Involvement of metabotropic glutamate receptors in excitatory amino acid and GABA release following spinal cord injury in rat.
Spinal cord injury (SCI) leads to an increase in extracellular excitatory amino acid (EAA) concentrations resulting in glutamate receptor-mediated excitotoxic events. The glutamate receptors include ionotropic (iGluRs) and metabotropic (mGluR) receptors. Of the three groups of mGluRs, group-I activation can initiate intracellular pathways that lead to further transmitter release. Groups II and III mGluRs function mainly as autoreceptors to regulate neurotransmitter release. In an effort to examine the role of mGluRs in the increase in EAAs following SCI, we administered AIDA, a potent group-I mGluR antagonist immediately after injury. To determine subtype specific roles of the group-I mGluRs, we evaluated EAA release following LY 367385 (mGluR1 antagonist) and MPEP (mGluR5 antagonist) administration. To evaluate group-II and -III mGluRs we administered APDC (group-II agonist) and L-AP4 (group-III agonist) immediately following injury; additionally, we initiated treatment with CPPG (group-II/-III antagonist) and LY 341495 (group-II antagonist) 5 min prior to injury. Subjects were adult male Sprague-Dawley rats (225-250 g), impact injured at T10 with an NYU impactor (12.5 mm drop). Agents were injected into the epicenter of injury, amino acids where collected by microdialysis fibers inserted 0.5 mm caudal from the edge of the impact region and quantified by HPLC. Treatment with AIDA significantly decreased extracellular EAA and GABA concentrations. MPEP reduced EAA concentrations without affecting GABA. Combining LY 367385 and MPEP resulted in a decrease in EAA and GABA concentrations greater than either agent alone. L-AP4 decreased EAA levels, while treatment with LY 341495 increased EAA levels. These results suggest that mGluRs play an important role in EAA toxicity following SCI.
Mills
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The Department of Anatomy and Neurosciences, The University of Texas Medical Branch at Galveston, Galveston, Texas 77555-1043, USA.
Xu
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McAdoo
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Hulsebosch
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D000818:Animals; D001224:Aspartic Acid / Q000032:analysis / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004195:Disease Models, Animal; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018846:Excitatory Amino Acids / Q000032:analysis / Q000378:metabolism*; D005110:Extracellular Space / Q000737:chemistry / Q000378:metabolism; D018698:Glutamic Acid / Q000032:analysis / Q000378:metabolism; D008297:Male; D017551:Microdialysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism; D013119:Spinal Cord Injuries / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000032:analysis / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D018846:Excitatory Amino Acids; D018094:Receptors, Metabotropic Glutamate; D001224:Aspartic Acid; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid