR-based metabolomics coupled with histopathology examinations for hippocampus, prefrontal cortex (PFC), and striatum were performed. The (1)H NMR spectra data were analyzed by using multivariate pattern recognition techniques to show the time-dependent biochemical variations induced by sorafenib. Excellent separation was obtained and distinguishing metabolites were observed between sorafenib-treated and control rats. A total of 36 differential metabolites in hippocampus of rats treated with sorafenib were identified, some of which were significantly changed. Furthermore, these modified metabolites mainly reflected the disturbances in neurotransmitters, energy metabolism, membrane, and amino acids. However, only a few metabolites in PFC and striatum were altered by sorafenib. Additionally, no apparent histological changes in these three brain regions were observed in sorafenib-treated rats. Together, our findings demonstrate the disturbed metabonomics pathways, especially, in hippocampus, which may underlie the sorafenib-induced cognitive deficits in patients. This work also shows the advantage of NMR-based metabolomics over traditional approach on the study of biochemical effects of drugs.

Maintaining the presynaptic glutamate supply for excitatory neurotransmission

Glutamate released from synapses during excitatory neurotransmission must be rapidly recycled to maintain neuronal communication. This review evaluates data from physiological experiments at hippocampal CA3 to CA1 synapses and the calyx of Held synapse in the brainstem to analyze quantitatively the rates of release and resupply of glutamate required to sustain neurotransmission. We calculate that, without efficient recycling, the presynaptic glutamate supply will be exhausted within about a minute of normal synaptic activity. We also discuss replenishment of the presynaptic pool by diffusion from the soma, direct uptake of glutamate back into the presynaptic terminal, and uptake of glutamate precursor molecules. Diffusion of glutamate from the soma is calculated to be fast enough to resupply presynaptic glutamate in the hippocampus but not at the calyx of Held. However, because the somatic cytoplasm will also quickly run out of glutamate and synapses can function continually even if the presynaptic axon is severed, mechanisms other than diffusion must be present to resupply glutamate for release. Direct presynaptic uptake of glutamate is not present at the calyx of Held but may play a role in glutamate recycling in the hippocampus. Alternatively, glutamine or tricarboxylic acid cycle intermediates released from glia can serve as a precursor for glutamate in synaptic terminals, and we calculate that the magnitude of presynaptic glutamine uptake is sufficient to supply enough glutamate to sustain neurotransmission. The nature of these mechanisms, their relative abundance, and the co-ordination between them remain areas of intensive investigation.

Distribution of immunoreactive glutamine synthetase in the adult human and mouse brain. Qualitative and quantitative observations with special emphasis on extra-astroglial protein localization

Glutamine synthetase catalyzes the ATP-dependent condensation of ammonia and glutamate to form glutamine, thus playing a pivotal role in glutamate and glutamine homoeostasis. Despite a plethora of studies on this enzyme, knowledge about the regional and cellular distribution of this enzyme in human brain is still fragmentary. Therefore, we mapped fourteen post-mortem brains of psychically healthy individuals for the distribution of the glutamine synthetase immunoreactive protein. It was found that glutamine synthetase immunoreactivity is expressed in multiple gray and white matter astrocytes, but also in oligodendrocytes, ependymal cells and certain neurons. Since a possible extra-astrocytic expression of glutamine synthetase is highly controversial, we paid special attention to its appearance in oligodendrocytes and neurons. By double immunolabeling of mouse brain slices and cultured mouse brain cells for glutamine synthetase and cell-type-specific markers we provide evidence that besides astrocytes subpopulations of oligodendrocytes, microglial cells and neurons express glutamine synthetase. Moreover, we show that glutamine synthetase-immunopositive neurons are not randomly distributed throughout human and mouse brain, but represent a subpopulation of nitrergic (i.e. neuronal nitric oxide synthase expressing) neurons. Possible functional implications of an extra-astrocytic localization of glutamine synthetase are discussed.

