NON-NMDA ANTAGONISTS PROTECT AGAINST KAINATE MORE THAN AMPA TOXICITY IN THE RAT HIPPOCAMPUS

Single focal injection of the excitatory amino acids (EAAs) kainic acid (KA, 1.1 nmol/mu-l) and (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (S)-AMPA, 6 nmol/mu-l) into rat dorsal hippocampus resulted in widespread neurodegeneration with 90-100% loss of hippocampal pyramidal cells in CA1, CA2, CA3 and CA4 subfields, and 50-70% loss of dentate granule (DG) cells. Focal injection of NMDA (30 nmol/mu-l) under the same conditions resulted in 70-90% loss of Ca1 cells with less damage in CA2, CA3, CA4 and DG cells (30-50%, 10-30%, 10-30% and 30-50%, respectively). The non-NMDA antagonists NBQX (2,3-dihydro-6-nitro-7-sulphamoyl-benzo(f)quinoxaline) and GYKI 52466 (1-(amino)phenyl-4-methyl-7,8-methylendioxy-5H-2,3,benzodiazepine.HCl) co-injected (24 nmol/mu-l) with EAAs or given as i.v. infusion (30 mg/kg/3 h), protected against KA toxicity in CA1, CA2 and DG cells, with no protection in CA3 and CA4. NBQX i.v. protected against (S)-AMPA toxicity in the DG cells but no protection was observed against (S)-AMPA toxicity in hippocampal subfields (CA1, CA2 and CA4). Intravenous administration of NBQX and GYKI 52466 (30 mg/kg/3 h) also failed to protect against NMDA toxicity in the hippocampus. Systemic injections of D(-)-CPPene, (E)-4-(3-phosphonoprop-2-enyl)-piperazine-2-carboxylic acid, (10 and 5 mg/kg, i.p., 20 min prior and 3 h post EAA injection) protected against NMDA and KA toxicity in the CA1, CA2 and DG subfield with no protective effect against (S)-AMPA toxicity.