Release of glutamate and GABA in the hippocampus under zinc deficiency

Zinc homeostasis in the brain is affected by dietary zinc deficiency, and its alteration may cause brain dysfunctions. On the basis of the previous evidence that hippocampal zinc was responsive to 12-week zinc deprivation, responsiveness of hippocampal zinc to dietary zinc deficiency was examined in rats fed a zinc-deficient diet for 4 weeks. Zinc concentration in the hippocampus was not decreased by zinc deprivation for 4 weeks. However, Timm's stain was extensively attenuated in the brain of the zinc-deficient rats. In the brain of the zinc-deficient rats, moreover, zinc concentration in the hippocampal extracellular fluid was approximately 30% of that of control rats. These results demonstrate that vesicular zinc is responsive to dietary zinc and may decrease easily under zinc deficiency. Zinc concentration in the hippocampal extracellular fluid during stimulation with high K(+) was significantly increased even in zinc-deficient rats, although the increased levels of zinc were lower than the basal levels of zinc in control rats. The basal glutamate concentration in the hippocampal extracellular fluid was not significantly different between the control and zinc-deficient rats. However, glutamate concentration in the hippocampal extracellular fluid during stimulation with high K(+) was more increased in the zinc-deficient rats than in the control rats. Gamma aminobutyric acid (GABA) concentration in the hippocampal extracellular fluid during stimulation with high K(+) was increased in the control rats, but not in the zinc-deficient rats. The present study suggests that the excitability of hippocampal glutamatergic neurons is enhanced by dietary zinc deficiency.     

Immunocytochemical localization of glutaminase-like and aspartate aminotransferase-like immunoreactivities in the rat and guinea pig hippocampus

There is considerable evidence that pathways of the hippocampus use an excitatory amino acids as transmitter. We have attempted to immunocytochemically identify excitatory amino acid neurons in the hippocampus of the rat and guinea pig using antiserum to glutaminase and antiserum to aspartate aminotransferase, which have been proposed as markers for aspartergic/glutamergic neurons. Glutaminase-like immunoreactivity was seen in granule cells in the dentate gyrus and fibers and puncta associated with the mossy fiber pathway in the hilus and stratum lucidum of the hippocampus. At the ultrastructural level, glutaminase-like immunoreactivity was observed in mossy fiber terminals in the stratum lucidum. Glutaminase-like immunoreactivity was also seen in pyramidal cells in regio inferior and regio superior and in cells in layer two of the entorhinal cortex. Schaffer collateral terminals, commissural fiber terminals and perforant pathway terminals were not seen at the light microscopic level. Glutaminase-like immunoreactivity is thus found in the cell bodies of proposed excitatory amino acid neurons of hippocampal pathways, but does not appear to label all terminals. Aspartate aminotransferase-like immunoreactivity was not seen in any cells, fibers or terminals in the rat or guinea pig hippocampus.     

Differential effects of zinc on glutamatergic and GABAergic neurotransmitter systems in the hippocampus

Approximately 10% of total zinc in the brain exists in synaptic vesicles of glutamatergic neurons; however, the function of vesicular zinc is poorly understood. The presynaptic action of zinc against excitatory and inhibitory neurotransmission was studied in rat hippocampus using in vivo microdialysis. When the hippocampal CA3 region was perfused with 10-300 microM ZnCl(2), the level of glutamate in the perfusate was decreased, whereas the level of gamma-aminobutyric acid (GABA) was increased. Chelation of endogenous zinc with CaEDTA increased the glutamate level in the perfusate but decreased the GABA level, suggesting that zinc released into the synaptic cleft acts differentially on glutamatergic and GABAergic neurons in the CA3 region. The increase of GABA level by zinc was antagonized by 2,3-dioxo-6-nitro-1,2.3,4-tetrahydrobenzo(f)quinoxaline-7-sulphonamide (NBQX), an antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors, but not affected by MK801, an antagonist of N-methyl-D-aspartate (NMDA) receptors, and verapamil, a blocker of voltage-dependent calcium channels. The present study suggests that zinc enhances GABA release via potentiation of AMPA/kainate receptors in the CA3 region, followed by a decrease in presynaptic glutamate release in the same region. Zinc seems to be an inhibitory neuromodulator of glutamate release.     