Mixed neurotransmission in the hippocampal mossy fibers

The hippocampal mossy fibers (MFs), the axons of the granule cells (GCs) of the dentate gyrus, innervate mossy cells and interneurons in the hilus on their way to CA3 where they innervate interneurons and pyramidal cells. Synapses on each target cell have distinct anatomical and functional characteristics. In recent years, the paradigmatic view of the MF synapses being only glutamatergic and, thus, excitatory has been questioned. Several laboratories have provided data supporting the hypothesis that the MFs can transiently release GABA during development and, in the adult, after periods of enhanced excitability. This transient glutamate-GABA co-transmission coincides with the transient up-regulation of the machinery for the synthesis and release of GABA in the glutamatergic GCs. Although some investigators have deemed this evidence controversial, new data has appeared with direct evidence of co-release of glutamate and GABA from single, identified MF boutons. However, this must still be confirmed by other groups and with other methodologies. A second, intriguing observation is that MF activation produced fast spikelets followed by excitatory postsynaptic potentials in a number of pyramidal cells, which, unlike the spikelets, underwent frequency potentiation and were strongly depressed by activation of metabotropic glutamate receptors. The spikelets persisted during blockade of chemical transmission and were suppressed by the gap junction blocker carbenoxolone. These data are consistent with the hypothesis of mixed electrical-chemical synapses between MFs and some pyramidal cells. Dye coupling between these types of principal cells and ultrastructural studies showing the co-existence of AMPA receptors and connexin 36 in this synapse corroborate their presence. A deeper consideration of mixed neurotransmission taking place in this synapse may expand our search and understanding of communication channels between different regions of the mammalian CNS.

A comparative study of the effect of diet and soda carbonated drinks on the histology of the cerebellum of adult female albino Wistar rats

BACKGROUND

Carbonated drinks are widely consumed because of their taste and their ability to refresh and quench thirst. These carbonated drinks also exist in the form of diet drinks, for example Diet Coke®, Pepsi®, extra.

OBJECTIVES

A comparative effect of the diet and regular soda carbonated drinks on the histology of the cerebellum of female albino Wistar rats was investigated.

METHODS

Fifteen adult female Wistar rats weighing between 180-200 g were divided into 3 groups; designated as groups A, B and C, and each group consisted of five rats. Group A was the Control group and received distilled water, while groups B and C were the experimental groups. Group B was administered 50 ml of regular soda (RS), and group C was administered 50 ml of diet soda (DS) each per day for 21 days, and the rats were sacrificed on Day 22, and their cerebellums excised and preserved.

RESULTS

Histological result of the sections of the cerebellum showed shrunken and degenerated Purkinje cells with hypertrophied dendrites, especially in the DS group, which was less in the RS group compared to the control group.

CONCLUSION

These results suggest that diet soda has adverse effect on the cerebellum of adult female albino Wistar rats.

Vesicular uptake and exocytosis of L-aspartate is independent of sialin

The mechanism of release and the role of l-aspartate as a central neurotransmitter are controversial. A vesicular release mechanism for l-aspartate has been difficult to prove, as no vesicular l-aspartate transporter was identified until it was found that sialin could transport l-aspartate and l-glutamate when reconstituted into liposomes. We sought to clarify the release mechanism of l-aspartate and the role of sialin in this process by combining l-aspartate uptake studies in isolated synaptic vesicles with immunocyotchemical investigations of hippocampal slices. We found that radiolabeled l-aspartate was taken up into synaptic vesicles. The vesicular l-aspartate uptake, relative to the l-glutamate uptake, was twice as high in the hippocampus as in the whole brain, the striatum, and the entorhinal and frontal cortices and was not inhibited by l-glutamate. We further show that sialin is not essential for exocytosis of l-aspartate, as there was no difference in ATP-dependent l-aspartate uptake in synaptic vesicles from sialin-knockout and wild-type mice. In addition, expression of sialin in PC12 cells did not result in significant vesicle uptake of l-aspartate, and depolarization-induced depletion of l-aspartate from hippocampal nerve terminals was similar in hippocampal slices from sialin-knockout and wild-type mice. Further, there was no evidence for nonvesicular release of l-aspartate via volume-regulated anion channels or plasma membrane excitatory amino acid transporters. This suggests that l-aspartate is exocytotically released from nerve terminals after vesicular accumulation by a transporter other than sialin.

