title: In vivo monitoring of extracellular 13N-glutamine derived from blood-borne 13N-ammonia in rat striatum using microdialysis with radio-LC method.
abstract: Glutamine synthetase (GS) is selectively localized in astrocytes and has important roles in the central nervous system (CNS). Cerebral extracellular excess ammonia and glutamate are taken up by astrocytes and converted to glutamine via GS to protect the CNS against neurotoxicity. In this study, we monitored cerebral extracellular 13N-glutamine derived from 13N-ammonia as a potential marker for astroglial metabolism using in vivo microdialysis combined with ultra performance liquid chromatography-radiometric detection. This method allowed rapid and highly sensitive radiometric analysis of 13N-ammonia and its metabolite, 13N-glutamine, in striatal extracellular fluid with good time resolution. Inhibition of GS with methionine sulfoximine resulted in a decrease of extracellular 13N-glutamine accompanied by an increase of 13N-ammonia as compared with control. Fluorocitrate, a selective inhibitor of glial metabolism, also decreased 13N-glutamine production and increased unmetabolized 13N-ammonia. In contrast, 13N-glutamine was increased with 5 mmol/kg of ammonium acetate without significant changes in 13N-ammonia as compared with control. These results suggest that the concentration of extracellular 13N-glutamine strongly reflects the biological changes in the metabolic activity of astroglial cells.
authors.affiliation: Molecular Probe Group, Molecular Imaging Center, National Institute of Radiological Sciences, Japan. mokada@nirs.go.jp
authors.forename: Maki
authors.initials: M
authors.lastname: Okada
authors.forename: Ryuji
authors.initials: R
authors.lastname: Nakao
authors.forename: Rie
authors.initials: R
authors.lastname: Hosoi
authors.forename: Ming-Rong
authors.initials: MR
authors.lastname: Zhang
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Fukumura
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Suzuki
authors.forename: Osamu
authors.initials: O
authors.lastname: Inoue
mesh_terms: D000085:Acetates / Q000494:pharmacology; D000641:Ammonia / Q000097:blood / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D002853:Chromatography, Liquid / Q000379:methods*; D002951:Citrates / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism*; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors; D005973:Glutamine / Q000378:metabolism; D008297:Male; D008717:Methionine Sulfoximine / Q000494:pharmacology; D017551:Microdialysis / Q000379:methods*; D009590:Nitrogen Radioisotopes / Q000097:blood / Q000378:metabolism; D011874:Radiometry / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D000085:Acetates; D002951:Citrates; D009590:Nitrogen Radioisotopes; D005973:Glutamine; D008717:Methionine Sulfoximine; C007744:fluorocitrate; D000641:Ammonia; D005974:Glutamate-Ammonia Ligase; C018824:ammonium acetate