The effects of iron deficiency and iron and zinc supplementation on rat hippocampus ferritin

Summary. Iron deficiency (ID), the most prevalent nutritional disorder in the world, impairs cognition in early development. The involvement of hippocampus in cognition has prompted investigation into distribution of the iron storage protein ferritin (FER) in rat hippocampus. (a) In normal rats, FER positive cells appeared first in lateral CA3 and hilus of dentate gyrus and then spread over the entire mossy fiber (MF) system. No such spread was observed in CA1 field. (b) Nutritional iron deficiency retarded development of FER in the MF system. No change in FER was observed in CA1 field. (c) Zinc distribution can be altered by iron deficiency. Thus, the effect of zinc added to iron supplementation was tested in iron-deficient rats. Significant FER recovery was observed only in hippocampal MF of rats receiving both zinc and iron. It is apparent that for accelerating recovery of hippocampal function in iron deficiency, both zinc and iron are required. Received July 11, 2001; accepted January 23, 2002 Published online June 28, 2002     

AMPA-selective glutamate receptor subunits in the rat hippocampus during aging

The levels of mRNAs for the subunits of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-selective glutamate receptors (GluR-1, -2, -3, -4) in the rat hippocampus during aging were measured by Northern blotting. The distribution of these receptors was also examined at the protein level by immunoblotting using antibodies to GluR-1 and to an epitope common to GluR-2 and GluR-3 (denoted GluR-2/3). During aging a significant decrease of GluR-1 protein, but no change in the corresponding mRNA level, was observed. No differences in the level of GluR-2/3 protein and GluR-2, -3, and -4 mRNAs at the various ages examined (4, 12, and 24 months) were detected. Our results show that AMPA receptors are only slightly influenced by the aging process in the rat hippocampus. The slight decrease in GluR-1 protein content, not accompanied by a parallel decrease in the GluR-1 mRNA level, might be explained by a decreased translational efficiency or an increased protein degradation of the GluR-1 subunit. © 1995 Wiley-Liss, Inc.     

Cytoarchitectonic distribution of zinc in the hippocampus of man and the rat

Zinc was measured in whole hippocampus and in hippocampal sub-regions by stable-isotope dilution mass spectrometry. In both man and the rat, the most zinc (102–145 ppm, dry weight) was found in the hilar region, the least (27–37) in the fimbria. The amount of zinc directly associated with mossy-fiber axons was estimated to be approximately 8% of the total zinc in the hippocampus, and the concentration of mossy-fiber zinc was estimated at 220–300 μM. Methodological and theoretical implications of the quantitative findings were discussed.     

Dual effect of glutamate and aspartate on the on-center bipolar cell in the carp retina

In on-center bipolar cells of the carp retina, glutamate and aspartate applied extracellularly by pressure injection produced hyperpolarizing potential changes. These responses were not blocked by Co²⁺. Examination of reversal potentials revealed two different conductance changes. One of them appears to be an increase in K⁺ and/or Cl⁻ conductance and other a decrease in Na⁺ conductance. The results are discussed with relation to the difference in ionic mechanisms of cone and rod inputs.     

Effects of kainic acid injection and cortical lesion on ornithine and aspartate aminotransferases in rat striatum

The effects of cortical lesions and intrastriatal kainic acid injections on various striatal enzyme activities were investigated. Ornithine aminotransferase decreased concomitantly with glutamate uptake in decorticated and chronic kainic acid-treated rats. It was also decreased in acute kainic acid-lesioned striatum where glutamate uptake was unaffected. Aspartate aminotransferase, however, decreased only after acute kainic acid treatment. Results for glutamate uptake, glutamate decarboxylase, and choline acetyltransferase were in agreement with previous findings. These results suggest that ornithine may act as a precursor for glutamate in nerve terminals, although the nonspecific localization does not allow ornithine aminotransferase to be a convenient biochemical marker. The decrease in aspartate aminotransferase is thought to be due to the widespread cell degeneration after acute kainic acid. Aspartate aminotransferase activities were also found to be reduced in the frontal cortex, caudate nucleus and putamen of Huntington's disease brains.     

Autoradiographic demonstration of glutamate structures after stereotaxic injection of kainic acid in rat hippocampus

Autoradiography of high affinity uptake ofl-glutamate in rat hippocampus after kainic acid lesion of CA3 and CA4 pyramidal cells has been used to identify the neurotransmitter of their ipsilateral connections. Glutamate or aspartate has tentatively been identified as the neurotransmitter of the projection from CA3 pyramidal cells to strata radiatum and oriens of CA1 and the projection from CA4 pyramidal cells to the inner parts of the molecular layer of area dentata.     

Stable-isotope dilution measurement of zinc and lead in rat hippocampus and spinal cord

Zinc and lead concentrations in hippocampus and spinal cord of rats were measured using the highly-accurate method of stable isotope dilution mass-spectrometry. In hippocampus, average zinc concentration was 72.7 ppm (dry weight), average lead, 0.053 ppm; in spinal cord, zinc averaged 26.1 ppm, lead, 0.018 ppm. Possible explanations for apparent overestimations of rat CNS metal content in previously publisjed work were discussed.     

Desentization to glutamate and aspartate in rat olfactory (prepyriform) cortex slice

Olfactory cortex brain slices were subject to multiple bath applications of either glutamate or aspartate. The effectiveness of these amino acids (measured by quantitating the amplitude of lateral olfactory tract-stimulated field potentials) was progressively reduced with each successive perfusion of the agonist. However, the effectiveness of the endogenous neurotransmitter recovered to control in each intervening wash period. Thus, repeated applications of glutamate or aspartate desensitized olfactory cortex receptors to these amino acids but did not desensitize the receptors to the endogenous transmitter. These data support the hypothesis that neither glutamate nor aspartate is the neurotransmitter released from the lateral olfactory tract onto pyramidal cells of the olfactory cortex.     

Desensitization to glutamate does not affect synaptic transmission in rat hippocampal slices

Response of lamina V medullary dorsal horn neurons to noxious thermal and noxious mechanical facial stimuli were challenged with iontophoretically applied cis-2,3-piperidine dicarboxylic acid, a broad spectrum excitatory amino acid antagonist. This antagonist reduced neuronal responses to noxious mechanical stimuli but not responses to noxious thermal stimuli. These results suggest that different neural mechanisms underlie the responses of lamina V neurons to different noxious stimuli, and that responses to noxious mechanical stimuli appear to involve excitatory amino acid receptors.     

Intracellularly-recorded effects of glutamate and aspartate on neurones in the guinea-pig olfactory cortex slice

The effects of bath-applied glutamate, aspartate (and some related amino acids) on neurones of the guinea pig olfactory cortex slice were recorded intracellularly. Neurones were activated either by intracellularly-applied current or orthodromically by stimulating the lateral olfactory tract. In response to orthodromic stimuli several neurones displayed a late hyperpolarizing potential (LHP) after the usual sequence of EPSP, spike and IPSP. Glutamate and aspartate evoked 3 types of response: (a) a depolarization with apparent increase in input conductance; (b) a depolarization with no detectable conductance change; and (c) a hyperpolarization with conductance increase. Some possible mechanisms by which these 3 response-types could be generated are discussed. Depolarizations evoked by the glutamate analogue, kainate, were usually irreversible. Our results emphasize that glutamate and aspartate can evoke a variety of neuronal responses from olfactory cortex neurones. Several of these responses were previously undetected in experiments based on extracellular recordings.     

海藻氨酸致癎大鼠中海马谷氨酸转运体功能的研究

目的　研究海藻氨酸(KA)致疒间大鼠海马谷氨酸转运体(GluTs)功能的变化,进一步探讨GluTs 参与癫疒间发生的机制。方法　60只Wistar大鼠随机分为KA组和对照组,每组再按点燃后4h、24h、48h、5 d、7d不同时点随机分为5个亚组,分别测定不同时点海马突触颗粒和海马组织切片对3H L 谷氨酸的摄取 量,观察GluTs于点燃后不同时点的活性。结果　KA组点燃后海马突触颗粒GluTs功能在各时点均降低(均 P<0.01),海马组织切片GluTs功能在点燃后初期上升而后下降(P<0.05)。结论　KA可引起海马GluTs 功能的变化,其可能与癫疒间的发生及易感性的形成有关。     

Effects of secretin on extracellular amino acid concentrations in rat hippocampus

Summary. In 1998, Horvath et al. (1998) observed a marked improvement in speech, eye contact, and attention in autistic children five weeks after treatment with secretin, which ocurred in the course of an endoscopic investigation. Since autism is hypothesized to be a hypoglutamatergic disorder we investigated the in vivo effects of secretin on extracellular amino acids in the rat brain. Studies were carried out on freely moving rats with microdialysis probes in the hippocampus. Amino acids were examined using tandem mass spectroscopy and HPLC/fluorometric detection. Following secretin injection (8.7µg/kg i.p.), considerable increases in microdialysate glutamate and gamma-aminobutyric acid (GABA) levels were observed; other amino acids were not affected. The observed increased microdialysate concentrations of glutamate and GABA following secretin application may explain the results of the Horvath study.     

Zinc signaling through glucocorticoid and glutamate signaling in stressful circumstances

Humans and animals are constantly exposed to environmental stress. The hypothalamic‐pituitary‐adrenal (HPA) axis responds to stress, followed by glucocorticoid secretion from the adrenal glands. This response serves to maintain homeostasis in the living body through energy mobilization or to restore it. The brain is an important target for glucocorticoids. The hippocampus participates in the regulation of the HPA axis. Stress activates glutamatergic neurons in the hippocampus, and serious stress induces dyshomeostasis of extracellular glutamate. This dyshomeostasis, which is potentiated by glucocorticoids, modifies cognitive and emotional behavior. On the other hand, zinc is necessary for glucocorticoid signaling and is released from glutamatergic (zincergic) neurons to modulate synaptic glutamate signaling. Stress also induces dyshomeostasis of extracellular zinc, which may be linked to dyshomeostasis of extracellular glutamate. Thus, glucocorticoid signaling might also contribute to dyshomeostasis of extracellular zinc. It is likely that zinc signaling participates in cognitive and emotional behavior through glucocorticoid and glutamate signaling under stressful circumstances. This Mini‐Review analyzes the relationship among signals of glucocorticoid, glutamate, and zinc under stressful circumstances to elucidate the significance of the zinc signaling in response to stress. © 2010 Wiley‐Liss, Inc.     