Effect of parenteral l-alanyl-l-glutamine administration on phagocytic responses of polymorphonuclear neutrophilic leukocytes in dogs undergoing high-dose methylprednisolone sodium succinate treatment

OBJECTIVE

To determine whether parenteral l-alanyl-l-glutamine (Ala-Gln) administration modulated phagocytic responses of polymorphonuclear neutrophilic leukocytes (PMNs) from dogs undergoing high-dose methylprednisolone sodium succinate (MPSS) treatment.

ANIMALS

15 healthy Beagles.

PROCEDURES

Dogs were randomly assigned to 3 treatment groups (n = 5/group): 38-hour IV infusion of saline (0.9% NaCl) solution (control group), saline solution with 8.5% amino acids (2.3 g/kg/d), or saline solution with 8.5% amino acids (1.8 g/kg/d) and 20% l-alanyl-l-glutamine (Ala-Gln; 0.5 g/kg/d). High-dose MPSS treatment was initiated at the same time that IV infusions began, such that a total dose of 85 mg of MPSS/kg was administered through multiple IV injections over a 26-hour period. The infusions were maintained until 12 hours after the last MPSS injection. Blood samples collected before MPSS injections began and 2, 12, and 24 hours after injections ceased were used to evaluate PMN function.

RESULTS

MPSS injections resulted in an increase in the total number of circulating leukocytes and increases in neutrophil and monocyte counts but did not affect lymphocyte, eosinophil, or basophil counts. Lymphocyte counts in the Ala-Gln group were higher than in the control group 12 hours after MPSS injections finished. Relative to preinfusion values, phagocytic capacity, oxidative burst activity, and filamentous actin polymerization of PMNs were suppressed in all dogs except those that received Ala-Gln.

CONCLUSIONS AND CLINICAL RELEVANCE

Parenteral Ala-Gln administration in dogs resulted in an increase in PMN phagocytic responses that were suppressed by high-dose MPSS treatment.

Inhibition of NMDA-type glutamate receptors induces arousal from torpor in hibernating arctic ground squirrels (Urocitellus parryii)

Hibernation is an adaptation to overcome periods of resource limitation often associated with extreme climatic conditions. The hibernation season consists of prolonged bouts of torpor that are interrupted by brief interbout arousals. Physiological mechanisms regulating spontaneous arousals are poorly understood, but may be related to a need for gluconeogenesis or elimination of metabolic wastes. Glutamate is derived from glutamine through the glutamate-glutamine cycle and from glucose via the pyruvate carboxylase pathway when nitrogen balance favors formation of glutamine. This study tests the hypothesis that activation of NMDA-type glutamate receptors (NMDAR) maintains torpor in arctic ground squirrel (arctic ground squirrel (AGS); Urocitellus parryii). Administration of NMDAR antagonists MK-801 (5 mg/kg, i.p.) that crosses the blood-brain barrier and AP5 (5 mg/kg, i.p.) that does not cross the blood-brain barrier induced arousal in AGS. Central administration of MK-801 (0.2, 2, 20 or 200 μg; icv) to hibernating AGS failed to induce arousal. Results suggest that activation of NMDAR at a peripheral or circumventricular site is necessary to maintain prolonged torpor and that a decrease in glutamate at these sites may contribute to spontaneous arousal in AGS.

¹H NMR-based metabonomics in brain nucleus accumbens and striatum following repeated cocaine treatment in rats

