Glutamate (Glu) is the major afferent excitatory neurotransmitter in the auditory system, and excessive Glu may play an important role in cochlear dysfunction. It is unclear how excessive Glu plays roles in cochlear dysfunction in cochlear organotypic cultures. In this study neonatal rat cochlear organotypic cultures were prepared, and then the cochlear tissues were incubated with a new medium containing specific concentrations of Glu (0.1, 0.5, 1, 10 or 20 mmol/L) for 24 h, or incubated with the medium containing a concentration of 20 mmol/L Glu for 6, 12, 24 or 72 h, respectively. It was found that when the cochlear tissues were cultured for 24 h, the inner hair cells (IHCs) were damaged at the concentration of 0.5 mmol/L Glu, and with the increases of the concentrations, the injury was gradually aggravated, and 20 mmol/L Glu resulted in the significant loss of IHCs. In the 20 mmol/L Glu groups, the stereocilia bundles were missing or disarrayed on a few IHCs after culture for 6 h and the damage effect was time-dependent. The missing of IHCs was more significant in the basal turn of the cochlea than in the middle turn of the cochlea under the same concentration of Glu exposure. These results suggest that excessive exogenous Glu affects the morphology of IHCs, but not affects the outer hair cells (OHCs) in cochlear organotypic cultures, and the excitotoxic effects are different on IHCs of different parts of the cochlea under the same concentration of Glu exposure.
Animals ; Cochlea ; drug effects ; Dose-Response Relationship, Drug ; Glutamic Acid ; toxicity ; Rats ; Rats, Sprague-Dawley

Animals ; Glutamic Acid ; analysis ; toxicity ; Guinea Pigs ; Microscopy, Immunoelectron ; Vestibule, Labyrinth ; chemistry

We studied the effects of organic and inorganic mercury (Hg) on the uptake of L-[3H] glutamate (L-GLU) in cultured mouse astrocytes. Following exposure to mercuric chloride (MC) [0.2 approximately 5.0 microM], selective and dose-dependent inhibition of L-GLU uptake to 50% of control levels was observed, whereas 2-deoxyglucose (2-DG) uptake was not significantly affected. Methylmercuric chloride (MMC) also inhibited L-GLU uptake but 50% reduction was reached only at a concentration of 10 microM. Inhibition of L-GLU uptake by MMC appears to be closely linked to voltage-sensitive calcium channels as evidenced by the lack of L-GLU uptake inhibition by MMC in calcium-free medium or in the presence of the channel blocker verapamil. Exposure to a variety of divalent metallic ions, including CuCl2, FeCl2 and ZnCl2, did not affect L-GLU uptake in astrocytes in vitro. Exposure to PbCl2, however, resulted in a decline in L-GLU uptake, though to a much smaller degree than that observed with Hg compounds. Selective impairment of astroglial L-GLU transport may represent a critical early pathogenetic feature of Hg-induced neurotoxicity.
Animal ; Astrocytes/*drug effects/metabolism ; Cells, Cultured ; Glutamic Acid/*metabolism ; Mercury/*toxicity ; Mice ; Mice, Inbred C57BL ; Support, U.S. Gov't, P.H.S.

AIMTo investigate the neuroprotective effect of learning on glutamate-induced neuronal damage.

METHODSSD rats were intraperitoneally injected with monosodium glutamate (MSG) during the period of 3-9 days after born, and were trained to find their food by light-dark discrimination at 1 month old or 2 months old. At 3 months old, all rats were killed and their brains were taken out and cut into sections and ultrathin sections. The survival neurons in hippocampus were counted under light microscope, and under electric microscope, the ultrastructure, the numbers of synapses and the length of synaptic active zone in fields CA1 of hippocampus were observed.

RESULTSThe survival neurons in field CA3 and CA4, the number of synapses and the length of synaptic active zone in field CA1 of hippocampus increased in learning group than non-learning group.

CONCLUSIONThese finding indicate that discriminative learning can alleviate neuronal injury of hippocampus induced by MSG.