Subtypes of beta-adrenergic receptors in rat cerebral microvessels

The 125I-labeled iodohydroxybenzylpindolol (IHYP) binding to beta-receptors on brain micro-vessels is inhibited by isoproterenol, epinephrine and norepinephrine, with Ki values of 2 X 10(-7) M, 2.5 X 10(-6) M and 1.2 X 10(-5) M, respectively. A modified Scatchard analysis of the inhibitory effects of practolol, metroprolol and zinterol on IHYP binding has shown that the proportion of beta 2-receptors in our preparation is about 80% of the total beta-adrenergic receptor population. Our data indicate that the beta-adrenergic receptors located on cerebral microvessels are of both beta 1 and beta 2 types, with a predominance of the beta 2 type.     

Distribution and stress-induced increase of glutamate and aspartate levels in discrete brain nuclei of rats

Concentrations of glutamate and aspartate have been measured in 45 microdissected brain areas and nuclei in rat. Both amino acids are ubiquitously present and distributed unevenly in the central nervous system. Very high glutamate levels were found in the cerebellum and the insular cortex, high levels in neocortical and limbic cortical areas, and in the nuclei of the medial hypothalamus. Aspartate is distributed rather uniformly with the highest concentration in the hypothalamic arcuate nucleus and the lowest in the midbrain central gray matter and the cerebellum. Acute formalin (pain) stress elevated glutamate and aspartate levels in the cortical areas and substantia nigra significantly, but had minor or no effects on other brain nuclei. Increased locomotor and behavioral activities due to a high dose of amphetamine resulted in a 2-5-fold increase of glutamate and aspartate concentrations, particularly in the biogenic amine-containing brain nuclei.     

Clozapine treatment increases serum glutamate and aspartate compared to conventional neuroleptics

Summary To examine whether serum excitatory amino acid concentrations change with clozapine treatment and whether these changes correlate with improvement in negative symptoms, serum excitatory amino acids were measured and clinical scales administered in seven subjects with schizophrenia before and after switching from conventional neuroleptics to clozapine. Clozapine treatment was associated with increased serum glutamate and aspartate concentrations. Clinical improvement was negatively correlated with baseline glycine concentrations. These results support the hypothesis that clozapine acts at least in part by increasing glutamatergic activity.     

Developmental distribution pattern of metabotropic glutamate receptor 5 in prenatal human hippocampus

Objective Metabotropic glutamate receptor 5(mGluR5) is concentrated in zones of active neurogenesis in the prenatal and postnatal rodent brain and plays an important role in the regulation of neurogenesis.However,little is known about mGluR5 in the prenatal human brain.Here,we aimed to explore the expression pattern and cellular distribution of mGluR5 in human fetal hippocampus.Methods Thirty-four human fetuses were divided into four groups according to gestational age:9-11,14-16,22-24 and 32-36 weeks.The hippocampus was dissected out and prepared.The protein and mRNA expression of mGluR5 were evaluated by Western blot and immunohistoehemistry or real-time PCR.The cellular distribution of mGluR5 was observed with double-labeling immunofluorescence.Results Both mGluR5 mRNA and protein were detected in the prenatal human hippocampus by real-time PCR and immunoblotting,and the expression levels increased gradually over time.The immunohistochemistry results were consistent with immunoblotting and showed that mGluR5 immunoreactivity was mainly present in the inner marginal zone(IMZ),hippocampal plate(HP) and ventricular zone(VZ).The double-labeling immunofluorescence showed that mGluR5 was present in neural stem cells (nestin-positive),neuroblasts(DCX-positive) and mature neurons(NeuN-positive),but not in typical astrocytes(GFAPpositive). The cells co-expressing mGluR5 and nestin were mainly located in the IMZ,HP and subplate at 11 weeks,all layers at 16 weeks,and CA1 at 24 weeks.As development proceeded,the number of mGluR5/nestin double-positive cells decreased gradually so that there were only a handful of double-labeled cells at 32 weeks.However,mGluR5/DCX double-positive cells were only found in the HP,IZ and IMZ at 11 weeks.Conclusion The pattern of mGluR5 expression by neural stem/progenitor cells,neuroblasts and neurons provides important anatomical evidence for the role of mGIuR5 in the regulation of human hippocampal development.