Studies have shown a few cerebral metabolites modified by cocaine in brain regions; however, endogenous metabolic profiling has been lacking. Ex vivo (1)H NMR (hydrogen-1 nuclear magnetic resonance) spectroscopy-based metabonomic approach coupled with partial least squares was applied to investigate the changes of cerebral metabolites in nucleus accumbens (NAc) and striatum of rats subjected to cocaine treatment. Our results showed that both single and repeated cocaine treatment can induce significant changes in a couple of cerebral metabolites. The increase of neurotransmitters glutamate and gamma-amino butyric acid (GABA) were observed in NAc and striatum from the rats repeatedly treated with cocaine. Creatine and taurine increased in NAc whereas taurine increased and creatine decreased in striatum after repeated cocaine treatment. Elevation of N-acetylaspartate in NAc and striatum and decrease of lactate in striatum were observed, which may reflect the mitochondria dysregulation caused by cocaine; moreover, alterations of choline, phosphocholine and glycerol in NAc and striatum could be related to membrane disruption. Moreover, groups of rats with and without conditioned place preference (CPP) apparatus are presenting difference in metabolites. Collectively, our results provide the first evidence of metabonomic profiling of NAc and striatum in response to cocaine, exhibiting a regionally-specific alteration patterns. We find that repeated cocaine administration leads to significant metabolite alterations, which are involved in neurotransmitter disturbance, oxidative stress, mitochondria dysregulation and membrane disruption in brain.

Roles of glutamine in neurotransmission

Glutamine (Gln) is found abundantly in the central nervous system (CNS) where it participates in a variety of metabolic pathways. Its major role in the brain is that of a precursor of the neurotransmitter amino acids: the excitatory amino acids, glutamate (Glu) and aspartate (Asp), and the inhibitory amino acid, γ-amino butyric acid (GABA). The precursor-product relationship between Gln and Glu/GABA in the brain relates to the intercellular compartmentalization of the Gln/Glu(GABA) cycle (GGC). Gln is synthesized from Glu and ammonia in astrocytes, in a reaction catalyzed by Gln synthetase (GS), which, in the CNS, is almost exclusively located in astrocytes (Martinez-Hernandez et al., 1977). Newly synthesized Gln is transferred to neurons and hydrolyzed by phosphate-activated glutaminase (PAG) to give rise to Glu, a portion of which may be decarboxylated to GABA or transaminated to Asp. There is a rich body of evidence which indicates that a significant proportion of the Glu, Asp and GABA derived from Gln feed the synaptic, neurotransmitter pools of the amino acids. Depolarization-induced-, calcium- and PAG activity-dependent releases of Gln-derived Glu, GABA and Asp have been observed in CNS preparations in vitro and in the brain in situ. Immunocytochemical studies in brain slices have documented Gln transfer from astrocytes to neurons as well as the location of Gln-derived Glu, GABA and Asp in the synaptic terminals. Patch-clamp studies in brain slices and astrocyte/neuron co-cultures have provided functional evidence that uninterrupted Gln synthesis in astrocytes and its transport to neurons, as mediated by specific carriers, promotes glutamatergic and GABA-ergic transmission. Gln entry into the neuronal compartment is facilitated by its abundance in the extracellular spaces relative to other amino acids. Gln also appears to affect neurotransmission directly by interacting with the NMDA class of Glu receptors. Transmission may also be modulated by alterations in cell membrane polarity related to the electrogenic nature of Gln transport or to uncoupled ion conductances in the neuronal or glial cell membranes elicited by Gln transporters. In addition, Gln appears to modulate the synthesis of the gaseous messenger, nitric oxide (NO), by controlling the supply to the cells of its precursor, arginine. Disturbances of Gln metabolism and/or transport contribute to changes in Glu-ergic or GABA-ergic transmission associated with different pathological conditions of the brain, which are best recognized in epilepsy, hepatic encephalopathy and manganese encephalopathy.

Glutamate receptor GRIA3--target of CUX1 and mediator of tumor progression in pancreatic cancer