Animals ; Cell Death ; Glutamic Acid ; toxicity ; Hippocampus ; drug effects ; metabolism ; Learning ; Male ; Rats ; Rats, Sprague-Dawley ; Synapses ; metabolism

Yi-Gan San (YGS), a traditional Chinese medicine for dementia-related symptoms, was previously fractionated. One active fraction, YGS40 exhibited a neuroprotective effect against glutamate-induced cytotoxicity. In the present study, high-performance liquid chromatography, coupled with diode-array detection and quadrupole time-of-flight mass spectrometry, was applied for the identification of its chemical constituents and for quantification studies. The chemical profile of YGS40 consisted of sixty-four identified or tentatively characterized compounds. The levels of the major marker compounds increased significantly in the mixed decoction compared with those in the single plant decoction. The results suggest the high precision of the analyses of most of the constituents in YGS40 and establish the quantitative variations of the major marker compounds between the single and mixed decoction processes.
Chromatography, Liquid ; Cytotoxins ; Drugs, Chinese Herbal ; analysis ; Glutamic Acid ; toxicity ; Mass Spectrometry ; Neuroprotective Agents ; analysis ; therapeutic use

OBJECTIVETo explore the effects of 1,2-dichloroethane (1,2-DCE) on the behavior and the brain neurotransmitter levels in mice.

METHODSThirty mice were randomly divided into four groups, which were control group and groups of low, middle and high exposure (225, 450 and 900 mg/m3) to 1,2-DCE for 10 days (3.5 h a day) by inhalation. After the last exposure, the open field test was performed immediately. After exposure all mice were killed and the brain tissues were taken up rapidly. The levels of aspartate (Asp), glutamate (Glu) and gamma-aminobutyric acid (GABA) in the brain were detected by high performance liquid chromatography (HPLC).

RESULTSLevels of Asp and Glu in all exposure groups increased with doses. As compared to the control group, levels of Glu in all exposure groups increased significantly (P < 0.05). Levels of GABA in the low exposure group were significantly lower than those in control group, but those in the high exposure group were significantly higher than those in control group. The results of the open field test showed that effect of low exposure to 1,2-DCE on the behavior was stimulant, but the high exposure to 1,2-DCE inhibited behavior of exploration, excitement and sport.

CONCLUSIONSSubacute exposure to 1,2-DCE could result in the change of amino acid neurotransmitter content and ratio in the brain, thereby change the behavior of mice appeared, which might be the mechanism of neurotoxicity caused by 1,2-DCE in part.

Animals ; Aspartic Acid ; analysis ; Behavior, Animal ; drug effects ; Brain ; metabolism ; Ethylene Dichlorides ; toxicity ; Female ; Glutamic Acid ; analysis ; Mice ; Mice, Inbred Strains ; Neurotransmitter Agents ; metabolism ; gamma-Aminobutyric Acid ; analysis

OBJECTIVEto investigate the changes of γ-aminobutyric acid (GABA) and glutamate (Glu) in the cerebral cortex following acute bromoxynil intoxication in mice and the protective effect of sodium dimercaptopropane sulfonate (Na-DMPS).

METHODS30 ICR mice were randomly divided into blank control group (10), exposure group (10) and Na-DMPS protection group (10). The levels of GABA and Glu in the cerebral cortex were measured by RP-HPLC. The glutamine (Gln) level and the glutamine synthetase (GS), glutamate decarboxylation enzyme (GAD), γ-aminobutyric acid transaminase (GABA-T) activity in the cerebral cortex were determined by UV colorimetric.

