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4. Amino acids and monoamines

401 EFFECTS OF METABOTROPIC GLUTAMATE RECEPTOR AGONIST ON AMPA-INDUCED ELEVATION ON

INTRACELLULAR CALCIUM LEVELS IN NIPPOCAMPAL NEURONS

YOSHIO NAGATSUGUI,TAKASHI BAN~,HARUHIDE ITO3,RYUZO SHINGAI 4,

XDepartment of Neurosurqery, Saiseikai Yamaquchi General Hospital r Yamaquchi 753, and Departments

of 2 Pharmacoloqy and 3Neurosurqery, School of Medicine,Yamaquchi University, Ube 755, and

Department of Information science, Faculty of Enqineerinq, Iwate University r Morioka 020.

Glutamate receptors cab be divided into two classes:ionotropic glutamate receptors and metabotropic glutamate receptors. Biochemical cascade activated by the stimulation of metabotropic receptors has still been unclear. So we investigated the influence of a selective agonist of metabotropic glutamate receptors, trans-l-amino-cyclopentyl-l, 3-dicarboxylic acid(trans-ACPD), on the potency of ~-amino-3-hydroxy-metylisoxazole-4-propionic acid(AMPA) to change the cytosolic Ca'*([Ca~]1 ) in cultured hippocampal neurons.

Hippocampal neurons were isolated from rat embryos of gestational day 18 and 19 and maintained more than 6 days. By using a fluorescent Ca 2. indicator, fura-2, we investigated the changes in [C~*]x.

After trans-ACPD at I-3NM had been applied to cells by superfusion for 30 s, the mixture of INM AMPA and 10~M trans-ACPD was applied to the cells for 15 s, which resulted in the larger increase in [Ca2*]x than the sum of the responses to Ab~A alone and trans-ACPD alone in 30% neurons.

Our results suggest that the activation of metabotropic glutamate receptors by trans-ACPD increases responses of AMPA.

4 0 2 ZINC-INDUCED PROTECTION OF RETINAL NEURONS AGAINST NMDA RECEPTOR-MEDIATED GLUTAMATE CYTOTOXICITY.

SATOSHI KASHIII, MASASHI KIKUCHI1, YOSHIHITO HONDAI, HISAMITSU UJIHARA2~ .MASASHI SASA3, YUTAKA TAMURA4, AND AKINORI AKAIKE4, l.Dept, of Ophthalmot., Faculty of Med., Kvoto University, Kvoto 606, 2Dept. of Pharmacol., School of Med., Yamaguchi .University, Ube 755,3Dept. of Pharmacol., Faculty of Med., Hiroshima University, Hiroshima 734, and 4Dept. of ~Neurot~harmacol., Faculty of Pharmacv and Pharmaceutical Sciences,.Fukuyama Univeristv, Fukuvama 729-02, Japan

This study was performed to elucidate the effects of Zn 2+ on glutamate cytotoxicity of cultured retinal neurons obtained from fetal rats. Brief exposure of cells to glutamate, kainate or NMDA but not AMPA induced delayed cytotoxicity. NMDA receptor antagonists, .MK-801 and CPP, prevented cytotoxicity induced by these excitatory amino acids. Kainate-induced cytotoxicity was inhibited by Ca2+-removal or tetrodotoxin. Zn2+ at concentrations of 0.3-300 ~tM prevented cytotoxicity induced by glutamate or NMDA. NMDA-induced whole cell currents were inhibited by CPP, Mg2+, or Zn 2+. CPP- and Zn 2+- induced blockade of NMDA-currents was not dependent on membrane potential xehereas Mg2+-induced blockade was voltage-dependent. These results suggest that Zn 2+ protects neurotoxic effects of glutamate in the retina by reducing NMDA receptor-activated channel currents.