Previously, we identified the transcription factor CUX1 as an important modulator of invasion and resistance to apoptosis. Expression profiles suggested that CUX1 regulates a complex transcriptional program mediating tumor progression. We aimed to identify functionally relevant targets of CUX1 by using RNA interference (RNAi)-based loss-of-function screens. Therefore, we generated an RNAi library containing putative transcriptional targets of CUX1 identified by microarrays and performed cell viability screens. Using this approach, several CUX1 targets with effect on tumor cell viability were identified, including the glutamate receptor GRIA3, which was validated in detail for its effects on proliferation, apoptosis, and cell migration using RNAi knock-down and overexpression strategies in vitro, as well as xenograft models in vivo. The expression of GRIA3 was evaluated in human pancreatic cancer tissues. We found that knock-down of GRIA3 significantly reduced proliferation and migration and enhanced apoptosis. In contrast, overexpression of GRIA3 significantly reduced apoptosis and enhanced both proliferation and tumor cell migration. GRIA3 could be confirmed as a downstream effector of CUX1 and was expressed in pancreatic cancer tissues. In vivo, GRIA3 significantly enhanced the growth of subcutaneous xenografts. Inhibitors of glutamate receptors such as GYKI52466 and SYM2206 significantly decreased survival of pancreatic cancer cells, suggesting the presence of glutamate signaling in pancreatic cancer. In conclusion, GRIA3 plays a role as a mediator of tumor progression in pancreatic cancer downstream CUX1. To our knowledge, this is the first report to identify a glutamate receptor as a modulator of tumor progression in a solid cancer outside the brain.

Zinc and glutamine improve brain development in suckling mice subjected to early postnatal malnutrition

OBJECTIVE

The effect of zinc and glutamine on brain development was investigated during the lactation period in Swiss mice.

METHODS

Malnutrition was induced by clustering the litter size from 6-7 pups/dam (nourished control) to 12-14 pups/dam (undernourished control) following birth. Undernourished groups received daily supplementation with glutamine by subcutaneous injections starting at day 2 and continuing until day 14. Glutamine (100 mM, 40-80 microL) was used for morphological and behavioral studies. Zinc acetate was added in the drinking water (500 mg/L) to the lactating dams. Synaptophysin and myelin basic protein brain expressions were evaluated by immunoblot. Zinc serum and brain levels and hippocampal neurotransmitters were also evaluated.

RESULTS

Zinc with or without glutamine improved weight gain as compared to untreated, undernourished controls. In addition, zinc supplementation improved cliff avoidance and head position during swim behaviors especially on days 9 and 10. Using design-based stereological methods, we found a significant increase in the volume of CA1 neuronal cells in undernourished control mice, which was not seen in mice receiving zinc or glutamine alone or in combination. Undernourished mice given glutamine showed increased CA1 layer volume as compared with the other groups, consistent with the trend toward increased number of neurons. Brain zinc levels were increased in the nourished and undernourished-glutamine treated mice as compared to the undernourished controls on day 7. Undernourished glutamine-treated mice showed increased hippocampal gamma-aminobutyric acid and synaptophysin levels on day 14.

CONCLUSION

We conclude that glutamine or zinc protects against malnutrition-induced brain developmental impairments.

SAT1, A Glutamine Transporter, is Preferentially Expressed in GABAergic Neurons

Subsets of GABAergic neurons are able to maintain high frequency discharge patterns, which requires efficient replenishment of the releasable pool of GABA. Although glutamine is considered a preferred precursor of GABA, the identity of transporters involved in glutamine uptake by GABAergic neurons remains elusive. Molecular analyses revealed that SAT1 (Slc38a1) features system A characteristics with a preferential affinity for glutamine, and that SAT1 mRNA expression is associated with GABAergic neurons. By generating specific antibodies against SAT1 we show that this glutamine carrier is particularly enriched in GABAergic neurons. Cellular SAT1 distribution resembles that of GAD67, an essential GABA synthesis enzyme, suggesting that SAT1 can be involved in translocating glutamine into GABAergic neurons to facilitate inhibitory neurotransmitter generation.

Immunogold quantification of amino acids and proteins in complex subcellular compartments

An increasing number of imaging techniques are in use to study the localization of molecules involved in cell-to-cell signaling. Here we describe the use of immunogold procedures to detect and quantify molecules on electron micrographs. To measure the areas of the subcellular compartments under investigation, the protocol uses an overlay screen with an array of regularly spaced points. On the basis of this, the densities of the gold-labeled molecules can be calculated. Despite the limited lateral resolution of the immunogold method as used by many investigators ( approximately 30 nm), it is possible to measure the content of molecules associated with tiny tissue compartments, e.g., synaptic vesicles and different types of membrane, such as plasma membranes and vesicle membranes. The quantification protocol can be carried out without using computer programs. The entire protocol can be completed in approximately 15 d.