title: In vivo studies on NMDA-evoked release of amino acids in the rat spinal cord.
abstract: In the present study, spontaneous and evoked release of selected amino acids in the rat spinal cord was studied using in vivo microdialysis. Perfusion of the microdialysis probe with 100 K+ evoked a 2-4-fold increase in release of the putative neurotransmitters aspartate, glutamate and taurine while glutamine was decreased. K(+)-evoked release of glutamate was almost completely Ca(2+)-dependent while that of aspartate was partially Ca(2+)-dependent. Taurine release was not affected by substituting Ca2+ with Co2+. Perfusion with 5 mM N-methyl-D-aspartate (NMDA) evoked 3-9-fold release of glutamate, glycine and taurine and a small increase in extracellular beta-alanine. No significant changes in glutamine and serine were found. 5 mM of the competitive NMDA antagonist 3-((+/-)-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) reduced NMDA-evoked release of glutamate and taurine by approx. 50%. 5 mM 3-amino-1-hydroxypyrrolid-2-one (HA-966), an agonist at the glycine site of the NMDA receptor with very low efficacy, completely inhibited NMDA-evoked release of taurine and reduced the levels of released glutamate below baseline, similar to the effect of 1 mM CPP alone. The present results show that in situations of excessive release of excitatory amino acids such as spinal ischemia and trauma. NMDA receptor-evoked release of glutamate may amplify the deleterious process and spread the damage.
authors.affiliation: Department of Clinical Neuroscience and Family Medicine, Karolinska Institutet, Huddinge, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Sundström
authors.forename: L L
authors.initials: LL
authors.lastname: Mo
authors.forename: A
authors.initials: A
authors.lastname: Seiger
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001481:Basal Metabolism; D008297:Male; D017551:Microdialysis; D016202:N-Methylaspartate / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism; D013268:Stimulation, Chemical
chemical_list: D000596:Amino Acids; D016202:N-Methylaspartate; D011188:Potassium