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POSSIBLE HETEROGENEITY OF GLUTAMATE RECEPTORS LINKED TO INOSITOL PHOSPHOLIPID METABO[/SM Hiroyuki Sugiyama, National Institute for Physiological Sciences, Myodaiji, Okazaki 444, Japan

Excitatory amino acids (EAAs) have been shown to stimulate phosphoinositides (PI) breakdown in brain slices or cul- tured neurons. In Xenopus ooeytes injected with rat brain mRNA, a subtype of glutamate receptors (activated by quis- qualate) has bee~ clearly identified that is coupled to pertussis toxin-sensitive G proteins and stimulates PI turnover and intracellular Ca z+ mobilization (metabotropic glutamate receptors). Pharmacological characteristics of the receptors involved in these reactions are, however, not completely consistent among different studies. For instance, in brain slices, F.AA-stimulated PI hydrolysis has been snown to be blocked by 2-amino-3-phosphonopropionate (AP3) or 2- amino-4-phosphonobutyrate (AP4), whereas G protein-mediated quisqualate responses in oocytes have been found to he insensitive to these antagonists. Although this discrepancy may represent the differences in the assay methods and/or materials examined, another possibility is that the reactions in the two systems may he mediated by distinct receptors with different pharmacological properties. To assess the problem, we examined in mRNA-injected oocytes the effects of trans-1-aminocyclopentyl-1,3-dicarboxylate (ACPD), a glutamate analog recently found to stimulate PI hydrolysis in hippocampal slices. ACPD was found to evoke oscillatory electrophysiological responses in the oocytes indistinguisha- ble from those evoked by qnisqualate or glutamate. In conuast to the quisqualate responses, however, ACPD responses were largely blocked by AP3. The results suggested the possible heterogeneity of glutamate receptors linked to inositol phospholipid metabolism.

s l,3

ROLE OF A R A C n l D O N I C A C I D 1 4 S T A B O L I T B S I N S I G N A L ~ k N S D U C T I O W OF N-14IF~I~YL-D-ASPARTATE RECEPTORS

J.T. Wroblewski, J.W. Lazarewicz, E. Costa, and B. Wroblewska*, Fidia-Georgetown Inst. Neurosci. and *Dept. Physiol., Georgetown Univ. Sch. Med., Washington, DC 20007 U.S.A. In primary cultures of cerebellar granule cells glutamate activates a subclass of ionotropic receptors sensitive to N-methyl-D-aspartate (NMDA) which are coupled to channels permeable to Ca 2+ ions. However, NMDA induces also several metabolotropic responses including the release of arachidonic acid ~AA) and the enhanced cGMP formation. Both processes depend on the presence of extracellular Ca ~+. The release of AA following glutamate receptor activation was induced only by agonists of NMDA receptors. This response was decreased by quinacrine in doses that selectively inhibit phospholipase A 2 (PLA2) activity. The receptor signal was transduced without the participation of a pertussis toxin-sensitive G protein but required a NMDA-induced increase of Ca 2+ influx. The inhibitors of PLA 2 failed to affect Ca 2+ influx but decreased the formation of cGMP elicited by NMDA, indicating a role for AA in guanylate cyclase activation. A similar decrease was induced by the lipoxygenase inhibitor nordihydroquaiaretic acid, but not the cyclooxygenase inhibitor indomethacin. Furthermore, the addition of 12-hydro- peroxyeicosatetraenoic acid to intact cells increased cGMP accumulation. Thus, in granule cells, the signal transduction at NMDA receptors includes an increase of Ca 2+ influx followed by the activation of both PLA 2 and 12-1ipoxygenase. An AA metabolite may be responsible for the stimulation of guanylate cyclase activity elicited by NMDA-sensitive glutamate receptors.

EAAandDrugA~ion

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CGP 37849 & CGP 39551: NOVEL COMPETITIVE NMDA RECEPTOR ANTAGONISTS WITH POTENT ORAL ANTICONVOLSANT ACTIVITY G.E. Fagg, M.F. Pozza, F. Brugger, H.-R. Olpe, M. Schmutz, H. van Riezen, R. Heckendorn and H. Allgeier, CIBA-GEIGY Ltd., CH-4002 Basel, Switzerland. CGP 37849 (or DL-4-methyl-APPA) was selected from a series of unsaturated analogues of the phosphono-amino acid AP5 based on its ability to inhibit L-3H-glutamate binding (Ki 220 nM) and 3H-CPP binding (Ki 35 nM) to rat brain postsynaptic densities, and to antagonize electroshock-induced seizures in rodents. Activity was associated exclusively with the trans configuration of the APPA molecule and with the D-stereoisomer. In the ra~ hippocampusv eortex ~.d spinal cord in vitro submicromolar concenLLatlons ~f CGP 37849 selectively antagonized NMDA- but not quisqualate- or kainate-evoked excitations, and suppressed the stimulus-evoked multiple population spikes evoked in CA1 pyramidal neurons bathed in low Mg2+-containing medium. Following oral administration, CGP 37849 suppressed electroshock seizures in rats and mice for about 8 h (ED50 8-22 mg/kg; 4 h pretreatment), whereas its ethylester, CGP 39551, was effective for about 24 h (ED50 4-8 mg/kg; 4 h pretreatment); both compounds were anticonvulsant at doses below those at which overt side effects were apparent. Systemic administration of either compound selectively blocked the increases in hippocampal neuronal firing rate elicited by ionophoretically-applied NMDA in rats in vivo.