RESULTScompared with the control group [GABA: (3.41 ± 0.12) micromol/g, Glu (14.00 ± 0.16) micromol/g, Gln (1.25 ± 0.19) micromol/g, GAD (13.50 ± 0.25) micromol × g(-1) × h(-1), GABA-T (25.51 ± 0.21) micromol × g(-1) × h(-1), GS(142.19 ± 1.31) U/mg pro], the level of GABA [(3.14 ± 0.14) micromol/g] was decreased (P < 0.05), whereas the level of Glu [(17.54 ± 0.40) micromol/g] and Gln [(3.35 ± 0.27) micromol/g] were increased (P < 0.05), the activity of GAD [(11.93 ± 0.15 micromol × g(-1) × h(-1)], GABA-T [(24.15 ± 0.22) micromol × g(-1) × h(-1)], GS [(140.75 ± 1.01) U/mg pro] was decreased (P < 0.05) in acute intoxication group; Compared with the acute intoxication group, the level of GABA [(3.52 ± 0.30) micromol/g] was increased (P < 0.05), whereas the level of Glu [(14.20 ± 0.32) micromol/g] and Gln [(1.32 ± 0.17) micromol/g] were decreased (P < 0.05), the activity of GAD [(13.01 ± 0.45 micromol × g(-1) × h(-1)], GABA-T [(25.19 ± 0.26) micromol × g(-1) × h(-1), GS [(142.35 ± 1.20) U/mg pro] was increased (P < 0.05); In contrast, the levels of GABA, Glu, Gln and the activity of GAD, GABA-T, and GS in Na-DMPS protection group were not significantly different in comparison with control group (P > 0.05).

CONCLUSIONthe central toxic effects of mice with acute bromoxynil intoxication may be related to the changes of GABA and Glu content in the cerebral cortex;Na-DMPS can protect mice from bromoxynil-induced central toxic effects and GABA and Glu abnormal change in the cerebral cortex.

Animals ; Cerebral Cortex ; drug effects ; metabolism ; Female ; Glutamic Acid ; metabolism ; Male ; Mice ; Mice, Inbred ICR ; Nitriles ; poisoning ; Toxicity Tests, Acute ; Unithiol ; pharmacology ; gamma-Aminobutyric Acid ; metabolism

OBJECTIVETo investigate the spatial learning and exploration along with the CNS excitatory amino acid neurotransmitters profiles in adult rats subchronically exposed to the anticholinesterase organophosphorus insecticide dimethoate.

METHODSRats were gavaged daily with dimethoate (0, 5, 10 or 20 mg/kg via oral) in NS. for 90 days. Morris water maze tasks were used to test the spatial learning and memory in the rats after the dimethoate exposure. Simultaneously, rats were decapitated for the determination of brain cholinesterase AChE activities, glutamate concentrations, and the NMDA receptor NMDA-R densities and affinities in hippocampus.

RESULTSLatencies to find a hidden escape platform were significantly longer in dimethoate dosed groups than that of the control group in the place navigation tests. Subsequently, the times of crossing the location of platform which had been removed obviously decreased in the highest dose group compared with that of the control in the spatial probe tests (P < 0.05). AChE activity was significantly reduced 42% approximately 78% by all three doses of dimethoate (P < 0.05). Glutamate concentrations were increased significantly 132.9% approximately 134.5% by the two highest doses of dimethoate (P < 0.05). In addition, the NMDA receptor bindings were reduced 21.2% approximately 23.2% with the statistical significance at the same two highest doses (P < 0.05). Furthermore, the receptor affinities was reduced 33.1% by the highest dose group (P < 0.05). The lesions of spatial memory were statistically corrected with the decrease of the NMDA-R affinities (P < 0.05).

CONCLUSIONThe cholinergic lesion as well as the excitatory amino acid system alteration might attribute to the inferior ability in spatial learning and memory in dimethoate subchronically exposed rats.

Acetylcholinesterase ; metabolism ; Animals ; Chronic Disease ; Dimethoate ; toxicity ; Disease Models, Animal ; Glutamic Acid ; metabolism ; Insecticides ; toxicity ; Learning ; drug effects ; Male ; Memory ; drug effects ; Rats ; Rats, Sprague-Dawley ; Receptors, N-Methyl-D-Aspartate ; metabolism ; Toxicity Tests, Subchronic

OBJECTIVETo investigate the neuroprotective effect of estradiol on the release of excitatory amino acid (EAAs) mediator, and the activity of ATPase in cerebro-cortical synaptosome membrane of rats exposed to deltamethrin.

METHODSUsing HPLC to detect EAAs release, and colorimeter method to measure the activities of Na(+)-K(+)-ATPase, Mg(2+)-ATPase, Ca(2+)-ATPase, Ca(2+)-Mg(2+)-ATPase in the cerebro-cortical synaptosomes of ovariectomized rats exposed to deltamethrin (2 x 10(-5)mol/L), and treated with different doses of 17beta estradiol (10(-5), 10(-8), 10(-11) mol/L). Meanwhile, the estrogen receptor (ER) antagonist, tamoxifen, was used to investigate the effect on estradiol.

RESULTSThe release of Asp and Glu from the cerebro-cortical synaptosomes was significantly increased by 2 x 10(-5)mol/L deltamethrin exposure at the depolarizing state evoked by 50 mmol/L KCl, while 10(-8), 10(-11) mol/L 17beta estradiol could partly inhibit the effect of deltamethrin on the release of Asp (28.42%, 24.36%, respectively), Glu (21.52%, 14.57%, respectively). The activities of 4 kinds of ATPase were inhibited by 2 x 10(-4) mol/L deltamethrin, and these effects could be blocked by 10(-5) mol/L estradiol, while the activity of Ca(2+)-ATPase was increased by 10(-8), 10(-11) mol/L of estradiol. However, no obvious antagonistic effect of tamoxifen on the function of estradial on EAAs release or the activities of ATPase was found.

CONCLUSIONEstradiol showed certain neuroprotective effect on the release of EAAs and the inhibition on ATPase induced by deltamethrin. The effect of estradiol on synaptosomes may indicate the nongenetic mechanism of estradiol.

Animals ; Aspartic Acid ; secretion ; Cerebral Cortex ; drug effects ; metabolism ; Estradiol ; pharmacology ; Glutamic Acid ; secretion ; Insecticides ; toxicity ; Neurotoxicity Syndromes ; prevention & control ; Nitriles ; Pyrethrins ; toxicity ; Rats ; Rats, Wistar ; Synaptosomes ; drug effects ; metabolism

OBJECTIVETo investigate the effect of lead-exposed astrocyte conditioned medium (ACM) on the synaptic formation of neurons and to provide reference for the mechanism of lead neurotoxicity.

METHODSAstrocytes were cultured in the medium containing 50, 100, 200, 400, and 800 µmol/L lead acetate for 72 h. Alamar Blue was used to assess the cell viability of astrocytes, and then ACM was collected. Primarily cultured neurons were divided into six groups: pure culture group, non-glutamic acid (Glu)-induced ACM treatment group, Glu-induced lead-free ACM treatment group, and Glu-induced 50, 100, and 200 µmol/L lead acetate-exposed ACM treatment groups. Neurons were collected after being cultured in ACM for 24, 48, or 72 h. The content of synaptophysin (SYP) in neurons was determined by Western blot. The SYP expression in neurons was measured by immunofluorescence after being cultured in ACMfor 72 h.

RESULTSIn all lead-exposed groups, the cell viability of astrocytes declined with increasing concentration of lead (P < 0.05). The Western blot showed that compared with the pure culture group, the non-Glu-induced ACM treatment group and Glu-induced lead- free ACM treatment group had significantly increased content of SYP in neurons (P < 0.01); compared with the non-Glu-induced ACM treatment group, the Glu-induced ACM treatment groups had significantly reduced SYP expression in neurons (P < 0.05); compared with the Glu-induced lead-free ACM treatment group, all lead-exposed ACM treatment groups had the content of SYP in neurons significantly reduced with increasing concentration of lead after 72-h culture (P < 0.01), the 200 µmol/L lead-exposed ACM treatment group had significantly reduced content of SYP in neurons after 48-h culture (P < 0.01), and all lead-exposed ACM treatment groups showed no significant changes in the content of SYP in neurons after 24-h culture. Double-labeling immunofluorescence of SYP showed that all lead-exposed ACM treatment groups had a significant decrease in the number of SYP-fluorescent particles after 72-h culture (P < 0.05).

CONCLUSIONAstrocytes promote synaptic formation of neurons, which may be inhibited during lead exposure.

Astrocytes ; drug effects ; physiology ; Cell Survival ; drug effects ; Cells, Cultured ; Culture Media, Conditioned ; metabolism ; Glutamic Acid ; metabolism ; Lead ; toxicity ; Neurons ; drug effects ; Synapses ; drug effects ; physiology