title: Transmitter self-regulation by extracellular glutamate in fresh human cortical slices.
abstract: Glutamate is thought to be the most important excitatory neurotransmitter in the CNS, while glutamine predominantly serves as a precursor and metabolite in the glutamate-glutamine cycle. To verify the interaction between intrinsic extracellular glutamate, y-aminobutyric acid (GABA) levels and glial glutamine outflow in human tissue, fresh brain slices from human frontal cortex were incubated in superfusion chambers in vitro. Human neocortical tissue was obtained during surgical treatment of subcortical brain tumors. For superfusion experiments, the white matter was separated and discarded from the gray matter, which finally contained all six neocortical layers. Outflows of endogenous glutamate, GABA and glutamine were established after a 40-min washout period and amounts were simultaneously quantified after two-phase derivatization by high-performance liquid chromatography with electrochemical detection. Under basal conditions, amounts of glutamate could be found 20-fold in comparison to the inhibitory neurotransmitter GABA, whereas this excitatory predominance markedly declined after veratridine-induced activation. The basal glutamate:glutamine ratio of extracellular levels was approximately 1:2. Blockade or activation of the voltage-gated sodium channel by tetrodotoxin or veratridine significantly modulated glutamate levels, but the glutamate:glutamine ratio was nearly constant with 1:2. When the EAAT blocker TBOA was employed, glutamine remained nearly unchanged whereas glutamate significantly enhanced. These results led us to suggest that glutamine release through glial SN1 is related to EAAT activity that can be modulated by intrinsic extracellular glutamate in human cortical slices.
authors.affiliation: Department of Neurology, Neurochemical Research Group, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany, katharina.prauss@neuro.uni-luebeck.de.
authors.forename: Katharina
authors.initials: K
authors.lastname: Prauss
authors.forename: Ramya
authors.initials: R
authors.lastname: Varatharajan
authors.forename: Kevin
authors.initials: K
authors.lastname: Joseph
authors.forename: Andreas
authors.initials: A
authors.lastname: Moser
mesh_terms: D000328:Adult; D000368:Aged; D001224:Aspartic Acid / Q000494:pharmacology; D002540:Cerebral Cortex / Q000166:cytology*; D002851:Chromatography, High Pressure Liquid; D045604:Extracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008715:Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D008875:Middle Aged; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014701:Veratridine / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: C120673:benzyloxyaspartate; C118016:methionine-hydroxamate; D005973:Glutamine; D001224:Aspartic Acid; D018698:Glutamic Acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D014701:Veratridine; D008715:Methionine