Mechanisms involved in the metabotropic glutamate receptor-enhancement of NMDA-mediated motoneurone responses in frog spinal cord.
1. The metabotropic glutamate receptor (mGluR) agonist trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (trans-ACPD) (10-100 microM) depolarized isolated frog spinal cord motoneurones, a process sensitive to kynurenate (1.0 mM) and tetrodotoxin (TTX) (0.783 microM). 2. In the presence of NMDA open channel blockers [Mg2+; (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK801); 3,5-dimethyl-1-adamantanamine hydrochloride (memantine)] and TTX, trans-ACPD significantly potentiated NMDA-induced motoneurone depolarizations, but not alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA)- or kainate-induced depolarizations. 3. NMDA potentiation was blocked by (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) (240 microM), but not by alpha-methyl-(2S,3S,4S)-alpha-(carboxycyclopropyl)-glycine (MCCG) (290 microM) or by alpha-methyl-(S)-2-amino-4-phosphonobutyrate (L-MAP4) (250 microM), and was mimicked by 3,5-dihydroxyphenylglycine (DHPG) (30 microM), but not by L(+)-2-amino-4-phosphonobutyrate (L-AP4) (100 microM). Therefore, trans-ACPD's facilitatory effects appear to involve group I mGluRs. 4. Potentiation was prevented by the G-protein decoupling agent pertussis toxin (3-6 ng ml(-1), 36 h preincubation). The protein kinase C inhibitors staurosporine (2.0 microM) and N-(2-aminoethyl)-5-isoquinolinesulphonamide HCI (H9) (77 microM) did not significantly reduce enhanced NMDA responses. Protein kinase C activation with phorbol-12-myristate 13-acetate (5.0 microM) had no effect. 5. Intracellular Ca2+ depletion with thapsigargin (0.1 microM) (which inhibits Ca2+/ATPase), 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetracetic acid acetyl methyl ester (BAPTA-AM) (50 microM) (which buffers elevations of [Ca2+]i), and bathing spinal cords in nominally Ca2+-free medium all reduced trans-ACPD's effects. 6. The calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W7) (100 microM) and chlorpromazine (100 microM) diminished the potentiation. 7. In summary, group I mGluRs selectively facilitate NMDA-depolarization of frog motoneurones via a G-protein, a rise in [Ca2+]i from the presumed generation of phosphoinositides, binding of Ca2+ to calmodulin, and lessening of the Mg2+-produced channel block of the NMDA receptor.
Veterans Affairs Medical Center, Department of Neurology, University of Miami School of Medicine, Florida 33101, USA.
A M
AM
Holohean
J C
JC
Hackman
R A
RA
Davidoff
D000600:Amino Acids, Dicarboxylic / Q000494:pharmacology; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002746:Chlorpromazine / Q000494:pharmacology; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D007736:Kynurenic Acid / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects* / Q000502:physiology; D016202:N-Methylaspartate / Q000494:pharmacology*; D018696:Neuroprotective Agents / Q000494:pharmacology; D037342:Pertussis Toxin; D011894:Rana pipiens; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012018:Reflex / Q000187:drug effects; D012118:Resorcinols / Q000494:pharmacology; D015290:Second Messenger Systems / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology; D013449:Sulfonamides / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
C089836:2-amino-2-methyl-4-phosphonobutyrate; C089837:2-methyl-2-(2-carboxycyclopropyl)glycine; D000600:Amino Acids, Dicarboxylic; D000613:Aminobutyrates; D001565:Benzoates; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018696:Neuroprotective Agents; D018094:Receptors, Metabotropic Glutamate; D012118:Resorcinols; D013449:Sulfonamides; D010566:Virulence Factors, Bordetella; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; C079694:alpha-methyl-4-carboxyphenylglycine; D013779:Tetrodotoxin; D004533:Egtazic Acid; C079215:3,5-dihydroxyphenylglycine; D016202:N-Methylaspartate; C017967:W 7; D019284:Thapsigargin; D037342:Pertussis Toxin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D007736:Kynurenic Acid; C012729:2-amino-4-phosphonobutyric acid; D008274:Magnesium; D002118:Calcium; D005998:Glycine; D002746:Chlorpromazine